A system and method for three-stage concentrated phosphoric acid

Abstract

The present invention is a system and method for three-stage concentrated phosphoric acid, belonging to the field of chemical industry. The system uses high-potential medium-pressure saturated steam to indirectly heat phosphoric acid to generate secondary steam and tertiary steam to continue to heat phosphoric acid, making full use of high-potential heat energy while reducing heat loss. The currently widely used low-pressure saturated steam one-stage concentrated phosphoric acid requires 1.2 to 1.3 tons of low-pressure saturated steam to evaporate 1 ton of water. The present invention uses medium-pressure saturated steam to concentrate phosphoric acid in three stages, and only consumes 0.5 to 0.6 tons of steam to evaporate 1 ton of water. The steam utilization efficiency is high, the steam consumption is saved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of chemical industry, and in particular to a system and method for three-stage concentrated phosphoric acid, and in particular to a new process for using medium-pressure saturated steam generated by a sulfuric acid production device to three-stage concentrate dilute phosphoric acid to obtain a target product, namely concentrated phosphoric acid, return condensed water to the sulfuric acid production device, remove phosphoric acid from the condensate, and use the fluorine-containing tail gas obtained by flash distillation to produce fluorosilicic acid. Background Art

[0002] Phosphoric acid is an important intermediate chemical product. Its uses can be summarized into two aspects, namely, fertilizer production and industrial phosphate production, and wet-process phosphoric acid is mainly used in fertilizer production.

[0003] The production process of wet phosphoric acid is mainly the dihydrate method, which accounts for more than 80%. The mass concentration of dihydrate phosphoric acid products is 22% to 28% P2O5. Due to the low concentration, it cannot be used directly and needs to be concentrated to a mass concentration of more than 40%. In 2021, the domestic production of phosphoric acid (equivalent to 100% P2O5) was nearly 17 million tons, and the low mass concentration of 22% to 28% P2O5 phosphoric acid (equivalent to 100% P2O5) was close to 13.6 million tons, and the actual amount was close to 54.4 million tons. The amount of water that needs to be evaporated and concentrated is 20.4 million tons each year. At present, low-concentration dilute phosphoric acid is concentrated using low-pressure steam of 0.3MPa (absolute pressure) and about 133°C. It takes about 1.25 tons of low-pressure steam to evaporate one ton of water, and about 25.5 million tons of low-pressure steam is consumed each year.

[0004] In 2021, the domestic sulfuric acid production was 85.56 million tons, most of which was used to produce phosphoric acid. At the same time, nearly 100 million tons of medium-pressure steam were produced, and about a quarter of the medium-pressure steam was used to concentrate phosphoric acid. If medium-pressure steam is used to concentrate dilute phosphoric acid in three stages, the steam consumption can be greatly reduced, and the steam consumption can be saved by more than half. The concentrated phosphoric acid obtained has a higher concentration, and the saved steam can be used for power generation. Therefore, it is necessary and feasible to make good use of medium-pressure steam to concentrate dilute phosphoric acid in three stages, save energy and reduce consumption, reduce carbon emissions of production equipment, and reduce operation and maintenance costs. Summary of the invention

[0005] The purpose of the present invention is to provide a system and method for three-stage phosphoric acid concentration, which utilizes the medium-pressure saturated steam produced by the sulfuric acid device to directly concentrate the dilute phosphoric acid without cooling and reducing pressure, thereby saving steam and reducing carbon emissions. The medium-pressure steam is used to heat the primary circulating phosphoric acid in the primary phosphoric acid heater, and the water is evaporated in the primary evaporation concentration demister to concentrate the primary circulating phosphoric acid to obtain the target product concentrated phosphoric acid; the water vapor evaporated from the primary evaporation concentration demister is used to heat the secondary circulating phosphoric acid in the secondary evaporation concentration demister, and the water is evaporated in the secondary evaporation concentration demister to concentrate the secondary circulating phosphoric acid; the water vapor evaporated from the secondary evaporation concentration demister is used to heat the tertiary phosphoric acid in the tertiary phosphoric acid heater, and the water is evaporated in the tertiary evaporation concentration demister to concentrate the tertiary circulating phosphoric acid. Through the system and method for three-stage phosphoric acid concentration, less medium-pressure saturated steam is used to concentrate the dilute phosphoric acid into concentrated phosphoric acid with higher concentration. The present invention optimizes the process operation, greatly reduces steam consumption, reduces production costs, and conforms to the green and low-carbon system and method.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A three-stage phosphoric acid concentration system, the system comprising a primary phosphoric acid heater, a primary evaporation concentration defoamer, a primary crystal separator, a secondary phosphoric acid heater, a secondary flash concentration defoamer, a secondary crystal separator, a tertiary phosphoric acid heater, a tertiary flash concentration defoamer and a tertiary crystal separator;

