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

Abstract

To provide an apparatus for cleaning and concentrating fine particle slurry capable of reducing the amount of cleaning water or the amount of cleaning waste water used in an apparatus for producing fine particle powder.SOLUTION: An apparatus for cleaning and concentrating fine particle slurry includes: a slurry tank 30 for storing fine particle slurry; a flow channel 56 for supplying the stored fine particle slurry to a stirring type crossflow filtration device 6; a return flow channel 76 for returning filtrate discharged from the stirring type crossflow filtration device 6 to the slurry tank 30; a waste flow channel 78 for discarding the filtrate discharged from the stirring type crossflow filtration device 6; a filtrate sensor including a conductivity sensor 71 for measuring the conductivity of the filtrate discharged from the stirring type crossflow filtration device 6 or a density sensor for measuring the density of the filtrate; a flow channel switching device 74 for performing flow channel switching as to cause the filtrate discharged from the stirring type crossflow filtration device 6 to flow in the return flow channel 76 or the waste flow channel 78; and a control part 69 for controlling the flow channel switching device 74 for causing the filtrate to flow in the waste flow channel 78 or the return flow channel 76.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus for cleaning and concentrating a fine particle slurry, and an apparatus and method for producing a fine particle powder, and more particularly to an apparatus and method suitable for producing a precursor of a positive electrode active material for a secondary battery, for example. [Background technology]

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

[0003] However, in this type of manufacturing method for 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 cake filtration methods such as commonly used filter presses (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 washing water is passed through a cake layer of non-uniform thickness to wash it, the washing water tends to concentrate and pass through areas where the cake is thin, while it is difficult for the washing water to pass through areas where the cake is thick. This necessitates an increase in the amount of washing 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] In view of this, there have been proposed methods 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 stock 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 concentrated slurry obtained.

[0006] The cross-flow filtration is a method in which the raw slurry is filtered while flowing 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 maintaining a relatively high filtration rate even when the raw slurry contains fine particles. For the cross-flow filtration method, a cartridge-type membrane module such as a hollow fiber membrane, a tubular membrane, or a spiral membrane can be used. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2012-87039 A [Patent Document 2] JP 2012-99470 A Summary of the Invention [Problem to be solved by the invention]

[0008] In the filtration and washing operations in the methods of Patent Documents 1 and 2, in order to reduce the running costs, it is important to reduce the amount of washing water used or the amount of washing wastewater. [Means for solving the problem]

[0009] The present invention has been made in consideration of the above problems, and has an object 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.

[0010] A particulate slurry cleaning and concentrating apparatus according to a first 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 agitating cross-flow filtration apparatus, a return flow path for returning filtrate discharged from the agitating cross-flow filtration apparatus to the 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 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 agitating cross-flow 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 as to cause the filtrate 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 to flow into the return flow path when the measurement result of the filtrate sensor is below the threshold value.

[0011] According to the apparatus for washing and concentrating a particulate slurry of aspect 1, when the electrical conductivity or density of the filtrate discharged from the stirring type cross-flow filtration device is smaller than a threshold value, the filtrate is reused as a washing liquid, so that the amount of washing water or washing wastewater used in the apparatus for washing and concentrating a particulate slurry can be reduced.

[0012] The microparticle slurry cleaning and concentrating apparatus according to aspect 2 of the present invention is characterized in that, in aspect 1, 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.

[0013] According to the microparticle slurry washing and concentrating apparatus of aspect 2, 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 microparticle slurry washing and concentrating apparatus.

[0014] The microparticle slurry cleaning and concentrating apparatus according to aspect 3 of the present invention is characterized in that, in aspect 1 or 2, the filtrate sensor is provided downstream of the stirring type crossflow filtration device and upstream of the flow path switching device.

[0015] According to the apparatus for concentrating a microparticle slurry of the third aspect, the filtrate sensor is provided downstream of the agitation type crossflow filtration device and upstream of the flow path switching device. This makes it 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 or wash wastewater used in the apparatus for washing and concentrating a microparticle slurry.

[0016] The apparatus for washing and concentrating a particulate slurry according to a fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the particulates are a precursor of a positive electrode material for a secondary battery.

[0017] According to the washing and concentrating device for a particulate slurry according to the fourth aspect, 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.

[0018] A fine-particle powder manufacturing apparatus according to a fifth aspect of the present invention includes a conduction heat transfer type dryer for drying the fine-particle slurry supplied from the fine-particle slurry cleaning and concentrating apparatus described in the first aspect, the dryer having an agitation heat transfer device, the agitation heat transfer device including a casing having an inlet at one end and an outlet at the other end, a plurality of rotating shafts arranged within the casing such that they can rotate 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 concentrated slurry supplied from the inlet and transport it to the outlet hole while drying the concentrated slurry in the process, thereby converting it into fine-particle powder.

[0019] According to the fine particle powder manufacturing apparatus of the fifth aspect, a fine particle slurry washing and concentrating apparatus capable of reducing the amount of washing water or washing wastewater used in a fine particle slurry manufacturing apparatus is used in combination with a dryer capable of drying the fine particle slurry by conductive heat transfer with excellent thermal efficiency to stably produce fine particle powder, thereby reducing the environmental impact.

