System and method for producing high-quality phosphoric acid by using hydrochloric acid

Abstract

The invention discloses a system and a method for producing high-purity concentrated phosphoric acid by using hydrochloric acid, in the system for producing high-purity concentrated phosphoric acid by using hydrochloric acid, an acidolysis tank is used for feeding phosphorite and reacting with acid from an acid preparation tank, and an acid liquor outlet of the acid preparation tank is communicated with an acid liquor inlet of the acidolysis tank; a bottom outlet of the acidolysis tank is communicated with a top inlet of the sedimentation thickener, a side outlet of the sedimentation thickener is communicated with a heavy phase inlet of the extractor, a light phase inlet of the extractor is communicated with a solvent pipeline, and a light phase outlet of the extractor is communicated with a light phase inlet of the washing purifier; a light phase outlet of the washing purifier is connected with a light phase inlet of the back extractor, a heavy phase outlet of the back extractor is connected with the evaporation equipment, and a target product outlet is formed in the bottom of the evaporation equipment; a bottom outlet of the sedimentation thickener is communicated with a top inlet of the countercurrent washing thickener, a side outlet of the countercurrent washing thickener is communicated with a hydrochloric acid inlet of the acid preparation tank, and a residue outlet is formed in the bottom of the countercurrent washing thickener.

Description

Technical Field

[0001] The present invention relates to a system and method for producing high-purity concentrated phosphoric acid with hydrochloric acid, belonging to the technical field of chemical production. Background Art

[0002] Broadly speaking, relative to thermal phosphoric acid (furnace phosphoric acid), any phosphoric acid made by decomposing phosphate rock with an acid can be collectively referred to as wet-process phosphoric acid. The acid used must be a strong inorganic acid that can provide sufficient hydrogen ions. In addition to the most commonly used sulfuric acid, hydrochloric acid, nitric acid, and fluorosilicic acid can also be used as the medium for decomposing phosphate rock. Compared with other methods, the method of decomposing phosphate rock with sulfuric acid to produce phosphoric acid has obvious technical advantages. The decomposition product is a phosphoric acid solution and calcium sulfate, and calcium sulfate is a solid with extremely low solubility in phosphoric acid. The separation of the liquid-solid two phases can be achieved by simple filtration operation. In the prior art, the process technology of decomposing phosphate rock with sulfuric acid is generally used for wet-process phosphoric acid, and phosphogypsum is the main by-product of this process technology. The main component of phosphogypsum is CaSO4·2H2O, and about 4 - 5 tons of phosphogypsum are produced for every 1 ton of phosphoric acid produced (calculated as 100% P2O5). The annual discharge of phosphogypsum in China is nearly 68 million tons, and the utilization rate of phosphogypsum is only about 5%. Since the long-term accumulation of phosphogypsum will cause pollution of surface water and groundwater, and the setting of storage yards occupies a large amount of land, with high costs and large investments. At present, phosphogypsum has become one of the solid wastes with the largest emissions in the chemical industry. The wet-process phosphoric acid produced by decomposing phosphate rock with sulfuric acid is mainly used in fertilizer production due to its high impurity content. In other industrial fields except fertilizers, it is difficult for wet-process phosphoric acid to be widely used.

[0003] At present, the annual output of sulfur-based compound fertilizers in China exceeds 10 million tons, and the by-product hydrochloric acid (with a mass concentration of HCl ≥ 31%) exceeds 3.2 million tons. These hydrochloric acids are all disposed of at low prices or even at a loss to other industries, resulting in waste of resources. If these hydrochloric acids are used to produce phosphoric acid, not only can the resource utilization of hydrochloric acid by-products be realized, but also the consumption of sulfuric acid can be reduced and the discharge of phosphogypsum can be reduced. Summary of the Invention

[0004] The purpose of the present invention is to provide a system for producing high-quality phosphoric acid with hydrochloric acid, which can produce high-purity concentrated phosphoric acid and can be directly used in occasions with higher purity requirements. At the same time, the present invention also provides a method for producing high-quality phosphoric acid with hydrochloric acid.

[0005] The system for producing high-quality phosphoric acid with hydrochloric acid of the present invention adopts the following technical solution: A system for producing high-purity concentrated phosphoric acid with hydrochloric acid, including an acid digestion tank, an acid preparation tank, a sedimentation thickener, a countercurrent washing thickener, an extractor, a washing and purifying device, a back-extractor and an evaporation device. The acid preparation tank is used for adding hydrochloric acid, and the acid digestion tank is used for adding phosphate minerals and reacting with the acid from the acid preparation tank. The acid liquid outlet of the acid preparation tank is communicated with the acid liquid inlet of the acid digestion tank. The bottom outlet of the acid digestion tank is communicated with the top inlet of the sedimentation thickener. The side outlet of the sedimentation thickener is communicated with the heavy phase inlet of the extractor. A solvent pipeline is connected to the light phase inlet of the extractor. The light phase outlet of the extractor is communicated with the light phase inlet of the washing and purifying device. The light phase outlet of the washing and purifying device is connected to the light phase inlet of the back-extractor. The heavy phase outlet of the back-extractor is connected to the evaporation device. A target product outlet is provided at the bottom of the evaporation device. The bottom outlet of the sedimentation thickener is communicated with the top inlet of the countercurrent washing thickener. The side outlet of the countercurrent washing thickener is communicated with the hydrochloric acid inlet of the acid preparation tank. A residue outlet is provided at the bottom of the countercurrent washing thickener.

[0006] The countercurrent washing thickener includes a primary countercurrent washing thickener and a secondary countercurrent washing thickener connected in series. The bottom outlet of the sedimentation thickener is communicated with the top inlet of the primary countercurrent washing thickener. The side outlet of the primary countercurrent washing thickener is communicated with the top inlet of the acid preparation tank through a dilute acid pump. The bottom outlet of the primary countercurrent washing thickener is communicated with the top inlet of the secondary countercurrent washing thickener through a thick slurry pump. The side outlet of the secondary countercurrent washing thickener is communicated with the top inlet of the primary countercurrent washing thickener. The bottom outlet of the secondary countercurrent washing thickener is connected to the residue conveying device going to the battery limit.