[0008] The outlet of the first phosphoric acid heater tube is connected to the top inlet of the first crystal separator through the first evaporation concentration defoamer, and the bottom outlet of the first crystal separator is connected to the inlet of the first phosphoric acid heater tube through the first phosphoric acid concentration circulation pump;

[0009] The output end of the top of the primary evaporation concentration demister is connected to the upper part of the secondary phosphoric acid heater, the top of the secondary phosphoric acid heater is connected to the secondary crystallization separator through the secondary flash concentration demister, and the output end of the secondary crystallization separator is connected to the bottom inlet of the secondary phosphoric acid heater;

[0010] The output end of the top of the secondary flash concentration demister is connected to the upper part of the tertiary phosphoric acid heater, the output end of the top of the tertiary phosphoric acid heater is connected to the top of the tertiary crystallization separator through the tertiary flash concentration demister, and the output end of the bottom of the tertiary crystallization separator is connected to the inlet of the bottom of the tertiary phosphoric acid heater.

[0011] In the technical solution of the present invention: the shell side inlet of the first-level phosphoric acid heater is connected to the medium-pressure steam delivery pipeline from the boundary zone, and the shell side outlet of the first-level phosphoric acid heater is connected to the condensate delivery pipeline of the de-boundary zone through the first-level condensate collection tank.

[0012] In the technical solution of the present invention: the concentrated phosphoric acid pipeline in the delimited area and the secondary concentrated phosphoric acid pipeline from the outlet of the secondary concentrated phosphoric acid circulation pump are both connected to the connecting pipeline from the outlet of the primary concentrated phosphoric acid circulation pump to the inlet of the primary phosphoric acid heater pipe line, the concentrated phosphoric acid pipeline in the delimited area is close to the outlet of the primary concentrated phosphoric acid circulation pump, and the secondary concentrated phosphoric acid pipeline from the outlet of the secondary concentrated phosphoric acid circulation pump is close to the inlet of the primary phosphoric acid heater pipe line.

[0013] In the technical solution of the present invention, the shell outlet of the secondary phosphoric acid heater is connected to the secondary condensate delivery pipeline of the dephosphorylation device through a secondary condensate collection tank.

[0014] In the technical solution of the present invention: the secondary concentrated phosphoric acid pipeline for the first-stage concentration and the tertiary concentrated phosphoric acid pipeline from the outlet of the tertiary concentrated phosphoric acid circulation pump are both connected to the connecting pipeline from the outlet of the secondary concentrated phosphoric acid circulation pump to the inlet of the secondary phosphoric acid heater pipe line, the secondary concentrated phosphoric acid pipeline for the first-stage concentration is as close to the outlet of the secondary concentrated phosphoric acid circulation pump as possible, and the tertiary concentrated phosphoric acid pipeline from the outlet of the tertiary concentrated phosphoric acid circulation pump is as close to the inlet of the secondary phosphoric acid heater pipe line as possible.

[0015] In the technical solution of the present invention, the shell outlet of the three-stage phosphoric acid heater is connected to the secondary condensate delivery pipeline of the dephosphorylation device through a three-stage condensate collection tank and a condensate delivery pump.

[0016] In the technical solution of the present invention: the tertiary concentrated phosphoric acid pipeline for secondary concentration and the dilute phosphoric acid pipeline from the boundary area are both connected to the connecting pipeline from the outlet of the tertiary concentrated phosphoric acid circulation pump to the inlet of the tertiary phosphoric acid heater pipe line, the tertiary concentrated phosphoric acid pipeline for secondary concentration is as close as possible to the outlet of the tertiary concentrated phosphoric acid circulation pump, and the dilute phosphoric acid pipeline from the boundary area is as close as possible to the inlet of the tertiary phosphoric acid heater pipe line.

[0017] A method for producing three-stage concentrated phosphoric acid using the above system comprises the following steps:

[0018] (1) Primary heating evaporation and concentration of phosphoric acid section: The medium-pressure saturated steam from the sulfuric acid production unit has a temperature of ≥211°C and an absolute pressure of ≥2.0 MPa and enters the shell side of the primary phosphoric acid heater to exchange heat with the primary circulating phosphoric acid in the tube side. The medium-pressure saturated steam is cooled to form condensed water, which is then sent from the shell side outlet of the primary phosphoric acid heater to the primary condensed water collection tank and then returned to the sulfuric acid production unit from the bottom of the primary condensed water collection tank;

