Preparation method of potassium sulfate

Abstract

The invention discloses a potassium sulfate preparation method, and relates to the field of potassium sulfate preparation. Comprising the following steps: raw material preparation and pretreatment: preparing sodium sulfate, potassium chloride and process water; converting, mixing sodium sulfate, potassium chloride and process water for reaction, centrifugally separating and drying after reaction to obtain a solid finished product, packaging and warehousing; salt evaporation: carrying out centrifugal separation on the converted and separated clear liquid, then evaporating to prepare salt, drying after evaporation to obtain a byproduct, packaging and warehousing. The potassium sulfate product is prepared through a two-step conversion method and a single-group or multi-group parallel MVR evaporation technology, the byproduct sodium chloride, the potassium conversion rate and the potassium oxide content of the potassium sulfate are high, the product potassium sulfate can be directly used as a drip irrigation fertilizer, meanwhile, hazardous chemical raw materials and products are not generated, hazardous chemical gas and hazardous chemical solid waste are not generated in the production process, and the method is suitable for industrial production. The method has the advantages of safety, environmental protection, energy conservation and no emission of three wastes.

Description

Technical Field

[0001] This invention relates to the field of potassium sulfate preparation, and more particularly to a method for preparing potassium sulfate. Background Technology

[0002] Currently, the main methods for preparing potassium sulfate in China are: firstly, potassium chloride is converted into potassium sulfate at high temperature using a Mannheim furnace; secondly, potassium sulfate is prepared by the metathesis method of ammonium sulfate and potassium chloride.

[0003] The potassium yield is low in the ammonium sulfate and potassium chloride metathesis method. The potassium oxide content of the product potassium sulfate can only reach about 48%, and it contains 2-3 nitrogen atoms. The by-product ammonium chloride contains potassium.

[0004] The Mannheim process is an old method for producing sulfates, pioneered in Germany at the end of the 19th century. Currently, the Mannheim process is one of the most important methods for producing potassium sulfate in my country. The main raw materials are potassium chloride and sulfuric acid. These two raw materials are mixed and reacted in a Mannheim furnace to produce potassium bisulfate. The potassium bisulfate is then heated at high temperature and reacts further with potassium chloride to finally produce potassium sulfate. The key technology of this process is the reactor (i.e., the Mannheim furnace), which affects product purity, conversion rate, production capacity, and ease of operation. Currently, the largest Mannheim furnace has a diameter of Φ6m and a capacity of 10,000 tons / year. While the Mannheim process is technologically mature, with high potassium yield and stable product quality, the materials used in the preparation process are highly corrosive, resulting in low production capacity per unit, high consumption, high maintenance workload, and high investment costs. Furthermore, the sales of the byproduct hydrochloric acid are a key challenge restricting its production.

[0005] Therefore, this invention proposes a method for preparing potassium sulfate. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing potassium sulfate.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing potassium sulfate, comprising: S1: Raw material preparation and pretreatment, including preparation of sodium sulfate, potassium chloride and process water; S2: Secondary conversion, sodium sulfate, potassium chloride and process water are mixed and reacted. After the primary conversion reaction, the potassium sulfate solid product is obtained by centrifugation. The overflow liquid from the evaporation of potassium sulfate and salt is hydrolyzed. The aqueous solution and potassium chloride enter the secondary conversion. After the secondary conversion reaction, the potassium sulfate solid product is obtained by centrifugation and drying. It is then packaged and stored. S3: Salt evaporation. The clear liquid separated by conversion is filtered, and then salt is produced by evaporation using MVR. After evaporation, the product sodium chloride is obtained by centrifugation and drying, and then packaged and stored.

[0008] Preferably, step S1 includes the following steps: S11: After the raw material sodium sulfate enters the stockpile, it is transported to the sodium sulfate silo by a loader. The feeder continuously feeds the material through the conveyor to the sodium sulfate metering silo, and after being measured by an electronic scale, it enters the chemical tank. S12: After passing through the automatic bag-breaking machine, potassium chloride is poured into the potassium chloride silo, then weighed by a metering scale, and the weighed potassium chloride is lifted by a bucket elevator into the chemical tank.

[0009] Preferably, step S2 includes a primary conversion process and a secondary conversion process; The chemical principle of the primary conversion process is as follows: ; The chemical principle of the secondary conversion process is as follows: .

