A low-magnetic energy-saving method for preparing battery-grade high-purity phosphate

Abstract

The application discloses a low-magnetic energy-saving method for preparing battery-grade high-purity phosphate, and relates to the technical field of preparation of phosphate for battery materials. In view of the problems of incomplete magnetic foreign matter control path and insufficient utilization of neutralization reaction heat, the method comprises the following steps: purifying and filtering crude wet-process phosphoric acid, and performing neutralization reaction in a neutralization kettle by adopting a carbon fiber reinforced composite stirring shaft and a carbon fiber reinforced composite stirring blade; ammonium phosphate dihydrogen phosphate crystal slurry is conveyed through a steel lining polytetrafluoroethylene pipeline, enters a centrifuge through a product slurry filtering unit and a product slurry electromagnetic iron removal unit; mother liquor slurry returns to the neutralization kettle through a mother liquor circulating filtering unit and a mother liquor circulating electromagnetic iron removal unit; after wet crystal drying and cooling, the wet crystal is fed into a material sealing pump through a gas locking unloading mechanism, and is conveyed through a uniform polypropylene pipeline by a Roots blower; and the neutralization kettle cooling water is heated in a step alternating flow mode through a mother liquor waste heat heat exchange coil.

Description

Technical Field

[0001] This invention relates to the field of phosphate preparation for battery materials and wet phosphate chemical process control technology, specifically to a low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate. Background Technology

[0002] Ammonium dihydrogen phosphate (MDH) can serve as a phosphorus source in the preparation of iron phosphate and lithium iron phosphate materials. When using MDH in battery materials, in addition to controlling the main content of MDH, moisture, and water-insoluble matter, it is also necessary to control metallic impurities such as iron, chromium, and nickel, as well as magnetically responsive particulate matter. When magnetically responsive particulate matter enters the subsequent cathode material, it may continue to disperse during grinding, mixing, and sintering, affecting the consistency of the subsequent battery materials.

[0003] The production process of ammonium dihydrogen phosphate from wet-process phosphoric acid typically includes wet-process phosphoric acid purification, ammonia neutralization, concentration and crystallization, solid-liquid separation, drying, and transportation. Wet-process phosphoric acid purification primarily removes sulfate ions, fluorine-containing components, and ionic metal impurities introduced from the raw materials. After raw material purification, solid metal particles may still be generated in the material contact components of the production equipment due to corrosion, erosion, or mechanical friction. The removal of ionic impurities cannot replace the control of solid magnetic foreign matter generated by the production equipment.

[0004] The stirring shaft and impeller of the neutralization vessel are constantly immersed in an acid-base slurry containing solid particles. After the protective layer on the surface of the metal stirring components is eroded by particles, the metal substrate may remain in continuous contact with the slurry. Localized flow velocity variations exist at bends, reductions in diameter, and near valves in the crystal slurry conveying pipeline; localized erosion can accelerate metal surface wear. The distribution plate, sprockets, chains, and metal conveying components during the wet crystal drying and dry material lifting processes may also become sources of magnetic foreign matter.

[0005] When magnetic rods or magnetic separators are only installed at the finished product outlet, particulate matter already encased in crystals cannot fully contact the magnetic medium. During the recycling of centrifugal filtrate and reprocessed ammonium dihydrogen phosphate, particulate matter in the mother liquor will re-enter the neutralization and crystallization process along with the recycled material. Cleaning with fixed excitation parameters and fixed time intervals cannot reflect the magnetic foreign matter load of different batches of mother liquor; the magnetic medium's capture capacity decreases after reaching a high load. Furthermore, in high-solids-content crystal slurries, small magnetic foreign matter is easily physically entrained by crystal clusters, and the static magnetic field generated by conventional constant DC excitation is insufficient to overcome spatial steric hindrance, causing magnetic foreign matter to penetrate the iron removal unit.

[0006] The heat released during the neutralization reaction is typically carried away by the cooling water in the neutralization vessel. The mother liquor slurry contains a high concentration of ammonium dihydrogen phosphate and other soluble components; as the temperature of the mother liquor slurry decreases, crystals easily precipitate, causing an increase in the pressure differential of the circulation pipeline. In conventional production processes, the temperature of the mother liquor slurry is maintained by externally supplied steam, and the heat carried by the cooling water in the neutralization vessel does not form a stable heat coupling with the mother liquor circulation process. Furthermore, when utilizing the waste heat from the mother liquor in the heat exchange coil to recover the heat of the neutralization reaction, constant flow heating easily leads to the formation of a stable fluid boundary layer and a salt-rich microscopic retention layer on the heat exchange surface, causing a continuous decrease in the heat transfer coefficient and forcing the system to consume additional high-grade steam.

[0007] Fixed-speed stirring, fixed-flow circulation, fixed-volume pneumatic conveying, and fixed-heat supply can cause a mismatch between equipment output and actual material load. When material concentration, crystal particle size, mother liquor saturation temperature, and equipment pressure difference change, fixed operating parameters may result in ineffective energy consumption, filter clogging, excessive magnetic medium load, mother liquor crystallization, or increased collisions during pneumatic conveying.

[0008] Therefore, a preparation method is needed that maintains the basic process boundaries of wet phosphoric acid purification, ammonia neutralization, concentration crystallization, and centrifugal separation, so that materials in different physical states correspond to different low magnetic contact interfaces, so that the product crystal slurry and mother liquor slurry pass through magnetic foreign matter removal paths respectively, so that wet crystal drying and cooling and dry material transportation form a closed continuous connection, and so that the heat of neutralization reaction is used to maintain the circulation and transportation state of the mother liquor slurry. At the same time, it can effectively remove the physical entrainment of magnetic foreign matter in high solid content crystal slurry and maintain the long-term efficient operation of the mother liquor waste heat exchange coil. Summary of the Invention

[0009] The purpose of this invention is to provide a low-magnetic-energy-saving method for preparing battery-grade high-purity phosphate, which solves the technical problems of incomplete magnetic foreign matter control path and insufficient utilization of neutralization reaction heat in the preparation of battery-grade ammonium dihydrogen phosphate.

[0010] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate includes: Crude wet-process phosphoric acid is subjected to desulfurization, defluorination, and chemical precipitation to remove heavy metals in sequence to obtain purified phosphoric acid. The purified phosphoric acid and ammonia source are filtered using a purified phosphoric acid pre-filter and an ammonia source pre-filter respectively, both equipped with polypropylene filter elements. The filtered purified phosphoric acid and ammonia source are fed into a neutralization vessel, where they undergo a neutralization reaction under the stirring action of a carbon fiber reinforced composite stirring shaft and a carbon fiber reinforced composite stirring blade to form a neutralized slurry. The neutralized slurry is evaporated, concentrated, and cooled to crystallize, forming an ammonium dihydrogen phosphate crystal slurry; The ammonium dihydrogen phosphate crystal slurry is transported through a steel-lined polytetrafluoroethylene (PTFE) pipe, with the PTFE lining of the pipe forming the pipe contact surface of the ammonium dihydrogen phosphate crystal slurry. The ammonium dihydrogen phosphate crystal slurry passes through a product slurry filtration unit and a product slurry electromagnetic iron removal unit in sequence before entering a centrifuge for solid-liquid separation, yielding wet crystals and centrifugal filtrate. The centrifuged filtrate and reprocessed ammonium dihydrogen phosphate are fed into a mother liquor collection tank, where they are mixed and dissolved to form a mother liquor slurry. The mother liquor slurry is then passed through a mother liquor circulation filtration unit and a mother liquor circulation electromagnetic iron removal unit before being returned to the neutralization vessel. The wet crystals are fed into a vacuum continuous drying and cooling machine, where they are pushed by a hollow spiral in a closed negative pressure environment to continuously complete the drying and cooling process. The dried and cooled ammonium dihydrogen phosphate is fed into a material sealing pump, and the dried and cooled ammonium dihydrogen phosphate is transported through a homopolymer polypropylene pipeline by a positive pressure airflow provided by a Roots blower; and the cooling water of the neutralization vessel, which absorbs the heat generated by the neutralization reaction, is sent to the mother liquor waste heat exchange coil set in the mother liquor collection tank, and the mother liquor waste heat exchange coil is used to heat the mother liquor slurry, so that the mother liquor slurry is kept in a molten state that can be circulated and transported.

[0011] As a preferred embodiment of the present invention, the purified phosphoric acid pre-filter and the ammonia source pre-filter are respectively equipped with inlet and outlet pressure difference detection components; when the inlet and outlet pressure difference of any pre-filter reaches the corresponding termination pressure difference, the feeding of the corresponding pre-filter is stopped and the polypropylene filter element is replaced; the polypropylene filter element is put back into use without backwashing.

[0012] As a preferred embodiment of the present invention, the carbon fiber reinforced composite material stirring shaft and the carbon fiber reinforced composite material stirring blade form a continuous non-metallic contact surface below the highest slurry level, the metal connecting component between the carbon fiber reinforced composite material stirring shaft and the transmission component is located above the highest slurry level, and a replaceable non-metallic wear-resistant component is provided at the high scouring position of the carbon fiber reinforced composite material stirring blade.

[0013] As a preferred embodiment of the present invention, the bend of the steel-lined polytetrafluoroethylene pipe adopts a long-radius flow transition, and a replaceable non-metallic wear-resistant internal component is provided at the high scouring position of the outer arc of the bend; the speed of the delivery pump is adjusted according to the volumetric flow rate of the ammonium dihydrogen phosphate crystal slurry and the pressure difference between the inlet and outlet of the bend.

[0014] In a preferred embodiment of the present invention, the filter opening of the product slurry filtration unit is larger than the upper limit of the characteristic particle size of the ammonium dihydrogen phosphate crystal slurry, and the filter opening of the mother liquor circulation filtration unit is smaller than the filter opening of the product slurry filtration unit. This ensures that the product slurry filtration unit does not retain product crystals that meet the particle size requirements, and that the mother liquor circulation filtration unit intercepts solid foreign matter in the mother liquor slurry. The upper limit of the characteristic particle size of the product crystals refers to the particle size corresponding to a cumulative volume fraction of 90% among the crystals that meet the product particle size requirements.