[0020] The method for producing fine particle powder according to aspect 6 of the present invention is characterized by 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 using an agitation type cross-flow filtration device to obtain a washing slurry; a concentration process in which the washing slurry is concentrated using 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.

[0021] According to the method for producing fine particle powder of the sixth aspect, the electrical conductivity or density of the filtrate discharged from the stirred 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 fine particle powder while reducing the amount of washing water or washing wastewater used in the fine particle powder production device. Effect of the Invention

[0022] As described above, according to the microparticle slurry washing and concentrating apparatus, and the microparticle powder manufacturing apparatus and manufacturing method of the present invention, the electrical conductivity or density of the filtrate discharged from the stirred cross-flow filtration apparatus 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 achieving the excellent effect of reducing the amount of washing water or washing wastewater used in the microparticle slurry washing and concentrating apparatus while stably manufacturing microparticle powder. [Brief description of the drawings]

[0023] [Figure 1] 1 is a block diagram showing a manufacturing apparatus for fine particle powder according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a block diagram showing a particulate slurry production apparatus according to the embodiment. [Diagram 3] FIG. 2 is a cross-sectional view showing the stirring type cross-flow filtration device in the embodiment. [Figure 4] FIG. 2 is a side cross-sectional view showing the drying device in the embodiment. [Diagram 5] FIG. 2 is a plan view showing the drying device in the embodiment with the top plate removed. [Figure 6] FIG. 2 is a front cross-sectional view showing the drying device in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, a manufacturing apparatus 1 for fine particle powder according to one embodiment of the present invention will be described in detail. The manufacturing apparatus 1 for fine particle powder according to this embodiment includes a fine particle slurry manufacturing apparatus 2 for manufacturing a fine particle slurry containing fine particles having a particle diameter 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 crystallizer 10 (reaction processor), a slurry tank 30 for washing the fine particle slurry obtained in the fine particle slurry manufacturing apparatus 2 by adding a washing liquid according to the processing stage while stirring the fine particle slurry, an agitation type cross-flow filtration apparatus 6 for concentrating the fine particle slurry or the washed slurry sent from the slurry tank 30 by removing a part of the mother liquor and the washing liquid, and a conductive heat transfer type drying apparatus (dryer) 8 for transferring the final concentrated slurry after the final concentration is completed in the agitation type cross-flow filtration apparatus 6 while mixing it with the wet powder previously held in a casing 92 with a heated agitation blade and drying it by conductive heat transfer. The final concentrated slurry may be simply called a concentrated slurry.

[0025] [Crystallizer] As shown in FIG. 2, the crystallizer 10 has a long and thin cylindrical reaction vessel 116, the upstream side of which is cylindrical, and the downstream side of which is a coaxial and conical tapered section 116A that narrows toward the downstream side. Inside the reaction vessel 116, a cylindrical outer tube 110 is coaxially arranged so as to reach the tapered section 116A from the upstream end, and the upstream end of the outer tube 110 opens to the upstream end of the reaction vessel 116. A first inner tube 112 and a second inner tube 114 are inserted into the outer tube 110, the first inner tube 112 protruding from the downstream end of the outer tube 110, and the second inner tube 114 protruding from the downstream end of the outer tube 110 longer 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 gaps between the outer tube 110 and each of the first inner tube 112 and the second inner tube 114.

[0026] An inlet 115 is formed on the outer periphery of the upstream end of the reaction vessel 116, and by blowing the reaction liquid from this inlet 115 at high speed, a swirling flow is generated in the reaction vessel 116, and the rotation speed increases as the inner diameter narrows at the tapered portion 116A, and the vortex is discharged from the discharge hole 14. The outer tube 110, the first inner tube 112, and the second inner tube 114 are located at the center of the swirling flow, and the first raw material 12A from the first inner tube 112 and the second raw material 12B from the second inner tube 114 are mixed while being vigorously stirred in the central region R of the swirling flow in the tapered portion 116A. In this mixing process, the first raw material 12A and the second raw material 12B are mixed and reacted at high speed, and the reaction product is generated as fine particles with a very small particle size, and flows out from the discharge hole 14 together with the reaction liquid.

[0027] A conduit 16 is connected to the discharge hole 14, and the reaction liquid containing the fine particles is supplied to the 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) according to the indicated value of a pressure gauge 122 that measures the inflow pressure from the inlet 115. When the value 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 value 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 allows the crystallization of the fine particles in the reaction vessel 116 to be performed appropriately.

[0028] 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 a 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.

[0029] In this embodiment, the types of the first raw material 12A and the second raw material 12B are not limited, but may be any that reacts with the first raw material 12A and the second raw material 12B to precipitate a compound with low solubility. As an example, when producing a secondary battery positive electrode material precursor, a solution containing a transition metal element such as nickel salt is used as the first raw material 12A, and an alkaline solution is used as the second raw material 12B, and the first raw material 12A and the second raw material 12B are reacted in the crystallizer 10 to obtain fine particles mainly composed of transition metal hydroxide. More specifically, the first raw material 12A may be an aqueous solution of nickel sulfate, cobalt sulfate, or manganese sulfate, and the second raw material 12B may be an aqueous solution of sodium hydroxide or ammonia water.