[0019] The two streams of phosphoric acid from the outlet of the primary concentrated phosphoric acid circulation pump and the outlet of the secondary concentrated phosphoric acid circulation pump are mixed and then enter the inlet of the primary phosphoric acid heater pipe process. The circulating phosphoric acid is heated in the primary phosphoric acid heater and the temperature rises to ≥189°C. Then the circulating concentrated phosphoric acid enters the primary evaporation concentration demister. When the gas phase temperature is ≥144°C and the gas phase absolute pressure is ≥0.41MPa, part of the water in the circulating phosphoric acid is evaporated and removed. The concentration of the circulating phosphoric acid is increased and the temperature is reduced to ≥186°C. The primary circulating concentrated phosphoric acid exiting the primary evaporation concentration demister is first filtered and crushed by a primary crystallization separator to separate crystals and then enters the primary phosphoric acid concentration circulation pump. Part of the phosphoric acid exiting the primary phosphoric acid concentration circulation pump is used as the primary circulating phosphoric acid to go to the primary phosphoric acid heater for the next cycle, and the other part is used as the target product phosphoric acid to go to the boundary area. The target product phosphoric acid contains a P2O5 mass concentration of ≥54%;

[0020] (2) Secondary heating flash evaporation concentrated phosphoric acid section: The low-pressure saturated steam from the top of the primary evaporation concentration demister has a temperature of ≥143°C and an absolute pressure of ≥0.4MPa and enters the shell side of the secondary phosphoric acid heater to exchange heat with the secondary circulating phosphoric acid in the tube side. The low-pressure saturated steam is cooled to form condensate and is sent from the shell side outlet of the secondary phosphoric acid heater to the secondary condensate collection tank. The condensate from the bottom of the secondary condensate collection tank is used for phosphoric acid reaction and filtration devices. The two streams of phosphoric acid from the outlet of the secondary concentrated phosphoric acid circulation pump and the outlet of the tertiary concentrated phosphoric acid circulation pump are mixed and then enter the tube side inlet of the secondary phosphoric acid heater. The circulating phosphoric acid in the secondary phosphoric acid heater is heated and the temperature rises to ≥110°C. Then the circulating concentrated phosphoric acid enters the secondary flash concentration demister, where a portion of the water in the circulating phosphoric acid is removed by flash evaporation at a gas phase absolute pressure of ≥0.062MPa and a gas phase temperature of ≥87°C, the circulating phosphoric acid concentration is increased, and the temperature is reduced to ≥107°C. The secondary circulating concentrated phosphoric acid exiting the secondary flash concentration demister is first filtered and crushed by a secondary crystallization separator to separate the crystals, and then enters the secondary phosphoric acid concentration circulation pump. A portion of the phosphoric acid exiting the secondary phosphoric acid concentration circulation pump is used as the secondary circulating phosphoric acid to go to the secondary phosphoric acid heater for the next cycle, and the other portion is used as the secondary phosphoric acid to go to the primary phosphoric acid heater pipe inlet, and the secondary phosphoric acid contains a P2O5 mass concentration of ≥42%;

[0021] (3) Three-stage heating flash evaporation phosphoric acid concentration section: The low-pressure saturated steam from the top of the second-stage flash evaporation concentration demister with a temperature of ≥85°C and an absolute pressure of ≥0.059 MPa enters the shell side of the three-stage phosphoric acid heater, exchanges heat with the three-stage circulating phosphoric acid in the tube side, and is cooled into condensate. It is sent from the shell side outlet of the three-stage phosphoric acid heater to the three-stage condensate collection tank, and is sent from the bottom of the three-stage condensate collection tank to the phosphoric acid reaction and filtration device through the condensate delivery pump; the two streams of phosphoric acid from the three-stage concentrated phosphoric acid circulation pump and the dilute phosphoric acid from the boundary area are mixed and enter the tube side inlet of the three-stage phosphoric acid heater. The circulating phosphoric acid is heated in the three-stage phosphoric acid heater and the temperature rises to ≥61°C. Then the circulating concentrated phosphoric acid enters the three-stage flash evaporation concentration demister and is heated at an absolute pressure of ≥9.82x10 -3 MPa, and the gas phase temperature is ≥46°C, and a part of the water in the circulating phosphoric acid is removed by flash evaporation, the concentration of the circulating phosphoric acid is increased, and the temperature is reduced to ≥58°C at the same time. The three-stage circulating concentrated phosphoric acid exiting the three-stage flash evaporation concentration and defoamer is first filtered and crushed by a three-stage crystallization separator to separate the crystals, and then enters the three-stage phosphoric acid concentration circulation pump. A part of the phosphoric acid exiting the three-stage phosphoric acid concentration circulation pump is used as the three-stage circulating phosphoric acid to go to the three-stage phosphoric acid heater for the next cycle, and the other part is used as the three-stage phosphoric acid to go to the pipe inlet of the second-stage phosphoric acid heater, and the three-stage phosphoric acid contains a mass concentration of P2O5 of ≥33%. In the technical solution of the present invention: the first-stage phosphoric acid heater is made of alloy steel, and the second-stage phosphoric acid heater and the third-stage phosphoric acid heater are made of alloy steel or graphite.