[0015] As a preferred embodiment of the present invention, the inlet magnetic foreign matter concentration, outlet magnetic foreign matter concentration, slurry flow rate, and cumulative treated mass of the product slurry electromagnetic iron removal unit and the mother liquor circulating electromagnetic iron removal unit are detected respectively; the excitation state or slurry flow rate is adjusted according to the difference between the inlet magnetic foreign matter concentration and the outlet magnetic foreign matter concentration, and the corresponding electromagnetic iron removal unit is isolated and the magnetic medium is cleaned when the outlet magnetic foreign matter concentration reaches the cleaning trigger value.

[0016] As a preferred embodiment of the present invention, after the reworked ammonium dihydrogen phosphate is added to the mother liquor collection tank, it is heated and circulated through the mother liquor waste heat exchange coil; after the content of undissolved crystals in the mother liquor slurry reaches the dissolution endpoint value, the mother liquor slurry is sequentially passed through the mother liquor circulation filtration unit and the mother liquor circulation electromagnetic iron removal unit, and returned to the neutralization kettle when the composition and magnetic foreign matter mass concentration of the mother liquor slurry meet the return conditions.

[0017] As a preferred embodiment of the present invention, the vacuum continuous drying and cooling machine includes a drying zone and a cooling zone arranged along the material movement direction; the rotational speed of the hollow screw and the flow rate of the heating medium are adjusted according to the material temperature in the drying zone, the moisture content of the discharged gas, the condensate generation state, and the torque of the hollow screw; and the material enters the cooling zone after the material moisture content reaches the drying endpoint value; and the material enters the material sealing pump after the material temperature reaches the cooling endpoint value.

[0018] As a preferred embodiment of the present invention, the outlet pressure of the Roots blower, the pipeline pressure difference of the homopolymer polypropylene pipeline, the dew point of the conveyed gas, the dry material temperature, and the conveying mass per unit time are detected; based on the detection results, the rotational speed of the Roots blower and the feeding state of the material sealing pump are adjusted so that the conveying speed in the homopolymer polypropylene pipeline is higher than the lower limit of stable conveying and lower than the upper limit of crystal collision control.

[0019] As a preferred embodiment of the present invention, the corresponding saturation temperature of the mother liquor is determined based on the concentration of the mother liquor slurry, and the temperature margin between the actual temperature of the mother liquor slurry and the saturation temperature of the mother liquor is calculated; when the temperature margin is lower than 4°C, the flow rate of cooling water entering the neutralization vessel into the waste heat exchange coil of the mother liquor is increased; when the temperature margin is higher than 8°C, the flow rate of cooling water entering the neutralization vessel into the waste heat exchange coil of the mother liquor is reduced or the cooling water of the neutralization vessel is returned to the cooling water circulation system via a bypass.

[0020] As a preferred embodiment of the present invention, the magnetic foreign matter mass concentration of the same production batch is obtained at the inlet and outlet of at least two production units, and the magnetic foreign matter increment of the corresponding production unit is determined according to the difference between the magnetic foreign matter mass concentration at the outlet and the magnetic foreign matter mass concentration at the inlet; the production units that need to be inspected for contact surfaces, maintained for filter units, or cleaned for electromagnetic iron removal units are located according to the magnetic foreign matter increment of each production unit.

[0021] As a preferred technical solution of the present invention, the power consumption, steam consumption, and product quality of the stirring drive equipment, evaporation and concentration equipment, mother liquor circulation equipment, vacuum continuous drying and cooling machine, and Roots blower are obtained to determine the power consumption and steam consumption per unit product; and the adjustment commands for stirring speed, transfer pump speed, mother liquor circulation flow rate, excitation state, hollow screw speed, heating medium flow rate, Roots blower speed, or neutralization kettle cooling water flow rate are output based on the increase in magnetic foreign matter, power consumption per unit product, and steam consumption per unit product.

[0022] In a preferred embodiment of the present invention, in the step of passing the ammonium dihydrogen phosphate crystal slurry sequentially through a product slurry filtration unit and a product slurry electromagnetic iron removal unit before entering a centrifuge for solid-liquid separation to obtain wet crystals and centrifugal filtrate: the real-time solid content and real-time dynamic viscosity of the ammonium dihydrogen phosphate crystal slurry are obtained; based on the real-time solid content and the real-time dynamic viscosity, a low-frequency pulsating AC excitation current is superimposed on the background DC excitation current of the product slurry electromagnetic iron removal unit, causing magnetic foreign matter in the product slurry electromagnetic iron removal unit to undergo forced vibration in the high-gradient static magnetic field established by the background DC excitation current, thereby detaching from the physical entrainment of crystal particles in the ammonium dihydrogen phosphate crystal slurry; wherein, the pulsation frequency of the low-frequency pulsating AC excitation current is negatively correlated with the real-time dynamic viscosity, and the pulsation amplitude of the low-frequency pulsating AC excitation current is positively correlated with the real-time solid content.

[0023] In a preferred embodiment of the present invention, in the step of feeding the cooling water from the neutralization vessel, after absorbing the heat generated by the neutralization reaction, into a mother liquor waste heat exchange coil disposed in the mother liquor collection tank, and supplying heat to the mother liquor slurry through the mother liquor waste heat exchange coil: obtaining the real-time concentration of the mother liquor slurry and determining the mother liquor saturation temperature corresponding to the real-time concentration; calculating the temperature margin between the actual temperature of the mother liquor slurry and the mother liquor saturation temperature; when the temperature margin is within a set safe range of 4°C to 8°C, feeding the cooling water from the neutralization vessel into the mother liquor waste heat exchange coil in a step-alternating flow mode; the step-alternating flow mode... The variable flow rate mode includes alternating high flow rate input phases and low flow rate input phases. During the high flow rate input phase, the transient shear force generated by the neutralization vessel cooling water within the mother liquor waste heat exchange coil is used to break the fluid boundary layer on the inner wall of the mother liquor waste heat exchange coil. During the low flow rate input phase, the residence time of the neutralization vessel cooling water within the mother liquor waste heat exchange coil is extended to extract sensible heat. The real-time total heat transfer coefficient of the mother liquor waste heat exchange coil is calculated. When the real-time total heat transfer coefficient is lower than the clean heat transfer coefficient threshold, the duration of the high flow rate input phase is extended and the duration of the low flow rate input phase is shortened.

[0024] Compared with the prior art, the present invention has the following beneficial effects: This invention solves the problem of magnetic foreign matter entering the product due to corrosion and wear of metal contact surfaces by configuring low-magnetic contact interfaces for the main material flow, circulating material flow, and crystal post-processing path in the production process of ammonium dihydrogen phosphate for batteries. Purified phosphoric acid and ammonia sources are filtered through polypropylene filter cartridges, reducing solid particles introduced by the raw materials; the neutralization reactor uses a carbon fiber reinforced composite stirring shaft and carbon fiber reinforced composite stirring blades, ensuring no metal exposure below the highest slurry level, thus suppressing the generation of magnetic foreign matter at the source; the ammonium dihydrogen phosphate crystal slurry is transported through steel-lined polytetrafluoroethylene pipes, with replaceable non-metallic wear-resistant internal components on the outer arc of the bends, avoiding metal contamination caused by pipe wear.

[0025] Before the product slurry enters the centrifuge, a product slurry filtration unit and a product slurry electromagnetic iron removal unit are set up to effectively remove free magnetic foreign matter in the main material flow before solid-liquid separation. Before the centrifugal filtrate and the mother liquor slurry formed by reprocessed ammonium dihydrogen phosphate return to the neutralization tank, they pass through a mother liquor circulation filtration unit and a mother liquor circulation electromagnetic iron removal unit to form an independent circulating material iron removal path, reducing the accumulation of magnetic foreign matter.

[0026] Furthermore, a low-frequency pulsating AC excitation current superposition control based on real-time solid content and real-time dynamic viscosity is introduced into the electromagnetic iron removal unit of the product slurry. This causes the magnetic foreign matter physically entrained by crystal clusters to vibrate under forced vibration and detach, improving the capture efficiency of magnetic foreign matter under high solid content conditions. Cooling water from the neutralization vessel is fed into the mother liquor waste heat exchange coil in a step-alternating flow mode. The transient shear force generated during the high-flow-rate input stage disrupts the fluid boundary layer, and the residence time is extended during the low-flow-rate input stage to extract sensible heat, improving the heat transfer efficiency of the mother liquor waste heat exchange coil and reducing supplementary steam consumption. An airlock unloading mechanism is installed between the vacuum continuous drying cooler and the material sealing pump to isolate the negative pressure drying environment from the positive pressure pneumatic conveying environment, preventing air backflow that could lead to excessive product moisture content. Joint diagnosis of magnetic foreign matter increment and unit product energy consumption across multiple production units can locate production units requiring maintenance, improving system stability. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is the main flowchart of the method of the present invention.

[0029] Figure 2 This is a flowchart of the slurry treatment and mother liquor recycling process of the product of this invention. Detailed Implementation

[0030] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0031] The following implementation describes the complete material flow, magnetic foreign matter control path, and heat flow of ammonium dihydrogen phosphate for batteries. The main material flow consists of a coarse wet phosphoric acid purification system, a purified phosphoric acid pre-filter, an ammonia source pre-filter, a neutralization kettle, an evaporation and concentration device, a cooling crystallization device, a product slurry filtration unit, a product slurry electromagnetic iron removal unit, and a centrifuge. The mother liquor collection tank, mother liquor circulation filtration unit, mother liquor circulation electromagnetic iron removal unit, and neutralization kettle constitute the mother liquor circulation flow. A vacuum continuous drying cooler, a material sealing pump, homopolymer polypropylene piping, and a Roots blower constitute the post-crystallization processing path. The neutralization kettle, mother liquor waste heat exchange coil, and cooling water circulation system constitute the neutralization reaction heat utilization path.

[0032] In this invention, the magnetic foreign matter concentration refers to the ratio of the sum of the masses of iron, chromium, and nickel contained in magnetically responsive particles obtained under the same sampling mass, the same magnetic extraction conditions, and the same elemental quantification conditions to the sample mass, expressed in μg / kg. The inlet and outlet samples of the production unit are identified using the same production batch identifier and are corresponding according to the average residence time of the material. The magnetic foreign matter concentration is not used interchangeably with the total amount of ionic iron, ionic chromium, or ionic nickel in the solution.

[0033] For magnetic foreign matter detection, a 1 kg liquid, slurry, or solid sample is weighed. For solid samples, a 10% (w / w) dispersion is formed using high-purity water. After dispersion in a sealed non-metallic container, the sample undergoes three magnetic extractions using a magnetic extraction assembly with consistent magnetic field strength and gradient. The iron, chromium, and nickel content of the magnetic extraction sample is determined after acid digestion. The sum of the iron, chromium, and nickel contents obtained from the three magnetic extractions is divided by the sample mass to obtain the magnetic foreign matter concentration. The same container, dispersion time, magnetic extraction time, and digestion process are used for both inlet and outlet samples.