[0007] A condenser and a phase separator are connected to the evaporation device. The cold source of the condenser comes from the circulating cooling water in the battery limit. The side outlet of the condenser is communicated with the circulating cooling return water pipeline going to the battery limit. The side inlet of the condenser is communicated with the circulating cooling supply water pipeline from the battery limit. The top inlet of the condenser is communicated with the top outlet of the evaporation device. The bottom outlet of the condenser is communicated with the side inlet of the phase separator. The heavy phase outlet of the phase separator is communicated with the heavy phase inlet of the back-extractor. The light phase outlet of the phase separator is communicated with the light phase inlet of the extractor.

[0008] The evaporation equipment includes a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator arranged in series. The heat source of the first-effect evaporator is steam from the battery limit. The side heat medium inlet of the first-effect evaporator is connected to the steam pipeline from the battery limit, and the side heat medium outlet of the first-effect evaporator is connected to the condensate pipeline going to the battery limit. A target product transfer pump is connected to the bottom liquid outlet of the first-effect evaporator. The steam outlet at the top of the first-effect evaporator is connected to the side heat medium inlet of the second-effect evaporator. The side heat medium outlet of the second-effect evaporator is connected to the dilute hydrochloric acid pipeline going to the battery limit through a first-effect condensate pump. The bottom liquid outlet of the second-effect evaporator is connected to the phosphoric acid liquid inlet on the side of the first-effect evaporator through a second-effect phosphoric acid pump. The steam outlet at the top of the second-effect evaporator is connected to the side heat medium inlet of the third-effect evaporator. The side heat medium outlet of the third-effect evaporator is connected to the heavy phase inlet of the back-extractor through a second-effect condensate pump. The steam outlet at the top of the third-effect evaporator is connected to the top inlet of the condenser. The bottom liquid outlet of the third-effect evaporator is connected to the phosphoric acid liquid inlet on the side of the second-effect evaporator through a third-effect phosphoric acid pump. The phosphoric acid liquid inlet on the side of the third-effect evaporator is connected to the heavy phase outlet of the back-extracting agent.

[0009] The acid digestion tank is equipped with an acid digestion tank agitator, the acid preparation tank is equipped with an acid preparation tank agitator, and the sedimentation thickener is equipped with a sedimentation thickener rake. The extractor, washing and purifying device, and back-extractor all adopt box-type mixer-settlers. Each mixer-settler includes a mixing zone and a clarification zone, and a stirrer is respectively arranged in each mixing zone.

[0010] The method for producing high-quality phosphoric acid with hydrochloric acid according to the present invention adopts the following technical solution: A method for producing high-purity concentrated phosphoric acid with hydrochloric acid, which includes the following sections: (1) Section for producing acid digestion liquid from hydrochloric acid and phosphate rock powder: Hydrochloric acid from the battery limit enters the acid preparation tank for acid preparation, and the prepared acid flows into the acid digestion tank. Phosphate rock powder from the battery limit enters the acid digestion tank. In the acid digestion tank, hydrochloric acid reacts with phosphate rock powder to generate phosphoric acid and calcium chloride. The molar ratio of Ca in the phosphate rock powder to HCl in the hydrochloric acid is 10:20 to 10:22. The reaction temperature in the acid digestion tank is 20°C to 50°C, and the residence time of the solution is 5 to 20 minutes. The gas escaping during the reaction is discharged from the top outlet of the acid digestion tank. (2) Thickening and washing section: The reacted slurry enters the sedimentation thickener from the bottom outlet of the acid digestion tank through the top inlet of the sedimentation thickener. The acid digestion liquid in the sedimentation thickener goes to the dilute phosphoric acid and calcium chloride separation section from the side outlet of the sedimentation thickener. The solid in the sedimentation thickener enters the countercurrent washing thickener from the bottom outlet of the sedimentation thickener. The solid in the sedimentation thickener is washed with process water from the battery limit, and the washed liquid enters the acid preparation tank. The residue is discharged from the bottom outlet of the countercurrent washing thickener. (3) Dilute phosphoric acid and calcium chloride separation section: s1. The acidolysis solution from the subsidence thickener enters the extractor through the heavy-phase inlet of the extractor, and the solvent from the solvent recovery system enters the extractor through the light-phase inlet of the extractor. The raffinate containing calcium chloride and impurities goes to the solvent recovery system from the heavy-phase outlet of the extractor. The extract containing dilute phosphoric acid enters the washing and purifying device from the light-phase outlet of the extractor through the light-phase inlet of the washing and purifying device. In the extractor, the acidolysis solution and the solvent are fully mixed and clarified to achieve the purpose of extraction. s2. The extract containing dilute phosphoric acid enters the washing and purifying device and is washed and purified into a purified solution. The washing solution enters the heavy-phase inlet of the extractor from the heavy-phase outlet of the washing and purifying device. The purified solution containing dilute phosphoric acid enters the counter-extractor through the light-phase inlet of the counter-extractor from the light-phase outlet of the washing and purifying device. s3. Process water enters the counter-extractor through the heavy-phase inlet of the counter-extractor. In the counter-extractor, the purified solution and the process water are fully mixed and clarified to achieve counter-extraction. The extracted phosphoric acid is discharged from the heavy-phase outlet of the counter-extractor, and the solvent after counter-extraction goes to the light-phase inlet of the extractor from the light-phase outlet of the counter-extractor. (4) Concentrated phosphoric acid production section: The extracted phosphoric acid discharged from the heavy-phase outlet of the counter-extractor is evaporated and concentrated in the evaporation equipment, and the concentrated phosphoric acid is discharged from the evaporation equipment as the target product.

[0011] In the step (2), the thickening and washing include two-stage washing processes. The solids in the subsidence thickener enter the top inlet of the first-stage counter-current washing thickener through the bottom outlet of the subsidence thickener. The solids in the first-stage counter-current washing thickener are washed with the liquid from the second-stage counter-current washing thickener. The washed liquid enters the acid mixing tank through the side outlet of the first-stage counter-current washing thickener by means of a dilute acid pump through the top inlet of the acid mixing tank, and the solids enter the top inlet of the second-stage counter-current washing thickener through the bottom outlet of the first-stage counter-current washing thickener by means of a thick slurry pump. The solids in the second-stage counter-current washing thickener are washed with the process water from the battery limit. The washed liquid enters the first-stage counter-current washing thickener through the side outlet of the second-stage counter-current washing thickener and through the top inlet of the first-stage counter-current washing thickener, and the residue goes to the battery limit from the bottom outlet of the second-stage counter-current washing thickener.

