Fine particle powder manufacturing method and manufacturing device, fine particle slurry washing and concentrating device, fine particle powder manufacturing device and manufacturing method, and fine particle slurry concentrating device

Abstract

A fine particle powder manufacturing device (1) comprises: a fine particle slurry manufacturing device (2) for manufacturing a slurry containing fine particles having a particle diameter of 7 μm or less by causing a plurality of starting materials to react in a mother liquor in which a swirling flow is generated, in a crystallization device (10); a slurry tank (30) for washing the slurry by adding a washing solution to the slurry while stirring the same; a stirring type cross flow filtration device (6) for concentrating the slurry by removing a portion of the mother liquor and the washing solution from the slurry; a switching device (70) for switching between an initial concentration step, a dilution / washing step, and a final concentration step; and a drying device (8) for drying the final concentrated slurry by means of conductive heat transfer, by transferring the final concentrated slurry while mixing the same using a heated stirring blade.

Description

Method and apparatus for producing fine particle powder, cleaning and concentrating apparatus for fine particle slurry, apparatus and method for producing fine particle powder, and concentrating apparatus for fine particle slurry

[0001] The present invention relates to a method and apparatus for producing fine particle powder, a cleaning and concentrating apparatus for fine particle slurry, a method and apparatus for producing fine particle powder, and a concentrating apparatus for fine particle slurry, and a method and apparatus for producing fine particle powder, for example, a method and apparatus suitable for producing a secondary battery positive electrode active material precursor, etc. This application claims priority based on Japanese Patent Application Nos. 2023-138382, 2023-138384, 2023-138383, and 2023-138385, filed in Japan on August 28, 2023, the contents of which are incorporated herein by reference.

[0002] In the production of fine particle powders, for example, in the production of secondary battery positive electrode active material precursors, it has recently become desirable to make the particle size of the fine particles as small as possible in order to improve the performance of the final product. A commonly used production method includes the steps of: bringing a solution containing a transition metal element into contact with an alkaline solution or alkali to obtain a stock slurry containing a precipitate component mainly composed of a transition metal hydroxide; washing and concentrating or concentrating the precipitate component in the slurry to obtain a washed and concentrated slurry or a concentrated slurry; and drying the washed and concentrated slurry or the concentrated slurry to obtain a fine particle powder.

[0003] However, in this type of method for producing fine particle powder, when fine particles are obtained by adjusting the conditions of the manufacturing process of the raw slurry, the filtration resistance of the cake layer formed during filtration with a filter in the filtration and washing process becomes very large, making it difficult to apply a cake filtration method such as a commonly used filter press (pressure filtration).

[0004] Furthermore, with the filter press method, it is difficult to achieve a uniform cake thickness throughout the entire filter chamber. When attempting to adopt a displacement washing method in which wash water is passed through a cake layer of uneven thickness to wash it, the wash water tends to concentrate and pass through areas where the cake is thin, while it is difficult for the wash water to pass through areas where the cake is thick. This necessitates an increase in the amount of wash water, but even with this, unevenness in the degree of washing cannot be avoided, making it difficult to wash the entire cake layer uniformly.

[0005] Therefore, methods have been proposed as disclosed in Patent Document 1 or Patent Document 2. The methods of Patent Documents 1 and 2 include a step of contacting a solution containing a transition metal element with an alkaline solution to obtain a raw liquid slurry containing a precipitate component mainly composed of a transition metal hydroxide, concentrating the precipitate component in the slurry by cross-flow filtration, and drying the concentrated slurry by a hot air drying method using convective heat transfer in which hot air is blown onto the obtained concentrated slurry.

[0006] Crossflow filtration is a method of filtering raw slurry while flowing it parallel to the inner wall of the filter. The shear force of the slurry flowing parallel to the inner wall of the filter prevents solids from accumulating as a cake layer on the filter surface, which has the advantage of being able to maintain a relatively high filtration rate and being less likely to clog, even when the raw slurry contains fine particles. Possible crossflow filtration methods include cartridge-type membrane modules such as hollow fiber membranes, tubular membranes, and spiral membranes, or rotary filters equipped with stirring blades that stir the filter surface.

[0007] JP 2012-87039 A JP 2012-99470 A

[0008] When producing fine particles of 7 μm or less using the methods of Patent Documents 1 and 2, a fine-mesh membrane filtration method such as a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) is required. However, cartridge-type cross-flow filtration methods using hollow fiber membranes, tubular membranes, spiral membrane modules, etc., have narrow flow paths through which the slurry flows within the module, making it impossible to increase the slurry concentration during the concentration process. Furthermore, even if fine particles of 7 μm or less could be produced, the washing and concentration process would be performed using cross-flow filtration at a low slurry concentration that would not cause blockage of the flow path, followed by a drying process using a hot air drying method that uses convective heat transfer by blowing hot air. As a result, the amount of cleaning solution required during the washing process would increase, and the energy costs during the drying process would be high, making it difficult to improve production efficiency.

[0009] In the filtration and washing operations of the methods of Patent Documents 1 and 2, in order to reduce running costs, it is important to reduce the amount of washing water used or the amount of washing wastewater.

[0010] In the methods of Patent Documents 1 and 2, it is preferable to perform the concentration operation so that the slurry in the system is as concentrated as possible, considering the filtration and washing operations. However, if the slurry is concentrated too much, the fluidity of the slurry circulating in the system decreases, making it impossible to transport using a pump or the like, resulting in blockages. Patent Document 1 therefore proposes a method for controlling the concentration state of the slurry circulating in the system by monitoring the current value and torque of the motor driving the rotating blades of a rotary crossflow filtration device. However, there is no linear relationship between the viscosity of the slurry circulating in the system and the current value and torque of the motor driving the rotating blades. Especially when the slurry is highly concentrated, the current value and torque can suddenly change unstably with even a slight difference in concentration, making it difficult to stably control the high concentration state using the motor current value and torque.

[0011] In the process of drying the concentrated slurry in the methods of Patent Documents 1 and 2, a large amount of heat is exhausted, particularly when drying by hot air drying using convective heat transfer. Therefore, improving energy efficiency is an issue when considering reducing running costs and environmental loads.

[0012] The present invention has been made in view of the above-mentioned problems, and aims to provide an apparatus and method for producing fine particle powder that can produce fine particle powder of 7 μm or less in the process of producing a raw slurry, while reducing energy costs and increasing production efficiency.

[0013] The present invention has been made in view of the above problems, and aims to provide an apparatus for washing and concentrating a fine particle slurry, which can reduce the amount of washing water used or the amount of washing wastewater, and an apparatus and method for stably producing a fine particle powder.

[0014] The present invention has been made in view of the above problems, and an object of the present invention is to provide a concentrating device for fine particle slurry, which can stably concentrate fine particle slurry even in a high concentration range, and a manufacturing device and manufacturing method for fine particle powder.

[0015] The present invention has been made in view of the above problems, and an object of the present invention is to provide an apparatus and method that can stably produce fine particle powder while improving energy efficiency in the process of drying concentrated slurry.

[0016] A method for producing a fine particle powder according to a first aspect of the present invention includes a fine particle slurry production step of producing a fine particle slurry containing fine particles having a particle size of 7 μm or less by reacting a plurality of raw materials in a mother liquor in which a swirling flow is generated in a reaction treatment vessel; an initial concentration step of supplying the fine particle slurry to a filtration facility comprising a slurry tank and an agitation type cross-flow filtration device arranged on a circulation path and performing initial concentration while circulating the fine particle slurry in the filtration facility to obtain an initially concentrated slurry; a dilution and washing step of filtering the initially concentrated slurry in the slurry tank with the agitation type cross-flow filtration device while supplying a washing liquid to obtain a washed slurry; and a dilution and washing step of filtering the washed slurry with the agitation type cross-flow filtration device. and a drying step of supplying the final concentrated slurry to a drying device, transferring the final concentrated slurry while stirring it with heated stirring blades, and drying it by conductive heat transfer to obtain a fine particle powder. The stirred cross-flow filtration device has a slurry chamber and a filtrate chamber separated by a filter, an agitator arranged along the filter in the slurry chamber, and a drive unit that moves the agitator along the filter to prevent the deposition of fine particles on the surface of the filter, and filtration is performed by supplying the fine particle slurry, the initially concentrated slurry, or the washed slurry supplied from the slurry tank to the slurry chamber.

[0017] According to the method for producing a fine particle powder of Aspect 1, in the fine particle slurry production step, a plurality of raw materials are reacted in a mother liquor in which a swirling flow is generated in a reaction treatment vessel to produce a fine particle slurry containing fine particles with a particle size of 7 μm or less, and in the initial concentration step, the fine particle slurry is circulated in the filtration equipment to obtain an initially concentrated slurry. Next, in the dilution and washing step, the initially concentrated slurry is filtered in the slurry tank with the agitation type cross-flow filtration device while a washing liquid is supplied to the initially concentrated slurry, to obtain a washed slurry. Then, in the final concentration step, the washed slurry is filtered with the agitation type cross-flow filtration device to obtain a final concentrated slurry. Furthermore, in the drying step, the final concentrated slurry is supplied to a drying device, and the final concentrated slurry is transported while being stirred with heated stirring blades, and dried by conduction heat transfer to obtain a fine particle powder. Therefore, the swirling flow suppresses particle growth during the reaction of the raw materials, making it possible to produce fine particles of 7 μm or less.Then, in the initial concentration process, dilution and washing process, and final concentration process, washing and advanced concentration using an agitation type cross-flow filtration device can be carried out efficiently without causing blockage of the filter or flow path.Furthermore, in the drying process, the final concentrated slurry is brought into contact with heated agitator blades and heated by conductive heat transfer, making it possible to produce fine particles of 7 μm or less with high production efficiency while keeping energy costs down.

[0018] A method for producing a microparticle powder according to Aspect 2 of the present invention is the same as Aspect 1, in which the microparticle powder is a precursor of a positive electrode material for a secondary battery, and in the microparticle slurry production step, a solution containing a transition metal element, which is a first raw material, is reacted with an alkaline solution, which is a second raw material, to obtain microparticles mainly composed of a transition metal hydroxide.

[0019] According to the method for producing a fine particle powder of Aspect 2, in the fine particle slurry production step, a solution containing a transition metal element as the first raw material is reacted with an alkaline solution as the second raw material to obtain fine particles mainly composed of a transition metal hydroxide, thereby making it possible to produce a fine particle powder as a precursor of a positive electrode material for a secondary battery with high production efficiency and reduced energy costs.

[0020] A method for producing a fine particle powder according to Aspect 3 of the present invention is the same as that according to Aspect 1 or 2, wherein the initial concentration step comprises filtering the fine particle slurry obtained in the fine particle slurry production step using the agitation cross-flow filtration device and concentrating the slurry to a solids concentration of 35 to 65 wt % to obtain the initially concentrated slurry.

[0021] According to the method for producing a fine particle powder of aspect 3, in the initial concentration step, the fine particle slurry is filtered by the agitation type cross-flow filtration device and concentrated until the solid content reaches 35 to 65 wt %, thereby obtaining the initially concentrated slurry. This prevents problems such as filter clogging due to fine particles, and improves the efficiency of removing impurities from the fine particle slurry. It also reduces the amount of washing liquid and washing time consumed in the dilution washing step, thereby reducing energy costs and improving production efficiency.

[0022] A method for producing a fine particle powder according to Aspect 4 of the present invention is the method for producing a fine particle powder according to any one of Aspects 1 to 3, wherein in the final concentration step, the washed slurry is concentrated using the agitation cross-flow filtration device until the solid content reaches 50 to 65 wt %, thereby obtaining the final concentrated slurry.

[0023] According to the method for producing a fine particle powder of Aspect 4, the final concentrated slurry is concentrated in the final concentration step until the solid content reaches 50 to 65 wt %, thereby eliminating problems such as filter clogging due to fine particles, while reducing the amount of liquid to be removed in the drying step, thereby reducing energy costs and improving production efficiency.

[0024] A method for producing a fine particle powder according to aspect 5 of the present invention is any of aspects 1 to 4, in which in the fine particle slurry production step, a reaction liquid containing the mother liquor and the raw materials in the reaction treatment vessel is once discharged to the outside, and the discharged reaction liquid is returned to the reaction treatment vessel to form a circulation system for the reaction liquid, a swirling flow is generated in the reaction treatment vessel by the flow input of the reaction liquid, and the fine particle slurry containing fine particles crystallized by the reaction of the raw materials is produced from the circulation system for the reaction liquid.

[0025] According to the method for producing a fine particle powder of aspect 5, it is easy to generate a high-speed swirling flow using simple equipment, and by uniformly mixing the raw materials in the high-speed swirling flow in a short period of time, it is possible to precipitate fine particles having a particle size of 7 μm or less, preferably 5 μm or less, and it is possible to reduce the particle size of the fine particle powder obtained in the end and narrow the particle size distribution.

[0026] A method for producing a fine-particle powder according to a sixth aspect of the present invention is, in any one of aspects 1 to 5, a method in which the drying step is a step of drying the final concentrated slurry that has undergone the final concentration step by using an agitation heat transfer device, the agitation heat transfer device having a casing with an inlet formed at one end and an outlet formed at the other end, a plurality of rotating shafts that are rotatable about their axes within the casing and are arranged with the axes parallel to one another, agitation blades fixed to each of the rotating shafts at intervals in the axial direction and such that the agitation blades of each rotating shaft partially overlap when viewed in the axial direction, and a heating mechanism for heating the agitation blades, and by rotating the rotating shafts, the heated agitation blades mix the final concentrated slurry supplied from the inlet with the wet powder held in the casing and transport it to the outlet hole, during which the mixture of the final concentrated slurry and the wet powder is dried by conduction heat transfer and converted into a fine-particle powder.

[0027] According to the method for producing fine particle powder of Aspect 6, as the stirring blades, which are fixed to each of the rotating shafts at intervals in the axial direction and so that the stirring blades of each rotating shaft partially overlap when viewed in the axial direction, rotate, the heated stirring blades mix the final concentrated slurry supplied from the inlet with the wet powder previously held in the casing and transport it to the outlet, during which the high-temperature stirring blades come into contact with the mixture of the final concentrated slurry and the wet powder, drying it by conductive heat transfer and converting it into fine particle powder. Thus, the mixture of the final concentrated slurry and the wet powder can be heated by conductive heat transfer through contact with the heated stirring blades, which has higher thermal efficiency than when using hot air, etc., reducing energy costs and improving production efficiency.

[0028] A seventh aspect of the present invention provides an apparatus for producing fine particle powder, comprising: a fine particle slurry production apparatus for producing a fine particle slurry containing fine particles having a particle size of 7 μm or less by reacting a plurality of raw materials in a mother liquor in which a swirling flow is generated in a reaction treatment vessel; a filtration system having a slurry tank and an agitation type cross-flow filtration system disposed on a circulation path; a cleaning liquid supply system for supplying a cleaning liquid into the slurry tank; (a) an initial concentration step for performing an initial concentration while circulating the fine particle slurry in the filtration system to obtain an initially concentrated slurry; (b) a dilution and washing step for filtering the initially concentrated slurry in the slurry tank with the agitation type cross-flow filtration system while supplying a cleaning liquid from the cleaning liquid supply system; and (c) a dilution and washing step for obtaining a washed slurry by filtering the initially concentrated slurry in the slurry tank with the agitation type cross-flow filtration system while supplying a cleaning liquid from the cleaning liquid supply system. and a drying device that transfers the final concentrated slurry while stirring it with heated stirring blades, and dries it by conductive heat transfer to obtain a fine particle powder. The agitation type crossflow filtration device has a slurry chamber and a filtrate chamber separated by a filter, an agitator disposed in the slurry chamber along the filter, and a drive unit that moves the agitator along the filter to prevent the deposition of fine particles on the surface of the filter, and filtration is performed by supplying the fine particle slurry, the initially concentrated slurry, or the washed slurry supplied from the slurry tank to the slurry chamber.

[0029] According to the apparatus for producing fine particle powder of Aspect 7, the apparatus for producing fine particle slurry produces a fine particle slurry containing fine particles having a particle size of 7 μm or less by reacting a plurality of raw materials in a mother liquor in which a swirling flow is generated in the reaction processor. Next, a filtration system including a slurry tank and an agitation-type cross-flow filtration system disposed on a circulation path is used, and the switching device sequentially switches between processes. (a) In the initial concentration step, the fine particle slurry is circulated through the filtration system to obtain an initially concentrated slurry. (b) In the dilution and washing step, the initially concentrated slurry is filtered through the agitation-type cross-flow filtration system while being supplied with a washing liquid from the washing liquid supply device to obtain a washed slurry. (c) In the final concentration step, the washed slurry is filtered through the agitation-type cross-flow filtration system to obtain a final concentrated slurry. Furthermore, in a drying device, the final concentrated slurry is transported while being agitated with heated agitation blades, and dried by conductive heat transfer to obtain a fine particle powder. Therefore, the swirling flow suppresses particle growth during the reaction of the raw materials, making it possible to produce fine particles of 7 μm or less, and then washing and high-level concentration using an agitation-type cross-flow filtration device can be carried out efficiently in the initial concentration step, dilution washing step, and final concentration step without causing blockage of the filter or flow path. Furthermore, in the drying step, the final concentrated slurry is brought into contact with heated agitation blades and heated by conduction heat transfer, making it possible to produce fine particles of 7 μm or less with high efficiency while keeping energy costs low.

[0030] A particulate slurry washing and concentrating apparatus according to an eighth aspect of the present invention comprises a slurry tank for storing particulate slurry containing particulates having a particle size of 7 μm or less; a flow path for supplying the stored particulate slurry to an agitation type crossflow filtration apparatus; a return flow path for returning filtrate discharged from the agitation type crossflow filtration apparatus to the slurry tank; a waste flow path for discarding the filtrate discharged from the agitation type crossflow filtration apparatus; a filtrate sensor including at least one of a conductivity sensor for measuring the conductivity of the filtrate discharged from the agitation type crossflow filtration apparatus and a density sensor for measuring the density of the filtrate; a flow path switching device for switching the flow path of the filtrate discharged from the agitation type crossflow filtration apparatus to either the return flow path or the waste flow path; and a control unit for controlling the flow path switching device so that the filtrate is allowed to flow into the waste flow path when the measurement result of the filtrate sensor is equal to or greater than a threshold value, and so that the filtrate is allowed to flow into the return flow path when the measurement result of the filtrate sensor is below the threshold value.

[0031] According to the apparatus for washing and concentrating a particulate slurry of Aspect 8, when the electrical conductivity or density of the filtrate discharged from the agitation type cross-flow filtration device is lower than a threshold value, the filtrate is reused as a washing liquid, and therefore the amount of washing water used or the amount of washing wastewater can be reduced in the apparatus for washing and concentrating a particulate slurry.

[0032] A ninth aspect of the present invention provides the apparatus for washing and concentrating particulate slurry according to the eighth aspect, wherein the filtrate sensor is a conductivity sensor, and the threshold value is set to a value in the range of 10 mS / cm or less.

[0033] According to the washing and concentrating apparatus for microparticle slurry of aspect 9, the filtrate sensor is a conductivity sensor, and by setting the threshold value to a value in the range of 10 mS / cm or less, the amount of washing water used or the amount of washing wastewater can be reduced in the washing and concentrating apparatus for microparticle slurry.

[0034] A tenth aspect of the present invention provides the apparatus for washing and concentrating particulate slurry according to the eighth or ninth aspect, wherein the filtrate sensor is provided downstream of the agitation crossflow filtration device and upstream of the flow path switching device.

[0035] According to the apparatus for concentrating a particulate slurry of Aspect 10, the filtrate sensor is provided downstream of the agitation type crossflow filtration device and upstream of the flow path switching device, so that it is possible to appropriately determine whether the filtrate discharged from the agitation type crossflow filtration device should be discarded or reused, thereby reducing the amount of wash water used or the amount of wash wastewater discharged in the apparatus for washing and concentrating a particulate slurry.

[0036] An eleventh aspect of the present invention provides the apparatus for washing and concentrating particulate slurry in any one of the eighth to tenth aspects, wherein the particulates are a precursor of a positive electrode material for a secondary battery.

[0037] According to the washing and concentrating apparatus for a particulate slurry of aspect 11, it is possible to stably produce a particulate slurry as a positive electrode material precursor for a secondary battery while reducing the amount of washing water used or the amount of washing wastewater.

[0038] A twelfth aspect of the present invention provides an apparatus for producing fine particle powder, comprising a conduction heat transfer dryer for drying the fine particle slurry supplied from the apparatus for washing and concentrating fine particle slurry according to the eighth aspect, the dryer having an agitation heat transfer device, the agitation heat transfer device comprising a casing having an inlet at one end and an outlet at the other end, a plurality of rotating shafts arranged within the casing so as to be rotatable about their axes and with the axes parallel to each other, agitation blades fixed to each of the rotating shafts at intervals in the axial direction and so that the agitation blades of each rotating shaft partially overlap when viewed in the axial direction, and a heating mechanism for heating the agitation blades, and by rotating the rotating shafts, the heated agitation blades heat the concentrated slurry supplied from the inlet and transport it to the outlet, during which the concentrated slurry is dried and converted into fine particle powder.

[0039] According to the apparatus for producing fine particle powder of aspect 12, a washing and concentrating apparatus for fine particle slurry, which can reduce the amount of washing water or washing wastewater used in an apparatus for producing fine particle slurry, and a dryer, which can dry the fine particle slurry by conductive heat transfer with excellent thermal efficiency and stably produce fine particle powder, are used in combination, thereby reducing the environmental load.

[0040] A method for producing a fine particle powder according to aspect 13 of the present invention comprises a dilution, washing, and filtration step of adding a washing liquid to a slurry containing fine particles having a particle size of 7 μm or less and a mother liquor, and filtering the resulting slurry through an agitation cross-flow filtration device to obtain a washing slurry; a concentration step of concentrating the washing slurry through the agitation cross-flow filtration device to obtain a concentrated slurry; a flow path switching step of measuring the electrical conductivity or density of the filtrate discharged from the agitation cross-flow filtration device, discarding the filtrate when the electrical conductivity or density is equal to or greater than a threshold value, and reusing the filtrate as the washing liquid when the electrical conductivity or density is below the threshold value; and a drying step of heating and drying the concentrated slurry to obtain a fine particle powder.

[0041] According to the method for producing a fine-particle powder of Aspect 13, the electrical conductivity or density of the filtrate discharged from the agitation-type cross-flow filtration device is measured, and the filtrate is discarded when the electrical conductivity or density of the filtrate is equal to or greater than a threshold value, and is reused when the electrical conductivity or density of the filtrate is less than the threshold value, thereby making it possible to stably produce a fine-particle powder while reducing the amount of washing water used or the amount of washing wastewater used in the fine-particle powder production device.

[0042] A fourteenth aspect of the present invention provides an apparatus for concentrating a particulate slurry, comprising: a slurry tank for storing the particulate slurry; a cleaning liquid supplying device for supplying a cleaning liquid to the slurry tank; an agitation type cross-flow filtration device for concentrating the particulate slurry; a first flow path for supplying the particulate slurry stored in the slurry tank to the agitation type cross-flow filtration device; a second flow path for returning the concentrated slurry discharged from the agitation type cross-flow filtration device to the slurry tank; a density sensor for generating a signal corresponding to the density of the concentrated slurry discharged from the agitation type cross-flow filtration device; and a control device for controlling the amount of the cleaning liquid supplied to the slurry tank by the cleaning liquid supplying device based on the output of the density sensor.

[0043] According to the apparatus for concentrating particulate slurry of Aspect 14, particulate slurry stored in the slurry tank is supplied to the agitation crossflow filtration device through the first flow path and concentrated, while the concentrated slurry discharged from the agitation crossflow filtration device is returned to the slurry tank through the second flow path as needed. During this process, the density sensor measures the density of the concentrated slurry discharged from the agitation crossflow filtration device, and the amount of cleaning liquid supplied to the slurry tank by the cleaning liquid supply device is controlled based on the output of the density sensor. Therefore, compared to means such as monitoring the stirring torque of the slurry, the use of the density sensor makes it possible to accurately grasp changes in the viscosity of the slurry even in high concentration ranges, enabling viscosity to be controlled with high precision, and particulate slurry can be stably concentrated even in high concentration ranges while suppressing clogging of the flow path.

[0044] A fifteenth aspect of the present invention provides an apparatus for concentrating a fine particle slurry according to the fourteenth aspect, further comprising a conductivity sensor that generates a signal corresponding to the conductivity of the filtrate discharged from the agitation type cross-flow filtration apparatus, wherein the control device switches from the initial concentration step (A) described below to the dilution and washing step (B) described below, or from the final concentration step (C) described below to the discharge step (D) described below, based on the output of the density sensor, or indicates the timing of the switching, and also switches from the dilution and washing step (B) described below to the final concentration step (C) described below, or indicates the timing of the switching, based on the output of the density sensor and the output of the conductivity sensor. (A) an initial concentration step in which the fine particle slurry stored in the slurry tank is supplied to the agitation type crossflow filtration apparatus through the first flow path, and the concentrated slurry discharged from the agitation type crossflow filtration apparatus is returned to the slurry tank through the second flow path, thereby separating mother liquor from the fine particle slurry and obtaining an initially concentrated slurry; (B) a dilution and washing step in which the washing liquid supply apparatus supplies a washing liquid to the slurry tank, the initially concentrated slurry stored in the slurry tank is supplied to the agitation type crossflow filtration apparatus through the first flow path, and the concentrated slurry discharged from the agitation type crossflow filtration apparatus is returned to the slurry tank through the second flow path, thereby diluting and washing the initially concentrated slurry to obtain a washed slurry; (C) a final concentration step of stopping the supply of the cleaning liquid to the slurry tank by the cleaning liquid supply device, supplying the cleaning slurry stored in the slurry tank to the agitation type cross-flow filtration device through the first flow path, and returning the concentrated slurry discharged from the agitation type cross-flow filtration device to the slurry tank through the second flow path, thereby separating the cleaning liquid from the cleaning slurry and obtaining a final concentrated slurry; and (D) a discharge step of discharging the final concentrated slurry from the agitation type cross-flow filtration device.

[0045] According to the device for concentrating a microparticle slurry of aspect 15, the slurry can be stably concentrated even in a high concentration range by switching between an initial concentration step (A) for obtaining an initial concentrated slurry, a dilution and washing step (B) for diluting and washing the initial concentrated slurry to obtain a washed slurry, a final concentration step (C) for concentrating the washed slurry to obtain a final concentrated slurry, and a discharge step (D) for discharging the final concentrated slurry, based on the output of the density sensor, or based on the output of the density sensor and the output of the conductivity sensor.

[0046] A sixteenth aspect of the present invention provides an apparatus for concentrating a fine particle slurry according to the fourteenth aspect, further comprising a second density sensor that generates a signal corresponding to the density of the filtrate discharged from the agitation type cross-flow filtration apparatus, and the control device switches, or indicates the timing of switching, from the initial concentration step (A) described below to the dilution and washing step (B) described below, from the dilution and washing step (B) described below to the final concentration step (C) described below, or from the final concentration step (C) described below to the discharge step (D) described below, based on the outputs of the density sensor and the second density sensor. (A) an initial concentration step in which the fine particle slurry stored in the slurry tank is supplied to the agitation type crossflow filtration apparatus through the first flow path, and the concentrated slurry discharged from the agitation type crossflow filtration apparatus is returned to the slurry tank through the second flow path, thereby separating mother liquor from the fine particle slurry and obtaining an initially concentrated slurry; (B) a dilution and washing step in which the washing liquid supply apparatus supplies a washing liquid to the slurry tank, the initially concentrated slurry stored in the slurry tank is supplied to the agitation type crossflow filtration apparatus through the first flow path, and the concentrated slurry discharged from the agitation type crossflow filtration apparatus is returned to the slurry tank through the second flow path, thereby diluting and washing the initially concentrated slurry to obtain a washed slurry; (C) a final concentration step of stopping the supply of the cleaning liquid to the slurry tank by the cleaning liquid supply device, supplying the cleaning slurry stored in the slurry tank to the agitation type cross-flow filtration device through the first flow path, and returning the concentrated slurry discharged from the agitation type cross-flow filtration device to the slurry tank through the second flow path, thereby separating the cleaning liquid from the cleaning slurry and obtaining a final concentrated slurry; and (D) a discharge step of discharging the final concentrated slurry from the agitation type cross-flow filtration device.