[0010] Preferably, the primary conversion process includes the following steps: A1: The solution in the chemical tank and the metered mixture enter the No. 1 primary conversion reaction tank and react continuously with stirring; A2: Pumped to the No. 2 primary conversion reactor, the clear liquid at the top of the No. 2 primary conversion reactor overflows to the No. 3 primary conversion reactor, and the thick material at the bottom of the reactor is pumped to the thickener. A3: After settling, the upper clear liquid in the No. 3 primary conversion reactor overflows into the clear liquid transfer tank; the thick material at the bottom of the tank is sent to the thickener and together with the thick material in the No. 2 primary conversion reactor, it is centrifuged and separated to obtain potassium sodium sulfate. A4: Potassium sulfate is metered and transported into the secondary conversion process. The centrifugal mother liquor and the thickener overflow mother liquor are returned to the No. 2 reaction tank of the primary conversion for recycling.

[0011] Preferably, the secondary conversion process includes the following steps: B1: The potassium sulfate solid, potassium chloride, and salt evaporation liquid separated by centrifugation in the primary conversion process are metered and fed into the No. 1 reaction tank of the secondary conversion, where they are continuously reacted by stirring. B2: Pumped to the No. 2 secondary conversion reactor, the clear liquid at the top of the reaction in the No. 2 secondary conversion reactor overflows to the No. 3 secondary conversion reactor, and the thick material at the bottom of the reactor is sent to the thickener; B3: After settling, the upper clear liquid in the No. 3 reaction tank of the secondary conversion overflows into the potassium mother liquor tank and is pumped to the mixing tank, where it enters the mixing tank together with the clear liquid evaporated from the primary conversion process; the thick material at the bottom of the tank is sent to the thickener and, together with the thick material in the No. 2 reaction tank of the secondary conversion, is separated into solid and liquid by a centrifuge. The centrifugal mother liquor and the mother liquor overflowing from the thickener are returned to the No. 2 reaction tank of the secondary conversion for recycling. B4: The separated solids are conveyed to the fluidized bed by a shaftless screw conveyor. After drying and cooling, the material is sent to the silo and then automatically packaged, stacked and stored.

[0012] Preferably, step S3 includes the following steps: C1: The clear liquid separated in the first conversion process is filtered and enters the clear liquid storage tank. The clear liquid is pumped from the clear liquid storage tank to the heat exchanger to exchange heat with the condensate and then enters the MVR evaporation system for evaporation and salt production. C2: After the clear liquid is evaporated in the evaporator, the salt slurry is collected in the salt collector of the evaporation system and then pumped to the thickener by the salt slurry pump. C3: After separation by centrifuge, the centrifuged mother liquor is returned to the evaporator for recycling and evaporation; C4: After being dried in a rotary drum, it enters the finished product silo and is then transferred to the packaging system.

[0013] Preferably, in steps S2 and S3, the drying heat source is natural gas, which is directly ignited by a burner and then enters the rotary drum for drying. The dust removal system of the dryer first uses cyclone dust removal and then bag filter dust removal.

[0014] Preferably, in step S2, the conversion temperature is 32-38 degrees Celsius, and in step S3, the crystallization temperature during evaporation salt production is 95-110 degrees Celsius.

[0015] Preferably, in step S3, the evaporation employs one or more MVRs connected in parallel.

[0016] Preferably, in step S3, evaporation is carried out using multiple sets of parallel MVR evaporators, and multiple sets of MVRs share a single steam compressor.

[0017] The beneficial effects of this invention are as follows: This invention produces potassium sulfate by means of a two-step conversion method and single or multiple parallel MVR evaporation technology, with sodium chloride as a byproduct. The potassium conversion rate and potassium oxide content of potassium sulfate are high. The potassium sulfate product can be directly used as drip irrigation fertilizer. At the same time, this invention has no hazardous raw materials or products, no hazardous gases are generated in the production process, and no hazardous solid waste is generated. It has the advantages of safety, environmental protection, energy saving and no emission of waste gas, wastewater, and solid waste. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of a potassium sulfate preparation method proposed in this invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] Example 1: A method for preparing potassium sulfate, comprising: S1: Raw material preparation and pretreatment, including preparation of sodium sulfate, potassium chloride and process water; S2: Secondary conversion, sodium sulfate, potassium chloride and process water are mixed and reacted. After the primary conversion reaction, the potassium sulfate solid product is obtained by centrifugation. The overflow liquid from the evaporation of potassium sulfate and salt is hydrolyzed. The aqueous solution and potassium chloride enter the secondary conversion. After the secondary conversion reaction, the potassium sulfate solid product is obtained by centrifugation and drying. It is then packaged and stored. S3: Salt evaporation. The clear liquid separated by conversion is filtered, and then salt is produced by evaporation using MVR. After evaporation, the product sodium chloride is obtained by centrifugation and drying, and then packaged and stored.