[0012] The top outlet of the evaporation equipment is sequentially connected with a condenser and a phase separator. The steam formed by the extracted phosphoric acid in the evaporation equipment enters the condenser through the top inlet of the condenser. In the condenser, the steam is condensed into a condensate, which is then discharged from the bottom outlet of the condenser and enters the phase separator through the side inlet of the phase separator. The light phase in the phase separator goes to the dilute phosphoric acid and calcium chloride separation section from the light-phase outlet of the phase separator and enters the extractor through the light-phase inlet of the extractor. The heavy phase in the phase separator goes to the heavy-phase inlet of the counter-extractor from the heavy-phase outlet of the phase separator.

[0013] The evaporation equipment includes a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator. The extracted phosphoric acid first enters the third-effect evaporator through the phosphoric acid liquid inlet on the side of the third-effect evaporator, and is evaporated and concentrated in the third-effect evaporator. The concentrated third-effect phosphoric acid exits from the bottom liquid outlet of the third-effect evaporator, and enters the second-effect evaporator through the phosphoric acid liquid inlet on the side of the second-effect evaporator via the third-effect phosphoric acid pump. The third-effect steam evaporated from the third-effect evaporator enters the condenser from the top steam outlet of the third-effect evaporator; the second-effect steam from the top steam outlet of the second-effect evaporator enters the third-effect evaporator through the heat medium inlet on the side of the third-effect evaporator, and the second-effect steam is condensed into second-effect condensate in the third-effect evaporator and then enters the heavy phase inlet of the back-extractor via the second-effect condensate pump from the heat medium outlet on the side of the third-effect evaporator; the third-effect phosphoric acid from the third-effect evaporator is evaporated and concentrated in the second-effect evaporator, and the concentrated second-effect phosphoric acid is discharged from the bottom outlet of the second-effect evaporator, and enters the first-effect evaporator through the phosphoric acid liquid inlet on the side of the first-effect evaporator via the second-effect phosphoric acid pump; the first-effect steam from the top steam outlet of the first-effect evaporator enters the second-effect evaporator through the heat medium inlet on the side of the second-effect evaporator, and the first-effect steam is condensed into first-effect condensate in the second-effect evaporator, and the first-effect condensate - dilute hydrochloric acid is sent to the battery limit through the first-effect condensate pump from the heat medium outlet on the side of the second-effect evaporator; the second-effect phosphoric acid from the second-effect evaporator is evaporated and concentrated in the first-effect evaporator, and the concentrated phosphoric acid is discharged from the bottom liquid outlet of the first-effect evaporator, and the target product - concentrated phosphoric acid is sent to the battery limit through the target product transfer pump; the steam from the battery limit enters the first-effect evaporator through the heat medium inlet on the side of the first-effect evaporator, and the steam is condensed into condensate in the first-effect evaporator and sent to the battery limit from the heat medium outlet on the side of the first-effect evaporator.

[0014] Part of the extracted phosphoric acid discharged from the heavy phase outlet of the back-extractor enters the evaporation equipment, and the other part enters the washing and purification device from the heavy phase inlet of the washing and purification device.

[0015] The beneficial effects of the present invention are as follows: The present invention uses hydrochloric acid to produce high-quality phosphoric acid. Through the acidolysis liquid production section of hydrochloric acid and phosphate rock powder, the dilute phosphoric acid and calcium chloride separation section, and the concentrated phosphoric acid production section, the decomposition of phosphate rock and the washing and separation of insoluble residues, the liquid-liquid solvent extraction of phosphoric acid and the separation of calcium chloride, and the evaporation and concentration of the extracted phosphoric acid are respectively realized. There is more than one solvent that can be selected during phosphoric acid production, which can be n-butanol. The reaction of hydrochloric acid decomposing phosphate rock proceeds very fast, so there is no need to grind the phosphate rock too finely, and generally grinding to a particle size ≤ 1 mm is sufficient. The acid-insoluble solid residue in the material after phosphate rock decomposition is regenerated during the process of hydrochloric acid decomposing phosphate rock, and it is a complex compound containing calcium, sulfate, aluminum, fluorine, and silicon. The formation of this compound is beneficial to removing impurities such as fluorine, aluminum, soluble silicon, and sulfur in the system, especially fluorine.

[0016] The material formed by decomposing phosphate rock with hydrochloric acid basically contains no easily fouling components, is easy to transport and process, and the produced phosphoric acid can be concentrated to a quite high concentration or made into superphosphate. The steam utilization rate can easily reach the index of consuming 0.4 - 0.5 tons of steam per ton of effluent. The purity of the finished phosphoric acid is higher than that of phosphoric acid produced by the sulfuric acid method and can be directly used in occasions with higher purity requirements, such as the preparation of industrial phosphates or feed-grade phosphates. When the phosphoric acid is concentrated to contain P2O5≥64.8%, the chloride ions in the phosphoric acid can be completely removed.

[0017] The present invention produces high-purity concentrated phosphoric acid, which can be directly used in occasions with higher purity requirements, such as industrial phosphates or feed-grade phosphates; the by-product raffinate goes to the solvent recovery system to recover the solvent and separate calcium chloride, and the calcium chloride is reused outside the battery limit. The present invention solves the problem of the outlet of by-product hydrochloric acid from sulfur-based compound fertilizers, turns waste into treasure and protects the environment, and the system operation does not produce phosphogypsum, so there is no problem of phosphogypsum stacking, which is environmentally friendly.

[0018] In the preferred embodiment, the extractor, washing and purifying device, and stripping device all adopt box-type mixer-settlers. The material is not transported by pumps between stages, and the material flow flows from one stage to another by gravity. This equipment has the characteristics of being compact and there are no complex connecting pipelines between stages. Description of the Drawings

[0019] Figure 1 is a schematic diagram of a system for producing high-purity concentrated phosphoric acid with hydrochloric acid according to an embodiment of the present invention; Figure 2 is Figure 1 an enlarged view of the connection of the extractor, washing and purifying device, and stripping device in Figure 3 is Figure 1 a schematic diagram of the connection of the evaporation equipment with the condenser and the phase separator in Figure 4 is a principle block diagram of a method for producing high-purity concentrated phosphoric acid with hydrochloric acid according to an embodiment of the present invention; Figure 5 is a performance assessment result table of a system for producing high-quality phosphoric acid (calculated based on 100% P2O5) (100 tons / day) with hydrochloric acid.

