Method for producing anhydrous sodium sulfate based on cold and hot coupling technology

Abstract

The invention discloses a method for producing anhydrous sodium sulfate based on a cold-hot coupling technology, and belongs to the technical field of anhydrous sodium sulfate preparation of chlor-alkali industrial systems. A device used in the method consists of a hot melting precipitation kettle, a first centrifugal machine, a hot melting kettle, a sodium sulfate decahydrate solution pump, a nanofiltration membrane system, a freezing crystallization kettle, a second centrifugal machine, a light salt brine storage tank, a light salt brine pump and a heat exchanger. According to the method, the anhydrous sodium sulfate is produced by adopting a hot melting method, the heat of the light salt brine is recovered, the energy required for cooling the light salt brine in the traditional process is saved, the heat of the light salt brine is effectively utilized to perform hot melting on the sodium sulfate decahydrate crystal and produce the anhydrous sodium sulfate, and the production is greatly reduced. Compared with the prior art, the method has the advantages that few new equipment is added, the method for producing anhydrous sodium sulfate has no influence on the operation of the original process device, the cooling energy consumption required for cooling light salt brine is saved, the originally generated solid waste is changed into a valuable anhydrous sodium sulfate product, the environmental pollution is reduced, and the economic benefit is good.

Description

Technical Field

[0001] The invention belongs to the technical field of anhydrous sodium sulfate preparation in a chlor-alkali industrial system, and particularly relates to a method for producing anhydrous sodium sulfate based on a cold-heat coupling technology. Background Art

[0002] In the caustic soda production process, the raw salt needs to be refined to remove the impurity sulfate ions, thus generating brine containing sodium sulfate (stored in Figure 1 The sodium sulfate in the salt water storage tank 8 needs to be removed. Currently, the removal of sodium sulfate is mainly carried out by separating using a nanofiltration membrane. The nanofiltration membrane (NF) mainly removes solute particles with a diameter of about 1 nanometer (nm) and has a molecular weight cut-off of 100 to 1000. The molecular weight of sodium chloride is 58.44, and the molecular weight of sodium sulfate is 142.04. Therefore, it can effectively intercept sodium sulfate molecules, while sodium chloride molecules can pass through. In addition, the nanofiltration membrane is provided with a negative charge layer, so that divalent anions are intercepted by the membrane surface, and most of them cannot pass through the membrane layer, while monovalent anions and cations are almost unaffected, thereby achieving the removal of sulfate radicals. This method is simple to operate, easy to maintain, has low operating costs, and has good treatment effects.

[0003] The nanofiltration membrane device is arranged in multiple sections in series, with a high-pressure pump and a concentrated liquid reflux method. The specific process includes the following: the brine containing sodium sulfate (5-8g / L) is cooled and then enters the nanofiltration membrane for separation, and the brine with high sodium sulfate content (50-100g / L) and low sodium sulfate content (1-2g / L) are obtained respectively. The brine with low sodium sulfate content enters the electrolysis system (i.e. Figure 1 During the "desalting" process, brine with a high sodium sulfate concentration is cooled to -3-10°C and crystallized to produce sodium sulfate decahydrate crystals. These crystals are then separated by centrifuge to yield sodium sulfate decahydrate crystals and low-temperature brine. The sodium sulfate decahydrate crystals contain only 44% anhydrous sodium sulfate by weight, while the water of crystallization is 56%. This significantly increases transportation costs, significantly limiting their use. Currently, most sodium sulfate decahydrate crystals produced by caustic soda plants become solid waste, polluting the environment and costing nearly 10 million yuan annually to dispose of. However, producing anhydrous sodium sulfate as a product would yield significant benefits. Since sodium sulfate decahydrate crystals become liquid at temperatures above 33°C, drying them to produce anhydrous sodium sulfate requires significant equipment investment, requiring both evaporation equipment and other drying equipment. The energy consumption alone exceeds the product's selling price. Consequently, sodium sulfate decahydrate has become a significant burden for caustic soda manufacturers, and there is an urgent need for industrial technologies that can produce anhydrous sodium sulfate using low-energy sodium sulfate decahydrate disposal. Summary of the Invention

[0004] In order to solve the problems of high energy consumption and complex process in the prior art method for preparing anhydrous sodium sulfate, the present invention provides a method for producing anhydrous sodium sulfate based on cold-heat coupling technology.

