Washing and concentrating apparatus for fine particle slurry, apparatus and method for producing fine particle powder
The washing and concentrating apparatus for fine particle slurries addresses filtration and washing challenges by recycling filtrate and using conductive heat transfer drying, resulting in efficient and environmentally friendly production of fine particle powders.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TSUKISHIMA KIKAI CO LTD
- Filing Date
- 2023-08-28
- Publication Date
- 2026-06-05
AI Technical Summary
Existing methods for producing fine particle powders, such as cathode active material precursors for secondary batteries, face challenges in filtration resistance and uneven washing due to non-uniform cake layers, leading to high water consumption and environmental impact.
A washing and concentrating apparatus using agitated cross-flow filtration with a conductivity sensor to recycle filtrate as washing solution and a conductive heat transfer dryer for efficient drying, reducing water usage and enhancing production stability.
The apparatus achieves stable production of fine particle powders with reduced water consumption and environmental burden, while maintaining product quality and efficiency.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a cleaning and concentration device for fine particle slurries, a manufacturing device for fine particle powders, and a manufacturing method, and more particularly to a device and method suitable for manufacturing, for example, a cathode active material precursor of a secondary battery.
Background Art
[0002] In the production of fine particle powders, for example, in the production of a cathode active material precursor of a secondary battery, in recent years, it has been desired to make the particle size of the fine particles as small as possible in order to improve the performance of the final product. A process of obtaining a stock solution slurry containing a precipitate component mainly composed of a transition metal hydroxide by bringing a solution containing a transition metal element into contact with an alkaline solution, a process of washing and concentrating the precipitate component in the slurry to obtain a washed and concentrated slurry, and a process of drying the washed and concentrated slurry to obtain a fine particle powder are generally used.
[0003] However, in this type of manufacturing method for fine particle powders, when fine particles are obtained by adjusting the conditions of the stock solution slurry manufacturing process, the filtration resistance of the cake layer formed during filtration with a filter in the filtration and washing process becomes extremely large. Therefore, it has been difficult to apply a cake filtration method such as a generally used filter press (pressure filtration).
[0004] In addition, in the filter press method, it is difficult to make the entire filter chamber have a uniform cake thickness. When attempting to adopt a displacement washing method in which washing water permeates through a non-uniform cake layer for washing, the washing water tends to concentrate and permeate at the thinner part of the cake, while it is difficult for the washing water to permeate through the thicker part of the cake. Therefore, it is necessary to increase the amount of washing water, but still unevenness in the degree of washing cannot be avoided, and it has been difficult to uniformly wash the entire cake layer.
[0005] Therefore, the methods disclosed in Patent Document 1 or Patent Document 2 have been proposed. The methods in Patent Documents 1 and 2 involve contacting a solution containing a transition metal element with an alkaline solution to obtain a raw slurry containing a precipitate component mainly composed of transition metal hydroxides, concentrating the precipitate component in the slurry by cross-flow filtration, and drying the obtained concentrated slurry by a hot air drying method using convection heat transfer by blowing hot air onto it.
[0006] The aforementioned cross-flow filtration is a method of filtration in which the raw slurry is flowed parallel to the inner wall of the filter. The shear force of the slurry flowing parallel to the inner wall of the filter suppresses the accumulation of solid matter as a cake layer on the filter surface, which has the advantage of maintaining a relatively fast filtration rate even when the raw slurry contains fine particles. In the cross-flow filtration method, the use of cartridge-type membrane modules such as hollow fiber membranes, tubular membranes, and spiral membranes can be considered. [Prior art documents] [Patent Documents]
[0007] [Patent Document 1] Japanese Patent Publication No. 2012-87039 [Patent Document 2] Japanese Patent Publication No. 2012-99470 [Overview of the Initiative] [Problems that the invention aims to solve]
[0008] In the filtration and washing operations described in Patent Documents 1 and 2, a challenge in reducing running costs is to reduce the amount of washing water or washing wastewater used. [Means for solving the problem]
[0009] This invention has been made in view of the above problems, and aims to provide a washing and concentrating apparatus for fine particle slurry and an apparatus and method for stably producing fine particle powder, which can reduce the amount of washing water or washing wastewater used.
[0010] A washing and concentrating apparatus for fine particle slurry according to Embodiment 1 of the present invention comprises: a slurry tank for storing a fine particle slurry containing fine particles with a particle size of 7 μm or less; a flow path for supplying the stored fine particle slurry to an agitated cross-flow filtration apparatus; a return flow path for returning the filtrate discharged from the agitated cross-flow filtration apparatus to the slurry tank; a waste flow path for discarding the filtrate discharged from the agitated 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 agitated cross-flow filtration apparatus or a density sensor for measuring the density of the filtrate; a flow path switching device for switching between flowing the filtrate discharged from the agitated cross-flow filtration apparatus to the return flow path or to the waste flow path; and a control unit that controls the flow path switching device so as to flow the filtrate to the waste flow path when the measurement result of the filtrate sensor is above a threshold, and to flow the filtrate to the return flow path when the measurement result of the filtrate sensor is below a threshold.
[0011] According to the fine particle slurry washing and concentrating apparatus of Embodiment 1, when the conductivity or density of the filtrate discharged from the agitated cross-flow filtration apparatus is less than a threshold, the filtrate is reused as a washing solution, thereby reducing the amount of washing water or washing wastewater used in the fine particle slurry washing and concentrating apparatus.
[0012] The washing and concentrating apparatus for a fine particle slurry according to Embodiment 2 of the present invention is characterized in that, in Embodiment 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 fine particle slurry washing and concentrating apparatus of Embodiment 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 or washing wastewater used in the fine particle slurry washing and concentrating apparatus can be reduced.
[0014] The washing and concentrating apparatus for fine particle slurry according to embodiment 3 of the present invention is characterized in that, in embodiment 1 or 2, the filtrate sensor is provided downstream of the agitated cross-flow filtration apparatus and upstream of the flow path switching device.
[0015] According to the particulate slurry concentration apparatus of Embodiment 3, since the filtrate sensor is located downstream of the agitated cross-flow filtration device and upstream of the flow path switching device, it is possible to appropriately determine whether to discard or reuse the filtrate discharged from the agitated cross-flow filtration device, thereby reducing the amount of washing water or washing wastewater used in the washing and concentration apparatus for particulate slurry.
[0016] The washing and concentrating apparatus for a fine particle slurry according to embodiment 4 of the present invention is characterized in that, in any of embodiments 1 to 3, the fine particles are a precursor of a positive electrode material for a secondary battery.
[0017] According to the fine particle slurry washing and concentrating apparatus of Embodiment 4, fine particle slurry as a cathode material precursor for secondary batteries can be stably produced while reducing the amount of washing water or washing wastewater used.