[0022] Step S1 includes the following steps: S11: After the raw material sodium sulfate enters the stockpile, it is transported to the sodium sulfate silo by a loader. The feeder continuously feeds the material through the conveyor to the sodium sulfate metering silo, and after being measured by an electronic scale, it enters the chemical tank. S12: After passing through the automatic bag-breaking machine, potassium chloride is poured into the potassium chloride silo, then weighed by a metering scale, and the weighed potassium chloride is lifted by a bucket elevator into the chemical tank.

[0023] Example 2: A method for preparing potassium sulfate, comprising: S1: Raw material preparation and pretreatment, including preparation of sodium sulfate, potassium chloride and process water; S2: Secondary conversion, sodium sulfate, potassium chloride and process water are mixed and reacted. After the primary conversion reaction, the potassium sulfate solid product is obtained by centrifugation. The overflow liquid from the evaporation of potassium sulfate and salt is hydrolyzed. The aqueous solution and potassium chloride enter the secondary conversion. After the secondary conversion reaction, the potassium sulfate solid product is obtained by centrifugation and drying. It is then packaged and stored. S3: Salt evaporation. The clear liquid separated by conversion is filtered, and then salt is produced by evaporation using MVR. After evaporation, the product sodium chloride is obtained by centrifugation and drying, and then packaged and stored.

[0024] Step S1 includes the following steps: S11: After the raw material sodium sulfate enters the stockpile, it is transported to the sodium sulfate silo by a loader. The feeder continuously feeds the material through the conveyor to the sodium sulfate metering silo, and after being measured by an electronic scale, it enters the chemical tank. S12: After passing through the automatic bag-breaking machine, potassium chloride is poured into the potassium chloride silo, then weighed by a metering scale, and the weighed potassium chloride is lifted by a bucket elevator into the chemical tank.

[0025] The S2 step includes a primary conversion process and a secondary conversion process. The chemical principle of the primary conversion process is as follows: ; The chemical principle of the secondary conversion process is as follows: .

[0026] Example 3: A method for preparing potassium sulfate, comprising: S1: Raw material preparation and pretreatment, including preparation of sodium sulfate, potassium chloride and process water; S2: Secondary conversion, sodium sulfate, potassium chloride and process water are mixed and reacted. After the primary conversion reaction, the potassium sulfate solid product is obtained by centrifugation. The overflow liquid from the evaporation of potassium sulfate and salt is hydrolyzed. The aqueous solution and potassium chloride enter the secondary conversion. After the secondary conversion reaction, the potassium sulfate solid product is obtained by centrifugation and drying. It is then packaged and stored. S3: Salt evaporation. The clear liquid separated by conversion is filtered, and then salt is produced by evaporation using MVR. After evaporation, the product sodium chloride is obtained by centrifugation and drying, and then packaged and stored.

[0027] Step S1 includes the following steps: S11: After the raw material sodium sulfate enters the stockpile, it is transported to the sodium sulfate silo by a loader. The feeder continuously feeds the material through the conveyor to the sodium sulfate metering silo, and after being measured by an electronic scale, it enters the chemical tank. S12: After passing through the automatic bag-breaking machine, potassium chloride is poured into the potassium chloride silo, then weighed by a metering scale, and the weighed potassium chloride is lifted by a bucket elevator into the chemical tank.

[0028] The S2 step includes a primary conversion process and a secondary conversion process. The chemical principle of the primary conversion process is as follows: ; The chemical principle of the secondary conversion process is as follows: .