[0005] The method of the present invention adopts a hot melt method to produce anhydrous sodium sulfate, recovers the heat of the light brine, saves the energy required for cooling the light brine in the traditional process, effectively utilizes the heat of the light brine to hot-melt sodium sulfate decahydrate crystals, produces anhydrous sodium sulfate, and greatly reduces the production. The present invention utilizes the original caustic soda production equipment, and the new equipment is very little, so the equipment investment is very small. The production of anhydrous sodium sulfate using the method of the present invention has no impact on the operation of the original process equipment, saves the cooling energy consumption required for cooling the light brine, and converts the solid waste originally generated into a valuable anhydrous sodium sulfate product, which not only reduces environmental pollution but also has good economic benefits.

[0006] The present invention provides a method for producing anhydrous sodium sulfate based on a cold-heat coupling technology. The device used in the method comprises a hot melt precipitation kettle 1, a first centrifuge 2, a hot melt kettle 3, a sodium sulfate decahydrate solution pump 4, a nanofiltration membrane system 5, a freezing crystallization kettle 6, a second centrifuge 7, a brine storage tank 8, a brine pump 9 and a heat exchanger 10. A stirrer is provided in the hot melt precipitation kettle 1, the hot melt kettle 3 and the freezing crystallization kettle 6. The hot melt precipitation kettle 1, the hot melt kettle 3, the freezing crystallization kettle 6 and the heat exchanger 10 are all partition-type heat exchangers. A nanofiltration membrane is provided in the nanofiltration membrane system 5, and the nanofiltration membrane model is GEDuraslick.

[0007] The method for producing anhydrous sodium sulfate based on a cold-heat coupling technology of the present invention comprises the following steps:

[0008] S1: Operation of the sulfate removal system: Before the start-up of the desulfation process, the brine with a sulfate content of 5-8 g / L and a temperature of 75-85°C in the electrolytic brine system of the caustic soda production process is stored in the brine storage tank 8. When the liquid level exceeds 30% of the brine storage tank capacity, the brine pump 9 is started to control the brine flow rate to 40-60 m 3 / h. During the initial start-up, the brine is cooled by circulating cooling water introduced through the partition wall of the heat exchanger 10. The inlet temperature of the circulating cooling water is 20-30°C. The temperature of the brine after being cooled by the circulating water partition wall is less than 40°C. The cooled brine passes through the hot melt precipitation kettle 1 and the jacket of the hot melt kettle 3 and enters the nanofiltration membrane system 5. Under the separation effect of the nanofiltration membrane in the nanofiltration membrane system 5, high-concentration sodium sulfate brine and low-concentration sodium sulfate brine are obtained. The high-concentration sodium sulfate brine enters the freezing crystallization kettle 6, and the low-concentration sodium sulfate brine is transported to the desalination system; the high-concentration sodium sulfate brine enters the freezing crystallization kettle 6, and the low-concentration sodium sulfate brine is transported to the desalination system; The sodium sulfate brine is cooled by passing chilled brine (temperature -10 to -5°C) through the partition wall of the crystallization kettle 6 to obtain a low-temperature brine containing sodium sulfate decahydrate crystals at a temperature of -3 to 10°C. The low-temperature brine containing sodium sulfate decahydrate crystals enters the second centrifuge 7 for centrifugal separation to obtain sodium sulfate decahydrate crystals and low-temperature brine. After the sodium sulfate decahydrate crystals are obtained in the second centrifuge 7, the circulating cooling water is stopped from entering the partition wall of the heat exchanger 10, and the 75-85°C light brine from the light brine storage tank 8 enters the partition wall of the hot melt precipitation kettle 1.

