Device and method for producing low-impurity full-water-soluble ammonium dihydrogen phosphate by concentrated acid method

Abstract

The invention relates to the technical field of ammonium dihydrogen phosphate production, and discloses a device and a method for producing low-impurity full-water-soluble ammonium dihydrogen phosphate by a concentrated acid method, and the device comprises an acid regulation system, a neutralization reaction system, an impurity removal aging system, a filtration separation system, a triple-effect concentration system, a continuous steady-state crystallization system and a drying system which are connected in sequence. The core is that the neutralization system adopts three-stage series connection of a rapid ammoniation reactor, a tubular reactor and a slurry tank to realize segmented pH control neutralization; self-produced ammonium fluoride is used as an impurity removal agent for the first time, and metal impurities such as Fe, Al and Mg in wet-process phosphoric acid are deeply removed by combining a pH reverse adjustment technology. And the concentrated slurry passes through a unique crystal elimination-steady-state crystallization system to obtain large-size and high-purity crystals. According to the method, low-cost wet-process phosphoric acid is taken as a raw material, high-end ammonium dihydrogen phosphate with the main content being more than or equal to 99% and the water insoluble matter being less than or equal to 0.01% is stably produced, the phosphorus yield reaches 71% or above, and a hot-process product can be replaced.

Description

Technical Field

[0001] This invention relates to the field of ammonium dihydrogen phosphate production technology, and in particular to an apparatus and method for producing low-impurity, fully water-soluble ammonium dihydrogen phosphate using a concentrated acid method. Background Technology

[0002] Industrial-grade monoammonium phosphate (MAP), with the chemical formula NH4H2PO4, is an important inorganic chemical product. It is widely used in agriculture as a high-efficiency compound fertilizer and plays a crucial role in industry, such as as a flame retardant in plastics, rubber, and wood; as a component of dry powder fire extinguishing agents; as a major raw material for lithium / phosphorus battery precursors; and as a feed additive and industrial dispersant. Market demand for MAP, especially for high-purity products, continues to grow.

[0003] Currently, the core of the production process for industrial-grade ammonium dihydrogen phosphate lies in the neutralization reaction between phosphoric acid and ammonia. Based on the source and purity of the raw material phosphoric acid, the mainstream processes can be divided into two main categories: 1. Thermal phosphoric acid process: This process uses high-purity thermal phosphoric acid as raw material. This process is mature, relatively simple, and yields high-purity MAP (typically ≥98%, up to 99.5%) products, meeting the standards for high-end applications such as flame retardants, electronic grade, and food grade. However, its fatal drawbacks are high cost, huge energy consumption, and significant environmental pollution from the upstream yellow phosphorus production process, which contradicts the national strategy of green and low-carbon development.

[0004] 2. Wet-process phosphoric acid: This process uses inexpensive wet-process phosphoric acid as raw material. However, wet-process phosphoric acid has a high impurity content, containing a large amount of SO4. 2- F - In addition to various metal ions such as Fe, Al, Mg, and Ca, it must undergo deep purification (such as chemical precipitation and ion exchange) before it can be used to produce industrial-grade MAP. Although the raw material cost advantage is obvious, the process has inherent defects: the process flow is lengthy and complex, the purification and subsequent reaction control are difficult, resulting in poor product quality (especially purity and water-insoluble content) stability, and low phosphorus yield.

[0005] To balance cost and quality, using purified wet-process concentrated phosphoric acid as raw material, combined with multi-effect concentration and crystallization processes to produce high-purity MAP has become an important development direction for the industry to achieve efficient utilization of phosphorus resources. However, the technical bottlenecks of this route remain prominent, specifically in the following core process steps: During the neutralization and impurity removal stages, impurities in wet-process phosphoric acid (such as Fe, Al, and Mg) form a series of complex colloidal compounds (e.g., (Al,Fe)NH4HPO4F2, MgNH4PO4·H2O, etc.) whose composition and properties dynamically change with pH. Traditional one-step or simple two-step neutralization processes struggle to precisely control the selective precipitation and separation of impurities in different pH ranges, resulting in impurity ions remaining in the liquid phase and ultimately affecting product purity and water solubility.