[0034] The upper limit of the characteristic particle size of the product crystals refers to the particle size corresponding to a cumulative volume fraction of 90% among the crystals that meet the product particle size requirements. The filter opening of the product slurry filtration unit is larger than the upper limit of the characteristic particle size of the product crystals. The product slurry filtration unit is used to intercept equipment debris, lining fragments, or aggregated foreign matter larger than the size of the filter opening. The mother liquor circulation filtration unit processes the dissolved mother liquor slurry. The mother liquor circulation filtration unit can use a filter opening smaller than that of the product slurry filtration unit.

[0035] The saturation temperature of the mother liquor is determined by the mother liquor concentration and isothermal equilibrium experiments. Mother liquor samples of different concentrations are gradually cooled, and the temperatures at which stable crystal nuclei first appear are recorded, creating a table corresponding to the mother liquor concentration and its saturation temperature. The detection and control unit retrieves this table based on the mother liquor density, phosphorus content, or total salt concentration to obtain the saturation temperature corresponding to the current mother liquor composition.

[0036] In one implementation, the calculations related to materials, magnetic foreign matter, and energy are based on the principle of the molar flow rate of phosphoric acid in purified phosphoric acid. Calculated based on the purified phosphoric acid mass flow rate and phosphoric acid mass fraction.

[0037] in The molar flow rate of phosphoric acid in the purified phosphoric acid is expressed in kmol / h. The mass flow rate of purified phosphoric acid is expressed in kg / h. To purify the phosphoric acid mass fraction in phosphoric acid, The molar mass of phosphate is taken as 98 kg / kmol. The ammonia source is expressed as the mass flow rate of anhydrous ammonia. Determined based on the molar flow rate of phosphate and the molar ratio of ammonia to phosphorus.

[0038] in This represents the mass flow rate of anhydrous ammonia in the ammonia source, expressed in kg / h. The molar mass of ammonia is taken as 17 kg / kmol. This represents the molar ratio of ammonia to phosphoric acid. It also represents the mass of water that needs to be removed during the evaporation and concentration stage. The concentration was determined based on the mass flow rate of the neutralized slurry, the mass flow rate of ammonium dihydrogen phosphate, and the mass fraction at the concentration endpoint.

[0039] in This is the mass flow rate of evaporated water, expressed in kg / h. The mass flow rate of the neutralized slurry entering the evaporation and concentration equipment is expressed in kg / h. The mass flow rate of ammonium dihydrogen phosphate in the neutralizing slurry is expressed in kg / h. This represents the mass fraction of ammonium dihydrogen phosphate in the final concentrated feed solution. Increment of magnetic foreign matter in the production unit. Calculated based on the difference between the mass concentration of magnetic foreign matter at the export port and the mass concentration of magnetic foreign matter at the inlet port in the same batch.

[0040] in For the first The increase in magnetic foreign matter per production unit, in μg / kg. For the first The mass concentration of magnetic foreign matter at the outlet of each production unit. For the first The mass concentration of magnetic foreign matter at the inlet of each production unit. The magnetic foreign matter capture efficiency of the electromagnetic iron removal unit. Calculated by dividing the difference in magnetic foreign matter mass concentration at the inlet and outlet by the inlet magnetic foreign matter mass concentration.

[0041] in To improve the magnetic foreign object capture efficiency of the electromagnetic iron removal unit, The mass concentration of magnetic foreign matter at the inlet of the electromagnetic iron removal unit. This refers to the mass concentration of magnetic foreign matter at the outlet of the electromagnetic iron removal unit. Mother liquor temperature margin. Calculated based on the difference between the actual temperature of the mother liquor and the saturation temperature of the mother liquor corresponding to the current concentration.

[0042] in This is the temperature margin for the mother liquor, in °C. This refers to the actual temperature of the mother liquor. Mother liquor mass concentration The corresponding saturation temperature of the mother liquor. The recovered heat provided by the cooling water in the neutralization vessel to the mother liquor slurry. Calculated based on cooling water mass flow rate, specific heat capacity, and temperature difference before and after heat exchange.

[0043] in The unit of heat recovery is kJ / h. The mass flow rate of cooling water from the neutralization vessel entering the waste heat exchange coil of the mother liquor is expressed in kg / h. The specific heat capacity of the cooling water is taken as 4.18 kJ / (kg·℃). This refers to the temperature at which the cooling water from the neutralization vessel enters the residual heat exchange coil of the mother liquor. This refers to the temperature of the cooling water in the neutralization vessel as it leaves the residual heat exchange coil of the mother liquor. The amount of supplementary steam reduced in response to the recovered heat. The calculation is based on multiplying the recovered heat by the effective heat exchange utilization coefficient and then dividing by the effective enthalpy drop of the makeup steam.

[0044] in The amount of steam lost per unit time is expressed in kg / h. The effective utilization coefficient of heat transfer from the mother liquor waste heat exchange coil to the mother liquor slurry was calibrated through cold mold testing. To compensate for the effective enthalpy drop of steam under mother liquor heating conditions, the steam parameters are obtained from a table, with units of kJ / kg. The mass of moisture to be removed by the vacuum continuous drying and cooling machine. Calculated based on the wet crystal feed mass flow rate and the moisture content of the wet basis before and after drying.

[0045] in The value represents the mass of water evaporated per unit time, expressed in kg / h. This is the mass flow rate of wet crystal feed, expressed in kg / h. The wet basis moisture content is the wet basis of the wet crystal feed. Moisture content of dried ammonium dihydrogen phosphate on a wet basis. Energy consumption per unit product. Calculated based on the ratio of the sum of electrical energy consumed by all electrical equipment to the quality of qualified products within the statistical period.

[0046] in This refers to the energy consumption per unit of product, expressed in kWh / kg. For the first time in the statistical period The average active power of the electrical equipment in the unit, expressed in kW. For the first The operating time of the electrical equipment used in Taiwan during the statistical period, in hours. The quantity represents the mass of qualified ammonium dihydrogen phosphate obtained within the statistical period, in kg. Number the electrical equipment. This represents the total number of electrical devices included in the statistics.

[0047] To facilitate a better understanding of the invention by those skilled in the art, the invention will be further illustrated below with specific implementation examples.

[0048] Example 1: In this example, purified phosphoric acid with a mass flow rate of 2000 kg / h was used as the neutralization feedstock. The purified phosphoric acid contained 50% phosphoric acid by mass. The purified phosphoric acid was obtained by desulfurization, defluorination, and heavy metal removal by chemical precipitation of crude wet-process phosphoric acid. Before entering the crude wet-process phosphoric acid purification system, the contents of sulfate, fluorine, iron, chromium, and nickel were tested.

[0049] The desulfurization process uses a 20% (w / w) barium carbonate slurry. The amount of barium carbonate added is determined based on the molar amount of sulfate in the crude wet-process phosphoric acid, and increased by 5% from the stoichiometric amount of sulfate. The desulfurization reaction temperature is controlled at 60℃, and the stirring time is 60 min. The defluorination process uses a silicon source with a silica content of not less than 95%. The amount of silicon source added is determined based on the fluorine content. The defluorination reaction temperature is controlled at 70℃, and the stirring time is 40 min. For the chemical precipitation to remove heavy metals, a sulfide precipitant is added to a closed reaction tank to convert metal ions that can form insoluble sulfides into precipitates. The sulfide precipitant, for example, is sodium sulfide, added at 1.2 times the stoichiometric amount of the total molar amount of iron, chromium, and nickel in the crude wet-process phosphoric acid. The reaction pH is controlled at 4.5 to 5.5, the reaction temperature at 55℃ to 65℃, and the stirring reaction time is 30 to 45 min. After chemical precipitation, the solution passes through a non-metallic-lined solid-liquid separation device to obtain purified phosphoric acid.

[0050] The purified phosphoric acid pre-filter uses a polypropylene shell and a pleated polypropylene filter element, with a nominal filtration accuracy of 10μm. The rated flow rate of the purified phosphoric acid pre-filter is 2.5m³ / h. 3 The initial inlet and outlet pressure difference is 0.02 MPa, and the final pressure difference is 0.15 MPa. When the inlet and outlet pressure difference reaches 0.15 MPa, close the feed valve and discharge valve of the purified phosphoric acid pre-filter, empty the purified phosphoric acid pre-filter, and replace the polypropylene filter element. After replacement, flush the polypropylene filter element with high-purity water until the conductivity of the effluent stabilizes before putting it into operation.

[0051] Polypropylene filter cartridges replaced from the purified phosphoric acid pre-filter are reused without backwashing. The ammonia source is gaseous ammonia formed by the vacuum vaporization of anhydrous liquid ammonia. A vaporizer is installed between the liquid ammonia storage equipment and the ammonia source pre-filter. The ammonia source pre-filter is used to intercept solid particles entrained during vaporization and transportation. It uses a polypropylene support structure and a polypropylene filter cartridge, with a nominal filtration accuracy of 20 μm. The final pressure differential of the ammonia source pre-filter is 0.08 MPa. After passing through the ammonia source pre-filter, the gaseous ammonia enters the gaseous ammonia distribution pipe of the neutralization reactor.

[0052] Based on a purified phosphoric acid mass flow rate of 2000 kg / h, a phosphoric acid mass fraction of 50%, and a phosphoric acid molar mass of 98 kg / kmol, the molar flow rate of phosphoric acid in the purified phosphoric acid is calculated to be 10.204 kmol / h. The ammonia-phosphorus molar ratio is set to 1.01. Based on an ammonia molar mass of 17 kg / kmol, the anhydrous ammonia mass flow rate is calculated to be 175.2 kg / h. The detection and control unit maintains the ammonia-phosphorus molar ratio through a purified phosphoric acid mass flow meter, an online density meter, and a gaseous ammonia mass flow meter.

[0053] The neutralization reactor employs a pressurized, sealed structure. The neutralization reaction temperature is controlled at 102℃, and the pressure in the reactor is controlled at 0.15 MPa (absolute pressure). Purified phosphoric acid is continuously added from the top of the reactor, while gaseous ammonia is added through a gaseous ammonia distribution pipe below the slurry surface. The effective volume of the reactor ensures an average residence time of 45 minutes for the neutralized slurry. The final pH of the neutralization reaction is controlled between 4.2 and 4.6. The tail gas from the neutralization reactor is returned to the ammonia source treatment system after condensation and absorption.

