A continuous separation method for iron phosphate

Abstract

This invention relates to the field of ferric phosphate separation technology and discloses a continuous ferric phosphate separation method. A feed pump pumps the reacted material from the synthesis reactor into a centrifuge. Under centrifugal force, the solid and liquid phases are separated by sedimentation due to the difference in their specific gravity. The separated liquid is further clarified using a disc separator to reduce the risk of MVR clogging and further improve the solid phase recovery rate. The sludge continuously falls into a dispersion tank below the centrifuge, while a fixed flow rate of washing water is continuously added to achieve the washing purpose. The suspension stirred in the dispersion tank is pumped into a subsequent centrifuge using a feed pump, undergoing multi-stage washing until the conductivity of the washed liquid phase meets the requirements.

Description

Technical Field

[0001] This invention relates to the field of ferric phosphate separation technology, and more specifically to a continuous ferric phosphate separation method. Background Technology

[0002] The production of ferric phosphate requires two important raw materials: an iron source, such as ferrous sulfate or iron powder; and a phosphorus source, such as purified phosphoric acid or monoammonium phosphate. During the ferric phosphate production process, due to differences in the raw materials used or their purity levels, it is inevitable that the newly synthesized ferric phosphate will contain impurities, the only difference being the amount. Therefore, after the ferric phosphate precipitate is synthesized, the mother liquor must be removed first, and then the ferric phosphate precipitate must be washed multiple times to remove impurities and improve product quality.

[0003] Currently, plate and frame washing and dehydration equipment is mainly used for intermittent washing and dehydration. The main problem in this application is that the process is intermittent, which makes it difficult to automate the process and results in unstable product quality. The washing method of this process is divided into the following two types:

[0004] 1) In-machine washing method: The iron phosphate mother liquor is dehydrated using a plate and frame washing machine. The material is then washed several times inside the plate and frame until the conductivity of the liquid phase exiting the plate and frame is qualified. After one washing and dehydration process is completed, the material is re-fed to enter the next washing and dehydration process, and this process is repeated continuously.

[0005] The main problem with this method is that, during washing inside the plate and frame filter press, the washing water only flows along the specific route designed for the plate and frame, resulting in insufficient contact between the washing water and the material. To achieve the desired cleaning effect, more washing water is required, leading to high water consumption. Furthermore, to achieve the desired cleaning effect, the washing water needs to fully wet the filter cake. However, after the filter cake is pressed dry in the plate and frame filter press, its permeability is poor, and the washing water needs a long time to effectively wet the filter cake, resulting in long washing time and low production efficiency.

[0006] 2) External washing method: The mother liquor of ferric phosphate is dehydrated using a plate and frame filter press (its solid phase moisture content is approximately 50%). Then, the solid residue is thoroughly stirred and washed with clean water in a dispersion tank. The next plate and frame filter press is then used for further dehydration until the conductivity of the liquid phase exiting the plate and frame filter press is qualified. After one washing and dehydration process is completed, the material is re-fed for the next washing and dehydration process, and this process is repeated continuously.

[0007] The main problems with this method are: the filter cake after processing by the plate and frame filter press is compressed into a block shape, and it takes a long time to break it up and make pulp outside the machine; the filter cake has poor dewatering properties, the pressing time is long, the production efficiency is low, and the release of production capacity is affected; the material has high viscosity, and multiple unloading processes require manual assistance, resulting in high labor intensity; multiple plate and frame filter presses need to be operated continuously, the number of sets of plate and frame filter presses is large, the area occupied is large, and the initial investment cost is increased. Summary of the Invention

[0008] The present invention aims to provide a continuous separation method for ferric phosphate, in order to solve the problems of discontinuous production, long washing time, unstable production capacity and large equipment footprint in the production of ferric phosphate using plate and frame equipment in the prior art.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: a continuous separation method for ferric phosphate, comprising the following steps:

[0010] A. The ferric phosphate suspension was separated into solid and liquid components using a horizontal screw centrifuge;

[0011] B. Disperse the solid phase separated in step A in a dispersion tank to make pulp;

[0012] C. Repeat steps A and B multiple times until the conductivity of the separated liquid phase meets the requirements, and then flash-dry the separated solid phase.

[0013] Multiple horizontal screw centrifuges and multiple dispersion tanks are arranged alternately in series to repeat steps A and B multiple times. Each repetition is completed by one horizontal screw centrifuge and one dispersion tank.

[0014] Preferably, as an improvement, the horizontal screw centrifuge used has a diameter of 500-800mm, a semi-cone angle of 6-15°, a length-to-diameter ratio of 2.5-4.8, a separation factor of 1200-3000, and a differential speed of 8-40rpm.