[0047] According to the device for concentrating a microparticle slurry of aspect 16, the slurry can be stably concentrated even in a high concentration range by switching between an initial concentration step (A) for obtaining an initial concentrated slurry, a dilution and washing step (B) for diluting and washing the initial concentrated slurry to obtain a washed slurry, a final concentration step (C) for concentrating the washed slurry to obtain a concentrated slurry, and a discharge step (D) for discharging the final concentrated slurry, based on the outputs of the density sensor and the second density sensor.

[0048] In the device for concentrating microparticle slurry according to aspect 17 of the present invention, in aspect 15 or 16, the control device performs feedback control based on the output of the density sensor during the dilution cleaning process, by reducing or stopping the supply of the cleaning liquid from the cleaning liquid supply device if the density of the concentrated slurry is lower than the lower limit of the target density range, and by increasing or starting the supply of the cleaning liquid from the cleaning liquid supply device if the density of the concentrated slurry is higher than the upper limit of the target density range.

[0049] According to the device for concentrating a particulate slurry of Aspect 17, by performing feedback control of the supply amount of the cleaning liquid based on the output of the density sensor, it is possible to stably concentrate the slurry even in a high concentration range while maintaining the density of the concentrated slurry discharged from the agitation type cross-flow filtration device within a certain range.

[0050] In the device for concentrating a microparticle slurry according to aspect 18 of the present invention, in aspect 15 or 17, the control device compares the output of the density sensor with a slurry density corresponding to a predetermined value within a range of a solid content concentration of the concentrated slurry of 35 to 65 wt % in the initial concentration step (A), and switches to the dilution washing step (B) when the density sensor reaches a slurry density corresponding to the predetermined value, or indicates the timing for switching to the dilution washing step (B).

[0051] According to the device for concentrating a fine particle slurry of aspect 18, the control device can switch to the dilution and washing process (B) in the initial concentration step (A) based on the output of the density sensor when the solid content of the concentrated slurry reaches a predetermined value within the range of 35 to 65 wt %, thereby enabling a smooth transition from the initial concentration step (A) to the dilution and washing process (B) at an appropriate timing and improving the washing efficiency.

[0052] Aspect 19 of the present invention relates to a microparticle slurry concentrating device in aspect 16, wherein the control device switches to the dilution and washing process (B) when the solids concentration of the concentrated slurry reaches a predetermined value within the range of 35 to 65 wt % based on the outputs of the density sensor and the second density sensor in the initial concentration process (A), or indicates the timing to switch to the dilution and washing process (B).

[0053] According to the device for concentrating a fine particle slurry of aspect 19, the control device can switch to the dilution and washing process (B) in the initial concentration step (A) based on the outputs of the density sensor and the second density sensor when the solid content of the concentrated slurry reaches a predetermined value within the range of 35 to 65 wt %, thereby enabling a smooth transition from the initial concentration step (A) to the dilution and washing process (B) at an appropriate timing and improving the washing efficiency.

[0054] In the device for concentrating a microparticle slurry according to aspect 20 of the present invention, in any of aspects 15, 17 and 18, the control device compares the output of the density sensor with a slurry density corresponding to a predetermined value within the range of a solids concentration of the concentrated slurry of 50 to 65 wt%, in the final concentration step, and transitions to the discharge step (D) when the density sensor reaches a slurry density corresponding to the predetermined value.

[0055] According to the concentrating device for fine particle slurry of aspect 20, in the final concentration step (C), the control device operates to stop returning the concentrated slurry to the slurry tank and transition to the discharge step (D) when the solids concentration of the concentrated slurry reaches a predetermined value within the range of 50 to 65 wt% based on the output of the density sensor, thereby making it possible to smoothly transition from the final concentration step (C) to the discharge step (D) at an appropriate timing. In addition, the amount of water removed in the drying step after the discharge step (D) can be reduced as much as possible, and the energy cost required for drying can also be suppressed.

[0056] In the device for concentrating a microparticle slurry according to aspect 21 of the present invention, in any of aspects 16, 17 and 19, the control device transitions to the discharge step (D) when, in the final concentration step (C), the solids concentration of the concentrated slurry reaches a predetermined value within the range of 50 to 65 wt % based on the outputs of the density sensor and the second density sensor.

[0057] According to the concentrating device for fine particle slurry of aspect 21, in the final concentration step (C), the control device operates to stop returning the concentrated slurry to the slurry tank and transition to the discharge step (D) when the solids concentration of the concentrated slurry reaches a predetermined value within the range of 50 to 65 wt% based on the outputs of the density sensor and the second density sensor, thereby making it possible to smoothly transition from the final concentration step (C) to the discharge step (D) at an appropriate timing. In addition, the amount of water removed in the drying step after the discharge step (D) can be reduced as much as possible, and the energy cost required for drying can also be suppressed.

[0058] In a twenty-second aspect of the present invention, in the apparatus for concentrating a particulate slurry according to any one of aspects 14 to 21, the density sensor is a vibrating in-line density sensor having a vibrator in contact with the concentrated slurry and a controller that vibrates the vibrator and measures its resonant frequency. Furthermore, in any one of aspects 16, 19, and 21, the second density sensor may be a vibrating in-line density sensor having a vibrator in contact with the concentrated slurry and a controller that vibrates the vibrator and measures its resonant frequency.

[0059] According to the device for concentrating a particulate slurry of aspect 22, the vibrating density sensor vibrates the vibrator in contact with the concentrated slurry, and the resonant frequency is measured as a function of the density of the concentrated slurry. Therefore, even if the concentrated slurry has a high concentration and a high viscosity, the density of the concentrated slurry can be measured with high accuracy without delay. This makes it possible to stably concentrate the particulate slurry even in a high concentration range while preventing clogging by the concentrated slurry. The same applies when the second density sensor is a vibrating inline density sensor.

[0060] Aspect 23 of the present invention provides an apparatus for concentrating a fine particle slurry, in any of aspects 14 to 22, wherein the agitation-type cross-flow filtration apparatus has a slurry chamber and a filtrate chamber separated by a filter, an agitator arranged along the filter in the slurry chamber, and a drive unit that moves the agitator along the filter to prevent the deposition of fine particles on the surface of the filter, and concentrates the fine particle slurry passing through the slurry chamber.

[0061] According to the device for concentrating a fine particle slurry of Aspect 23, the agitation-type cross-flow filtration device having the above-described configuration makes it possible to produce concentrated slurry in a high concentration range, and to prevent clogging of the high-concentration slurry while increasing production efficiency in the initial concentration step, dilution-washing step, final concentration step, and drying step, and also to reduce energy costs.

[0062] A twenty-fourth aspect of the present invention provides the device for concentrating particulate slurry according to any one of the fourteenth to twenty-third aspects, wherein the particulates are a precursor of a positive electrode material for a secondary battery.

[0063] According to the concentrating device for fine particle slurry of aspect 24, even when the average particle diameter of the fine particles is extremely small, for example, 7 μm or less, the fine particle slurry can be stably concentrated even in a high concentration range, and a positive electrode material precursor for a secondary battery having a small average particle diameter can be stably obtained.

[0064] A manufacturing apparatus for fine particle powder according to aspect 25 of the present invention comprises the concentrating apparatus for fine particle slurry according to any one of aspects 14 to 24, and an agitation heat transfer drying apparatus for drying the concentrated slurry supplied from the concentrating apparatus for fine particle slurry, wherein the agitation heat transfer drying apparatus comprises a casing having an inlet formed at one end and an outlet formed at the other end, a plurality of rotating shafts arranged within the casing so as to be rotatable about their axes and with the axes parallel to each other, agitator blades fixed to each of the rotating shafts at intervals in the axial direction and so that the agitator blades of each rotating shaft partially overlap when viewed in the axial direction, and a heating mechanism for heating these agitator blades, wherein by rotating the rotating shafts, the heated agitator blades heat the concentrated slurry supplied from the inlet and transfer it to the outlet hole, during which the concentrated slurry is dried and converted into fine particle powder.

[0065] According to the apparatus for producing a fine particle powder of Aspect 25, even when the average particle size of the fine particles is extremely small, for example, 7 μm or less, the fine particle slurry can be stably concentrated even in a high concentration range, and fine particle powder with a small average particle size can be stably produced. Furthermore, the agitation heat transfer drying apparatus evaporates water by conductive heat transfer when the heated agitator blades rotate and come into contact with the slurry, thereby making it possible to reduce energy costs.

[0066] A method for producing a fine particle powder according to Aspect 26 of the present invention comprises a dilution, washing, and filtering step of adding a washing liquid to a slurry containing fine particles having a particle size of 7 μm or less and a mother liquor, and filtering the resulting slurry using an agitation cross-flow filtration device to obtain a washing slurry; a concentration step of concentrating the washing slurry using the agitation cross-flow filtration device to obtain a concentrated slurry; and a drying step of heating and drying the concentrated slurry to obtain a fine particle powder. In the dilution, washing, and filtering step, the density of the washing slurry is measured with a density sensor, and if the density of the washing slurry measured with the density sensor is lower than the lower limit of a target range, the supply amount of the washing liquid in the dilution, washing, and filtering step is reduced or the supply is stopped, and if the density is higher than the upper limit of the target range, the supply amount of the washing liquid in the dilution, washing, and filtering step is increased or the supply is started, thereby performing feedback control.

[0067] According to the method for producing a fine particle powder of aspect 26, even though the average particle size of the fine particles is extremely small, at 7 μm or less, the use of a density sensor makes it possible to accurately grasp the change in viscosity of the slurry even in high concentration ranges, compared to means such as monitoring the stirring torque of the slurry, and it is possible to stably concentrate the slurry even in high concentration ranges while suppressing clogging, making it possible to stably produce fine particle powder with a small average particle size.

[0068] A twenty-seventh aspect of the present invention provides an apparatus for producing a fine particle powder, the apparatus comprising: a slurry tank for storing a fine particle slurry; a cleaning liquid supplying device for supplying a cleaning liquid to the slurry tank; an agitation type cross-flow filtration device for concentrating the fine particle slurry; a first flow path for supplying the fine particle slurry stored in the slurry tank to the agitation type cross-flow filtration device; and a second flow path for returning the concentrated slurry discharged from the agitation type cross-flow filtration device to the slurry tank; and an agitation heat transfer device for drying the concentrated slurry supplied from the apparatus for concentrating the fine particle slurry. and a drying device, the agitation heat transfer drying device having a casing with an inlet formed at one end and an outlet formed at the other end, a plurality of rotating shafts arranged within the casing so as to be rotatable about their axes and with the axes parallel to one another, agitating blades fixed to each of the rotating shafts at axial intervals and so as to partially overlap when viewed in the axial direction, and a heating mechanism for heating the agitating blades, and by rotating the rotating shafts, the heated agitating blades heat the concentrated slurry supplied from the inlet and transfer it to the outlet hole, during which the concentrated slurry is dried and converted into a fine particle powder.

[0069] According to the microparticle powder manufacturing apparatus of aspect 27, the concentrated slurry is dried by conductive heat transfer, which has excellent thermal efficiency, using an agitation heat transfer drying device, so that microparticle powder can be stably manufactured while improving energy efficiency.

[0070] In the apparatus for manufacturing fine particle powder according to aspect 28 of the present invention, in aspect 27, the rotating shaft is rotated so that the heated stirring blade mixes the concentrated slurry supplied from the inlet with the wet powder held in the casing, heats it, and transports it to the outlet hole, during which time the concentrated slurry is dried and converted into fine particle powder.

[0071] According to the fine particle powder manufacturing apparatus of aspect 28, the concentrated slurry is mixed with the wet powder held in the casing and heated, thereby avoiding abnormal adhesion that would impede the function of the stirring heat transfer drying device and facilitating the transport of the mixture within the casing.

[0072] Aspect 29 of the present invention is an apparatus for manufacturing fine particle powder, in either aspect 27 or 28, wherein, on each of two adjacent rotating shafts, the pair of stirring blades is fixed at positions rotationally symmetrical by 180° around the rotating shaft, and on each of the rotating shafts, the stirring blades are inclined in opposite directions relative to the rotating shaft and have a twist along an imaginary spiral plane around the rotating shaft, and the two adjacent rotating shafts rotate in opposite directions to each other.

[0073] According to the apparatus for producing fine particle powder in Aspect 29, the locus of the agitating blade oscillates in the axial direction within a certain angular range every time the rotating shaft rotates 180°, so that the final concentrated slurry and the wet powder can be mixed between adjacent agitating blades in the axial direction while preventing the final concentrated slurry and the wet powder from adhering to the agitating blades. Furthermore, because the agitating blades have a twist along an imaginary helical plane about the rotating shaft, the mixture of the final concentrated slurry and the wet powder can be gradually transported from the upstream side to the downstream side of the casing as the rotating shaft rotates.

[0074] A 30th aspect of the present invention provides the apparatus for producing a fine particle powder in any one of Aspects 27 to 29, wherein the fine particle powder is a precursor of a positive electrode material for a secondary battery.

[0075] According to the apparatus for producing a fine particle powder according to Aspect 30, it is possible to stably produce a positive electrode material precursor for a secondary battery while improving the energy efficiency when drying the concentrated slurry.

[0076] A method for producing a fine particle powder according to a thirty-first aspect of the present invention includes a concentrating device for fine particle slurry, the concentrating device including a slurry tank for storing fine particle slurry, a cleaning liquid supplying device for supplying a cleaning liquid to the slurry tank, an agitation type cross-flow filtration device for concentrating the fine particle slurry, a first flow path for supplying the fine particle slurry stored in the slurry tank to the agitation type cross-flow filtration device, and a second flow path for returning the concentrated slurry discharged from the agitation type cross-flow filtration device to the slurry tank, and an agitation heat transfer dryer for drying the concentrated slurry supplied from the concentrating device for fine particle slurry. and a drying device, the agitation heat transfer drying device having a casing with an inlet formed at one end and an outlet formed at the other end, a plurality of rotating shafts arranged within the casing so as to be rotatable about their axes and with the axes parallel to one another, agitating blades fixed to each of the rotating shafts at intervals in the axial direction and so as to partially overlap when viewed in the direction of the axes, and a heating mechanism for heating the agitating blades, and by rotating the rotating shafts, the heated agitating blades heat the concentrated slurry supplied from the inlet and transfer it to the outlet hole, during which the concentrated slurry is dried and converted into a fine particle powder.

[0077] According to the method for producing a fine particle powder of Aspect 31, the concentrated slurry is heated and dried by conductive heat transfer, which has excellent thermal efficiency, and thus, in the step of drying the concentrated slurry, the fine particle powder can be stably produced while improving energy efficiency.

[0078] As described above, the method and apparatus for producing fine particle powder of the present invention can produce fine particles of 7 μm or less in the fine particle slurry production process, and the subsequent washing, concentration, and drying can be carried out efficiently, thereby reducing energy costs and increasing production efficiency.

[0079] As described above, according to the apparatus for washing and concentrating a microparticle slurry, and the apparatus and method for producing a microparticle powder of the present invention, the electrical conductivity or density of the filtrate discharged from the agitation type cross-flow filtration device is measured, and the filtrate is discarded if the electrical conductivity or density of the filtrate is equal to or greater than a threshold value, and is reused if the electrical conductivity or density of the filtrate is less than the threshold value, thereby achieving the excellent effect of reducing the amount of washing water or washing wastewater used in the apparatus for washing and concentrating a microparticle slurry while stably producing a microparticle powder.

[0080] As described above, according to the microparticle slurry concentrating device, microparticle powder manufacturing device, and manufacturing method of each aspect of the present invention, the density sensor accurately detects the viscosity change of the slurry even in a high concentration range, and the control device controls the amount of cleaning liquid supplied to the slurry tank by the cleaning liquid supply device, so that it is possible to stably concentrate the microparticle slurry even in a high concentration range while suppressing blockage of the filter and associated flow paths.

[0081] As described above, according to the apparatus and method for producing fine particle powder of the present invention, it is possible to stably produce fine particle powder while improving energy efficiency in the step of drying concentrated slurry.

[0082] FIG. 1 is a block diagram showing a fine particle powder manufacturing apparatus according to a first embodiment of the present invention. FIG. 2 is a block diagram showing a fine particle slurry manufacturing apparatus according to the same embodiment. FIG. 3 is a cross-sectional view showing an agitation type crossflow filtration apparatus according to the same embodiment. FIG. 4 is a side cross-sectional view showing a drying apparatus according to the same embodiment. FIG. 5 is a plan view showing the drying apparatus according to the same embodiment with the top plate removed. FIG. 6 is a front cross-sectional view showing the drying apparatus according to the same embodiment. FIG. 7 is a block diagram showing a fine particle powder manufacturing apparatus according to a second embodiment of the present invention. FIG. 8 is a block diagram showing a fine particle powder manufacturing apparatus according to third and fourth embodiments of the present invention. FIG. 9 is a cross-sectional view showing an agitation type crossflow filtration apparatus, a density sensor, a conductivity sensor, and a second density sensor according to the third and fourth embodiments. FIG. 10 is a flowchart showing an example of process switching control according to the third embodiment. FIG. 11 is a flowchart showing an example of process switching control according to the fourth embodiment. FIG. 12 is a graph showing the operation of a control device according to the third and fourth embodiments. FIG. 13 is a graph showing another example of the operation of a control device according to the third and fourth embodiments. FIG. 14 is a block diagram showing a fine particle powder manufacturing apparatus according to a fifth embodiment of the present invention.

[0083] A first embodiment of the apparatus for producing fine particle powder 1 according to the present invention will now be described in detail. The apparatus for producing fine particle powder 1 includes a crystallizer 10 (reaction reactor) for producing a fine particle slurry containing fine particles with a particle size of 7 μm or less by reacting a plurality of raw materials in a mother liquor swirling in the crystallizer 10 (reaction reactor), a slurry tank 30 for stirring the fine particle slurry produced in the apparatus for producing fine particle slurry 2 and washing the slurry with a washing solution according to the processing stage, an agitation cross-flow filtration device 6 for concentrating the fine particle slurry or the washed slurry delivered from the slurry tank 30 by removing a portion of the mother liquor and the washing solution, and a conduction heat transfer drying device (dryer) 8 for transferring the final concentrated slurry after the final concentration in the agitation cross-flow filtration device 6 while mixing it with wet powder previously stored in a casing 92 using heated agitation blades and drying the final concentrated slurry by conduction heat transfer. The final concentrated slurry may also be simply referred to as "concentrated slurry."

[0084] [Crystallizer] As shown in FIG. 2, the crystallizer 10 has an elongated cylindrical reaction vessel 116. The upstream side of the reaction vessel 116 is cylindrical, and the downstream side has a coaxial, conically tapered section 116A that narrows toward the downstream side. A cylindrical outer tube 110 is coaxially disposed within the reaction vessel 116, extending from the upstream end to the tapered section 116A. The upstream end of the outer tube 110 opens at the upstream end of the reaction vessel 116. A first inner tube 112 and a second inner tube 114 are inserted within the outer tube 110. The first inner tube 112 protrudes from the downstream end of the outer tube 110, and the second inner tube 114 protrudes from the downstream end of the outer tube 110 by a distance greater than the first inner tube 112. A first raw material 12A is supplied into the reaction vessel 116 from the first inner tube 112, and a second raw material 12B is supplied from the second inner tube 114. If necessary, the mother liquor 12C can be supplied into the reaction vessel 116 through the gaps between the outer tube 110 and each of the first inner tube 112 and the second inner tube 114.

[0085] An inlet 115 is formed on the outer periphery of the upstream end of reaction vessel 116. By injecting a reaction liquid from inlet 115 at high speed, a swirling flow is generated within reaction vessel 116. As the inner diameter narrows at tapered section 116A, the rotation speed increases, and the resulting vortex is discharged from discharge hole 14. Outer tube 110, first inner tube 112, and second inner tube 114 are located at the center of the swirling flow, and first raw material 12A from first inner tube 112 and second raw material 12B from second inner tube 114 are mixed while being vigorously stirred in central region R of the swirling flow within tapered section 116A. During this mixing process, first raw material 12A and second raw material 12B are mixed and reacted at high speed, producing a reaction product as very small particles that flow out of discharge hole 14 together with the reaction liquid.

[0086] A conduit 16 is connected to the discharge hole 14, and the reaction liquid containing the microparticles is supplied to a reservoir 18 through the conduit 16. A flow rate control valve 118 is provided upstream of the conduit 16 connected to the discharge hole 14, and is opened and closed by a drive unit 120 to adjust the outflow rate of the reaction liquid from the discharge hole 14. The drive unit 120 is controlled manually or automatically by a control panel (not shown) in accordance with the reading of a pressure gauge 122 that measures the inflow pressure from the inlet 115. When the reading of the pressure gauge 122 is high, the opening of the flow rate control valve 118 is increased to promote the outflow of the reaction liquid, and when the reading of the pressure gauge 122 is low, the opening of the flow rate control valve 118 is decreased to suppress the outflow of the reaction liquid. This ensures that the crystallization of microparticles in the reaction vessel 116 is carried out appropriately.

[0087] A stirring blade 128 rotated by a motor 126 is disposed in the reservoir 18 to stir the reaction liquid uniformly and prevent the fine particles from settling. A conduit 20 is connected to the lower end of the reservoir 18, and the slurry containing the fine particles flowing out from the lower end of the reservoir 18 is pressurized by a pump 22, passes through a temperature regulator 124, passes through the conduit 24 and a pressure gauge 122, and is blown into the reaction vessel 116 from an inlet 115. The temperature regulator 124 serves to appropriately adjust the temperature of the reaction liquid in the reaction vessel 116.

[0088] In this embodiment, the types of the first raw material 12A and the second raw material 12B are not limited, but may be any materials that can precipitate a compound with low solubility by reacting the first raw material 12A and the second raw material 12B. As an example, when producing a positive electrode material precursor for a secondary battery, a solution containing a transition metal element such as nickel salt can be used as the first raw material 12A and an alkaline solution can be used as the second raw material 12B, and the materials can be reacted in the crystallizer 10 to obtain fine particles mainly composed of a transition metal hydroxide. More specifically, as the raw material for the positive electrode material precursor for a secondary battery, an aqueous solution of nickel sulfate, cobalt sulfate, manganese sulfate, or the like can be used as the first raw material 12A, and an aqueous sodium hydroxide solution, ammonia water, or the like can be used as the second raw material 12B.

[0089] The particle size of the microparticles in the microparticle slurry produced by the crystallizer 10 is preferably 7 μm or less, more preferably 1 μm or more and 5 μm or less, and even more preferably 1 μm or more and 3 μm or less. In this specification, the particle size of the microparticles in the microparticle slurry is measured by laser diffraction and scattering. Furthermore, the particle size in this specification refers to the average particle size at 50% of the integrated value in the particle size distribution measured by the above measurement method. The crystallizer 10 using a swirling flow can suppress the growth of crystal grains after they are formed, making it easy to produce a slurry containing microparticles with such fine particle sizes. When producing a precursor for a positive electrode material for a secondary battery, for example, a microparticle particle size of 7 μm or less can improve the homogeneity of the positive electrode material for the secondary battery, thereby improving performance. In other applications, having the particle size of the microparticles as small and uniform as possible can be expected to improve the performance of the final product. However, the present invention may also target microparticles with an average particle size greater than 7 μm, if necessary.

[0090] The reservoir 18 stores the fine particle slurry containing fine particles produced in the crystallizer 10. A wave-breaking partition plate 130 is arranged in a portion of the reservoir 18 near the liquid surface, and a fine particle slurry outlet 26 is formed in the side wall of the reservoir 18 facing the partition plate 130, to which a conduit 28 leading to a slurry tank 30 is connected. A withdrawal valve 132 and a pump 134 are provided in the conduit 28, and the fine particle slurry is transferred from the reservoir 18 to the slurry tank 30 at an appropriate timing and flow rate. Note that a portion of the fine particle slurry stored in the reservoir 18 may be withdrawn and concentrated, and the concentrated slurry may then be returned to the reservoir 18. By performing the concentration operation, crystallization can be carried out with the slurry at a high concentration.

[0091] The solids concentration in the particulate slurry transferred from outlet 26 to slurry tank 30 is not limited, but is preferably 5 wt % to 40 wt %, more preferably 10 wt % to 40 wt %, and even more preferably 15 wt % to 40 wt %, when producing a positive electrode material precursor for a secondary battery, for example. Within this concentration range, the particulates can be produced stably, and the load balance in the subsequent slurry tank 30, agitation type cross-flow filtration device 6, and drying device 8 is good, making it possible to improve overall processing efficiency and energy efficiency without overloading each process and impairing stability.

[0092] [Slurry Tank] As shown in FIG. 1 , the slurry tank 30 has the function of temporarily storing the fine particle slurry sent from the reservoir 18 and sending it to the agitation type cross-flow filtration device 6, or of adding a cleaning liquid to an initially concentrated slurry obtained by initially concentrating the fine particle slurry to wash it, and sending the resulting washed slurry to the agitation type cross-flow filtration device 6.

[0093] The slurry tank 30 is cylindrical with a bottom, and the inner surface of the bottom is hemispherical. A semicircular anchor-shaped agitator blade 34 is arranged along the inner surface of the bottom of the slurry tank 30 with a small, constant gap between it and the inner surface of the bottom, and is rotated coaxially with the slurry tank 30 by a motor 36. A cleaning liquid source 38 is provided for supplying clean cleaning liquid to the slurry tank 30, and a first port of a three-way valve 42 is connected via a conduit 40. A second port of the three-way valve 42 is connected to the slurry tank 30 via an on-off valve 44, and a third port of the three-way valve 42 is connected via a conduit 46 to a pump 48 and a cleaning liquid tank 50.

[0094] The amount of gap between the outer periphery of the anchor-shaped agitator blade 34 and the inner bottom surface of the slurry tank 30 is not limited, but a gap of, for example, approximately 0.5 to 3.0 cm is preferred in order to prevent fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 30. Furthermore, the length of the semicircular outer periphery of the anchor-shaped agitator blade 34 is preferably long enough to face the entire inner bottom surface of the anchor-shaped agitator blade 34. The rotational peripheral speed of the outer periphery of the anchor-shaped agitator blade 34 driven by the motor 36 is not limited, but is preferably approximately 0.1 to 3.0 m / sec. A gap within this range is highly effective in preventing fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 30.

[0095] When concentrating the slurry in each process, the slurry is circulated between the slurry tank 30 and the agitation type cross-flow filtration device 6 while the filtrate is withdrawn from the agitation type cross-flow filtration device 6. This gradually concentrates the slurry, but when it reaches a high concentration, the viscosity of the slurry also increases, and with a conventional paddle-type agitator, only the slurry liquid near the agitator can be convected. As a result, it is not possible to maintain a uniform slurry throughout the slurry tank 30, and fine particles settle within the slurry tank 30, creating a hard, compressed solid layer at the bottom of the slurry tank 30, making it impossible to withdraw the slurry. The anchor-type agitator blade 34 can solve this problem.

[0096] Furthermore, although each step in this apparatus can be performed batchwise, if the subsequent drying device 8 is operated continuously, a buffer means for holding the slurry in each step for a relatively long period of time is required. Therefore, by using the slurry tank 30 equipped with the anchor-shaped stirring blades 34 as described above, it is possible to cause uniform convection throughout the slurry in the slurry tank 30, preventing the accumulation and adhesion of fine particles.