[0020] In the figure: 1 - acid digestion tank, 2 - agitator for acid digestion tank, 3 - acid preparation tank, 4 - agitator for acid preparation tank, 5 - sedimentation thickener, 6 - rake for sedimentation thickener, 7 - first-stage countercurrent washing thickener, 8 - rake for first-stage countercurrent washing thickener, 9 - second-stage countercurrent washing thickener, 10 - rake for second-stage countercurrent washing thickener, 11 - dilute acid pump, 12 - thick slurry pump, 13 - extractor, 14 - agitator for extractor, 15 - washing and purification unit, 16 - agitator for washing and purification unit, 17 - stripping unit, 18 - agitator for stripping unit, 19 - washing liquid pump, 20 - extraction phosphoric acid pump, 21 - first-effect evaporator, 22 - second-effect evaporator, 23 - third-effect evaporator, 24 - condenser, 25 - phase separator, 26 - target product transfer pump, 27 - first-effect condensate pump, 28 - second-effect phosphoric acid pump, 29 - third-effect phosphoric acid pump, 30 - second-effect condensate pump, 31 - third-effect condensate heavy phase pump, 32 - solvent pump. Detailed implementation mode

[0021] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] As Figure 1 shown, a system for producing high-purity concentrated phosphoric acid with hydrochloric acid according to an embodiment of the present invention includes an acid digestion tank 1, an acid preparation tank 3, a sedimentation thickener 5, a countercurrent washing thickener, an extractor 13, a washing and purification unit 15, a stripping unit 17 and evaporation equipment. The acid digestion tank 1 is equipped with an agitator 2 for the acid digestion tank, the acid preparation tank 3 is equipped with an agitator 4 for the acid preparation tank, and the sedimentation thickener 5 is equipped with a rake 6 for the sedimentation thickener; the extractor 13, the washing and purification unit 15, and the stripping unit 17 all adopt a box-type mixer-settler, and each mixer-settler includes a mixing zone and a clarification zone, and a stirrer is respectively arranged in each mixing zone. The stirrer in the extractor 13 is an extraction stirrer 14, the stirrer in the washing and purification unit 15 is a stirrer 16 for the washing and purification unit, and the stirrer in the stripping unit 17 is a stirrer 18 for the stripping unit.

[0023] The acid preparation tank 1 is used for adding hydrochloric acid, and the hydrochloric acid pipeline from the battery limit is connected to the top inlet of the acid preparation tank 3. The acid digestion tank 3 is used for adding phosphate minerals and reacting with the acid from the acid preparation tank 1. The phosphate powder conveying equipment from the battery limit is connected to the top inlet of the acid digestion tank 1. The acid liquid outlet of the acid preparation tank 1 is communicated with the acid liquid inlet of the acid digestion tank 1. The bottom outlet of the acid digestion tank 3 is communicated with the top inlet of the sedimentation thickener 5. The side outlet of the sedimentation thickener 5 is communicated with the heavy phase inlet of the extractor 13. As Figure 2As shown in the figure, the light-phase inlet of the extractor 13 is connected to a solvent pipeline from the solvent recovery system. The light-phase outlet of the extractor 13 is connected to the light-phase inlet of the washing and purification device 15. The light-phase outlet of the washing and purification device 15 is connected to the light-phase inlet of the back-extractor 17. The light-phase outlet of the back-extractor 17 is connected to the light-phase inlet of the extractor 13 via a solvent pump 32. The heavy-phase outlet of the back-extractor 17 is connected to an evaporation device via an extraction phosphoric acid pump 20. The bottom of the evaporation device is provided with a target product outlet. The heavy-phase outlet of the back-extractor 17 is also connected to the heavy-phase inlet of the washing and purification device 15 through a branch pipeline. The heavy-phase outlet of the washing and purification device 15 is connected to the heavy-phase inlet of the extractor 13 via a washing liquid pump 19. The bottom outlet of the sedimentation thickener 5 is connected to the top inlet of the countercurrent washing thickener. The side outlet of the countercurrent washing thickener is connected to the hydrochloric acid inlet of the acid mixing tank 3. The bottom of the countercurrent washing thickener is provided with a residue outlet.

[0024] The countercurrent washing thickener includes a primary countercurrent washing thickener 7 and a secondary countercurrent washing thickener 9 connected in series. The rakes of the primary countercurrent washing thickener 7 and the secondary countercurrent washing thickener 9 are the primary countercurrent washing thickener rake 8 and the primary countercurrent washing thickener rake 10 respectively. The bottom outlet of the sedimentation thickener 5 is connected to the top inlet of the primary countercurrent washing thickener 7. The side outlet of the primary countercurrent washing thickener 7 is connected to the top inlet of the acid mixing tank 3 via a dilute acid pump 11. The bottom outlet of the primary countercurrent washing thickener 7 is connected to the top inlet of the secondary countercurrent washing thickener 9 via a thick slurry pump 12. The top inlet of the secondary countercurrent washing thickener 9 is connected to a process water pipeline from the battery limit. The side outlet of the secondary countercurrent washing thickener 9 is connected to the top inlet of the primary countercurrent washing thickener 7. The bottom outlet of the secondary countercurrent washing thickener 9 is connected to a residue conveying device to the battery limit.

[0025] A condenser 24 and a phase separator 25 are connected to the evaporation device. The cold source of the condenser 24 comes from the circulating cooling water in the battery limit. The side outlet of the condenser 24 is connected to the circulating cooling return water pipeline to the battery limit. The side inlet of the condenser 24 is connected to the circulating cooling supply water pipeline from the battery limit. The top inlet of the condenser 24 is connected to the top outlet of the evaporation device. The bottom outlet of the condenser 24 is connected to the side inlet of the phase separator 25. The heavy-phase outlet of the phase separator 25 is connected to the heavy-phase inlet of the back-extractor 17 via a three-effect condensate heavy-phase pump 31. The light-phase outlet of the phase separator 25 is connected to the light-phase inlet of the extractor 13.