[0029] The primary conversion process includes the following steps: A1: The solution in the chemical tank and the metered mixture enter the No. 1 primary conversion reaction tank and react continuously with stirring; A2: Pumped to the No. 2 primary conversion reactor, the clear liquid at the top of the No. 2 primary conversion reactor overflows to the No. 3 primary conversion reactor, and the thick material at the bottom of the reactor is pumped to the thickener. A3: After settling, the upper clear liquid in the No. 3 primary conversion reactor overflows into the clear liquid transfer tank; the thick material at the bottom of the tank is sent to the thickener and together with the thick material in the No. 2 primary conversion reactor, it is centrifuged and separated to obtain potassium sodium sulfate. A4: Potassium sulfate is metered and transported into the secondary conversion process. The centrifugal mother liquor and the thickener overflow mother liquor are returned to the No. 2 reaction tank of the primary conversion for recycling.

[0030] The secondary conversion process includes the following steps: B1: The potassium sulfate solid, potassium chloride, and salt evaporation liquid separated by centrifugation in the primary conversion process are metered and fed into the No. 1 reaction tank of the secondary conversion, where they are continuously reacted by stirring. B2: Pumped to the No. 2 secondary conversion reactor, the clear liquid at the top of the reaction in the No. 2 secondary conversion reactor overflows to the No. 3 secondary conversion reactor, and the thick material at the bottom of the reactor is sent to the thickener; B3: After settling, the upper clear liquid in the No. 3 reaction tank of the secondary conversion overflows into the potassium mother liquor tank and is pumped to the mixing tank, where it enters the mixing tank together with the clear liquid evaporated from the primary conversion process; the thick material at the bottom of the tank is sent to the thickener and, together with the thick material in the No. 2 reaction tank of the secondary conversion, is separated into solid and liquid by a centrifuge. The centrifugal mother liquor and the mother liquor overflowing from the thickener are returned to the No. 2 reaction tank of the secondary conversion for recycling. B4: The separated solids are conveyed to the fluidized bed by a shaftless screw conveyor. After drying and cooling, the material is sent to the silo and then automatically packaged, stacked and stored.

[0031] Example 4: A method for preparing potassium sulfate, comprising: S1: Raw material preparation and pretreatment, including preparation of sodium sulfate, potassium chloride and process water; S2: Secondary conversion, sodium sulfate, potassium chloride and process water are mixed and reacted. After the primary conversion reaction, the potassium sulfate solid product is obtained by centrifugation. The overflow liquid from the evaporation of potassium sulfate and salt is hydrolyzed. The aqueous solution and potassium chloride enter the secondary conversion. After the secondary conversion reaction, the potassium sulfate solid product is obtained by centrifugation and drying. It is then packaged and stored. S3: Salt evaporation. The clear liquid separated by conversion is filtered, and then salt is produced by evaporation using MVR. After evaporation, the product sodium chloride is obtained by centrifugation and drying, and then packaged and stored.

[0032] Step S1 includes the following steps: S11: After the raw material sodium sulfate enters the stockpile, it is transported to the sodium sulfate silo by a loader. The feeder continuously feeds the material through the conveyor to the sodium sulfate metering silo, and after being measured by an electronic scale, it enters the chemical tank. S12: After passing through the automatic bag-breaking machine, potassium chloride is poured into the potassium chloride silo, then weighed by a metering scale, and the weighed potassium chloride is lifted by a bucket elevator into the chemical tank.

[0033] The S2 step includes a primary conversion process and a secondary conversion process. The chemical principle of the primary conversion process is as follows: ; The chemical principle of the secondary conversion process is as follows: .

[0034] The primary conversion process includes the following steps: A1: The solution in the chemical tank and the metered mixture enter the No. 1 primary conversion reaction tank and react continuously with stirring; A2: Pumped to the No. 2 primary conversion reactor, the clear liquid at the top of the No. 2 primary conversion reactor overflows to the No. 3 primary conversion reactor, and the thick material at the bottom of the reactor is pumped to the thickener. A3: After settling, the upper clear liquid in the No. 3 primary conversion reactor overflows into the clear liquid transfer tank; the thick material at the bottom of the tank is sent to the thickener and together with the thick material in the No. 2 primary conversion reactor, it is centrifuged and separated to obtain potassium sodium sulfate. A4: Potassium sulfate is metered and transported into the secondary conversion process. The centrifugal mother liquor and the thickener overflow mother liquor are returned to the No. 2 reaction tank of the primary conversion for recycling.