[0018] A fine particle powder manufacturing apparatus according to aspect 5 of the present invention comprises a conductive heat transfer dryer for drying the fine particle slurry supplied from the fine particle slurry washing and concentration apparatus described in aspect 1, wherein the dryer has an agitation heat transfer device, and the agitation heat transfer device comprises a casing having an inlet at one end and an outlet hole at the other end, a plurality of rotating shafts rotatable around an axis and arranged parallel to each other within the casing, agitation blades fixed to each of the rotating shafts at axial intervals and such that the agitation blades of each rotating shaft partially overlap when viewed in the axial direction, and a heating mechanism for heating these agitation blades, wherein by rotating the rotating shafts, the heated agitation blades heat the concentrated slurry supplied from the inlet and transfer it to the outlet hole, drying the concentrated slurry and converting it into fine particle powder during this process.
[0019] According to the fine particle powder manufacturing apparatus of Embodiment 5, the environmental burden can be reduced because it uses a fine particle slurry washing and concentrating apparatus that can reduce the amount of washing water or washing wastewater used in the fine particle slurry manufacturing apparatus, and a dryer that can dry the fine particle slurry by conductive heat transfer with excellent thermal efficiency and stably produce fine particle powder.
[0020] A method for producing fine particle powder according to embodiment 6 of the present invention is characterized by comprising: a dilution-washing-filtration step to obtain a washing slurry by adding a washing solution to a slurry containing fine particles with a particle size of 7 μm or less and a mother liquor, and filtering the slurry using a stirring-type cross-flow filtration device; a concentration step to obtain a concentrated slurry by concentrating the washing slurry using the stirring-type cross-flow filtration device; a flow path switching step to measure the conductivity or density of the filtrate discharged from the stirring-type cross-flow filtration device, discarding the filtrate if the conductivity or density is above a threshold, and reusing the filtrate as the washing solution if the conductivity or density is below the threshold; and a drying step to obtain fine particle powder by heating and drying the concentrated slurry.
[0021] According to the method for producing the particulate powder of Aspect 6, the conductivity or density of the filtrate discharged from the stirring cross-flow filtration device is measured. When the conductivity or density of the filtrate is equal to or higher than the threshold value, the filtrate is discarded. When the conductivity or density of the filtrate is less than the threshold value, the filtrate is reused, thereby reducing the amount of washing water or washing wastewater used in the particulate powder production device and enabling stable production of the particulate powder.
Advantages of the Invention
[0022] As described above, according to the washing and concentration device for the particulate slurry, the production device for the particulate powder, and the production method of the present invention, the conductivity or density of the filtrate discharged from the stirring cross-flow filtration device is measured. When the conductivity or density of the filtrate is equal to or higher than the threshold value, the filtrate is discarded. When the conductivity or density of the filtrate is less than the threshold value, the filtrate is reused, thereby reducing the amount of washing water or washing wastewater used in the washing and concentration device for the particulate slurry and enabling stable production of the particulate powder, thus obtaining an excellent effect.
[0002] 6>
Brief Description of the Drawings
[0023] [Figure 1] It is a block diagram showing a particulate powder production device according to an embodiment of the present invention. [Figure 2] It is a block diagram showing a particulate slurry production device in the same embodiment. [Figure 3] It is a cross-sectional view showing a stirring cross-flow filtration device in the same embodiment. [Figure 4] It is a side cross-sectional view showing a drying device in the same embodiment. [Figure 5] It is a plan view showing a drying device in the same embodiment with the top plate removed. [Figure 6] It is a front cross-sectional view showing a drying device in the same embodiment.
Modes for Carrying Out the Invention
[0024] The following describes in detail an apparatus 1 for producing fine particle powder according to one embodiment of the present invention. The apparatus 1 for producing fine particle powder according to this embodiment includes: a fine particle slurry producing apparatus 2 that produces 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 that generates a swirling flow in a crystallizing apparatus 10 (reaction processor); a slurry tank 30 that washes the fine particle slurry obtained in the fine particle slurry producing apparatus 2 by adding a washing liquid according to the processing stage while stirring; a stirring type cross-flow filter 6 that concentrates the fine particle slurry or the slurry after washing by removing a portion of the mother liquor and the washing liquid from the slurry tank 30; and a conductive heat transfer drying apparatus (dryer) 8 that, after the final concentration is completed in the stirring type cross-flow filter 6, transfers the final concentrated slurry while mixing it with a wet powder pre-held in a casing 92 using a heated stirring blade and dries it by conductive heat transfer. The final concentrated slurry may sometimes be simply called concentrated slurry.
[0025] [Crystallization apparatus] As shown in Figure 2, the crystallization apparatus 10 has an elongated cylindrical reaction vessel 116. The upstream side of the reaction vessel 116 is cylindrical, while the downstream side is a coaxial and conical tapered section 116A that narrows towards the downstream. Inside the reaction vessel 116, a cylindrical outer tube 110 is coaxially arranged from the upstream end to the tapered section 116A, 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 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 longer than the first inner tube 112. The first raw material 12A is supplied into the reaction vessel 116 from the first inner tube 112, and the 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 gap between the outer tube 110 and each of the first inner tubes 112 and second inner tubes 114.
[0026] An inlet 115 is formed on the outer circumference of the upstream end of the reaction vessel 116. By blowing the reaction liquid at high speed through this inlet 115, a swirling flow is generated inside the reaction vessel 116. As the inner diameter narrows in the tapered section 116A, the rotation speed increases, and the flow becomes a vortex that 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. The first raw material 12A from the first inner tube 112 and the second raw material 12B from the second inner tube 114 are vigorously stirred and mixed in the central region R of the swirling flow within the tapered section 116A. During this mixing process, the first raw material 12A and the second raw material 12B are mixed and react at high speed, and reaction products are generated as very small particles, which flow out from the discharge hole 14 along with the reaction liquid.
[0027] A conduit 16 is connected to the discharge port 14, and the reaction liquid containing fine particles is supplied to the storage container 18 through the conduit 16. A flow control valve 118 is interposed upstream of the conduit 16 connected to the discharge port 14, and can be opened and closed by the drive unit 120 to adjust the outflow rate of the reaction liquid from the discharge port 14. The drive unit 120 is controlled manually or automatically by a control panel (not shown) according to the reading 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 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 control valve 118 is decreased to suppress the outflow of the reaction liquid. This ensures that the crystallization of fine particles in the reaction vessel 116 is carried out appropriately.