[0015] Preferably, as an improvement, the moisture content of the solid phase is controlled to be ≤40% during the repeated execution of steps A and B.

[0016] Preferably, as an improvement, the solid moisture content is controlled to be ≤38% during flash drying.

[0017] Preferably, as an improvement, during the repeated execution of steps A and B, the liquid phases separated in the first two steps are subjected to solid-liquid separation using a mother liquor disc separator. The separated liquid phases are then evaporated and crystallized using an MVR device, and then dehydrated using a piston centrifuge to form ammonium salt or sodium salt products.

[0018] Preferably, as an improvement, during the repeated execution of steps A and B, the liquid phases separated more than twice are subjected to solid-liquid separation using a washing disc separator, and the separated liquid phases are treated by a wastewater treatment system and then recycled for use in the reaction vessel to prepare ferric phosphate suspension.

[0019] Preferably, as an improvement, the filtrate obtained by dehydration in a piston centrifuge is recovered and sent to an MVR device for circulating evaporation.

[0020] Preferably, as an improvement, the solid phase separated by the mother liquor disc separator and the wash water disc separator is sent back to the dispersion tank for further dispersing and pulping.

[0021] Preferably, as an improvement, after dispersing and slurrying in any dispersion tank during the repeated processes of steps A and B, the suspension is aged in an aging kettle, and then subjected to solid-liquid separation in a horizontal screw centrifuge.

[0022] Preferably, as an improvement, steps A and B are repeated 3-8 times.

[0023] The principle of this invention is as follows: The reacted material from the synthesis reactor is pumped into a horizontal screw centrifuge using a feed pump. Under centrifugal force, the solid and liquid phases are separated by sedimentation due to the difference in their specific gravity. The separated liquid is further clarified using a disc separator. The solid phase is returned to the process flow and washed together with the raw materials. The clarified liquid phase enters an MVR (Mechanical Vapor Recycling) system for evaporation and crystallization, reducing the risk of MVR blockage and further improving the solid phase recovery rate. Meanwhile, the sludge continuously falls into a dispersion tank below the centrifuge, while a fixed flow rate of washing water is continuously added to achieve the cleaning purpose. The suspension stirred in the dispersion tank is pumped into a subsequent centrifuge using a feed pump, undergoing multi-stage washing until the conductivity of the washed liquid phase meets the requirements.

[0024] The advantages of this invention include:

[0025] 1. The moisture content of the dehydrated material is lower (the solid phase moisture content of the horizontal screw method is 40%, which is less than 50% of the plate and frame method), which can reduce the number of washing times, shorten the process flow, reduce supporting facilities, and reduce the floor space.

[0026] 2. Differences in working methods: The horizontal screw centrifuge method is a continuous production method, which uses a series of horizontal screw centrifuges and dispersion tanks to achieve continuous washing and separation. The plate and frame centrifuge method is an intermittent production method. Under the same production capacity, the equipment required by this invention occupies less space and requires less investment.

[0027] 3. Different filtration methods: Plate and frame filter presses use filter cloth filtration, while decanter filters use centrifugal sedimentation separation. Decanter filters avoid the problem of material clogging the screen, which can lead to a decrease in production capacity; they offer stable production and create more economic value for customers.

[0028] 4. The entire process is designed with a closed pipeline, which can provide power for material transportation through an electric pump, keeping the site environment clean and tidy.

[0029] 5. High degree of automation, can be controlled by DCS interlocking, requires fewer personnel, and has low labor intensity.

[0030] 6. The liquid phase after MVR evaporation and crystallization is then dehydrated using a piston centrifuge. The piston centrifuge is a filter centrifuge with high dehydration efficiency, large capacity, low moisture content, and high economic benefits. It can effectively separate ammonium salt or sodium salt products.

[0031] 7. Controlling the solid phase moisture content during repeated washing helps reduce the number of washing cycles, shorten the process flow, reduce supporting facilities, and reduce the floor space required.

[0032] 8. Controlling the moisture content of the solid phase during flash drying can reduce energy consumption in the drying process and lower production costs.