[0030] The particle size of the fine particles in the fine particle 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 fine particles in the fine particle slurry is measured by laser diffraction and scattering methods. In addition, the particle size in this specification means the average particle size at 50% of the integrated value in the particle size distribution measured by the above-mentioned measurement method. According to the crystallizer 10 using a swirling flow, the growth of the crystal grains can be suppressed after the crystal grains are generated, and it is easy to produce a slurry containing fine particles of such a fine grain size. If the particle size of the fine particles is 7 μm or less, for example, when producing a secondary battery positive electrode material precursor, it is possible to improve the performance by improving the homogeneity of the secondary battery positive electrode material. In other applications, the particle size of the fine particles is as small as possible and is uniform, so that the performance of the final product can be improved.

[0031] The reservoir 18 stores the fine particle slurry containing fine particles generated in the crystallizer 10. A wave-breaking partition plate 130 is disposed in a portion of the reservoir 18 near the liquid level, and a fine particle slurry outlet 26 is formed on 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 take-out 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 performed in a state where the slurry is highly concentrated.

[0032] 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. This concentration range allows stable production of particulates, and provides a good load balance in the subsequent slurry tank 30, agitation cross-flow filtration device 6, and drying device 8, making it possible to increase the total processing efficiency and energy efficiency without overdoing each process and impairing stability.

[0033] [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 adding a cleaning liquid to an initially concentrated slurry obtained by initially concentrating the fine particle slurry to wash it, and sending it to the agitation type cross-flow filtration device 6 as a washed slurry.

[0034] The slurry tank 30 is cylindrical with a bottom, and the inner bottom surface is formed in a hemispherical shape. A semicircular anchor-shaped impeller 34 is arranged along the inner bottom surface of the slurry tank 30 with a small constant gap between it and the inner bottom surface, 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 to a pump 48 and a cleaning liquid tank 50 via a conduit 46.

[0035] The amount of the gap between the outer periphery of the anchor-shaped agitating blade 34 and the inner bottom surface of the slurry tank 30 is not limited, but in order to prevent fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 30, it is preferable that the gap is, for example, about 0.5 to 3.0 cm. In addition, the length of the semicircular outer periphery of the anchor-shaped agitating blade 34 is preferably long enough to face the entire inner bottom surface of the anchor-shaped agitating blade 34. The rotational peripheral speed of the motor 36 at the outer periphery of the anchor-shaped agitating blade 34 is not limited, but is preferably about 0.1 to 3.0 m / sec. Within this range, it is highly effective in preventing fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 30.

[0036] 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 extracted 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 normal paddle-type agitator, only the slurry liquid near the agitator can be circulated, making it impossible to keep the entire inside of the slurry tank 30 uniform, and fine particles settle in the slurry tank 30, forming a hard, compressed solid layer at the bottom of the slurry tank 30, making it impossible to extract the slurry. The anchor-type agitator 34 can solve this problem.

[0037] Furthermore, although each process in this apparatus can be operated batchwise, if the downstream drying device 8 is operated continuously, a buffer means for holding the slurry in each process for a relatively long time is required. Therefore, by applying the slurry tank 30 equipped with the anchor-shaped stirring blades 34 as described above, it is possible to uniformly circulate the entire slurry in the slurry tank 30, and it is possible to prevent accumulation and adhesion of fine particles.

[0038] In particular, when producing a cathode material precursor for secondary batteries, the fine particles are metal compounds with a large specific gravity, and therefore if the slurry tank 30 is not stirred uniformly, the solid matter will quickly settle to the bottom of the tank, become hard and compacted, and become impossible to extract. Furthermore, since 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 maintain a dispersed state by causing uniform convection throughout the entire slurry tank 30.

[0039] The cleaning solution tank 50 is a container for storing a fraction of the filtrate discharged from the agitation type cross-flow filtration device 6 that contains relatively few impurities. The conductivity of the filtrate can be used as an index for grasping the tendency of impurities to be contained. When the conductivity is higher than a preset threshold, the filtrate contains a large amount of electrolyte as an impurity, and the electrolyte adversely affects, for example, a positive electrode material precursor for a secondary battery. For example, when the detected conductivity is higher than a preset threshold, the three-way valve 42 and the on-off valve 44 are operated to select either the clean cleaning solution from the cleaning solution source 38 or the clean cleaning solution recovered from the agitation type cross-flow filtration device 6 in the cleaning solution tank 50 and supply it to the slurry tank 30.

[0040] A discharge hole 52 is formed at the bottom end of the slurry tank 30, and slurries in various states (fine particle slurry, initial concentrated slurry, washing slurry, or final concentrated slurry) discharged from the slurry tank 30 are sent via a pump 54 to a conduit 56, through which the slurries in various states can be transported to the stirred cross-flow filtration device 6.

[0041] [Agitation type cross-flow filtration device, conductivity sensor, control unit, flow path switching device] As shown in FIG. 3, the agitation cross-flow filtration device 6 has a cylindrical casing 60 arranged almost horizontally. A rotating shaft 140 is arranged along the center line of the casing 60 and rotated by a motor 62. A plurality of disk-shaped agitation blades 142 are fixed to the rotating shaft 140 at regular intervals in the axial direction. The outer diameter of the agitation blades 142 is smaller than the inner diameter of the casing 60. A ring-shaped filter 146 of a certain thickness is fixed coaxially with the casing 60 on the inner peripheral surface of the casing 60 between adjacent agitation blades 142, and a disk-shaped filtrate chamber 148 is formed inside each filter 146. The number of agitation blades 142 and filters 146 is determined by the processing capacity required for the agitation cross-flow filtration device 6. A gap of a certain thickness is formed between the inner surface of the casing 60, the agitation blade 142, and the filter 146, and this gap serves as a slurry chamber 150.