[0028] The reservoir 18 is equipped with a stirring blade 128, which is rotated by a motor 126, to uniformly agitate the reaction solution and prevent fine particles from settling. A conduit 20 is connected to the lower end of the reservoir 18, and the slurry containing fine particles that flows out from the lower end of the reservoir 18 is pressurized by a pump 22 and blown into the reaction vessel 116 through the inlet 115 via a temperature controller 124, conduit 24 and pressure gauge 122. The temperature controller 124 plays a role in appropriately adjusting the temperature of the reaction solution 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 any compound with low solubility that precipitates when the first raw material 12A and the second raw material 12B are reacted is acceptable. For example, when producing a cathode material precursor for secondary batteries, a solution containing a transition metal element such as a nickel salt can be used as the first raw material 12A, and an alkaline solution can be used as the second raw material 12B. By reacting these in the crystallizer 10, fine particles mainly composed of transition metal hydroxides can be obtained. More specifically, as raw materials for a cathode material precursor for secondary batteries, aqueous solutions of nickel sulfate, cobalt sulfate, or manganese sulfate can be used as the first raw material 12A, and aqueous sodium hydroxide solution or ammonia water can be used as the second raw material 12B.
[0030] The particle size of the fine particles in the fine particle slurry produced by the crystallization apparatus 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 to be measured by laser diffraction and scattering methods. Furthermore, the particle size in this specification refers to the average particle diameter at 50% of the cumulative value of the particle size distribution measured by the above measurement method. The crystallization apparatus 10 using swirling flow can suppress the growth of crystal grains after they have formed, and it is easy to produce a slurry containing fine particles of such fine size. If the particle size of the fine particles is 7 μm or less, for example, when producing a cathode material precursor for secondary batteries, it is possible to improve performance by improving the homogeneity of the cathode material for secondary batteries. In other applications as well, if the particle size of the fine particles is as small as possible and uniform in size, it is possible to expect improved performance of the final product.
[0031] The reservoir 18 stores a particulate slurry containing fine particles generated in the crystallizer 10. A wave-damping partition plate 130 is placed near the liquid surface of the reservoir 18, and a particulate slurry outlet 26 is formed on the side wall of the reservoir 18 opposite the partition plate 130, to which a conduit 28 leading to the slurry tank 30 is connected. The conduit 28 is equipped with a take-off valve 132 and a pump 134, and the particulate slurry is transferred from the reservoir 18 to the slurry tank 30 at an appropriate timing and flow rate. Alternatively, a portion of the particulate slurry stored in the reservoir 18 may be withdrawn, concentrated, and then the concentrated slurry returned to the reservoir 18. Performing a concentration operation allows crystallization to be carried out at a high slurry concentration.
[0032] The concentration of solids in the fine particle slurry transferred from the outlet 26 to the slurry tank 30 is not limited, but for example, when manufacturing a cathode material precursor for secondary batteries, it is preferably 5 wt% or more and 40 wt% or less, more preferably 10 wt% or more and 40 wt% or less, and even more preferably 15 wt% or more and 40 wt% or less. With this concentration range, fine particles can be manufactured stably, and the load balance in the subsequent slurry tank 30, agitated cross-flow filtration device 6, and drying device 8 is good, making it possible to improve the overall processing efficiency and energy efficiency without putting undue strain on each process and compromising stability.
[0033] [Slurry Tank] As shown in Figure 1, the slurry tank 30 has the function of temporarily storing the fine particle slurry sent from the storage unit 18 and sending it to the agitated cross-flow filtration device 6, or adding a washing solution to the initially concentrated slurry obtained by initially concentrating the fine particle slurry and sending the washed slurry to the agitated cross-flow filtration device 6.
[0034] The slurry tank 30 is cylindrical with a closed bottom, and the inner surface of the bottom is formed in a hemispherical shape. A semicircular anchor-shaped stirring blade 34 is positioned 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 to supply clean cleaning liquid to the slurry tank 30, and the first port of a three-way valve 42 is connected to it via a conduit 40. The second port of the three-way valve 42 is connected to the slurry tank 30 via an on-off valve 44, and the 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 gap between the outer edge of the anchor-shaped stirring blade 34 and the inner bottom surface of the slurry tank 30 is not limited, but to prevent fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 30, a gap of about 0.5 to 3.0 cm is preferable. Furthermore, the length of the semicircular outer edge of the anchor-shaped stirring blade 34 is preferably long enough to face the entire inner bottom surface of the anchor-shaped stirring blade 34. The rotational speed of the outer edge of the anchor-shaped stirring blade 34 by the motor 36 is not limited, but is preferably about 0.1 to 3.0 m / sec. Within this range, the effect of preventing fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 30 is high.
[0036] During the concentration of the slurry in each process, the slurry is circulated between the slurry tank 30 and the agitated cross-flow filter 6, while the filtrate is extracted from the agitated cross-flow filter 6. This gradually concentrates the slurry, but as it reaches a high concentration, the viscosity of the slurry also increases. With a normal paddle-type agitator, only the slurry liquid near the agitator can be circulated, making it impossible to maintain uniformity throughout the slurry tank 30. As a result, fine particles settle in the slurry tank 30, creating a hard, compressed solid layer at the bottom of the slurry tank 30, which cannot be extracted. The anchor-type agitator 34 can solve this problem.
[0037] Furthermore, while batch operation can be selected for each process in this apparatus, if the subsequent drying apparatus 8 operates continuously, a buffer means is required to hold the slurry in each process for a relatively long period of time. Therefore, by applying a slurry tank 30 equipped with the anchor-shaped stirring blades 34 described above, it becomes possible to uniformly convect the entire slurry in the slurry tank 30, thereby preventing the accumulation and adhesion of fine particles.
[0038] In particular, when manufacturing cathode material precursors for secondary batteries, the fine particles are metal compounds and have a high specific gravity. If the slurry tank 30 is not uniformly agitated, the solid material will quickly settle to the bottom of the tank, become hard and compacted, and become impossible to extract. Furthermore, highly concentrated slurry has a high specific gravity and extremely high viscosity, so a typical paddle-type agitator can only create convection in the slurry near the agitator, making it difficult to maintain a uniform dispersion state by creating convection throughout the entire slurry tank 30.
[0039] The washing liquid tank 50 is a container for storing a fraction of the filtrate discharged from the agitated cross-flow filtration device 6 that contains relatively few impurities. The conductivity of the filtrate can be used as an indicator to understand the tendency of impurity content. If the conductivity is higher than a preset threshold, the filtrate will contain a large amount of electrolyte as an impurity, and electrolytes will adversely affect, for example, the cathode material precursor for secondary batteries. For example, if the detected conductivity is higher than a preset threshold, the three-way valve 42 and the on-off valve 44 can be operated to select either the clean washing liquid from the washing liquid source 38 or the highly clean washing liquid recovered from the agitated cross-flow filtration device 6 in the washing liquid tank 50 and supply it to the slurry tank 30.
[0040] A discharge hole 52 is formed at the lower bottom 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 to the conduit 56 via the pump 54, and the slurries in various states can be transferred to the agitated cross-flow filtration device 6 through the conduit 56.