[0006] In the crystallization control stage, the crystallization process is crucial to the final crystal form, particle size distribution, and purity of the product. If supersaturation is not properly controlled (such as cooling too quickly), a large number of fine crystals are easily generated, which have a large specific surface area and are prone to encapsulating or adsorbing impurity ions, thus reducing crystal purity. On the other hand, traditional intermittent crystallization methods have problems such as uneven product particle size and poor batch stability.

[0007] As phosphate rock grades decrease and raw material impurities fluctuate more, traditional wet MAP production units generally face problems such as low operational flexibility, reduced phosphorus yield (usually below 70%), and increased production costs.

[0008] In summary, existing technologies present a significant contradiction: thermal processes offer superior quality but come with high costs and environmental impact; while wet processes are low-cost but struggle to consistently produce MAP products with high purity, low impurities, and high yields comparable to thermal processes. In particular, how to achieve deep and targeted impurity removal within the framework of wet processes through innovative process design and control methods, coupled with efficient steady-state crystallization technology, to stably produce fully water-soluble MAP with a main content ≥99%, extremely low water-insoluble matter content (e.g., <0.01%), and high phosphorus yield, thus replacing some thermal process products, has become a pressing technical challenge in this field.

[0009] In view of this, the present invention aims to provide a novel production apparatus and method to solve the above-mentioned problems. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the purpose of this invention is to provide an apparatus and method for producing low-impurity, fully water-soluble ammonium dihydrogen phosphate using a concentrated acid method.

[0011] The solution of the present invention is: An apparatus for producing low-impurity, fully water-soluble ammonium dihydrogen phosphate by concentrated acid method includes an acid adjustment system, a neutralization reaction system, an impurity removal and aging system, a filtration and separation system, a concentration system, a continuous steady-state crystallization system, a drying system, a tail gas scrubbing system, and a vacuum system connected in sequence by pipelines. The acid adjustment system, consisting of a static mixer and an acid adjustment tank, is used to adjust the phosphoric acid concentration and mix it into the mother liquor; The neutralization reaction system consists of a rapid ammoniation reactor, a first tubular reactor, and a second-stage neutralization slurry tank connected in series; it is used for the staged neutralization reaction of ammonia / liquid ammonia with phosphoric acid to produce ammonium dihydrogen phosphate, while simultaneously precipitating metal impurities; the first tubular reactor is a tubular reactor with internal nozzles; The impurity removal and aging system consists of a second tubular reactor and an ammonium fluoride solution tank; it is used to prepare the ammonium fluoride solution as a reaction impurity removal additive to promote the formation of metal precipitates. The filtration and separation system includes a vertical filter press, a pH adjustment system, and a plate and frame filter press connected in sequence; it is used for two-stage filtration to separate solid impurities. The concentration system is a triple-effect countercurrent concentration device, which includes a first-effect evaporation chamber and a first-effect heating chamber, a second-effect evaporation chamber and a second-effect heating chamber, and a third-effect evaporation chamber and a third-effect heating chamber. By adopting the triple-effect countercurrent concentration method, the evaporation pressure and temperature can be controlled to ensure the smooth operation of the subsequent crystallization system. A continuous steady-state crystallization system consists of a circulating crystal elimination system and a crystallization system. The circulating crystal elimination system includes a crystal elimination device, a crystal elimination heater, and a crystal elimination circulation pump. The crystallization system includes a DTB crystallizer, a crystallization circulation pump, a crystallization extraction pump, and a centrifuge. The centrifuge is a double-push centrifuge. Drying system, including vibrating fluidized bed; An exhaust gas scrubbing system is connected to the exhaust end of the neutralization reaction system; Vacuum systems, including separate concentration vacuum systems and crystallization vacuum systems; The static mixer is internally constructed from welded spiral blades that twist left and right in a single channel; the second tubular reactor is internally constructed from a cylindrical structure assembled from corrugated plates, with adjacent sets of corrugated plate units offset by 90 degrees; the mixing gas phase space of the crystallizer is greater than 1m. 3 .