[0042] An inlet 144 is formed at the upstream end of the casing 60, and slurry in various states supplied from the inlet 144 is transported downstream while meandering through a slurry chamber 150 while being squeezed between the rotating agitator blade 142 and a fixed filter 146. The slurry chamber 150 is pressurized by the liquid sending pressure of the pump 54, and during this transport process, the slurry is pressed against the filter 146 while being agitated by the rotation of the agitator blade 142, and the mother liquor and washing liquid in the slurry pass through the filter 146 and enter the filtrate chamber 148. The material of the filter 146 may be any material that does not allow fine particles in the slurry to pass through but allows the filtrate to pass through, and has sufficient mechanical strength.

[0043] Filtrate discharge valves 154 are attached to the casing 60, each communicating with the filtrate chamber 148, and the outlets of the filtrate discharge valves 154 are connected together to a conduit 156. The filtrate that has entered the filtrate chamber 148 flows out through the filtrate discharge valves 154 to the conduit 156. As shown in Fig. 1, this conduit 156 is connected to a first port of a three-way valve 74, which is a flow path switching device, and a second port of the three-way valve 74 is connected to a 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.

[0044] As shown in FIG. 1, a conductivity sensor 71 is installed in the conduit 156 which is 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, detects the progress of the dilution cleaning process from the output result and the conductivity of the filtrate stored in advance, and determines the completion timing of the dilution cleaning process. Specifically, when the output result falls below a threshold value set in the control unit 69, it is determined that the dilution cleaning process is completed. Note that the sensor is not limited to the conductivity sensor 71, and other sensors may be used to determine the completion timing of the dilution cleaning process. For example, a second density sensor (not shown) may be installed in the conduit 156 which is 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 completion timing of the dilution cleaning process.

[0045] The three-way valve 74 and the conductivity sensor 71 are connected by wire or wirelessly so as to be able to communicate electrical signals with the control unit 69. The control unit 69 judges whether the measurement result of the conductivity sensor 71 is equal to or greater than a threshold value, and when 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, and when the measurement result is below the threshold value (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 when the conductivity of the filtrate is equal to or greater than the threshold value, a valve (not shown) in the three-way valve 74 is set so that the filtrate discharged from the stirring cross-flow 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 flows into the drainage path 80. When the conductivity of the filtrate falls below the threshold, a valve (not shown) in the three-way valve 74 is switched so that the filtrate discharged from the stirring cross-flow filtration device 6 through the conduit 156 is discharged from the first port of the three-way valve 74 to the third port of the three-way valve 74 and flows into the cleaning liquid tank 50. Although not shown, the three-way valve 74 is provided with a driving device for switching the valve, and the valve in the three-way valve 74 is switched by a signal input from the control unit 69. The control unit 69 and the pump 48 may be connected by wire or wirelessly so that they can communicate with each other by electric signals. A motor may be used as an example of the driving device. Here, the above-mentioned threshold value of the conductivity is preferably set to a value in the range of 10 [mS / cm] or less, more preferably set to a value in the range of 5 [mS / cm] or less, and even more preferably set to a value in the range of 0.2 to 5 [mS / cm]. Here, the control unit 69 is a computer equipped with a processor such as a CPU (Central Processing Unit) and a memory. The processor executes arithmetic processing for executing the functions of the control unit 69. The memory stores a rewritable program in which the functions to be executed by the CPU are written.The control unit 69 may realize these functions using hardware (including circuitry) such as a large-scale integration (LSI), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a graphics processing unit (GPU), etc. Alternatively, the functions of the control unit 69 may be realized by a combination of software and hardware.

[0046] During the initial concentration by the agitation type cross-flow filtration device 6 and for a while after the start of cleaning, the filtrate that enters the filtrate chamber 148 contains a lot of impurities, but as the filtration time passes, the filtrate contains less impurities, so the conductivity detected by the conductivity sensor 71 decreases. Therefore, when the conductivity reaches a predetermined threshold value, the control unit 69 switches the three-way valve 74 so that the filtrate that was flowing to the drainage path 80 is stored in the cleaning liquid tank 50. The relatively clean filtrate stored in the cleaning liquid tank 50 is used as a cleaning liquid by operating the pump 48 in the next dilution cleaning process through the conduit 46, the three-way valve 42, and the on-off valve 44 to be supplied to the slurry tank 30 as a cleaning liquid in the initial stage of the dilution cleaning process. This reduces the amount of cleaning liquid used in the cleaning liquid source 38, which helps reduce the cost of producing fine particle powder. Furthermore, the amount of filtrate and cleaning waste liquid that is discarded outside the fine particle powder production device 1 can be reduced, reducing the burden on the environment.

[0047] The downstream part of the casing 60 is a conical tapered part 152 narrowing downstream, and a discharge port 64 is formed at the tip of the tapered part 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, and filtered and concentrated in the agitation type cross-flow filtration device 6. The concentrated slurry, which has become highly viscous, is discharged from the discharge port 64.