[0054] The neutralization reactor is equipped with a carbon fiber reinforced composite stirring shaft and four carbon fiber reinforced composite stirring blades. The carbon fiber reinforced composite stirring shaft is made of continuous carbon fiber reinforced polyetheretherketone (PEEK) composite material. The carbon fiber reinforced composite stirring blades are molded from carbon fiber fabric reinforced PEEK composite material. The metal connection between the carbon fiber reinforced composite stirring shaft and the drive shaft is located 200 mm above the highest slurry level. The reactor lid is equipped with a polytetrafluoroethylene (PTFE) isolation sleeve and a double-end sealing structure to prevent slurry from contacting the metal connection structure during normal liquid level fluctuations and foam fluctuations.

[0055] The carbon fiber reinforced composite impeller blades feature replaceable non-metallic wear-resistant components at their leading edge. These components consist of zirconia ceramic strips combined with polyetheretherketone (PEEK) clamps, with no exposed metal fasteners on the zirconia ceramic strips. The carbon fiber reinforced composite stirring shaft, impeller blades, replaceable non-metallic wear-resistant components, and PTFE isolation sleeve form a continuous non-metallic contact surface below the highest slurry level. The stirring speed is 120 r / min, and the stirring motor is frequency-controlled.

[0056] The neutralization slurry mass flow rate was 2175.2 kg / h. Based on the stoichiometric relationship, the theoretical mass flow rate of ammonium dihydrogen phosphate in the neutralization slurry was 1173.5 kg / h. The evaporation and concentration equipment used a reduced pressure evaporation method with an evaporation pressure of 45 kPa (absolute pressure). The final concentration fraction of ammonium dihydrogen phosphate was 68%. Based on the neutralization slurry mass flow rate of 2175.2 kg / h, the ammonium dihydrogen phosphate mass flow rate of 1173.5 kg / h, and the final concentration fraction of 68%, the evaporation water mass flow rate was 449.5 kg / h. The concentrated liquid was at a temperature of 82℃ before entering the cooling crystallization equipment. The cooling crystallization equipment used jacket cooling and internal circulation mixing. Ammonium dihydrogen phosphate seed crystals with a particle size ranging from 100 μm to 200 μm from the previous production batch were added to the concentrated liquid at 80℃; the seed crystal mass was 0.2% of the concentrated liquid mass. The cooling process involves reducing the temperature from 80℃ to 50℃ at a rate of 8℃ / h, then reducing it from 50℃ to 30℃ at a rate of 4℃ / h, and holding it at 30℃ for 40 minutes. The stirring speed of the cooling crystallization equipment is 60 r / min.

[0057] After cooling and crystallization, the solid content of the ammonium dihydrogen phosphate crystal slurry was 48%. Laser particle size analysis showed that a cumulative volume fraction of 10% corresponded to a particle size of 90 μm, 50% to 210 μm, and 90% to 420 μm. 420 μm was designated as the upper limit of the characteristic particle size of the product crystals in this embodiment. The ammonium dihydrogen phosphate crystal slurry was transported through a steel-lined PTFE pipe. The nominal diameter of the PTFE-lined pipe was 100 mm, with the steel outer layer bearing internal pressure and providing external support, and the PTFE inner lining thickness being 6 mm. The actual transport temperature of the ammonium dihydrogen phosphate crystal slurry was 30°C. Long-radius bends with a curvature radius 1.5 times the nominal diameter were used. A replaceable, 4 mm thick, wear-resistant polyetheretherketone (PEEK) inner component was installed on the outer arc of the bend.

[0058] The volumetric flow rate of the steel-lined PTFE pipe is 3.2 m³ / s. 3 / h. The normal pressure difference between the inlet and outlet of the bend is 0.012MPa. When the pressure difference between the inlet and outlet of the bend exceeds 0.02MPa, the detection and control unit will reduce the speed of the delivery pump by 10% and check the pressure difference of the product slurry filtration unit. If the pressure difference between the inlet and outlet of the bend is still higher than 0.02MPa after reducing the speed of the delivery pump, the corresponding pipeline will be stopped, the blockage of the product slurry filtration unit will be checked, and the replaceable polyetheretherketone wear-resistant internal components of the outer arc of the bend will be inspected.

[0059] In this embodiment, samples were taken from both the inlet and outlet of the neutralization reactor. The mass concentration of magnetic foreign matter at the inlet of the neutralization reactor was 3.2 μg / kg, and the mass concentration at the outlet was 3.7 μg / kg, resulting in a magnetic foreign matter increment of 0.5 μg / kg in the neutralization reaction unit. During operation of the carbon fiber reinforced composite stirring component, the torque fluctuation of the stirring motor was controlled within ±8% of the set torque.

[0060] Example 2: This example sets up a product slurry treatment path and a mother liquor circulation treatment path based on the ammonium dihydrogen phosphate crystal slurry obtained in Example 1.

[0061] In this embodiment, the product slurry treatment path includes a product slurry filtration unit, a product slurry electromagnetic iron removal unit, and a centrifuge. The mother liquor circulation treatment path includes a mother liquor collection tank, a mother liquor circulation filtration unit, a mother liquor circulation electromagnetic iron removal unit, and a neutralization vessel. The product slurry filtration unit uses a non-metallic filter basket and a polyetheretherketone (PEEK) support mesh, with a filtration opening of 600 μm. The upper limit of the characteristic particle size of the product crystals is 420 μm, and the filtration opening of the product slurry filtration unit is larger than the upper limit of the characteristic particle size of the product crystals. The function of the product slurry filtration unit is not to separate ammonium dihydrogen phosphate product crystals, but to intercept lining fragments, sealing fragments, and aggregated foreign matter with a size greater than 600 μm and having a sheet-like, strip-like, or irregular shape. The product slurry filtration unit adopts a dual-unit structure; when one filtration branch is operating, the other filtration branch is in a clean standby state.

[0062] The initial inlet and outlet pressure difference of the product slurry filtration unit is 0.01 MPa. When the inlet and outlet pressure difference reaches 0.06 MPa, the detection and control unit switches to the standby filtration branch. Before and after switching, the flow rate of ammonium dihydrogen phosphate crystal slurry entering the product slurry electromagnetic iron removal unit is kept within 5% of the set flow rate. The switched filtration branch is closed-loop flushed with high-purity water, and the flushing material enters the foreign matter collection container and does not return to the mother liquor collection tank.

[0063] The electromagnetic iron removal unit for the product slurry employs two parallel wet high-gradient electromagnetic separators. Each unit contains a removable magnetic media box, which is encased in a non-magnetic, corrosion-resistant shell with fine filament magnetic media. The average residence time of the ammonium dihydrogen phosphate crystal slurry within the magnetic media channel is 30 seconds. During normal operation, one unit processes the material while the other remains in a clean, standby state.

[0064] The inlet magnetic foreign matter concentration of the electromagnetic iron removal unit for the product slurry is 4.4 μg / kg, and the outlet magnetic foreign matter concentration is 1.1 μg / kg. According to the magnetic foreign matter capture efficiency calculation formula, the magnetic foreign matter capture efficiency of the electromagnetic iron removal unit for the product slurry is 75%. The detection and control unit obtains inlet and outlet samples every 20 tons of ammonium dihydrogen phosphate crystal slurry processed. When the outlet magnetic foreign matter concentration exceeds 2 μg / kg, the detection and control unit reduces the slurry flow rate by 15% and takes a sample again. If the resampling result still exceeds 2 μg / kg, the detection and control unit switches to the backup electromagnetic iron removal unit for the product slurry and cleans the original operating magnetic media box.

[0065] The centrifuge employs a closed, top-suspended centrifugal structure, with a polytetrafluoroethylene (PTFE) liner on the crystal contact surface. The ammonium dihydrogen phosphate crystal slurry is centrifuged at a speed of 2.8 m... 3 A flow rate of [amount] / h is fed into the centrifuge. The centrifugation speed is 900 r / min, the feeding time is 6 min, and the desiccation time is 4 min. The wet crystals obtained by centrifugation have a wet basis moisture content of 12%. The centrifugal filtrate enters the mother liquor collection tank. The effective volume of the mother liquor collection tank is 30 m³. 3 The mother liquor collection tank is lined with a non-metallic material and equipped with a mother liquor waste heat exchange coil. The mother liquor circulation pump is a fluoroplastic-lined centrifugal pump. The mother liquor circulation flow rate is 12 m³ / s. 3 / h. The mother liquor circulation filtration unit uses a polypropylene filter element with a 50μm filter opening. The filter opening of the mother liquor circulation filtration unit is smaller than that of the product slurry filtration unit. The mother liquor slurry remains in a dissolved state before entering the mother liquor circulation filtration unit, allowing the 50μm polypropylene filter element to intercept solid foreign matter without performing the function of separating product crystals.

[0066] The mother liquor circulation electromagnetic iron removal unit employs two series-connected wet high-gradient electromagnetic separators. The first unit handles a higher load of magnetic foreign matter, while the second unit controls the concentration of magnetic foreign matter in the mother liquor returned to the neutralization vessel. Sampling ports are installed at the inlet of the first unit and the outlet of the second unit. The concentration of magnetic foreign matter in the mother liquor returned to the neutralization vessel is controlled to be no higher than 5 μg / kg.

[0067] Reworked ammonium dihydrogen phosphate includes ammonium dihydrogen phosphate with particle size not meeting product requirements, ammonium dihydrogen phosphate that fails to meet magnetic foreign matter control values ​​during pre-packaging testing, and ammonium dihydrogen phosphate formed during equipment startup. Before entering the mother liquor collection tank, reworked ammonium dihydrogen phosphate is screened to remove packaging debris. Reworked ammonium dihydrogen phosphate is added to the mother liquor collection tank at a rate of 500 kg per batch. After adding the reworked ammonium dihydrogen phosphate, the mother liquor circulation pump maintains a flow rate of 12 m³ / h. 3 With a circulation flow rate of / h, the mother liquor waste heat exchange coil maintains the temperature of the mother liquor slurry at 58℃.