[0041] [Agitated cross-flow filtration system, conductivity sensor, control unit, flow path switching device] As shown in Figure 3, the agitated cross-flow filtration apparatus 6 has a cylindrical casing 60 that is positioned almost horizontally. A rotating shaft 140 is positioned along the centerline of the casing 60 and is rotated by a motor 62. Multiple disc-shaped stirring blades 142 are fixed to the rotating shaft 140 at regular intervals in the axial direction. The outer diameter of the stirring blades 142 is smaller than the inner diameter of the casing 60. On the inner circumferential surface of the casing 60, ring-shaped filters 146 of a certain thickness are fixed coaxially with the casing 60 between adjacent stirring blades 142, and disc-shaped filtrate chambers 148 are formed inside each filter 146. The number of stirring blades 142 and filters 146 is determined by the processing capacity required for the agitated cross-flow filtration apparatus 6. Gaps of a certain thickness are formed between the inner surface of the casing 60, the stirring blades 142, and the filters 146, and these gaps form slurry chambers 150.
[0042] An inlet 144 is formed at the upstream end of the casing 60, and slurries of various states supplied from the inlet 144 are agitated between a rotating agitator 142 and a fixed filter 146, and are transported downstream in a meandering manner through the slurry chamber 150. The slurry chamber 150 is pressurized by the liquid supply pressure of the pump 54, and during this transport process, the slurry is agitated by the rotation of the agitator 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 does not need to be such that fine particles in the slurry pass through, but the filtrate passes through, and it needs to have sufficient mechanical strength.
[0043] The casing 60 is fitted with filtrate discharge valves 154, each leading to a filtrate chamber 148, and the outlets of the filtrate discharge valves 154 are connected together to a conduit 156. The filtrate that enters the filtrate chamber 148 flows out through the filtrate discharge valves 154 into the conduit 156. As shown in Figure 1, this conduit 156 is connected to the first port of a three-way valve 74, which is a flow path switching device, and the second port of the three-way valve 74 is connected to the drainage passage 80 via a conduit (waste flow path) 78. The third port of the three-way valve 74 is connected to the washing liquid tank 50 via a conduit (return flow path) 76.
[0044] As shown in Figure 1, a conductivity sensor 71 is installed in the conduit 156 that serves as the filtrate outlet of the agitated cross-flow filtration device 6. The conductivity sensor 71 continuously measures the conductivity of the filtrate discharged from the agitated cross-flow filtration device 6 and transmits this information to the control unit 69, which will be described later. Upon receiving the output of the conductivity sensor 71, the control unit 69 detects the progress of the dilution and washing process based on the output result and the previously stored conductivity of the filtrate, and determines the timing of completion of the dilution and washing process. Specifically, the control unit 69 determines that the dilution and washing process is complete when the output result falls below a threshold set by the control unit 69. Note that the timing of completion of the dilution and washing process may be determined using other sensors, not just the conductivity sensor 71. For example, a second density sensor (not shown) may be provided in the conduit 156 that serves as the filtrate outlet of the agitated cross-flow filtration device 6. The second density sensor continuously measures the density of the filtrate discharged from the agitated cross-flow filtration device 6 and transmits this information to the control unit 69. Upon receiving the output from the second density sensor, the control unit 69 detects the progress of the dilution and washing process from the density of the filtrate and determines the timing of completion of the dilution and washing process.
[0045] The three-way valve 74 and the conductivity sensor 71 are connected to the control unit 69 by wire or wireless connection so that they can communicate electrical signals. The control unit 69 determines whether the measurement result of the conductivity sensor 71 is above a threshold. If the measurement result is above the threshold, the filtrate is flowed into a channel for discarding the filtrate. If the measurement result is below the threshold (less than the threshold), the filtrate is flowed into a channel for reusing the filtrate as a washing liquid. Specifically, the conductivity sensor 71 is a conductivity meter, and if the conductivity of the filtrate is above the threshold, the valve (not shown) inside the three-way valve 74 is set so that the filtrate discharged from the agitated 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 channel 80. When the conductivity of the filtrate falls below a threshold, the valve (not shown) inside the three-way valve 74 is switched so that the filtrate discharged from the agitated cross-flow filtration device 6 via 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 washing liquid tank 50. Although not shown, the three-way valve 74 is equipped with a drive device for switching the valve, and the valve inside 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 wireless so that electrical signals can be communicated. A motor may be used as an example of a drive device. Here, the above-mentioned conductivity threshold is preferably set to a value in the range of 10 [mS / cm] or less, more preferably to a value in the range of 5 [mS / cm] or less, and even more preferably 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 memory. The processor performs calculations to execute the functions of the control unit 69. Memory stores a rewritable program that describes the functions to be performed by the CPU.The control unit 69 may implement these functions using hardware (including circuitry) such as LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), or GPU (Graphics Processing Unit). Alternatively, the functions of the control unit 69 may be implemented through the cooperation of software and hardware.
[0046] During the initial concentration by the agitated cross-flow filtration device 6 and for a while after the start of washing, the filtrate entering the filtrate chamber 148 contains many impurities. However, as the filtration time 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 was flowing to the drainage channel 80 in the washing liquid tank 50. The relatively clean filtrate stored in the washing liquid tank 50 is used as washing liquid, and in the next dilution washing process, the pump 48 is activated to supply it to the slurry tank 30 via the conduit 46, three-way valve 42, and on-off valve 44, where it is used as washing liquid in the initial stage of the dilution washing process. This reduces the amount of washing liquid used in the washing liquid source 38, which helps to reduce the cost of manufacturing fine particle powder. Furthermore, it reduces the amount of filtrate and washing waste liquid discarded outside the fine particle powder manufacturing apparatus 1, thereby reducing the environmental burden.
[0047] The downstream portion of the casing 60 is a conical tapered section 152 that narrows towards the downstream side, and an outlet 64 is formed at the tip of the tapered section 152. The slurry is transported downstream in a meandering manner through the slurry chamber 150, and water is removed. The slurry is filtered and concentrated in the agitated cross-flow filter 6 while circulating between the slurry tank 30 and the agitated cross-flow filter 6, and the concentrated slurry, which has become highly viscous, is discharged from the outlet 64.
[0048] The solid content concentration of the concentrated slurry discharged from the agitated cross-flow filtration device 6 differs from the optimal value in the initial concentration step, the dilution and washing step, and the final concentration step, and is not necessarily limited. For example, when manufacturing a cathode material precursor for secondary batteries, the solid content concentration of the initial concentrated slurry is preferably 35 wt% or more and 65 wt% or less at the completion of the initial concentration step, and more preferably 45 wt% or more and 65 wt% or less. The solid content concentration of the washing slurry at the completion of the dilution and washing step is preferably 35 wt% or more and 60 wt% or less, and 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%, and more preferably 60 wt% or more and 65 wt% or less.