[0048] The solid content concentration of the concentrated slurry discharged from the stirring cross-flow filtration device 6 is different from one another in the initial concentration step, the dilution washing step, and the final concentration step, and is not necessarily limited. As a preferred example, when producing a secondary battery positive electrode material precursor, the solid content concentration of the initial 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 solid content concentration of the washed slurry at the completion of the dilution 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 solid content 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.

[0049] In each process, when the concentration is within the above-mentioned range, the transportation of the concentrated slurry within the casing 60 of the agitation type crossflow filtration device 6 does not become difficult, and it is possible to effectively reduce the amount of impurities in the final concentrated slurry while limiting the consumption of the washing liquid. Therefore, the load balance of the agitation type crossflow filtration device 6 and the drying device 8 is good, and it is possible to improve the total processing efficiency and energy efficiency without overloading each process.

[0050] As shown in FIG. 1, the outlet 64 of the casing 60 of the agitation type cross-flow 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 rate control valve 68. The three-way valve 70 is switched by a control panel (not shown) or manually by receiving an instruction from the control panel. The three-way valve 70 may 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, the slurry in various states discharged from the outlet 64 of the agitation type cross-flow 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.

[0051] The slurry density of the concentrated slurry discharged from the discharge port 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 the control unit 69, the output signal of the density sensor 66 is 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 dehydrated and reaches a predetermined density, and to grasp at least one of the timings of the completion of the initial concentration step and the timing of the completion of the final concentration step, and to use this information to control the transition to the next step.

[0052] In addition, when determining the timing of completion of the dilution cleaning process, it is preferable to satisfy either one 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 criterion).

[0053] The second purpose of the slurry density measurement by 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 the washing liquid from the washing liquid source 38 to the slurry tank 30 is increased (or resumed after a temporary stop) when the upper limit is reached, and the supply of the washing liquid from the washing liquid source 38 is reduced (or temporarily stopped) when the lower limit is reached, thereby maintaining the solid concentration of the concentrated slurry discharged from the agitation type cross-flow filtration device 6 in the dilution washing step within a certain range and adjusting the degree of washing until the conductivity of the filtrate discharged from the agitation type cross-flow filtration device 6 is sufficiently reduced. Here, the part from the slurry tank 30 to the agitation type cross-flow filtration device 6 in the fine particle powder production device 1 may be called a fine particle slurry washing and concentrating device.

[0054] 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 by a control panel (not shown) or manually according to the value of the density sensor 66. When 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. When 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 solid 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 the control unit 69.

[0055] The slurry tank 82 performs a buffer function for adjusting the supply amount of the final concentrated slurry to the drying device 8. The slurry tank 82 is cylindrical with a bottom, and the inner bottom surface is formed in a hemispherical shape. A semicircular anchor-shaped stirring blade 84 is arranged along the inner bottom surface of the slurry tank 82 with a small constant gap between it and the inner bottom surface, 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 to a conduit 94 via a pump 90 and sent to the drying device 8.

[0056] The amount of the gap between the outer periphery of the anchor-shaped stirring blade 84 and the inner bottom surface of the slurry tank 82 is not limited, but in order to prevent the accumulation and adhesion of fine particles to the inner bottom surface of the slurry tank 82, similar to the anchor-shaped stirring blade 34 described above, it is preferable that the length of the semicircular outer periphery of the anchor-shaped stirring blade 84 is a length that can face the entire inner bottom surface of the slurry tank 82. Furthermore, the rotational peripheral speed of the anchor-shaped stirring blade 84 at the outer periphery by the motor 86 is not limited, but is preferably about 0.1 to 3.0 m / sec. Within such a range, the effect of preventing the accumulation and adhesion of fine particles to the inner bottom surface of the slurry tank 82 is obtained. In particular, when a positive electrode material precursor for a secondary battery is produced, this is an important effect because the fine particles are metal compounds and have a large specific gravity.

[0057] [Drying equipment] 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 gutter-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 passage 199, and the outer wall 198 is formed with a heat medium inlet 200 and a heat medium outlet (not shown) communicating with the heat medium passage 199. The inside of the casing 92 can be heated uniformly by supplying high-temperature steam or heat medium oil from the heat medium inlet 200 to the heat medium outlet.

[0058] An inlet (flow inlet) 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 or the like is blown in from the gas inlet 174, and the moist air or the like is discharged from the gas outlet 175 together with the water vapor generated in the casing 92 with the evaporation of the mother liquor and the cleaning liquid, thereby discharging the water vapor generated in the casing 92 to the outside of the machine, thereby making it 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 in the casing 92 is discharged.

[0059] Two hollow rotating shafts 176 are arranged symmetrically along the longitudinal direction within the casing 92, and both ends or one end are supported by bearings so as to be rotatable about the axes of the two hollow rotating shafts 176. 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 in the axial direction of the hollow agitating blade 178 of the other hollow rotating shaft 176. The two hollow rotating shafts 176 may be parallel to each other.

[0060] As shown in Fig. 6, each hollow agitating blade 178 is in the shape of a sector with a central angle of less than 180°, and a pair 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 certain width is formed between the pair of hollow agitating blades 178 so that the mixture of the final concentrated slurry and the wet powder can pass in the axial direction. The inside 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 inside of the hollow agitating blade 178 and heats the hollow agitating blade 178. This is sometimes called the heating mechanism of the hollow agitating blade 178.