[0097] In particular, when producing a cathode material precursor for a secondary battery, the fine particles are metal compounds with a large specific gravity, and therefore, if the slurry tank 30 is not stirred uniformly, the solids will quickly settle to the bottom of the tank, become hard and compacted, and become impossible to extract, etc. Furthermore, because the highly concentrated slurry has a large specific gravity and an extremely high viscosity, a typical paddle-type stirring blade can only cause convection in the slurry near the stirring blade, making it difficult to cause uniform convection throughout the entire slurry tank 30 and maintain a dispersed state.

[0098] The cleaning solution tank 50 is a container for storing a fraction of the filtrate discharged from the agitation-type crossflow filtration device 6 that contains relatively few impurities. The conductivity of the filtrate can be used as an indicator of the impurity content. If the conductivity is higher than a preset threshold, the filtrate contains a large amount of electrolyte impurities, which can adversely affect, for example, a positive electrode material precursor for a secondary battery. For example, if the detected conductivity is higher than the preset threshold, the three-way valve 42 and the on-off valve 44 can be operated to select and supply either clean cleaning solution from the cleaning solution source 38 or clean cleaning solution recovered from the agitation-type crossflow filtration device 6 in the cleaning solution tank 50 to the slurry tank 30.

[0099] A discharge hole 52 is formed at the bottom lower end of the slurry tank 30, and slurries in various states (fine particle slurry, initial concentrated slurry, washing slurry, or final concentrated slurry) extracted from the slurry tank 30 are sent via a pump 54 to a conduit 56, so that the slurries in various states can be transferred to the agitation type cross-flow filtration device 6 through the conduit (first flow path) 56.

[0100] [Agitation-Type Crossflow Filtration Apparatus] As shown in FIG. 3 , the agitation-type crossflow filtration apparatus 6 has a cylindrical casing 60 arranged substantially horizontally. A rotating shaft 140 is disposed along the centerline of the casing 60 and is rotated by a motor 62. A plurality of disk-shaped agitation blades 142 are fixed to the rotating shaft 140 at regular intervals along the axial direction. The outer diameter of the agitation blades 142 is smaller than the inner diameter of the casing 60. Ring-shaped filters 146 of a constant thickness are fixed coaxially with the casing 60 on the inner circumferential surface of the casing 60 between adjacent agitation blades 142, and each filter 146 forms a disk-shaped filtrate chamber 148. The number of agitation blades 142 and filters 146 is determined based on the processing capacity required for the agitation-type crossflow filtration apparatus 6. Gaps of a constant thickness are formed between the inner surface of the casing 60, the agitation blades 142, and the filters 146, and these gaps form slurry chambers 150.

[0101] An inlet 144 is formed at the upstream end of the casing 60, and slurry in various states supplied from the inlet 144 is conveyed downstream, meandering through a slurry chamber 150, while being kneaded between the rotating agitator blades 142 and a fixed filter 146. The slurry chamber 150 is pressurized by the liquid-transfer pressure of the pump 54, and during this conveyance process, the slurry is agitated by the rotation of the agitator blades 142 and pressed against the filter 146, causing the mother liquor and washing liquid in the slurry to pass through the filter 146 and enter the filtrate chamber 148. The material of the filter 146 need only be one that does not allow fine particles in the slurry to pass through, allows the filtrate to pass through, and has sufficient mechanical strength.

[0102] Filtrate discharge valves 154 communicating with the respective filtrate chambers 148 are attached to the casing 60, and the outlets of the filtrate discharge valves 154 are connected together to a conduit 156. The filtrate that has entered the filtrate chambers 148 flows out through the filtrate discharge valves 154 to the conduit 156. As shown in Figure 1, this conduit 156 is connected to a first port of a three-way valve 74, which serves as a flow path switching device, and a second port of the three-way valve 74 is connected to the drain path 80 via a conduit (waste flow path) 78. A third port of the three-way valve 74 is connected to the cleaning liquid tank 50 via a conduit (return flow path) 76.

[0103] [Conductivity Sensor] As shown in FIG. 1 , a conductivity sensor 71 is installed in the conduit 156, which serves as the filtrate outlet of the agitation type crossflow filtration device 6. The conductivity sensor 71 continuously measures the conductivity of the filtrate discharged from the agitation type crossflow filtration device 6 and transmits the measured value to the control device 67. The control device 67 receives the output of the conductivity sensor 71 and uses the output result and the pre-stored filtrate conductivity to detect the progress of the dilution cleaning process and determine the completion timing of the dilution cleaning process. Specifically, the control device 67 determines that the dilution cleaning process has been completed when the output result falls below a threshold value set in the control device 67. Note that the completion timing of the dilution cleaning process may be determined by other sensors, not limited to the conductivity sensor 71. For example, a second density sensor (not shown) may be installed in the conduit 156, which serves as the filtrate outlet of the agitation type crossflow filtration device 6. The second density sensor continuously measures the density of the filtrate discharged from the agitation type crossflow filtration device 6 and transmits the measured value to the control device 67. The control device 67 receives the output of the second density sensor, detects the progress of the dilution cleaning process from the density of the filtrate, and determines the timing for completing the dilution cleaning process.

[0104] During initial concentration by the agitation crossflow filtration device 6 and for a while after the start of cleaning, the filtrate entering the filtrate chamber 148 contains a large amount of impurities. However, as filtration progresses, the filtrate becomes less impurity-rich, and the conductivity detected by the conductivity sensor 71 decreases. Therefore, when the conductivity reaches a predetermined threshold, the control device 67 switches the three-way valve 74, so that the filtrate previously flowing to the drain 80 is stored in the cleaning liquid tank 50. The relatively clean filtrate stored in the cleaning liquid tank 50 is supplied as cleaning liquid to the slurry tank 30 via the conduit 46, the three-way valve 42, and the on-off valve 44 by operating the pump 48 in the next dilution cleaning process. This reduces the amount of cleaning liquid used in the cleaning liquid source 38, helping to reduce the cost of producing fine-particle powder. Furthermore, the amount of filtrate and cleaning waste liquid disposed of outside the fine-particle powder production apparatus 1 is reduced, thereby reducing the environmental impact.

[0105] The downstream portion of the casing 60 is a conical tapered portion 152 that narrows downstream, and a discharge port 64 is formed at the tip of the tapered portion 152. The slurry is transported downstream while snaking through the slurry chamber 150, and moisture is removed. The slurry is circulated between the slurry tank 30 and the agitation type cross-flow filtration device 6, where it is filtered and concentrated. The highly viscous concentrated slurry is discharged from the discharge port 64.

[0106] The solids concentration of the concentrated slurry discharged from the outlet 64 of the agitation crossflow filtration device 6 is not necessarily limited, as optimal values ​​differ among the initial concentration step, the dilution and washing step, and the final concentration step. For example, when producing a cathode material precursor for a secondary battery, the solids concentration of the initially concentrated slurry at the completion of the initial concentration step is preferably 35 wt % or more and 65 wt % or less, more preferably 45 wt % or more and 65 wt % or less. The solids concentration of the washed slurry at the completion of the dilution and washing step is preferably 35 wt % or more and 60 wt % or less, more preferably 35 wt % or more and 45 wt % or less. The solids concentration of the final concentrated slurry at the completion of the final concentration step is preferably 50 wt % to 65 wt %, more preferably 60 wt % or more and 65 wt % or less.

[0107] When the concentration is within the above range in each step, the transport of the concentrated slurry within the casing 60 of the agitation type crossflow filtration device 6 is not difficult, and it is possible to effectively reduce the amount of impurities in the final concentrated slurry while limiting the consumption of washing liquid. Therefore, the load on the agitation type crossflow filtration device 6 and the drying device 8 is well balanced, and it is possible to improve the total processing efficiency and energy efficiency without overloading each step.

[0108] As shown in FIG. 1 , the discharge port 64 of the casing 60 is connected to a first port of a three-way valve 70 (a process switching device) via a density sensor 66 and a flow control valve 68. The three-way valve 70 is switched by a control device 67 or manually in response to instructions from a control panel. The second port of the three-way valve 70 is connected to the slurry tank 30 via a conduit 72. The third port of the three-way valve 70 is connected to a slurry tank 82 for storing the final concentrated slurry, which is provided upstream of the drying device 8. By operating the three-way valve 70, the slurry in various states discharged from the discharge port 64 of the agitation type crossflow filtration device 6 can be returned to the slurry tank 30 for circulation or supplied to the slurry tank 82, which serves as a buffer for the drying device 8.

[0109] The density of the concentrated slurry discharged from the outlet 64 of the agitation type crossflow filtration device 6 is measured by a density sensor 66, and the output signal of the density sensor 66 is transmitted to a control device 67. The density sensor 66 has two main purposes. The first is to measure the timing at which the concentrated slurry discharged from the agitation type crossflow filtration device 6 is sufficiently dewatered and reaches a predetermined density, and to grasp the timing of completion of at least one of the initial concentration step (a) and the final concentration step (c), and use this timing to control the transition to the next step.

[0110] When determining the timing of completion of the dilution washing process (b), it is preferable to satisfy either of the following conditions: (1) the conductivity of the filtrate decreases to a predetermined threshold based on the output of the conductivity sensor 71, and the density of the concentrated slurry increases to a predetermined threshold based on the output of the density sensor 66, or (2) the conductivity of the filtrate decreases to a predetermined threshold based on the output of the conductivity sensor 71 (the output of the density sensor 66 is not involved in the determination criteria).

[0111] A second purpose of measuring the slurry density using the density sensor 66 is to improve the washing effect of the slurry in the dilution washing step (b). Specifically, a lower limit and an upper limit are set for the density value corresponding to the output signal of the density sensor 66, and the supply of washing liquid from the washing liquid source 38 to the slurry tank 30 is increased (or temporarily stopped and then resumed) when the upper limit is reached, and the supply of washing liquid from the washing liquid source 38 is reduced (or temporarily stopped) when the lower limit is reached, thereby maintaining the solids concentration of the concentrated slurry discharged from the agitation type crossflow filtration device 6 within a certain range and adjusting the degree of cleanliness until the conductivity of the filtrate discharged from the agitation type crossflow filtration device 6 is sufficiently reduced.

[0112] The slurry tank 82 functions as a buffer to adjust the amount of final concentrated slurry supplied to the drying device 8. The slurry tank 82 is cylindrical with a bottom, and the inner surface of the bottom is formed in a hemispherical shape. A semicircular anchor-shaped stirring blade 84 is arranged along the inner surface of the bottom of the slurry tank 82, with a small, fixed gap between it and the inner surface of the bottom, and is rotated by a motor 86. The rotation speed of the motor 86 is adjusted so that the final concentrated slurry does not settle and solidify in the slurry tank 82. A discharge port 88 is formed at the lower end of the bottom of the slurry tank 82, and the highly viscous final concentrated slurry extracted from the slurry tank 82 is sent via a pump 90 to a conduit 94 and then to the drying device 8.

[0113] The gap between the outer periphery of the anchor-shaped agitator blade 84 and the inner bottom surface of the slurry tank 82 is not limited, but similar to the anchor-shaped agitator blade 34 described above, it is preferably approximately 0.5 to 3.0 cm to prevent fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 82. Furthermore, the length of the semicircular outer periphery of the anchor-shaped agitator blade 84 is preferably long enough to face the entire inner bottom surface of the slurry tank 82. Furthermore, the rotational peripheral speed of the outer periphery of the anchor-shaped agitator blade 84 driven by the motor 86 is not limited, but is preferably approximately 0.1 to 3.0 m / s. Within this range, the effect of preventing fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 82 is achieved. This effect is particularly important when producing a cathode material precursor for secondary batteries because the fine particles are metal compounds with a high specific gravity.

[0114] 4 to 6 are a side cross-sectional view, a plan view with the top plate removed, and a front cross-sectional view showing an agitation heat transfer device as the drying device 8. The drying device 8 has a rectangular parallelepiped casing 92, which has a trough-shaped inner wall 194, an outer wall 198 covering the outer peripheral surface of the inner wall 194, and a rectangular top plate 196 closing the upper end of the inner wall 194. An airtight gap of a certain thickness is formed between the inner wall 194 and the outer wall 198, which serves as a heat medium flow path 199. The outer wall 198 is formed with a heat medium inlet 200 and a heat medium outlet (not shown) that communicate with the heat medium flow path 199. By supplying high-temperature steam or heat medium oil from the heat medium inlet 200 to the heat medium outlet, the inside of the casing 92 can be uniformly heated.

[0115] An inlet 96 is formed at the upper end of the upstream side of the casing 92, and a conduit 94 is connected to it. A gas inlet 174 is formed at the upper surface of the upstream side of the casing 92, and a gas outlet 175 is formed at the upper surface of the downstream side. Room temperature or heated air or the like is blown in through the gas inlet 174, and the moist air or the like is discharged from the gas outlet 175 together with water vapor generated as the mother liquor and cleaning liquid evaporate in the casing 92, thereby maintaining an appropriate humidity level by discharging the water vapor generated inside the casing 92 to the outside of the apparatus. Meanwhile, an outlet 98 is formed at the lower surface of the downstream end of the casing 92, and the fine particle powder dried inside the casing 92 is discharged from there.

[0116] Two hollow rotating shafts 176 are arranged symmetrically along the longitudinal direction within the casing 92, and both ends or one end are rotatably supported by bearings. Hollow agitating blades 178 are fixed to each hollow rotating shaft 176 at regular intervals in the axial direction, and in the region between the two hollow rotating shafts 176, the hollow agitating blade 178 of one hollow rotating shaft 176 is located midway between the hollow agitating blades 178 of the other hollow rotating shaft 176.

[0117] As shown in Figure 6, each hollow agitating blade 178 is fan-shaped with a central angle of less than 180°, and pairs of hollow agitating blades 178 are fixed at positions that are 180° rotationally symmetrical about the hollow rotating shaft 176. A notch 190 of a fixed width is formed between the pair of hollow agitating blades 178 to allow the mixture of the final concentrated slurry and wet powder to pass axially. The interior of the hollow agitating blade 178 is hollow and communicates with the internal space of the hollow rotating shaft 176, so that the heat medium supplied to the hollow rotating shaft 176 also enters the interior of the hollow agitating blade 178 and heats it.

[0118] The wet powder is a dried product of the final concentrated slurry that is previously stored in the casing 92. It is not completely dry and is moist. By mixing the previously stored wet powder with the final concentrated slurry, abnormal adhesion that may impede the function of the drying device 8 can be avoided, and transportation within the casing 92 by the hollow agitating blades 178 can be facilitated.

[0119] 4 and 5, the pair of hollow agitator blades 178 are inclined in opposite directions relative to the hollow rotary shaft 176, and each time the hollow rotary shaft 176 rotates 180°, the locus of the hollow agitator blade 178 oscillates in the axial direction within a certain angular range, as shown by the solid and dotted lines in the figures. This oscillation serves to mix the final concentrated slurry and the wet powder while preventing the final concentrated slurry and the wet powder from adhering to the hollow agitator blades 178 adjacent in the axial direction. In addition, the hollow agitator blade 178 also has a twist along an imaginary helical plane around the hollow rotary shaft 176, and serves to gradually transport the mixture of the final concentrated slurry and the wet powder from the upstream side to the downstream side of the casing 92 as the hollow rotary shaft 176 rotates.

[0120] The hollow agitator blade 178 and the hollow rotating shaft 176 are made of a metal with high thermal conductivity, and a heat medium inlet hole 184 and a heat medium outlet hole 182 are formed at the upstream end of the hollow rotating shaft 176. A heat medium such as high-temperature steam or heat medium oil is continuously supplied from a heat medium source (not shown) through the heat medium inlet hole 184 to the heat medium outlet hole 182. The heat medium spreads throughout the entire length of the hollow rotating shaft 176 and also penetrates into the hollow agitator blade 178, heating the entire hollow rotating shaft 176 and hollow agitator blade 178 to a temperature above the boiling points of the mother liquor and washing liquid contained in the final concentrated slurry and the wet powder. Therefore, the mixture of the final concentrated slurry and the wet powder is heated by conduction heat every time it comes into contact with the hollow rotating shaft 176 and hollow agitator blade 178, evaporating the mother liquor and washing liquid contained in the mixture and eventually becoming a fine powder. A rotation mechanism 180 is provided at one end of the hollow rotary shaft 176, and the hollow rotary shaft 176 is simultaneously rotated in the reverse direction by a motor (not shown), and the mixture of the final concentrated slurry and the wet powder held in the casing 92 is transported in the transport direction T from upstream to downstream of the casing 92 while being heated by conductive heat transfer with the hollow stirring blades 178. Furthermore, the positional relationship between the heat medium inlet hole 184 and the heat medium outlet hole 182 shown in FIG. 4 may be reversed. That is, the heat medium outlet hole 182 may be provided radially inward of the heat medium inlet hole 184.

[0121] The fine particle powder discharged from the discharge port 98 of the drying device 8 is stored in a storage container 102 through a discharge path 100 as shown in FIG. 1. The number of hollow rotating shafts 176 is not limited to two, and may be two or more. Therefore, it can be said that a plurality of hollow rotating shafts 176 is sufficient. In the case of a plurality of hollow rotating shafts 176, they may be parallel to each other.

[0122] The method for producing fine powder using the above-described apparatus 1 for producing fine powder is carried out as follows. [Fine Particle Slurry Production Process] First, in the initial state, the crystallizer 10 and the reservoir 18 are filled with mother liquor. The motor 126 rotates the stirring blade 128, and the pump 22 is operated to blow the mother liquor in the reservoir 18 into the reaction vessel 116 through the inlet 115, generating a swirling flow within the reaction vessel 116. The first raw material 12A is supplied through the first inner tube 112, and the second raw material 12B is supplied through the second inner tube 114. The two are vigorously mixed in the central region R within the tapered section 116A, and fine particles are produced by reaction between the first raw material 12A and the second raw material 12B. The mother liquor containing the fine particles is returned to the reservoir 18 through the conduit 16, and as the mother liquor circulates repeatedly, a fine particle slurry is produced within the reservoir 18. The pressure of the mother liquor introduced from the inlet 115 is measured by a pressure gauge 122, and the flow rate of the microparticle slurry flowing out from the discharge hole 14 is appropriately adjusted by a flow control valve 118, thereby adjusting the solids concentration of the microparticle slurry in the reservoir 18 to an appropriate range.

[0123] [Initial concentration step] When the solids concentration of the particulate slurry in the reservoir 18 reaches an appropriate range, an initial concentration step (a) is initiated to concentrate the particulate slurry and convert it into an initially concentrated slurry. The initial concentration step (a) is, in a sense, a step of dehydrating the particulate slurry before washing. In the initial concentration step (a), the three-way valve 70 is controlled to set a circulation path so that the slurry discharged from the agitation type crossflow filtration device 6 returns to the slurry tank 30 through the conduit 72. Furthermore, in the initial concentration step (a), the supply of the washing liquid is stopped.

[0124] The discharge valve 132 is opened, and the fine particle slurry in the reservoir 18 is discharged from the outlet 26 through the conduit 28 and transferred to the slurry tank 30 by the pump 134. In the slurry tank 30, the anchor-shaped stirring blade 34 is rotated by the motor 36 to prevent the settling of fine particles in the fine particle slurry, and the pump 54 is operated to supply the fine particle slurry from the discharge hole 52 to the agitation type crossflow filtration device 6. As shown in Figure 3, the fine particle slurry is continuously introduced from the inlet 144 of the agitation type crossflow filtration device 6 into the slurry chamber 150 in the casing 60.

[0125] The slurry chamber 150 is pressurized by the discharge pressure of the pump 54, and the agitator blade 142 is continuously rotated by the motor 62. The particulate slurry is agitated by the agitator blade 142 and pressed against the side of the filter 146, and the mother liquor in the particulate slurry is filtered by the filter 146 and flows into the filtrate chamber 148. As the particulate slurry advances downstream in the casing 60, the amount of mother liquor in the particulate slurry decreases, and the particulate slurry is discharged from the discharge port 64 as a somewhat concentrated slurry. The discharged slurry is returned to the slurry tank 30 via the three-way valve 70 and the conduit 72.

[0126] The filtrate that flows into the filtrate chamber 148 passes through the filtrate discharge valve 154 and is collected in a conduit 156. In the initial state, the conduit 156 is connected to the conduit 78 by the three-way valve 74, and the initial filtrate containing a large amount of impurities is discarded in the drain 80. This process is repeated while measuring the density of the slurry with the density sensor 66 until the density of the fine particle slurry reaches a predetermined value and an initial concentrated slurry having the aforementioned solid concentration is obtained.

[0127] [Dilution and Washing Step] When an initially concentrated slurry of a predetermined concentration is obtained in the slurry tank 30, the initial concentration step (a) is completed, and the dilution and washing step (b) is initiated, in which the initially concentrated slurry is diluted with a washing liquid for washing. In the dilution and washing step, the three-way valve 70 maintains a circulation path in which the slurry discharged from the agitation type cross-flow filtration device 6 returns to the slurry tank 30 via the conduit 72. Even in this state, the filtrate collected in the conduit 156 via the filtrate discharge valve 154 is discharged to the drain 80 via the three-way valve 74 and the conduit 78 as filtrate with a high impurity content.

[0128] While controlling the density using the density sensor 66 and the level in the slurry tank 30, the on-off valve 44 is opened, the conduit 46 is connected to the slurry tank 30 via the three-way valve 42, and the pump 48 is operated to first supply cleaning liquid from the cleaning liquid tank 50 to the slurry tank 30. The cleaning liquid tank 50 stores relatively clean cleaning liquid obtained during the previous production of fine particle powder. Immediately after the start of the dilution and washing process (first stage), the initially concentrated slurry contains a large amount of impurities, so even a cleaning liquid with a low level of cleanliness can provide a sufficient cleaning effect. As a result, the initially concentrated slurry continues to circulate between the slurry tank 30 and the agitation type cross-flow filtration device 6, while being washed in the slurry tank 30 and filtered by the agitation type cross-flow filtration device 6.

[0129] As the cleaning liquid from the cleaning liquid tank 50 is continuously supplied to the slurry tank 30 and the cleaning of the initially concentrated slurry progresses, the impurities (electrolyte components, non-electrolyte components, and ultrafine particles) in the filtrate discharged from the agitation type crossflow filtration device 6 decrease, and the conductivity (or density) of the filtrate indicated by the conductivity sensor 71 (or a second density sensor, not shown) installed in the conduit 156 decreases. When the value of the conductivity sensor 71 reaches a target value (the target value for switching from the cleaning liquid in the cleaning liquid tank 50 to the clean cleaning liquid in the cleaning liquid source 38) (or when the amount of liquid in the cleaning liquid tank 50 has sufficiently decreased), the pump 48 is stopped automatically or manually by the control device 67 to stop the supply of the reused cleaning liquid from the cleaning liquid tank 50. After that, the three-way valve 42 is automatically or manually operated by the control device 67 to start the supply of the clean cleaning liquid from the cleaning liquid source 38 to the slurry tank 30.

[0130] As the cleaning and filtration of the initially concentrated slurry progresses using clean cleaning liquid from the cleaning liquid source 38, the impurities (electrolyte components, non-electrolyte components, and ultrafine particles) in the filtrate discharged from the agitation type crossflow filtration device 6 are further reduced, and the conductivity (or density) of the filtrate indicated by the conductivity sensor 71 (or a second density sensor, not shown) installed in the conduit 156 decreases. When the conductivity or density reaches the next target value (the target value indicating the completion of cleaning) and the density of the fine particle slurry reaches a predetermined value, the cleaning liquid source 38 is stopped, and the three-way valve 42 and the on-off valve 44 are automatically controlled by the control device 67 or manually operated to stop the supply of cleaning liquid.

[0131] [Final Concentration Step] After the supply of the washing liquid is stopped and the dilution washing step is completed, a final concentration step (c) is performed to finally concentrate the washed slurry. In the final concentration step (c), the washed slurry is supplied to the agitation type crossflow filtration device 6, where it is separated into a concentrated washed slurry and a filtrate. The concentrated washed slurry is returned to the slurry tank 30. In this way, the washed slurry is continuously filtered by the agitation type crossflow filtration device 6 while circulating between the slurry tank 30 and the agitation type crossflow filtration device 6. Therefore, the slurry in the slurry tank 30 is gradually concentrated.

[0132] When the conductivity of the filtrate measured by the conductivity sensor 71 provided in the conduit 156 eventually falls below a predetermined target value, it is determined that the filtrate has become clean enough to be used for primary washing in the slurry tank 30, and the three-way valve 74 is switched automatically by the control device 67 or manually, and the filtrate from the conduit 156 is stored in the washing liquid tank 50 through the conduit 76. When the filtrate becomes sufficiently clean, storage in the washing liquid tank 50 may start from the final concentration step (c) as well as from the subsequent stage of the dilution washing step (b).

[0133] When the density of the final concentrated slurry discharged from the outlet 64 of the agitation type crossflow filtration device 6, as measured by the density sensor 66, reaches the target density value for the final concentration step, the flow control valve 68 and the three-way valve 70 are operated automatically or manually by the control device 67 to send the final concentrated slurry to the slurry tank 82. The final concentrated slurry stored in the slurry tank 82 is stirred with the anchor-shaped stirring blade 84 to prevent precipitation, while the drying step is initiated. In this embodiment, the concentrated slurry is returned to the slurry tank 30 and filtered while being circulated, but the present invention is not limited to this and the concentrated slurry can also be supplied to the slurry tank 82 without being circulated.

[0134] [Drying Process] The drying process is a process in which the final concentrated slurry is dried to a fine powder state. In the drying process, the final concentrated slurry in the slurry tank 82 is sent to the drying device 8 by the pump 90 and introduced into the casing 92 from the inlet 96 via the conduit 94. Two hollow rotary shafts 176 rotate continuously within the casing 92, and hollow agitator blades 178 are heated by high-temperature steam or heat transfer oil supplied to the heat transfer medium inlet 184. As the hollow agitator blades 178 rotate, the final concentrated slurry and the wet powder held within the casing 92 are mixed, and the mixture is sent in the transfer direction T. During this process, the oscillation of the hollow agitator blades 178 prevents the mixture from adhering to the hollow agitator blades 178, and the mixture is heated by conduction heat transfer between the heated hollow agitator blades 178, thereby progressing the drying process of the mixture. By blowing in room temperature or heated air or the like through gas inlet 174 and discharging moist air or the like through gas outlet 175, the water vapor generated inside casing 92 is discharged to the outside of the apparatus, thereby maintaining an appropriate humidity level inside the apparatus. When the mixture reaches the downstream side of casing 92, it becomes fine particle powder, which is sequentially discharged from outlet 98. The fine particle powder discharged from outlet 98 is stored in storage container 102 through discharge path 100.

[0135] [Effects of this embodiment] According to the above-described method for producing fine particle powder and apparatus 1 for producing fine particle powder, in the fine particle slurry production step, the first raw material 12A and the second raw material 12B are reacted in a mother liquor in which a high-speed swirling flow is generated in the crystallizer 10 to produce a slurry containing fine particles with a particle size of 7 μm or less. Thereafter, in the initial concentration step, dilution and washing step, and final concentration step, washing and a high degree of concentration using the agitation type cross-flow filtration device 6 can be efficiently carried out without clogging the filters or flow paths. Furthermore, in the drying step, the final concentrated slurry and wet powder are mixed, and heated hollow stirring blades 178 are brought into contact with the mixture to heat it by conductive heat transfer, so that it is possible to produce fine particle powder of 7 μm or less with high production efficiency while keeping energy costs low.

