Method and system for producing phosphoric acid by semi-hydrated-dihydrated wet process

Abstract

This invention discloses a method and system for producing hemihydrate-dihydrate wet-process phosphoric acid, specifically relating to the field of phosphoric acid chemical technology. The system includes a hemihydrate reaction process and a dihydrate reaction process. The hemihydrate reaction unit includes a pressure filter, a dissolution module, a crystallization module, a hemihydrate flash cooler, a hemihydrate filter feed tank, a fluorine recovery module, and a hemihydrate filter. The dihydrate reaction unit includes a dihydrate conversion module, a dihydrate flash cooler, and a dihydrate filter, and a crystallization modifier is added to the crystallization module. This invention can use both wet and dry phosphate rock powder as raw materials to produce wet-process phosphoric acid, demonstrating strong adaptability to phosphate rock. It features a high start-up rate and produces high-quality phosphoric acid and fluorosilicic acid as a byproduct. The equipment is more energy-efficient and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of phosphoric acid technology, specifically to a wet process method and system for producing hemihydrate-dihydrate phosphoric acid. Background Technology

[0002] Wet-process phosphoric acid production is categorized by the type of phosphogypsum produced. Currently, mature industrialized processes include: dihydrate, hemihydrate, hemihydrate-dihydrate, and dihydrate-hemihydrate. Among these, the traditional dihydrate phosphoric acid process is highly adaptable to phosphate rock, offers stable operation, high utilization rates, and can use medium- to low-grade phosphate rock; it is still used by over 80% of companies worldwide. However, the dihydrate process suffers from problems such as low P2O5 concentration in the produced dilute phosphoric acid, low phosphate rock conversion rate, and difficulties in the comprehensive utilization of phosphogypsum. The hemihydrate-dihydrate process, as an improved wet-process phosphoric acid production process, offers advantages such as high phosphoric acid yield, high concentration of dilute phosphoric acid in the product, and good quality phosphogypsum. However, existing hemihydrate-dihydrate processes have high requirements for the quality of raw phosphate rock and its materials. Furthermore, the fine crystals of hemihydrate phosphogypsum significantly increase filtration difficulty, leading to severe equipment and pipeline blockage, low start-up rates, and high product costs. Therefore, we propose a hemihydrate-dihydrate wet-process phosphoric acid production method and system to address these issues. Summary of the Invention

[0003] The purpose of this invention is to provide a wet process method and system for producing hemihydrate-dihydrate phosphoric acid, in order to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a hemihydrate-dihydrate wet process phosphoric acid production system, comprising a hemihydrate reaction unit and a dihydrate reaction unit, wherein the hemihydrate reaction unit comprises a pressure filter, a dissolution module, a crystallization module, a hemihydrate flash cooler, a hemihydrate filter feed tank, a fluorine recovery module, and a hemihydrate filter. The pressure filter is connected to the dissolution module; the dissolution module is connected to the crystallization module; the crystallization module is connected to the semi-aqueous flash cooler; the gas phase outlet of the semi-aqueous flash cooler is connected to the fluorine recovery module; the liquid phase outlet of the semi-aqueous flash cooler is connected to the semi-aqueous filter feed tank; the semi-aqueous filter feed tank is connected to the crystallization module and the semi-aqueous filter; the semi-aqueous filter is connected to the dissolution module and the crystallization module. The dihydrate reaction unit includes a dihydrate conversion module, a dihydrate flash cooler, and a dihydrate filter. The inlet and outlet of the dihydrate flash evaporator are connected to the dihydrate conversion module; the outlet of the dihydrate conversion module is connected to the dihydrate filter; and the liquid phase outlet of the dihydrate filter is connected to the washing liquid inlet of the half-water filter.

[0005] In a preferred embodiment of the present invention, the dissolving module includes a dissolving tank #1, a dissolving tank #2, a dissolving tank #3, and a dissolving tank #4 connected in sequence; the crystallization module includes a crystallization tank #1 and a crystallization tank #2 connected in sequence; the dissolving tank #4 is connected to the crystallization tank #1; the crystallization tank #2 is connected to a semi-water flash cooler; and the outlet of the crystallization tank #2 is connected to the inlet of the dissolving tank #1 via a circulation pipeline to return a portion of the slurry to the dissolving module for recycling.