[0012] As a preferred technical feature, the drying system further includes a hot air system, a bag dust collection system, and a screening machine; In the neutralization reaction system, the rapid ammoniation reactor, the first tubular reactor, and the second-stage neutralization slurry tank form a three-stage ammonia-flowing, interconnected series structure. The second-stage neutralization slurry tank is configured to operate under a slightly positive pressure environment, with its operating pressure (gauge pressure) maintained at 6 kPa. This pressure environment is controlled collaboratively by a blower and a tail gas condenser to maintain a low ammonia partial pressure in the gas phase, thereby suppressing ammonia escape, optimizing reaction equilibrium, and reducing material loss.

[0013] The present invention also discloses a method for producing low-impurity, fully water-soluble ammonium dihydrogen phosphate using the above-described apparatus, comprising the following steps: S1. Acid adjustment: The purified concentrated phosphoric acid is diluted with water through a static mixer, and the mother liquor is added to the acid adjustment tank and mixed with the diluted phosphoric acid. S2, First stage of neutralization: The acidified phosphoric acid is fed into a rapid ammoniation reactor for ammonia neutralization, and the final pH of the reaction is controlled at 2.3-2.5. S3, Second-stage neutralization: The first-stage neutralization slurry from step S2 is pumped into the first tubular reactor for further ammonia neutralization, and then enters the second-stage neutralization slurry tank to complete the reaction. The pH at the final neutralization point is controlled to be 4.8–5.2. The second-stage neutralization slurry tank is configured to operate under a slightly positive pressure environment, with its operating pressure (gauge pressure) maintained at 6 kPa. S4. Impurity removal and aging: Add ammonium fluoride solution to the second-stage neutralization slurry tank and stir for aging. S5. Filtration and separation: The aged slurry is first filtered through a vertical filter press to obtain coarse filtrate; the pH of the coarse filtrate is adjusted back to 4.5-5.0 using dilute phosphoric acid through a pH adjustment system; the adjusted slurry is then filtered through a plate and frame filter press to obtain fine filtrate. S6. Triple-effect countercurrent concentration: The fine filtrate is concentrated by a triple-effect countercurrent concentration device, and the discharge temperature of the first-effect evaporation chamber is controlled to be 100-110℃. S7. Continuous steady-state crystallization: The concentrated slurry from step S6 is mixed with the mother liquor from the DTB crystallizer in a crystallizer, and then heated to 95-100°C by a crystallizer heater for circulating crystallization. The slurry is then fed into the DTB crystallizer for crystallization at 52-60°C. The resulting crystal slurry is sent to a centrifuge for separation to obtain wet crystals and mother liquor. Part of the mother liquor is returned to the acid conditioning tank in step S1, and the other part of the mother liquor is returned to the concentration system in step S6. S8. Drying and sieving: Dry and sieve the wet crystals to obtain ammonium dihydrogen phosphate product.

[0014] As a preferred technical feature, in step S2, the molar ratio of ammonia to phosphoric acid is 0.85 to 0.88; in step S3, the molar ratio of ammonia to phosphoric acid is 1.2 to 1.3, and the reaction time is 5 to 7 minutes.

[0015] As a preferred technical feature, in step S4, the ammonium fluoride solution is prepared by reacting fluorosilicic acid and ammonia in a molar ratio of 1:1 in a second tubular reactor and preparing a solution with a mass concentration of 8-15%; the amount of ammonium fluoride solution added is 0.5%-2% of the mass of the second-stage neutralization slurry.

[0016] As a preferred technical feature, the pH value of the coarse filtrate after primary filtration in step S5 is 5.0 to 5.5; after pH rebalancing, the molar ratio of ammonia to phosphoric acid is adjusted back to 1.04 to 1.05; the pH rebalancing system uses dilute phosphoric acid (WPA) as a pH rebalancing agent.

[0017] As a preferred technical feature, in step S6, the triple-effect countercurrent concentration device adopts stepped pressure operation, controlling the pressure of the triple-effect evaporation chamber to be -80 to -68 kPa (gauge pressure), the pressure of the second-effect evaporation chamber to be -50 to -30 kPa (gauge pressure), and the pressure of the first-effect evaporation chamber to be 70 to 100 kPa (gauge pressure).