[0136] Furthermore, in the microparticle slurry production process, by using a solution containing a transition metal element as the first raw material 12A and an alkaline solution as the second raw material 12B and reacting the two, it is possible to obtain microparticles whose main component is a transition metal hydroxide, and it is possible to produce a microparticle powder as a precursor of a positive electrode material for a secondary battery with high production efficiency while reducing energy costs.

[0137] Furthermore, in the initial concentration step, the fine particle slurry is filtered using an agitation cross-flow filtration device 6 and concentrated to a solids concentration of, for example, 35 to 65 wt % to obtain an initially concentrated slurry. This solves problems such as filter clogging due to fine particles, while also efficiently removing impurities from the slurry before washing. It also reduces the amount of washing liquid and washing time consumed in the dilution washing step, thereby reducing energy costs and improving production efficiency.

[0138] Furthermore, by concentrating the washed slurry in the final concentration step by removing a portion of the mother liquor and washing liquid using the agitation cross-flow filtration device 6 to a solids concentration of, for example, 50 to 65 wt %, the amounts of mother liquor and washing liquid to be removed in the drying step can be reduced, thereby reducing energy costs and improving production efficiency.

[0139] Furthermore, in the crystallizer 10, by circulating the mother liquor with the pump 22, it is easy to generate a high-speed swirling flow with simple equipment, and by uniformly mixing the first raw material 12A and the second raw material 12B in the high-speed swirling flow in an extremely short time, it is possible to precipitate fine particles having a particle size of 7 μm or less, preferably 5 μm or less, and since the particle size of the fine particle powder finally obtained can be made small and the particle size distribution can be narrowed, a high-quality final product can be expected.

[0140] Furthermore, in the drying device 8, the hollow rotating shafts 176 are each fixed with a gap in the axial direction, and the hollow stirring blades 178 of each hollow rotating shaft 176 are fixed so as to partially overlap when viewed in the axial direction. As a result, as the hollow stirring blades 178 rotate, the heated hollow stirring blades 178 mix and transport the final concentrated slurry and the wet powder held in the casing 92, during which time the mixture of the final concentrated slurry and the wet powder held in the casing 92 is dried by conduction heat transfer and converted into fine particle powder. This allows moisture to evaporate more efficiently than hot air drying using convection heat transfer in which hot air is blown, resulting in the excellent effect of reducing energy costs and increasing production efficiency.

[0141] The present invention is not limited to the above-described embodiment, and additions, deletions, and substitutions with well-known techniques of constituent elements are possible within the scope of the claims.

[0142] Next, a detailed description will be given of a fine particle powder manufacturing apparatus 21 according to a second embodiment of the present invention. Description of the same configuration as in the first embodiment will basically be omitted, and the description will focus on the differences from the first embodiment.

[0143] The microparticle powder manufacturing apparatus 21 of the second embodiment differs from the first embodiment in that a pump 41 is provided in the conduit 40, and that a control unit 69 is provided that is communicatively connected to the three-way valve 74 and the conductivity sensor 71, and the control device 67 of the first embodiment is not provided.

[0144] That is, as shown in FIG. 7 , a conductivity sensor 71 is installed in the conduit 156, which serves as the filtrate outlet of the agitation type crossflow filtration device 6. The conductivity sensor 71 continuously measures the conductivity of the filtrate discharged from the agitation type crossflow filtration device 6 and transmits the measured value to the control unit 69 (described later). The control unit 69 receives the output of the conductivity sensor 71 and uses the output result and the pre-stored filtrate conductivity to detect the progress of the dilution cleaning process and determine the completion timing of the dilution cleaning process. Specifically, the control unit 69 determines that the dilution cleaning process has been completed when the output result falls below a threshold value set in the control unit 69. Note that the completion timing of the dilution cleaning process may be determined by other sensors, not limited to the conductivity sensor 71. For example, a second density sensor (not shown) may be installed in the conduit 156, which serves as the filtrate outlet of the agitation type crossflow filtration device 6. The second density sensor continuously measures the density of the filtrate discharged from the agitation type crossflow filtration device 6 and transmits the measured value to the control unit 69. The control unit 69 receives the output of the second density sensor, detects the progress of the dilution cleaning process from the density of the filtrate, and determines the timing for completing the dilution cleaning process.

[0145] The three-way valve 74 and the conductivity sensor 71 are connected by wire or wirelessly to the control unit 69 so as to be able to communicate electrical signals. The control unit 69 determines whether the measurement result of the conductivity sensor 71 is equal to or greater than a threshold value, and if the measurement result is equal to or greater than the threshold value, causes the filtrate to flow through a flow path for discarding the filtrate. If the measurement result is below the threshold value (i.e., smaller than the threshold value), causes the filtrate to flow through a flow path for reusing the filtrate as a cleaning liquid. Specifically, the conductivity sensor 71 is a conductivity meter, and sets a valve (not shown) within the three-way valve 74 so that, if the conductivity of the filtrate is equal to or greater than the threshold value, the filtrate discharged from the agitation type crossflow filtration device 6 via the conduit 156 is discharged from the first port of the three-way valve 74 to the second port of the three-way valve 74 and then flows into the drainage path 80. When the conductivity of the filtrate falls below the threshold, a valve (not shown) within the three-way valve 74 is switched so that the filtrate discharged from the agitation-type crossflow filtration device 6 via the conduit 156 flows from the first port of the three-way valve 74 to the third port of the three-way valve 74 and into the cleaning liquid tank 50. Although not shown, the three-way valve 74 is provided with a drive device for switching the valve, which switches the valve within the three-way valve 74 in response to a signal input from the control unit 69. The control unit 69 and the pump 48 may be connected by wire or wirelessly to enable communication of electrical signals. An example of a drive device is a motor. The conductivity threshold is preferably set to a value in the range of 10 mS / cm or less, more preferably in the range of 5 mS / cm or less, and even more preferably in the range of 0.2 to 5 mS / cm. The control unit 69 is a computer equipped with a processor such as a central processing unit (CPU) and memory. The processor executes arithmetic processing to execute the functions of the control unit 69. The memory stores a rewritable program that describes the functions executed by the CPU.The control unit 69 may realize these functions using hardware (including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit). Alternatively, the functions of the control unit 69 may be realized by a combination of software and hardware.

[0146] During initial concentration by the agitation crossflow filtration device 6 and for a while after the start of cleaning, the filtrate entering the filtrate chamber 148 contains a large amount of impurities. However, as filtration progresses, the filtrate becomes less impurity-rich, and the conductivity detected by the conductivity sensor 71 decreases. Therefore, when the conductivity reaches a predetermined threshold, the control unit 69 switches the three-way valve 74 to store the filtrate that had been flowing to the drain 80 in the cleaning liquid tank 50. The relatively clean filtrate stored in the cleaning liquid tank 50 is supplied as cleaning liquid to the slurry tank 30 via the conduit 46, the three-way valve 42, and the on-off valve 44 by operating the pump 48 in the next dilution cleaning process. This reduces the amount of cleaning liquid used in the cleaning liquid source 38, thereby contributing to cost reduction in the production of fine-particle powder. Furthermore, the amount of filtrate and cleaning waste liquid disposed of outside the fine-particle powder production apparatus 21 is reduced, thereby reducing the environmental impact.

[0147] The downstream portion of the casing 60 is a conical tapered portion 152 that narrows downstream, and a discharge port 64 is formed at the tip of the tapered portion 152. The slurry is transported downstream while snaking through the slurry chamber 150, and moisture is removed. The slurry is circulated between the slurry tank 30 and the agitation type cross-flow filtration device 6, where it is filtered and concentrated. The highly viscous concentrated slurry is discharged from the discharge port 64.

[0148] The solids concentration of the concentrated slurry discharged from the agitation crossflow filtration device 6 is not necessarily limited, as optimal values ​​differ among the initial concentration step, the dilution and washing step, and the final concentration step. For example, when producing a cathode material precursor for a secondary battery, the solids concentration of the initially concentrated slurry at the completion of the initial concentration step is preferably 35 wt % or more and 65 wt % or less, more preferably 45 wt % or more and 65 wt % or less. The solids concentration of the washed slurry at the completion of the dilution and washing step is preferably 35 wt % or more and 60 wt % or less, more preferably 35 wt % or more and 45 wt % or less. The solids concentration of the final concentrated slurry at the completion of the final concentration step is preferably 50 wt % to 65 wt %, more preferably 60 wt % or more and 65 wt % or less.

[0149] When the concentration is within the above range in each step, the transport of the concentrated slurry within the casing 60 of the agitation type crossflow filtration device 6 is not difficult, and it is possible to effectively reduce the amount of impurities in the final concentrated slurry while limiting the consumption of washing liquid. Therefore, the load on the agitation type crossflow filtration device 6 and the drying device 8 is well balanced, and it is possible to improve the total processing efficiency and energy efficiency without overloading each step.

[0150] As shown in FIG. 7 , the discharge port 64 of the casing 60 of the agitation type crossflow filtration device 6 is connected to a first port of a three-way valve 70 (path switching device) via a density sensor 66 and a flow control valve 68. The three-way valve 70 is controlled by a control panel (not shown) or manually switched in response to instructions from the control panel. The three-way valve 70 may also be controlled by a control unit 69. The second port of the three-way valve 70 is connected to the slurry tank 30 via a conduit 72. The third port of the three-way valve 70 is connected to a slurry tank 82 for storing concentrated slurry, which is provided upstream of the drying device 8. By operating the three-way valve 70, slurry in various states discharged from the discharge port 64 of the agitation type crossflow filtration device 6 can be returned to the slurry tank 30 for circulation or supplied to the slurry tank 82, which serves as a buffer for the drying device 8.

[0151] The density of the concentrated slurry discharged from the outlet 64 of the agitation type crossflow filtration device 6 is measured by a density sensor 66, and the output signal of the density sensor 66 is transmitted to a control panel (not shown). When the three-way valve 70 is controlled by a control unit 69, the output signal of the density sensor 66 is also transmitted to the control unit 69. The density sensor 66 has two main purposes. The first is to measure the timing at which the concentrated slurry discharged from the agitation type crossflow filtration device 6 is sufficiently dewatered and reaches a predetermined density, and to grasp at least one of the timings of completion of the initial concentration step and the timing of completion of the final concentration step, and to use this timing to control the transition to the next step.

[0152] When determining the timing for completing the dilution cleaning process, it is preferable to satisfy either of the following conditions: (1) the conductivity of the filtrate decreases to a predetermined threshold based on the output of the conductivity sensor 71, and the density of the concentrated slurry increases to a predetermined threshold based on the output of the density sensor 66; or (2) the conductivity of the filtrate decreases to a predetermined threshold based on the output of the conductivity sensor 71 (the output of the density sensor 66 is not involved in the determination criteria).

[0153] A second purpose of measuring the slurry density using the density sensor 66 is to improve the washing effect of the slurry in the dilution washing step. Specifically, a lower limit and an upper limit are set for the density value corresponding to the output signal of the density sensor 66, and the supply of washing liquid from the washing liquid source 38 to the slurry tank 30 is increased (or temporarily stopped and then resumed) when the upper limit is reached, and the supply of washing liquid from the washing liquid source 38 is reduced (or temporarily stopped) when the lower limit is reached. This maintains the solids concentration of the concentrated slurry discharged from the agitation type crossflow filtration device 6 in the dilution washing step within a certain range, thereby adjusting the degree of cleanliness, until the conductivity of the filtrate discharged from the agitation type crossflow filtration device 6 is sufficiently reduced. Here, the components from the slurry tank 30 to the agitation type crossflow filtration device 6 in the fine particle powder production apparatus 21 are sometimes referred to as the fine particle slurry washing and concentration device.

[0154] To control the cleaning liquid in the dilution cleaning step, the three-way valve 42 and the on-off valve 44 are controlled manually or by a control panel (not shown) according to the value of the density sensor 66. If the density of the concentrated slurry detected by the density sensor 66 is too high, the three-way valve 42 and the on-off valve 44 are controlled to increase or start the flow of cleaning liquid from the cleaning liquid source 38 to the slurry tank 30. If the density of the concentrated slurry detected by the density sensor 66 is too low, the three-way valve 42 and the on-off valve 44 are controlled to reduce or stop the flow of cleaning liquid from the cleaning liquid source 38 to the slurry tank 30, thereby performing feedback control so that the solids concentration in the concentrated slurry falls within a certain range. The three-way valve 42 and the on-off valve 44 may be controlled by a control unit 69.

[0155] The slurry tank 82 functions as a buffer to adjust the amount of final concentrated slurry supplied to the drying device 8. The slurry tank 82 is cylindrical with a bottom, and the inner surface of the bottom is formed in a hemispherical shape. A semicircular anchor-shaped stirring blade 84 is arranged along the inner surface of the bottom of the slurry tank 82, with a small, fixed gap between it and the inner surface of the bottom, and is rotated by a motor 86. The rotation speed of the motor 86 is adjusted so that the final concentrated slurry does not settle and solidify in the slurry tank 82. A discharge port 88 is formed at the lower end of the bottom of the slurry tank 82, and the highly viscous final concentrated slurry extracted from the slurry tank 82 is sent via a pump 90 to a conduit 94 and then to the drying device 8.

[0156] The gap between the outer periphery of the anchor-shaped agitator blade 84 and the inner bottom surface of the slurry tank 82 is not limited, but similar to the anchor-shaped agitator blade 34 described above, it is preferably approximately 0.5 to 3.0 cm to prevent fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 82. Furthermore, the length of the semicircular outer periphery of the anchor-shaped agitator blade 84 is preferably long enough to face the entire inner bottom surface of the slurry tank 82. Furthermore, the rotational peripheral speed of the outer periphery of the anchor-shaped agitator blade 84 driven by the motor 86 is not limited, but is preferably approximately 0.1 to 3.0 m / s. Within this range, the effect of preventing fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 82 is achieved. This effect is particularly important when producing a cathode material precursor for secondary batteries because the fine particles are metal compounds with a high specific gravity.

[0157] 4 to 6 are a side cross-sectional view, a plan view with the top plate removed, and a front cross-sectional view showing an agitation heat transfer device as the drying device 8. The drying device 8 has a rectangular parallelepiped casing 92, which has a trough-shaped inner wall 194, an outer wall 198 covering the outer peripheral surface of the inner wall 194, and a rectangular top plate 196 closing the upper end of the inner wall 194. An airtight gap of a certain thickness is formed between the inner wall 194 and the outer wall 198, which serves as a heat medium flow path 199. The outer wall 198 is formed with a heat medium inlet 200 and a heat medium outlet (not shown) that communicate with the heat medium flow path 199. By supplying high-temperature steam or heat medium oil from the heat medium inlet 200 to the heat medium outlet, the inside of the casing 92 can be uniformly heated.

[0158] An inlet (inflow port) 96 is formed at the upper end of the upstream side (one end) of the casing 92, and a conduit 94 is connected to it. A gas inlet 174 is formed at the upper surface of the upstream side of the casing 92, and a gas outlet 175 is formed at the upper surface of the downstream side (the other end). Room temperature or heated air, etc. is blown in through the gas inlet 174, and the moist air, etc. is discharged from the gas outlet 175 together with water vapor generated as the mother liquor and cleaning liquid evaporate within the casing 92, thereby maintaining an appropriate humidity level by discharging the water vapor generated within the casing 92 to the outside of the apparatus. Meanwhile, an outlet (outlet hole) 98 is formed at the lower surface of the downstream end of the casing 92, and the fine particle powder dried within the casing 92 is discharged from there.

[0159] Two hollow rotary shafts 176 are arranged symmetrically along the longitudinal direction within the casing 92, and both ends or one end are supported by bearings so that the two hollow rotary shafts 176 can rotate about their axes. Hollow agitating blades 178 are fixed to each hollow rotary shaft 176 at regular intervals in the axial direction, and in the region between the two hollow rotary shafts 176, the hollow agitating blade 178 of one hollow rotary shaft 176 is located midway in the axial direction of the hollow agitating blade 178 of the other hollow rotary shaft 176. The two hollow rotary shafts 176 may be parallel to each other.

[0160] As shown in Figure 6, each hollow agitator blade 178 is fan-shaped with a central angle of less than 180°, and pairs of hollow agitator blades 178 are fixed at positions that are 180° rotationally symmetrical about the hollow rotary shaft 176. A notch 190 of a fixed width is formed between the pair of hollow agitator blades 178 to allow the mixture of the final concentrated slurry and wet powder to pass axially. The interior of the hollow agitator blade 178 is hollow and communicates with the internal space of the hollow rotary shaft 176, so that the heat medium supplied to the hollow rotary shaft 176 also enters the interior of the hollow agitator blade 178 and heats the hollow agitator blade 178. This is sometimes called the heating mechanism of the hollow agitator blade 178.

[0161] The wet powder is a dried product of the final concentrated slurry that is previously stored in the casing 92. It is not completely dry and is moist. By mixing the previously stored wet powder with the final concentrated slurry, abnormal adhesion that may impede the function of the drying device 8 can be avoided, and transportation within the casing 92 by the hollow agitating blades 178 can be facilitated.

[0162] As shown in Figures 4 and 5, the pair of hollow agitator blades 178 are inclined in opposite directions relative to the hollow rotary shaft 176, and each time the hollow rotary shaft 176 rotates 180°, the trajectory of the hollow agitator blade 178 oscillates in the axial direction within a certain angular range, as shown by the solid and dotted lines in the figures. This oscillation serves to mix the final concentrated slurry and the wet powder while preventing the final concentrated slurry and the wet powder from adhering to the hollow agitator blades 178 adjacent in the axial direction. In addition, the hollow agitator blade 178 also has a twist along an imaginary helical plane around the hollow rotary shaft 176, and serves to gradually transport the mixture of the final concentrated slurry and the wet powder from the upstream side to the downstream side of the casing 92 as the hollow rotary shaft 176 rotates.

[0163] The hollow agitator blade 178 and the hollow rotating shaft 176 are made of a metal with high thermal conductivity, and a heat medium inlet hole 184 and a heat medium outlet hole 182 are formed at the upstream end of the hollow rotating shaft 176. A heat medium such as high-temperature steam or heat medium oil is continuously supplied from a heat medium source (not shown) through the heat medium inlet hole 184 to the heat medium outlet hole 182. The heat medium spreads throughout the entire length of the hollow rotating shaft 176 and also penetrates into the hollow agitator blade 178, heating the entire hollow rotating shaft 176 and hollow agitator blade 178 to a temperature above the boiling points of the mother liquor and washing liquid contained in the final concentrated slurry and the wet powder. Therefore, the mixture of the final concentrated slurry and the wet powder is heated by conduction heat every time it comes into contact with the hollow rotating shaft 176 and hollow agitator blade 178, evaporating the mother liquor and washing liquid contained in the mixture and eventually becoming a fine powder. A rotation mechanism 180 is provided at one end of the hollow rotary shaft 176, and the hollow rotary shaft 176 is simultaneously rotated in the reverse direction by a motor (not shown), and the mixture of the final concentrated slurry and the wet powder held in the casing 92 is heated by the hollow agitating blades 178 through conductive heat transfer, which has excellent thermal efficiency, and transported in the transport direction T from upstream to downstream of the casing 92. Heating through conductive heat transfer is sometimes called indirect heating. Furthermore, the positional relationship between the heat medium inlet hole 184 and the heat medium outlet hole 182 shown in FIG. 4 may be reversed. That is, the heat medium outlet hole 182 may be provided radially inward of the heat medium inlet hole 184.

[0164] The fine particle powder discharged from the discharge port 98 of the drying device 8 is stored in a storage container 102 through a discharge path 100 as shown in FIG. 7. The number of hollow rotating shafts 176 is not limited to two, and may be two or more. Therefore, it can be said that a plurality of hollow rotating shafts 176 is sufficient. In the case of a plurality of hollow rotating shafts 176, they may be parallel to each other.

[0165] The method for producing fine particle powder using the above-described apparatus 21 for producing fine particle powder is carried out as follows. [Fine particle slurry production process] First, in the initial state, the crystallizer 10 and the reservoir 18 are filled with mother liquor. The motor 126 rotates the stirring blade 128, and the pump 22 is operated to blow the mother liquor in the reservoir 18 into the reaction vessel 116 through the inlet 115, generating a swirling flow within the reaction vessel 116. The first raw material 12A is supplied through the first inner tube 112, and the second raw material 12B is supplied through the second inner tube 114. The two are vigorously mixed in the central region R within the tapered section 116A, and fine particles are produced by reaction between the first raw material 12A and the second raw material 12B. The mother liquor containing the fine particles is returned to the reservoir 18 through the conduit 16, and as the mother liquor circulates repeatedly, a fine particle slurry is produced within the reservoir 18. The pressure of the mother liquor introduced from the inlet 115 is measured by a pressure gauge 122, and the flow rate of the microparticle slurry flowing out from the discharge hole 14 is appropriately adjusted by a flow control valve 118, thereby adjusting the solids concentration of the microparticle slurry in the reservoir 18 to an appropriate range.

[0166] [Initial concentration step] When the solids concentration of the particulate slurry in the reservoir 18 reaches an appropriate range, an initial concentration step is initiated to concentrate the particulate slurry and convert it into an initially concentrated slurry. The initial concentration step is a step of dehydrating the particulate slurry before washing. In the initial concentration step, the three-way valve 70 is controlled to set a circulation path so that the slurry discharged from the agitation type crossflow filtration device 6 returns to the slurry tank 30 through the conduit 72. In addition, the supply of the washing liquid is stopped in the initial concentration step.

[0167] The discharge valve 132 is opened, and the fine particle slurry in the reservoir 18 is discharged from the outlet 26 through the conduit 28 and transferred to the slurry tank 30 by the pump 134. In the slurry tank 30, the anchor-shaped stirring blade 34 is rotated by the motor 36 to prevent the settling of fine particles in the fine particle slurry, and the pump 54 is operated to supply the fine particle slurry from the discharge hole 52 to the agitation type crossflow filtration device 6. As shown in Figure 3, the fine particle slurry is continuously introduced from the inlet 144 of the agitation type crossflow filtration device 6 into the slurry chamber 150 in the casing 60.

[0168] The slurry chamber 150 is pressurized by the discharge pressure of the pump 54, and the agitator blade 142 is continuously rotated by the motor 62. The particulate slurry is agitated by the agitator blade 142 and pressed against the side of the filter 146, and the mother liquor in the particulate slurry is filtered by the filter 146 and flows into the filtrate chamber 148. As the particulate slurry advances downstream in the casing 60, the amount of mother liquor in the particulate slurry decreases, and the particulate slurry is discharged from the discharge port 64 as a somewhat concentrated slurry. The discharged slurry is returned to the slurry tank 30 via the three-way valve 70 and the conduit 72.

[0169] The filtrate that flows into the filtrate chamber 148 passes through the filtrate discharge valve 154 and is collected in a conduit 156. In the initial state, the three-way valve 74 connects the conduit 156 to the waste flow path 78, and the initial filtrate containing a large amount of impurities is discarded in a drain 80. This process is repeated while measuring the density of the slurry with the density sensor 66 until the density of the fine particle slurry reaches a predetermined value and an initial concentrated slurry having the aforementioned solid concentration is obtained.

[0170] [Dilution and Washing Process] When an initially concentrated slurry of a predetermined concentration is obtained in the slurry tank 30, the initial concentration process is completed, and the dilution and washing process is initiated, in which the initially concentrated slurry is diluted with a washing liquid for washing. In the dilution and washing process, the three-way valve 70 maintains a circulation path in which the slurry discharged from the agitation type cross-flow filtration device 6 returns to the slurry tank 30 via the conduit 72. Even in this state, the filtrate collected in the conduit 156 via the filtrate discharge valve 154 is discharged to the drain 80 via the three-way valve 74 and the waste flow path 78 as filtrate with a high impurity content.

[0171] While controlling the density using the density sensor 66 and the level in the slurry tank 30, the on-off valve 44 is opened, the conduit 46 is connected to the slurry tank 30 via the three-way valve 42, and the pump 48 is operated to first supply cleaning liquid from the cleaning liquid tank 50 to the slurry tank 30. The cleaning liquid tank 50 stores relatively clean cleaning liquid obtained during the previous production of fine particle powder. Immediately after the start of the dilution and washing process (first stage), the initially concentrated slurry contains a large amount of impurities, so even a cleaning liquid with a low level of cleanliness can provide sufficient cleaning effectiveness. As a result, the initially concentrated slurry circulates between the slurry tank 30 and the agitation type cross-flow filtration device 6, and is continuously washed in the slurry tank 30 and filtered by the agitation type cross-flow filtration device 6. Because filtration is continuous in this manner, the dilution and washing process is sometimes referred to as the dilution and washing filtration process.

[0172] As the cleaning liquid from the cleaning liquid tank 50 is continuously supplied to the slurry tank 30 and the cleaning of the initially concentrated slurry progresses, the impurities (electrolyte components, non-electrolyte components, and ultrafine particles) in the filtrate discharged from the agitation type crossflow filtration device 6 are reduced, and the conductivity of the filtrate indicated by the conductivity sensor 71 installed in the conduit 156 decreases. When the value of the conductivity sensor 71 reaches a target value (the target value for switching the cleaning liquid supplied to the slurry tank 30 from the cleaning liquid in the cleaning liquid tank 50 to the clean cleaning liquid in the cleaning liquid source 38) (or when the amount of liquid in the cleaning liquid tank 50 has sufficiently decreased), the pump 48 is stopped automatically or manually by the control unit 69 to stop the supply of the reused cleaning liquid from the cleaning liquid tank 50. After that, the three-way valve 42 is automatically controlled by a control panel (not shown) or manually operated to start the supply of the clean cleaning liquid from the cleaning liquid source 38 to the slurry tank 30. Note that the three-way valve 42 may also be controlled by the control unit 69.

[0173] As the cleaning and filtration of the initially concentrated slurry progresses using clean cleaning liquid from the cleaning liquid source 38, the impurities in the filtrate discharged from the agitation type crossflow filtration device 6 are further reduced, and the conductivity of the filtrate indicated by the conductivity sensor 71 installed in the conduit 156 decreases. When the value of the conductivity sensor 71 reaches the next target value (the target value indicating completion of cleaning) and the density of the fine particle slurry reaches a predetermined value, the cleaning liquid source 38 is stopped, and the three-way valve 42 and the on-off valve 44 are automatically controlled by a control panel (not shown) or manually operated to stop the supply of cleaning liquid. The three-way valve 42 and the on-off valve 44 may also be controlled by the control unit 69.

[0174] [Final Concentration Step] After the supply of the washing liquid is stopped and the dilution washing step is completed, a final concentration step is performed to finally concentrate the washed slurry. In the final concentration step, the washed slurry is supplied to the agitation type cross-flow filtration device 6 and separated into a concentrated washed slurry and filtrate. The concentrated washed slurry is returned to the slurry tank 30. In this way, the washed slurry is continuously filtered by the agitation type cross-flow filtration device 6 while circulating between the slurry tank 30 and the agitation type cross-flow filtration device 6. Therefore, the slurry in the slurry tank 30 is gradually concentrated. The final concentration step may also be referred to as the concentration step.

[0175] [Flow Path Switching Process] When the conductivity of the filtrate measured by the conductivity sensor 71 installed in the conduit 156 eventually falls below a predetermined target value, it is determined that the filtrate is clean enough to be used for primary cleaning in the slurry tank 30. The three-way valve 74 is automatically switched by the control unit 69, and the filtrate from the conduit 156 is stored in the cleaning liquid tank 50 via the return flow path 76. If the filtrate becomes sufficiently clean, storage in the cleaning liquid tank 50 may begin not only in the final concentration process but also from the subsequent stage of the dilution cleaning process. If a second density sensor (not shown) is installed in the conduit 156, the density of the filtrate measured by the second density sensor can be used as an indicator of the cleanliness of the filtrate. In this case, the density is set as a threshold value in advance, and when the measured density falls below the threshold value, the three-way valve 74 is switched and the filtrate is stored in the cleaning liquid tank 50. In this case, a configuration including at least one of the conductivity sensor 71 and the second density sensor is referred to as a filtrate sensor. Therefore, a filtrate sensor including at least one of the conductivity sensor 71 and a second density sensor that measures the density of the filtrate may be provided in the conduit 156, and the control unit 69 may switch the three-way valve 74 so that the filtrate flows into the waste flow path 78 when the measurement result of the filtrate sensor is equal to or greater than a threshold value, and flows into the return flow path 76 when the measurement result of the filtrate sensor is below the threshold value. In this case, the filtrate sensor is provided downstream of the agitation type crossflow filtration device 6 and upstream of the three-way valve 74, which serves as a flow path switching device.

