Preparation method of crude desulfurized hemihydrate phosphoric acid in a semi-hydrated wet-process phosphoric acid process

Abstract

This invention provides a method for preparing crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet phosphoric acid process. This invention utilizes CaO in the decomposition tank and SO4 in the crystal growth tank. 2‑ The slurry from both tanks is fed together into the coarse desulfurization reaction tank for mixing and reaction to achieve desulfurization, further simplifying the desulfurization slurry filtration step. Furthermore, vacuum flash evaporation is used to cool the desulfurized slurry before it enters the vacuum filtration system, avoiding excessive scaling within the system. Fluorine generated during vacuum flash evaporation and vacuum filtration is recovered. This invention achieves desulfurization without the need for external desulfurizing agents, reducing the cost of coarse desulfurization reagents and shortening the coarse desulfurization process. It also avoids the P2O5 waste caused by adding phosphate concentrate in traditional coarse desulfurization processes. This invention offers a simple desulfurization process, low cost, and methods to reduce the frequency of cleaning the slurry vacuum filtration system and increase system operating rate.

Description

Technical Field

[0001] This invention belongs to the field of hemihydrate wet phosphoric acid process technology, and relates to a method for preparing crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet phosphoric acid process, and particularly to a method for crude desulfurization and slurry cooling in a hemihydrate wet phosphoric acid process. Background Technology

[0002] Currently, wet phosphoric acid desulfurization mainly involves reacting concentrate with phosphoric acid (calcium desulfurization) and then separating solids and liquids. Because the reaction temperature between concentrate and phosphoric acid is low, the reaction activity is affected, resulting in a significant reduction in concentrate yield. At the same time, a separate pressure filtration system is required, making the entire process lengthy, with high operating costs, and also causing P2O5 waste.

[0003] Because the temperature of the slurry in the semi-aqueous wet phosphoric acid process is high, solid-liquid separation under vacuum conditions can easily cause flash evaporation of the filtrate, resulting in the precipitation of large amounts of fluorosilicates (sodium and potassium) and calcium sulfate, which can clog the system. In actual production, these deposits tend to accumulate on pump casings and valves, leading to reduced pump flow and loss of instrument valve control. This significantly affects the filtration rate of phosphogypsum and reduces system operating rates, severely hindering wet phosphoric acid production.

[0004] In existing industrial production techniques, the removal of sulfate from wet-process phosphoric acid generally involves adding phosphate rock slurry or phosphate rock powder as a desulfurizing agent to the dilute phosphoric acid obtained after slurry filtration to reduce the sulfate content. Chinese patent CN102431981 discloses a method for reducing SO4 in dilute phosphoric acid. 2- One method involves adding phosphate rock slurry to dilute phosphoric acid obtained through extraction and filtration in a phosphoric acid extraction tank, and then reacting the mixture in a desulfurization tank to reduce the free sulfuric acid content. While adding phosphate rock to dilute phosphoric acid can reduce the sulfate content, it has drawbacks such as long desulfurization time, the need for sedimentation and filtration of the desulfurized phosphoric acid, difficult treatment of the sedimentation sludge, and high residual phosphorus content in the filter residue. Furthermore, the pipelines in the wet-process phosphoric acid slurry vacuum filtration system are prone to blockage due to the formation of fluorosilicates (sodium and potassium) and calcium sulfate. Existing technologies often use scale inhibitors, which contain organophosphonic acid polymers. This increases operating costs, and the added organic matter can potentially affect subsequent production processes.

[0005] Therefore, finding a more suitable desulfurization method for the semi-aqueous wet phosphoric acid process and solving the aforementioned problems in the existing desulfurization process of the semi-aqueous wet phosphoric acid process has become one of the urgent problems to be solved by many front-line researchers in the industry. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet phosphoric acid process, particularly a method for crude desulfurization and slurry cooling in a hemihydrate wet phosphoric acid process. The desulfurization process provided by the present invention is simple and low in cost, and also reduces the frequency of cleaning the slurry vacuum filtration system and improves the system's start-up rate.

[0007] This invention provides a method for preparing crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet phosphoric acid process, comprising the following steps:

[0008] 1) The slurry after crystal growth in the crystal growth tank is returned to the dissolving tank and phosphate concentrate is added for dissolution. The resulting dissolved slurry enters the decomposition tank for decomposition reaction. The resulting decomposition slurry overflows into the crystallization tank and concentrated sulfuric acid is added for reaction and crystallization. The slurry then enters the crystal growth tank again for crystal growth to obtain the crystal-grown slurry.

[0009] A portion of the slurry after crystal growth is returned to the dissolving tank;

[0010] 2) The slurry after crystal growth in the crystal growth tank and the slurry in the decomposition tank are fed together into the coarse desulfurization reaction tank for mixing and stirring reaction to obtain coarse desulfurization reaction slurry.