[0022] Beneficial effects of the present invention:

[0023] The present invention provides a system and method for three-stage phosphoric acid concentration. The method uses medium-pressure saturated steam to concentrate phosphoric acid in three stages. For every ton of water evaporated, only 0.5-0.6 tons of 2.3MPa (absolute pressure) medium-pressure saturated steam is consumed. For 0.3MPa (absolute pressure) and 133°C low-pressure saturated steam, 1.2-1.3 tons are consumed. One ton of 2.3MPa (absolute pressure) medium-pressure saturated steam is cooled and decompressed by 25°C water to obtain only 1.029 tons of 0.3MPa (absolute pressure) and 133°C low-pressure saturated steam. Therefore, the use of medium-pressure saturated steam to concentrate phosphoric acid saves more than 50% of steam, and the target product phosphoric acid has a higher mass concentration of P2O5, which can reach more than 54%. The phosphoric acid heater is made of alloy steel, and the phosphoric acid flow rate in the phosphoric acid heater pipe can adopt a high flow rate (the flow rate can be greater than 2.3 meters / second), which can prevent scaling and frequent washing in the phosphoric acid heater, and can be applied to high-solid phosphoric acid without being easily corroded. In particular, the first-stage phosphoric acid heater is made of alloy steel to avoid the contamination of condensate by the first-stage phosphoric acid heater, which may affect the return water of the steam system and corrode the steam system. This patent aims to save energy and reduce consumption, reduce carbon emissions of production equipment, and reduce operating and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the process flow diagram of this patent

[0025] Among them, there are a first-stage phosphoric acid heater 1, a first-stage evaporation concentration demister 2, a first-stage crystallization separator 3, a first-stage concentrated phosphoric acid circulation pump 4, a first-stage condensed water collecting tank 5, a second-stage phosphoric acid heater 6, a second-stage flash concentration demister 7, a second-stage crystallization separator 8, a second-stage concentrated phosphoric acid circulation pump 9, a second-stage condensate collecting tank 10, a tertiary phosphoric acid heater 11, a tertiary flash concentration demister 12, a tertiary crystallization separator 13, a tertiary concentrated phosphoric acid circulation pump 14, a tertiary condensate collecting tank 15, and a condensate delivery pump 16. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with embodiments, but the protection scope of the present invention is not limited thereto: Figure 1 , a three-stage phosphoric acid concentration system, the system comprising a primary phosphoric acid heater 1, a primary evaporation concentration defoamer 2, a primary crystal separator 3, a secondary phosphoric acid heater 6, a secondary flash concentration defoamer 7, a secondary crystal separator 8, a tertiary phosphoric acid heater 11, a tertiary flash concentration defoamer 12 and a tertiary crystal separator 13;

[0027] The pipe side outlet of the primary phosphoric acid heater 1 is connected to the top inlet of the primary crystal separator 3 through the primary evaporation concentration defoamer 2, and the bottom outlet of the primary crystal separator 3 is connected to the pipe side inlet of the primary phosphoric acid heater 1 through the primary phosphoric acid concentration circulation pump 4;

[0028] The output end of the top of the primary evaporation concentration demister 2 is connected to the upper part of the secondary phosphoric acid heater 6, the top of the secondary phosphoric acid heater 6 is connected to the secondary crystallization separator 8 through the secondary flash concentration demister 7, and the output end of the secondary crystallization separator 8 is connected to the bottom inlet of the secondary phosphoric acid heater 6;

[0029] The output end of the top of the secondary flash concentration demister 7 is connected to the upper part of the tertiary phosphoric acid heater 11, the output end of the top of the tertiary phosphoric acid heater 11 is connected to the top of the tertiary crystallization separator 13 through the tertiary flash concentration demister 12, and the output end of the bottom of the tertiary crystallization separator 13 is connected to the inlet at the bottom of the tertiary phosphoric acid heater 11.

[0030] The shell side inlet of the first phosphoric acid heater 1 is connected to the medium-pressure steam delivery pipeline from the boundary area, and the shell side outlet of the first phosphoric acid heater 1 is connected to the condensate delivery pipeline of the deboundary area through the first condensate collecting tank 5. The concentrated phosphoric acid pipeline of the deboundary area and the second concentrated phosphoric acid pipeline from the outlet of the second concentrated phosphoric acid circulation pump 9 are both connected to the connecting pipeline from the outlet of the first concentrated phosphoric acid circulation pump 4 to the pipe side inlet of the first phosphoric acid heater 1. The concentrated phosphoric acid pipeline of the deboundary area is close to the outlet of the first concentrated phosphoric acid circulation pump 4, and the second concentrated phosphoric acid pipeline from the outlet of the second concentrated phosphoric acid circulation pump 9 is close to the pipe side inlet of the first phosphoric acid heater 1.

[0031] The shell side outlet of the secondary phosphoric acid heater 6 is connected to the secondary condensate delivery pipeline of the dephosphorylation device through the secondary condensate collection tank 10.