[0061] The wet powder is a dried product of the final concentrated slurry that is previously stored in the casing 92, and is not completely dry but 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 the transportation within the casing 92 by the hollow agitating blade 178 can be facilitated.

[0062] 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 the locus of the hollow agitating blade 178 swings in the axial direction within a certain angle range every time the hollow rotating shaft 176 rotates 180°, as shown by the solid and dotted lines in the figures. This swinging prevents the final concentrated slurry and the wet powder from adhering to the hollow agitating blades 178 between the axially adjacent hollow agitating blades 178, while mixing the final concentrated slurry and the wet powder. In addition, the hollow agitating blade 178 also has a twist along a virtual spiral surface around the hollow rotating shaft 176, and also functions 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 rotating shaft 176 rotates.

[0063] 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) to the heat medium outlet hole 182 from the heat medium inlet hole 184, and the heat medium is distributed over the entire length of the hollow rotating shaft 176, and the heat medium also enters the inside of the hollow agitator blade 178, so that the entire hollow rotating shaft 176 and the hollow agitator blade 178 are heated to a temperature higher than the boiling point of the mother liquor and washing liquid contained in the final concentrated slurry and the wet powder. Therefore, every time the mixture of the final concentrated slurry and the wet powder touches the hollow rotating shaft 176 and the hollow agitator blade 178, it is heated by conduction heat transfer, and the mother liquor and washing liquid contained in the mixture evaporate, and eventually become fine powder. A rotating mechanism 180 is provided at one end of the hollow rotating shaft 176, and the hollow rotating shaft 176 is 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 the upstream to the downstream of the casing 92 while being heated by the hollow stirring blade 178 through conductive heat transfer, which has excellent thermal efficiency. Heating by conductive heat transfer is sometimes called indirect heating. In addition, 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 inside the heat medium inlet hole 184.

[0064] 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. 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 it is sufficient to have a plurality of hollow rotating shafts 176. In the case of a plurality of hollow rotating shafts 176, they may be parallel to each other.

[0065] The method for producing fine-particle powder using the fine-particle powder production apparatus 1 described above is carried out as follows. [Microparticle slurry manufacturing 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 from the inlet 115, generating a swirling flow in the reaction vessel 116. The first raw material 12A is supplied from the first inner tube 112, and the second raw material 12B is supplied from the second inner tube 114. The two are vigorously mixed in the central region R in the tapered portion 116A, and fine particles are generated by the reaction of 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 a fine particle slurry is generated in the reservoir 18 as the mother liquor circulates repeatedly. 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.

[0066] [Initial concentration process] When the solids concentration of the particulate slurry in the reservoir 18 reaches an appropriate range, an initial concentration step is started 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 cross-flow 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.

[0067] The discharge valve 132 is opened, and the fine particle slurry in the reservoir 18 is discharged from the discharge port 26 through the conduit 28, and transferred to the slurry tank 30 by the pump 134. In the slurry tank 30, the anchor-shaped agitator blade 34 is rotated by the motor 36 to prevent the fine particles in the fine particle slurry from settling, 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.

[0068] In the slurry chamber 150, the interior is pressurized by the discharge pressure of the pump 54, and the stirring blade 142 is continuously rotated by the motor 62. The fine particle slurry is pressed against the side of the filter 146 while being stirred by the stirring blade 142, and the mother liquor in the fine particle slurry is filtered by the filter 146 and flows into the filtrate chamber 148. As the fine particle slurry advances downstream in the casing 60, the mother liquor in the fine particle slurry decreases, and the 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.

[0069] 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 waste flow path 78 by the three-way valve 74, 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.

[0070] [Dilution and washing process] When an initially concentrated slurry of a predetermined concentration is obtained in the slurry tank 30, the initial concentration step is terminated, and a dilution washing step is started in which the initially concentrated slurry is diluted with a washing liquid for washing. 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. 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.

[0071] Also, while controlling the density by the density sensor 66 and the level of the slurry tank 30, the on-off valve 44 is opened, the conduit 46 is connected to the slurry tank 30 by the three-way valve 42, and the pump 48 is operated to first supply the cleaning liquid from the cleaning liquid tank 50 to the slurry tank 30. The cleaning liquid tank 50 stores a relatively clean cleaning liquid obtained in the previous production of fine powder. This is because, immediately after the start of the dilution and washing process (first stage), the initial concentrated slurry contains a large amount of impurities, so that even a cleaning liquid with a low degree of cleanliness can provide a sufficient cleaning effect. As a result, the initial concentrated slurry continues to be washed in the slurry tank 30 and 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. Since the filtration continues in this manner, the dilution and washing process is sometimes called the dilution and washing filtration process.

[0072] As the cleaning liquid from the cleaning liquid tank 50 is continuously supplied to the slurry tank 30 and the cleaning of the initial concentrated slurry proceeds, the impurities (electrolyte components, non-electrolyte components, ultrafine particles) in the filtrate discharged from the stirring cross-flow 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 (a 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 is sufficiently reduced), 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, and then 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. The three-way valve 42 may be controlled by the control unit 69.