[0176] When the density of the final concentrated slurry discharged from the outlet 64 of the agitation type crossflow filtration device 6, as measured by the density sensor 66, reaches the target density value for the final concentration step, the flow rate control valve 68 and the three-way valve 70 are operated automatically or manually by a control panel (not shown) to send the final concentrated slurry to the slurry tank 82. The flow rate control valve 68 and the three-way valve 70 may also be controlled by a control unit 69. The final concentrated slurry stored in the slurry tank 82 is stirred with the anchor-shaped stirring blade 84 to prevent precipitation, while the drying step is initiated. In this embodiment, the concentrated slurry is returned to the slurry tank 30 and filtered while being circulated, but this is not limited thereto, and the concentrated slurry can also be supplied to the slurry tank 82 without being circulated.

[0177] [Drying Process] The drying process is a process in which the final concentrated slurry is dried to a fine powder state. In the drying process, the final concentrated slurry in the slurry tank 82 is sent to the drying device 8 by the pump 90 and introduced into the casing 92 from the inlet 96 via the conduit 94. Two hollow rotary shafts 176 continuously rotate within the casing 92, and hollow agitator blades 178 are heated by high-temperature steam or heat transfer oil supplied to the heat transfer medium inlet 184. As the hollow agitator blades 178 rotate, the final concentrated slurry and the wet powder held within the casing 92 are mixed, and the mixture is sent in the transfer direction T. During this process, the oscillation of the hollow agitator blades 178 prevents the mixture from adhering to adjacent hollow agitator blades 178, while the heated hollow agitator blades 178 heat the mixture by conduction heat transfer, thereby proceeding with the drying process of the mixture. In other words, the mixture is heated and dried. By blowing in room temperature or heated air or the like through gas inlet 174 and discharging moist air or the like through gas outlet 175, the water vapor generated inside casing 92 is discharged to the outside of the apparatus, thereby maintaining an appropriate humidity level inside the apparatus. When the mixture reaches the downstream side of casing 92, it becomes fine particle powder, which is sequentially discharged from outlet 98. The fine particle powder discharged from outlet 98 is stored in storage container 102 through discharge path 100.

[0178] [Effects of the Present Embodiment] According to the above-described microparticle slurry cleaning and concentration device, microparticle powder manufacturing method, and microparticle powder manufacturing device 21, the filtrate sensor constantly monitors indicators such as the conductivity or density of the filtrate discharged from the agitation crossflow filtration device 6 via the conduit 156. If the conductivity or density of the filtrate is equal to or greater than a threshold, the filtrate is discarded. On the other hand, if the conductivity or density of the filtrate falls below the threshold, the filtrate is determined to be clean enough to be used for primary cleaning in the slurry tank 30. The control unit 69 switches the three-way valve 74, which serves as a flow path switching device, and the filtrate from the conduit 156 is stored in the cleaning liquid tank 50 via the return flow path 76. This reduces the amount of cleaning liquid used in the cleaning liquid source 38, which helps reduce the cost of microparticle powder manufacturing. Furthermore, the amount of filtrate and cleaning waste liquid discarded outside the microparticle powder manufacturing device 21 can be reduced, thereby reducing the environmental impact. In addition, in this embodiment, in the fine particle slurry production process, the first raw material 12A and the second raw material 12B are reacted in a mother liquor in which a high-speed swirling flow is generated in the crystallizer 10 to produce a slurry containing fine particles with a particle size of 7 μm or less.After that, washing and a high level of concentration using the agitation-type cross-flow filtration device 6 can be efficiently performed in the initial concentration process, dilution and washing process, and final concentration process without causing blockage of the filter or flow path.Furthermore, in the drying process, the final concentrated slurry and wet powder are mixed, and heated hollow agitation blades 178 are brought into contact with the mixture to heat it by conductive heat transfer, so that fine particles of 7 μm or less can be produced with high production efficiency while keeping energy costs down.

[0179] Furthermore, in the microparticle slurry production process, by using a solution containing a transition metal element as the first raw material 12A and an alkaline solution as the second raw material 12B and reacting the two, it is possible to obtain microparticles whose main component is a transition metal hydroxide, and it is possible to produce a microparticle powder as a precursor of a positive electrode material for a secondary battery with high production efficiency while reducing energy costs.

[0180] Furthermore, in the initial concentration step, the fine particle slurry is filtered using an agitation cross-flow filtration device 6 and concentrated to a solids content of, for example, 35 to 65 wt % to obtain an initially concentrated slurry. This solves problems such as filter clogging due to fine particles, while also efficiently removing impurities from the slurry before washing. It also reduces the amount of washing liquid and washing time consumed in the dilution washing step, thereby reducing energy costs and improving production efficiency.

[0181] In the final concentration step, the washed slurry is concentrated to a solid content of, for example, 50 to 65 wt % by removing part of the mother liquor and washing liquid through an agitation cross-flow filtration device 6. This reduces the amounts of mother liquor and washing liquid to be removed in the drying step, thereby reducing energy costs and improving production efficiency.

[0182] Furthermore, in the crystallizer 10, by circulating the mother liquor with the pump 22, it is easy to generate a high-speed swirling flow with simple equipment, and by uniformly mixing the first raw material 12A and the second raw material 12B in the high-speed swirling flow in an extremely short time, it is possible to precipitate fine particles having a particle size of 7 μm or less, preferably 5 μm or less, and since the particle size of the fine particle powder finally obtained can be made small and the particle size distribution can be narrowed, a high-quality final product can be expected.

[0183] In addition, in the drying device 8, the hollow rotating shafts 176 are fixed with gaps in the axial direction and the hollow agitating blades 178 of each hollow rotating shaft 176 are fixed so as to partially overlap when viewed in the axial direction, so that as the hollow agitating blades 178 rotate, the heated hollow agitating blades 178 mix and transport the final concentrated slurry and the wet powder held in the casing 92, during which the mixture of the final concentrated slurry and the wet powder held in the casing 92 is dried by conductive heat transfer and converted into fine particle powder. Therefore, moisture can be evaporated more efficiently than in hot air drying using convective heat transfer in which hot air is blown, and the excellent effects of reducing energy costs and increasing production efficiency are achieved.

[0184] The present invention is not limited to the above-described embodiment, and additions, deletions, and substitutions with well-known techniques of constituent elements are possible within the scope of the claims.

[0185] In the above embodiment, a case has been described in which the three-way valve 74, which is a flow path switching device, is used to switch between discarding the filtrate discharged from the agitation type cross-flow filtration device 6 via the conduit 156 and storing it in the cleaning liquid tank 50 via the return flow path 76. However, the flow path switching device is not necessarily limited to the three-way valve 74, and the return flow path 76 and the waste flow path 78 may each be provided with an on-off valve, and the opening degree of each on-off valve may be controllable.

[0186] In the above embodiment, the conduit 46 is connected to the three-way valve 42, but it may be connected directly from the pump 48 to the slurry tank 30. With this configuration, the cleaning liquid from the cleaning liquid source 38 and the cleaning liquid from the cleaning liquid tank 50 can be supplied to the slurry tank 30 simultaneously.

[0187] Next, a detailed description will be given of the apparatus 31 for producing fine particle powder according to the third and fourth embodiments of the present invention. Description of the same configuration as in the first embodiment will basically be omitted, and the description will focus on the differences from the first embodiment.

[0188] The apparatus 31 for producing fine particle powder according to the third and fourth embodiments differs from the first embodiment in that a pump 41 is provided in the conduit 40. The apparatus 31 for producing fine particle powder according to the fourth embodiment also differs from the first embodiment in that a second density sensor 73 is provided in the conduit 156.

[0189] [Second Density Sensor] In the apparatus 31 for producing fine-particle powder according to the third and fourth embodiments of the present invention shown in FIG. 8 , a sensor for measuring another physical property may be provided instead of or in addition to the conductivity sensor 71, and the timing of completion of the dilution washing process may be determined using the output of the sensor. For example, as described in Modification 2 of the third embodiment, the fourth embodiment, and Modifications 1 and 2 of the fourth embodiment below, a second density sensor 73 may be provided in the conduit 156 serving as the filtrate outlet of the agitation-type cross-flow filtration device 6 to measure the density of the filtrate. The second density sensor 73 continuously measures the density of the filtrate discharged from the agitation-type cross-flow filtration device 6 and transmits the measured value to the control device 67. The control device 67, upon receiving the output of the second density sensor 73, may detect the progress of the dilution washing process from the density of the filtrate and determine the timing of completion of the dilution washing process.

[0190] During initial concentration by the agitation crossflow filtration device 6 and for a while after the start of cleaning, the filtrate entering the filtrate chamber 148 contains a large amount of impurities. However, as filtration progresses, the filtrate becomes less impurity-rich, and the conductivity detected by the conductivity sensor 71 decreases. Therefore, when the conductivity reaches a predetermined threshold, the control device 67 switches the three-way valve 74, so that the filtrate previously flowing to the drain 80 is stored in the cleaning liquid tank 50. The relatively clean filtrate stored in the cleaning liquid tank 50 is supplied as cleaning liquid to the slurry tank 30 via the conduit 46, the three-way valve 42, and the on-off valve 44 by operating the pump 48 in the next dilution cleaning process. This reduces the amount of cleaning liquid used in the cleaning liquid source 38, helping to reduce the cost of producing fine-particle powder. Furthermore, the amount of filtrate and cleaning waste liquid disposed of outside the fine-particle powder production apparatus 31 is reduced, thereby reducing the environmental impact.

[0191] The downstream portion of the casing 60 is a conical tapered portion 152 that narrows downstream, and a discharge port 64 is formed at the tip of the tapered portion 152. Slurries in various states are transported downstream while snaking through the slurry chamber 150, and moisture is removed. The slurry is circulated between the slurry tank 30 and the agitation type cross-flow filtration device 6, where it is filtered and concentrated. The concentrated slurry, which has become highly viscous, is discharged from the discharge port 64.

[0192] The solids concentration of the concentrated slurry discharged from the outlet 64 of the agitation crossflow filtration device 6 is not necessarily limited, as optimal values ​​differ among the initial concentration step, the dilution and washing step, and the final concentration step. For example, when producing a cathode material precursor for a secondary battery, the solids concentration of the initially concentrated slurry at the completion of the initial concentration step is preferably 35 wt % or more and 65 wt % or less, more preferably 45 wt % or more and 65 wt % or less. The solids concentration of the washed slurry at the completion of the dilution and washing step is preferably 35 wt % or more and 60 wt % or less, more preferably 35 wt % or more and 45 wt % or less. The solids concentration of the concentrated slurry at the completion of the final concentration step is preferably 50 wt % to 65 wt %, more preferably 60 wt % or more and 65 wt % or less.

[0193] When the concentration is within the above range in each step, the transport of the concentrated slurry within the casing 60 of the agitation type crossflow filtration device 6 is not difficult, and it is possible to effectively reduce the amount of impurities in the final concentrated slurry while limiting the consumption of washing liquid. Therefore, the load on the agitation type crossflow filtration device 6 and the drying device 8 is well balanced, and it is possible to improve the total processing efficiency and energy efficiency without overloading each step.

[0194] [Density Sensor] As shown in Figures 8 and 9, the discharge outlet 64 of the casing 60 is connected to a first port of a three-way valve 70 (a path switching device) via a conduit 63 and a flow control valve 68. A density sensor 66 is installed in a portion of the conduit 63, and its output is connected to a control device 67. The density sensor 66 may be, but is not limited to, a vibrating in-line density sensor having a vibrator 66A that contacts the concentrated slurry whose concentration is to be measured and a controller (not shown) that vibrates the vibrator 66A and measures its resonant frequency. The vibrator 66A of the density sensor 66 is airtightly inserted into the conduit 63 extending from the outlet 64 to the flow control valve 68 and is in contact with the concentrated slurry flowing through the conduit 63. As a result, when the vibrator 66A vibrates, the resonant frequency of the vibrator 66A decreases as the density of the concentrated slurry contacting the vibrator 66A increases. Therefore, by measuring the resonant frequency, the density of the concentrated slurry can be measured with high accuracy. In the present invention, a density sensor other than a vibration type or an inline type may be used, and any sensor that can measure some physical property of the slurry and indirectly estimate the density of the slurry based on that physical property can be used as the density sensor. The second density sensor 73 may be similar to the density sensor 66.

[0195] The following formula 1 is the solid concentration c (wt%) in the slurry and the density ρ of the slurry. slurry (g / cm ３ ) and the true density ρ of the particles in the slurry solid (g / cm ３ ) and the density of the liquid in the slurry, ρ liquid (g / cm ３ ) is shown. To set the solid content concentration c (wt%) in the slurry to, for example, 50 wt%, substitute c = 50 and calculate the density ρ of the slurry so that Equation 1 is satisfied. slurry (g / cm ３ ) and the true density ρ of the particles in the slurry solid (g / cm ３ ) and the density of the liquid in the slurry, ρ liquid (g / cm ３ ) can be adjusted.

[0196] Slurry density ρ slurry(g / cm ３ ) is the density in a slurry state in which the liquid (mother liquor + washing liquid), the fine particles, and the impurities are mixed, and can be measured by the density sensor 66. The true density ρ of the fine particles in the slurry solid (g / cm ３ ) is a value determined by the type of fine particles to be produced (substance type, particle form / shape, particle size), and can be calculated in advance. liquid (g / cm ３ ) is the density of the medium (mainly water), the electrolyte solutes and non-electrolyte solutes dissolved in the medium, and the ultrafine particles that have passed through the filter of the agitation type cross-flow filtration device 6 and are dispersed in the medium. In the third embodiment, the amount of the electrolyte solutes is measured as conductivity using the conductivity sensor 71, and ρ liquid (g / cm ３ ) can be approximately estimated, but in the fourth embodiment in which the second density sensor 73 is provided, the density ρ of the liquid is detected by the second density sensor 73. liquid (g / cm ３ ) can be directly measured by the conductivity sensor 71. liquid (g / cm ３ In the fourth embodiment, the density ρ of the liquid is detected by the second density sensor 73, unlike the third embodiment in which the density ρ of the liquid is detected indirectly. liquid (g / cm ３ ) can be directly measured, thereby making it possible to grasp and control the solids concentration c (wt %) in the slurry more accurately.

[0197]

[0198] A second port of the three-way valve 70 is connected to the slurry tank 30 via a conduit 72 (second flow path). A third port of the three-way valve 70 is connected to a slurry tank 82 for storing concentrated slurry, which is provided upstream of the drying device 8. The three-way valve 70 is switched under the control of a control device 67, or can be switched manually in response to an instruction from the control device 67. By operating the three-way valve 70, slurry in various states discharged from the discharge port 64 of the agitation type crossflow filtration device 6 can be returned to the slurry tank 30 for circulation, or supplied to the slurry tank 82, which serves as a buffer for the drying device 8.

[0199] The density of the concentrated slurry discharged from the outlet 64 of the agitation type crossflow filtration device 6 is measured by a density sensor 66, and the output signal of the density sensor 66 is transmitted to a control device 67. The density sensor 66 has two main purposes. The first is to measure the timing at which the concentrated slurry discharged from the agitation type crossflow filtration device 6 is sufficiently dewatered and reaches a predetermined density, and to grasp the timing of completion of at least one of the initial concentration step (A) and the final concentration step (C), and use this timing to control the transition to the next step.

[0200] When determining the timing of completion of the dilution washing process (B), it is preferable to satisfy either of the following conditions: (1) the conductivity of the filtrate decreases to a predetermined threshold based on the output of the conductivity sensor 71, and the density of the concentrated slurry increases to a predetermined threshold based on the output of the density sensor 66; or (2) the conductivity of the filtrate decreases to a predetermined threshold based on the output of the conductivity sensor 71 (the output of the density sensor 66 is not involved in the determination criteria).

[0201] A second purpose of measuring the slurry density using the density sensor 66 is to improve the washing effect of the slurry in the dilution washing step. Specifically, a lower limit and an upper limit are set for the density value corresponding to the output signal of the density sensor 66, and the supply of washing liquid from the washing liquid source 38 to the slurry tank 30 is increased (or temporarily stopped and then resumed) when the upper limit is reached, and the supply of washing liquid from the washing liquid source 38 is reduced (or temporarily stopped) when the lower limit is reached, thereby maintaining the solids concentration of the concentrated slurry discharged from the agitation type crossflow filtration device 6 within a certain range and adjusting the degree of cleanliness until the conductivity of the filtrate discharged from the agitation type crossflow filtration device 6 is sufficiently reduced.

[0202] [Control Device] The control device 67 may be realized by hardware such as a computer including a circuit unit executing a software program. Examples of the hardware include a central processing unit (CPU), a large-scale integration (LSI), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), and a graphics processing unit (GPU). The program is stored in a storage device including a storage medium, such as a hard disk drive (HDD), a flash memory, a read-only memory (ROM), or a digital versatile disc (DVD). The program may be a differential program that realizes part of the functions of the control device 67. The control device 67 may have output devices such as a display and a speaker, and may generate images or sounds through these devices to instruct the operator to switch between the various components instead of directly controlling the components.

[0203] [Process Switching Control of Third Embodiment] A specific example of switching control of the initial concentration process (A), dilution cleaning process (B), final concentration process (C), and discharge process (D) by the control device 67 in the third embodiment will be described using the flowchart of Figure 10.

[0204] In the initial concentration step (A), the amount of impurity components dissolved in the filtrate is relatively large, and the density of the filtrate is high. On the other hand, in the final concentration step (C) after the dilution and washing step (B), the amount of impurity components dissolved in the filtrate is small, and the density of the filtrate is lower than that of the filtrate in the initial concentration step (A). Thus, the density (g / cm) of the filtrate in each step ３ ) are different, so even if the slurry concentration (wt%) is the same, the slurry density (g / cm ３ Therefore, the slurry density (g / cm3) corresponding to the desired density of the filtrate at the end of each step is different. ３) are stored in advance in the control device 67 as threshold values ​​A, B, and C for each process, and the control is preferably performed to grasp the completion timing of each process.

[0205] When the program is started, the control device 67 of the third embodiment sets up the initial concentration step (A) in step S1. The pump 41 is stopped to stop the supply of cleaning liquid from the cleaning liquid source 38 to the slurry tank 30. The particulate slurry stored in the slurry tank 30 is continuously supplied to the agitation type cross-flow filtration device 6 through a conduit 56 (first flow path) by a pump 54, which is a slurry supply device. The flow paths between the agitation type cross-flow filtration device 6 and the slurry tank 30 are connected through a conduit 72 (second flow path) by a three-way valve 70, which is a flow path switching device, so that the slurry discharged from the agitation type cross-flow filtration device 6 is continuously returned to the slurry tank 30. After the setting is completed, the process proceeds to step S2, where the density sensor 66 intermittently or continuously measures the density of the slurry discharged from the agitation type cross-flow filtration device 6, and a density D corresponding to the output signal is detected. Ｓ The determination is repeated to see if it exceeds the threshold value A. If it does not exceed the threshold value A, the process is repeated from step S1.

[0206] The density D corresponding to the output signal Ｓ exceeds threshold A, the process proceeds to step S3, where the dilution washing process (B) is set. Since the filtrate density differs for each process, threshold B is set according to the filtrate density appropriate for completing the dilution washing process (B). Pump 41 or pump 48 is operated to start supplying the washing liquid from washing liquid source 38 or washing liquid tank 50 to slurry tank 30. Pump 54 continuously supplies the fine particle slurry stored in slurry tank 30 through conduit 56 to agitation type crossflow filtration device 6, and three-way valve 70 continuously returns the slurry discharged from agitation type crossflow filtration device 6 through conduit 72 to slurry tank 30.

[0207] After the setting is completed, the process proceeds to step S4, and the density sensor 66 measures the density D of the slurry discharged from the agitation type cross-flow filtration device 6. Ｓ is measured intermittently or continuously, and the conductivity C of the filtrate is measured by the conductivity sensor 71. Ｒ(S / m) is measured intermittently or continuously. Ｒ is below a preset conductivity threshold D (S / m) and the density D corresponding to the signal from the density sensor 66 Ｓ exceeds the threshold B (C Ｒ <D? and D Ｓ If the condition is not satisfied, the process is repeated from step S3.

[0208] [Process Switching Control of Modified Example 1 of Third Embodiment] As modified example 1 of the third embodiment, the determination condition of S4 in FIG. 10 is changed to "the conductivity C corresponding to the output signal of the conductivity sensor 71" Ｒ is below the threshold D (C Ｒ <D?)) may be used. In this case, it is not necessary to determine whether the concentration in the dilution and washing step (B) is sufficient, but in other respects, the same effects as those of the third embodiment can be obtained. This is because even if the concentration in the dilution and washing step (B) is insufficient, concentration is possible in the subsequent final concentration step (C).

[0209] [Process Switching Control of Modified Example 2 of Third Embodiment] As modified example 2 of the third embodiment, a second density sensor 73 is provided instead of the conductivity sensor 71, and the determination condition of S4 in FIG. 10 is changed to "density D of the filtrate corresponding to the output signal of the second density sensor 73" Ｒ is below a preset filtrate density threshold E and the density D corresponding to the signal from the density sensor 66 Ｓ exceeds the threshold B (D Ｒ <E? and D Ｓ >B?) condition is satisfied, or the density D of the filtrate corresponding to the output signal of the second density sensor 73 is Ｒ is below a preset filtrate density threshold E (D Ｒ<E?) condition may be satisfied. The threshold value E is the density of the filtrate that is appropriate at the stage when the dilution cleaning process (B) should be terminated. In this case, when the density of the filtrate detected by the second density sensor 73 becomes smaller than the threshold value E, it is determined that the impurities in the filtrate (in this case, electrolyte solutes, non-electrolyte solutes, and ultrafine particles that have passed through the filter and are dispersed in the filtrate) have decreased, and sufficient cleaning has been achieved. In other respects, the same effects as those of the third embodiment can be obtained. This embodiment differs from the third embodiment in that it can determine the impurity concentration not only of electrolyte solutes but also of non-electrolyte solutes and ultrafine particles.

[0210] In the third embodiment, "density D Ｓ exceeds threshold B and conductivity C Ｒ is lower than the threshold value D” or in the first modification of the third embodiment, “the conductivity C Ｒ is below the threshold value D" or in the second modification of the third embodiment, "the density D of the filtrate corresponding to the output signal of the second density sensor 73 is Ｒ is below the threshold value E and the density D corresponding to the signal of the density sensor 66 Ｓ exceeds the threshold value B” or “the density D of the filtrate corresponding to the output signal of the second density sensor 73 Ｒ is below the threshold value E,” the process proceeds to step S5 in FIG. 10, where the final concentration step (C) is set.

[0211] The threshold value C is determined according to the filtrate density pre-stored in the control device 67 at the stage at which the final concentration step (C) should be terminated, and is pre-stored in the control device 67. The pump 41 is stopped to stop the supply of cleaning liquid from the cleaning liquid source 38 to the slurry tank 30. The fine particle slurry stored in the slurry tank 30 is continuously supplied to the agitation type cross-flow filtration device 6 through the conduit 56 by the pump 54. The slurry discharged from the agitation type cross-flow filtration device 6 is continuously returned to the slurry tank 30 by the three-way valve 70. After the setting is completed, the process proceeds to step S6, where the density sensor 66 detects the density D of the slurry discharged from the agitation type cross-flow filtration device 6. Ｓ is measured intermittently or continuously, and the density D corresponding to the output signal is ＳThe determination is repeated to see if exceeds the threshold C. If the condition is not met, the process is repeated from step S5.

[0212] Density D Ｓ exceeds the threshold C, the discharge step (D) is set. The slurry stored in the slurry tank 30 is continuously supplied to the agitation type cross-flow filtration device 6 through the conduit 56 by the pump 54. The three-way valve 70 is switched to set the slurry discharged from the agitation type cross-flow filtration device 6 to be continuously supplied to the slurry tank 82 which is connected to the drying device 8. In this way, the concentrated slurry is stored in the slurry tank 82.

[0213] [Process Switching Control of Fourth Embodiment] In the process switching control of the fourth embodiment, instead of the conductivity sensor 71 used in the third embodiment, a second density sensor 73 is provided in the conduit 156, which is the filtrate outlet of the agitation type crossflow filtration device 6. This is the same as in the second modification of the third embodiment, but the control flow is different. In the fourth embodiment, as shown in FIG. 11 , the density D of the filtrate is measured in each of the processes (A) to (C). Ｒ (g / cm ３ ) is measured in real time by the second density sensor 73, and the target value N of the solid content concentration (wt%) for each process inputted in advance to the control device 67 is calculated. Ａ , N Ｂ , N Ｃ (wt%) and the density ρ of the microparticles to be produced solid (g / cm ３ ) and using Equation 1, the slurry density (g / cm ３ ) thresholds A, B, C (g / cm ３ ) are calculated for each judgment cycle, and the threshold values ​​A, B, and C (g / cm ３ ) and the slurry density D Ｓ (g / cm ３ ) to compare.

[0214] As shown in Fig. 11, when the program is started, the control device 67 of the fourth embodiment sets up the initial concentration step (A) in step S1. The contents are the same as step S1 of the third embodiment, so the explanation will be cited. After the settings are complete, the process proceeds to step S2, where the density sensor 66 detects the density D of the slurry discharged from the agitation type cross-flow filtration device 6.Ｓ (g / cm ３ ) is measured intermittently or continuously, and the density ρ of the filtrate discharged from the agitation type cross-flow filtration device 6 is measured by the second density sensor 73. liquid (g / cm ３ ) is measured intermittently or continuously. Furthermore, the true density ρ of the fine particles in the slurry, which has been measured in advance, is added to Equation 1. solid (g / cm ３ ), the real-time density ρ of the filtrate measured by the second density sensor 73 liquid (g / cm ３ ), and the target value N of the solid content concentration in the initial concentration step (A) Ａ By inputting (wt%), the slurry density ρ that becomes the threshold value A at this time can be calculated. slurry (g / cm ３ ) is calculated.

[0215] Next, proceed to step S3, and determine the threshold value A (g / cm ３ ) and the slurry density D measured in real time by the density sensor 66 Ｓ (g / cm ３ ) and the slurry density D Ｓ does not exceed the threshold value A, the process returns to step S1, the setting of step S1 is maintained, and the real-time density ρ of the filtrate is calculated in step S2. liquid (g / cm ３ ) and the newly calculated threshold value A in step S3 is compared with the slurry density D measured in real time by the density sensor 66. Ｓ (g / cm ３ ) is repeatedly compared. Eventually, the slurry density D Ｓ exceeds the threshold A, the process proceeds to step S4.

[0216] In step S4, the dilution and washing step (B) is set. The contents are the same as in step S3 of the third embodiment, so the explanation will be used here. After the setting is completed, the process proceeds to step S5, where the density sensor 66 measures the density D of the slurry discharged from the agitation type cross-flow filtration device 6. Ｓ (g / cm ３ ) is measured intermittently or continuously, and the density ρ of the filtrate discharged from the agitation type cross-flow filtration device 6 is measured by the second density sensor 73. liquid (g / cm３ ) is measured intermittently or continuously. Furthermore, the true density ρ of the fine particles in the slurry, which has been measured in advance, is added to Equation 1. solid (g / cm ３ ), the real-time density ρ of the filtrate measured by the second density sensor 73 liquid (g / cm ３ ), and the target value N of the solid content concentration in the dilution washing step (B) Ｂ By inputting (wt%), the slurry density ρ that becomes the threshold value B at this time can be calculated. slurry (g / cm ３ ) is calculated.