[0049] In each process, maintaining the concentration range described above prevents difficulties in transferring the concentrated slurry within the casing 60 of the agitated cross-flow filter 6, while limiting the consumption of washing solution and effectively reducing the amount of impurities in the final concentrated slurry. Therefore, the load balance between the agitated cross-flow filter 6 and the drying device 8 is good, and overall processing efficiency and energy efficiency can be increased without putting undue strain on each process.
[0050] As shown in Figure 1, the outlet 64 of the casing 60 of the agitated cross-flow filter 6 is connected to the 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 by manual switching 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 located upstream of the drying device 8. By operating the three-way valve 70, the slurry of various states discharged from the outlet 64 of the agitated cross-flow filter 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 concentrated slurry discharged from the outlet 64 of the agitated cross-flow filtration device 6 has its slurry density measured by a density sensor 66, and the output signal of the density sensor 66 is transmitted to a control panel (not shown). If 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. First, it measures the timing at which the concentrated slurry discharged from the agitated cross-flow filtration device 6 has been sufficiently dewatered and reached a predetermined density, and uses this timing to determine the completion timing of at least one of the initial concentration process and the final concentration process, and to control the transition to the next process.
[0052] When determining the completion timing of the dilution and washing process, it is preferable that either of the following conditions is met: (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).
[0053] The second purpose of measuring slurry density using the density sensor 66 is to enhance the cleaning effect of the slurry in the dilution and washing process. Specifically, lower and upper limits 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 cleaning liquid from the cleaning liquid source 38 to the slurry tank 30 is increased (or resumed after being temporarily stopped), and when the lower limit is reached, the supply of cleaning liquid from the cleaning liquid source 38 is decreased (or temporarily stopped). This maintains the solid content concentration of the concentrated slurry discharged from the agitated cross-flow filter 6 in the dilution and washing process within a certain range, thereby adjusting the degree of cleaning until the conductivity of the filtrate discharged from the agitated cross-flow filter 6 is sufficiently reduced. Here, the section from the slurry tank 30 to the agitated cross-flow filter 6 in the fine particle powder manufacturing apparatus 1 is sometimes referred to as the fine particle slurry cleaning and concentration apparatus.
[0054] To control the cleaning solution in the dilution and cleaning process, 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. 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 solution from the cleaning solution source 38 to the slurry tank 30. Conversely, 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 decrease or stop the amount of cleaning solution from the cleaning solution source 38 to the slurry tank 30, performing feedback control to keep the solid content concentration in the concentrated slurry within a certain range. The three-way valve 42 and the on-off valve 44 may also be controlled by the control unit 69.
[0055] The slurry tank 82 serves as a buffer to regulate 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 surface of the bottom is formed in a hemispherical shape. A semicircular anchor-shaped stirring blade 84 is positioned 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 final concentrated slurry does not settle and solidify in the slurry tank 82. An outlet 88 is formed at the lower end of the bottom of the slurry tank 82, and the high-viscosity final concentrated slurry extracted from the slurry tank 82 is sent to the conduit 94 via a pump 90 and then to the drying device 8.
[0056] The gap between the outer edge of the anchor-shaped stirring blade 84 and the inner bottom surface of the slurry tank 82 is not limited, but, similar to the anchor-shaped stirring blade 34 described earlier, it is preferable to have a gap of about 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, it is preferable that the length of the semicircular outer edge of the anchor-shaped stirring blade 84 is long enough to face the entire inner bottom surface of the slurry tank 82. In addition, the rotational speed of the outer edge of the anchor-shaped stirring blade 84 by the motor 86 is not limited, but it is preferable to have a speed of about 0.1 to 3.0 m / sec. Within this range, the effect of preventing fine particles from accumulating and adhering to the inner bottom surface of the slurry tank 82 can be obtained. This is a particularly important effect when manufacturing cathode material precursors for secondary batteries, as the fine particles are metal compounds and have a high specific gravity.
[0057] [Drying equipment] Figures 4 to 6 are a side cross-sectional view, a plan view with the top plate removed, and a cross-sectional view, respectively, of the stirring heat transfer device as a drying apparatus 8. The drying apparatus 8 has a rectangular parallelepiped casing 92, which has a trough-shaped inner wall 194, an outer wall 198 covering the outer circumferential surface of the inner wall 194, and a rectangular top plate 196 closing the upper end of the inner wall 194. A tight, airtight gap of a certain thickness is formed between the inner wall 194 and the outer wall 198, which serves as a heat transfer medium passage 199. The outer wall 198 has a heat transfer medium inlet 200 and a heat transfer medium outlet (not shown) that communicate with the heat transfer medium passage 199. By supplying high-temperature steam or heat transfer oil from the heat transfer medium inlet 200 to the heat transfer medium outlet, the inside of the casing 92 can be heated uniformly.
[0058] An 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 on the upper surface of the upstream side of the casing 92, and a gas outlet 175 is formed on the upper surface of the downstream side (the other end). Air at room temperature or heated air is blown in from the gas inlet 174, and moist air is discharged from the gas outlet 175 along with water vapor generated as the mother liquor and cleaning liquid evaporate inside the casing 92. By discharging the water vapor generated inside the casing 92 to the outside of the machine, the humidity can be maintained at an appropriate level. On the other hand, an outlet 98 is formed on the lower surface of the downstream end of the casing 92, and dried fine powder particles are discharged from inside the casing 92.
[0059] Within the casing 92, two hollow rotating shafts 176 are arranged symmetrically along the longitudinal direction, and one or both ends are supported by bearings so as to be rotatable around the axis of the two hollow rotating shafts 176. Hollow stirring 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 stirring blades 178 of one hollow rotating shaft 176 are positioned midway in the axial direction between the hollow stirring blades 178 of the other hollow rotating shaft 176. The two hollow rotating shafts 176 may be parallel to each other.
[0060] As shown in Figure 6, each hollow stirring blade 178 is fan-shaped with a central angle of less than 180°, and pairs of hollow stirring blades 178 are fixed in positions that are 180° rotationally symmetric with respect to the hollow rotating shaft 176. Between the pairs of hollow stirring blades 178, a notch 190 of a certain width is formed to allow the mixture of the final concentrated slurry and wet powder to pass through in the axial direction. The inside of the hollow stirring blade 178 is hollow and communicates with the internal space of the hollow rotating shaft 176, so that the heat transfer medium supplied to the hollow rotating shaft 176 also enters the inside of the hollow stirring blade 178 and heats the hollow stirring blade 178. This is sometimes called the heating mechanism of the hollow stirring blade 178.
[0061] The wet powder is the dried final concentrated slurry that is pre-held inside the casing 92; it is not completely dry and retains moisture. Mixing the pre-held wet powder with the final concentrated slurry prevents abnormal adhesion that would hinder the function of the drying device 8, and also facilitates its transfer within the casing 92 by the hollow stirring blades 178.