[0009] S2: Sodium sulfate decahydrate hot melt treatment: Sodium sulfate decahydrate crystals separated by the second centrifuge 7 in step S1 are continuously added to a 10-20m3 container at a rate of 0.5-1 t / h. 3 In the hot melt kettle 3, the heat is exchanged with the brine (containing 190-210 g / L of sodium chloride and 5-8 g / L of sodium sulfate) from the partition wall of the hot melt precipitation kettle 1, and the brine flow rate is 40-60 m 3 / h, the inlet temperature of the brine in the hot melt kettle 3 is 70-75°C, and the outlet temperature of the brine in the hot melt kettle 3 is 40-50°C, thereby controlling the temperature of the hot melt kettle 3 to 35-40°C; the stirring in the hot melt kettle 3 is turned on, and the sodium sulfate decahydrate crystals are melted into a sodium sulfate decahydrate solution after heat exchange with the brine wall in the hot melt kettle 3;

[0010] S3: Hot melt precipitation to produce anhydrous sodium sulfate: The sodium sulfate decahydrate solution obtained in the hot melt kettle 3 in step S2 is continuously added to the hot melt precipitation kettle 1 at a rate of 0.5 to 1 t / h using the sodium sulfate decahydrate solution pump 4, and the brine from the brine storage tank 8 is used for inter-wall heat exchange. The brine flow rate is 40 to 60 m 3 / h, the inlet temperature of the brine of the hot melt precipitation kettle 1 is 75-85°C, and the outlet temperature of the brine of the hot melt precipitation kettle 1 is 70-75°C, thereby controlling the temperature of the hot melt precipitation kettle 1 to 70-75°C; starting the stirring in the hot melt precipitation kettle 1, the sodium sulfate decahydrate liquid generates anhydrous sodium sulfate precipitate under the action of stirring, and obtaining a solution containing the anhydrous sodium sulfate precipitate;

[0011] S4: Separation of anhydrous sodium sulfate: The solution containing anhydrous sodium sulfate precipitate obtained in step S3 is transported to the first centrifuge 2 for solid-liquid separation to obtain anhydrous sodium sulfate product and brine containing 25-35% by mass of sodium sulfate; the first centrifuge 2 is a continuous filtering centrifuge with a separation factor Fr = 500-1000 and a processing flow rate of 2-2.5 t / h;

[0012] S5: Membrane separation treatment: The low-temperature brine (temperature -3 to 10°C) separated by the second centrifuge 7 is mixed with the brine from the brine outlet of the hot melt kettle 3 to obtain a first mixed brine which enters the nanofiltration membrane system 5. Under the separation effect of the nanofiltration membrane in the nanofiltration membrane system 5, a high-concentration sodium sulfate brine and a low-concentration sodium sulfate brine are obtained; the high-concentration sodium sulfate brine is then mixed with the brine containing 25 to 35% sodium sulfate by mass from the first centrifuge 2 to obtain a second mixed brine which enters the freezing crystallization kettle 6; the low-concentration sodium sulfate brine is transported to the deionized water tank 6. The salt system is then added to the low-concentration sodium sulfate brine with raw salt particles. The raw salt dissolves to form brine, and the sulfate ions in the raw salt enter the brine. The brine is precipitated to remove sediment, and sodium carbonate is added to remove calcium and magnesium ions. After fine filtration, the refined brine is formed and enters the ion membrane for electrolysis. The sulfate content generated after electrolysis is 5-8g / L and the temperature is 75-85°C. The brine is stored in the brine storage tank 8; the temperature of the first mixed brine entering the nanofiltration membrane system 5 is 30-35°C, and the flow rate is 40-60m 3 / h, the pressure is 0.1~3MPa; the sodium sulfate content in the high-concentration sodium sulfate brine obtained is 50~110g / L, and the flow rate is 4~10m 3 / h; the sodium sulfate content in the obtained low-concentration sodium sulfate brine is 1-2 g / L, and the flow rate is 35-55 m 3 / h;