[0018] The filtered monoammonium phosphate solution is first pumped into a triple-effect evaporator (i.e., flash evaporator), and after being circulated and heated in a triple-effect heating chamber (i.e., shell and tube heat exchanger), the superheated solution is returned to the triple-effect evaporator for flash evaporation. The concentrated solution is then pumped to a double-effect evaporator via a triple-effect transfer pump, circulated and heated in the double-effect heating chamber, flash evaporated, and then sent to a single-effect evaporator. After being circulated and heated in the single-effect heating chamber, flash evaporated, and then sent to the crystallization process.

[0019] As a preferred technical feature, in step S7, the mass ratio of concentrated slurry to mother liquor is 1:1 to 2; both the crystallization and crystallization processes are carried out under vacuum conditions of -80 to -90 kPa. The concentrated slurry from step S6 is mixed with the DTB crystallizer mother liquor in the crystallizer, with a concentrated slurry to mother liquor ratio of 1:1 to 2. After being heated by the crystallization heater and circulated to eliminate fine crystals, the mixture is then pumped to the crystallizer for flash cooling and crystallization. The crystallizer and the top of the crystallizer are connected to a crystallization vacuum system, maintaining a negative pressure of -80 to -90 kPa (gauge pressure). The crystallizer temperature is controlled at 95 to 100°C, and the crystallization temperature is controlled at 52 to 60°C. The crystal slurry is taken from the lower part of the DTB crystallizer and sent to a double-push centrifuge to separate the mother liquor. Part of the mother liquor is returned to the acid conditioning tank, and the other part is returned to the feed end of the triple-effect evaporator.

[0020] As a preferred technical feature, the drying in step S8 is carried out using a vibrating fluidized bed, with a hot air temperature of 100-140°C; the large particles after sieving are dissolved and returned to the acid-adjusting tank in step S1.

[0021] As a preferred technical feature, in step S1, the P2O5 content of concentrated phosphoric acid is ≥42%, and the amount of mother liquor added is 30-60% of the amount of diluted phosphoric acid solution.

[0022] Compared with the prior art, the advantages of the present invention are: Deeply purified to achieve high product purity, the product utilizes a combined process of "segmented neutralization + ammonium fluoride synergistic purification + pH reversal" to specifically promote the deep precipitation and removal of metallic impurities such as Fe, Al, and Mg in the form of thiocyanate-soluble compounds. The product has a main content ≥99% and a water-insoluble content ≤0.01%, meeting high-end application standards.

[0023] The system achieves a high phosphorus yield and makes full use of resources. It optimizes the process route and mother liquor circulation path, and the system phosphorus yield can reach more than 71%, reducing raw material consumption.

[0024] With excellent crystal quality, the "de-crystallization-steady-state crystallization" process effectively controls supersaturation and avoids the formation of fine crystals, resulting in large-size, uniform single crystals with an average particle size of 624μm. The product has good flowability and high purity.

[0025] With significant cost advantages, the use of purified wet-process phosphoric acid to replace thermal-process phosphoric acid significantly reduces production costs while ensuring high product quality. It can replace thermal-process MAP in high-end fields such as battery materials.