[0217] Next, proceed to step S6, and determine the threshold value B (g / cm ３ ) and the slurry density D measured in real time by the density sensor 66 Ｓ (g / cm ３ ) and the slurry density D Ｓ exceeds the threshold B and the real-time density ρ of the filtrate liquid (g / cm ３ ) is smaller than a preset threshold value F of the filtrate density. If the condition is not met, the process returns to step S4, the setting of step S4 is maintained, and in step S5, the real-time filtrate density ρ liquid (g / cm ３ ) and the newly calculated threshold value B in step S5 is compared with the slurry density D measured in real time by the density sensor 66. Ｓ (g / cm ３ ) and real-time filtrate density ρ liquid (g / cm ３ ) is smaller than a preset filtrate density threshold value F. When the determination condition is met, the process proceeds to step S7.

[0218] In step S7, the final concentration step (C) is set. The details are the same as in step S5 of the third embodiment, so the explanation will be used here. After the settings are complete, the process proceeds to step S8, where the density sensor 66 measures the density D of the slurry discharged from the agitation type cross-flow filtration device 6. Ｓ (g / cm ３) is measured intermittently or continuously, and the density ρ of the filtrate discharged from the agitation type cross-flow filtration device 6 is measured by the second density sensor 73. liquid (g / cm ３ ) is measured intermittently or continuously. Furthermore, the true density ρ of the fine particles in the slurry, which has been measured in advance, is added to Equation 1. solid (g / cm ３ ), the real-time density ρ of the filtrate measured by the second density sensor 73 liquid (g / cm ３ ), and the target value N of the solid content concentration in the final concentration step (C) Ｃ By inputting (wt%), the slurry density ρ that becomes the threshold value C at this time is slurry (g / cm ３ ) is calculated.

[0219] Next, proceed to step S9, and determine the threshold value C (g / cm ３ ) and the slurry density D measured in real time by the density sensor 66 Ｓ (g / cm ３ ) and the slurry density D Ｓ is greater than the threshold value C. If the condition is not met, the process returns to step S7, the setting of step S7 is maintained, and the real-time density ρ of the filtrate is calculated in step S8. liquid (g / cm ３ ) and the slurry density D measured in real time by the density sensor 66 is calculated. Ｓ (g / cm ３ ) exceeds the newly calculated threshold C in step S8. When the determination condition is met, the process proceeds to step S10.

[0220] In step S10, the discharge step (D) is set up. The pump 54 continuously supplies the slurry stored in the slurry tank 30 to the agitation type cross-flow filtration device 6 through the conduit 56. The three-way valve 70 is switched to set up the slurry discharged from the agitation type cross-flow filtration device 6 to be continuously supplied to the slurry tank 82 communicating with the drying device 8. In this way, the concentrated slurry is stored in the slurry tank 82.

[0221] According to the process switching control of the fourth embodiment, the density D of the filtrate in each of the processes (A) to (C)Ｒ (g / cm ３ ) is measured in real time by the second density sensor 73, and the target value N of the solid content concentration (wt%) for each process inputted in advance to the control device 67 is calculated. Ａ , N Ｂ , N Ｃ (wt%) and the density ρ of the microparticles to be produced solid (g / cm ３ ) and using Equation 1, the slurry density (g / cm ３ ) thresholds A, B, C (g / cm ３ ) are calculated for each judgment cycle, and the threshold values ​​A, B, and C (g / cm ３ ) and the slurry density D Ｓ (g / cm ３ ) is compared, so the density of the filtrate D Ｒ (g / cm ３ ) based on the slurry density thresholds A, B, C (g / cm ３ ) can be corrected, and even if the impurity concentration in the slurry fluctuates, the target value N of the solid content concentration in each process can be Ａ , N Ｂ , N Ｃ This has the advantage that more accurate control can be performed based on the weight percent (wt%).

[0222] [Process Switching Control of Modification 1 of Fourth Embodiment] As a modification 1 of the fourth embodiment, the conductivity sensor 71 is used in combination with the second density sensor 73, and in addition to the flow of FIG. 11, a condition that the conductivity of the filtrate is equal to or less than a threshold value (C Ｒ <D?) may be added to the determination conditions. That is, the determination condition in S6 of FIG. 11 may be changed to "Ds>B? and D Ｒ <F? and C Ｒ <D? ". This allows for double monitoring of the concentration of electrolyte solutes, which have a large impact on the quality of the final product, and makes it possible to improve the quality of electrolyte impurities management.

[0223] [Process Switching Control of Modified Example 2 of Fourth Embodiment] As a modified example 2 of the fourth embodiment, the density D of the filtrate is Ｒ Instead, the conductivity C of the filtrate Ｒ is measured intermittently or continuously by the conductivity sensor 71, and the measured conductivity CＲ and the conductivity threshold D. That is, the determination condition in S6 of FIG. 11 may be changed to "Ds>B? and C Ｒ <D? The threshold value D is the conductivity that is appropriate at the stage when the dilution cleaning step (B) should be completed, and is set in advance.

[0224] [Process Switching Control of Modification 3 of Fourth Embodiment] In Modification 3 of the fourth embodiment, the slurry concentration can be used instead of the slurry density as the threshold value used in each process. In this case, in each of the processes (A) to (C), the slurry density D measured in real time by the density sensor and the second density sensor 73 using Equation 1 is Ｓ (g / cm ３ ), density of the filtrate D Ｒ (g / cm ３ ), and the true density ρ of the microparticles to be produced solid (g / cm ３ ) from the slurry concentration C in each step (A) to (C) Ａ , C Ｂ , C Ｃ (wt%) is calculated continuously or at predetermined intervals, and the solid content concentration W Ａ , W Ｂ , W Ｃ (wt%).

[0225] In the initial concentration step (A), the control device 67 controls the calculated slurry concentration C Ａ and a preset solid concentration threshold W Ａ Compared with the slurry concentration C Ａ is the threshold W Ａ When the concentration exceeds C, it is determined that the dilution washing step should be switched to. Ａ >W Ａ ?"

[0226] In the dilution washing step (B), the slurry concentration C Ｂ and the solid concentration threshold W Ｂ Compared with the slurry concentration C Ｂ is the threshold W ＢWhen it is determined that the density of the filtrate or the conductivity of the filtrate exceeds the threshold value stored in the control device 67, and at least one of the density of the filtrate or the conductivity of the filtrate falls below the threshold value stored in the control device 67, it is determined to switch to the final concentration step. Ｂ >W Ｂ ? and D Ｒ <F? " or "C Ｂ >W Ｂ ? and C Ｒ <D? " or "C Ｂ >W Ｂ ? and D Ｒ <F? and C Ｒ <D? ". The thresholds F and D are as explained above.

[0227] In the final concentration step (C), the calculated slurry concentration C Ｃ and threshold W Ｃ Compared with the slurry concentration C Ｃ is the threshold W ｃ When the concentration exceeds 0.05, the final concentration step (C) is judged to be completed. Ｃ >W Ｃ ?"

[0228] In this way, in the third modification of the fourth embodiment, the slurry density Ds and the density D of the filtrate measured in real time are Ｒ By calculating the slurry concentration from the above and comparing and judging it with a threshold value, precise control that reflects the properties of the slurry and filtrate can be performed. By using the slurry concentration as the threshold value, the operator can easily change the setting of the threshold value.

[0229] In addition, in variant example 3 of the fourth embodiment, in the dilution washing process (B), it is preferable to calculate the current slurry concentration from the density sensor 66, the second density sensor 73, and the true density of the microparticles to be produced, and to control the increase / decrease, or supply / stop of the washing water supply flow rate so that the current slurry concentration falls within the range of the lower and upper limits of the slurry concentration in the dilution washing process that are preset.

[0230] Next, a specific example of control by the control device 67 for enhancing the washing effect of the slurry in the dilution washing step (B) will be described. The following control is performed until the conductivity of the filtrate discharged from the agitation type cross-flow filtration device 6 is sufficiently reduced. When the conductivity has been sufficiently reduced, the process proceeds to step S5 in Fig. 10 in the third embodiment (and modified examples 1 and 2), and to step S7 in Fig. 11 in the fourth embodiment.

[0231] 12 to 14 show specific examples of cleaning liquid volume control by the control device 67 that can be implemented in each of the above-described embodiments. In the control example of FIG. 12, when the density of the slurry in the dilution cleaning process (B) is within the target density range D2 to D3, the flow rate of the cleaning liquid is constant at a reference flow rate F2. When the density of the concentrated slurry falls below the lower limit D2 of the target density range, for example, to D1, the flow rate F1 is calculated by subtracting a value proportional to the value D2 - D1 from the reference value F2. When the density of the concentrated slurry rises above the upper limit D3 of the target density range, for example, to D4, the flow rate F3 is calculated by adding a value proportional to the value D4 - D3 to the reference value F2.

[0232] In the control example of FIG. 13, the flow rate of the cleaning liquid is increased linearly to F1, F2, F3, and F4 as the density of the concentrated slurry increases to D1, D2, D3, and D4, including when the density of the concentrated slurry is within the target density range D2 to D3.

[0233] In the control example of Figure 14, when the density of the concentrated slurry is within the target density range D2 to D3, the flow rate of the cleaning liquid is constant at a reference flow rate F2. When the density of the concentrated slurry falls below the lower limit D2 of the target density range (for example, D1), the flow rate F1, which is lower than the reference value F2, is fixed. When the density of the concentrated slurry rises above the upper limit D3 of the target density range, for example to D4, the flow rate F3, which is higher than the reference value F2, is fixed. Even with this simple control, it is possible to maintain the density of the concentrated slurry within the target density range D2 to D3.

[0234] Alternatively, the supply flow rate of the cleaning water may be kept constant, and the supply of cleaning water may be stopped when the slurry density falls below a set lower threshold, while the supply of cleaning water may be started when the slurry density exceeds a set upper threshold.

[0235] In either case, a certain time T is required from the time the washing slurry is introduced into the agitation type crossflow filtration device 6 by the pump 54 until filtration is completed, after the washing liquid flow rate is increased by the pump 41, until this increase is reflected in the density of the concentrated slurry discharged from the agitation type crossflow filtration device 6. Therefore, each of the above controls may be performed intermittently at regular intervals of time T', which is longer than time T, so that the same washing liquid flow rate is maintained throughout time T'. Alternatively, a control method that takes into account the "dead time" from the time the washing liquid flow rate is increased by the pump 41 until this increase is reflected in the density of the concentrated slurry discharged from the agitation type crossflow filtration device 6, for example, a Smith predictor may be incorporated into the control device 67, allowing for more advanced feedback control.

[0236] The control method by the control device 67 is not limited to the examples shown in Figures 10 to 14 and may be modified as needed. For example, it is possible to perform switching control only at one of the timings of completion of the initial concentration step (A), the timing of completion of the dilution cleaning step (B), and the timing of completion of the final concentration step (C), or it may be possible to perform switching control only at two of these timings. The other switching may be performed at the discretion of an operator without relying on the control device 67.

[0237] Returning to Figure 8, the rest of the apparatus will be explained. The slurry tank 82 functions as a buffer to adjust the amount of concentrated slurry supplied to the drying device 8. The slurry tank 82 is cylindrical with a bottom, and the inner surface of the bottom is formed in a hemispherical shape. A semicircular anchor-shaped stirring blade 84 is arranged along the inner surface of the bottom of the slurry tank 82, with a small, constant gap between it and the inner surface of the bottom, and is rotated by a motor 86. The rotation speed of the motor 86 is adjusted so that the concentrated slurry does not settle and solidify in the slurry tank 82. A discharge port 88 is formed at the lower end of the bottom of the slurry tank 82, and the highly viscous concentrated slurry extracted from the slurry tank 82 is sent via a pump 90 to a conduit 94 and then to the drying device 8.

[0238] The gap between the outer periphery of the anchor-shaped agitator blade 84 and the inner bottom surface of the slurry tank 82 is not limited, but similar to the anchor-shaped agitator blade 34 described above, it is preferably approximately 0.5 to 3.0 cm to prevent fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 82. Furthermore, the length of the semicircular outer periphery of the anchor-shaped agitator blade 84 is preferably long enough to face the entire inner bottom surface of the slurry tank 82. Furthermore, the rotational peripheral speed of the anchor-shaped agitator blade 84 at the outer periphery driven by the motor 86 is not limited, but is preferably approximately 0.1 to 3.0 m / s. Within this range, the effect of preventing fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 82 is achieved. This effect is particularly important when producing a secondary battery cathode material precursor because the fine particles are metal compounds with a high specific gravity.

[0239] 4 to 6 are a side cross-sectional view, a plan view with the top plate removed, and a front cross-sectional view showing an agitation heat transfer device as the drying device 8. The drying device 8 has a rectangular parallelepiped casing 92, which has a trough-shaped inner wall 194, an outer wall 198 covering the outer peripheral surface of the inner wall 194, and a rectangular top plate 196 closing the upper end of the inner wall 194. An airtight gap of a certain thickness is formed between the inner wall 194 and the outer wall 198, which serves as a heat medium flow path 199. The outer wall 198 is formed with a heat medium inlet 200 and a heat medium outlet (not shown) that communicate with the heat medium flow path 199. By supplying high-temperature steam or heat medium oil from the heat medium inlet 200 to the heat medium outlet, the inside of the casing 92 can be uniformly heated.

[0240] An inlet 96 is formed at the upper end of the upstream side of the casing 92, and a conduit 94 is connected to it. A gas inlet 174 is formed at the upper surface of the upstream side of the casing 92, and a gas outlet 175 is formed at the upper surface of the downstream side. Room temperature or heated air or the like is blown in through the gas inlet 174, and the moist air or the like is discharged from the gas outlet 175 together with water vapor generated as the mother liquor and cleaning liquid evaporate in the casing 92, thereby maintaining an appropriate humidity level by discharging the water vapor generated inside the casing 92 to the outside of the apparatus. Meanwhile, an outlet 98 is formed at the lower surface of the downstream end of the casing 92, and the fine particle powder dried inside the casing 92 is discharged from there.

[0241] Two hollow rotating shafts 176 are arranged symmetrically along the longitudinal direction within the casing 92, and both ends or one end are rotatably supported by bearings. Hollow agitating blades 178 are fixed to each hollow rotating shaft 176 at regular intervals in the axial direction, and in the region between the two hollow rotating shafts 176, the hollow agitating blade 178 of one hollow rotating shaft 176 is located midway between the hollow agitating blades 178 of the other hollow rotating shaft 176.

[0242] As shown in Figure 6, each hollow agitating blade 178 is fan-shaped with a central angle of less than 180°, and pairs of hollow agitating blades 178 are fixed at positions that are 180° rotationally symmetrical about the hollow rotating shaft 176. A notch 190 of a fixed width is formed between the pair of hollow agitating blades 178 to allow the mixture of concentrated slurry and wet powder to pass axially. The interior of the hollow agitating blade 178 is hollow and communicates with the internal space of the hollow rotating shaft 176, so that the heat medium supplied to the hollow rotating shaft 176 also enters the interior of the hollow agitating blade 178 and heats it.

[0243] The wet powder is a dried product of concentrated slurry that is previously stored in the casing 92. It is not completely dry and is moist. By mixing the previously stored wet powder with the concentrated slurry, abnormal adhesion that may impede the function of the drying device 8 can be avoided, and transportation within the casing 92 by the hollow agitating blades 178 can be facilitated.

[0244] As shown in Figures 4 and 5, the pair of hollow agitating blades 178 are inclined in opposite directions relative to the hollow rotating shaft 176, and each time the hollow rotating shaft 176 rotates 180°, the agitating blades 178 oscillate in the axial direction within a certain angular range, as shown by the solid and dotted lines in the figures. This oscillation serves to mix the concentrated slurry and the wet powder contained in the casing 92 while preventing the concentrated slurry and the wet powder contained in the casing 92 from adhering to the hollow agitating blades 178 between axially adjacent agitating blades 178. In addition, the agitating blades 178 are twisted along an imaginary helical plane around the hollow rotating shaft 176, and serve to gradually transport the mixture of concentrated slurry and wet powder contained in the casing 92 from the upstream side to the downstream side of the casing 92 as the hollow rotating shaft 176 rotates.

[0245] The hollow agitator blade 178 and the hollow rotating shaft 176 are made of a metal with high thermal conductivity, and a heat medium inlet hole 184 and a heat medium outlet hole 182 are formed at the upstream end of the hollow rotating shaft 176. A heat medium such as high-temperature steam or heat medium oil is continuously supplied from a heat medium source (not shown) through the heat medium inlet hole 184 to the heat medium outlet hole 182. The heat medium spreads throughout the entire length of the hollow rotating shaft 176 and also penetrates into the hollow agitator blade 178, heating the entire hollow rotating shaft 176 and hollow agitator blade 178 to a temperature above the boiling points of the mother liquor and washing liquid contained in the concentrated slurry and wet powder. Therefore, the mixture of concentrated slurry and wet powder is heated by conduction heat every time it comes into contact with the hollow rotating shaft 176 and hollow agitator blade 178, evaporating the mother liquor and washing liquid contained in the mixture and eventually becoming a fine powder. A rotation mechanism 180 is provided at one end of the hollow rotary shaft 176, and the hollow rotary shaft 176 is simultaneously rotated in the reverse direction by a motor (not shown), and the mixture of concentrated slurry and wet powder held in the casing 92 is heated by conductive heat transfer with the hollow stirring blades 178 and transported in the transport direction T from upstream to downstream of the casing 92. Furthermore, the positional relationship between the heat medium inlet hole 184 and the heat medium outlet hole 182 shown in FIG. 4 may be reversed. That is, the heat medium outlet hole 182 may be provided radially inward of the heat medium inlet hole 184.

[0246] The fine particle powder discharged from the discharge port 98 of the drying device 8 is stored in a storage container 102 through a discharge path 100 as shown in FIG. 8. The number of hollow rotating shafts 176 is not limited to two, and may be more than two. Therefore, it can be said that a plurality of hollow rotating shafts 176 is sufficient. In the case of a plurality of hollow rotating shafts 176, they may be parallel to each other.

[0247] The method for producing fine particle powder using the above-described apparatus 31 for producing fine particle powder is carried out as follows. [Fine particle slurry production process] First, in the initial state, the crystallizer 10 and the reservoir 18 are filled with mother liquor. The motor 126 rotates the stirring blade 128, and the pump 22 is operated to blow the mother liquor in the reservoir 18 into the reaction vessel 116 through the inlet 115, generating a swirling flow within the reaction vessel 116. The first raw material 12A is supplied through the first inner tube 112, and the second raw material 12B is supplied through the second inner tube 114. The two are vigorously mixed in the central region R within the tapered section 116A, and fine particles are produced by reaction between the first raw material 12A and the second raw material 12B. The mother liquor containing the fine particles is returned to the reservoir 18 through the conduit 16, and as the mother liquor circulates repeatedly, a fine particle slurry is produced within the reservoir 18. The pressure of the mother liquor introduced from the inlet 115 is measured by a pressure gauge 122, and the flow rate of the microparticle slurry flowing out from the discharge hole 14 is appropriately adjusted by a flow control valve 118, thereby adjusting the solids concentration of the microparticle slurry in the reservoir 18 to an appropriate range.

[0248] [Initial Concentration Step] When the solids concentration of the particulate slurry in the reservoir 18 reaches an appropriate range, an initial concentration step (A) is initiated to concentrate the particulate slurry and convert it into an initially concentrated slurry. The initial concentration step is, in a sense, a step of dehydrating the particulate slurry before washing. In the initial concentration step, the three-way valve 70 is controlled to set a circulation path so that the slurry discharged from the agitation type cross-flow filtration device 6 returns to the slurry tank 30 through the conduit 72. In addition, in the initial concentration step, the supply of the washing liquid is stopped (step S1 in FIG. 10 and step S1 in FIG. 11).

[0249] The discharge valve 132 is opened, and the fine particle slurry in the reservoir 18 is discharged from the outlet 26 through the conduit 28 and transferred to the slurry tank 30 by the pump 134. In the slurry tank 30, the anchor-shaped stirring blade 34 is rotated by the motor 36 to prevent the settling of fine particles in the fine particle slurry, and the pump 54 is operated to supply the fine particle slurry from the discharge hole 52 to the agitation type crossflow filtration device 6. As shown in Figure 9, the fine particle slurry is continuously introduced from the inlet 144 of the agitation type crossflow filtration device 6 into the slurry chamber 150 in the casing 60.

[0250] The slurry chamber 150 is pressurized by the discharge pressure of the pump 54, and the agitator blade 142 is continuously rotated by the motor 62. The particulate slurry is agitated by the agitator blade 142 and pressed against the side of the filter 146, and the mother liquor in the particulate slurry is filtered by the filter 146 and flows into the filtrate chamber 148. As the particulate slurry advances downstream in the casing 60, the amount of mother liquor in the particulate slurry decreases, and the particulate slurry is discharged from the discharge port 64 as a somewhat concentrated slurry. The discharged slurry is returned to the slurry tank 30 via the three-way valve 70 and the conduit 72.

[0251] The filtrate that flows into the filtrate chamber 148 passes through the filtrate discharge valve 154 and is collected in a conduit 156. In the initial state, the conduit 156 is connected to the conduit 78 by the three-way valve 74, and the initial filtrate containing a large amount of impurities is discarded in a drain line 80. This process is repeated while measuring the density of the slurry with the density sensor 66 until the density of the fine particle slurry reaches a predetermined value and an initial concentrated slurry having the aforementioned solid concentration is obtained (step S2 in FIG. 10, step S3 in FIG. 11).

[0252] [Dilution Washing Step] When an initially concentrated slurry of a predetermined concentration is obtained in the slurry tank 30, the initial concentration step is terminated, and the dilution washing step (B) is initiated, in which the initially concentrated slurry is diluted with a washing liquid for washing (step S3 in FIG. 10 and step S4 in FIG. 11). In the dilution washing step, the three-way valve 70 maintains a circulation path in which the slurry discharged from the agitation type cross-flow filtration device 6 returns to the slurry tank 30 via the conduit 72. The filtrate collected in the conduit 156 via the filtrate discharge valve 154 is discharged to the drain 80 as a filtrate with a high impurity content via the three-way valve 74 and the conduit 78.

[0253] While controlling the density using the density sensor 66 and the level in the slurry tank 30, the on-off valve 44 is opened, the conduit 46 is connected to the slurry tank 30 via the three-way valve 42, and the pump 48 is operated to first supply cleaning liquid from the cleaning liquid tank 50 to the slurry tank 30. The cleaning liquid tank 50 stores relatively clean cleaning liquid obtained during the previous production of fine particle powder. Immediately after the start of the dilution and washing process (first stage), the initially concentrated slurry contains a large amount of impurities, so even a cleaning liquid with a low level of cleanliness can provide a sufficient cleaning effect. As a result, the initially concentrated slurry continues to circulate between the slurry tank 30 and the agitation type cross-flow filtration device 6, while being washed in the slurry tank 30 and filtered by the agitation type cross-flow filtration device 6.

[0254] As the cleaning liquid from the cleaning liquid tank 50 is continuously supplied to the slurry tank 30 and the cleaning of the initially concentrated slurry progresses, the impurities (electrolyte components, non-electrolyte components, and ultrafine particles) in the filtrate discharged from the agitation type crossflow filtration device 6 decrease, and the conductivity (or density) of the filtrate indicated by the conductivity sensor 71 (or the second density sensor 73) installed in the conduit 156 decreases. When the conductivity or density reaches a target value (the target value for switching from the cleaning liquid in the cleaning liquid tank 50 to the clean cleaning liquid in the cleaning liquid source 38) (or when the amount of liquid in the cleaning liquid tank 50 has sufficiently decreased), the pump 48 is stopped automatically or manually by the control device 67 to stop the supply of the reused cleaning liquid from the cleaning liquid tank 50, and then the three-way valve 42 is automatically or manually operated by the control device 67 to start the supply of the clean cleaning liquid from the cleaning liquid source 38 to the slurry tank 30.

[0255] As the cleaning and filtration of the initially concentrated slurry progresses using clean cleaning liquid from the cleaning liquid source 38, the impurities in the filtrate discharged from the agitation type crossflow filtration device 6 are further reduced, and the conductivity (or density) of the filtrate indicated by the conductivity sensor 71 (or second density sensor 73) installed in the conduit 156 decreases. When the conductivity or density reaches the next target value (the target value indicating the completion of cleaning) and the density of the fine particle slurry reaches a predetermined value (step S4 in FIG. 10 , step S6 in FIG. 11 ), the cleaning liquid source 38 is stopped, and the three-way valve 42 and the on-off valve 44 are automatically controlled by the control device 67 or manually operated to stop the supply of cleaning liquid.

[0256] [Final Concentration Step] After the supply of the washing liquid is stopped and the dilution washing step is completed, a final concentration step is performed to finally concentrate the washed slurry (step S5 in FIG. 10 and step S7 in FIG. 11). In the final concentration step, the washed slurry is supplied to the agitation type cross-flow filtration device 6, where it is separated into a concentrated washed slurry and a filtrate. The concentrated washed slurry is returned to the slurry tank 30. In this way, the washed slurry is continuously filtered (dehydrated) by the agitation type cross-flow filtration device 6 while circulating between the slurry tank 30 and the agitation type cross-flow filtration device 6. Therefore, the slurry in the slurry tank 30 is gradually concentrated (step S6 in FIG. 10 and step S9 in FIG. 11).

[0257] When the conductivity of the filtrate measured by the conductivity sensor 71 provided in the conduit 156 eventually falls below a predetermined target value, it is determined that the filtrate has become clean enough to be used for primary cleaning in the slurry tank 30, and the three-way valve 74 is switched automatically by the control device 67 or manually, and the filtrate from the conduit 156 is stored in the cleaning liquid tank 50 via the conduit 76. If the filtrate becomes sufficiently clean, storage in the cleaning liquid tank 50 may start from the final concentration step as well as from the subsequent stage of the dilution cleaning step.

[0258] The density of the concentrated slurry discharged from the outlet 64 of the agitation crossflow filtration device 6 is continuously or intermittently measured by a density sensor 66. If the density of the concentrated slurry measured by the density sensor 66 is higher than the target range, the rotation speed of the pump 41 is increased or the pump 41 is started to increase the amount of cleaning liquid from the cleaning liquid source 38 to the slurry tank 30, thereby diluting the slurry in the slurry tank 30. Conversely, if the density of the concentrated slurry measured by the density sensor 66 is lower than the target range, the rotation speed of the pump 41 is decreased or the pump 41 is stopped to reduce or stop the amount of cleaning liquid from the cleaning liquid source 38 to the slurry tank 30, thereby preventing the slurry in the slurry tank 30 from being diluted. In this way, feedback control is performed to keep the solids concentration in the concentrated slurry within a certain range ( FIGS. 12 to 14 ).

[0259] The concentrated slurry, the solids concentration of which has been adjusted to fall within a certain range, is sent to a slurry tank 82 via a flow control valve 68 and a three-way valve 70 (step S7 in FIG. 10, step S10 in FIG. 11). The concentrated slurry stored in the slurry tank 82 is continuously stirred with an anchor-shaped stirring blade 84 to prevent settling.