[0011] 3) After the crude desulfurization reaction slurry obtained in the above steps is cooled by vacuum flash evaporation, the resulting low-temperature slurry enters the liquid seal tank, and after vacuum filtration, hemihydrate phosphoric acid after crude desulfurization is obtained.

[0012] Preferably, the phosphate concentrate comprises, by mass percentage: P2O5: 30%–38%, CaO: 45%–55%, MgO: 0.3%–1.6%, H2O: 5%–15%, Fe2O3: 0.3%–2.3%, and Al2O3: 0.4%–1%.

[0013] Preferably, the ratio of the slurry returned to the melting tank after crystal growth to the phosphate concentrate is (15-30) m. 3 1t;

[0014] The mass content of P2O5 in the liquid phase of the decomposition tank is 40% to 45%.

[0015] In the liquid phase of the decomposition tank, SO4 2- The mass content is 0.2% to 0.6%;

[0016] The mass content of CaO in the liquid phase of the decomposition tank is 1.0% to 1.6%.

[0017] Preferably, the temperature of the decomposition reaction is 90–105°C;

[0018] The mass ratio of the phosphate concentrate to concentrated sulfuric acid is (0.5–1.0):1;

[0019] The crystallization temperature is 95–105°C.

[0020] Preferably, the mass content of P2O5 in the liquid phase of the crystallization tank is 40% to 45%;

[0021] In the liquid phase of the crystallization tank, SO4 2- The mass content is 1.8% to 2.2%;

[0022] The mass content of CaO in the liquid phase of the crystallization tank is 0.1% to 0.5%.

[0023] Preferably, the mass content of P2O5 in the liquid phase of the crystal growth tank is 40% to 45%;

[0024] In the liquid phase of the crystal growth tank, SO4 2- The mass content is 1.5% to 2.0%;

[0025] The mass content of CaO in the liquid phase of the crystal growth tank is 0.1% to 0.5%.

[0026] Preferably, the temperature for crystal growth is 95–105°C;

[0027] In step 2), the mass ratio of the slurry after crystal growth to the slurry in the decomposition tank is (1-2):(1-2).

[0028] Preferably, the residence time of the mixing and stirring reaction is 0.15 to 1.5 hours;

[0029] The temperature of the mixing and stirring reaction is 70–105°C;

[0030] The temperature of the low-temperature slurry is 70–105°C.

[0031] Preferably, a portion of the low-temperature slurry entering the liquid seal tank is returned to the coarse desulfurization reaction tank, while the other portion undergoes subsequent vacuum filtration.

[0032] The mass ratio of one portion of the low-temperature slurry to the other portion of the low-temperature slurry is (3-8):1;

[0033] The preparation method further includes recovering fluorine from the fluorine-containing secondary steam generated during the vacuum flash evaporation cooling process through multi-stage countercurrent washing.

[0034] Preferably, the mass content of P2O5 in the hemihydrate phosphoric acid after crude desulfurization is 40% to 45%.

[0035] In the hemihydrate phosphoric acid after crude desulfurization, SO4 2-The mass content is 0.2% to 1.1%;

[0036] The mass content of CaO in the hemihydrate phosphoric acid after crude desulfurization is 0.1% to 0.9%.

[0037] The preparation method further includes recovering fluorine from the exhaust gas generated after vacuum filtration by washing the exhaust gas.

[0038] This invention provides a method for preparing crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet-process phosphoric acid production process, comprising the following steps: First, the slurry after crystal growth in the crystal growth tank is returned to the dissolving tank and phosphate concentrate is added for dissolution. The resulting dissolved slurry enters the decomposition tank for decomposition reaction. The resulting decomposition slurry overflows into the crystallization tank and concentrated sulfuric acid is added for reaction and crystallization. The slurry then enters the crystal growth tank again for crystal growth, obtaining a crystal-grown slurry. A portion of the crystal-grown slurry is returned to the dissolving tank. Then, the crystal-grown slurry from the crystal growth tank and the slurry from the decomposition tank are jointly fed into a crude desulfurization reaction tank for mixing and stirring reaction, obtaining a crude desulfurization reaction slurry. Finally, the crude desulfurization reaction slurry obtained in the above steps is cooled by vacuum flash evaporation, and the resulting low-temperature slurry enters the liquid seal tank, and after vacuum filtration, the crude desulfurized hemihydrate phosphoric acid is obtained. Compared with the prior art, this invention addresses the problems of long process flow, high operating cost, and large P2O5 loss in the crude desulfurization technology of the existing hemihydrate wet-process phosphoric acid production process, as well as the problem of easy clogging of the hemihydrate slurry filtration system. This invention features a specially designed coarse desulfurization process with specific steps, utilizing CaO in the decomposition tank and SO4 in the crystal growth tank. 2- The slurries from both tanks are fed together into a coarse desulfurization reaction tank for mixing and reaction to achieve desulfurization, which simplifies the desulfurization slurry filtration process. Furthermore, vacuum flash evaporation is used to cool the desulfurized slurry before it enters the vacuum filtration system, avoiding large-scale scaling in the system. The fluorine generated during vacuum flash evaporation and vacuum filtration is recovered.