[0062] As shown in Figures 4 and 5, the pair of hollow stirring blades 178 are inclined in opposite directions with respect to the hollow rotating shaft 176. Each time the hollow rotating shaft 176 rotates 180°, the trajectory of the hollow stirring blades 178 oscillates axially within a certain angular range, as shown by the solid and dotted lines in the figures. This oscillation prevents the final concentrated slurry and wet powder from adhering to the hollow stirring blades 178 adjacent to each other in the axial direction, while simultaneously mixing the final concentrated slurry and wet powder. Furthermore, the hollow stirring blades 178 also have a twist along a virtual helical plane around the hollow rotating shaft 176, and as the hollow rotating shaft 176 rotates, they gradually transfer the mixture of the final concentrated slurry and wet powder from the upstream to the downstream side of the casing 92.
[0063] The hollow stirring blades 178 and the hollow rotating shaft 176 are made of a metal with high thermal conductivity, and a heat transfer medium inlet hole 184 and a heat transfer medium outlet hole 182 are formed at the upstream end of the hollow rotating shaft 176. A heat transfer medium such as high-temperature steam or heat transfer oil is continuously supplied from a heat transfer medium source (not shown) from the heat transfer medium inlet hole 184 to the heat transfer medium outlet hole 182, spreading throughout the entire length of the hollow rotating shaft 176, and also entering the interior of the hollow stirring blades 178, so that the entire hollow rotating shaft 176 and hollow stirring blades 178 are heated to a temperature above the boiling point of the mother liquor and washing liquid contained in the final concentrated slurry and wet powder. Therefore, each time the mixture of the final concentrated slurry and wet powder comes into contact with the hollow rotating shaft 176 and the hollow stirring blades 178, it is heated by conductive heat transfer, causing the mother liquor and washing liquid contained in the mixture to 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 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 conductive heat transfer, which has excellent thermal efficiency, and transferred in the transfer direction T from upstream to downstream of the casing 92. Note that 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 discharge hole 182 shown in Figure 4 may be reversed. That is, the heat medium discharge hole 182 may be provided radially inside the heat medium inlet hole 184.
[0064] The fine powder particles discharged from the outlet 98 of the drying apparatus 8 are stored in the storage container 102 via the discharge passage 100, as shown in Figure 1. Note that the number of hollow rotating shafts 176 is not limited to two; there may be more than two. Therefore, it can be said that there may be multiple hollow rotating shafts 176. Even with multiple 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 as follows. [Process for manufacturing fine particle slurry] First, the crystallizer 10 and the reservoir 18 are filled with mother liquor as the initial state. The motor 126 rotates the stirring blade 128 and operates the pump 22 to blow the mother liquor in the reservoir 18 into the reaction vessel 116 from the inlet 115, creating a swirling flow in the reaction vessel 116. The first raw material 12A is supplied from the first inner pipe 112 and the second raw material 12B is supplied from the second inner pipe 114, and the two are vigorously mixed in the central region R within the tapered section 116A, generating fine particles through 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 as the mother liquor circulates repeatedly, a fine particle slurry is generated in the reservoir 18. The pressure of the mother liquor introduced from the inlet 115 is measured by the pressure gauge 122, and the flow rate of the particulate slurry flowing out from the discharge hole 14 is appropriately adjusted by the flow control valve 118 to adjust the solid content concentration of the particulate slurry in the storage container 18 to an appropriate range.
[0066] [Initial concentration process] Once the solid content concentration of the particulate slurry in the storage container 18 reaches an appropriate range, an initial concentration process is started to concentrate the particulate slurry and convert it into an initial concentrated slurry. The initial concentration process is, so to speak, a dewatering process before washing. In the initial concentration process, the three-way valve 70 is controlled to set up a circulation path so that the slurry discharged from the agitated cross-flow filtration device 6 returns to the slurry tank 30 through the conduit 72. Also, the supply of washing liquid is stopped during the initial concentration process.
[0067] The outlet valve 132 is opened, and the particulate slurry in the storage container 18 is discharged through the outlet 26 and conduit 28, and transferred to the slurry tank 30 by the pump 134. Inside the slurry tank 30, the motor 36 rotates the anchor-shaped stirring blade 34 to prevent the settling of particulate matter in the particulate slurry, while the pump 54 is operated to supply the particulate slurry from the discharge hole 52 to the agitated cross-flow filter 6. As shown in Figure 3, the particulate slurry is continuously introduced from the inlet 144 of the agitated cross-flow filter 6 into the slurry chamber 150 inside the casing 60.
[0068] Inside the slurry chamber 150, the discharge pressure from the pump 54 creates a pressurized state, and the motor 62 continuously rotates the stirring blades 142. The stirring blades 142 agitate the fine particle slurry, pressing it against the side of the filter 146. 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 moves downstream through the casing 60, the mother liquor in the slurry decreases, and the slurry, now somewhat concentrated, is discharged from the outlet 64. 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 is collected in the conduit 156 via the filtrate discharge valve 154. Initially, the conduit 156 is connected to the waste channel 78 by a three-way valve 74, and the initial filtrate with many impurities is discarded into the drain channel 80. This process is repeated while measuring the density of the slurry with a density sensor 66 until the density of the fine particle slurry reaches a predetermined value and an initial concentrated slurry with the aforementioned solid content concentration is obtained.
[0070] [Dilution and washing process] Once an initial concentrated slurry of a predetermined concentration is obtained in the slurry tank 30, the initial concentration process is completed, and a dilution and washing process is started in which the initial concentrated slurry is diluted with a washing solution and washed. In the dilution and washing process, the three-way valve 70 maintains a circulation path in which the slurry discharged from the agitated cross-flow filtration device 6 returns to the slurry tank 30 through the conduit 72. The filtrate collected in the conduit 156 via the filtrate discharge valve 154 is still discharged into the drainage channel 80 as a filtrate with many impurities via the three-way valve 74 and the waste channel 78.
[0071] Furthermore, while managing the density using 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 with the three-way valve 42, and the pump 48 is activated to first supply cleaning liquid from the cleaning liquid tank 50 to the slurry tank 30. The cleaning liquid tank 50 contains relatively clean cleaning liquid obtained during the previous production of fine particle powder. This is because, immediately after the start of the dilution cleaning process (first stage), sufficient cleaning effect can be obtained even with a cleaning liquid of low purity because there are many impurities in the initial concentrated slurry. As a result, the initial concentrated slurry circulates between the slurry tank 30 and the agitated cross-flow filtration device 6, and cleaning in the slurry tank 30 and filtration by the agitated cross-flow filtration device 6 continue. Because filtration is continued in this way, the dilution cleaning process is sometimes called the dilution cleaning and filtration process.