[0026] The equipment is highly efficient and operates stably. It adopts a dedicated tubular reactor, multi-stage neutralization and precise pressure control (including micro-positive pressure and stepped vacuum), resulting in high reaction efficiency, effective control of ammonia partial pressure, low ammonia loss, easy adjustment of process parameters, and strong adaptability. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0028] Figure 1 This is a flow chart of the acid adjustment process to the filtration and separation process of this invention; Figure 2 This is a flow chart of the process from the triple-effect countercurrent concentration process to the continuous steady-state crystallization process of the present invention; Figure 3 This is a flowchart of the drying and screening process of the present invention; Figure 4 This is a structural diagram of the tubular reactor with internal nozzles according to the present invention; Among them, 1-static mixer, 2-acidification tank, 3-rapid ammoniation reactor, 4-first tubular reactor, 5-second-stage neutralization slurry tank, 6-second tubular reactor, 7-ammonium fluoride solution tank, 8-vertical filter press, 9-plate and frame filter press, 10-pH reverse adjustment system, 11-triple-effect evaporator, 12-triple-effect heating chamber, 13-second-effect evaporator, 14-second-effect heating chamber, 15-first-effect evaporator, 16-first-effect heating chamber, 17-crystallizer, 18-crystallizer heater, 19-crystallizer circulation pump, 20-DTB crystallizer, 21-crystallization circulation pump, 22-crystallization collection pump, 23-centrifuge, 24-vibrating fluidized bed, 25-hot air system, 26-bag dust collection system, 27-screening machine, 28-tail gas scrubbing system, 29-concentration vacuum system, 30-crystallization vacuum system, 31-cooling tower. Detailed Implementation

[0029] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0030] The specifications for concentrated phosphoric acid are: P2O5% ≥ 42%, solid content % ≤ 1.5%, AS ≤ 10 ppm, SO42- 2- %≤1% In this embodiment, the concentrated phosphoric acid has a P2O5% content of 45.84%, a solid content of 1.29%, an AS content of 10 ppm, and an SO4 content of 10 ppm. 2- %≤0.82%; such as Figure 1 , Figure 2 and Figure 3 As shown, S1. Acid Adjustment: Purified wet-process concentrated phosphoric acid is diluted with water at a volume ratio of 1:1.2 through static mixer 1, while mother liquor equivalent to 50% of the phosphoric acid solution volume is added to acid adjustment tank 2 for mixing.

[0031] S2, First stage of neutralization: Diluted phosphoric acid enters the rapid ammoniation reactor 3, and ammonia is introduced to neutralize it to pH=2.3, controlling the NH3 / H3PO4 molar ratio to be 0.85~0.88.

[0032] S3, Second-stage neutralization: The slurry enters the first tubular reactor 4 for further neutralization (NH3 / H3PO4 molar ratio 1.2, reaction time 5-7 min), and finally completes the reaction in the second-stage neutralization slurry tank 5, with an overall endpoint pH of 5.0 and a cumulative NH3 / H3PO4 molar ratio of 1.25. The second-stage neutralization slurry tank 5 is configured for a slightly positive pressure operating environment, with its operating pressure (gauge pressure) maintained at 6 kPa; the water vapor generated in the rapid ammoniation reactor 3 and the second-stage neutralization slurry tank 5 is treated by the tail gas scrubbing system 28. S4. Impurity Removal and Aging: Fluorosilicic acid and ammonia are fed together into the second tubular reactor 6 at a molar ratio of 1:1. In the second tubular reactor 6, the fluorosilicic acid and ammonia react, and water is added to make a 10%W ammonium fluoride solution, which is stored in the ammonium fluoride solution tank 7. The solution is then added to the second-stage neutralization slurry tank 5 at 1% of the slurry mass using a metering pump. After stirring and aging for 30 minutes, the solution is sent to the filtration and separation process.

[0033] S5. Filtration and Separation: First, the liquid is filtered through a vertical filter press 8 to obtain a coarse filtrate with pH=5.0. The pH is then adjusted to 4.6 with dilute phosphoric acid (NH3 / H3PO4 molar ratio is adjusted back to 1.04~1.05). The adjusted coarse filtrate is then finely filtered through a plate and frame filter press 9, and then the fine filtrate is sent to a triple-effect countercurrent concentration process.