[0039] This invention achieves desulfurization without the need for external desulfurizing agents, utilizing excess CaO in the decomposition tank and excess SO4 in the crystal growth tank. 2- By mixing the slurry in a certain proportion and reacting, the SO4 in the hemihydrate acid can be removed. 2-The sulfur dioxide (P2O5) is reduced to 0.5%, achieving a coarse desulfurization effect. This invention reduces the cost of coarse desulfurization reagents and shortens the coarse desulfurization process, while also avoiding the P2O5 waste caused by adding phosphate concentrate in traditional coarse desulfurization processes. This invention also employs vacuum flash evaporation to cool the slurry after coarse desulfurization, which is then pumped to a vacuum filtration system. Because the reaction slurry temperature is relatively low, the filtrate is less prone to flash evaporation during solid-liquid separation under vacuum, thus preventing the generation of large amounts of fluorosilicates (sodium potassium) and calcium sulfate in the pipeline, which could cause system blockage and improve the start-up rate. Furthermore, the fluorine-containing secondary steam obtained from vacuum flash evaporation and the fluorine-containing tail gas generated from vacuum filtration are recovered through multi-stage countercurrent washing, improving the fluorine recovery rate. This invention provides a method for preparing coarse desulfurized hemihydrate phosphoric acid in a hemihydrate wet phosphoric acid process, offering a simple desulfurization process, low cost, and methods to reduce the frequency of cleaning the slurry vacuum filtration system and improve the system start-up rate. Attached Figure Description

[0040] Figure 1 A simplified process flow diagram for the preparation of crude desulfurized hemihydrate phosphoric acid in the hemihydrate wet phosphoric acid process provided by the present invention. Detailed Implementation

[0041] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims.

[0042] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0043] The purity of all raw materials used in this invention is not particularly limited, but industrial-grade pure or conventionally pure as used in the semi-aqueous wet phosphoric acid process is preferred.

[0044] This invention provides a method for preparing crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet phosphoric acid process, comprising the following steps:

[0045] 1) The slurry after crystal growth in the crystal growth tank is returned to the dissolving tank and phosphate concentrate is added for dissolution. The resulting dissolved slurry enters the decomposition tank for decomposition reaction. The resulting decomposition slurry overflows into the crystallization tank and concentrated sulfuric acid is added for reaction and crystallization. The slurry then enters the crystal growth tank again for crystal growth to obtain the crystal-grown slurry.

[0046] A portion of the slurry after crystal growth is returned to the dissolving tank;

[0047] 2) The slurry after crystal growth in the crystal growth tank and the slurry in the decomposition tank are fed together into the coarse desulfurization reaction tank for mixing and stirring reaction to obtain coarse desulfurization reaction slurry.

[0048] 3) After the crude desulfurization reaction slurry obtained in the above steps is cooled by vacuum flash evaporation, the resulting low-temperature slurry enters the liquid seal tank, and after vacuum filtration, hemihydrate phosphoric acid after crude desulfurization is obtained.

[0049] The present invention first returns the slurry after crystal growth in the crystal growth tank to the dissolution tank and adds phosphate concentrate for dissolution. The resulting dissolved slurry enters the decomposition tank for decomposition reaction. The resulting decomposition slurry overflows into the crystallization tank and is reacted and crystallized by adding concentrated sulfuric acid. The slurry then enters the crystal growth tank again for crystal growth to obtain the crystal-grown slurry.

[0050] A portion of the slurry after crystal growth is returned to the dissolving tank.

[0051] In this invention, the phosphate concentrate, by mass percentage, preferably comprises: P2O5: 30%–38%, CaO: 45%–55%, MgO: 0.3%–1.6%, H2O: 5%–15%, Fe2O3: 0.3%–2.3%, and Al2O3: 0.4%–1%, more preferably P2O5: 31%–37%, CaO: 47%–53%, and MgO: 0%. The composition is 0.6%–1.3%, H2O: 7%–13%, Fe2O3: 0.7%–2.0%, and Al2O3: 0.5%–0.9%, more preferably P2O5: 32%–35%, CaO: 49%–51%, MgO: 0.9%–1.0%, H2O: 9%–11%, Fe2O3: 1.0%–1.6%, and Al2O3: 0.6%–0.8%.

[0052] In this invention, the ratio of the slurry returned to the dissolving tank after crystal growth to the phosphate concentrate is preferably (15-30) m. 3 1t, more preferably (18-27)m 3 1t, more preferably (21-24)m 3 1t. Specifically, in this invention, the circulating flow rate Q / concentrate quantity = 15~30m³. 3 / t concentrate.