[0035] The secondary conversion process includes the following steps: B1: The potassium sulfate solid, potassium chloride, and salt evaporation liquid separated by centrifugation in the primary conversion process are metered and fed into the No. 1 reaction tank of the secondary conversion, where they are continuously reacted by stirring. B2: Pumped to the No. 2 secondary conversion reactor, the clear liquid at the top of the reaction in the No. 2 secondary conversion reactor overflows to the No. 3 secondary conversion reactor, and the thick material at the bottom of the reactor is sent to the thickener; B3: After settling, the upper clear liquid in the No. 3 reaction tank of the secondary conversion overflows into the potassium mother liquor tank and is pumped to the mixing tank, where it enters the mixing tank together with the clear liquid evaporated from the primary conversion process; the thick material at the bottom of the tank is sent to the thickener and, together with the thick material in the No. 2 reaction tank of the secondary conversion, is separated into solid and liquid by a centrifuge. The centrifugal mother liquor and the mother liquor overflowing from the thickener are returned to the No. 2 reaction tank of the secondary conversion for recycling. B4: The separated solids are conveyed to the fluidized bed by a shaftless screw conveyor. After drying and cooling, the material is sent to the silo and then automatically packaged, stacked and stored.

[0036] Step S3 includes the following steps: C1: The clear liquid separated in the first conversion process is filtered and enters the clear liquid storage tank. The clear liquid is pumped from the clear liquid storage tank to the heat exchanger to exchange heat with the condensate and then enters the MVR evaporation system for evaporation and salt production. C2: After the clear liquid is evaporated in the evaporator, the salt slurry is collected in the salt collector of the evaporation system and then pumped to the thickener by the salt slurry pump. C3: After separation by centrifuge, the centrifuged mother liquor is returned to the evaporator for recycling and evaporation; C4: After being dried in a rotary drum, it enters the finished product silo and is then transferred to the packaging system.

[0037] Example 5: A method for preparing potassium sulfate, comprising: S1: Raw material preparation and pretreatment, including preparation of sodium sulfate, potassium chloride and process water; S2: Secondary conversion, sodium sulfate, potassium chloride and process water are mixed and reacted. After the primary conversion reaction, the potassium sulfate solid product is obtained by centrifugation. The overflow liquid from the evaporation of potassium sulfate and salt is hydrolyzed. The aqueous solution and potassium chloride enter the secondary conversion. After the secondary conversion reaction, the potassium sulfate solid product is obtained by centrifugation and drying. It is then packaged and stored. S3: Salt evaporation. The clear liquid separated by conversion is filtered, and then salt is produced by evaporation using MVR. After evaporation, the product sodium chloride is obtained by centrifugation and drying, and then packaged and stored.

[0038] Step S1 includes the following steps: S11: After the raw material sodium sulfate enters the stockpile, it is transported to the sodium sulfate silo by a loader. The feeder continuously feeds the material through the conveyor to the sodium sulfate metering silo, and after being measured by an electronic scale, it enters the chemical tank. S12: After passing through the automatic bag-breaking machine, potassium chloride is poured into the potassium chloride silo, then weighed by a metering scale, and the weighed potassium chloride is lifted by a bucket elevator into the chemical tank.

[0039] The S2 step includes a primary conversion process and a secondary conversion process. The chemical principle of the primary conversion process is as follows: ; The chemical principle of the secondary conversion process is as follows: .

[0040] The primary conversion process includes the following steps: A1: The solution in the chemical tank and the metered mixture enter the No. 1 primary conversion reaction tank and react continuously with stirring; A2: Pumped to the No. 2 primary conversion reactor, the clear liquid at the top of the No. 2 primary conversion reactor overflows to the No. 3 primary conversion reactor, and the thick material at the bottom of the reactor is pumped to the thickener. A3: After settling, the upper clear liquid in the No. 3 primary conversion reactor overflows into the clear liquid transfer tank; the thick material at the bottom of the tank is sent to the thickener and together with the thick material in the No. 2 primary conversion reactor, it is centrifuged and separated to obtain potassium sodium sulfate. A4: Potassium sulfate is metered and transported into the secondary conversion process. The centrifugal mother liquor and the thickener overflow mother liquor are returned to the No. 2 reaction tank of the primary conversion for recycling.