[0068] The dissolution endpoint of reworked ammonium dihydrogen phosphate was determined by a combination of online turbidity and residual mass of the bypass filter membrane. The dissolution endpoint was considered reached when the online turbidity remained below 15 NTU for 10 consecutive minutes, and the residual solid mass of a 1 kg sample taken from the mother liquor bypass and passed through a 10 μm polypropylene filter membrane was less than 0.1 g. The mother liquor slurry that reached the dissolution endpoint was then sequentially passed through a mother liquor circulation filtration unit and a mother liquor circulation electromagnetic iron removal unit.

[0069] Before returning to the neutralization reactor, the mass fractions of ammonium dihydrogen phosphate, free phosphoric acid, ammonia nitrogen, and magnetic foreign matter in the mother liquor slurry are measured. When the mass fraction of ammonium dihydrogen phosphate in the mother liquor slurry is 32% and the mass concentration of magnetic foreign matter is 4.3 μg / kg, the mother liquor slurry is returned to the neutralization reactor at 15% of the purified phosphoric acid mass flow rate. The detection and control unit performs mass balance corrections on the purified phosphoric acid flow rate and gaseous ammonia flow rate based on the phosphorus and nitrogen carried in by the mother liquor slurry.

[0070] During an 8-hour continuous operation cycle, the inlet magnetic foreign matter concentrations of the mother liquor circulation electromagnetic iron removal unit were 12.5 μg / kg, 13.1 μg / kg, 14.4 μg / kg, and 15.2 μg / kg, respectively, while the outlet magnetic foreign matter concentrations of the second mother liquor circulation electromagnetic iron removal unit were 3.8 μg / kg, 4.1 μg / kg, 4.3 μg / kg, and 5.1 μg / kg, respectively. When the outlet magnetic foreign matter concentration reached 5.1 μg / kg, the detection and control unit switched to the backup mother liquor circulation electromagnetic iron removal branch and performed magnetic media cleaning. After the switch, the outlet magnetic foreign matter concentration returned to 3.7 μg / kg.

[0071] Example 3: This example processes the wet crystals obtained by centrifugation in Example 2. The feed mass flow rate of the wet crystals was 1300 kg / h, the wet basis moisture content was 12%, and the feed temperature was 32℃. In the particle size distribution of the wet crystals, the particle size corresponding to a cumulative volume fraction of 10% was 95 μm, the particle size corresponding to a cumulative volume fraction of 50% was 205 μm, and the particle size corresponding to a cumulative volume fraction of 90% was 410 μm.

[0072] The vacuum continuous dryer-cooler comprises two drying zones, one transition zone, and one cooling zone. Each zone is equipped with two sets of parallel hollow spirals. The main body of the hollow spirals uses a non-magnetic metal pressure-bearing frame, and the material contact surface of the hollow spirals is covered with a continuous zirconia ceramic wear-resistant layer, while the material contact surface of the silo walls is lined with polyetheretherketone (PEEK) plates. A non-metallic isolation sleeve is installed between the hollow spirals and the drive end, and leakage from the shaft seal enters an independent collection chamber, preventing it from entering the material chamber.

[0073] The inlet temperature of the heating medium in the first drying zone is 95℃, and the inlet temperature of the heating medium in the second drying zone is 85℃. The pressure of the vacuum continuous drying and cooling machine is controlled between 12kPa and 18kPa, and the pressure is absolute pressure. The rotation speed of the hollow spiral in the first drying zone is 6r / min, and the rotation speed of the hollow spiral in the second drying zone is 4r / min. The total average residence time of the wet crystals in the two drying zones is 65min.

[0074] The vacuum continuous drying and cooling machine connects a condenser, a receiving tank, and a vacuum pump. A condensate flow meter is installed at the condenser outlet, and a dew point detection component is installed in the vacuum pipeline. The detection and control unit acquires the material temperature, vacuum level, exhaust gas dew point, condensate flow rate, and hollow screw torque in the drying zone every 5 minutes. The drying endpoint is reached when the condensate flow rate is continuously below 3 kg / h for 15 minutes, the exhaust gas dew point is below -5℃, and the wet basis moisture content of the material obtained from the bypass sampling is not higher than 0.2%. Based on a wet crystal feed mass flow rate of 1300 kg / h, a feed wet basis moisture content of 12%, and a post-drying wet basis moisture content of 0.2%, the evaporation water mass per unit time is 153.7 kg / h, and the post-drying ammonium dihydrogen phosphate mass flow rate is 1146.3 kg / h. The deviation between the condensate collection volume and the calculated evaporation water value of the vacuum continuous drying and cooling machine is controlled within 5%.

[0075] Ammonium dihydrogen phosphate, having reached its drying endpoint, enters the cooling zone through the transition zone. Circulating cooling water at 20°C is introduced into the hollow spiral of the cooling zone. The hollow spiral rotates at 5 r / min. When the material temperature at the cooling zone outlet does not exceed 45°C, and the wet basis moisture content of the material does not exceed 0.2% for two consecutive sampling cycles, the sealed discharge valve between the vacuum continuous drying cooler and the material sealing pump is opened, and ammonium dihydrogen phosphate enters the material sealing pump via the airlock unloading mechanism. When the material temperature exceeds 45°C, the sealed discharge valve is closed, and the rotation speed of the hollow spiral in the cooling zone is reduced to prolong the cooling residence time. The material sealing pump is equipped with a non-metallic lined hopper and a rotating material sealing component. A Roots blower supplies the material sealing pump with air that has undergone oil removal, water removal, and precision filtration. The dew point of the conveyed gas is controlled to be no higher than -20°C. The nominal diameter of the homopolymer polypropylene pipe is 80 mm, the total horizontal and vertical conveying length is 60 m, the number of bends is 6, and the radius of curvature of the bends is twice the nominal diameter.

[0076] The Roots blower outlet pressure is 0.08 MPa to 0.12 MPa, and the conveying mass per unit time is 1140 kg / h. The normal pipeline pressure differential for homopolymer polypropylene is 0.05 MPa. Based on empty pipe tests, step-by-step feeding tests, and product crystal particle size variation detection, this embodiment sets the stable conveying lower limit to 16 m / s and the crystal collision control upper limit to 22 m / s. The detection and control unit controls the conveying speed between 18 m / s and 20 m / s by adjusting the Roots blower speed and the feed frequency of the material conveying pump. When the pipeline pressure differential is higher than 0.07 MPa, the detection and control unit pauses the material conveying pump feed and increases the Roots blower speed by 8%, continuing for 30 seconds before re-detecting the pipeline pressure differential. When the pipeline pressure differential recovers to below 0.05 MPa, the material conveying pump resumes feeding at 80% of the original feed frequency, gradually recovering to the set feed frequency within 2 minutes. If the pipeline pressure differential does not recover, the material inlet is closed and a segmented inspection is performed.

[0077] The magnetic foreign matter concentration of ammonium dihydrogen phosphate at the outlet of the vacuum continuous drying and cooling machine is 1.5 μg / kg, while the magnetic foreign matter concentration of wet crystals at the inlet is 1.3 μg / kg, resulting in a magnetic foreign matter increment of 0.2 μg / kg for the vacuum continuous drying and cooling unit. The magnetic foreign matter concentration of ammonium dihydrogen phosphate at the outlet of the homopolymer polypropylene pipe is 1.7 μg / kg, and the magnetic foreign matter increment for the positive pressure pneumatic conveying unit is 0.2 μg / kg. In the particle size distribution of the homopolymer polypropylene pipe outlet product, the particle size corresponding to a cumulative volume fraction of 10% is 92 μm, 50% is 201 μm, and 90% is 403 μm. Compared to the pneumatic conveying inlet, the particle size corresponding to a cumulative volume fraction of 50% is reduced by 1.9%, which is within the crystal collision control range set in this embodiment.

[0078] Under the same wet crystal feed mass flow rate and the same feed and discharge moisture content, the hot air heating power, induced draft fan power, and vibration drive power of the existing hot air drying equipment were recorded and compared with the heating medium heat supply, vacuum pump power, and hollow screw drive power of the vacuum continuous drying and cooling machine. The operational data comparison was used to determine the changes in energy consumption after equipment modification and was not used as a comparative example of a single technical variable. The operational data comparison used the same statistical boundary, starting from the entry of wet crystals into the drying equipment and ending with the exit of ammonium dihydrogen phosphate that meets the moisture content and temperature requirements from the drying and cooling equipment.

[0079] Example 4: In this example, a mother liquor waste heat exchange coil is installed in the mother liquor collection tank of Example 2. The mother liquor waste heat exchange coil uses a non-magnetic, corrosion-resistant metal tube as the pressure-bearing layer, and a continuous polytetrafluoroethylene (PTFE) coating is provided on the outer surface of the pressure-bearing layer. The mother liquor slurry only contacts the PTFE coating. The effective heat exchange area of ​​the mother liquor waste heat exchange coil is 45 m². 2A waste water regulating valve is installed between the cooling water outlet of the neutralization vessel and the inlet of the mother liquor waste heat exchange coil. A flow meter and temperature detection device are installed between the outlet of the mother liquor waste heat exchange coil and the cooling water circulation system.

[0080] The table corresponding to the mother liquor concentration and saturation temperature was obtained through a constant temperature equilibrium experiment. When the soluble phosphate mass fraction in the mother liquor is 28%, 30%, 32%, 34%, and 36%, the corresponding saturation temperatures are 44℃, 48℃, 52℃, 56℃, and 60℃, respectively. The detection and control unit selects the corresponding saturation temperature based on the mother liquor density and phosphorus content.

[0081] In this embodiment, the soluble phosphate mass fraction in the mother liquor is 32%, corresponding to a mother liquor saturation temperature of 52°C. The actual temperature of the mother liquor is 58°C, with a mother liquor temperature margin of 6°C. When the mother liquor temperature margin is below 4°C, the detection and control unit increases the opening of the waste hot water regulating valve. When the mother liquor temperature margin is above 8°C, the detection and control unit decreases the opening of the waste hot water regulating valve or opens the bypass valve.

[0082] The mass flow rate of cooling water entering the neutralization reactor's waste heat exchange coil is 12000 kg / h, with an inlet temperature of 82℃ and an outlet temperature of 68℃. Based on the specific heat capacity of the cooling water of 4.18 kJ / (kg·℃), the heat recovered per unit time is 702240 kJ / h. The effective utilization coefficient of the waste heat exchange coil is taken as 0.88, the effective enthalpy drop of the supplementary steam is taken as 2100 kJ / kg, and the reduction in supplementary steam per unit time is 294.3 kg / h. Two differential pressure detection devices are installed in the mother liquor circulation pipeline. When the mother liquor temperature margin is not lower than 4℃, the differential pressure in the mother liquor circulation pipeline is maintained between 0.03 MPa and 0.04 MPa. When the mother liquor temperature margin is lower than 2℃ for 10 minutes, the detection and control unit opens the supplementary steam valve to restore the mother liquor temperature to 6℃ above the mother liquor saturation temperature. Supplementary steam is only used when the cooling water in the neutralization reactor is insufficient or during the production line start-up phase.