[0013] S6: Freezing to produce sodium sulfate decahydrate crystals: Chilled brine (temperature -10 to -5°C) is introduced into the freezing crystallization kettle 6 of step S5 to perform inter-wall heat exchange on the second mixed brine from the nanofiltration membrane system 5 to obtain low-temperature brine (temperature of -3 to 10°C) containing sodium sulfate decahydrate crystals; the low-temperature brine containing sodium sulfate decahydrate crystals enters the second centrifuge 7 to separate the sodium sulfate decahydrate crystals and the low-temperature brine; the sodium sulfate decahydrate crystals re-enter the hot melt kettle 3 to perform the cycle of steps S2 to S6 to continuously produce anhydrous sodium sulfate products; the sodium sulfate content in the second mixed brine is 60 to 130 g / L, and the flow rate is 5 to 15 m 3 / h temperature of 35-40 ° C (the second mixed brine entering the frozen crystallization kettle 6 is composed of two parts, one part is the high-concentration sodium sulfate brine from the nanofiltration membrane, with a sodium sulfate content of 50-110 g / L, and the other part is the brine with a sodium sulfate mass fraction of 25-35% from the first centrifuge; the brine flow rate of the first centrifuge is 0.8-1.2m 3 / h, the high concentration sodium sulfate brine flow rate of the nanofiltration membrane is 5~14m 3 / h, the sodium sulfate content is increased to 60-130g / L after the two are mixed); the output of sodium sulfate decahydrate crystals is 0.5-1t / h, the temperature of the low-temperature brine is -3-10℃, and the flow rate is 4-12m 3 / h; the second centrifuge 7 is a continuous filtering centrifuge with a separation factor of Fr = 500 to 1000 and a processing flow rate of 2 to 2.5 t / h.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The method of the present invention utilizes a hot melt method to melt sodium sulfate decahydrate to obtain anhydrous sodium sulfate precipitate, and does not utilize steam evaporation crystallization, thereby saving a large amount of energy and reducing equipment investment;

[0016] (2) The present invention recovers the heat of the brine and uses it to melt sodium sulfate decahydrate, thereby saving energy consumption for cooling the brine;

[0017] (3) The method of the present invention solves the problem that the nanofiltration membrane method can only produce sodium sulfate decahydrate, solves the problem of large amounts of hazardous waste sodium sulfate decahydrate generated in the production process of caustic soda enterprises, reduces environmental pollution, produces anhydrous sodium sulfate, and creates good economic benefits;

[0018] (4) The system of the present invention is simple and only requires simple modification of existing equipment of caustic soda enterprises to produce anhydrous sodium sulfate products. The process flow is simple and does not affect the original caustic soda production process. Energy consumption is reduced and equipment investment is very low. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : Process flow chart for producing anhydrous sodium sulfate using the hot-cold coupling technology of the present invention after the desulfation process is started;

[0020] The names of the components in the figure are: hot melt precipitation kettle 1, first centrifuge 2, hot melt kettle 3, sodium sulfate decahydrate solution pump 4, nanofiltration membrane system 5, frozen crystallization kettle 6, second centrifuge 7, brine storage tank 8, brine pump 9, heat exchanger 10. Agitators are installed in the hot melt precipitation kettle 1, hot melt kettle 3, and frozen crystallization kettle 6. The hot melt precipitation kettle 1, hot melt kettle 3, frozen crystallization kettle 6, and heat exchanger 10 are all partition-type heat exchangers. A nanofiltration membrane is installed in the nanofiltration membrane system 5. The nanofiltration membrane model is GEDuraslick; type: energy-saving; effective area: 37.2m 2 Desalination rate: 97%; maximum operating pressure: 4.14Mpa. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0022] Example 1:

[0023] A method for producing anhydrous sodium sulfate based on hot-cold coupling technology, the steps of which are as follows:

[0024] S1: Operation of sulfate removal system: Before starting work, in the electrolytic brine system of caustic soda production process, the brine with sulfate content of 6g / L and temperature of 80℃ is stored in the brine storage tank 8. When the liquid level exceeds 30% of the brine storage tank capacity, the brine pump 9 is started to control the brine flow rate to 50m 3 / h. During the initial start-up, the brine is cooled by circulating cooling water introduced through the partition wall of the heat exchanger 10. The inlet temperature of the circulating cooling water is 25°C. The temperature of the brine after being cooled by the circulating water partition wall is less than 40°C. The cooled brine passes through the hot melt precipitation kettle 1 and the jacket of the hot melt kettle 3 and enters the nanofiltration membrane system 5. Under the separation effect of the nanofiltration membrane in the nanofiltration membrane system 5, high-concentration sodium sulfate brine and low-concentration sodium sulfate brine are obtained. The high-concentration sodium sulfate brine enters the freezing crystallization kettle 6, and the low-concentration sodium sulfate brine is transported to the desalination system. The high-concentration sodium sulfate brine is cooled by passing chilled brine (temperature -10°C) through the partition wall of the crystallization kettle 6 to obtain a low-temperature brine containing sodium sulfate decahydrate crystals at a temperature of 0°C. The low-temperature brine containing sodium sulfate decahydrate crystals enters the second centrifuge 7 for centrifugal separation to obtain sodium sulfate decahydrate crystals and low-temperature brine. After the sodium sulfate decahydrate crystals are obtained in the second centrifuge 7, the circulating cooling water is stopped from entering the partition wall of the heat exchanger 10, and the 80°C light brine from the light brine storage tank 8 enters the partition wall of the hot melt precipitation kettle 1.

[0025] S2: Sodium sulfate decahydrate hot melt treatment: Sodium sulfate decahydrate crystals separated by the second centrifuge 7 in step S1 are continuously added to a 15m3 jar at a rate of 0.8 t / h. 3 In the hot melt kettle 3, the heat exchange is carried out by using the brine (containing 200g / L of sodium chloride and 6g / L of sodium sulfate) from the wall of the hot melt precipitation kettle 1 passed through the wall of the hot melt kettle 3. The brine flow rate is 50m 3 / h, the inlet temperature of the brine in the hot melt kettle 3 is 70°C, and the outlet temperature of the brine in the hot melt kettle 3 is 40°C, thereby controlling the temperature of the hot melt kettle 3 to 35°C; the stirring in the hot melt kettle 3 is turned on, and the sodium sulfate decahydrate crystals in the hot melt kettle 3 exchange heat with the brine partition wall and melt to form a sodium sulfate decahydrate solution;

[0026] S3: Hot melt precipitation to produce anhydrous sodium sulfate: The sodium sulfate decahydrate solution obtained in the hot melt kettle 3 in step S2 is continuously added to the hot melt precipitation kettle 1 at a rate of 0.8 t / h using the sodium sulfate decahydrate solution pump 4, and the brine from the brine storage tank 8 is used for inter-wall heat exchange. The brine flow rate is 50m 3 / h, the inlet temperature of the brine of the hot melt precipitation kettle 1 is 80°C, and the outlet temperature of the brine of the hot melt precipitation kettle 1 is 70°C, thereby controlling the temperature of the hot melt precipitation kettle 1 to 72°C; starting the stirring in the hot melt precipitation kettle 1, the sodium sulfate decahydrate liquid generates anhydrous sodium sulfate precipitate under the action of stirring, and obtaining a solution containing the anhydrous sodium sulfate precipitate;

[0027] S4: Separation of anhydrous sodium sulfate: The solution containing anhydrous sodium sulfate precipitate obtained in step S3 is transported to the first centrifuge 2 for solid-liquid separation to obtain anhydrous sodium sulfate product and brine containing 30% by mass of sodium sulfate; the first centrifuge 2 is a continuous filtering centrifuge with a separation factor Fr = 800 and a processing flow rate of 2 t / h;