[0006] In a preferred embodiment of the present invention, the fluorine recovery module includes a fluorine absorption system, a fluorosilicic acid filter, and a silica gel reslurry tank. The gas phase outlet of the semi-aqueous flash cooler is connected to the fluorine absorption system, the liquid phase outlet of the fluorine absorption system is connected to the fluorosilicic acid filter, the fluorosilicic acid filter is connected to the silica gel reslurry tank, and the silica gel reslurry tank is connected to a No. 1 dissolution tank and a No. 1 dihydrate conversion tank.

[0007] In a preferred embodiment of the present invention, the dihydrate conversion module includes a dihydrate conversion high-level tank, a #1 dihydrate conversion tank, and a #2 dihydrate conversion tank. The dihydrate conversion high-level tank is a rectangular tank with multiple stirring paddles inside. The dihydrate conversion high-level tank is connected to a semi-water filter. The outlet of the dihydrate conversion high-level tank is connected to the #1 dihydrate conversion tank. The #1 dihydrate conversion tank is connected to the #2 dihydrate conversion tank. The inlet and outlet of the dihydrate flash evaporator are connected to the #1 dihydrate conversion tank.

[0008] A method for producing hemihydrate-dihydrate wet-process phosphoric acid includes the following steps: S1. Dehydrate the phosphate rock slurry to obtain phosphate rock powder with a water content of ≤15%; S2. Add phosphate rock powder, sulfuric acid, and the acid returned from the hemihydrate flash evaporator to the dissolution module. In the presence of active SiO2, the mixture reacts to produce a hemihydrate reaction slurry containing hemihydrate phosphogypsum and phosphoric acid. S3. The hemihydrate reaction slurry obtained in step S2 is introduced into the crystallization module. Sulfuric acid and the back acid returned from the hemihydrate flash cooler are added to the crystallization module. An amide crystallization modifier is added to the crystallization module. Part of the slurry is refluxed from the crystallization module to the dissolution module, and the other part of the slurry is sent to the hemihydrate flash cooler for cooling. Fluorine-containing gas and cooling slurry are separated. The fluorine-containing gas is sent to the fluorine recovery module for processing. S4. Most of the cooling slurry obtained in step S3 is returned to the crystallization module, and a small portion is sent to the hemihydrate filter to obtain hemihydrate phosphogypsum filter cake and finished phosphoric acid. S5. The hemihydrate phosphogypsum filter cake obtained in step S4 is washed with the filtrate from the dihydrate filter and then introduced into the dihydrate conversion module. Part of the filtrate is returned to the dissolution module and the crystallization module as acid backflow. S6. Sulfuric acid is added to the dihydrate conversion module and reacts with the washed hemihydrate phosphogypsum filter cake from step 5 in the presence of active SiO2 to convert hemihydrate phosphogypsum into dihydrate phosphogypsum. S7. Part of the dihydrate slurry obtained in step S6 is flash-cooled in a dihydrate flash cooler and then fed back to the dihydrate conversion module. The other part is sent to a dihydrate filter for solid-liquid separation to obtain dihydrate phosphogypsum and filtrate. The filtrate is returned to step S5 as washing water for the hemihydrate phosphogypsum filter cake.

[0009] In a preferred embodiment of the present invention, in step S3, after the fluorine-containing gas is absorbed by the fluorine absorption system, 12-18% fluorosilicic acid is sent to the fluorosilicic acid filter for liquid-solid separation. The separated silica gel and diatomaceous earth are re-slurried together to form active SiO2, which is then sent to the No. 1 dissolving tank and the No. 1 dihydrate conversion tank.

[0010] In a preferred embodiment of the present invention, in step S2, the reaction temperature is controlled at 92~100℃, and the SO4 in the semi-aqueous reaction slurry is... 2- The content should be controlled to be 0.5-2% lower than the CaO content.

[0011] In a preferred embodiment of the present invention, in step S3, the crystallization temperature is controlled at 90~98℃, and the SO4 content in the slurry is... 2- The content is controlled to be 1~3.5% higher than the CaO content.

[0012] In a preferred embodiment of the present invention, in step S6, the dihydrate conversion temperature is controlled at 60~65℃, and the SO4 content in the slurry is... 2- The content is controlled at 7-9%.