[0083] The detection and control unit assigns production unit numbers to the raw material filtration unit, neutralization reaction unit, evaporation concentration and cooling crystallization unit, product slurry conveying unit, product slurry filtration and iron removal unit, centrifugal separation unit, mother liquor circulation unit, vacuum continuous drying and cooling unit, and positive pressure pneumatic conveying unit. The inlet and outlet sampling locations of each production unit use fixed numbers. Sample records include production batch identification, sampling time, material flow rate, average residence time, magnetic foreign matter concentration, and equipment operating status.

[0084] Within a stable operating cycle, the magnetic foreign matter concentration at the inlet of the raw material filtration unit is 4.0 μg / kg, the outlet magnetic foreign matter concentration is 3.2 μg / kg, and the increase in magnetic foreign matter is -0.8 μg / kg; the increase in magnetic foreign matter in the neutralization reaction unit is 0.5 μg / kg; the increase in magnetic foreign matter in the evaporation concentration and cooling crystallization unit is 0.3 μg / kg; the increase in magnetic foreign matter in the product slurry conveying unit is 0.4 μg / kg; the increase in magnetic foreign matter in the product slurry filtration and iron removal unit is -3.3 μg / kg; the increase in magnetic foreign matter in the centrifugal separation unit is 0.2 μg / kg; the outlet magnetic foreign matter concentration of the mother liquor circulation unit is 4.3 μg / kg; the increase in magnetic foreign matter in the vacuum continuous drying and cooling unit is 0.2 μg / kg; and the increase in magnetic foreign matter in the positive pressure pneumatic conveying unit is 0.2 μg / kg. The detection and control unit compares the increase in magnetic foreign matter in each production unit with the corresponding maintenance control value. When the increase in magnetic foreign matter in the neutralization reaction unit exceeds 2 μg / kg, an inspection command is issued for the carbon fiber reinforced composite stirring impeller, replaceable non-metallic wear-resistant components, and shaft seal isolation structure. When the increase in magnetic foreign matter in the product slurry conveying unit exceeds 1.5 μg / kg, an inspection command is issued for the pressure difference of the steel-lined PTFE pipe bend and for the replacement non-metallic wear-resistant internal components. When the increase in magnetic foreign matter in the vacuum continuous drying and cooling unit exceeds 1 μg / kg, an inspection command is issued for the hollow spiral receiving surface and bin wall lining.

[0085] The energy consumption statistics period is 1 hour. The average active power of the stirring drive equipment is 45kW, the average active power of the auxiliary electrical equipment of the evaporation and concentration equipment is 90kW, the average active power of the mother liquor circulation equipment is 30kW, the average active power of the product slurry filtration and electromagnetic iron removal equipment is 40kW, the average active power of the vacuum pump and hollow screw drive equipment of the vacuum continuous drying and cooling machine is 160kW, and the average active power of the Roots blower is 85kW. The total electrical energy of the equipment during the statistics period is 450kWh, the mass of qualified ammonium dihydrogen phosphate is 1146.3kg, and the unit product electrical energy consumption is 0.393kWh / kg. The mass of supplementary steam during the statistics period is 260kg, the mass of qualified ammonium dihydrogen phosphate is 1146.3kg, and the unit product steam consumption is 0.227kg / kg. The detection and control unit compares the unit product electrical energy consumption and unit product steam consumption with the operating control range under the same product load. When the unit product's power consumption exceeds the control range, the detection and control unit outputs the adjustment targets according to the power deviation of the mother liquor circulation pump, vacuum pump, hollow screw drive equipment, and Roots blower. When the unit product's steam consumption exceeds the control range, the detection and control unit checks the mother liquor temperature margin, the opening of the waste hot water regulating valve, and the inlet and outlet temperature difference of the mother liquor waste heat exchange coil.

[0086] When the power of the mother liquor circulation equipment increases and the differential pressure in the mother liquor circulation pipeline increases simultaneously, the detection and control unit does not directly increase the speed of the mother liquor circulation pump. Instead, it judges the mother liquor temperature margin and the differential pressure of the mother liquor circulation filtration unit. When the mother liquor temperature margin is lower than 4°C, the opening of the waste hot water regulating valve is increased; when the differential pressure of the mother liquor circulation filtration unit reaches the termination differential pressure, the standby filtration branch is switched.

[0087] After the mother liquor temperature and filtration status have been restored, the mother liquor circulation pump speed is adjusted according to the target circulation flow rate. When the mass concentration of magnetic foreign matter at the outlet of the electromagnetic iron removal unit of the product slurry increases and the power consumption of the electromagnetic iron removal unit remains unchanged, the detection and control unit determines the magnetic medium load instead of directly increasing the excitation current. The detection and control unit reduces the product slurry flow rate and obtains a retest sample. If the retest result still exceeds the cleaning trigger value, the standby product slurry electromagnetic iron removal unit is switched on and the original operating magnetic medium box is cleaned.

[0088] When the differential pressure in the homopolymer polypropylene pipeline increases and the conveying mass per unit time decreases, the detection and control unit suspends the feed pump and briefly increases the Roots blower speed. Once the differential pressure recovers, a stable conveying process is re-established at a lower feed frequency. If the differential pressure does not recover, conveying is stopped and bends and vertical pipe sections are inspected; abnormal conveying is not maintained by continuously increasing the blower speed.

[0089] Example 5: This example, based on the product slurry processing path of Example 2, adds a pulsating magnetic field modulation control logic based on solid-liquid rheological state to the electromagnetic iron removal unit of the product slurry. Ammonium dihydrogen phosphate crystal slurry belongs to a solid-liquid two-phase suspension system. During the concentration and crystallization process, the ammonium dihydrogen phosphate crystals tend to collide and agglomerate within the pipeline transport and iron removal channels. Some small magnetic foreign objects are physically entrained by clusters formed by multiple ammonium dihydrogen phosphate crystals, or adhere to the surface of the ammonium dihydrogen phosphate crystals. The high-gradient static magnetic field established by conventional constant DC excitation can only apply a directional magnetic force to ionized magnetic foreign objects. When the magnetic force established by constant DC excitation cannot overcome the spatial steric hindrance and fluid drag of the ammonium dihydrogen phosphate crystal clusters, the entrained magnetic foreign objects will penetrate the electromagnetic iron removal unit of the product slurry along with the ammonium dihydrogen phosphate crystal slurry, causing an increase in the iron content of the centrifuged filtrate or the final product.

[0090] To eliminate the physical entrainment of magnetic foreign matter by crystal clusters, this embodiment employs a composite excitation power supply architecture for the electromagnetic iron removal unit of the product slurry. This architecture includes an adjustable DC power supply providing a basic constant magnetic field and a programmable AC pulse generator providing forced vibration energy. The detection and control unit acquires the physical parameters of the ammonium dihydrogen phosphate crystal slurry online and dynamically calculates the composite excitation parameters.

[0091] Before entering the product slurry filtration unit, the real-time density of the ammonium dihydrogen phosphate crystal slurry is obtained using a Coriolis mass flow meter, and the real-time dynamic viscosity is obtained using an online vibratory viscometer. The detection and control unit has a built-in density-to-solids conversion model to convert the real-time density into the real-time solids content.

[0092] The pulsation frequency of the low-frequency pulsating AC excitation current is calculated using the following formula:

[0093] In the formula, The pulsation frequency, expressed in Hz, represents the low-frequency pulsating AC excitation current. This represents the reference pulsation frequency, which is 15Hz in this embodiment; The viscosity response coefficient is determined by cold-mold rheological experiments; in this embodiment, it is taken as 0.85. The real-time dynamic viscosity of the ammonium dihydrogen phosphate crystal slurry obtained online is expressed in mPa·s. The reference dynamic viscosity is 25 mPa·s in this embodiment. The above calculation logic reflects the influence of fluid damping characteristics on the forced vibration of magnetic foreign objects. The higher the real-time dynamic viscosity of ammonium dihydrogen phosphate crystal slurry, the greater the viscous resistance of the fluid to the magnetic foreign object. High-frequency vibration in a high-viscosity environment will cause energy to dissipate rapidly inside the fluid and cannot be effectively transferred to the interior of the crystal cluster. The control method in which the pulsation frequency is negatively correlated with the real-time dynamic viscosity allows high-viscosity materials to obtain a low-frequency deep-penetrating vibration magnetic field, while low-viscosity materials obtain a high-frequency rapid peeling vibration magnetic field.

[0094] The pulsation amplitude of the low-frequency pulsating AC excitation current is calculated using the following formula:

[0095] In the formula, The pulsation amplitude represents the low-frequency pulsating AC excitation current, expressed in amperes (A). The background DC excitation current set by the electromagnetic iron removal unit for the product slurry is expressed in amperes (A). In this embodiment, it is 45A. This represents the basic amplitude coefficient, which is set to 0.12 in this embodiment. Represents the real-time solids content, expressed as a mass fraction; This represents the baseline solids content, which is 45% in this example. The nonlinear enhancement index is 1.2 in this embodiment. Solid content directly determines the density and steric hindrance of the crystal clusters. Higher real-time solid content requires a greater mechanical impulse to free the magnetic foreign object from physical entrainment. The pulsation amplitude is nonlinearly positively correlated with the real-time solid content, ensuring sufficient alternating magnetic field force at high solid content levels, causing drastic fluctuations in the magnetic field gradient on the magnetic medium surface. The fluctuating magnetic field gradient, superimposed on the background static magnetic field, subjectes iron, chromium, and nickel particles in the crystal gaps to periodic pushing and pulling forces, breaking the static friction lock between the crystal and the magnetic foreign object. After being released, the magnetic foreign object is firmly adsorbed by the magnetic medium box inside the electromagnetic iron removal unit of the product slurry under the guidance of the high-gradient static magnetic field established by the background DC excitation current.