[0032] The secondary concentrated phosphoric acid pipeline for the first-stage concentration and the tertiary concentrated phosphoric acid pipeline from the outlet of the tertiary concentrated phosphoric acid circulation pump 14 are both connected to the connecting pipeline from the outlet of the secondary concentrated phosphoric acid circulation pump 9 to the inlet of the secondary phosphoric acid heater 6 pipe line. The secondary concentrated phosphoric acid pipeline for the first-stage concentration is as close to the outlet of the secondary concentrated phosphoric acid circulation pump 9 as possible, and the tertiary concentrated phosphoric acid pipeline from the outlet of the tertiary concentrated phosphoric acid circulation pump 14 is as close to the inlet of the secondary phosphoric acid heater 6 pipe line as possible.

[0033] The shell side outlet of the tertiary phosphoric acid heater 11 is connected to the secondary condensate delivery pipeline of the dephosphorylation device through a tertiary condensate collection tank 15 and a condensate delivery pump 16.

[0034] The tertiary concentrated phosphoric acid pipeline for secondary concentration and the dilute phosphoric acid pipeline from the boundary area are both connected to the connecting pipeline from the outlet of the tertiary concentrated phosphoric acid circulation pump 14 to the inlet of the pipe side of the tertiary phosphoric acid heater 11. The tertiary concentrated phosphoric acid pipeline for secondary concentration is as close as possible to the outlet of the tertiary concentrated phosphoric acid circulation pump 14, and the dilute phosphoric acid pipeline from the boundary area is as close as possible to the inlet of the pipe side of the tertiary phosphoric acid heater 11.

[0035] The method for producing three-stage concentrated phosphoric acid using the above system comprises the following steps:

[0036] (1) Primary heating evaporation and concentration of phosphoric acid section: the medium-pressure saturated steam from the sulfuric acid production unit has a temperature of ≥219-220°C and a pressure of 2.3-2.4 MPa (absolute pressure) and enters the shell side of the primary phosphoric acid heater 1, exchanges heat with the primary circulating phosphoric acid in the tube side, and is cooled to form condensed water with a temperature of 216-217°C and a pressure of 2.2-2.3 MPa (absolute pressure). It is then sent from the shell side outlet of the primary phosphoric acid heater 1 to the primary condensed water collection tank 5, and then returned to the sulfuric acid production unit from the bottom of the primary condensed water collection tank 5; the primary circulating concentrated phosphoric acid has a temperature of 186-187°C and comes from the primary concentrated phosphoric acid circulation pump 4, and the secondary concentrated phosphoric acid has a temperature of 107-108°C and comes from the outlet of the secondary concentrated phosphoric acid circulation pump 9. The two streams of phosphoric acid are mixed and enter the tube side inlet of the primary phosphoric acid heater 1. The circulating phosphoric acid in the primary phosphoric acid heater 1 is heated to a temperature of 189-190° C., and then the circulating concentrated phosphoric acid enters the primary evaporation concentration demister 2, where a portion of the water in the circulating phosphoric acid is evaporated and removed at a gas phase temperature of 144-145° C. and a gas phase pressure of 0.41-0.42 MPa (absolute pressure), and the concentration of the circulating phosphoric acid is increased. At the same time, the temperature is reduced to 186-187° C. The primary circulating concentrated phosphoric acid exiting the primary evaporation concentration demister 2 is first filtered and crushed by a primary crystallization separator 3 to separate crystals, and then enters the primary phosphoric acid concentration circulation pump 4. A portion of the phosphoric acid exiting the primary phosphoric acid concentration circulation pump 4 is used as the primary circulating phosphoric acid to go to the primary phosphoric acid heater 1 for the next cycle, and the other portion is used as the target product phosphoric acid to go to the boundary area. The target product phosphoric acid contains a P2O5 mass concentration of 54-55%.