[0013] To address the issue of poor filtration due to the small particle size of hemihydrate phosphogypsum produced during the hemihydrate reaction process, for example, when using a certain phosphate rock as raw material for the production of hemihydrate-dihydrate wet-process phosphoric acid, the average particle size of the hemihydrate phosphogypsum produced during the hemihydrate reaction is 8 mm. m, filtration intensity 4tP2O5·m -2 ·d -1 The filtration performance was poor. Adding an amide-based crystallization modifier to crystallization tank #1 promoted crystal nucleus growth, resulting in larger and more uniform hemihydrate phosphogypsum particles. After adding the crystallization modifier, the average particle size of the hemihydrate phosphogypsum was 55 mm. m, filtration intensity 9tP2O5·m -2 ·d -1 It has good filtration performance and improves the operating rate of the unit.

[0014] The production of hemihydrate-dihydrate wet-process phosphoric acid requires high-quality phosphate rock, typically with an impurity factor (MER) ≤ 0.1. If the content of these metal oxide impurities in the phosphate rock exceeds the required value, the hemihydrate phosphogypsum crystals will be finer, making filtration more difficult. For phosphate rock with a high MER, a crystallization modifier is added during the crystallization process, and the SO4 concentration in the dissolution module is adjusted. 2- The content of SO4 during acid hydrolysis is high when the impurity content is high. 2- The increased content of SO4 is beneficial to the initial formation of hemihydrate phosphogypsum crystal nuclei, and SO4 in a suitable crystallization module... 2- At a certain concentration, the SO4 in the dissolution module 2- Increased content leads to increased filtration intensity.

[0015] If a certain phosphate rock with a MER of 0.146 is used as raw material for the production of hemihydrate-dihydrate wet-process phosphoric acid, an amide crystallization modifier is added to crystallization tank #1: SO4 in the control dissolution module 2- The content is 0.5%, SO4 in the crystallization module 2- When the content is 5%, the filtration intensity is 5.6tP2O5·m. -2 ·d -1 ; SO4 in the control dissolution module 2- The content is 2%, SO4 in the crystallization module 2- When the content is 5%, the filtration intensity is 10.3tP2O5·m -2 ·d -1 The filtration intensity is significantly improved; SO4 in the control dissolution module 2- The content is 2%, SO4 in the crystallization module 2- When the content is 8%, the filtration intensity is 10.45tP2O5·m. -2 ·d -1 The increase in filtration intensity is not significant.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This hemihydrate-dihydrate wet process for producing phosphoric acid uses wet phosphate rock powder with a water content of ≤15% as the raw material. The raw phosphate rock can be wet-milled, and the phosphate rock slurry is dewatered using a fully automated pressure filter that is stable, efficient, energy-saving, and environmentally friendly. No further drying is required, making it more energy-efficient and environmentally friendly than dry milling.

[0017] 2. This hemihydrate-dihydrate wet process for producing phosphoric acid involves filtering and separating the fluorosilicic acid recovered from the hemihydrate flash-cooled fluorine absorption system. The separated silica gel is then added to the dissolving tank and the dihydrate conversion tank, which reduces equipment corrosion and improves the quality of the product phosphoric acid and the byproduct fluorosilicic acid.

[0018] 3. This wet process for producing hemihydrate-dihydrate phosphoric acid promotes crystal growth by adding amide crystallization modifiers, resulting in coarser and more uniform hemihydrate phosphogypsum, which can increase filtration intensity by at least 100% and improve the plant's start-up rate.

[0019] 4. This wet process for producing hemihydrate-dihydrate phosphoric acid involves adding a crystallization modifier during the crystallization process of phosphate rock with high MER (Mean Interval), while simultaneously adjusting the SO4 levels in the dissolution tank. 2- The content of phosphogypsum promotes the increase of crystal particle size, improves filtration strength, and increases the operating rate. The technology of this invention can use phosphate rock with a high impurity coefficient, which increases the adaptability to phosphate rock. Attached Figure Description

[0020] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the present invention.