[0073] As the cleaning and filtration of the initially concentrated slurry progresses using clean cleaning liquid from the cleaning liquid source 38, impurities in the filtrate discharged from the agitation type cross-flow 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 (a 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 the cleaning liquid. The three-way valve 42 and the on-off valve 44 may be controlled by the control unit 69.

[0074] [Final concentration process] After the supply of the washing liquid is stopped and the dilution washing process is completed, a final concentration process is carried out to finally concentrate the washing slurry. In the final concentration process, the washing slurry is supplied to the agitation type cross-flow filtration device 6 and separated into a concentrated washing slurry and a filtrate. The concentrated washing slurry is returned to the slurry tank 30. In this way, the washing 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 process may also be called the concentration process.

[0075] [Flow path switching process] 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 by automatic control by the control unit 69, and the filtrate from the conduit 156 is stored in the cleaning liquid tank 50 through the return flow path 76. When the filtrate becomes sufficiently clean, storage in the cleaning liquid tank 50 may start from the subsequent stage of the dilution cleaning process, as well as from the final concentration 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 index of the cleanliness of the filtrate. In this case, the density is set in advance as a threshold value, and when the measured density falls below the threshold value, the three-way valve 74 is switched to store the filtrate 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 called a filtrate sensor. Therefore, a filtrate sensor including at least one of the conductivity sensor 71 or the 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 the filtrate 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 stirring crossflow filtration device 6 and upstream of the three-way valve 74, which is a flow path switching device.

[0076] When the density of the final concentrated slurry discharged from the outlet 64 of the stirring cross-flow filtration device 6 reaches the density target 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), and the final concentrated slurry is sent to the slurry tank 82. The flow rate control valve 68 and the three-way valve 70 may be controlled by a control unit 69. The final concentrated slurry stored in the slurry tank 82 is stirred by the anchor-shaped stirring blade 84 to prevent precipitation, while the drying step is started. 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 be supplied to the slurry tank 82 without being circulated.

[0077] [Drying process] The drying process is a process of drying the final concentrated slurry 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 is introduced into the casing 92 from the inlet 96 through the conduit 94. In the casing 92, two hollow rotating shafts 176 are continuously rotating, 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 final concentrated slurry and the wet powder held in the casing 92 are mixed, and the mixture is sent in the transfer direction T. In the process, the mixture is heated by conduction heat transfer at the heated hollow agitating blades 178 while preventing the mixture from adhering to the hollow agitating blades 178 between the adjacent hollow agitating blades 178 due to the oscillation of the hollow agitating blades 178, and the drying process of the mixture progresses. That is, the mixture is heated and dried. Room temperature or heated air or the like is blown in from gas inlet 174 and moist air or the like is discharged from gas outlet 175, thereby discharging water vapor generated within casing 92 to the outside of the apparatus, thereby maintaining an appropriate humidity level within the apparatus. When the mixture reaches the downstream side of casing 92, it becomes fine particle powder, which is successively discharged from outlet 98. The fine particle powder discharged from outlet 98 is stored in storage container 102 through discharge path 100.

[0078] [Effects of this embodiment] According to the above-mentioned device for cleaning and concentrating fine particle slurry, method for producing fine particle powder, and device 1 for producing fine particle powder, an indicator such as the conductivity or density of the filtrate discharged from the stirring cross-flow filtration device 6 through the conduit 156 is constantly monitored by the filtrate sensor, and when the conductivity or density of the filtrate is equal to or higher than a threshold value, the filtrate is discarded. On the other hand, when the conductivity or density of the filtrate falls below the threshold value, the filtrate is determined to be clean enough to be used for primary cleaning in the slurry tank 30, and the control unit 69 switches the three-way valve 74, which is a flow path switching device, and the filtrate from the conduit 156 is stored in the cleaning liquid tank 50 through the return flow path 76. Therefore, the amount of cleaning liquid used in the cleaning liquid source 38 can be reduced, which helps to reduce the cost of producing fine particle powder. Furthermore, the amount of filtrate and cleaning waste liquid discarded outside the device 1 for producing fine particle powder can be reduced, which reduces the burden on the environment. 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, in the initial concentration process, dilution washing process, and final concentration process, washing and advanced concentration using the stirring cross-flow filtration device 6 can be efficiently performed without causing blockage of the filter or flow path. Furthermore, in the drying process, the final concentrated slurry is mixed with wet powder, and the mixture is brought into contact with the heated hollow stirring blade 178 to heat the mixture 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.

[0079] In addition, in the microparticle slurry production process, a solution containing a transition metal element is used as the first raw material 12A, and an alkaline solution is used as the second raw material 12B, and the two are reacted to obtain microparticles mainly composed of transition metal hydroxide, and the microparticle powder as a precursor of the positive electrode material for secondary batteries can be produced with high production efficiency while reducing energy costs.

[0080] In addition, in the initial concentration step, the fine particle slurry is filtered using an agitation cross-flow filtration device 6 and concentrated to a solid 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 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.

[0081] In addition, in the final concentration step, the washed slurry is concentrated to, for example, a solid content of 50 to 65 wt % by removing a portion of the mother liquor and washing liquid using an agitation cross-flow filtration device 6. This makes it possible to reduce the amounts of mother liquor and washing liquid to be removed in the drying step, thereby reducing energy costs and improving production efficiency.