[0041] The secondary conversion process includes the following steps: B1: The potassium sulfate solid, potassium chloride, and salt evaporation liquid separated by centrifugation in the primary conversion process are metered and fed into the No. 1 reaction tank of the secondary conversion, where they are continuously reacted by stirring. B2: Pumped to the No. 2 secondary conversion reactor, the clear liquid at the top of the reaction in the No. 2 secondary conversion reactor overflows to the No. 3 secondary conversion reactor, and the thick material at the bottom of the reactor is sent to the thickener; B3: After settling, the upper clear liquid in the No. 3 reaction tank of the secondary conversion overflows into the potassium mother liquor tank and is pumped to the mixing tank, where it enters the mixing tank together with the clear liquid evaporated from the primary conversion process; the thick material at the bottom of the tank is sent to the thickener and, together with the thick material in the No. 2 reaction tank of the secondary conversion, is separated into solid and liquid by a centrifuge. The centrifugal mother liquor and the mother liquor overflowing from the thickener are returned to the No. 2 reaction tank of the secondary conversion for recycling. B4: The separated solids are conveyed to the fluidized bed by a shaftless screw conveyor. After drying and cooling, the material is sent to the silo and then automatically packaged, stacked and stored.

[0042] Step S3 includes the following steps: C1: The clear liquid separated in the first conversion process is filtered and enters the clear liquid storage tank. The clear liquid is pumped from the clear liquid storage tank to the heat exchanger to exchange heat with the condensate and then enters the MVR evaporation system for evaporation and salt production. C2: After the clear liquid is evaporated in the evaporator, the salt slurry is collected in the salt collector of the evaporation system and then pumped to the thickener by the salt slurry pump. C3: After separation by centrifuge, the centrifuged mother liquor is returned to the evaporator for recycling and evaporation; C4: After being dried in a rotary drum, it enters the finished product silo and is then transferred to the packaging system.

[0043] In steps S2 and S3, the drying heat source is natural gas, which is directly ignited by the burner and then enters the rotary drum for drying. The dust removal system of the dryer first uses cyclone dust removal and then bag filter dust removal.

[0044] In step S2, the conversion temperature is 32-38 degrees Celsius, and in step S3, the crystallization temperature during evaporation salt production is 95-110 degrees Celsius.

[0045] In step S3, evaporation is performed using one MVR or multiple MVRs connected in parallel.

[0046] In step S3, evaporation is carried out using multiple sets of parallel MVR evaporators, and multiple sets of MVRs share a single vapor compressor.

[0047] The table below compares the preparation data of this invention with those of the prior art using the Mannheim method:

[0048] As shown in the table above, the present invention has the following advantages over the prior art Mannheim method: Cost advantages: This invention reduces energy consumption by 70% due to MVR evaporation technology (multiple parallel units + steam compressor), and requires less equipment investment. The Mannheim process, however, is affected by hydrochloric acid subsidies, leading to increased actual costs.

[0049] Breakthrough in raw material utilization: The 99% potassium conversion rate of this invention stems from the "two-stage conversion" process and the application of potassium-containing sodium sulfate. The low yield of the ammonium sulfate method is due to incomplete conversion of double salts.

[0050] Pollutant emission comparison: This invention achieves closed-loop circulation: primary conversion mother liquor → secondary conversion → evaporator reuse, while hydrochloric acid (accounting for 30% of the output) produced by the Mannheim process requires additional treatment.

[0051] Emission ratio quantification: The solid waste of this invention is 0%, and the proportion of solid waste (corrosion residue) from the Mannheim process is not quantified but is significant.

[0052] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing potassium sulfate, characterized in that, include: S1: Raw material preparation and pretreatment, including preparation of sodium sulfate, potassium chloride and process water; S2: Secondary conversion, sodium sulfate, potassium chloride and process water are mixed and reacted. After the primary conversion reaction, the potassium sulfate solid product is obtained by centrifugation. The overflow liquid from the evaporation of potassium sulfate and salt is hydrolyzed. The aqueous solution and potassium chloride enter the secondary conversion. After the secondary conversion reaction, the potassium sulfate solid product is obtained by centrifugation and drying. It is then packaged and stored. S3: Salt evaporation. The clear liquid separated by conversion is filtered, and then salt is produced by evaporation using MVR. After evaporation, the product sodium chloride is obtained by centrifugation and drying, and then packaged and stored.