[0022] In the diagram: 1. Pressure filter; 2. Dissolving tank #1; 3. Dissolving tank #2; 4. Dissolving tank #3; 5. Dissolving tank #4; 6. Crystallization tank #1; 7. Crystallization tank #2; 8. Semi-aqueous flash cooler; 9. Semi-aqueous filter feeder; 10. Fluorine absorption system; 11. Fluorosilicic acid filter; 12. Semi-aqueous filter; 13. Dihydrate conversion high-level tank; 14. Dihydrate conversion tank #1; 15. Dihydrate conversion tank #2; 16. Dihydrate flash cooler; 17. Dihydrate filter; 18. Silica gel reslurry tank. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 A wet process phosphoric acid production system of hemihydrate-dihydrate includes a hemihydrate reaction unit and a dihydrate reaction unit. The hemihydrate reaction unit includes a pressure filter 1, a dissolution module, a crystallization module, a hemihydrate flash cooler 8, a hemihydrate filter feed tank 9, a fluorine recovery module, and a hemihydrate filter 12. The pressure filter 1 is connected to the dissolution module; the dissolution module is connected to the crystallization module; the crystallization module is connected to the semi-water flash cooler 8; the gas phase outlet of the semi-water flash cooler 8 is connected to the fluorine recovery module; the liquid phase outlet of the semi-water flash cooler 8 is connected to the semi-water filter feed tank 9; the semi-water filter feed tank 9 is connected to the crystallization module and the semi-water filter 12; and the semi-water filter 12 is connected to the dissolution module and the crystallization module. The dihydrate reaction unit includes a dihydrate conversion module, a dihydrate flash cooler 16, and a dihydrate filter 17; The inlet and outlet of the dihydrate flash evaporator 16 are connected to the dihydrate conversion module; the outlet of the dihydrate conversion module is connected to the dihydrate filter 17; and the liquid phase outlet of the dihydrate filter 17 is connected to the washing liquid inlet of the half-water filter 12.

[0025] Furthermore, the dissolving module includes dissolving tank 2 (1#), dissolving tank 3 (2#), dissolving tank 4 (3#), and dissolving tank 5 (4#) connected in sequence. The crystallization module includes crystallization tank 6 (1#) and crystallization tank 7 (2#) connected in sequence. Dissolving tank 5 (4#) is connected to crystallization tank 6 (1#), and crystallization tank 7 (2#) is connected to a semi-water flash cooler 8. The outlet of crystallization tank 7 (2#) is connected to the inlet of dissolving tank 2 (1#) through a circulation pipeline to return part of the slurry to the dissolving module for recycling reaction.

[0026] Furthermore, the fluorine recovery module includes a fluorine absorption system 10, a fluorosilicic acid filter 11, and a silica gel reslurry tank 18. The gas phase outlet of the semi-water flash cooler 8 is connected to the fluorine absorption system 10, the liquid phase outlet of the fluorine absorption system 10 is connected to the fluorosilicic acid filter 11, the fluorosilicic acid filter 11 is connected to the silica gel reslurry tank 18, and the silica gel reslurry tank 18 is connected to the No. 1 dissolution tank 2 and the No. 1 dihydrate conversion tank 14.

[0027] Furthermore, the dihydrate conversion module includes a dihydrate conversion high-level tank 13, a #1 dihydrate conversion tank 14, and a #2 dihydrate conversion tank 15. The dihydrate conversion high-level tank 13 is a rectangular tank with multiple stirring paddles inside. The dihydrate conversion high-level tank 13 is connected to the semi-water filter 12. The outlet of the dihydrate conversion high-level tank 13 is connected to the #1 dihydrate conversion tank 14. The #1 dihydrate conversion tank 14 is connected to the #2 dihydrate conversion tank 15. The inlet and outlet of the dihydrate flash evaporator 16 are connected to the #1 dihydrate conversion tank 14.

[0028] The various devices are connected by pipes, which are equipped with valves and pumps to control the flow rate and direction of the slurry. For example, pressure filter 1 and dissolving tank 2 are connected by a belt conveyor for conveying phosphate rock powder; dissolving tank 2 is connected to dissolving tanks 3, 4, and 5 via bottom pipes, allowing the slurry to circulate between the dissolving tanks; crystallization tank 6 is connected to crystallization tank 7 via bottom pipes, allowing the slurry to circulate between the crystallization tanks; semi-aqueous flash cooling tower 8 is connected to semi-aqueous filter feed tank 9 via pipes; semi-aqueous filter feed tank 9 is connected to semi-aqueous filter 12 via pipes; semi-aqueous filter 12 is connected to dihydrate conversion high-level tank 13 via pipes; dihydrate conversion high-level tank 13 is connected to dihydrate conversion tank 14 via pipes; dihydrate conversion tank 14 is connected to dihydrate conversion tank 15 via bottom pipes; dihydrate conversion tank 15 is connected to dihydrate filter 17 via pipes; dihydrate filter 17 is connected to semi-aqueous filter 12 via pipes for conveying washing water.