[0053] In this invention, the mass content of P2O5 in the liquid phase of the decomposition tank is preferably 40% to 45%, more preferably 41% to 44%, and even more preferably 42% to 43%.

[0054] In this invention, the liquid phase of the decomposition tank contains SO4. 2- The mass content is preferably 0.2% to 0.6%, more preferably 0.25% to 0.55%, even more preferably 0.3% to 0.5%, and even more preferably 0.35% to 0.45%.

[0055] In this invention, the mass content of CaO in the liquid phase of the decomposition tank is preferably 1.0% to 1.6%, more preferably 1.1% to 1.5%, and even more preferably 1.2% to 1.4%.

[0056] In this invention, the solid content in the crystallization tank is preferably 25% to 35%, more preferably 25% to 32%, and even more preferably 25% to 28%.

[0057] In this invention, the temperature of the decomposition reaction is preferably 90-105°C, more preferably 93-102°C, and even more preferably 96-99°C.

[0058] In this invention, the mass ratio of the phosphate concentrate to concentrated sulfuric acid is preferably (0.5-1.0):1, more preferably (0.6-0.9):1, and even more preferably (0.7-0.8):1.

[0059] In this invention, the crystallization temperature is preferably 95-105°C, more preferably 97-103°C, and even more preferably 99-101°C.

[0060] In this invention, the mass content of P2O5 in the liquid phase of the crystallization tank is preferably 40% to 45%, more preferably 41% to 44%, and even more preferably 42% to 43%.

[0061] In this invention, the liquid phase in the crystallization tank contains SO4. 2- The mass content is preferably 1.8% to 2.2%, more preferably 1.85% to 2.15%, even more preferably 1.9% to 2.1%, and even more preferably 1.95% to 2.05%.

[0062] In this invention, the mass content of CaO in the liquid phase of the crystallization tank is preferably 0.1% to 0.5%, more preferably 0.15% to 0.45%, more preferably 0.2% to 0.4%, and even more preferably 0.25% to 0.35%.

[0063] In this invention, the solid content in the crystallization tank is preferably 25% to 35%, more preferably 25% to 32%, and even more preferably 25% to 28%.

[0064] In this invention, the mass content of P2O5 in the liquid phase of the crystal growth tank is preferably 40% to 45%, more preferably 41% to 44%, and even more preferably 42% to 43%.

[0065] In this invention, the liquid phase in the crystal growth tank contains SO4. 2- The mass content is preferably 1.5% to 2.0%, more preferably 1.6% to 1.9%, and even more preferably 1.7% to 1.8%.

[0066] In this invention, the mass content of CaO in the liquid phase of the crystal growth tank is preferably 0.1% to 0.5%, more preferably 0.15% to 0.45%, more preferably 0.2% to 0.4%, and even more preferably 0.25% to 0.35%.

[0067] In this invention, the solid content in the crystal growth tank is preferably 25% to 35%, more preferably 25% to 32%, and even more preferably 25% to 28%.

[0068] In this invention, the crystal growth temperature is preferably 90-105°C, more preferably 93-102°C, and even more preferably 96-99°C.

[0069] In this invention, in step 2), the mass ratio of the slurry after crystal growth to the slurry in the decomposition tank is preferably (1-2):(1-2), more preferably (1.2-1.8):(1-2), even more preferably (1.4-1.6):(1-2), or (1-2):(1.2-1.8), even more preferably (1-2):(1.4-1.6). Specifically, it can be 1:1.

[0070] In this invention, the slurry after crystal growth in the crystal growth tank and the slurry in the decomposition tank are fed together into the coarse desulfurization reaction tank for mixing and stirring reaction to obtain the coarse desulfurization reaction slurry.

[0071] In this invention, the residence time of the mixing and stirring reaction is preferably 0.15 to 1.5 h, more preferably 0.25 to 1.0 h, even more preferably 0.25 to 0.5 h, and can be 15 min.

[0072] In this invention, the temperature of the mixing and stirring reaction is preferably 70-105°C, more preferably 75-100°C, more preferably 80-95°C, and even more preferably 85-90°C.

[0073] Finally, the crude desulfurization reaction slurry obtained in the above steps is cooled by vacuum flash evaporation. The resulting low-temperature slurry is then introduced into a liquid sealing tank and filtered under vacuum to obtain hemihydrate phosphoric acid after crude desulfurization.

[0074] In this invention, the temperature of the low-temperature slurry is preferably 70–105°C, more preferably 75–100°C, even more preferably 80–95°C, and even more preferably 85–90°C. Specifically, the preparation method provided by this invention is a continuous production process. During continuous production, the temperature of the crude desulfurization reaction slurry after mixing and stirring reaction continues to rise. In the subsequent vacuum flash evaporation cooling process, the temperature is lowered to maintain stability. Typically, the temperature of the cooled low-temperature slurry is lower than that of the crude desulfurization reaction slurry.