[0034] S6. Triple-Effect Countercurrent Concentration: The fine filtrate is pumped to the triple-effect evaporator 11, circulated and concentrated in the triple-effect heating chamber 12, then pumped to the second-effect evaporator 13 via a triple-effect transfer pump. After circulated and concentrated in the second-effect heating chamber 14, it is pumped to the first-effect evaporator 15 via a second-effect transfer pump. After circulated and concentrated in the first-effect heating chamber 16, it is sent to the crystallization process. The triple-effect countercurrent concentration adopts a stepped pressure operation. The heat source for the first-effect heating chamber 16 is low-pressure steam, while the heat source for the second-effect heating chamber 14 and the triple-effect heating chamber 12 is the secondary steam from the previous effect. Through the concentration vacuum system 29, the pressure of the triple-effect evaporator 11 is controlled at -70 kPa, the pressure of the second-effect evaporator 13 is controlled at -45 kPa, and the pressure of the first-effect evaporator 15 is controlled at 90 kPa. The outlet temperature of the first-effect evaporator 15 is controlled at 110℃, and the concentrated slurry is sent to the continuous steady-state crystallization process.

[0035] S7. Continuous Steady-State Crystallization: The concentrated slurry and the clear liquid (i.e., mother liquor) from the upper layer of the DTB crystallizer 20 are mixed at a mass ratio of 1:1 in the crystallizer 17. The mixture is then heated to 95°C by the crystallizer heater 18 and circulated for crystallization at -80 kPa (gauge pressure). After crystallization, the mixture is sent to the crystallizer 20 and crystallized at 52°C and -80 kPa (gauge pressure). The wet crystals are then sent to the drying and screening process. After centrifugation by the double-push centrifuge 23, 60% of the mother liquor is returned to the acidification tank 2, and 40% is returned to the feed section of the triple-effect evaporator.

[0036] S8. Drying and sieving: After the wet crystals are dried in a vibrating fluidized bed 24 at 120℃, they are sieved. After sieving, the large particles dissolve and are returned to the acid conditioning tank. The sieved material is ammonium dihydrogen phosphate product.

[0037] Product specifications: Ammonium dihydrogen phosphate content ≥99%, total nutrients (N+P2O5) 73.4%, water-insoluble matter 0.01%, arsenic content 0.001%, phosphorus yield 71.93%. Example 2:

[0038] The steps are the same as in Example 1, except that the cumulative NH3 / H3PO4 molar ratio in the two-stage neutralization is adjusted to 1.22, and the pH is reversed to 4.7.

[0039] Product specifications: Ammonium dihydrogen phosphate content ≥99%, total nutrients 73.35%, water-insoluble matter 0.01%, phosphorus yield 71.56%. Example 3:

[0040] The steps are the same as in Example 1, except that the cumulative NH3 / H3PO4 molar ratio in the two-stage neutralization is adjusted to 1.28, and the amount of ammonium fluoride added is 0.8%.

[0041] Product specifications: Ammonium dihydrogen phosphate content 98.9%, total nutrients 73%, water-insoluble matter 0.01%, phosphorus yield 72.05%. Example 4

[0042] like Figure 1 , Figure 2 and Figure 3 As shown, an apparatus for producing low-impurity, fully water-soluble ammonium dihydrogen phosphate by concentrated acid method includes an acid adjustment system, a neutralization reaction system, an impurity removal and aging system, a filtration and separation system, a concentration system, a continuous steady-state crystallization system, a drying system, a tail gas scrubbing system, and a vacuum system connected in sequence by pipelines. The acid adjustment system consists of a static mixer 1 and an acid adjustment tank 2, which is used to adjust the phosphoric acid concentration and mix it into the mother liquor; The neutralization reaction system consists of a rapid ammoniation reactor 3, a first tubular reactor 4, and a second-stage neutralization slurry tank 5 connected in series; it is used for the staged neutralization reaction of ammonia / liquid ammonia with phosphoric acid to generate ammonium dihydrogen phosphate, while simultaneously precipitating out metal impurities. The impurity removal and aging system consists of a second tubular reactor 6 and an ammonium fluoride solution tank 7; it is used to prepare the ammonium fluoride solution as a reaction impurity removal additive to promote the formation of metal precipitation. The filtration and separation system includes a vertical filter press 8, a pH adjustment system 10, and a plate and frame filter press 9 connected in sequence; it is used for two-stage filtration to separate solid impurities. The concentration system is a triple-effect countercurrent concentration device; the triple-effect countercurrent concentration device includes a first-effect evaporation chamber 15, a first-effect heating chamber 16, a second-effect evaporation chamber 13, a second-effect heating chamber 14, a third-effect evaporation chamber 11, and a third-effect heating chamber 12; by adopting the triple-effect countercurrent concentration method, the pressure and temperature of the evaporation chambers can be controlled to ensure the good operation of the subsequent crystallization system; The continuous steady-state crystallization system consists of a circulating crystal removal system and a crystallization system. The circulating crystal removal system includes a crystal remover 17, a crystal removal heater 18, and a crystal removal circulation pump 19. The crystallization system includes a DTB crystallizer 20, a crystallization circulation pump 21, a crystallization extraction pump 22, and a centrifuge 23. The centrifuge 23 is a double-push centrifuge 23. The drying system includes a vibrating fluidized bed 24; The exhaust gas scrubbing system 28 is connected to the exhaust end of the neutralization reaction system; The vacuum system includes a separate concentration vacuum system 29 and a crystallization vacuum system 30; The static mixer 1 is internally constructed from welded spiral blades that twist left and right in a single channel; the second tubular reactor 6 is internally constructed from a cylindrical structure assembled from corrugated plates, with adjacent sets of corrugated plate units installed at a 90° offset; the mixing gas phase space of the crystal eliminator 17 is greater than 1m. 3 .