[0029] Example 2 This embodiment provides a method for producing hemihydrate-dihydrate wet-process phosphoric acid, using the hemihydrate-dihydrate wet-process phosphoric acid production system provided in Example 1, including the following steps: S1. Dehydrate the phosphate rock slurry to obtain phosphate rock powder with a water content of ≤15%; S2. Add phosphate rock powder, sulfuric acid, and the acid returned from the semi-aqueous flash cooler 8 to the dissolution module. The temperature is controlled at 92~100℃. The reaction is carried out in the presence of active SiO2 to generate a semi-aqueous reaction slurry containing hemihydrate phosphogypsum and phosphoric acid. The above hemihydrate reaction equation is as follows: Ca5F(PO4)3+5H2SO4=5CaSO4·1 / 2H2O↓+3H3PO4+HF↑ 6HF + SiO2 = H2SiF6 + 2H2O S3. Introduce the hemihydrate reaction slurry obtained in step S2 into the crystallization module. Add sulfuric acid and the return acid from the hemihydrate flash cooler 8 into the crystallization module. Control the temperature at 90~98℃. SO4 in the slurry... 2- The content is controlled to be 1-3.5% higher than the CaO content. Amide crystallization modifiers are added in the crystallization module to control the supersaturation of the solution and avoid material encapsulation, so that the phosphate rock can be decomposed in a system with constant concentration. Part of the slurry is recycled from the crystallization module to the dissolution module for circulation, and the circulation slurry ratio is controlled to be 10-20. In order to remove the heat of reaction and control the reaction temperature, another part of the slurry is sent to the semi-water flash cooler 8 for cooling. The temperature of the cooled slurry exiting the semi-water flash cooler 8 is controlled to be 80-85℃. Fluorine-containing gas and cooled slurry are separated. The fluorine-containing gas is sent to the fluorine recovery module for treatment. S4. Most of the cooling slurry obtained in step S3 is returned to the crystallization module, and a small portion is sent to the hemihydrate filter 12 to obtain hemihydrate phosphogypsum filter cake and finished phosphoric acid. The finished phosphoric acid (P2O5 concentration 38~45%) is the hemihydrate filtrate and is sent to the tank area for storage. S5. The hemihydrate phosphogypsum filter cake obtained in step S4 is washed with the filtrate from the dihydrate filter 17 and then introduced into the dihydrate conversion module. Part of the filtrate is returned to the dissolution module and the crystallization module as acid backflow. In order to avoid uneven mixing and local overheating due to heat expansion when sulfuric acid and acid backflow are directly added to the dissolution module and the crystallization module, the acid backflow from the hemihydrate filter is first premixed with sulfuric acid in the mixing tee installed on the No. 2 dissolution tank 3, No. 3 dissolution tank 4 and No. 1 crystallization tank 6, and then evenly dispersed into the liquid through the dilution tube. It should be noted that the mixing tee is made of corrosion-resistant material and the dilution tube is equipped with multiple distribution holes to ensure that the sulfuric acid and acid backflow are fully mixed before entering the reaction system. S6. The hemihydrate phosphogypsum from the hemihydrate filter 12 enters the dihydrate conversion high-level tank 13. The dihydrate conversion high-level tank is a rectangular tank equipped with several stirring paddles. Sulfuric acid is added to the dihydrate conversion module and reacts with the hemihydrate phosphogypsum filter cake washed in step 5 in the presence of active SiO2 to convert the hemihydrate phosphogypsum into dihydrate phosphogypsum. S7. Part of the dihydrate slurry obtained in step S6 is flash-cooled in the dihydrate flash evaporator 16 and then fed back to the dihydrate conversion module. The other part is sent to the dihydrate filter 17 for solid-liquid separation to obtain dihydrate phosphogypsum and filtrate. The filtrate is returned to step S5 as washing water for the hemihydrate phosphogypsum filter cake to recover P2O5 released from the calcium sulfate lattice, thereby improving the P2O5 recovery rate.

[0030] Furthermore, in step S3, after the fluorine-containing gas is absorbed by the fluorine absorption system 10, 12-18% fluorosilicic acid is sent to the fluorosilicic acid filter 11 for liquid-solid separation. The separated silica gel and diatomaceous earth are re-slurried together to form active SiO2, which is then sent to the No. 1 dissolution tank 2 and the No. 1 dihydrate conversion tank 14.