[0037] (2) Secondary heating flash evaporation phosphoric acid concentration section: The low-pressure saturated steam from the top of the primary evaporation concentration demister 2 has a temperature of 143-144° C. and a pressure of 0.40-0.41 MPa (absolute pressure) and enters the shell side of the secondary phosphoric acid heater 6, and exchanges heat with the secondary circulating phosphoric acid in the tube side. The low-pressure saturated steam is cooled to form a condensate with a temperature of 140-141° C. and a pressure of 0.37-0.38 MPa (absolute pressure). The condensate is sent from the shell side outlet of the secondary phosphoric acid heater 6 to the secondary condensate collection tank 10, and the condensate is sent from the bottom of the secondary condensate collection tank 10 to the phosphoric acid reaction and filtration device; the secondary circulating concentrated phosphoric acid has a temperature of 107-108° C. and comes from the secondary concentrated phosphoric acid circulation pump 9, and the tertiary concentrated phosphoric acid has a temperature of 58-59° C. and comes from the outlet of the tertiary concentrated phosphoric acid circulation pump 14. The two streams of phosphoric acid are mixed and enter the tube side of the secondary phosphoric acid heater 6 for In the secondary phosphoric acid heater 6, the circulating phosphoric acid is heated and the temperature rises to 110-111° C. Then, the circulating concentrated phosphoric acid enters the secondary flash evaporation concentration demister 7, where a portion of the water in the circulating phosphoric acid is removed by flash evaporation at a gas phase pressure of 0.063-0.066 MPa (absolute pressure) and a gas phase temperature of 87-88° C., thereby increasing the concentration of the circulating phosphoric acid and reducing the temperature to 107-108° C. The secondary circulating concentrated phosphoric acid exiting the secondary flash evaporation concentration demister 7 is first filtered and crushed by a secondary crystallization separator 8 to separate the crystals, and then enters the secondary phosphoric acid concentration circulation pump 9. A portion of the phosphoric acid exiting the secondary phosphoric acid concentration circulation pump 9 is used as the secondary circulating phosphoric acid to go to the secondary phosphoric acid heater 6 for the next cycle, and the other portion is used as the secondary phosphoric acid to go to the inlet of the primary phosphoric acid heater 1 pipe side. The secondary phosphoric acid contains a P2O5 mass concentration of 42-43%.

[0038] (3) Three-stage heating flash evaporation phosphoric acid concentration section: The low-pressure saturated steam from the top of the second-stage flash evaporation concentration demister 7 enters the shell side of the three-stage phosphoric acid heater 11 with a temperature of 85-86° C. and a pressure of 0.059-0.061 MPa (absolute pressure), and exchanges heat with the three-stage circulating phosphoric acid in the tube side. The low-pressure saturated steam is cooled to form a condensate with a temperature of 82-83° C. and a pressure of 0.052-0.055 MPa (absolute pressure). The condensate is then discharged from the shell side outlet of the three-stage phosphoric acid heater 11 to the three-stage condensate collecting tank 15. The bottom of the tank 15 is used for phosphoric acid reaction and filtering by the condensate delivery pump 16; the temperature of the three-stage circulating concentrated phosphoric acid is 58-59°C, which comes from the three-stage concentrated phosphoric acid circulation pump 14, and the dilute phosphoric acid temperature is room temperature and contains 22-24% of P2O5 by mass concentration from the boundary area. The two streams of phosphoric acid are mixed and enter the pipe inlet of the three-stage phosphoric acid heater 11. The circulating phosphoric acid is heated in the three-stage phosphoric acid heater 11, and the temperature rises to 61-62°C. Then the circulating concentrated phosphoric acid enters the three-stage flash concentration demister 12, and at the gas phase pressure ≥9.82x10 -3 ~1.08x10 -2MPa (absolute pressure) and a gas phase temperature of 46-47°C are used to flash off a portion of the water in the circulating phosphoric acid, thereby increasing the concentration of the circulating phosphoric acid and reducing the temperature to 58-59°C. The tertiary circulating concentrated phosphoric acid exiting the tertiary flash concentration demister 12 is first filtered, crushed and separated into crystals by a tertiary crystallization separator 13, and then enters a tertiary phosphoric acid concentration circulation pump 14. A portion of the phosphoric acid exiting the tertiary phosphoric acid concentration circulation pump 14 is used as tertiary circulating phosphoric acid to go to the tertiary phosphoric acid heater 11 for the next cycle, and the other portion is used as tertiary phosphoric acid to go to the inlet of the secondary phosphoric acid heater 6 pipe pass. The tertiary phosphoric acid contains a P2O5 mass concentration of 33-34%.

[0039] The results of the operation of the present invention are shown in Table 1.

[0040] Table 1 Performance evaluation results of 10,000 tons / year three-stage concentrated phosphoric acid unit

[0041] Table 1 Performance evaluation results of 10,000 tons / year three-stage concentrated phosphoric acid unit

[0042]

Claims

1. A three-stage concentrated phosphoric acid system, characterized in that: The system comprises a primary phosphoric acid heater (1), a primary evaporation concentration defoamer (2), a primary crystallization separator (3), a secondary phosphoric acid heater (6), a secondary flash concentration defoamer (7), a secondary crystallization separator (8), a tertiary phosphoric acid heater (11), a tertiary flash concentration defoamer (12) and a tertiary crystallization separator (13); The pipe side outlet of the primary phosphoric acid heater (1) is connected to the top inlet of the primary crystal separator (3) through the primary evaporation concentration defoamer (2), and the bottom end outlet of the primary crystal separator (3) is connected to the pipe side inlet of the primary phosphoric acid heater (1) through the primary phosphoric acid concentration circulation pump (4); The output end of the top of the primary evaporation concentration demister (2) is connected to the upper part of the secondary phosphoric acid heater (6), the top of the secondary phosphoric acid heater (6) is connected to the secondary crystallization separator (8) through the secondary flash evaporation concentration demister (7), and the output end of the secondary crystallization separator (8) is connected to the bottom inlet of the secondary phosphoric acid heater (6); The output end of the top of the secondary flash concentration demister (7) is connected to the upper part of the tertiary phosphoric acid heater (11), the output end of the top of the tertiary phosphoric acid heater (11) is connected to the top of the tertiary crystallization separator (13) through the tertiary flash concentration demister (12), and the output end of the bottom of the tertiary crystallization separator (13) is connected to the inlet at the bottom of the tertiary phosphoric acid heater (11).