[0028] S5: membrane separation treatment: the low-temperature brine (temperature 0°C) separated by the second centrifuge 7 is mixed with the brine from the brine outlet of the hot melt kettle 3 to obtain a first mixed brine which enters the nanofiltration membrane system 5. Under the separation effect of the nanofiltration membrane in the nanofiltration membrane system 5, a high-concentration sodium sulfate brine and a low-concentration sodium sulfate brine are obtained; the high-concentration sodium sulfate brine is then mixed with the brine containing 30% sodium sulfate by mass from the first centrifuge 2 to obtain a second mixed brine which enters the freezing crystallization kettle 6; the low-concentration sodium sulfate brine is transported to the desalting system, and then raw salt particles are added to the low-concentration sodium sulfate brine. The raw salt is dissolved to form brine, and the sulfate ions in the raw salt enter the brine. The brine is precipitated to remove sediment, and sodium carbonate is added to remove calcium and magnesium ions. After fine filtration, the refined brine is formed and enters the ion membrane for electrolysis. The brine with a sulfate content of 6g / L and a temperature of 80°C produced after electrolysis is stored in the brine storage tank 8; the temperature of the first mixed brine entering the nanofiltration membrane system 5 is 30°C and the flow rate is 50m 3 / h, the pressure is 0.2MPa; the sodium sulfate content in the high-concentration sodium sulfate brine obtained is 75g / L, and the flow rate is 10m 3 / h; the sodium sulfate content in the obtained low-concentration sodium sulfate brine is 1.5g / L, and the flow rate is 40m 3 / h;

[0029] S6: Freezing to produce sodium sulfate decahydrate crystals: Refrigerated brine (temperature -10°C) is introduced into the freezing crystallization kettle 6 of step S5 to perform inter-wall heat exchange on the second mixed brine from the nanofiltration membrane system 5 to obtain low-temperature brine (temperature 0°C) containing sodium sulfate decahydrate crystals; the low-temperature brine containing sodium sulfate decahydrate crystals enters the second centrifuge 7 to separate the sodium sulfate decahydrate crystals and the low-temperature brine; the sodium sulfate decahydrate crystals re-enter the hot melt kettle 3 to carry out the cycle of steps S2 to S6 to continuously produce anhydrous sodium sulfate products; the sodium sulfate content in the second mixed brine is 90g / L, and the flow rate is 10m 3 / h, temperature 35 ℃ (the second mixed brine entering the frozen crystallization kettle 6 is composed of two parts, one part is the high-concentration sodium sulfate brine from the nanofiltration membrane, with a sodium sulfate content of 75g / L, and the other part is the brine with a sodium sulfate mass fraction of 30% from the first centrifuge; the brine flow rate of the first centrifuge is 1.0m 3 / h, the high concentration sodium sulfate brine flow rate of the nanofiltration membrane is 10m 3 / h, the sodium sulfate content is increased to 90g / L after the two are mixed); the output of sodium sulfate decahydrate crystals is 0.8t / h, the temperature of the low-temperature brine is 0℃, and the flow rate is 8m 3 / h; the second centrifuge 7 is a continuous filtering centrifuge, the centrifuge separation factor Fr = 800, the processing flow rate is 2t / h, and the annual output of anhydrous sodium sulfate products can be more than 600,000 tons.