[0031] Furthermore, in step S2, the reaction temperature is controlled at 92~100℃, and the SO4 in the semi-aqueous reaction slurry is... 2- The content should be controlled to be 0.5-2% lower than the CaO content.

[0032] Furthermore, in step S3, the crystallization temperature is controlled at 90~98℃, and the SO4 content in the slurry is reduced. 2- The content is controlled to be 1~3.5% higher than the CaO content.

[0033] Furthermore, in step S6, the dihydrate conversion temperature is controlled at 60~65℃, and the SO4 content in the slurry is... 2- The content is controlled at 7-9%.

[0034] The method for producing 200,000 tons / year of hemihydrate-dihydrate wet-process phosphoric acid using phosphate rock slurry with 62% solids content (MER=0.14) and 98% concentrated sulfuric acid as raw materials is as follows: 1. The phosphate rock slurry containing 62% solids is sent to pressure filter 1 for dewatering, controlling the moisture content of the phosphate rock to ≤15%. The dewatered phosphate rock powder is then metered and conveyed by belt to dissolving tank 2 (No. 1), using a filter with a filtration area of ​​120m². 2 Three pressure filters are installed, two in operation and one on standby, to ensure continuous operation of the equipment.

[0035] 2. Diatomaceous earth and silica gel filter residue from fluorosilicic acid filter 11 are fed into silica gel reslurry tank 18. After reslurrying, they are sent to dissolving tank 2 and dihydrate conversion tank 14. The SiO2 addition amount in dissolving tank 2 is 10~15 kg / t P2O5, and the SiO2 addition amount in dihydrate conversion tank 14 is 2 t / h.

[0036] 3. 98% concentrated sulfuric acid and the back acid from the semi-aqueous filter 12 are mixed and added to dissolving tanks 3 and 4 (2# and 3# respectively). The phosphate rock powder, 98% concentrated sulfuric acid, and back acid react in the presence of active SiO2, with the reaction temperature controlled at 92-100℃. SO42- in the semi-aqueous reaction slurry... 2- The content is controlled at 2%. The solid content of the reaction slurry is controlled at 32%; the acid concentration in the liquid phase is controlled at 41% P2O5, and the reaction produces calcium sulfate hemihydrate (CaSO4). (1 / 2H₂O) crystals react with phosphoric acid. The reaction equation is as follows: Ca5F(PO4)3+5H2SO4=5CaSO4·1 / 2H2O↓+3H3PO4+HF↑ 6HF + SiO2 = H2SiF6 + 2H2O 4. The generated semi-aqueous reaction slurry overflows from dissolving tank 5 (4#) to crystallizing tank 6 (1#). 98% concentrated sulfuric acid and the backflow acid from the semi-aqueous filter 12 are mixed and added to crystallizing tank 6 (1#) for crystallization. 80 mg / kg of [acid concentration not specified] is added to crystallizing tank 6 (1#). -1 Polyacrylamide crystallization modifier. Crystallization temperature should be controlled between 90~98℃, and SO4 content in the slurry should be controlled. 2- The content is controlled at 5%.

[0037] 5. A portion of the slurry is drawn from crystallization tank 7 (No. 2) and circulated into dissolving tank 2 (No. 1), with the slurry-to-circulation ratio controlled at 16.5. The remaining portion is sent to a semi-aqueous flash cooler 8 for cooling to maintain the crystallization temperature. The cooling slurry temperature is controlled at 80-85℃. Most of the cooled slurry is returned to crystallization tank 6 (No. 1), and a small portion is sent to a semi-aqueous filter 12 for filtration and washing.

[0038] 6. Semi-water flash cooler 8 (belt filter): The fluorine-containing gas flashed out is absorbed by the fluorine absorption system 10, and the 12~18% fluorosilicic acid is sent to the filter with a filtration area of ​​25m². 2 The fluorosilicic acid filter 11 performs liquid-solid separation. The separated silica gel is sent to the No. 1 dissolution tank 2 and the No. 1 dihydrate conversion tank 14. The purified by-product fluorosilicic acid is sent to the tank area for storage.