[0033] 9. Controlling the solid content of the liquid phase helps reduce material loss, improve product recovery rate, and reduce the treatment pressure on the wastewater treatment system. Attached Figure Description

[0034] Figure 1 This is a flowchart illustrating Embodiment 1 of the present invention. Detailed Implementation

[0035] The following detailed description illustrates the specific implementation method:

[0036] The reference numerals in the accompanying drawings of the instruction manual include: 1. Reactor; 2. Primary horizontal decanter centrifuge; 3. Primary dispersion tank; 4. Secondary horizontal decanter centrifuge; 5. Secondary dispersion tank; 6. Aging vessel; 7. Tertiary horizontal decanter centrifuge; 8. Tertiary dispersion tank; 9. Quaternary horizontal decanter centrifuge; 10. Quaternary dispersion tank; 11. Fifth-stage horizontal decanter centrifuge; 12. Mother liquor disc separator; 13. Piston centrifuge; 14. Wash water disc separator; 15. Flash dryer; 16. Wastewater treatment system; 17. MVR device.

[0037] Example 1, basically as shown in the attached document. Figure 1 As shown: A continuous separation method for ferric phosphate, after the reaction in reactor 1 is completed, the ferric phosphate suspension is pumped into a primary horizontal screw centrifuge 2 by a feed pump. Under the action of centrifugal force, the solid and liquid phases are separated into layers, and the solid phase enters the primary dispersion tank 3 for slurry preparation.

[0038] Next, the suspension in the primary dispersion tank 3 is pumped into the secondary horizontal screw centrifuge 4 by a feed pump. Under the action of centrifugal force, the solid and liquid phases are separated into layers, and the solid phase enters the secondary dispersion tank 5 for pulping.

[0039] The filtrates from the first-stage horizontal decanter centrifuge 2 and the second-stage horizontal decanter centrifuge need to be further processed by the mother liquor disc separator 12. The solid residue is returned to the first-stage dispersion tank 3, and the clarified liquid enters the MVR device 17 for evaporation and crystallization. After being dehydrated by the piston centrifuge 13, the final product ammonium salt or sodium salt is formed. The filtrate separated by the piston centrifuge 13 is transported to the mother liquor tank and then recycled to the MVR device 17 for cyclic evaporation and crystallization.

[0040] Next, the suspension in the secondary dispersion tank 5 is pumped into the aging tank 6 for aging treatment using a feed pump. After aging treatment, the suspension is pumped into the tertiary horizontal screw centrifuge 7. Under the action of centrifugal force, the solid and liquid phases are separated into layers, and the solid phase enters the tertiary dispersion tank 8 for pulping.

[0041] Next, the suspension in the three-stage dispersion tank 8 is pumped into the four-stage horizontal screw centrifuge 9 by a feed pump. Under the action of centrifugal force, the solid and liquid phases are separated into layers, and the solid phase enters the four-stage dispersion tank 10 for pulping.

[0042] Next, the suspension in the fourth-stage dispersion tank 10 is pumped into the fifth-stage horizontal decanter centrifuge 11. Under the high-speed rotation of the centrifugal force, the solid and liquid phases separate into layers, with the solid phase entering the flash dryer 15 for drying. The filtrates from the third-stage, fourth-stage, and fifth-stage horizontal decanter centrifuges 7 and 9 are further processed by a washing disc separator 14. The solid residue is returned to the third-stage dispersion tank 8, and the clarified liquid enters the wastewater treatment system 16. Thus, the continuous washing and dehydration process of ferric phosphate is completed using a combination of centrifuges and separators.

[0043] The treated clear liquid from the wastewater treatment system 16 is recycled back to the reactor for use in the reaction to generate ferric phosphate suspension.

[0044] During the process, each stage of the horizontal screw centrifuge adopts a structure with a diameter of 500-800mm, a semi-cone angle of 6-15°, and a length-to-diameter ratio of 2.5-4.8, applying parameters of a separation factor of 1200-3000 and a differential speed of 8-40rpm. This ensures continuous separation of ferric phosphate. During the washing process using the horizontal screw centrifuge and dispersion tank, controlling the solid phase moisture content to ≤40% reduces the number of washing cycles, shortens the process flow, reduces auxiliary facilities, and minimizes the floor space required. Controlling the solid phase moisture content in the flash drying process to ≤38% reduces energy consumption and production costs. Controlling the liquid phase solid content to ≤0.3% helps reduce material loss, improves product recovery rate, and reduces the pressure on the wastewater treatment system.

[0045] Example 2 differs from Example 1 in that four horizontal screw centrifuges and three dispersion tanks are arranged in series in a continuous alternating manner to continuously wash the ferric phosphate suspension three times.

[0046] Example 3 differs from Example 1 in that: six horizontal screw centrifuges and five dispersion tanks are arranged in series in a continuous alternating manner to continuously wash the ferric phosphate suspension five times.

[0047] Example 4 differs from Example 1 in that seven horizontal screw centrifuges and six dispersion tanks are arranged in series in a continuous alternating manner to continuously wash the ferric phosphate suspension six times.