2. The method for preparing potassium sulfate according to claim 1, characterized in that, Step S1 includes the following steps: S11: After the raw material sodium sulfate enters the stockpile, it is transported to the sodium sulfate silo by a loader. The feeder continuously feeds the material through the conveyor to the sodium sulfate metering silo, and after being measured by an electronic scale, it enters the chemical tank. S12: After passing through the automatic bag-breaking machine, potassium chloride is poured into the potassium chloride silo, then weighed by a metering scale, and the weighed potassium chloride is lifted by a bucket elevator into the chemical tank.

3. The method for preparing potassium sulfate according to claim 1, characterized in that, The S2 step includes a primary conversion process and a secondary conversion process. The chemical principle of the primary conversion process is as follows: ; The chemical principle of the secondary conversion process is as follows: .

4. The method for preparing potassium sulfate according to claim 3, characterized in that, The first conversion process Includes the following steps: A1: The solution in the chemical tank and the metered mixture enter the No. 1 primary conversion reaction tank and react continuously with stirring; A2: Pumped to the No. 2 primary conversion reactor, the clear liquid at the top of the No. 2 primary conversion reactor overflows to the No. 3 primary conversion reactor, and the thick material at the bottom of the reactor is pumped to the thickener. A3: After settling, the upper clear liquid in the No. 3 primary conversion reactor overflows into the clear liquid transfer tank; the thick material at the bottom of the tank is sent to the thickener and together with the thick material in the No. 2 primary conversion reactor, it is centrifuged and separated to obtain potassium sodium sulfate. A4: Potassium sulfate is metered and transported into the secondary conversion process. The centrifugal mother liquor and the thickener overflow mother liquor are returned to the No. 2 reaction tank of the primary conversion for recycling.

5. The method for preparing potassium sulfate according to claim 3, characterized in that, The secondary conversion process includes the following steps: B1: The potassium sulfate solid, potassium chloride, and salt evaporation liquid separated by centrifugation in the primary conversion process are metered and fed into the No. 1 reaction tank of the secondary conversion, where they are continuously reacted by stirring. B2: Pumped to the No. 2 secondary conversion reactor, the clear liquid at the top of the reaction in the No. 2 secondary conversion reactor overflows to the No. 3 secondary conversion reactor, and the thick material at the bottom of the reactor is sent to the thickener; B3: After settling, the upper clear liquid in the No. 3 reaction tank of the secondary conversion overflows into the potassium mother liquor tank and is pumped to the mixing tank, where it enters the mixing tank together with the clear liquid evaporated from the primary conversion process; the thick material at the bottom of the tank is sent to the thickener and, together with the thick material in the No. 2 reaction tank of the secondary conversion, is separated into solid and liquid by a centrifuge. The centrifugal mother liquor and the mother liquor overflowing from the thickener are returned to the No. 2 reaction tank of the secondary conversion for recycling. B4: The separated solids are conveyed to the fluidized bed by a shaftless screw conveyor. After drying and cooling, the material is sent to the silo and then automatically packaged, stacked and stored.

6. The method for preparing potassium sulfate according to claim 1, characterized in that, Step S3 includes the following steps: C1: The clear liquid separated in the first conversion process is filtered and enters the clear liquid storage tank. The clear liquid is pumped from the clear liquid storage tank to the heat exchanger to exchange heat with the condensate and then enters the MVR evaporation system for evaporation and salt production. C2: After the clear liquid is evaporated in the evaporator, the salt slurry is collected in the salt collector of the evaporation system and then pumped to the thickener by the salt slurry pump. C3: After separation by centrifuge, the centrifuged mother liquor is returned to the evaporator for recycling and evaporation; C4: After being dried in a rotary drum, it enters the finished product silo and is then transferred to the packaging system.

7. The method for preparing potassium sulfate according to claim 1, characterized in that, In steps S2 and S3, the drying heat source is natural gas, which is directly ignited by the burner and then enters the rotary drum for drying. The dust removal system of the dryer first uses cyclone dust removal and then bag filter dust removal.

8. The method for preparing potassium sulfate according to claim 1, characterized in that, In step S2, the conversion temperature is 32-38 degrees Celsius, and in step S3, the crystallization temperature during evaporation salt production is 95-110 degrees Celsius.

9. A method for preparing potassium sulfate according to claim 1, characterized in that, In step S3, evaporation is performed using one MVR or multiple MVRs connected in parallel.

10. A method for preparing potassium sulfate according to claim 9, characterized in that, In step S3, evaporation is carried out using multiple sets of parallel MVR evaporators, and multiple sets of MVRs share a single steam compressor.

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