Claims

1. A method for producing anhydrous sodium sulfate based on hot-cold coupling technology, characterized in that: The device used in the method comprises a hot melt precipitation kettle (1), a first centrifuge (2), a hot melt kettle (3), a sodium sulfate decahydrate solution pump (4), a nanofiltration membrane system (5), a freezing crystallization kettle (6), a second centrifuge (7), a salt water storage tank (8), a salt water pump (9) and a heat exchanger (10); a stirrer is provided in the hot melt precipitation kettle (1), the hot melt kettle (3) and the freezing crystallization kettle (6); the hot melt precipitation kettle (1), the hot melt kettle (3), the freezing crystallization kettle (6) and the heat exchanger (10) are all partition-type heat exchangers; a nanofiltration membrane is provided in the nanofiltration membrane system (5); the steps of the method are as follows: S1: Operation of the sulfate removal system: Before the desulfation process is started, the brine with a sulfate content of 5 to 8 g / L and a temperature of 75 to 85°C in the electrolytic brine system of the caustic soda production process is stored in the brine storage tank (8). When the liquid level exceeds 30% of the brine storage tank capacity, the brine pump (9) is started to control the brine flow rate to 40 to 60 m3. 3 / h, during the initial start-up, the brine is cooled by circulating cooling water introduced through the partition wall of the heat exchanger (10), the inlet temperature of the circulating cooling water is 20-30°C, and the temperature of the brine after being cooled by the circulating water partition wall is less than 40°C. The cooled brine passes through the hot melt precipitation kettle (1) and the hot melt kettle (3) jacket and enters the nanofiltration membrane system (5). Under the separation effect of the nanofiltration membrane in the nanofiltration membrane system (5), high-concentration sodium sulfate brine and low-concentration sodium sulfate brine are obtained. The high-concentration sodium sulfate brine enters the freezing crystallization kettle (6), and the low-concentration sodium sulfate brine is transported to the desalination system; the high-concentration sodium sulfate brine enters the freezing crystallization kettle (6), and the low-concentration sodium sulfate brine is transported to the desalination system; The sodium sulfate brine is cooled by passing a refrigerated brine having a temperature of -10 to -5°C through the partition wall of the crystallization kettle (6) to obtain a low-temperature brine having a temperature of -3 to 10°C containing sodium sulfate decahydrate crystals; the low-temperature brine containing sodium sulfate decahydrate crystals enters a second centrifuge (7) for centrifugal separation to obtain sodium sulfate decahydrate crystals and low-temperature brine; after sodium sulfate decahydrate crystals are obtained in the second centrifuge (7), the circulating cooling water is stopped from being passed into the partition wall of the heat exchanger (10), and the 75 to 85°C light brine from the light brine storage tank (8) is directly passed into the partition wall of the hot melt precipitation kettle (1); S2: Sodium sulfate decahydrate hot melt treatment: The sodium sulfate decahydrate crystals separated by the second centrifuge (7) in step S1 are continuously added to a 10-20m3 container at a rate of 0.5-1 t / h. 3 In the hot melt kettle (3), the temperature of the hot melt kettle (3) is controlled to be 35-40° C. by using the light brine from the partition wall of the hot melt precipitation kettle (1) introduced into the partition wall of the hot melt kettle (3); stirring in the hot melt kettle (3) is turned on, and the sodium sulfate decahydrate crystals are melted into a sodium sulfate decahydrate solution after heat exchange with the light brine partition wall in the hot melt kettle (3); S3: Production of anhydrous sodium sulfate by hot melt precipitation: The sodium sulfate decahydrate solution obtained in the hot melt kettle (3) in step S2 is continuously added to the hot melt precipitation kettle (1) at a rate of 0.5 to 1 t / h using a sodium sulfate decahydrate solution pump (4), and the temperature of the hot melt precipitation kettle (1) is controlled to 70 to 75° C. by using the brine from the brine storage tank (8) for inter-wall heat exchange; the stirring in the hot melt precipitation kettle (1) is turned on, and the sodium sulfate decahydrate liquid generates anhydrous sodium sulfate precipitate under the action of stirring, thereby obtaining a solution containing the anhydrous sodium sulfate precipitate; S4: Separation of anhydrous sodium sulfate: The solution containing anhydrous sodium sulfate precipitate obtained in step S3 is transported to a first centrifuge (2) for solid-liquid separation to obtain anhydrous sodium sulfate product and brine containing 25-35% by mass of sodium sulfate; S5: membrane separation treatment: the low-temperature brine separated by the second centrifuge (7) with a temperature of -3 to 10°C is mixed with the brine from the brine outlet of the hot melt kettle (3) to obtain a first mixed brine, which enters the nanofiltration membrane system (5). Under the separation effect of the nanofiltration membrane in the nanofiltration membrane system (5), a high-concentration sodium sulfate brine and a low-concentration sodium sulfate brine are obtained; the high-concentration sodium sulfate brine is then mixed with the brine containing 25 to 35% sodium sulfate by mass from the first centrifuge (2) to obtain a second mixed brine, which enters the freezing crystallization kettle (6); the low-concentration sodium sulfate brine is transported to the desalination system; S6: Freezing to produce sodium sulfate decahydrate crystals: A frozen brine with a temperature of -10 to -5°C is introduced into the frozen crystallization kettle (6) of step S5 to perform inter-wall heat exchange on the second mixed brine from the nanofiltration membrane system (5), thereby obtaining a low-temperature brine containing sodium sulfate decahydrate crystals with a temperature of -3 to 10°C; the low-temperature brine containing sodium sulfate decahydrate crystals enters a second centrifuge (7) to separate the sodium sulfate decahydrate crystals and the low-temperature brine; the sodium sulfate decahydrate crystals re-enter the hot melt kettle (3) to cycle through steps S2 to S6, thereby continuously producing anhydrous sodium sulfate products.