2. The system for three-stage concentrated phosphoric acid according to claim 1, characterized in that: The shell side inlet of the first-stage phosphoric acid heater (1) is connected to the medium-pressure steam delivery pipeline from the boundary zone, and the shell side outlet of the first-stage phosphoric acid heater (1) is connected to the condensate delivery pipeline of the de-boundary zone through the first-stage condensate collection tank (5).

3. The system for three-stage concentrated phosphoric acid according to claim 1, characterized in that: The concentrated phosphoric acid pipeline in the delimited area and the secondary concentrated phosphoric acid pipeline from the outlet of the secondary concentrated phosphoric acid circulation pump (9) are both connected to the connecting pipeline from the outlet of the primary concentrated phosphoric acid circulation pump (4) to the inlet of the pipe line of the primary phosphoric acid heater (1). The concentrated phosphoric acid pipeline in the delimited area is close to the outlet of the primary concentrated phosphoric acid circulation pump (4), and the secondary concentrated phosphoric acid pipeline from the outlet of the secondary concentrated phosphoric acid circulation pump (9) is close to the inlet of the pipe line of the primary phosphoric acid heater (1).

4. The system for three-stage concentrated phosphoric acid according to claim 1, characterized in that: The shell side outlet of the secondary phosphoric acid heater (6) is connected to the secondary condensate delivery pipeline of the dephosphorylation device through a secondary condensate collection tank (10).

5. The system for three-stage concentrated phosphoric acid according to claim 1, characterized in that: The secondary concentrated phosphoric acid pipeline for the primary concentration and the tertiary concentrated phosphoric acid pipeline from the outlet of the tertiary concentrated phosphoric acid circulation pump (14) are both connected to the connecting pipeline from the outlet of the secondary concentrated phosphoric acid circulation pump (9) to the inlet of the secondary phosphoric acid heater (6) pipe line. The secondary concentrated phosphoric acid pipeline for the primary concentration is as close to the outlet of the secondary concentrated phosphoric acid circulation pump (9) as possible, and the tertiary concentrated phosphoric acid pipeline from the outlet of the tertiary concentrated phosphoric acid circulation pump (14) is as close to the inlet of the secondary phosphoric acid heater (6) pipe line as possible.

6. The system for three-stage concentrated phosphoric acid according to claim 1, characterized in that: The shell side outlet of the tertiary phosphoric acid heater (11) is connected to the secondary condensate delivery pipeline of the dephosphorylation device through a tertiary condensate collection tank (15) and a condensate delivery pump (16).

7. The system for three-stage concentrated phosphoric acid according to claim 5, characterized in that: The tertiary concentrated phosphoric acid pipeline for secondary concentration and the dilute phosphoric acid pipeline from the boundary area are both connected to the connecting pipeline from the outlet of the tertiary concentrated phosphoric acid circulation pump (14) to the pipe inlet of the tertiary phosphoric acid heater (11). The tertiary concentrated phosphoric acid pipeline for secondary concentration is as close as possible to the outlet of the tertiary concentrated phosphoric acid circulation pump (14), and the dilute phosphoric acid pipeline from the boundary area is as close as possible to the pipe inlet of the tertiary phosphoric acid heater (11).