[0096] To verify the technical effectiveness of the composite excitation modulation control logic, this embodiment uses 10 tons of high-solids-content ammonium dihydrogen phosphate crystal slurry from the same batch for comparative verification. The actual temperature of the ammonium dihydrogen phosphate crystal slurry is 31°C, the real-time solids content fluctuates between 52% and 55%, and the real-time dynamic viscosity fluctuates between 38 mPa·s and 45 mPa·s.

[0097] The first 5 tons of ammonium dihydrogen phosphate crystal slurry adopts the traditional constant DC excitation mode. The electromagnetic iron removal unit of the product slurry only inputs a background DC excitation current of 45A, without superimposing low-frequency pulsating AC excitation current.

[0098] The latter 5 tons of ammonium dihydrogen phosphate crystal slurry utilize the composite excitation power supply architecture of this embodiment. The detection and control unit dynamically adjusts the pulsation frequency and amplitude based on the real-time solid content and real-time dynamic viscosity. According to the formula, the pulsation frequency is dynamically adjusted between 3.2Hz and 4.1Hz, and the pulsation amplitude is dynamically adjusted between 6.6A and 7.1A.

[0099] The sampling and testing results are shown in Table 1 below.

[0100] Table 1:

[0101]

[0102] Based on the data in the table above, under high solids content and high viscosity conditions, due to the large amount of magnetic foreign matter being entrained by ammonium dihydrogen phosphate crystal clusters, the magnetic foreign matter capture efficiency under constant DC excitation is only 56.25%. This results in a high concentration of magnetic foreign matter entering the mother liquor collection tank with the centrifuged filtrate, exacerbating the iron removal load on the mother liquor circulation treatment path. After adopting a superimposed pulsating magnetic field modulation control logic, without increasing the background magnetic field strength, the magnetic foreign matter capture efficiency increased to 87.23%, and the outlet magnetic foreign matter mass concentration decreased significantly from 2.1 μg / kg to 0.6 μg / kg. The forced vibration induced by the pulsating magnetic field successfully broke the physical entrainment between solid particles, released the hidden magnetic contamination source, and effectively blocked magnetic impurities between the main material flow and the circulating material flow.

[0103] Example 6: This example, based on the mother liquor waste heat exchange coil of Example 4, introduces dynamic heat flow boundary layer disruption control logic for the neutralization kettle cooling water. In Example 4, the mother liquor waste heat exchange coil is coated with a polytetrafluoroethylene (PTFE) layer. PTFE effectively prevents the release of magnetic foreign matter caused by metal pipe corrosion, but it also has inherent properties such as low surface free energy and low thermal conductivity. The mother liquor slurry has an extremely high salt concentration. When a constant flow of neutralization kettle cooling water continuously flows through the mother liquor waste heat exchange coil, a stable laminar or transitional boundary layer is formed inside the tube; simultaneously, the local temperature of the mother liquor near the PTFE coating on the outside of the coil rises, easily forming a salt-rich microscopic retention layer on the PTFE surface, hindering heat transfer to the depths of the mother liquor collection tank.

[0104] To enhance heat transfer and prevent microscale scaling on the surface, this embodiment employs a stepped alternating flow rate mode instead of the traditional constant flow rate heating mode. The detection and control unit controls the waste hot water regulating valve to perform high-frequency, large-amplitude opening switches.

[0105] The specific control process is as follows: The detection and control unit acquires the concentration and actual temperature of the mother liquor slurry in real time, determines the corresponding saturation temperature of the mother liquor by referring to a table, and calculates the temperature margin between the actual temperature of the mother liquor slurry and the saturation temperature of the mother liquor. When the temperature margin is within the set safe range of 4℃ to 8℃, the step alternating flow mode is activated.

[0106] The step-alternating flow mode divides an operating cycle into a high-flow-input phase and a low-flow-input phase. During the high-flow-input phase, the detection and control unit instantly adjusts the opening of the waste hot water regulating valve to 95% of its rated opening, and the neutralization vessel cooling water rushes into the mother liquor waste heat exchange coil at high speed. The high-speed flowing fluid generates strong transient shear forces within the tube. The localized turbulent vortices induced by the sudden change in flow velocity effectively strip away the fluid thermal resistance layer on the inner wall of the tube. Simultaneously, the slight mechanical vibrations of the tube caused by changes in fluid momentum are transmitted to the outside of the tube, disturbing the microscopic retention layer of mother liquor on the surface of the polytetrafluoroethylene coating, accelerating the elimination of concentration polarization.

[0107] During the low-flow-rate input phase, the detection and control unit instantly reduces the opening of the waste hot water regulating valve to 30% of its rated opening. The flow rate of the cooling water in the neutralization vessel within the mother liquor waste heat exchange coil decreases significantly, and the residence time is significantly prolonged. This extended residence time allows the fluid inside the coil to fully release sensible heat, substantially reducing the outlet temperature of the cooling water in the neutralization vessel and maximizing the extraction of heat carried away by the neutralization reaction.

[0108] The core parameter of the step-alternating flow mode is dynamically determined by the real-time total heat transfer coefficient. The detection and control unit calculates the real-time total heat transfer coefficient of the mother liquor waste heat exchange coil online.

[0109] In the formula, Represents the real-time overall heat transfer coefficient, with calculated values ​​in kW / (m²). 2 ·K), converted to the commonly used unit W / (m 2 Multiply by 1000 when K is used; This represents the average mass flow rate of cooling water in the neutralization vessel over one alternating cycle, expressed in kg / s. This represents the specific heat capacity of the cooling water, taken as 4.18 kJ / (kg·℃); and These represent the average inlet and outlet temperatures of the cooling water in the neutralization vessel, respectively, in °C. The effective heat exchange area of ​​the mother liquor waste heat exchange coil is represented by the unit m. 2 ; Represents the logarithmic mean temperature difference, in K, calculated as the logarithmic mean of the hot and cold end temperature differences of the heat exchanger. ,in and These represent the average inlet and outlet temperatures of the mother liquor slurry outside the mother liquor waste heat exchange coil, respectively, in °C.

[0110] Set the clean heat transfer coefficient threshold This refers to the standard heat transfer coefficient under conditions where the equipment is free of scaling and fluid boundary layer retention. Clean heat transfer coefficient threshold. The clean heat transfer coefficient threshold in this embodiment is determined by measuring the heat transfer coefficient under constant low flow conditions during the initial operation of the equipment. Take 0.62kW / (m 2 ·K) (i.e., 620W / (m 2 ·K)).

[0111] When the real-time total heat transfer coefficient Above the clean heat transfer coefficient threshold When the flow rate is 90%, maintain the basic alternating ratio: the high flow rate input phase duration is set to 15 seconds, and the low flow rate input phase duration is set to 45 seconds. When the real-time overall heat transfer coefficient... Falling to the clean heat transfer coefficient threshold When the flow rate is below 90%, it is determined that there is a tendency for boundary layer thickening or micro-fouling on both sides of the pipe wall. At this time, the detection and control unit extends the duration of the high flow input phase and shortens the duration of the low flow input phase, adjusting both the high flow input phase and the low flow input phase to 30 seconds. The duration of the high flow impact is increased to forcibly destroy the thermal resistance layer with more frequent and sustained transient shear force until the real-time total heat transfer coefficient recovers to more than 90% of the clean heat transfer coefficient threshold, and then the cycle is switched back to the basic alternating ratio.

[0112] To verify the energy-saving and scale-prevention effects of the stepped alternating flow mode, this embodiment underwent a continuous 72-hour engineering control test. For the first 36 hours, the alternating mode was turned off, and the waste hot water regulating valve was maintained at a fixed 60% opening, i.e., a constant flow input. For the following 36 hours, the stepped alternating flow mode was turned on. During this period, the amount of additional steam required to maintain the mother liquor temperature was monitored using a steam flow meter. The test data are summarized in Table 2 below.

[0113] Table 2:

[0114]

[0115] According to the data in the table above, when a constant flow rate is used, the heat transfer coefficient of the mother liquor waste heat exchange coil decreased significantly by 21.77% within 36 hours. Due to the reduced heat exchange efficiency, the heat carried by the cooling water in the neutralization vessel could not be effectively transferred to the mother liquor slurry, resulting in a mother liquor temperature margin difference of 3.5℃. The system was forced to consume a large amount of additional high-grade supplementary steam, totaling 3150 kg, to prevent mother liquor crystallization.

[0116] After switching to the step-alternating flow mode, transient shear force and tube micro-vibration effectively prevented the thickening of the inner and outer boundary layers. The heat transfer coefficient at the end of the cycle remained at 0.598 kW / (m²). 2 The attenuation rate was only 2.76% (·K). Stable heat transfer efficiency ensured full utilization of the waste heat from the neutralization vessel's cooling water, precisely locking the mother liquor temperature margin and reducing fluctuation range to 1.1℃. The total supplementary steam consumption was drastically reduced to 820kg throughout the 36-hour cycle. This dynamic heat flow boundary layer disruption logic, without increasing any additional heat exchange area, utilizes unsteady fluid dynamics characteristics to completely release the heat transfer potential of the mother liquor waste heat exchange coil, achieving energy savings and long-term anti-fouling operation.

[0117] In some embodiments, the ammonia source can be ammonia water with a defined ammonia mass fraction. When ammonia water is used, a pre-filter for the ammonia source is installed between the ammonia water storage tank and the neutralization vessel, and the amount of water brought in by the ammonia water is included in the mass flow rate of the neutralization slurry and the mass flow rate of the evaporated water. When the ammonia source is changed from anhydrous liquid ammonia to ammonia water, the ammonia mass flow rate is still calculated according to the ammonia-phosphorus molar ratio, without changing the stoichiometric relationship for the formation of ammonium dihydrogen phosphate in the neutralization reaction.

[0118] In some embodiments, the carbon fiber reinforced composite stirring shaft can be made of carbon fiber reinforced polyphenylene sulfide composite material. The resin matrix of the carbon fiber reinforced composite stirring shaft is determined based on the neutralization temperature, acid-base contact conditions, and design torque. Material adjustments do not alter the structural relationship where the metal drive connection components form a continuous non-metallic contact surface above and below the highest slurry level.

[0119] In some embodiments, the filtration opening of the product slurry filtration unit is adjusted to 500 μm to 1000 μm based on the upper limit of the characteristic particle size of the product crystals. The filtration opening of the product slurry filtration unit is always larger than the upper limit of the characteristic particle size of the product crystals for the corresponding production batch. The filtration opening of the mother liquor circulation filtration unit can be selected in the range of 20 μm to 80 μm, and the selection result is determined based on the particle size of solid foreign matter in the mother liquor and the rate of increase of the pressure difference in the mother liquor circulation filtration unit.