[0072] As the cleaning solution from the cleaning solution tank 50 is continuously supplied to the slurry tank 30 and the initial concentrated slurry is cleaned, the amount of impurities (electrolyte components, non-electrolyte components, and ultrafine particles) in the filtrate discharged from the agitated cross-flow filtration device 6 decreases, 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 target value (the target value for switching the cleaning solution supplied to the slurry tank 30 from the cleaning solution in the cleaning solution tank 50 to the clean cleaning solution from the cleaning solution source 38) (or when the amount of liquid in the cleaning solution tank 50 has decreased sufficiently), the pump 48 is stopped by automatic control by the control unit 69 or manually, stopping the supply of reused cleaning solution from the cleaning solution tank 50. Then, the three-way valve 42 is automatically controlled by a control panel (not shown) or operated manually to start supplying clean cleaning solution from the cleaning solution source 38 to the slurry tank 30. The three-way valve 42 may also be controlled by the control unit 69.
[0073] As the washing and filtration of the initial concentrated slurry progresses using the clean washing liquid from the washing liquid source 38, impurities in the filtrate discharged from the agitated 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 the completion of washing) and the density of the fine particle slurry reaches a predetermined value, the washing liquid source 38 is stopped, and the supply of the washing liquid is stopped by automatically controlling the three-way valve 42 and the on-off valve 44 using a control panel (not shown) or by manually operating them. The three-way valve 42 and the on-off valve 44 may also be controlled by the control unit 69.
[0074] [Final concentration process] After the washing solution supply is stopped and the dilution washing process is complete, a final concentration process is performed to concentrate the washing slurry. In the final concentration process, the washing slurry is supplied to the agitated cross-flow filter 6, where it is separated into concentrated washing slurry and filtrate. The concentrated washing slurry is returned to the slurry tank 30. In this way, the washing slurry circulates between the slurry tank 30 and the agitated cross-flow filter 6, and is continuously filtered by the agitated cross-flow filter 6. Therefore, the slurry in the slurry tank 30 is gradually concentrated. Note that the final concentration process is sometimes referred to as the concentration process.
[0075] [Flow path switching process] When the conductivity of the filtrate measured by the conductivity sensor 71 installed in the conduit 156 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. The control unit 69 then automatically switches the three-way valve 74, and the filtrate from the conduit 156 is stored in the washing liquid tank 50 through the return channel 76. If the filtrate is sufficiently clean, storage in the washing liquid tank 50 may be started not only in the final concentration process but also in the later stages of the dilution washing process. Furthermore, 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, a threshold density is set in advance, and if the measured density falls below that threshold, the three-way valve 74 is switched, and the filtrate is stored in the washing 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 for measuring the density of the filtrate is 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 channel 78 when the measurement result of the filtrate sensor is above a threshold, and flows into the return channel 76 when the measurement result of the filtrate sensor falls below the threshold. In this case, the filtrate sensor is provided downstream of the agitated cross-flow filtration device 6 and upstream of the three-way valve 74, which is a channel switching device.
[0076] When the density of the final concentrated slurry discharged from the outlet 64 of the agitated cross-flow filtration device 6, as measured by the density sensor 66, reaches the density target value for the final concentration process, the flow rate adjustment 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 adjustment valve 68 and the three-way valve 70 may also be controlled by the control unit 69. The final concentrated slurry stored in the slurry tank 82 is agitated by the anchor-shaped agitator blade 84 to prevent sedimentation, and the drying process is started. In this embodiment, the concentrated slurry is returned to the slurry tank 30 and filtered while being circulated, but it is not limited to this and it is also possible to supply the concentrated slurry to the slurry tank 82 without circulation.
[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 apparatus 8 by the pump 90 and introduced into the casing 92 through the inlet 96 via the conduit 94. Inside the casing 92, two hollow rotating shafts 176 rotate continuously, and the hollow stirring blades 178 are heated by high-temperature steam or heat transfer oil supplied to the heat transfer medium inlet hole 184. As the hollow stirring blades 178 rotate, the final concentrated slurry and the wet powder held inside the casing 92 are mixed, and the mixture is sent in the transfer direction T. In this process, the oscillation of the hollow stirring blades 178 prevents the mixture from adhering to adjacent hollow stirring blades 178, and the mixture is heated by conductive heat transfer from the heated hollow stirring blades 178, and the drying process of the mixture proceeds. That is, it is heated and dried. By blowing in ambient temperature or heated air from the gas inlet 174 and discharging moist air from the gas outlet 175, the water vapor generated inside the casing 92 is expelled from the machine, thereby maintaining an appropriate humidity level inside the machine. By the time the mixture reaches the downstream side of the casing 92, it has become a fine powder and is sequentially discharged from the discharge port 98. The fine powder discharged from the discharge port 98 is stored in the storage container 102 via the discharge passage 100.
[0078] [Effects of this embodiment] According to the above-described fine particle slurry washing and concentration apparatus, fine particle powder manufacturing method, and fine particle powder manufacturing apparatus 1, the conductivity or density of the filtrate discharged from the agitated cross-flow filtration device 6 via the conduit 156 is constantly monitored by a filtrate sensor. If the conductivity or density of the filtrate is above a threshold, the filtrate is discarded. On the other hand, if the conductivity or density of the filtrate falls below the threshold, it is determined that the filtrate has become clean enough to be used for primary washing in the slurry tank 30. The control unit 69 switches the three-way valve 74, which is a flow path switching device, and stores the filtrate from the conduit 156 in the washing liquid tank 50 via the return flow path 76. As a result, the amount of washing liquid used from the washing liquid source 38 can be reduced, which helps to reduce the cost of manufacturing fine particle powder. Furthermore, the amount of filtrate and washing waste liquid discarded outside the fine particle powder manufacturing apparatus 1 can be reduced, thereby reducing the burden on the environment. Furthermore, in this embodiment, in the fine particle slurry manufacturing process, the first raw material 12A and the second raw material 12B are reacted in a mother liquor that generates a high-speed swirling flow in the crystallizer 10 to produce a slurry containing fine particles with a particle size of 7 μm or less. Then, in the initial concentration process, dilution and washing process, and final concentration process, washing and high concentration using the agitated cross-flow filtration device 6 can be efficiently performed without causing blockage of filters or flow paths. In addition, in the drying process, the final concentrated slurry and wet powder are mixed, and a heated hollow stirring blade 178 is brought into contact with the mixture to heat it by conductive heat transfer. Thus, it is possible to manufacture fine particles of 7 μm or less with high production efficiency while keeping energy costs down.
[0079] Furthermore, in the fine particle slurry manufacturing process, by reacting a solution containing a transition metal element as the first raw material 12A and an alkaline solution as the second raw material 12B, fine particles mainly composed of transition metal hydroxides can be obtained, enabling the production of fine particle powder as a precursor for positive electrode materials for secondary batteries with high production efficiency while keeping energy costs down.