8. A method for producing three-stage concentrated phosphoric acid using the system of claim 1, characterized in that: The method comprises the following steps: (1) Primary heating evaporation and concentration phosphoric acid section: The medium-pressure saturated steam from the sulfuric acid production unit has a temperature of ≥211°C and an absolute pressure of ≥2.0 MPa and enters the shell side of the primary phosphoric acid heater (1), exchanges heat with the primary circulating phosphoric acid in the tube side, and the medium-pressure saturated steam is cooled to form condensed water. The condensed water is sent from the shell side outlet of the primary phosphoric acid heater (1) to the primary condensed water collection tank (5), and then returns to the sulfuric acid production unit from the bottom of the primary condensed water collection tank (5); The two streams of phosphoric acid from the outlet of the primary concentrated phosphoric acid circulation pump (4) and the outlet of the secondary concentrated phosphoric acid circulation pump (9) are mixed and then enter the pipe inlet of the primary phosphoric acid heater (1). The circulating phosphoric acid is heated in the primary phosphoric acid heater (1) and the temperature rises to ≥189°C. Then the circulating concentrated phosphoric acid enters the primary evaporation concentration demister (2). When the gas phase temperature is ≥144°C and the gas phase absolute pressure is ≥0.41MPa, part of the water in the circulating phosphoric acid is evaporated and removed. The concentration of the circulating phosphoric acid is increased and the temperature is reduced to ≥186°C. The primary circulating concentrated phosphoric acid exiting the primary evaporation concentration demister (2) is first filtered and crushed by a primary crystal separator (3) to separate crystals. Then, the phosphoric acid enters the primary phosphoric acid concentration circulation pump (4). Part of the phosphoric acid exiting the primary phosphoric acid concentration circulation pump (4) is used as the primary circulating phosphoric acid to go to the primary phosphoric acid heater (1) for the next cycle, and the other part is used as the target product phosphoric acid to go to the boundary area. The target product phosphoric acid contains a P2O5 mass concentration of ≥54%. (2) Secondary heating flash evaporation concentrated phosphoric acid section: The low-pressure saturated steam with a temperature of ≥143°C and an absolute pressure of ≥0.4 MPa from the top of the primary evaporation concentration demister (2) enters the shell side of the secondary phosphoric acid heater (6) and exchanges heat with the secondary circulating phosphoric acid in the tube side. The low-pressure saturated steam is cooled to form a condensate and is sent from the shell side outlet of the secondary phosphoric acid heater (6) to the secondary condensate collecting tank (10). The condensate from the bottom of the secondary condensate collecting tank (10) is used for phosphoric acid reaction and filtering devices; the two streams of phosphoric acid from the outlet of the secondary concentrated phosphoric acid circulating pump (9) and the outlet of the tertiary concentrated phosphoric acid circulating pump (14) are mixed and then enter the tube side inlet of the secondary phosphoric acid heater (6). The circulating phosphoric acid in the secondary phosphoric acid heater (6) is heated and the temperature rises to ≥ 110°C, and then the circulating concentrated phosphoric acid enters the secondary flash concentration demister (7), where a portion of the water in the circulating phosphoric acid is removed by flash evaporation under the condition that the gas phase absolute pressure is ≥0.062MPa and the gas phase temperature is ≥87°C, the concentration of the circulating phosphoric acid is increased, and the temperature is reduced to ≥107°C at the same time. The secondary circulating concentrated phosphoric acid exiting the secondary flash concentration demister (7) is first filtered and crushed by the secondary crystallization separator (8) to separate the crystals, and then enters the secondary phosphoric acid concentration circulation pump (9). A portion of the phosphoric acid exiting the secondary phosphoric acid concentration circulation pump (9) is used as the secondary circulating phosphoric acid to go to the secondary phosphoric acid heater (6) for the next cycle, and the other portion is used as the secondary phosphoric acid to go to the pipe inlet of the primary phosphoric acid heater (1), and the secondary phosphoric acid contains a P2O5 mass concentration of ≥42%; (3) Three-stage heating flash phosphoric acid concentration section: The low-pressure saturated steam from the top of the second-stage flash concentration demister (7) with a temperature of ≥85°C and an absolute pressure of ≥0.059 MPa enters the shell side of the third-stage phosphoric acid heater (11), exchanges heat with the third-stage circulating phosphoric acid in the tube side, and is cooled to form a condensate. The steam is sent from the shell side outlet of the third-stage phosphoric acid heater (11) to the third-stage condensate collection tank (15), and is sent from the bottom of the third-stage condensate collection tank (15) to the dephosphorization reaction and filtering device via the condensate delivery pump (16); the two streams of phosphoric acid from the third-stage concentrated phosphoric acid circulation pump (14) and the dilute phosphoric acid from the boundary zone are mixed and then enter the tube side inlet of the third-stage phosphoric acid heater (11), where the circulating phosphoric acid is heated to ≥61°C, and then the circulating concentrated phosphoric acid enters the third-stage flash concentration demister (12) and is heated to ≥9.82x10 -3 MPa and a gas phase temperature of ≥46°C, a portion of the water in the circulating phosphoric acid is removed by flash evaporation, the concentration of the circulating phosphoric acid is increased, and the temperature is reduced to ≥58°C at the same time. The tertiary circulating concentrated phosphoric acid exiting the tertiary flash evaporation concentration demister (12) is first filtered, crushed and separated into crystals by a tertiary crystallization separator (13), and then enters a tertiary phosphoric acid concentration circulation pump (14). A portion of the phosphoric acid exiting the tertiary phosphoric acid concentration circulation pump (14) is used as the tertiary circulating phosphoric acid to go to the tertiary phosphoric acid heater (11) for the next cycle, and the other portion is used as the tertiary phosphoric acid to go to the pipe inlet of the secondary phosphoric acid heater (6). The tertiary phosphoric acid contains a P2O5 mass concentration of ≥33%.

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