[0043] As a preferred technical feature, the drying system further includes a hot air system 25, a bag dust collection system 26, and a screening machine 27; In the neutralization reaction system, the rapid ammoniaation reactor 3, the first tubular reactor 4, and the second-stage neutralization slurry tank 5 form a three-stage ammonia-passing, interconnected series structure. The first tubular reactor 4 is a tubular reactor with internal nozzles (see...). Figure 4 ).

[0044] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An apparatus for producing low-impurity, fully water-soluble ammonium dihydrogen phosphate using a concentrated acid method, characterized in that: It includes an acid adjustment system, a neutralization reaction system, a purification and aging system, a filtration and separation system, a concentration system, a continuous steady-state crystallization system, a drying system, a tail gas scrubbing system, and a vacuum system, all connected in sequence via pipelines. The acid conditioning system consists of a static mixer and an acid conditioning tank; The neutralization reaction system consists of a rapid ammoniation reactor, a first tubular reactor, and a second-stage neutralization slurry tank connected in series. The impurity removal and aging system consists of a second tubular reactor and an ammonium fluoride solution tank. The filtration and separation system includes a vertical filter press, a pH adjustment system, and a plate and frame filter press connected in sequence. The concentration system is a triple-effect countercurrent concentration device; A continuous steady-state crystallization system consists of a circulating crystal elimination system and a crystallization system. The circulating crystal elimination system includes a crystal elimination device, a crystal elimination heater, and a crystal elimination circulation pump. The crystallization system includes a DTB crystallizer, a crystallization circulation pump, a crystallization extraction pump, and a centrifuge. Drying system, including vibrating fluidized bed; An exhaust gas scrubbing system is connected to the exhaust end of the neutralization reaction system; Vacuum systems, including separate concentration vacuum systems and crystallization vacuum systems; The static mixer is internally constructed from welded spiral blades that twist left and right in a single channel; the second tubular reactor is internally constructed from a cylindrical structure assembled from corrugated plates, with adjacent sets of corrugated plate units offset by 90 degrees; the mixing gas phase space of the crystallizer is greater than 1m. 3 .

2. The apparatus for producing low-impurity, fully water-soluble ammonium dihydrogen phosphate by concentrated acid method as described in claim 1, characterized in that: The drying system also includes a hot air system, a bag dust collection system, and a screening machine; In the neutralization reaction system, the rapid ammoniation reactor, the first tubular reactor, and the second-stage neutralization slurry tank are connected in series in a three-stage ammonia-passing manner. The second-stage neutralization slurry tank is configured to operate under a slightly positive pressure environment, with its operating pressure maintained at 6 kPa, which is gauge pressure.