[0260] [Drying Process] The drying process is a process in which the concentrated slurry is dried to a fine powder state. In the drying process, the concentrated slurry in the slurry tank 82 is sent to the drying device 8 by the pump 90 and introduced into the casing 92 from the inlet 96 via the conduit 94. Two hollow rotary shafts 176 rotate continuously within the casing 92, and the hollow agitating blades 178 are heated by high-temperature steam or heat transfer oil supplied to the heat transfer medium inlet 184. As the hollow agitating blades 178 rotate, the concentrated slurry and the wet powder held within the casing 92 are mixed, and the mixture is sent in the transfer direction T. During this process, the oscillation of the hollow agitating blades 178 prevents the mixture from adhering to the hollow agitating blades 178, while the heated hollow agitating blades 178 heat the mixture by conduction heat transfer, thereby progressing the drying process of the mixture. By blowing in room temperature or heated air or the like through gas inlet 174 and discharging moist air or the like through gas outlet 175, the water vapor generated inside casing 92 is discharged to the outside of the apparatus, thereby maintaining an appropriate humidity level inside the apparatus. When the mixture reaches the downstream side of casing 92, it becomes fine particle powder, which is sequentially discharged from outlet 98. The fine particle powder discharged from outlet 98 is stored in storage container 102 through discharge path 100.

[0261] [Effects of this embodiment] According to the device for concentrating fine particle slurry, the method for producing fine particle powder, and the production device 31 of the above-described embodiments, the density of the concentrated slurry after filtration by the agitation-type cross-flow filtration device 6 is measured by the density sensor 66, and the rotation speed of the pump 41 is adjusted by the control device 67, and the amount of cleaning liquid supplied to the slurry tank 30 is feedback-controlled. Therefore, even when the material to be treated has extremely small average particle diameters of fine particles, for example, 7 μm or less, the concentration of the concentrated slurry can be stably controlled even in a high concentration range of, for example, 35 wt % to 65 wt %, and fine particle powder can be stably produced while preventing clogging due to the concentrated slurry.

[0262] Furthermore, by controlling or instructing the timing using the control device 67, the slurry can be stably concentrated even in a high concentration range by appropriately switching between the initial concentration step (A) for obtaining an initial concentrated slurry, the dilution and washing step (B) for diluting and washing the initial concentrated slurry to obtain a washed slurry, and the final concentration step (C) for concentrating the washed slurry to obtain a concentrated slurry.

[0263] Furthermore, according to this embodiment, when the solids concentration of the washing slurry is adjusted to 30 wt % or more and 60 wt % or less and the solids concentration of the concentrated slurry produced by the agitation type cross-flow filtration device 6 is adjusted to 35 wt % or more and 65 wt % or less, it is possible to prevent clogging due to high-concentration slurry, optimize production efficiency in the filtration step and drying step, and reduce energy costs.

[0264] Furthermore, when a vibrating inline density sensor is used as the density sensor 66, and the vibrator 66A in contact with the concentrated slurry is vibrated to measure its resonant frequency as a function of the density of the concentrated slurry, the density of the concentrated slurry can be measured with high accuracy and without delay even if the concentrated slurry is highly concentrated and viscous. This allows for stable production of fine particle powder while preventing clogging due to the concentrated slurry.

[0265] Furthermore, because the agitation-type cross-flow filtration device 6 is used, concentrated slurry can be produced at a higher concentration range even when the average particle size of the fine particles is extremely small, for example, 7 μm or less. This makes it possible to prevent clogging due to high-concentration slurry, increase production efficiency in the filtration and drying processes, and reduce energy costs.

[0266] Furthermore, when the microparticles are a precursor of a positive electrode material for a secondary battery, it is possible to produce a precursor of a positive electrode material for a secondary battery while preventing clogging at the concentrated slurry stage, improving production efficiency in the filtration and drying processes, and reducing energy costs.

[0267] In addition, in the drying device 8, the hollow rotating shafts 176 are fixed with gaps in the axial direction and the hollow agitating blades 178 of each hollow rotating shaft 176 are fixed so as to partially overlap when viewed in the axial direction, so that as the hollow agitating blades 178 rotate, the heated hollow agitating blades 178 heat and transport the concentrated slurry, drying the concentrated slurry and converting it into fine particle powder. Therefore, compared to methods using hot air, water can be evaporated more efficiently, and the excellent effects of reducing energy costs and increasing production efficiency are achieved.

[0268] The present invention is not limited to the above-described embodiment, and additions, deletions, and substitutions with well-known techniques of constituent elements are possible within the scope of the claims.

[0269] Next, a detailed description will be given of a fine-particle powder manufacturing apparatus 41 according to a fifth embodiment of the present invention. Description of the same configuration as in the first embodiment will basically be omitted, and the description will focus on the differences from the first embodiment. The fine-particle powder manufacturing apparatus 41 according to the fifth embodiment differs from the first embodiment in that it does not include the control device 67 of the first embodiment.

[0270] As shown in FIG. 15 , a conductivity sensor 71 is installed in the conduit 156, which serves as the filtrate outlet of the agitation type crossflow filtration device 6. The conductivity sensor 71 continuously measures the conductivity of the filtrate discharged from the agitation type crossflow filtration device 6 and transmits the measured value to a control panel (not shown). The control panel receives the output of the conductivity sensor 71 and uses the output result and the pre-stored filtrate conductivity to detect the progress of the dilution cleaning process and determine the completion timing of the dilution cleaning process. Specifically, the completion timing of the dilution cleaning process is determined when the output result falls below a threshold value set in the control panel. Note that the completion timing of the dilution cleaning process may be determined using other sensors, not limited to the conductivity sensor 71. For example, a second density sensor (not shown) may be installed in the conduit 156, which serves as the filtrate outlet of the agitation type crossflow filtration device 6. The second density sensor continuously measures the density of the filtrate discharged from the agitation type crossflow filtration device 6 and transmits the measured value to a control panel (not shown). A control panel (not shown) receives the output of the second density sensor, detects the progress of the dilution cleaning process from the density of the filtrate, and determines the timing for completing the dilution cleaning process.

[0271] During the initial concentration by the agitation crossflow filtration device 6 and for a while after the start of cleaning, the filtrate entering the filtrate chamber 148 contains a large amount of impurities. However, as filtration progresses, the filtrate becomes less impurity-rich, and the conductivity detected by the conductivity sensor 71 decreases. Therefore, when the conductivity reaches a predetermined threshold, the three-way valve 74 is switched by a control panel (not shown), and the filtrate previously flowing to the drain 80 is stored in the cleaning liquid tank 50. The relatively clean filtrate stored in the cleaning liquid tank 50 is supplied as cleaning liquid to the slurry tank 30 via the conduit 46, the three-way valve 42, and the on-off valve 44 by operating the pump 48 in the next dilution cleaning process. This reduces the amount of cleaning liquid used in the cleaning liquid source 38, thereby contributing to cost reduction in the production of fine-particle powder. Furthermore, the amount of filtrate and cleaning waste liquid disposed of outside the fine-particle powder production apparatus 41 is reduced, thereby reducing the burden on the environment.

[0272] The downstream portion of the casing 60 is a conical tapered portion 152 that narrows downstream, and a discharge port 64 is formed at the tip of the tapered portion 152. The slurry is transported downstream while snaking through the slurry chamber 150, and moisture is removed. The slurry is circulated between the slurry tank 30 and the agitation type cross-flow filtration device 6, where it is filtered and concentrated. The highly viscous concentrated slurry is discharged from the discharge port 64.

[0273] The solids concentration of the concentrated slurry discharged from the agitation crossflow filtration device 6 is not necessarily limited, as optimal values ​​differ among the initial concentration step, the dilution and washing step, and the final concentration step. For example, when producing a cathode material precursor for a secondary battery, the solids concentration of the initially concentrated slurry at the completion of the initial concentration step is preferably 35 wt % or more and 65 wt % or less, more preferably 45 wt % or more and 65 wt % or less. The solids concentration of the washed slurry at the completion of the dilution and washing step is preferably 35 wt % or more and 60 wt % or less, more preferably 35 wt % or more and 45 wt % or less. The solids concentration of the final concentrated slurry at the completion of the final concentration step is preferably 50 wt % to 65 wt %, more preferably 60 wt % or more and 65 wt % or less.

[0274] When the concentration is within the above range in each step, the transport of the concentrated slurry within the casing 60 of the agitation type crossflow filtration device 6 is not difficult, and it is possible to effectively reduce the amount of impurities in the final concentrated slurry while limiting the consumption of washing liquid. Therefore, the load on the agitation type crossflow filtration device 6 and the drying device 8 is well balanced, and it is possible to improve the total processing efficiency and energy efficiency without overloading each step.

[0275] As shown in FIG. 15 , the discharge port 64 of the casing 60 of the agitation type crossflow filtration device 6 is connected to a first port of a three-way valve 70 (path switching device) via a density sensor 66 and a flow control valve 68. The three-way valve 70 is switched by a control panel (not shown) or manually in response to instructions from the control panel. The second port of the three-way valve 70 is connected to the slurry tank 30 via a conduit 72 (second flow path). The third port of the three-way valve 70 is connected to a slurry tank 82 for storing concentrated slurry, which is provided upstream of the drying device 8. By operating the three-way valve 70, slurry in various states discharged from the discharge port 64 of the agitation type crossflow filtration device 6 can be returned to the slurry tank 30 for circulation or supplied to the slurry tank 82, which serves as a buffer for the drying device 8.

[0276] The density of the concentrated slurry discharged from the outlet 64 of the agitation type crossflow filtration device 6 is measured by a density sensor 66, and the output signal of the density sensor 66 is transmitted to a control panel (not shown). The density sensor 66 has two main purposes. The first is to measure the timing when the concentrated slurry discharged from the agitation type crossflow filtration device 6 is sufficiently dewatered and reaches a predetermined density, and to grasp at least one of the timings of completion of the initial concentration step and the final concentration step, and to use this timing to control the transition to the next step.

[0277] When determining the timing for completing the dilution cleaning process, it is preferable to satisfy either of the following conditions: (1) the conductivity of the filtrate decreases to a predetermined threshold based on the output of the conductivity sensor 71, and the density of the concentrated slurry increases to a predetermined threshold based on the output of the density sensor 66; or (2) the conductivity of the filtrate decreases to a predetermined threshold based on the output of the conductivity sensor 71 (the output of the density sensor 66 is not involved in the determination criteria).

[0278] The second purpose of measuring the slurry density using the density sensor 66 is to improve the washing effect of the slurry in the dilution washing step. Specifically, a lower limit and an upper limit are set for the density value corresponding to the output signal of the density sensor 66. When the upper limit is reached, the supply of washing liquid from the washing liquid source 38 to the slurry tank 30 is increased (or temporarily stopped and restarted), and when the lower limit is reached, the supply of washing liquid from the washing liquid source 38 is reduced (or stopped). This maintains the solids concentration of the concentrated slurry discharged from the agitation type crossflow filtration device 6 in the dilution washing step within a certain range, thereby adjusting the degree of cleanliness, until the conductivity of the filtrate discharged from the agitation type crossflow filtration device 6 is sufficiently reduced. Here, the components from the slurry tank 30 to the agitation type crossflow filtration device 6 in the fine particle powder production apparatus 41 are sometimes referred to as a fine particle slurry concentration device. The washing liquid source 38 is sometimes referred to as a washing liquid supply device.

[0279] In order to control the cleaning liquid in the dilution cleaning step, the three-way valve 42 and the on-off valve 44 are controlled manually or by a control panel (not shown) according to the value of the density sensor 66, and if the density of the concentrated slurry detected by the density sensor 66 is too high, the three-way valve 42 and the on-off valve 44 are controlled to increase or start the amount of cleaning liquid from the cleaning liquid source 38 to the slurry tank 30. If the density of the concentrated slurry detected by the density sensor 66 is too low, the three-way valve 42 and the on-off valve 44 are controlled to reduce or stop the amount of cleaning liquid from the cleaning liquid source 38 to the slurry tank 30, thereby performing feedback control so that the solids concentration in the concentrated slurry falls within a certain range.

[0280] The slurry tank 82 functions as a buffer to adjust the amount of final concentrated slurry supplied to the drying device 8. The slurry tank 82 is cylindrical with a bottom, and the inner surface of the bottom is formed in a hemispherical shape. A semicircular anchor-shaped stirring blade 84 is arranged along the inner surface of the bottom of the slurry tank 82, with a small, fixed gap between it and the inner surface of the bottom, and is rotated by a motor 86. The rotation speed of the motor 86 is adjusted so that the final concentrated slurry does not settle and solidify in the slurry tank 82. A discharge port 88 is formed at the lower end of the bottom of the slurry tank 82, and the highly viscous final concentrated slurry extracted from the slurry tank 82 is sent via a pump 90 to a conduit 94 and then to the drying device 8.

[0281] The gap between the outer periphery of the anchor-shaped agitator blade 84 and the inner bottom surface of the slurry tank 82 is not limited, but similar to the anchor-shaped agitator blade 34 described above, it is preferably approximately 0.5 to 3.0 cm to prevent fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 82. Furthermore, the length of the semicircular outer periphery of the anchor-shaped agitator blade 84 is preferably long enough to face the entire inner bottom surface of the slurry tank 82. Furthermore, the rotational peripheral speed of the outer periphery of the anchor-shaped agitator blade 84 driven by the motor 86 is not limited, but is preferably approximately 0.1 to 3.0 m / s. Within this range, the effect of preventing fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 82 is achieved. This effect is particularly important when producing a cathode material precursor for secondary batteries because the fine particles are metal compounds with a high specific gravity.

[0282] 4 to 6 are a side cross-sectional view, a plan view with the top plate removed, and a front cross-sectional view showing an agitation heat transfer drying device as the drying device 8. The drying device 8 has a rectangular parallelepiped casing 92, which has a trough-shaped inner wall 194, an outer wall 198 covering the outer peripheral surface of the inner wall 194, and a rectangular top plate 196 closing the upper end of the inner wall 194. An airtight gap of a certain thickness is formed between the inner wall 194 and the outer wall 198, which serves as a heat medium flow path 199. The outer wall 198 is formed with a heat medium inlet 200 and a heat medium outlet (not shown) that communicate with the heat medium flow path 199. The inside of the casing 92 can be uniformly heated by supplying high-temperature steam or heat medium oil from the heat medium inlet 200 to the heat medium outlet.

[0283] An inlet (inflow port) 96 is formed at the upper end of the upstream side (one end) of the casing 92, and a conduit 94 is connected thereto. The final concentrated slurry is sent to the conduit 94 via the pump 90 and supplied from the inlet 96. The final concentrated slurry is preferably supplied continuously. A gas inlet 174 is formed at the upper surface of the upstream side of the casing 92, and a gas outlet 175 is formed at the upper surface of the downstream side (the other end). Room temperature or heated air is blown in through the gas inlet 174, and the moist air is discharged from the gas outlet 175 together with water vapor generated by evaporation of the mother liquor and washing liquid within the casing 92. By discharging the water vapor generated within the casing 92 to the outside of the apparatus, it is possible to maintain an appropriate humidity level. Meanwhile, an outlet (outlet hole) 98 is formed at the lower surface of the downstream end of the casing 92, and the fine particle powder dried within the casing 92 is discharged.

[0284] Two hollow rotary shafts 176 are arranged symmetrically along the longitudinal direction within the casing 92, and both ends or one end are supported by bearings so that they can rotate around the axes of the two hollow rotary shafts 176 (with the axes as the rotation center). Hollow agitating blades 178 are fixed to each hollow rotary shaft 176 at regular intervals in the axial direction, and in the region between the two hollow rotary shafts 176, the hollow agitating blade 178 of one hollow rotary shaft 176 is located midway in the axial direction of the hollow agitating blade 178 of the other hollow rotary shaft 176. The two hollow rotary shafts 176 may be parallel to each other. Note that the hollow rotary shafts 176 may also be simply referred to as rotary shafts.

[0285] As shown in Figure 6, each hollow agitator blade 178 is fan-shaped with a central angle of less than 180°, and pairs of hollow agitator blades 178 are fixed at positions that are 180° rotationally symmetrical about the hollow rotary shaft 176. A notch 190 of a fixed width is formed between the pair of hollow agitator blades 178 to allow the mixture of the final concentrated slurry and wet powder to pass axially. The interior of the hollow agitator blade 178 is hollow and communicates with the internal space of the hollow rotary shaft 176, so that the heat medium supplied to the hollow rotary shaft 176 also enters the interior of the hollow agitator blade 178 and heats the hollow agitator blade 178. This is sometimes called the heating mechanism of the hollow agitator blade 178.

[0286] The wet powder is a dried product of the final concentrated slurry that is previously stored within the casing 92. It is not completely dry and is moist. For metal microparticles with an average particle size of 7 μm or less, the moisture content should be 5 wt% to 65 wt%, preferably 5 wt% to 25 wt%. The wet powder should be stored in the casing 92 to the extent that it covers the hollow rotary shaft 176. The wet powder should be stored within the casing 92 in an amount equal to or greater than half, by weight, of the hourly supply amount of a slurry with a slurry concentration of 50 to 65 wt%, preferably the same amount or more. Mixing the previously stored wet powder with the final concentrated slurry prevents abnormal adhesion that could impede the function of the drying device 8 and enables proper transport within the casing 92 by the hollow stirring blade 178.

[0287] As shown in Figures 4 and 5, the pair of hollow agitator blades 178 are inclined in opposite directions relative to the hollow rotary shaft 176, and each time the hollow rotary shaft 176 rotates 180°, the locus of the hollow agitator blade 178 oscillates in the axial direction within a certain angular range, as shown by the solid and dotted lines in the figures. This oscillation serves to mix the final concentrated slurry and the wet powder while preventing the final concentrated slurry and the wet powder from adhering to the hollow agitator blades 178 adjacent in the axial direction. In addition, the hollow agitator blade 178 also has a twist along an imaginary helical plane around the hollow rotary shaft 176, and serves to gradually transport the mixture of the final concentrated slurry and the wet powder from the upstream side to the downstream side of the casing 92 as the hollow rotary shaft 176 rotates.

[0288] The hollow agitator blade 178 and the hollow rotating shaft 176 are made of a metal with high thermal conductivity, and a heat medium inlet hole 184 and a heat medium outlet hole 182 are formed at the upstream end of the hollow rotating shaft 176. A heat medium such as high-temperature steam or heat medium oil is continuously supplied from a heat medium source (not shown) through the heat medium inlet hole 184 to the heat medium outlet hole 182. The heat medium spreads throughout the entire length of the hollow rotating shaft 176 and also penetrates into the hollow agitator blade 178, heating the entire hollow rotating shaft 176 and hollow agitator blade 178 to a temperature above the boiling points of the mother liquor and washing liquid contained in the final concentrated slurry and the wet powder. Therefore, the mixture of the final concentrated slurry and the wet powder is heated by conduction heat every time it comes into contact with the hollow rotating shaft 176 and hollow agitator blade 178, evaporating the mother liquor and washing liquid contained in the mixture and eventually becoming a fine powder. A rotation mechanism 180 is provided at one end of the hollow rotary shaft 176, and the hollow rotary shaft 176 is simultaneously rotated in the reverse direction by a motor (not shown), and the mixture of the final concentrated slurry and the wet powder held in the casing 92 is heated by the hollow agitating blades 178 through conductive heat transfer, which has excellent thermal efficiency, and transported in the transport direction T from upstream to downstream of the casing 92. Heating through conductive heat transfer is sometimes called indirect heating. Furthermore, the positional relationship between the heat medium inlet hole 184 and the heat medium outlet hole 182 shown in FIG. 4 may be reversed. That is, the heat medium outlet hole 182 may be provided radially inward of the heat medium inlet hole 184.

[0289] The fine powder discharged from the discharge port 98 of the drying device 8 is stored in a storage container 102 through a discharge path 100 as shown in FIG. 15 . The number of hollow rotating shafts 176 is not limited to two, and may be more than two. Therefore, it can be said that a plurality of hollow rotating shafts 176 is sufficient. In the case of a plurality of hollow rotating shafts 176, the hollow rotating shafts 176 may be parallel to each other. When a plurality of rotating shafts is provided, the hollow stirring blades 178 provided on two adjacent rotating shafts are configured to be positioned midway in the axial direction between the hollow stirring blade 178 of one hollow rotating shaft 176 and the hollow stirring blade 178 of the other hollow rotating shaft 176. In this case, the hollow stirring blades 178 are inclined in opposite directions relative to the hollow rotating shaft 176 and twist along an imaginary helical plane around the hollow rotating shaft 176, so that the two adjacent hollow rotating shafts 176 rotate in opposite directions to each other.

[0290] The method for producing fine particle powder using the above-described apparatus 41 for producing fine particle powder is carried out as follows. [Fine particle slurry production process] First, in the initial state, the crystallizer 10 and the reservoir 18 are filled with mother liquor. The motor 126 rotates the stirring blade 128, and the pump 22 is operated to blow the mother liquor in the reservoir 18 into the reaction vessel 116 through the inlet 115, generating a swirling flow within the reaction vessel 116. The first raw material 12A is supplied through the first inner tube 112, and the second raw material 12B is supplied through the second inner tube 114. The two are vigorously mixed in the central region R within the tapered section 116A, and fine particles are produced by reaction between the first raw material 12A and the second raw material 12B. The mother liquor containing the fine particles is returned to the reservoir 18 through the conduit 16, and as the mother liquor circulates repeatedly, a fine particle slurry is produced within the reservoir 18. The pressure of the mother liquor introduced from the inlet 115 is measured by a pressure gauge 122, and the flow rate of the microparticle slurry flowing out from the discharge hole 14 is appropriately adjusted by a flow control valve 118, thereby adjusting the solids concentration of the microparticle slurry in the reservoir 18 to an appropriate range.

[0291] [Initial concentration step] When the solids concentration of the particulate slurry in the reservoir 18 reaches an appropriate range, an initial concentration step is initiated to concentrate the particulate slurry and convert it into an initially concentrated slurry. The initial concentration step is a step of dehydrating the particulate slurry before washing. In the initial concentration step, the three-way valve 70 is controlled to set a circulation path so that the slurry discharged from the agitation type crossflow filtration device 6 returns to the slurry tank 30 through the conduit 72. In addition, the supply of the washing liquid is stopped in the initial concentration step.

[0292] The discharge valve 132 is opened, and the fine particle slurry in the reservoir 18 is discharged from the outlet 26 through the conduit 28 and transferred to the slurry tank 30 by the pump 134. In the slurry tank 30, the anchor-shaped stirring blade 34 is rotated by the motor 36 to prevent the settling of fine particles in the fine particle slurry, and the pump 54 is operated to supply the fine particle slurry from the discharge hole 52 to the agitation type crossflow filtration device 6. As shown in Figure 3, the fine particle slurry is continuously introduced from the inlet 144 of the agitation type crossflow filtration device 6 into the slurry chamber 150 in the casing 60.

[0293] The slurry chamber 150 is pressurized by the discharge pressure of the pump 54, and the agitator blade 142 is continuously rotated by the motor 62. The particulate slurry is agitated by the agitator blade 142 and pressed against the side of the filter 146, and the mother liquor in the particulate slurry is filtered by the filter 146 and flows into the filtrate chamber 148. As the particulate slurry advances downstream in the casing 60, the amount of mother liquor in the particulate slurry decreases, and the particulate slurry is discharged from the discharge port 64 as a somewhat concentrated slurry. The discharged slurry is returned to the slurry tank 30 via the three-way valve 70 and the conduit 72.

[0294] The filtrate that flows into the filtrate chamber 148 passes through the filtrate discharge valve 154 and is collected in a conduit 156. In the initial state, the conduit 156 is connected to the conduit 78 by the three-way valve 74, and the initial filtrate containing a large amount of impurities is discarded in the drain 80. This process is repeated while measuring the density of the slurry with the density sensor 66 until the density of the fine particle slurry reaches a predetermined value and an initial concentrated slurry having the aforementioned solid concentration is obtained.

[0295] [Dilution and Washing Process] When an initially concentrated slurry of a predetermined concentration is obtained in the slurry tank 30, the initial concentration process is completed, and the dilution and washing process is initiated, in which the initially concentrated slurry is diluted with a washing liquid for washing. In the dilution and washing process, the three-way valve 70 maintains a circulation path in which the slurry discharged from the agitation type cross-flow filtration device 6 returns to the slurry tank 30 via the conduit 72. The filtrate collected in the conduit 156 via the filtrate discharge valve 154 is discharged to the drain 80 via the three-way valve 74 and the conduit 78 as filtrate with a high impurity content.

[0296] While controlling the density using the density sensor 66 and the level in the slurry tank 30, the on-off valve 44 is opened, the conduit 46 is connected to the slurry tank 30 via the three-way valve 42, and the pump 48 is operated to first supply cleaning liquid from the cleaning liquid tank 50 to the slurry tank 30. The cleaning liquid tank 50 stores relatively clean cleaning liquid obtained during the previous production of fine particle powder. Immediately after the start of the dilution and washing process (first stage), the initially concentrated slurry contains a large amount of impurities, so even a cleaning liquid with a low level of cleanliness can provide a sufficient cleaning effect. As a result, the initially concentrated slurry continues to circulate between the slurry tank 30 and the agitation type cross-flow filtration device 6, while being washed in the slurry tank 30 and filtered by the agitation type cross-flow filtration device 6.

[0297] As the cleaning liquid from the cleaning liquid tank 50 is continuously supplied to the slurry tank 30 and the cleaning of the initially concentrated slurry progresses, the impurities (electrolyte components, non-electrolyte components, and ultrafine particles) in the filtrate discharged from the agitation type crossflow filtration device 6 decrease, and the conductivity (or density) of the filtrate indicated by the conductivity sensor 71 (or a second density sensor, not shown) installed in the conduit 156 decreases. When the conductivity or density reaches a target value (the target value for switching from the cleaning liquid in the cleaning liquid tank 50 to the clean cleaning liquid in the cleaning liquid source 38) (or when the amount of liquid in the cleaning liquid tank 50 has sufficiently decreased), the pump 48 is stopped automatically or manually by a control panel, not shown, to stop the supply of the reused cleaning liquid from the cleaning liquid tank 50. After that, the three-way valve 42 is automatically or manually operated by a control panel, not shown, to start the supply of the clean cleaning liquid from the cleaning liquid source 38 to the slurry tank 30.

[0298] As the cleaning and filtration of the initially concentrated slurry progresses using clean cleaning liquid from the cleaning liquid source 38, the impurities in the filtrate discharged from the agitation type crossflow filtration device 6 are further reduced, and the conductivity (or density) of the filtrate indicated by the conductivity sensor 71 (or a second density sensor, not shown) installed in the conduit 156 decreases. When the conductivity or density reaches the next target value (the target value indicating the completion of cleaning) and the density of the fine particle slurry reaches a predetermined value, the cleaning liquid source 38 is stopped, and the three-way valve 42 and the on-off valve 44 are automatically controlled by a control panel, not shown, or manually operated to stop the supply of cleaning liquid.

[0299] [Final Concentration Step] After the supply of the washing liquid is stopped and the dilution washing step is completed, a final concentration step is performed to finally concentrate the washed slurry. In the final concentration step, the washed slurry is supplied to the agitation type cross-flow filtration device 6 and separated into a concentrated washed slurry and filtrate. The concentrated washed slurry is returned to the slurry tank 30. In this way, the washed slurry is continuously filtered by the agitation type cross-flow filtration device 6 while circulating between the slurry tank 30 and the agitation type cross-flow filtration device 6. Therefore, the slurry in the slurry tank 30 is gradually concentrated.

[0300] When the conductivity of the filtrate measured by the conductivity sensor 71 provided in the conduit 156 eventually falls below a predetermined target value, it is determined that the filtrate has become clean enough to be used for primary cleaning in the slurry tank 30, and the three-way valve 74 is switched automatically by a control panel (not shown) or manually, and the filtrate from the conduit 156 is stored in the cleaning liquid tank 50 through the conduit 76. When the filtrate becomes sufficiently clean, storage in the cleaning liquid tank 50 may begin not only from the final concentration step but also from the subsequent stage of the dilution cleaning step.