[0039] 7. The hemihydrate reaction slurry undergoes liquid-solid separation via hemihydrate filter 12 (belt filter). Two hemihydrate filters are in operation, with one on standby. The 41% P2O5 filtrate obtained after filtration is the finished phosphoric acid, which is sent to the tank area for storage. The hemihydrate phosphogypsum filter cake is washed with filtrate from dihydrate filter 17 and then sent to the dihydrate reaction process. The acid from hemihydrate filter 12 is returned to dissolving tanks 3 (2#), 4 (3#), and 6 (1#).

[0040] 8. The hemihydrate phosphogypsum from the hemihydrate filter 12 enters the dihydrate conversion high-level tank 13. The dihydrate conversion high-level tank 13 is a rectangular tank with dimensions of 27750 (L) x 4000 (W) x 2500 (H). The tank is equipped with 5 agitators. The hemihydrate phosphogypsum slurry is pushed into the No. 1 dihydrate conversion tank 14 by the agitators, which reduces the risk of clogging and makes the operation of the device more stable. It should be noted that the rotation speed of the agitators can be adjusted according to the properties of the slurry and the delivery volume to ensure that the slurry flows evenly and does not produce sediment.

[0041] 9. 98% concentrated sulfuric acid is added to tank 14 of dihydrate conversion tank #1. A hydration reaction is carried out in the presence of concentrated sulfuric acid and active SiO2 to produce hemihydrate phosphogypsum (CaSO4). 1 / 2H2O) water synthesizes gypsum dihydrate (CaSO4) 2H₂O). Control the temperature at 60~65℃, SO₄²⁻ 2- The content is controlled at 7-9%.

[0042] 10. The slurry coming out of the No. 1 dihydrate conversion tank 14 enters the dihydrate flash cooling 16 for flash cooling, and the cooled slurry returns to the No. 1 dihydrate conversion tank 14.

[0043] 11. The slurry from the No. 2 dihydrate conversion tank 15 enters the dihydrate filter 17 for liquid-solid separation. After three countercurrent washings, the filtrate is sent to the semi-aqueous filter 12 as filter cake washing water. The resulting dihydrate phosphogypsum is sent to the slag yard for storage or comprehensive utilization.

[0044] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A wet-process phosphoric acid production system consisting of a hemihydrate and a dihydrate reaction unit, characterized in that: The hemi-aqueous reaction unit includes a pressure filter (1), a dissolution module, a crystallization module, a hemi-aqueous flash cooler (8), a hemi-aqueous filter feed tank (9), a fluorine recovery module, and a hemi-aqueous filter (12). The pressure filter (1) is connected to the dissolution module; the dissolution module is connected to the crystallization module; the crystallization module is connected to the semi-water flash cooler (8); the gas phase outlet of the semi-water flash cooler (8) is connected to the fluorine recovery module; the liquid phase outlet of the semi-water flash cooler (8) is connected to the semi-water filter feed tank (9); the semi-water filter feed tank (9) is connected to the crystallization module and the semi-water filter (12); the semi-water filter (12) is connected to the dissolution module and the crystallization module. The dihydrate reaction unit includes a dihydrate conversion module, a dihydrate flash cooler (16), and a dihydrate filter (17). The inlet and outlet of the dihydrate flash evaporator (16) are connected to the dihydrate conversion module; the outlet of the dihydrate conversion module is connected to the dihydrate filter (17); and the liquid phase outlet of the dihydrate filter (17) is connected to the washing liquid inlet of the half-water filter (12).

2. The wet-process phosphoric acid production system according to claim 1, characterized in that: The dissolving module includes a dissolving tank 1 (2), a dissolving tank 2 (3), a dissolving tank 3 (4), and a dissolving tank 4 (5) connected in sequence. The crystallization module includes a crystallization tank 1 (6) and a crystallization tank 2 (7) connected in sequence. The dissolving tank 4 (5) is connected to the crystallization tank 1 (6). The crystallization tank 2 (7) is connected to the semi-water flash cooler (8). The outlet of the crystallization tank 2 (7) is connected to the inlet of the dissolving tank 1 (2) through a circulation pipeline to return part of the slurry to the dissolving module for circulation reaction.

3. The wet-process phosphoric acid production system according to claim 2, characterized in that: The fluorine recovery module includes a fluorine absorption system (10), a fluorosilicic acid filter (11), and a silica gel reslurry tank (18). The gas phase outlet of the semi-water flash cooler (8) is connected to the fluorine absorption system (10), the liquid phase outlet of the fluorine absorption system (10) is connected to the fluorosilicic acid filter (11), the fluorosilicic acid filter (11) is connected to the silica gel reslurry tank (18), and the silica gel reslurry tank (18) is connected to the No. 1 dissolution tank (2) and the No. 1 dihydrate conversion tank (14).