3. A method for producing low-impurity, fully water-soluble ammonium dihydrogen phosphate using the apparatus described in claim 1 or 2, characterized in that, Includes the following steps: S1. Acid adjustment: The purified concentrated phosphoric acid is diluted with water through a static mixer, and the mother liquor is added to the acid adjustment tank and mixed with the diluted phosphoric acid. S2, First stage of neutralization: The acidified phosphoric acid is fed into a rapid ammoniation reactor for ammonia neutralization, and the final pH of the reaction is controlled at 2.3-2.

5. S3, Second-stage neutralization: The first-stage neutralization slurry from step S2 is pumped into the first tubular reactor for further ammonia neutralization, and then enters the second-stage neutralization slurry tank to complete the reaction. The pH at the final neutralization point is controlled to be 4.8–5.

2. The second-stage neutralization slurry tank is configured for a slightly positive pressure operating environment, with its operating pressure maintained at 6 kPa, which is the gauge pressure. S4. Impurity removal and aging: Add ammonium fluoride solution to the second-stage neutralization slurry tank and stir for aging. S5. Filtration and separation: The aged slurry is first filtered through a vertical filter press to obtain coarse filtrate; the pH of the coarse filtrate is adjusted back to 4.5-5.0 using dilute phosphoric acid through a pH adjustment system; the adjusted slurry is then filtered through a plate and frame filter press to obtain fine filtrate. S6. Triple-effect countercurrent concentration: The fine filtrate is concentrated by a triple-effect countercurrent concentration device, and the discharge temperature of the first-effect evaporation chamber is controlled to be 100-110℃. S7. Continuous steady-state crystallization: The concentrated slurry from step S6 is mixed with the mother liquor from the DTB crystallizer in a crystallizer, and then heated to 95-100°C by a crystallizer heater for circulating crystallization. The slurry is then fed into the DTB crystallizer for crystallization at 52-60°C. The resulting crystal slurry is sent to a centrifuge for separation to obtain wet crystals and mother liquor. Part of the mother liquor is returned to the acid conditioning tank in step S1, and the other part of the mother liquor is returned to the concentration system in step S6. S8. Drying and sieving: Dry and sieve the wet crystals to obtain ammonium dihydrogen phosphate product.

4. The method as described in claim 3, characterized in that: In step S2, the molar ratio of ammonia to phosphoric acid is 0.85–0.88; in step S3, the molar ratio of ammonia to phosphoric acid is 1.2–1.3, and the reaction time is 5–7 min.

5. The method as described in claim 3, characterized in that: In step S4, the ammonium fluoride solution is prepared by reacting fluorosilicic acid and ammonia in a molar ratio of 1:1 in a second tubular reactor and preparing a solution with a mass concentration of 8-15%. The amount of ammonium fluoride solution added is 0.5%-2% of the mass of the neutralized slurry in the second stage.

6. The method as described in claim 3, characterized in that: In step S5, the pH value of the coarse filtrate after primary filtration is 5.0–5.5; after pH rebalancing, the molar ratio of ammonia to phosphoric acid is adjusted back to 1.04–1.05; the pH rebalancing system uses dilute phosphoric acid as a pH rebalancing agent.

7. The method as described in claim 3, characterized in that: In step S6, the triple-effect countercurrent concentration device operates under stepped pressure. The triple-effect evaporation chamber operates at a gauge pressure of -80 to -68 kPa, the second-effect evaporation chamber operates at a gauge pressure of -50 to -30 kPa, and the first-effect evaporation chamber operates at a gauge pressure of 70 to 100 kPa.

8. The method as described in claim 3, characterized in that: In step S7, the mass ratio of concentrated slurry to mother liquor is 1:1 to 2; both the crystallization and crystallization processes are carried out under vacuum conditions with a gauge pressure of -80 to -90 kPa.

9. The method as described in claim 3, characterized in that: In step S8, drying is carried out using a vibrating fluidized bed with a hot air temperature of 100–140°C; the large particles after sieving are dissolved and returned to the acid-adjusting tank in step S1.

10. The method as described in claim 3, characterized in that: In step S1, the P2O5 content of concentrated phosphoric acid is ≥42%, and the amount of mother liquor added is 30-60% of the amount of diluted phosphoric acid solution.

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