[0301] The density of the final concentrated slurry discharged from the outlet 64 of the agitation type crossflow filtration device 6 is continuously or intermittently measured by a density sensor 66, and when the density reaches a target density value for the final concentration step, the flow control valve 68 and the three-way valve 70 are operated automatically or manually by a control panel (not shown) to send the final concentrated slurry to a slurry tank 82. The final concentrated slurry stored in the slurry tank 82 is stirred with an anchor-shaped stirring blade 84 to prevent precipitation, while the drying step is initiated. In this embodiment, the concentrated slurry is returned to the slurry tank 30 and filtered while being circulated, but the present invention is not limited to this, and the concentrated slurry can also be supplied to the slurry tank 82 without being circulated.

[0302] [Drying Process] The drying process is a process in which the final concentrated slurry is dried to a fine powder state. In the drying process, the final concentrated slurry in the slurry tank 82 is sent to the drying device 8 by the pump 90 and introduced into the casing 92 from the inlet 96 via the conduit 94. Two hollow rotary shafts 176 continuously rotate within the casing 92, and hollow agitator blades 178 are heated by high-temperature steam or heat transfer oil supplied to the heat transfer medium inlet 184. As the hollow agitator blades 178 rotate, the final concentrated slurry and the wet powder held within the casing 92 are mixed, and the mixture is sent in the transfer direction T. During this process, the oscillation of the hollow agitator blades 178 prevents the mixture from adhering to adjacent hollow agitator blades 178, while the heated hollow agitator blades 178 heat the mixture by conduction heat transfer, thereby proceeding with the drying process of the mixture. In other words, the mixture is heated and dried. By blowing in room temperature or heated air or the like through gas inlet 174 and discharging moist air or the like through gas outlet 175, the water vapor generated inside casing 92 is discharged to the outside of the apparatus, thereby maintaining an appropriate humidity level inside the apparatus. When the mixture reaches the downstream side of casing 92, it becomes fine particle powder, which is sequentially discharged from outlet 98. The fine particle powder discharged from outlet 98 is stored in storage container 102 through discharge path 100.

[0303] [Effects of this embodiment] According to the above-described method for producing fine particle powder and apparatus 41 for producing fine particle powder, in the fine particle slurry production step, first raw material 12A and second raw material 12B are reacted in a mother liquor in which a high-speed swirling flow is generated in crystallizer 10 to produce a slurry containing fine particles with a particle size of 7 μm or less. Thereafter, in the initial concentration step, dilution and washing step, and final concentration step, washing and a high level of concentration using agitation-type cross-flow filtration device 6 can be efficiently carried out without clogging the filters or flow paths. Furthermore, in the drying step, the final concentrated slurry and wet powder are mixed, and heated hollow stirring blade 178 is brought into contact with the mixture to perform heating by conductive heat transfer, which has excellent thermal efficiency. Therefore, it is possible to produce fine particle powder of 7 μm or less with high production efficiency while keeping energy costs low.

[0304] Furthermore, in the microparticle slurry production process, by using a solution containing a transition metal element as the first raw material 12A and an alkaline solution as the second raw material 12B and reacting the two, it is possible to obtain microparticles whose main component is a transition metal hydroxide, and it is possible to produce a microparticle powder as a precursor of a positive electrode material for a secondary battery with high production efficiency while reducing energy costs.

[0305] Furthermore, in the initial concentration step, the fine particle slurry is filtered using an agitation cross-flow filtration device 6 and concentrated to a solids content of, for example, 35 to 65 wt % to obtain an initially concentrated slurry. This solves problems such as filter clogging due to fine particles, while also efficiently removing impurities from the slurry before washing. It also reduces the amount of washing liquid and washing time consumed in the dilution washing step, thereby reducing energy costs and improving production efficiency.

[0306] In the final concentration step, the washed slurry is concentrated to a solid content of, for example, 50 to 65 wt % by removing part of the mother liquor and washing liquid through an agitation cross-flow filtration device 6. This reduces the amounts of mother liquor and washing liquid to be removed in the drying step, thereby reducing energy costs and improving production efficiency.

[0307] Furthermore, in the crystallizer 10, by circulating the mother liquor with the pump 22, it is easy to generate a high-speed swirling flow with simple equipment, and by uniformly mixing the first raw material 12A and the second raw material 12B in the high-speed swirling flow in an extremely short time, it is possible to precipitate fine particles having a particle size of 7 μm or less, preferably 5 μm or less, and since the particle size of the fine particle powder finally obtained can be made small and the particle size distribution can be narrowed, a high-quality final product can be expected.

[0308] In addition, in the drying device 8, the hollow rotating shafts 176 are fixed with gaps in the axial direction and the hollow agitating blades 178 of each hollow rotating shaft 176 are fixed so as to partially overlap when viewed in the axial direction, so that as the hollow agitating blades 178 rotate, the heated hollow agitating blades 178 mix and transport the final concentrated slurry and the wet powder held in the casing 92, during which the mixture of the final concentrated slurry and the wet powder held in the casing 92 is dried by conductive heat transfer and converted into fine particle powder. Therefore, moisture can be evaporated more efficiently than in hot air drying using convective heat transfer in which hot air is blown, and the excellent effects of reducing energy costs and increasing production efficiency are achieved.

[0309] The present invention is not limited to the above-described embodiment, and additions, deletions, and substitutions with well-known techniques of constituent elements are possible within the scope of the claims.

[0310] As described above, the method and apparatus for producing fine particle powder of the present invention can produce fine particles of 7 μm or less in size in the fine particle slurry production process, and the subsequent washing and concentration can be carried out efficiently, thereby reducing energy costs and increasing production efficiency. Therefore, the present invention is industrially applicable.

[0311] As described above, the apparatus for washing and concentrating fine particle slurry, and the apparatus and method for producing fine particle powder according to the present invention can reduce the amount of washing water used or the amount of washing wastewater, and can stably produce fine particle powder. Therefore, the present invention is industrially applicable.

[0312] As described above, according to the device for concentrating particulate slurry, the device and method for producing particulate powder of the present invention, the density sensor accurately detects the change in viscosity of the slurry even in a high concentration range, and the control device controls the amount of cleaning liquid supplied to the slurry tank by the cleaning liquid supply device, so that even when the average particle size of the particulates is small, it is possible to stably concentrate the particulate slurry even in a high concentration range while suppressing clogging of the filter and associated flow paths. Thus, the present invention is industrially applicable.

[0313] As described above, the apparatus and method for producing fine particle powder according to the present invention can stably produce fine particle powder while improving energy efficiency in the process of drying concentrated slurry. Therefore, the present invention is industrially applicable.

[0314] DESCRIPTION OF SYMBOLS 1...Apparatus for producing fine particle powder 2...Apparatus for producing fine particle slurry 6...Agitation type cross flow filtration apparatus 8...Drying apparatus 10...Crystallizer 12A...First raw material 12B...Second raw material 12C...Mother liquor 14...Discharge hole 16...Conduit 18...Reservoir 20...Conduit 21...Apparatus for producing fine particle powder 22...Pump 24...Conduit 26...Outlet 28...Conduit 30...Slurry tank 31...Apparatus for producing fine particle powder 34...Anchor type agitator blade 36...Motor 38...Cleaning liquid source 40...Conduit 41...Apparatus for producing fine particle powder 42...Three-way valve 44...On-off valve 46...Conduit 48...Pump 50...Cleaning liquid tank 52...Discharge hole 54...Pump 56...Conduit 60...Casing 62...Motor 64...Discharge outlet 66...Density sensor 67...Control device 68...Flow rate adjusting valve 69...Controller 70...Three-way valve (switching device) 71...Conductivity sensor 72...Conduit 74...Three-way valve 76...Conduit 78...Conduit 80...Drainage path 82...Slurry tank 84...Anchor-shaped stirring blade 86...Motor 88...Discharge port 90...Pump 92...Casing T...Transfer direction 94...Conduit 96...Inlet 98...Discharge port 100...Discharge path 102...Storage vessel 110...Outer pipe 112...First inner pipe 114...Second inner pipe 115...Inlet 116...Reaction vessel 116A...Tapered portion 118...Flow rate adjusting valve 120...Driver 122...Pressure gauge 124...Temperature regulator 126...Motor 128...Stirring blade 130...Partition plate DESCRIPTION OF SYMBOLS 132: Extraction valve 134: Pump 140: Rotating shaft 142: Stirring blade 144: Inlet 146: Filter 148: Filtrate chamber 150: Slurry chamber 152: Tapered portion 154: Filtrate discharge valve 156: Conduit 174: Gas inlet 175: Gas outlet 176: Hollow rotating shaft 178: Hollow stirring blade 180: Rotation mechanism 182: Heat medium outlet hole 184: Heat medium introduction hole 190: Notch 194: Inner wall 196: Top plate 198: Outer wall 199: Heat medium flow path 200: Heat medium inlet

Claims

1. A fine particle slurry production process in which a plurality of raw materials are reacted in a mother liquor in which a swirling flow is generated in a reaction treatment vessel to produce a fine particle slurry containing fine particles having a particle size of 7 μm or less; an initial concentration process in which the fine particle slurry is supplied to a filtration equipment comprising a slurry tank and an agitation type cross-flow filtration equipment arranged on a circulation path, and the fine particle slurry is circulated in the filtration equipment while being subjected to initial concentration to obtain an initially concentrated slurry; a dilution and washing process in which a washing liquid is supplied to the initially concentrated slurry in the slurry tank while the slurry is filtered with the agitation type cross-flow filtration equipment to obtain a washed slurry; a final concentration process in which the washed slurry is filtered with the agitation type cross-flow filtration equipment to be finally concentrated to obtain a final concentrated slurry; and a drying process in which the final concentrated slurry is supplied to a drying equipment, and the final concentrated slurry is transported while being agitated with a heated agitator blade, and dried by conductive heat transfer to obtain a fine particle powder. The stirred cross-flow filtration device has a slurry chamber and a filtrate chamber separated by a filter, an agitator arranged along the filter in the slurry chamber, and a drive unit that moves the agitator along the filter to prevent the deposition of fine particles on the surface of the filter, and the method for producing fine particle powder performs filtration by supplying the fine particle slurry, the initial concentrated slurry, or the washing slurry supplied from the slurry tank to the slurry chamber.

2. The method for producing fine particle powder according to claim 1, wherein the fine particle powder is a precursor of a positive electrode material for a secondary battery, and in the fine particle slurry production process, a solution containing a transition metal element, which is a first raw material, is reacted with an alkaline solution, which is a second raw material, to obtain fine particles mainly composed of transition metal hydroxide.

3. A method for producing fine particle powder as described in claim 1 or 2, wherein the initial concentration step comprises filtering the fine particle slurry obtained from the fine particle slurry production step using the stirred cross-flow filtration device and concentrating the slurry until the solid content reaches 35 to 65 wt % to obtain the initially concentrated slurry.

4. A method for producing fine particle powder as described in claim 1 or 2, wherein the final concentration step comprises concentrating the washed slurry using the stirred cross-flow filtration device until the solid content reaches 50 to 65 wt % to obtain the final concentrated slurry.

5. The method for producing fine particle powder described in claim 1 or 2, wherein the fine particle slurry production process comprises first discharging the reaction liquid containing the mother liquor and the raw materials in the reaction processor to the outside, and then returning the discharged reaction liquid to the reaction processor to form a circulation system for the reaction liquid, generating a swirling flow in the reaction processor by inputting the flow of the reaction liquid, and producing the fine particle slurry containing fine particles crystallized by the reaction of the raw materials from the circulation system for the reaction liquid.

6. The drying process is a process in which the final concentrated slurry after the final concentration process is completed is dried by an agitation heat transfer device, the agitation heat transfer device having a casing with an inlet formed at one end and an outlet formed at the other end, a plurality of rotating shafts arranged within the casing such that they are rotatable about their axes and the axes are parallel to each other, agitation blades fixed to each of the rotating shafts at intervals in the axial direction and such that the agitation blades of each rotating shaft overlap partially when viewed in the axial direction, and a heating mechanism for heating the agitation blades, and by rotating the rotating shafts, the heated agitation blades mix the final concentrated slurry supplied from the inlet and the wet powder held in the casing while transferring them to the outlet hole, during which the mixture of the final concentrated slurry and the wet powder is dried by conductive heat transfer and converted into fine particle powder. A method for producing fine particle powder as described in claim 1 or 2.

7. A microparticle slurry production apparatus for producing a microparticle slurry containing microparticles having a particle size of 7 μm or less by reacting a plurality of raw materials in a mother liquor in which a swirling flow is generated in a reaction treatment vessel; a filtration facility having a slurry tank and an agitation type cross-flow filtration device disposed on a circulation path; a washing liquid supplying device for supplying a washing liquid into the slurry tank; a switching device for switching among (a) an initial concentration step for performing initial concentration while circulating the microparticle slurry in the filtration facility to obtain an initially concentrated slurry, (b) a dilution and washing step for obtaining a washed slurry by filtering the initially concentrated slurry in the slurry tank with the agitation type cross-flow filtration device while supplying a washing liquid from the washing liquid supplying device; and (c) a final concentration step for filtering the washed slurry with the agitation type cross-flow filtration device to perform final concentration to obtain a final concentrated slurry; and a drying device for transporting the final concentrated slurry while stirring it with a heated agitator blade, and drying it by conductive heat transfer to obtain a microparticle powder. The agitator type cross-flow filtration device has a slurry chamber and a filtrate chamber separated by a filter, an agitator arranged along the filter in the slurry chamber, and a drive unit that moves the agitator along the filter to prevent the deposition of fine particles on the surface of the filter, and is a fine particle powder manufacturing device that performs filtration by supplying the fine particle slurry, the initial concentrated slurry, or the washing slurry supplied from the slurry tank to the slurry chamber.

8. A cleaning and concentrating apparatus for fine particle slurry, comprising: a slurry tank for storing a fine particle slurry containing fine particles having a particle size of 7 μm or less; a flow path for supplying the stored fine particle slurry to an agitating cross-flow filtration apparatus; a return flow path for returning filtrate discharged from the agitating cross-flow filtration apparatus to a slurry tank; a waste flow path for disposing of the filtrate discharged from the agitating cross-flow filtration apparatus; a filtrate sensor including at least one of a conductivity sensor for measuring the conductivity of the filtrate discharged from the agitating cross-flow filtration apparatus or a density sensor for measuring the density of the filtrate; a flow path switching device for switching the flow path to either the return flow path or the waste flow path for the filtrate discharged from the agitating cross-flow filtration apparatus; and a control unit for controlling the flow path switching device so that the filtrate is caused to flow into the waste flow path when a measurement result of the filtrate sensor is equal to or greater than a threshold value, and is caused to flow into the return flow path when the measurement result of the filtrate sensor is below the threshold value.

9. The apparatus for cleaning and concentrating fine particle slurry according to claim 8, wherein the filtrate sensor is a conductivity meter, and the threshold value is set to a value within a range of 10 mS / cm or less.

10. The apparatus for cleaning and concentrating fine particle slurry according to claim 8 or 9, wherein the filtrate sensor is provided downstream of the agitation type cross-flow filtration device and upstream of the flow path switching device.

11. The apparatus for cleaning and concentrating fine particle slurry according to claim 8 or 9, wherein the fine particles are a precursor of a positive electrode material for a secondary battery.

12. A fine particle powder manufacturing apparatus comprising a conduction heat transfer type dryer for drying the fine particle slurry supplied from the fine particle slurry cleaning and concentrating apparatus described in claim 8, the dryer having an agitation heat transfer device, the agitation heat transfer device comprising a casing having an inlet at one end and an outlet hole at the other end, a plurality of rotating shafts arranged within the casing such that they are rotatable about their axes and the axes are parallel to each other, agitator blades fixed to each of the rotating shafts at intervals in the axial direction and such that the agitator blades of each rotating shaft overlap partially when viewed in the axial direction, and a heating mechanism for heating the agitator blades, and by rotating the rotating shaft, the heated agitator blades heat the fine particle slurry supplied from the inlet and transport it to the outlet hole while drying the fine particle slurry in the process, converting it into fine particle powder.

13. A method for producing fine particle powder, comprising: a dilution washing filtration process in which a washing liquid is added to a slurry containing fine particles having a particle size of 7 μm or less and a mother liquor, and the resulting slurry is filtered through an agitation type cross-flow filtration device to obtain a washing slurry; a concentration process in which the washing slurry is concentrated through the agitation type cross-flow filtration device to obtain a concentrated slurry; a flow path switching process in which the electrical conductivity or density of the filtrate discharged from the agitation type cross-flow filtration device is measured, and the filtrate is discarded when the electrical conductivity or density is equal to or higher than a threshold value, and the filtrate is reused as the washing liquid when the electrical conductivity or density is below the threshold value; and a drying process in which the concentrated slurry is heated and dried to obtain fine particle powder.

14. An apparatus for concentrating a fine particle slurry comprising: a slurry tank for storing a fine particle slurry; a cleaning liquid supplying device for supplying a cleaning liquid to the slurry tank; an agitating type cross-flow filtration device for concentrating the fine particle slurry; a first flow path for supplying the fine particle slurry stored in the slurry tank to the agitating type cross-flow filtration device; a second flow path for returning concentrated slurry discharged from the agitating type cross-flow filtration device to the slurry tank; a density sensor for generating a signal corresponding to the density of the concentrated slurry discharged from the agitating type cross-flow filtration device; and a control device for controlling the amount of the cleaning liquid supplied to the slurry tank by the cleaning liquid supplying device based on the output of the density sensor.

15. A device for concentrating a fine particle slurry as described in claim 14, further comprising a conductivity sensor which generates a signal corresponding to the conductivity of the filtrate discharged from the stirred cross-flow filtration device, and wherein the control device switches from the initial concentration process described below to the dilution and washing process described below, or from the final concentration process described below to the discharge process described below, based on the output of the density sensor, or indicates the timing at which the control device should switch, while switching from the dilution and washing process described below to the final concentration process described below, or indicates the timing at which the control device should switch, based on the output of the density sensor and the output of the conductivity sensor. an initial concentration step of separating a mother liquor in the fine particle slurry by supplying the fine particle slurry stored in the slurry tank to the agitation type cross-flow filtration apparatus through the first flow path and returning the concentrated slurry discharged from the agitation type cross-flow filtration apparatus to the slurry tank through the second flow path to obtain an initial concentrated slurry; a dilution and washing step of diluting and washing the initial concentrated slurry by supplying a washing liquid to the slurry tank using the washing liquid supply apparatus, supplying the initially concentrated slurry stored in the slurry tank to the agitation type cross-flow filtration apparatus through the first flow path and returning the concentrated slurry discharged from the agitation type cross-flow filtration apparatus to the slurry tank through the second flow path to obtain a washed slurry; a final concentration step of separating the washing liquid from the washing slurry to obtain a final concentrated slurry by stopping the supply of the washing liquid to the slurry tank by the washing liquid supply device, supplying the washing slurry stored in the slurry tank to the agitation type cross-flow filtration device through the first flow path, and returning the concentrated slurry discharged from the agitation type cross-flow filtration device to the slurry tank through the second flow path; and a discharge step of discharging the final concentrated slurry from the agitation type cross-flow filtration device.

16. A device for concentrating a fine particle slurry as described in claim 14, further comprising a second density sensor which generates a signal corresponding to the density of the filtrate discharged from the stirred cross-flow filtration device, and the control device switches, or indicates the timing of switching, from the initial concentration process described below to the dilution and washing process described below, from the dilution and washing process described below to the final concentration process described below, or from the final concentration process described below to the discharge process described below, based on the outputs of the density sensor and the second density sensor. an initial concentration step of separating a mother liquor in the fine particle slurry by supplying the fine particle slurry stored in the slurry tank to the agitation type cross-flow filtration apparatus through the first flow path and returning the concentrated slurry discharged from the agitation type cross-flow filtration apparatus to the slurry tank through the second flow path to obtain an initial concentrated slurry; a dilution and washing step of diluting and washing the initial concentrated slurry by supplying a washing liquid to the slurry tank using the washing liquid supply apparatus, supplying the initially concentrated slurry stored in the slurry tank to the agitation type cross-flow filtration apparatus through the first flow path and returning the concentrated slurry discharged from the agitation type cross-flow filtration apparatus to the slurry tank through the second flow path to obtain a washed slurry; a final concentration step of separating the washing liquid from the washing slurry to obtain a final concentrated slurry by stopping the supply of the washing liquid to the slurry tank by the washing liquid supply device, supplying the washing slurry stored in the slurry tank to the agitation type cross-flow filtration device through the first flow path, and returning the concentrated slurry discharged from the agitation type cross-flow filtration device to the slurry tank through the second flow path; and a discharge step of discharging the final concentrated slurry from the agitation type cross-flow filtration device.

17. A microparticle slurry concentrating device as described in claim 15 or 16, wherein the control device performs feedback control in the dilution cleaning process by reducing the amount of cleaning liquid supplied by the cleaning liquid supply device or stopping the supply if the density of the concentrated slurry is lower than the lower limit of the target density range based on the output of the density sensor, and increasing the amount of cleaning liquid supplied by the cleaning liquid supply device or starting the supply if the density of the concentrated slurry is higher than the upper limit of the target density range.

18. The device for concentrating fine particle slurry as described in claim 15, wherein the control device compares the output of the density sensor with a slurry density corresponding to a predetermined value within the range of a solids concentration of the concentrated slurry of 35 to 65 wt % during the initial concentration process, and switches to the dilution washing process when the density sensor reaches a slurry density corresponding to the predetermined value, or indicates the timing for switching to the dilution washing process.

19. The device for concentrating fine particle slurry as described in claim 16, wherein the control device switches to the dilution and washing process when the solids concentration of the concentrated slurry reaches a predetermined value within the range of 35 to 65 wt % based on the outputs of the density sensor and the second density sensor during the initial concentration process, or indicates the timing for switching to the dilution and washing process.

20. A device for concentrating fine particle slurry as described in claim 15, wherein the control device compares the output of the density sensor with a slurry density corresponding to a predetermined value within the range of 50 to 65 wt% solids concentration of the concentrated slurry in the final concentration process, and transitions to the discharge process when the density sensor reaches a slurry density corresponding to the predetermined value.

21. The device for concentrating fine particle slurry as described in claim 16, wherein the control device transitions to the discharge process when the solids concentration of the concentrated slurry reaches a predetermined value within the range of 50 to 65 wt % based on the output of the density sensor and the second density sensor in the final concentration process.

22. An apparatus for concentrating a fine particle slurry as described in any one of claims 14 to 16, characterized in that the density sensor is a vibrating in-line density sensor having a vibrator in contact with the concentrated slurry and a controller that vibrates the vibrator and measures its resonant frequency.

23. The stirring type cross-flow filtration device has a slurry chamber and a filtrate chamber separated by a filter, an agitator arranged along the filter in the slurry chamber, and a drive unit that moves the agitator along the filter to prevent the deposition of fine particles on the surface of the filter, and is an apparatus for concentrating fine particle slurry as described in any one of claims 14 to 16, and concentrates the fine particle slurry passing through the slurry chamber.

24. The device for concentrating a microparticle slurry according to any one of claims 14 to 16, wherein the microparticles in the microparticle slurry are a precursor of a positive electrode material for a secondary battery.

25. A fine particle powder manufacturing apparatus comprising: an apparatus for concentrating fine particle slurry according to any one of claims 14 to 16; and an agitation heat transfer drying apparatus for drying concentrated slurry supplied from the apparatus for concentrating fine particle slurry, the agitation heat transfer drying apparatus comprising: a casing having an inlet formed at one end and an outlet hole formed at the other end; a plurality of rotating shafts arranged within the casing such that they are rotatable about their axes and the axes are parallel to each other; agitator blades fixed to each of the rotating shafts at intervals in the axial direction and such that the agitator blades of each rotating shaft overlap partially when viewed in the axial direction; and a heating mechanism for heating the agitator blades, and by rotating the rotating shafts, the heated agitator blades heat the concentrated slurry supplied from the inlet and transport it to the outlet hole while drying the concentrated slurry in the process, converting it into fine particle powder.

26. A method for producing fine particle powder, comprising: a dilution, washing and filtration process in which a washing liquid is added to a slurry containing fine particles having a particle size of 7 μm or less and a mother liquor, and the resulting slurry is filtered through an agitation type cross-flow filtration device to obtain a washing slurry; a concentration process in which the washing slurry is concentrated through the agitation type cross-flow filtration device to obtain a concentrated slurry; and a drying process in which the concentrated slurry is heated and dried to obtain fine particle powder, wherein in the dilution, washing and filtration process, the density of the washing slurry is measured with a density sensor, and if the density of the washing slurry measured by the density sensor is lower than the lower limit of a target range, the amount of the washing liquid supplied in the dilution, washing and filtration process is reduced or the supply is stopped, and if the density is higher than the upper limit of the target range, the amount of the washing liquid supplied in the dilution, washing and filtration process is increased or the supply is started, thereby performing feedback control.

27. A particulate slurry concentrating device comprising: a slurry tank for storing particulate slurry; a cleaning liquid supplying device for supplying a cleaning liquid to the slurry tank; an agitating cross-flow filtration device for concentrating the particulate slurry; a first flow path for supplying the particulate slurry stored in the slurry tank to the agitating cross-flow filtration device; and a stirring heat transfer drying device for drying the concentrated slurry supplied from the particulate slurry concentrating device, the stirring heat transfer drying device having: a casing having an inlet formed at one end and an outlet formed at the other end; a plurality of rotating shafts arranged within the casing to be rotatable about their axes and with the axes parallel to each other; agitating blades fixed to each of the rotating shafts at intervals in the axial direction and so as to overlap partially when viewed in the direction of the axis; and a heating mechanism for heating the agitating blades, By rotating the rotating shaft, the heated stirring blade heats the concentrated slurry supplied from the inlet and transports it to the outlet hole, during which the concentrated slurry is dried and converted into fine particle powder.

28. An apparatus for producing fine particle powder as described in claim 27, in which, by rotating the rotating shaft, the heated agitator blade mixes the concentrated slurry supplied from the inlet with the wet powder held in the casing, heats it, and transports it to the outlet hole, during which the concentrated slurry is dried and converted into fine particle powder.

29. An apparatus for producing fine particle powder as described in claim 27 or 28, wherein, on each of two adjacent ones of the rotating shafts, the pair of stirring blades is fixed at positions that are rotationally symmetrical by 180° around the rotating shaft, and on each of the rotating shafts, the stirring blades are inclined in opposite directions relative to the rotating shaft and have a twist along an imaginary spiral plane around the rotating shaft, and the two adjacent ones of the rotating shafts rotate in opposite directions to each other.

30. An apparatus for producing fine particle powder according to claim 27 or 28, wherein the fine particle powder is a precursor of a positive electrode material for a secondary battery.

31. A particulate slurry concentrating device comprising: a slurry tank for storing particulate slurry; a cleaning liquid supplying device for supplying a cleaning liquid to the slurry tank; an agitating cross-flow filtration device for concentrating the particulate slurry; a first flow path for supplying the particulate slurry stored in the slurry tank to the agitating cross-flow filtration device; and a stirring heat transfer drying device for drying the concentrated slurry supplied from the particulate slurry concentrating device, the stirring heat transfer drying device having: a casing having an inlet formed at one end and an outlet formed at the other end; a plurality of rotating shafts arranged within the casing to be rotatable about their axes and with the axes parallel to each other; agitating blades fixed to each of the rotating shafts at intervals in the axial direction and so as to overlap partially when viewed in the direction of the axis; and a heating mechanism for heating the agitating blades, By rotating the rotating shaft, the heated stirring blade heats the concentrated slurry supplied from the inlet and transports it to the outlet hole, during which the concentrated slurry is dried and converted into fine particle powder.

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