[0075] In this invention, a portion of the low-temperature slurry entering the liquid sealing tank is preferably returned to the coarse desulfurization reaction tank, while the other portion of the low-temperature slurry undergoes subsequent vacuum filtration.

[0076] In this invention, the mass ratio of the portion of low-temperature slurry to the other portion of low-temperature slurry is preferably (3-8):1, more preferably (4-7):1, and even more preferably (5-6):1. Specifically, the ratio of the portion of low-temperature slurry, i.e., the circulating volume of the cooling slurry to the feed (discharge) volume, is k = 3-8.

[0077] In this invention, the preparation method preferably includes, during the vacuum flash evaporation cooling process, the generated fluorine-containing secondary steam is subjected to multi-stage countercurrent washing to recover fluorine.

[0078] In this invention, the mass content of P2O5 in the crude desulfurized hemihydrate phosphoric acid is preferably 40% to 45%, more preferably 41% to 44%, and even more preferably 42% to 43%.

[0079] In this invention, the hemihydrate phosphoric acid after crude desulfurization contains SO4. 2- The mass content is preferably 0.2% to 1.1%, more preferably 0.4% to 0.9%, and even more preferably 0.6% to 0.7%.

[0080] In this invention, the mass content of CaO in the hemihydrate phosphoric acid after crude desulfurization is preferably 0.1% to 0.9%, more preferably 0.2% to 0.8%, more preferably 0.3% to 0.7%, and even more preferably 0.4% to 0.6%.

[0081] In this invention, the preparation method preferably further includes recovering fluorine from the exhaust gas generated after vacuum filtration by washing the exhaust gas.

[0082] This invention aims to complete and refine the overall technical solution, thereby improving the desulfurization effect in the preparation of hemihydrate phosphoric acid during the coarse desulfurization process. Specifically, the methods for coarse desulfurization and slurry cooling in the aforementioned hemihydrate wet phosphoric acid process may include the following:

[0083] This invention utilizes the characteristics of hemihydrate wet phosphoric acid production: the decomposition tank in the hemihydrate reaction tank has a high CaO content, while the crystal growth tank contains SO4. 2- With a high content, the desulfurization effect can be achieved by mixing the slurries in the two tanks in a certain proportion.

[0084] In the semi-aqueous wet phosphoric acid process provided by this invention, a dissolving tank, a decomposition tank, a crystallization tank, and a crystal growth tank are connected in series. The slurry in the dissolving tank flows sequentially through the decomposition tank, the crystallization tank, and the crystal growth tank. Part of the slurry in the crystal growth tank is returned to the dissolving tank to dissolve the phosphate rock, and part of it is sent to the coarse desulfurization process along with the slurry from the decomposition tank in a certain proportion. The crystallization tank acts as a buffer tank before the crystal growth tank.

[0085] (1) The slurry in the decomposition tank and the crystal growth tank are respectively transported to the coarse desulfurization reaction tank in a 1:1 ratio by a transfer pump for mixing and stirring reaction. The reaction time is 15 min and the temperature is 95-105℃ to obtain coarse desulfurization reaction slurry.

[0086] (2) The reaction slurry is then transported to the vacuum flash chamber for cooling by a flash circulation pump. The cooled slurry enters the liquid seal tank. Part of the slurry in the liquid seal tank is returned to the desulfurization reaction tank, and the other part is transported to the vacuum filtration system for filtration by a slurry conveying pump. The fluorine-containing secondary steam coming out of the vacuum flash chamber is washed by multi-stage countercurrent washing to recover fluorine, and the tail gas is discharged in compliance with standards.

[0087] (3) After being filtered by a vacuum filtration system, hemihydrate phosphoric acid and hemihydrate gypsum (hemihydrate phosphogypsum) are obtained after crude desulfurization. The generated tail gas is treated by a tail gas scrubbing system to recover fluorine, and then discharged in compliance with standards.

[0088] See Figure 1 , Figure 1 A simplified process flow diagram for the preparation of crude desulfurized hemihydrate phosphoric acid in the hemihydrate wet phosphoric acid process provided by the present invention.

[0089] The present invention provides a method for coarse desulfurization and slurry cooling in a semi-aqueous wet phosphoric acid process. The coarse desulfurization process designed in this invention utilizes CaO in the decomposition tank and SO4 in the crystal growth tank. 2- The slurries from both tanks are fed together into a coarse desulfurization reaction tank for mixing and reaction to achieve desulfurization, which simplifies the desulfurization slurry filtration process. Furthermore, vacuum flash evaporation is used to cool the desulfurized slurry before it enters the vacuum filtration system, avoiding large-scale scaling in the system. The fluorine generated during vacuum flash evaporation and vacuum filtration is recovered.