[0080] Furthermore, in the initial concentration process, the fine particle slurry is filtered using a stirring-type cross-flow filtration device 6 and concentrated to, for example, a solid content of 35-65 wt% to obtain an initial concentrated slurry. This eliminates problems such as filter clogging by fine particles, while also providing high efficiency in removing impurities from the slurry before washing. This reduces the amount of washing solution and washing time consumed in the dilution washing process, thereby lowering energy costs and increasing production efficiency.
[0081] Furthermore, in the final concentration step, the washing slurry is concentrated to, for example, a solid content of 50-65 wt% by removing a portion of the mother liquor and washing liquid using a stirring cross-flow filtration device 6. This reduces the amount of mother liquor and washing liquid that needs to be removed in the drying step, thereby lowering energy costs and increasing production efficiency.
[0082] Furthermore, in the crystallization apparatus 10, by circulating the mother liquor with the pump 22, it is easy to generate a high-speed swirling flow with simple equipment. By uniformly mixing the first raw material 12A and the second raw material 12B in a very short time within the high-speed swirling flow, fine particles with a particle size of 7 μm or less, preferably 5 μm or less, can be precipitated. This reduces the particle size of the final obtained fine particle powder and narrows the particle size distribution, thus enabling the production of a high-quality final product.
[0083] Furthermore, in the drying apparatus 8, the hollow stirring blades 178 of each hollow rotating shaft 176 are fixed at axial intervals and partially overlap when viewed in the axial direction. 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, and during this process, 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, compared to hot air drying by convection heat transfer using hot air, moisture can be evaporated more efficiently, resulting in the excellent effect of reducing energy costs and increasing production efficiency.
[0084] It should be noted that the present invention is not limited to the embodiments described above, and additions, deletions, and substitutions of constituent elements with well-known technologies are possible within the scope of the claims.
[0085] In the above description of the embodiment, a case was explained in which the flow path is switched by a three-way valve 74, which is a flow path switching device, to either discard the filtrate discharged from the agitated cross-flow filtration device 6 via the conduit 156 or to store it in the washing liquid tank 50 via the return flow path 76. However, the flow path switching device is not necessarily limited to a three-way valve 74, and the return flow path 76 and the waste flow path 78 may each be equipped with on-off valves, and the opening degree of each on-off valve may be controlled.
[0086] Furthermore, in the above embodiment, the conduit 46 is connected to the three-way valve 42, but it may also 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. [Industrial applicability]
[0087] As described above, the present invention provides a washing and concentrating apparatus for fine particle slurry, a manufacturing apparatus for fine particle powder, and a manufacturing method that can reduce the amount of washing water or washing wastewater used, and enable the stable production of fine particle powder. Therefore, the present invention is applicable to industrial use. [Explanation of Symbols]
[0088] 1. Apparatus for manufacturing fine particle powder 2. Apparatus for manufacturing fine particle slurry 6. Agitated cross-flow filtration system 8. Drying system 10 Crystallizer 12A First raw material 12B Second raw material 12C Mother liquor 14 Discharge hole 16 Conduit 18 reservoirs 20 conduits 22 Pumps 24 Conduits 26 Outlet 28 Conduit 30 Slurry tank 34 Anchor-shaped stirring blades 36 Motor 38 Cleaning fluid source 40 Conduit 42 Three-way valve 44 Shut-off valve 46 Conduit 48 pumps 50 cleaning solution tanks 52 Discharge port 54 Pump 56 Conduit 60 Casing 62 Motor 64 Outlet 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 Drainage channel 82 Slurry tank 84 Anchor-shaped stirring blade 86 Motor 88 Outlet 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 Outlet valve 134 Pump 140 Rotating shaft 142 Agitation 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 fluid discharge port 184 Heat transfer fluid inlet hole 190 Notch 194 Interior wall 196 Top panel 198 Exterior wall 199 Heat transfer fluid channel 200 Heat medium inlet T Transfer direction
Claims
1. A slurry tank for storing a particulate slurry containing fine particles with a particle size of 7 μm or less, A flow path for supplying the stored fine particle slurry to a stirring cross-flow filtration device, A return channel for returning the filtrate discharged from the aforementioned agitated cross-flow filtration device to a slurry tank, A waste channel for discarding the filtrate discharged from the aforementioned agitated cross-flow filtration apparatus, A filtrate sensor comprising at least one of the following: a conductivity sensor for measuring the conductivity of the filtrate discharged from the agitated cross-flow filtration apparatus, or a density sensor for measuring the density of the filtrate, A flow path switching device that switches the flow path between the filtrate discharged from the agitated cross-flow filtration device and the return flow path, A control unit controls the flow path switching device so that when the measurement result of the filtrate sensor is above a threshold, the filtrate flows into the waste flow path, and when the measurement result of the filtrate sensor is below the threshold, the filtrate flows into the return flow path. A washing and concentrating apparatus for fine particle slurry, equipped with [a specific feature].
2. The washing and concentrating apparatus for fine particle slurry according to claim 1, characterized in that 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. The washing and concentrating apparatus for fine particle slurry according to claim 1 or 2, characterized in that the filtrate sensor is provided downstream of the agitated cross-flow filtration apparatus and upstream of the flow path switching device.
4. The washing and concentrating apparatus for a fine particle slurry according to claim 1 or 2, characterized in that the fine particles are a precursor material for a positive electrode for a secondary battery.
5. An apparatus for producing fine particle powder, comprising a conduction heat transfer dryer for drying the fine particle slurry supplied from the fine particle slurry washing and concentration apparatus described in claim 1, wherein the dryer has an agitation heat transfer device, the agitation heat transfer device having a casing with an inlet formed at one end and an outlet hole formed at the other end, a plurality of rotating shafts rotatable about an axis and arranged parallel to each other within the casing, agitation blades fixed to each of the rotating shafts at axial intervals and such that the agitation blades of each rotating shaft partially overlap when viewed in the axial direction, and a heating mechanism for heating these agitation blades, wherein by rotating the rotating shafts, the heated agitation blades heat the fine particle slurry supplied from the inlet and transfer it to the outlet hole, drying the fine particle slurry and converting it into fine particle powder during this process.
6. A dilution-washing-filtration step to obtain a washing slurry by adding a washing solution to a slurry containing fine particles with a particle size of 7 μm or less and a mother liquor, and filtering the slurry using a stirring-type cross-flow filtration device; and a concentration step to obtain a concentrated slurry by concentrating the washing slurry using the stirring-type cross-flow filtration device. A flow path switching step is performed which involves measuring the conductivity or density of the filtrate discharged from the agitated cross-flow filtration device, discarding the filtrate if the conductivity or density is above a threshold, and reusing the filtrate as the washing liquid if the conductivity or density falls below the threshold. A method for producing fine particle powder, comprising a drying step of heating and drying the concentrated slurry to obtain fine particle powder.