2. The method for producing anhydrous sodium sulfate based on hot-cold coupling technology according to claim 1, wherein: The first centrifuge (2) is a continuous filtering centrifuge with a separation factor Fr of 500-1000 and a processing flow rate of 2-2.5 t / h. The second centrifuge (7) is a continuous filtering centrifuge with a separation factor Fr of 500-1000 and a processing flow rate of 2-2.5 t / h.

3. The method for producing anhydrous sodium sulfate based on hot-cold coupling technology according to claim 1, wherein: In step S2, the salt water contains 190-210 g / L of sodium chloride and 5-8 g / L of sodium sulfate, and the flow rate of the salt water is 40-60 m 3 / h, the inlet temperature of the hot melt kettle (3) is 70-75°C, and the outlet temperature of the hot melt kettle (3) is 40-50°C.

4. The method for producing anhydrous sodium sulfate based on hot-cold coupling technology according to claim 1, wherein: In step S3, the flow rate of the light salt water is 40-60m 3 / h, the inlet temperature of the hot melt precipitation kettle (1) is 75-85°C, and the outlet temperature of the hot melt precipitation kettle (1) is 70-75°C.

5. The method for producing anhydrous sodium sulfate based on hot-cold coupling technology according to claim 1, wherein: In step S5, the low-concentration sodium sulfate brine is transported to the desalting system, and then raw salt particles are added to the low-concentration sodium sulfate brine. The raw salt dissolves to form brine, and sulfate ions in the raw salt enter the brine. The brine is precipitated to remove sediment, and sodium carbonate is added to remove calcium and magnesium ions. After fine filtration, refined brine is formed and enters the ion membrane for electrolysis. The brine produced after electrolysis has a sulfate content of 5 to 8 g / L and a temperature of 75 to 85° C. and is stored in a brine storage tank (8).

6. The method for producing anhydrous sodium sulfate based on cold-heat coupling technology according to claim 1, characterized in that: In step S5, the temperature of the first mixed brine entering the nanofiltration membrane system (5) is 30-35°C, and the flow rate is 40-60m 3 / h, the pressure is 0.1~3MPa; the sodium sulfate content in the high-concentration sodium sulfate brine obtained is 50~110g / L, and the flow rate is 4~10m 3 / h; the sodium sulfate content in the obtained low-concentration sodium sulfate brine is 1-2 g / L, and the flow rate is 35-55 m 3 / h.

7. The method for producing anhydrous sodium sulfate based on cold-heat coupling technology according to claim 1, characterized in that: In step S6, the sodium sulfate content in the second mixed brine is 60-130 g / L, and the flow rate is 5-15 m 3 / h temperature is 35~40℃; the output of sodium sulfate decahydrate crystal is 0.5~1t / h, the temperature of low-temperature brine is -3~10℃, the flow rate is 4~12m 3 / h.

8. The method for producing anhydrous sodium sulfate based on hot-cold coupling technology according to claim 1, wherein: The nanofiltration membrane model is GEDuraslick.

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