[0090] This invention achieves desulfurization without the need for external desulfurizing agents, utilizing excess CaO in the decomposition tank and excess SO4 in the crystal growth tank. 2- By mixing the slurry in a certain proportion and reacting, the SO4 in the hemihydrate acid can be removed. 2-The sulfur dioxide (P2O5) is reduced to 0.5%, achieving a coarse desulfurization effect. This invention reduces the cost of coarse desulfurization reagents and shortens the coarse desulfurization process, while also avoiding the P2O5 waste caused by adding phosphate concentrate in traditional coarse desulfurization processes. This invention also employs vacuum flash evaporation to cool the slurry after coarse desulfurization, which is then pumped to a vacuum filtration system. Because the reaction slurry temperature is relatively low, the filtrate is less prone to flash evaporation during solid-liquid separation under vacuum, thus preventing the generation of large amounts of fluorosilicates (sodium potassium) and calcium sulfate in the pipeline, which could cause system blockage and improve the start-up rate. Furthermore, the fluorine-containing secondary steam obtained from vacuum flash evaporation and the fluorine-containing tail gas generated from vacuum filtration are recovered through multi-stage countercurrent washing, improving the fluorine recovery rate. This invention provides a method for preparing coarse desulfurized hemihydrate phosphoric acid in a hemihydrate wet phosphoric acid process, offering a simple desulfurization process, low cost, and methods to reduce the frequency of cleaning the slurry vacuum filtration system and improve the system start-up rate.

[0091] To further illustrate the present invention, the following detailed description of the preparation method of crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet phosphoric acid process provided by the present invention is provided in conjunction with embodiments. However, it should be understood that these embodiments are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. They are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0092] Example 1

[0093] 1) A portion of the crystallized slurry from the crystallization tank is returned to the dissolving tank and phosphate concentrate is added for dissolution. The ratio of the crystallized slurry returned to the dissolving tank to the phosphate concentrate is 15m. 3 The resulting dissolved slurry, at a rate of 1 t, enters a decomposition tank. After decomposition at 90°C, the resulting slurry overflows into a crystallization tank where concentrated sulfuric acid is added for further reaction and crystallization at 95°C. The mass ratio of phosphate concentrate to concentrated sulfuric acid is 0.5 t: 1 m³. 3 The slurry is then fed into a crystal growth tank for crystal growth at 95°C to obtain the crystal-grown slurry.

[0094] See Table 1, which shows the composition of the phosphate concentrate in Example 1 of this invention.

[0095] Table 1

[0096] <![CDATA[P2O5]]> CaO MgO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> <![CDATA[H2O]]> 30％ 45％ 0.3％ 0.3％ 0.4％ 5％

[0097] See Table 2, which shows the concentrations of P2O5, CaO, and SO4 in different reaction tanks in Example 1 of this invention. 2- Mass content.

[0098] Table 2

[0099] Reactor name <![CDATA[P2O5 / %]]> <![CDATA[SO4 2- / %]]> CaO / % Decomposition tank 40 0.2 1.0 Crystallization tank 40 1.8 0.1 Crystal growth tank 40 1.5 0.1

[0100] 2) The slurry after crystal growth in the crystal growth tank and the slurry in the decomposition tank are fed into the coarse desulfurization reaction tank at a mass ratio of 1:2 for mixing and stirring reaction. The reaction residence time is 0.15h and the reaction temperature is 70℃. After the reaction, coarse desulfurization reaction slurry is obtained.

[0101] 3) After the crude desulfurization reaction slurry obtained in the above steps is cooled by vacuum flash evaporation, the resulting low-temperature slurry enters the liquid seal tank. A portion of the low-temperature slurry is returned to the crude desulfurization reaction tank at a ratio of 3:1, and the other portion of the low-temperature slurry is subjected to subsequent vacuum filtration to obtain hemihydrate phosphoric acid after crude desulfurization.

[0102] The hemihydrate phosphoric acid contains 40% P2O5 by mass, 0.6% CaO by mass, and SO42-. 2- The mass content is 0.5%.

[0103] 4) During the vacuum flash evaporation cooling process, the fluorine-containing secondary steam generated is subjected to multi-stage countercurrent washing to recover fluorine; the tail gas generated after vacuum filtration is washed and then fluorine is recovered.

[0104] Example 2

[0105] 1) A portion of the crystallized slurry from the crystallization tank is returned to the dissolving tank and phosphate concentrate is added for dissolution. The ratio of the returned crystallized slurry to phosphate concentrate in the dissolving tank is 20m. 3 The resulting dissolved slurry, at a rate of 1 t, enters a decomposition tank. After decomposition at 96°C, the resulting slurry overflows into a crystallization tank where concentrated sulfuric acid is added for a 99°C reaction and crystallization. The mass ratio of phosphate concentrate to concentrated sulfuric acid is 0.8 t: 1 m³. 3 The slurry is then fed into a crystal growth tank for crystal growth at 99°C to obtain the crystal-grown slurry.

[0106] See Table 3, which shows the composition of the phosphate concentrate in Example 2 of this invention.