[0082] In addition, 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. 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.

[0083] In the drying device 8, the hollow agitating blades 178 of the hollow rotating shafts 176 are fixed to each other at intervals in the axial direction and so as to overlap partially 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 powder. Therefore, moisture can be evaporated more efficiently than in hot air drying by convection heat transfer in which hot air is blown, and the excellent effect of reducing energy costs and increasing production efficiency is achieved.

[0084] It should be noted that the present invention is not limited to the above-described embodiment, and additions, deletions, and replacements with well-known techniques of constituent elements are possible within the scope of the claims.

[0085] 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 stirring 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.

[0086] In the above embodiment, the conduit 46 is connected to the three-way valve 42, but it may be directly connected 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. [Industrial Applicability]

[0087] As described above, the washing and concentrating apparatus for fine particle slurry, the manufacturing apparatus for fine particle powder, and the manufacturing method thereof according to the present invention can reduce the amount of washing water or washing wastewater used, and can stably manufacture fine particle powder. Therefore, the present invention is industrially applicable. [Explanation of symbols]

[0088] 1. Fine particle powder manufacturing equipment 2. Fine particle slurry manufacturing equipment 6 Agitated cross-flow filtration device 8 Drying device 10 Crystallizer 12A First raw material 12B Second raw material 12C Mother liquor 14 Discharge hole 16 Conduit 18 Reservoir 20 Conduit 22 Pump 24 Conduit 26 Outlet 28 Conduit 30 Slurry tank 34 Anchor-shaped mixing blade 36 Motor 38 Cleaning fluid source 40 Conduit 42 Three-way valve 44 On-off valve 46 Conduit 48 Pump 50 Cleaning solution tank 52 Drain hole 54 Pump 56 Conduit 60 Casing 62 Motor 64 Exhaust port 66 Density sensor 68 Flow control valve 69 Control unit 70 Three-way valve 71 Conductivity sensor 72 Conduit 74 Three-way valve 76 Conduit 78 Conduit 80 Drain 82 Slurry tank 84 Anchor-shaped mixing blade 86 Motor 88 Exhaust port 90 Pump 92 Casing 94 Conduit 96 Inlet 98 Discharge port 100 Export path 102 Storage container 110 Outer tube 112 1st inner pipe 114 2nd inner pipe 115 inlet 116 reaction vessel 116A Tapered section 118 Flow control valve 120 Drive unit 122 Pressure gauge 124 Temperature Controller 126 Motor 128 Agitator blade 130 Partition plate 132 Extraction valve 134 Pump 140 Rotating shaft 142 Mixing blade 144 Inlet 146 Filter 148 Filtrate chamber 150 Slurry chamber 152 Tapered section 154 Filtrate discharge valve 156 Conduit 174 Gas inlet 176 hollow rotating shaft 178 hollow stirring blade 180 Rotation mechanism 182 Heat transfer medium discharge hole 184 Heat transfer medium inlet hole 190 Notch 194 Inner wall 196 Top plate 198 Outer wall 199 Heat transfer medium flow path 200 Heat medium inlet T Transfer direction

Claims

1. a slurry tank for storing a particulate slurry containing particulates having a particle size of 7 μm or less; a flow path for supplying the stored fine particle slurry to an agitation type cross-flow filtration device; a return flow path for returning the filtrate discharged from the agitation cross-flow filtration device to a slurry tank; a waste flow path for disposing of the filtrate discharged from the agitation type cross-flow filtration device; 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 device and a density sensor for measuring the density of the filtrate; a flow path switching device that switches the flow path of the filtrate discharged from the agitation type cross-flow filtration device to either the return flow path or the waste flow path; a control unit that controls the flow path switching device so as to cause the filtrate 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 to cause the filtrate to flow into the return flow path when the measurement result of the filtrate sensor is below the threshold value; A washing and concentrating apparatus for fine particle slurry comprising:

2. 2. The apparatus for cleaning and concentrating a fine particle slurry according to claim 1, wherein the filtrate sensor is a conductivity meter, and the threshold value is set to a value in the range of 10 mS / cm or less.

3. 3. The apparatus for cleaning and concentrating a particulate slurry according to claim 1, wherein the filtrate sensor is provided downstream of the agitation type cross-flow filtration device and upstream of the flow path switching device.

4. 3. The apparatus for cleaning and concentrating a fine particle slurry according to claim 1, wherein the fine particles are a precursor of a positive electrode material for a secondary battery.

5. 2. 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 washing and concentrating apparatus according to claim 1, the dryer having 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 can rotate 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 the fine particle slurry is dried and converted into fine particle powder by rotating the rotating shaft, and the heated agitator blades transport the fine particle slurry supplied from the inlet to the outlet hole while heating it, during which the fine particle slurry is converted into fine particle powder.

6. a dilution washing 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 using an agitation type cross-flow filtration device to obtain a washing slurry; and a concentration step of concentrating the washing slurry using the agitation type 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 type crossflow filtration device, discarding the filtrate when the electrical conductivity or density is equal to or higher than a threshold value, and reusing the filtrate as the cleaning liquid when the electrical conductivity or density is lower than the threshold value; and a drying step of heating and drying the concentrated slurry to obtain a fine particle powder.

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