[0026] As Figure 3As shown in the figure, the evaporation equipment includes a first-effect evaporator 21, a second-effect evaporator 22, and a third-effect evaporator 23 arranged in series. The heat source of the first-effect evaporator 21 is steam from the battery limit. The side heat medium inlet of the first-effect evaporator 21 is connected to the steam pipeline from the battery limit, and the side heat medium outlet of the first-effect evaporator 21 is connected to the condensate pipeline going to the battery limit. A target product transfer pump 26 is connected to the bottom liquid outlet of the first-effect evaporator 21. The top steam outlet of the first-effect evaporator 21 is connected to the side heat medium inlet of the second-effect evaporator 22. The side heat medium outlet of the second-effect evaporator 22 is connected to the dilute hydrochloric acid pipeline going to the battery limit through a first-effect condensate pump 27. The bottom liquid outlet of the second-effect evaporator 22 is connected to the phosphoric acid liquid inlet on the side of the first-effect evaporator 21 through a second-effect phosphoric acid pump 28. The top steam outlet of the second-effect evaporator 22 is connected to the side heat medium inlet of the third-effect evaporator 23. The side heat medium outlet of the third-effect evaporator 23 is connected to the heavy phase inlet of the back-extractor 17 through a second-effect condensate pump 30. The top steam outlet of the third-effect evaporator 23 is connected to the top inlet of the condenser 24. The bottom liquid outlet of the third-effect evaporator 23 is connected to the phosphoric acid liquid inlet on the side of the second-effect evaporator 22 through a third-effect phosphoric acid pump 29. The phosphoric acid liquid inlet on the side of the third-effect evaporator 23 is connected to the heavy phase outlet of the back-extractor 17.

[0027] The method for producing high-quality phosphoric acid with hydrochloric acid by using the above system includes the following sections, and its principle is as Figure 4 shown. There is more than one selectable solvent. Taking n-butanol as an example for now: (1) Section for producing acidolysis liquid from hydrochloric acid and phosphate rock powder: Hydrochloric acid (with a mass concentration of HCl of 31%) from the battery limit enters the acid mixing tank 3 for acid mixing. The prepared acid (with a mass concentration of HCl of 19.5%) flows into the acidolysis tank 1. Phosphate rock powder (with a mass concentration of P2O5 of 30.3% and a particle size ≤ 1 mm) from the battery limit enters the acidolysis tank. In the acidolysis tank 1, hydrochloric acid reacts with phosphate rock powder to generate phosphoric acid and calcium chloride. The molar ratio of Ca in the phosphate rock powder to HCl in hydrochloric acid is 100:204 (the molar ratio range of Ca to HCl is 10:20 - 10:22). The reaction temperature in the acidolysis tank 1 is 40°C (the reaction temperature range is 20°C - 50°C), and the solution residence time is 5 - 20 minutes. The gas escaping during the reaction is discharged from the top outlet of the acidolysis tank 1.

[0028] (2) Thickening and washing section: The reacted slurry enters the settling thickener 5 from the bottom outlet of the acidolysis tank 3 through the top inlet of the settling thickener. The acidolysis liquid (with a mass concentration of P2O5 of 7.26%) in the settling thickener 5 goes to the dilute phosphoric acid and calcium chloride separation section from the side outlet of the settling thickener 5. The solids in the settling thickener 5 enter the countercurrent washing thickener from the bottom outlet of the settling thickener 5. The solids in the settling thickener 5 are washed with process water from the battery limit. The washed liquid enters the acid mixing tank 3, and the residue is discharged from the bottom outlet of the countercurrent washing thickener. In this step, the thickening and washing includes two - stage washing processes. The solids in the settling thickener 5 enter the first - stage counter - current washing thickener 7 from the bottom outlet of the settling thickener and the top inlet of the first - stage counter - current washing thickener 7. The solids in the first - stage counter - current washing thickener 7 are washed with the liquid from the second - stage counter - current washing thickener 9. The washed liquid exits from the side outlet of the first - stage counter - current washing thickener 7, passes through the dilute acid pump 11, and enters the acid mixing tank 3 from the top inlet of the acid mixing tank. The solids exit from the bottom outlet of the first - stage counter - current washing thickener 7, pass through the thick slurry pump 12, and enter the second - stage counter - current washing thickener 9 from the top inlet of the second - stage counter - current washing thickener 9. The solids in the second - stage counter - current washing thickener 9 are washed with the process water from the battery limit. The washed liquid exits from the side outlet of the second - stage counter - current washing thickener 9, enters the first - stage counter - current washing thickener 7 from the top inlet of the first - stage counter - current washing thickener 7, and the residue exits from the bottom outlet of the second - stage counter - current washing thickener 9 to the battery limit.