4. The wet-process phosphoric acid production system according to claim 3, characterized in that: The dihydrate conversion module includes a dihydrate conversion high-level tank (13), a #1 dihydrate conversion tank (14), and a #2 dihydrate conversion tank (15). The dihydrate conversion high-level tank (13) is a rectangular tank with multiple stirring paddles inside. The dihydrate conversion high-level tank (13) is connected to a semi-water filter (12). The outlet of the dihydrate conversion high-level tank (13) is connected to the #1 dihydrate conversion tank (14). The #1 dihydrate conversion tank (14) is connected to the #2 dihydrate conversion tank (15). The inlet and outlet of the dihydrate flash evaporator (16) are connected to the #1 dihydrate conversion tank (14).

5. A method for producing hemihydrate-dihydrate wet-process phosphoric acid, the method using the phosphoric acid production system according to any one of claims 1-4, characterized in that: Includes the following steps: S1. Dehydrate the phosphate rock slurry to obtain phosphate rock powder with a water content of ≤15%; S2. Add phosphate rock powder, sulfuric acid, and the acid returned from the semi-water flash cooler (8) to the dissolution module and carry out a mixed reaction in the presence of active SiO2 to generate a semi-water reaction slurry containing semi-water phosphogypsum and phosphoric acid. S3. The semi-aqueous reaction slurry obtained in step S2 is introduced into the crystallization module. Sulfuric acid and the acid returned from the semi-aqueous flash cooler (8) are added to the crystallization module. An amide crystallization modifier is added to the crystallization module. Part of the slurry is returned from the crystallization module to the dissolution module, and the other part of the slurry is sent to the semi-aqueous flash cooler (8) for cooling. Fluorine-containing gas and cooling slurry are separated. The fluorine-containing gas is sent to the fluorine recovery module for processing. S4. Most of the cooling slurry obtained in step S3 is returned to the crystallization module, and a small portion is sent to the hemihydrate filter (12) to obtain hemihydrate phosphogypsum filter cake and finished phosphoric acid. S5. The hemihydrate phosphogypsum filter cake obtained in step S4 is washed with the filtrate from the dihydrate filter (17) and then introduced into the dihydrate conversion module. Part of the filtrate is returned to the dissolution module and the crystallization module as acid backflow. S6. Sulfuric acid is added to the dihydrate conversion module and reacts with the washed hemihydrate phosphogypsum filter cake from step 5 in the presence of active SiO2 to convert hemihydrate phosphogypsum into dihydrate phosphogypsum. S7. Part of the dihydrate slurry obtained in step S6 is flash-cooled in a dihydrate flash evaporator (16) and returned to the dihydrate conversion module. The other part is sent to a dihydrate filter (17) for solid-liquid separation to obtain dihydrate phosphogypsum and filtrate. The filtrate is returned to step S5 as washing water for the hemihydrate phosphogypsum filter cake.

6. The method for producing hemihydrate-dihydrate wet-process phosphoric acid according to claim 5, characterized in that: In step S3, after the fluorine-containing gas is absorbed by the fluorine absorption system (10), 12~18% fluorosilicic acid is sent to the fluorosilicic acid filter (11) for liquid-solid separation. The separated silica gel and diatomaceous earth are re-slurried together to form active SiO2, which is sent to the No. 1 dissolution tank (2) and the No. 1 dihydrate conversion tank (14).

7. The method for producing hemihydrate-dihydrate wet-process phosphoric acid according to claim 6, characterized in that: In step S2, the reaction temperature is controlled at 92~100℃, and the SO4 in the semi-aqueous reaction slurry is... 2- The content should be controlled to be 0.5-2% lower than the CaO content.

8. The method for producing hemihydrate-dihydrate wet-process phosphoric acid according to claim 7, characterized in that: In step S3, the crystallization temperature is controlled at 90~98℃, and the SO4 content in the slurry is... 2- The content is controlled to be 1~3.5% higher than the CaO content.

9. The method for producing hemihydrate-dihydrate wet-process phosphoric acid according to claim 8, characterized in that: In step S6, the dihydrate conversion temperature is controlled at 60~65℃, and the SO4 content in the slurry is... 2- The content is controlled at 7-9%.

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