[0107] Table 3

[0108] <![CDATA[P2O5]]> CaO MgO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> <![CDATA[H2O]]> 35％ 50％ 1.2％ 1.0％ 0.8％ 12％

[0109] See Table 4, which shows the concentrations of P2O5, CaO, and SO4 in different reaction tanks in Example 2 of this invention. 2- Mass content.

[0110] Table 4

[0111] Reactor name <![CDATA[P2O5 / %]]> <![CDATA[SO4 2- / %]]> CaO / % Decomposition tank 42 0.5 1.2 Crystallization tank 42 2.0 0.2 Crystal growth tank 42 1.6 0.2

[0112] 2) The slurry after crystal growth in the crystal growth tank and the slurry in the decomposition tank are fed into the coarse desulfurization reaction tank at a mass ratio of 1:1 for mixing and stirring reaction. The reaction residence time is 0.5h and the reaction temperature is 85℃. After the reaction, coarse desulfurization reaction slurry is obtained.

[0113] 3) After the crude desulfurization reaction slurry obtained in the above steps is cooled by vacuum flash evaporation, the resulting low-temperature slurry enters the liquid seal tank. A portion of the low-temperature slurry is returned to the crude desulfurization reaction tank at a ratio of 5:1, and the other portion of the low-temperature slurry is subjected to subsequent vacuum filtration to obtain hemihydrate phosphoric acid after crude desulfurization.

[0114] The hemihydrate phosphoric acid contains 42% P2O5 by mass, 0.5% CaO by mass, and SO42% by mass. 2- The mass content is 0.2%.

[0115] 4) During the vacuum flash evaporation cooling process, the fluorine-containing secondary steam generated is subjected to multi-stage countercurrent washing to recover fluorine; the tail gas generated after vacuum filtration is washed and then fluorine is recovered.

[0116] Example 3

[0117] 1) A portion of the slurry after crystal growth in the crystal growth tank is returned to the dissolving tank and phosphate concentrate is added for dissolution. The ratio of the returned slurry to phosphate concentrate in the dissolving tank is 30m. 3 The resulting dissolved slurry, at a rate of 1 t, enters a decomposition tank. After decomposition at 105°C, the resulting slurry overflows into a crystallization tank where concentrated sulfuric acid is added for further reaction and crystallization at 105°C. The mass ratio of phosphate concentrate to concentrated sulfuric acid is 1.0 t: 1 m³. 3 The slurry is then fed into a crystal growth tank for crystal growth at 105°C to obtain the crystal-grown slurry.

[0118] See Table 5, which shows the composition of the phosphate concentrate in Example 3 of this invention.

[0119] Table 5

[0120] <![CDATA[P2O5]]> CaO MgO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> <![CDATA[H2O]]> 38％ 55％ 1.6％ 2.3％ 1％ 15％

[0121] See Table 6, which shows the concentrations of P2O5, CaO, and SO4 in different reaction tanks in Example 3 of this invention. 2- Mass content.

[0122] Table 6

[0123] Reactor name <![CDATA[P2O5 / %]]> <![CDATA[SO4 2- / %]]> CaO / % Decomposition tank 45 0.6 1.6 Crystallization tank 45 2.2 0.5 Crystal growth tank 45 2.0 0.5

[0124] 2) The slurry after crystal growth in the crystal growth tank and the slurry in the decomposition tank are fed into the coarse desulfurization reaction tank at a mass ratio of 2:1 for mixing and stirring reaction. The reaction residence time is 1.5h and the reaction temperature is 105℃. After the reaction, coarse desulfurization reaction slurry is obtained.

[0125] 3) After the crude desulfurization reaction slurry obtained in the above steps is cooled by vacuum flash evaporation, the resulting low-temperature slurry enters the liquid seal tank. A portion of the low-temperature slurry is returned to the crude desulfurization reaction tank at a return ratio of 8:1, and the other portion of the low-temperature slurry is subjected to subsequent vacuum filtration to obtain hemihydrate phosphoric acid after crude desulfurization.

[0126] The hemihydrate phosphoric acid contains 45% P2O5 by mass, 0.2% CaO by mass, and SO42-. 2- The mass content is 0.8%.

[0127] 4) During the vacuum flash evaporation cooling process, the fluorine-containing secondary steam generated is subjected to multi-stage countercurrent washing to recover fluorine; the tail gas generated after vacuum filtration is washed and then fluorine is recovered.

[0128] Statistical analysis of the technical solutions adopted in this invention shows that:

[0129] The original desulfurization process used phosphate concentrate, which partially encapsulated the phosphate concentrate after entering the coarse desulfurization reaction tank. The slurry solids content was 5%, leading to severe system blockage and an operating rate of approximately 85%. Through the implementation of this new technology, the slurry solids content was reduced to 2%, improving system blockage and increasing the operating rate to 92%. Compared to the phosphate concentrate desulfurization route, this technology reduces phosphate concentrate consumption by 7200 tons / year (dry basis), resulting in an annual cost reduction of 9.63 million yuan based on a phosphate concentrate price of 1300 yuan / ton. Furthermore, the increased operating rate allows for the production of an additional 14,000 tons / year of desulfurized phosphoric acid.