[0029] (3) Dilute phosphoric acid and calcium chloride separation section: s1. The acidolysis liquid from the settling thickener 5 enters the extractor 13 from the heavy - phase inlet of the extractor 13. The solvent (with a mass concentration of 80% n - butanol) from the solvent recovery system, the light phase of the triple - effect condensate (with a mass concentration of 80% n - butanol) from the phase separator 25, and the solvent (with a mass concentration of 80% n - butanol) from the solvent pump 32 enter the extractor 13 from the light - phase inlet of the extractor 13. The raffinate containing calcium chloride and impurities (with a mass concentration of 1% n - butanol) exits from the heavy - phase outlet of the extractor 13 to the solvent recovery system. The extract containing dilute phosphoric acid exits from the light - phase outlet of the extractor 13 and enters the washing and purifying device 15 from the light - phase inlet of the washing and purifying device 15. In the extractor 13, the acidolysis liquid, the washing liquid, the triple - effect condensate, and the solvent are fully mixed and clarified to achieve the purpose of extraction. s2. The extract containing dilute phosphoric acid (with a mass concentration of 8.75% P2O5) enters the washing and purifying device 15 and is washed and purified into a purified liquid. The washing liquid exits from the heavy - phase outlet of the washing and purifying device 15, passes through the washing liquid pump 19, and enters the heavy - phase inlet of the extractor 13. The purified liquid containing dilute phosphoric acid (with a mass concentration of 7.62% P2O5) exits from the light - phase outlet of the washing and purifying device 15 and enters the counter - extractor 17 from the light - phase inlet of the counter - extractor 17. S3, the secondary-effect condensate (with a mass concentration of HCl of 1.65%) from the secondary-effect condensate pump 30, the heavy phase of the tertiary-effect condensate from the tertiary-effect condensate heavy-phase pump 31 (with a mass concentration of n-butanol of 6%), and the process water from the battery limit enter the back-extractor 17 through the heavy-phase inlet of the back-extractor 17. In the back-extractor 17, the purified liquid is fully mixed and clarified with the secondary-effect condensate, the tertiary-effect condensate, and the process water to achieve back-extraction. The extracted phosphoric acid is discharged from the heavy-phase outlet of the back-extractor 17. Part of the extracted phosphoric acid (with a mass concentration of P2O5 of 11%) discharged from the heavy-phase outlet of the back-extractor 17 enters the evaporation equipment through the extracted phosphoric acid pump 20, and the other part enters the washing and purifier 15 through the heavy-phase inlet of the washing and purifier 15. The solvent after back-extraction (with a mass concentration of n-butanol of 80%) goes from the light-phase outlet of the back-extractor 17 to the light-phase inlet of the extractor 13 through the solvent pump 32.

[0030] (4) Concentrated phosphoric acid production section: The extracted phosphoric acid (with a mass concentration of P2O5 of 11% and a temperature of 50°C) discharged from the heavy-phase outlet of the back-extractor 17 is evaporated and concentrated in the evaporation equipment through the extracted phosphoric acid pump 20. The concentrated phosphoric acid is discharged from the evaporation equipment as the target product.

[0031] The top steam outlet of the evaporation equipment 17 is sequentially connected to a condenser 24 and a phase separator 25. The steam formed by the extracted phosphoric acid in the evaporation equipment enters the condenser 24 from the top inlet of the condenser 24. In the condenser 24, the steam is condensed into a condensate (with a mass concentration of n-butanol of 12%), and then discharged from the bottom outlet of the condenser 24 and enters the phase separator 25 from the side inlet of the phase separator 25. The light phase (with a mass concentration of n-butanol of 80%) in the phase separator 25 goes to the dilute phosphoric acid and calcium chloride separation section from the light-phase outlet of the phase separator 25 and enters the extractor through the light-phase inlet of the extractor 13. The heavy phase (with a mass concentration of n-butanol of 6%) in the phase separator 25 goes to the heavy-phase inlet of the back-extractor 17 through the tertiary-effect condensate heavy-phase pump 31 from the heavy-phase outlet of the phase separator 25.

[0032] The evaporation equipment includes a first-effect evaporator 21, a second-effect evaporator 22, and a third-effect evaporator 23. The extracted phosphoric acid (with a P2O5 mass concentration of 11% and a temperature of 50°C) first enters the third-effect evaporator 23 through the phosphoric acid liquid inlet on the side of the third-effect evaporator 23, and is evaporated and concentrated in the third-effect evaporator 23. The concentrated third-effect phosphoric acid exits from the bottom liquid outlet of the third-effect evaporator 23, passes through the third-effect phosphoric acid pump 29, and enters the second-effect evaporator 22 through the phosphoric acid liquid inlet on the side of the second-effect evaporator 22. The third-effect steam evaporated from the third-effect evaporator 23 enters the condenser 24 from the top steam outlet of the third-effect evaporator 23; the second-effect steam from the top steam outlet of the second-effect evaporator 22 enters the third-effect evaporator through the heat medium inlet on the side of the third-effect evaporator 23. In the third-effect evaporator 23, the second-effect steam is condensed into second-effect condensate (with an HCl mass concentration of 1.65%), exits from the heat medium outlet on the side of the third-effect evaporator 23, and then enters the heavy-phase inlet of the back-extractor 17 through the second-effect condensate pump 30; the third-effect phosphoric acid (with a P2O5 mass concentration of 15.94%) from the third-effect evaporator 23 is evaporated and concentrated in the second-effect evaporator 22. The second-effect phosphoric acid obtained after concentration (with a P2O5 mass concentration of 23.19%) is discharged from the bottom liquid outlet of the second-effect evaporator 22, passes through the second-effect phosphoric acid pump 28, and enters the first-effect evaporator 21 through the phosphoric acid liquid inlet on the side of the first-effect evaporator 21; the first-effect steam from the top steam outlet of the first-effect evaporator 21 enters the second-effect evaporator 22 through the heat medium inlet on the side of the second-effect evaporator 22. In the second-effect evaporator 22, the first-effect steam is condensed into first-effect condensate (with an HCl mass concentration of 6.6%), exits from the heat medium outlet on the side of the second-effect evaporator 22, and the first-effect condensate - dilute hydrochloric acid is sent to the battery limit through the first-effect condensate pump 27; the second-effect phosphoric acid (with a P2O5 mass concentration of 23.19%) from the second-effect evaporator 22 is evaporated and concentrated in the first-effect evaporator 21. The concentrated phosphoric acid is sent to the battery limit as the target product - concentrated phosphoric acid (with a P2O5 mass concentration of 58%) through the target product transfer pump 26 from the bottom liquid outlet of the first-effect evaporator 21; the steam from the battery limit enters the first-effect evaporator 21 through the heat medium inlet on the side of the first-effect evaporator 21. In the first-effect evaporator 21, the steam is condensed into condensate water and sent to the battery limit from the heat medium outlet on the side of the first-effect evaporator.

[0033] According to the above embodiments, the operation results are as Figure 5 shown in the table below. The system can produce more than 500,000 tons of high-quality phosphoric acid (calculated as 100% P2O5). This phosphoric acid can be used to produce sulfur-based compound fertilizers and can also be used in other industries. At the same time, the consumption of sulfuric acid (with an H2SO4 mass concentration of 98%) is reduced by more than 1.5 million tons, and the discharge of phosphogypsum is reduced by more than 2.5 million tons.