[0120] In some embodiments, the product slurry electromagnetic iron removal unit and the mother liquor circulation electromagnetic iron removal unit can be configured in series, in parallel, or in a combination of series and parallel. The electromagnetic iron removal unit is provided with at least one operating branch and one isolated backup branch for cleaning, so that slurry that has not undergone electromagnetic iron removal is not directly fed into the downstream production unit during magnetic media cleaning.

[0121] In some embodiments, the mother liquor collection tank is equipped with a separate rework material dissolution zone and a mother liquor circulation zone. After the reworked ammonium dihydrogen phosphate reaches its dissolution endpoint in the rework material dissolution zone, it enters the mother liquor circulation zone through the overflow port. The separate rework material dissolution zone reduces the possibility of undissolved crystals directly entering the mother liquor circulation filtration unit.

[0122] In some embodiments, the vacuum continuous drying and cooling machine is provided with three or more drying zones and two or more cooling zones. The speed of the hollow spiral and the flow rate of the heat exchange medium in each zone can be independently adjusted. The number of zones is determined based on the moisture content of the wet crystals, the allowable temperature of the product, and the processing capacity of the equipment.

[0123] In some embodiments, nitrogen is used as the conveying gas in positive pressure pneumatic conveying. When nitrogen is used, the conveying gas is de-oiled, de-hydrated, and filtered before entering the Roots blower or gas booster. When the conveying gas is recycled, the recirculated gas undergoes dust separation and condensation dehydration before returning to the gas booster.

[0124] In some embodiments, the mother liquor waste heat exchange coil employs multiple parallel heat exchange branches. Each heat exchange branch is equipped with an independent inlet valve and an outlet water temperature detection component. The detection and control unit switches the heat exchange branch according to the temperature difference at different locations in the mother liquor collection tank, ensuring that the temperature distribution within the mother liquor collection tank meets the requirements for circulation and transportation.

[0125] In some embodiments, the detection and control unit generates production batch records based on the increase in magnetic foreign matter in the production unit, the pressure difference between the inlet and outlet of the filtration unit, the capture efficiency of the electromagnetic iron removal unit, the mother liquor temperature margin, the energy consumption per unit of evaporation water in the vacuum continuous drying and cooling machine, and the electrical energy consumption per unit of transported mass in the homopolymer polypropylene pipeline. These production batch records are used to determine the maintenance sequence and the initial operating parameters for the next production batch.

[0126] The core process of this invention maintains the continuous relationship between crude wet phosphoric acid purification, ammonia neutralization, evaporation and concentration, cooling crystallization, and centrifugal separation. When different implementation methods adjust the filter openings, material matrix, equipment zoning, magnetic media structure, and control parameters, the product slurry treatment path, the mother liquor circulation treatment path, the connection between closed drying and cooling and positive pressure pneumatic conveying, and the technical relationship of heat transfer from the neutralization reaction to the mother liquor circulation process remain unchanged.

[0127] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0128] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate, characterized in that: include: Crude wet-process phosphoric acid is subjected to desulfurization, defluorination, and chemical precipitation to remove heavy metals in sequence to obtain purified phosphoric acid. The purified phosphoric acid and ammonia source are filtered using a purified phosphoric acid pre-filter and an ammonia source pre-filter respectively, both equipped with polypropylene filter elements. The filtered purified phosphoric acid and ammonia source are fed into a neutralization vessel, where they undergo a neutralization reaction under the stirring action of a carbon fiber reinforced composite stirring shaft and a carbon fiber reinforced composite stirring blade to form a neutralized slurry. The neutralized slurry is evaporated, concentrated, and cooled to crystallize, forming an ammonium dihydrogen phosphate crystal slurry; The ammonium dihydrogen phosphate crystal slurry is transported through a steel-lined polytetrafluoroethylene (PTFE) pipe, with the PTFE lining of the pipe forming the pipe contact surface of the ammonium dihydrogen phosphate crystal slurry. The ammonium dihydrogen phosphate crystal slurry passes through a product slurry filtration unit and a product slurry electromagnetic iron removal unit in sequence before entering a centrifuge for solid-liquid separation, yielding wet crystals and centrifugal filtrate. The centrifuged filtrate and reprocessed ammonium dihydrogen phosphate are fed into a mother liquor collection tank, where they are mixed and dissolved to form a mother liquor slurry. The mother liquor slurry is then passed through a mother liquor circulation filtration unit and a mother liquor circulation electromagnetic iron removal unit before being returned to the neutralization vessel. The wet crystals are fed into a vacuum continuous drying and cooling machine, where they are pushed by a hollow spiral in a closed negative pressure environment to continuously complete the drying and cooling process. The dried and cooled ammonium dihydrogen phosphate is fed into a material sealing pump, and the dried and cooled ammonium dihydrogen phosphate is transported through a homopolymer polypropylene pipeline by a positive pressure airflow provided by a Roots blower; and the cooling water of the neutralization vessel, which absorbs the heat generated by the neutralization reaction, is sent to the mother liquor waste heat exchange coil set in the mother liquor collection tank, and the mother liquor waste heat exchange coil is used to heat the mother liquor slurry, so that the mother liquor slurry is kept in a molten state that can be circulated and transported.

2. The low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate according to claim 1, characterized in that: The purified phosphoric acid pre-filter and the ammonia source pre-filter are respectively equipped with inlet and outlet pressure difference detection components; when the inlet and outlet pressure difference of any pre-filter reaches the corresponding termination pressure difference, the feeding of the corresponding pre-filter is stopped and the polypropylene filter element is replaced; the polypropylene filter element is put back into use without backwashing.

3. The low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate according to claim 1, characterized in that: The carbon fiber reinforced composite stirring shaft and the carbon fiber reinforced composite stirring blade form a continuous non-metallic contact surface below the highest slurry level. The metal connecting component between the carbon fiber reinforced composite stirring shaft and the transmission component is located above the highest slurry level. A replaceable non-metallic wear-resistant component is provided at the high scouring position of the carbon fiber reinforced composite stirring blade.

4. The low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate according to claim 1, characterized in that: The bend of the steel-lined polytetrafluoroethylene pipe adopts a long-radius flow transition, and a replaceable non-metallic wear-resistant internal component is set at the high scouring position of the outer arc of the bend; the speed of the delivery pump is adjusted according to the volumetric flow rate of the ammonium dihydrogen phosphate crystal slurry and the pressure difference between the inlet and outlet of the bend.

5. The low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate according to claim 1, characterized in that: The filter opening of the product slurry filtration unit is larger than the upper limit of the characteristic particle size of the ammonium dihydrogen phosphate crystal slurry, and the filter opening of the mother liquor circulation filtration unit is smaller than the filter opening of the product slurry filtration unit. This ensures that the product slurry filtration unit does not retain product crystals that meet the particle size requirements, and that the mother liquor circulation filtration unit intercepts solid foreign matter in the mother liquor slurry. The upper limit of the characteristic particle size of the product crystals refers to the particle size corresponding to a cumulative volume fraction of 90% among the crystals that meet the product particle size requirements.

6. The low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate according to claim 1, characterized in that: The inlet magnetic foreign matter concentration, outlet magnetic foreign matter concentration, slurry flow rate, and cumulative treated mass of the product slurry electromagnetic iron removal unit and the mother liquor circulating electromagnetic iron removal unit are detected respectively. The excitation state or slurry flow rate is adjusted according to the difference between the inlet and outlet magnetic foreign matter concentrations. When the outlet magnetic foreign matter concentration reaches the cleaning trigger value, the corresponding electromagnetic iron removal unit is isolated and the magnetic medium is cleaned.

7. The low-magnetic-energy-saving method for preparing battery-grade high-purity phosphate according to claim 1, characterized in that: After the reworked ammonium dihydrogen phosphate is added to the mother liquor collection tank, it is heated and circulated through the mother liquor waste heat exchange coil. After the content of undissolved crystals in the mother liquor slurry reaches the dissolution endpoint value, the mother liquor slurry is sequentially passed through the mother liquor circulation filtration unit and the mother liquor circulation electromagnetic iron removal unit, and returned to the neutralization kettle when the composition and magnetic foreign matter mass concentration of the mother liquor slurry meet the return conditions.

8. The low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate according to claim 1, characterized in that: The vacuum continuous drying and cooling machine includes a drying zone and a cooling zone arranged along the material movement direction; the rotation speed of the hollow screw and the flow rate of the heating medium are adjusted according to the material temperature in the drying zone, the moisture content of the exhaust gas, the condensate generation state, and the torque of the hollow screw; the material enters the cooling zone after the material moisture content reaches the drying endpoint value; and the material enters the material sealing pump after the material temperature reaches the cooling endpoint value.

9. The low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate according to claim 1, characterized in that: The outlet pressure of the Roots blower, the differential pressure in the homopolymer polypropylene pipeline, the dew point of the conveyed gas, the dry material temperature, and the conveying mass per unit time are detected. Based on the detection results, the rotational speed of the Roots blower and the feeding state of the material sealing pump are adjusted so that the conveying speed in the homopolymer polypropylene pipeline is higher than the lower limit of stable conveying and lower than the upper limit of crystal collision control.

10. The low-magnetic, energy-saving method for preparing battery-grade high-purity phosphate according to claim 1, characterized in that: In the step of passing the ammonium dihydrogen phosphate crystal slurry sequentially through a product slurry filtration unit and a product slurry electromagnetic iron removal unit before entering a centrifuge for solid-liquid separation to obtain wet crystals and centrifugal filtrate: the real-time solid content and real-time dynamic viscosity of the ammonium dihydrogen phosphate crystal slurry are obtained; based on the real-time solid content and the real-time dynamic viscosity, a low-frequency pulsating AC excitation current is superimposed on the background DC excitation current of the product slurry electromagnetic iron removal unit, causing magnetic foreign matter in the product slurry electromagnetic iron removal unit to undergo forced vibration in the high-gradient static magnetic field established by the background DC excitation current, thereby detaching from the physical entrainment of crystal particles in the ammonium dihydrogen phosphate crystal slurry; wherein, the pulsation frequency of the low-frequency pulsating AC excitation current is negatively correlated with the real-time dynamic viscosity, and the pulsation amplitude of the low-frequency pulsating AC excitation current is positively correlated with the real-time solid content.

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