[0048] Example 5 differs from Example 1 in that it uses eight horizontal screw centrifuges and seven dispersion tanks arranged in series in a continuous alternating manner to continuously wash the ferric phosphate suspension seven times.

[0049] Example 6 differs from Example 1 in that nine horizontal screw centrifuges and eight dispersion tanks are arranged in series in a continuous alternating manner to continuously wash the ferric phosphate suspension eight times.

[0050] Example 7 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a 500mm diameter structure to ensure continuous separation of ferric phosphate.

[0051] Example 8 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a structure with a diameter of 800mm to ensure continuous separation of ferric phosphate.

[0052] Example 8 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a 700mm diameter structure to ensure continuous separation of ferric phosphate.

[0053] Example 9 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a 6° semi-cone angle structure to ensure continuous separation of ferric phosphate.

[0054] Example 10 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a 15° semi-cone angle structure to ensure continuous separation of ferric phosphate.

[0055] Example 11 differs from Example 1 in that each stage of the horizontal screw centrifuge adopts a structure with a half-cone angle of 10°, which ensures the continuous separation of ferric phosphate.

[0056] Example 12 differs from Example 1 in that each stage of the horizontal screw centrifuge adopts a length-to-diameter ratio of 2.5, which ensures the continuous separation of ferric phosphate.

[0057] Example 13 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a length-to-diameter ratio of 4.8 to ensure continuous separation of ferric phosphate.

[0058] Example 14 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a length-to-diameter ratio of 3.0 to ensure continuous separation of ferric phosphate.

[0059] Example 15: The difference between this example and Example 1 is that each stage of the horizontal screw centrifuge uses a separation factor of 1200 to ensure continuous separation of ferric phosphate.

[0060] Example 16 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a separation factor of 3000 to ensure continuous separation of ferric phosphate.

[0061] Example 17 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a separation factor of 2000 to ensure continuous separation of ferric phosphate.

[0062] Example 18 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a differential speed of 8 rpm to ensure continuous separation of ferric phosphate.

[0063] Example 19 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a differential speed of 40 rpm to ensure continuous separation of ferric phosphate.

[0064] Example 20 differs from Example 1 in that each stage of the horizontal screw centrifuge uses a differential speed of 22 rpm to ensure continuous separation of ferric phosphate.

[0065] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A continuous separation method for ferric phosphate, characterized in that: Includes the following steps: A. The ferric phosphate suspension was separated into solid and liquid components using a horizontal screw centrifuge; B. Disperse the solid phase separated in step A in a dispersion tank to make pulp; C. Repeat steps A and B multiple times until the conductivity of the separated liquid phase meets the requirements, and then flash-dry the separated solid phase. Multiple horizontal screw centrifuges and multiple dispersion tanks are arranged alternately in series to repeat steps A and B multiple times. Each repetition is completed by one horizontal screw centrifuge and one dispersion tank. During the repeated execution of steps A and B, the moisture content of the solid phase was controlled to be ≤40%. During the repeated execution of steps A and B, the liquid phases separated in the first two steps are separated into solid and liquid phases using a mother liquor disc separator. The separated liquid phases are evaporated and crystallized using an MVR device, and then dehydrated by a piston centrifuge to form ammonium salt or sodium salt products. During the repeated execution of steps A and B, the liquid phase that was separated for the third time was subjected to solid-liquid separation using a washing disc separator. The separated liquid phase was treated by a wastewater treatment system and then recycled for use in the reactor to prepare ferric phosphate suspension. The solid phase separated by the mother liquor disc separator and the wash water disc separator is sent back to the dispersion tank for further dispersing and pulping. During the repeated processes of steps A and B, after dispersing and slurrying in any dispersion tank, the suspension is aged in an aging kettle, and then subjected to solid-liquid separation in a horizontal screw centrifuge.

2. The continuous separation method for ferric phosphate according to claim 1, characterized in that: The horizontal screw centrifuge used has a diameter of 500-800mm, a half-cone angle of 6-15°, a length-to-diameter ratio of 2.5-4.8, a separation factor of 1200-3000, and a differential speed of 8-40rpm.

3. The continuous separation method for ferric phosphate according to claim 1, characterized in that: During flash drying, the moisture content of the solid phase should be controlled to be ≤38%.

4. The continuous separation method for ferric phosphate according to claim 1, characterized in that: The filtrate obtained by dehydration in a piston centrifuge is recovered and sent to an MVR unit for circulating evaporation.

5. The continuous separation method for ferric phosphate according to claim 1, characterized in that: Repeat steps A and B 3-8 times consecutively.

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