Claims

1. A system for producing high-purity concentrated phosphoric acid using hydrochloric acid, characterized in that: It includes an acid digestion tank, an acid preparation tank, a sedimentation thickener, a countercurrent washing thickener, an extractor, a washing and purifying device, a back-extractor and an evaporation device. The acid preparation tank is used for adding hydrochloric acid. The acid digestion tank is used for adding phosphate minerals and reacting with the acid from the acid preparation tank. The acid liquid outlet of the acid preparation tank is communicated with the acid liquid inlet of the acid digestion tank. The bottom outlet of the acid digestion tank is communicated with the top inlet of the sedimentation thickener. The side outlet of the sedimentation thickener is communicated with the heavy phase inlet of the extractor. The light phase inlet of the extractor is connected with a solvent pipeline. The light phase outlet of the extractor is communicated with the light phase inlet of the washing and purifying device. The light phase outlet of the washing and purifying device is connected with the light phase inlet of the back-extractor. The heavy phase outlet of the back-extractor is connected with the evaporation device. A target product outlet is provided at the bottom of the evaporation device. The bottom outlet of the sedimentation thickener is communicated with the top inlet of the countercurrent washing thickener. The side outlet of the countercurrent washing thickener is communicated with the hydrochloric acid inlet of the acid preparation tank. A residue outlet is provided at the bottom of the countercurrent washing thickener.

2. The system for producing high-purity concentrated phosphoric acid with hydrochloric acid according to claim 1, wherein: The countercurrent washing thickener includes a first-stage countercurrent washing thickener and a second-stage countercurrent washing thickener connected in series. The bottom outlet of the sedimentation thickener is communicated with the top inlet of the first-stage countercurrent washing thickener. The side outlet of the first-stage countercurrent washing thickener is communicated with the top inlet of the acid preparation tank through a dilute acid pump. The bottom outlet of the first-stage countercurrent washing thickener is communicated with the top inlet of the second-stage countercurrent washing thickener through a thick slurry pump. The side outlet of the second-stage countercurrent washing thickener is communicated with the top inlet of the first-stage countercurrent washing thickener. The bottom outlet of the second-stage countercurrent washing thickener is connected with a residue conveying device going to the battery limit.

3. The system for producing high-purity concentrated phosphoric acid with hydrochloric acid according to claim 1, characterized in that: A condenser and a phase separator are connected to the evaporation device. The cold source of the condenser comes from the circulating cooling water in the battery limit. The side outlet of the condenser is communicated with the circulating cooling return water pipeline going to the battery limit. The side inlet of the condenser is communicated with the circulating cooling supply water pipeline from the battery limit. The top inlet of the condenser is communicated with the top outlet of the evaporation device. The bottom outlet of the condenser is communicated with the side inlet of the phase separator. The heavy phase outlet of the phase separator is communicated with the heavy phase inlet of the back-extractor. The light phase outlet of the phase separator is communicated with the light phase inlet of the extractor.

4. The system for producing high-purity concentrated phosphoric acid with hydrochloric acid according to claim 3, wherein: The evaporation equipment includes a first-effect evaporator, a second-effect evaporator and a third-effect evaporator which are arranged in series. The heat source of the first-effect evaporator is steam from the battery limit. The heat medium inlet on the side of the first-effect evaporator is communicated with the steam pipeline from the battery limit, and the heat medium outlet on the side of the first-effect evaporator is communicated with the condensate pipeline going to the battery limit. A target product transfer pump is connected to the bottom liquid outlet of the first-effect evaporator, and the steam outlet at the top of the first-effect evaporator is communicated with the heat medium inlet on the side of the second-effect evaporator; the heat medium outlet on the side of the second-effect evaporator is communicated with the dilute hydrochloric acid pipeline going to the battery limit through a first-effect condensate pump, and the bottom liquid outlet of the second-effect evaporator is communicated with the phosphoric acid liquid inlet on the side of the first-effect evaporator through a second-effect phosphoric acid pump. The steam outlet at the top of the second-effect evaporator is communicated with the heat medium inlet on the side of the third-effect evaporator; the heat medium outlet on the side of the third-effect evaporator is communicated with the heavy phase inlet of the counter-extractor through a second-effect condensate pump, the steam outlet at the top of the third-effect evaporator is communicated with the top inlet of the condenser, and the bottom liquid outlet of the third-effect evaporator is communicated with the phosphoric acid liquid inlet on the side of the second-effect evaporator through a third-effect phosphoric acid pump. The phosphoric acid liquid inlet on the side of the third-effect evaporator is communicated with the heavy phase outlet of the counter-extraction agent.

5. The system for producing high-purity concentrated phosphoric acid with hydrochloric acid according to claim 1, characterized in that: The acid digestion tank is equipped with an acid digestion tank agitator, the acid preparation tank is equipped with an acid preparation tank agitator, and the sedimentation thickener is equipped with a sedimentation thickener rake; the extractor, the washing and purification device, and the counter-extractor all adopt a box-type mixer-settler. Each mixer-settler includes a mixing zone and a clarification zone, and a stirrer is respectively arranged in each mixing zone.

6. A method for producing high-purity concentrated phosphoric acid using hydrochloric acid, characterized in that, It includes the following sections: (1) Section for producing acid digestion liquid from hydrochloric acid and phosphate rock powder: Hydrochloric acid from the battery limit enters the acid preparation tank for acid preparation, and the prepared acid flows into the acid digestion tank. Phosphate rock powder from the battery limit enters the acid digestion tank. Hydrochloric acid in the acid digestion tank reacts with phosphate rock powder to generate phosphoric acid and calcium chloride. The molar ratio of Ca in the phosphate rock powder to HCl in the hydrochloric acid is 10:20 - 10:

22. The reaction temperature in the acid digestion tank is 20°C - 50°C, and the solution residence time is 5 - 20 minutes. The gas escaping during the reaction is discharged from the top outlet of the acid digestion tank; (2) Thickening and washing section: The reacted slurry enters the sedimentation thickener from the bottom outlet of the acid digestion tank through the top inlet of the sedimentation thickener. The acid digestion liquid in the sedimentation thickener goes to the dilute phosphoric acid and calcium chloride separation section from the side outlet of the sedimentation thickener; the solids in the sedimentation thickener enter the counter-current washing thickener from the bottom outlet of the sedimentation thickener. The solids in the sedimentation thickener are washed with process water from the battery limit, and the washed liquid enters the acid preparation tank. The residue is discharged from the bottom outlet of the counter-current washing thickener; (3) Dilute phosphoric acid and calcium chloride separation section: s1. The acid digestion liquid from the sedimentation thickener enters the extractor from the heavy phase inlet of the extractor, and the solvent from the solvent recovery system enters the extractor from the light phase inlet of the extractor. The raffinate containing calcium chloride and impurities goes to the solvent recovery system from the heavy phase outlet of the extractor, and the extract containing dilute phosphoric acid enters the washing and purification device from the light phase outlet of the extractor from the light phase inlet. In the extractor, the acid digestion liquid and the solvent are fully mixed and clarified to achieve the purpose of extraction; The extraction liquid containing dilute phosphoric acid enters the washing and purification device, where it is washed and purified into a purified liquid. The washing liquid enters the heavy-phase inlet of the extractor from the heavy-phase outlet of the washing and purification device, and the purified liquid containing dilute phosphoric acid enters the counter-extractor from the light-phase outlet of the washing and purification device through the light-phase inlet of the counter-extractor. Process water enters the counter-extractor from the heavy-phase inlet of the counter-extractor. In the counter-extractor, the purified liquid and the process water are fully mixed and clarified to achieve counter-extraction. The extracted phosphoric acid is discharged from the heavy-phase outlet of the counter-extractor, and the solvent after counter-extraction goes to the light-phase inlet of the extractor from the light-phase outlet of the counter-extractor. (4) Concentrated phosphoric acid production section: The extracted phosphoric acid discharged from the heavy-phase outlet of the counter-extractor is evaporated and concentrated in the evaporation equipment. The concentrated phosphoric acid is discharged from the evaporation equipment as the target product.

7. The method for producing high-purity concentrated phosphoric acid with hydrochloric acid according to claim 6, characterized in that: In the step (2), the thickening and washing include two-stage washing processes. The solids in the settling thickener enter the first-stage counter-current washing thickener from the bottom outlet of the settling thickener through the top inlet of the first-stage counter-current washing thickener. The solids in the first-stage counter-current washing thickener are washed with the liquid from the second-stage counter-current washing thickener. The washed liquid enters the acid mixing tank from the side outlet of the first-stage counter-current washing thickener through the dilute acid pump and the top inlet of the acid mixing tank, and the solids enter the second-stage counter-current washing thickener from the bottom outlet of the first-stage counter-current washing thickener through the thick slurry pump and the top inlet of the second-stage counter-current washing thickener. The solids in the second-stage counter-current washing thickener are washed with the process water from the boundary area. The washed liquid enters the first-stage counter-current washing thickener from the side outlet of the second-stage counter-current washing thickener through the top inlet of the first-stage counter-current washing thickener, and the residue goes to the boundary area from the bottom outlet of the second-stage counter-current washing thickener.

8. The method for producing high-purity concentrated phosphoric acid with hydrochloric acid according to claim 6, characterized in that: The top outlet of the evaporation equipment is sequentially connected with a condenser and a phase separator. The steam formed by the extracted phosphoric acid in the evaporation equipment enters the condenser from the top inlet of the condenser. In the condenser, the steam is condensed into a condensate, which is then discharged from the bottom outlet of the condenser and enters the phase separator from the side inlet of the phase separator. The light phase in the phase separator goes to the dilute phosphoric acid and calcium chloride separation section from the light-phase outlet of the phase separator and enters the extractor from the light-phase inlet of the extractor. The heavy phase in the phase separator goes to the heavy-phase inlet of the counter-extractor from the heavy-phase outlet of the phase separator.

9. The method for producing high-purity concentrated phosphoric acid with hydrochloric acid according to claim 8, characterized in that: The evaporation equipment includes a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator. The extracted phosphoric acid first enters the third-effect evaporator through the phosphoric acid liquid inlet on the side of the third-effect evaporator, and evaporation and concentration are carried out in the third-effect evaporator. The concentrated third-effect phosphoric acid exits from the bottom liquid outlet of the third-effect evaporator and enters the second-effect evaporator through the phosphoric acid liquid inlet on the side of the second-effect evaporator via the third-effect phosphoric acid pump. The third-effect steam evaporated from the third-effect evaporator enters the condenser through the steam outlet at the top of the third-effect evaporator; the second-effect steam from the steam outlet at the top of the second-effect evaporator enters the third-effect evaporator through the heat medium inlet on the side of the third-effect evaporator. In the third-effect evaporator, the second-effect steam is condensed into second-effect condensate and exits from the heat medium outlet on the side of the third-effect evaporator and then enters the heavy-phase inlet of the back-extractor through the second-effect condensate pump; the third-effect phosphoric acid from the third-effect evaporator undergoes evaporation and concentration in the second-effect evaporator. The concentrated second-effect phosphoric acid is discharged from the bottom outlet of the second-effect evaporator and enters the first-effect evaporator through the phosphoric acid liquid inlet on the side of the first-effect evaporator via the second-effect phosphoric acid pump; the first-effect steam from the steam outlet at the top of the first-effect evaporator enters the second-effect evaporator through the heat medium inlet on the side of the second-effect evaporator. In the second-effect evaporator, the first-effect steam is condensed into first-effect condensate and exits from the heat medium outlet on the side of the second-effect evaporator. The first-effect condensate - dilute hydrochloric acid is sent to the battery limit through the first-effect condensate pump; the second-effect phosphoric acid from the second-effect evaporator undergoes evaporation and concentration in the first-effect evaporator. The concentrated phosphoric acid is discharged from the bottom liquid outlet of the first-effect evaporator, and the target product - concentrated phosphoric acid is sent to the battery limit through the target product transfer pump; the steam from the battery limit enters the first-effect evaporator through the heat medium inlet on the side of the first-effect evaporator. In the first-effect evaporator, the steam is condensed into condensate water and sent to the battery limit through the heat medium outlet on the side of the first-effect evaporator.

10. The method for producing high-purity concentrated phosphoric acid with hydrochloric acid according to claim 6, characterized in that: A part of the extracted phosphoric acid discharged from the heavy-phase outlet of the back-extractor enters the evaporation equipment, and the other part enters the washing and purification device through the heavy-phase inlet of the washing and purification device.

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