[0130] The foregoing provides a detailed description of a method for crude desulfurization and slurry cooling in a semi-aqueous wet phosphoric acid process according to the present invention. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of these embodiments are merely for the purpose of helping to understand the method and core ideas of the present invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those skilled in the art, several improvements and modifications can be made to the invention without departing from the principles of the invention, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements that are not different from the wording of the claims, or if they include equivalent structural elements that are not substantially different from the wording of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet phosphoric acid process, characterized in that, Includes the following steps: 1) The slurry after crystal growth in the crystal growth tank is returned to the dissolving tank and phosphate concentrate is added for dissolution. The resulting dissolved slurry enters the decomposition tank for decomposition reaction. The resulting decomposition slurry overflows into the crystallization tank and concentrated sulfuric acid is added for reaction and crystallization. The slurry then enters the crystal growth tank again for crystal growth to obtain the crystal-grown slurry. A portion of the slurry after crystal growth is returned to the dissolving tank; The ratio of the slurry returned to the melting tank after crystal growth to the phosphate concentrate is (15~30) m. 3 1t; 2) The slurry after crystal growth in the crystal growth tank and the slurry in the decomposition tank are fed together into the coarse desulfurization reaction tank for mixing and stirring reaction to obtain coarse desulfurization reaction slurry. 3) After the crude desulfurization reaction slurry obtained in the above steps is cooled by vacuum flash evaporation, the resulting low-temperature slurry enters the liquid seal tank and is then filtered under vacuum to obtain hemihydrate phosphoric acid after crude desulfurization.

2. The preparation method according to claim 1, characterized in that, The phosphate concentrate, by mass percentage, comprises: P2O5: 30%~38%, CaO: 45%~55%, MgO: 0.3%~1.6%, H2O: 5%~15%, Fe2O3: 0.3%~2.3%, and Al2O3: 0.4%~1%.

3. The preparation method according to claim 1, characterized in that, The P2O5 content in the liquid phase of the decomposition tank is 40%~45% by mass; In the liquid phase of the decomposition tank, SO4 2- The mass content is 0.2%~0.6%; The mass content of CaO in the liquid phase of the decomposition tank is 1.0%~1.6%.

4. The preparation method according to claim 1, characterized in that, The temperature of the decomposition reaction is 90~105℃; The mass ratio of the phosphate concentrate to concentrated sulfuric acid is (0.5~1.0):1; The crystallization temperature is 95~105℃.

5. The preparation method according to claim 1, characterized in that, The mass content of P2O5 in the liquid phase of the crystallization tank is 40%~45%; In the liquid phase of the crystallization tank, SO4 2- The mass content is 1.8%~2.2%; The mass content of CaO in the liquid phase of the crystallization tank is 0.1%~0.5%.

6. The preparation method according to claim 1, characterized in that, The P2O5 content in the liquid phase of the crystal growth tank is 40%~45% by mass; In the liquid phase of the crystal growth tank, SO4 2- The mass content is 1.5%~2.0%; The mass content of CaO in the liquid phase of the crystal growth tank is 0.1%~0.5%.

7. The preparation method according to claim 1, characterized in that, The temperature for crystal growth is 95~105℃; In step 2), the mass ratio of the slurry after crystal growth to the slurry in the decomposition tank is (1~2):(1~2).

8. The preparation method according to claim 1, characterized in that, The residence time for the mixing and stirring reaction is 0.15~1.5h; The temperature of the mixing and stirring reaction is 70~105℃; The temperature of the low-temperature slurry is 70~105℃.

9. The preparation method according to claim 1, characterized in that, The low-temperature slurry that enters the liquid seal tank is partially returned to the coarse desulfurization reaction tank, and the other part of the low-temperature slurry is subjected to subsequent vacuum filtration. The mass ratio of one portion of the low-temperature slurry to the other portion of the low-temperature slurry is (3~8):1; The preparation method further includes recovering fluorine from the fluorine-containing secondary steam generated during the vacuum flash evaporation cooling process through multi-stage countercurrent washing.

10. The preparation method according to claim 1, characterized in that, The mass content of P2O5 in the hemihydrate phosphoric acid after crude desulfurization is 40%~45%; In the hemihydrate phosphoric acid after crude desulfurization, SO4 2- The mass content is 0.2%~1.1%; The mass content of CaO in the hemihydrate phosphoric acid after crude desulfurization is 0.1%~0.9%; The preparation method further includes recovering fluorine from the exhaust gas generated after vacuum filtration by washing the exhaust gas.

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