Device and process method for producing potassium chloride through two-stage negative pressure evaporation by utilizing MVR (Mechanical Vapor Recompression) technology

Abstract

The invention belongs to the technical field of preparation of compounds, and particularly relates to a device and a process method for producing potassium chloride through two-stage negative pressure evaporation by utilizing an MVR (mechanical vapor recompression) technology. The device comprises an evaporation system, a compression heating system, a negative pressure system and an air supply system, the evaporation system comprises at least two sets of evaporation devices forming continuous production, and each evaporation device comprises an evaporation tank, a heating chamber, a circulating pump and a condensate water tank; the compression heating system comprises a scrubber tower, an evaporation compressor and a steam superheat degree eliminating device; the negative pressure system comprises a water ring vacuum pump, an evaporation compressor and a vacuum cooler; and the air supply system supplies live steam to each section of evaporation device. The method comprises the following steps: blending raw material brine; a first-stage evaporation process and a second-stage evaporation process; a compressor heating procedure; a negative pressure process; and supplementing air. According to the invention, the heat pump technology is utilized to optimize and improve the existing process for producing potassium chloride from bittern, electricity is utilized to replace steam, the production cost can be reduced, and the deficit and even twisting of the process for producing potassium chloride from bittern are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of compound preparation, and relates to a device and a process method for producing potassium chloride by two-stage negative pressure evaporation using MVR technology, and specifically relates to a device and a process method for producing potassium chloride from bittern by two-stage negative pressure evaporation using MVR technology. Background Art

[0002] Potassium chloride is an important industrial raw material, which can be used to make potassium carbonate, potassium hydroxide, potassium sulfate, potassium chlorate, etc. Potassium chloride itself can be used as a flame extinguisher to extinguish the flames of gun muzzles and cannons at night. When electrolyzing magnesium chloride to make metallic magnesium, potassium chloride is often used as one of the components of the electrolyte. It is used as a diuretic and potassium deficiency agent in medicine. In agriculture, potassium chloride is one of the important fertilizers, which can make the stems of crops thick, the branches and leaves dense, and not easy to lodging. It can also increase the ability to resist diseases and pests, promote photosynthesis, and increase the yield and quality of crops.

[0003] Traditional methods for producing potassium chloride mainly include positive flotation, reverse flotation, and evaporative cooling crystallization. The above methods all have their own shortcomings: positive flotation and reverse flotation are both suitable for producing potassium chloride from carnallite ore; evaporative cooling crystallization uses two-effect or multi-effect evaporation, which has wide applicability but high energy consumption. At present, the production of potassium chloride by two-effect or multi-effect evaporation has high energy consumption and high costs, which has caused the entire industry to be in a loss-making state and needs to be solved urgently. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a device and process method for producing potassium chloride by two-stage negative pressure evaporation using MVR technology, realizes the optimization and upgrading of the existing bittern potassium chloride production process by heat pump technology, replaces steam with electricity, can reduce production costs, and realize the reduction or even reversal of losses in the process of producing potassium chloride using bittern.

[0005] The present invention adopts the following technical solutions: A device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology, comprising an evaporation system, a compression and heating system, a negative pressure system and an air supply system, wherein: An evaporation system, comprising at least two groups of evaporation devices for continuous production, wherein the evaporation devices include an evaporation tank, a heating chamber, a circulation pump and a condensed water tank; The compression and heating system includes a scrubbing tower, an evaporation compressor and a steam superheat elimination device. The secondary steam evaporated from the evaporation tanks of each group of evaporation devices is collected together, and after being neutralized and washed in the scrubbing tower, it enters the evaporation compressor. After being compressed and pressurized by the evaporation compressor and heated, the secondary steam is made into saturated steam by the steam superheat elimination device and then enters the heating chamber of each group of evaporation devices respectively. Negative pressure system, which includes a water ring vacuum pump, an evaporation compressor and a vacuum cooler, is used to maintain negative pressure in each group of evaporation tanks and heating chambers; The air supplement system is used to supplement the raw steam to each section of the evaporation device.

[0006] In the above technical solution, the evaporation device includes a first-stage evaporation device and a second-stage evaporation device, and the first-stage evaporation device transfers the feed liquid to the second-stage evaporation device through a transfer pump, wherein: The first stage evaporation device comprises a first stage evaporation tank, a first stage heating chamber, a first stage circulation pump and a first stage condensation water tank, wherein the first stage evaporation tank, the first stage heating chamber and the first stage circulation pump are connected through a first stage circulation pipeline to form a circulation loop, and the first stage condensation water tank is connected to the first stage heating chamber; The two-stage evaporation device comprises a two-stage evaporation tank, a two-stage heating chamber, a two-stage circulation pump and a two-stage condensed water tank. The two-stage evaporation tank, the two-stage heating chamber and the two-stage circulation pump are connected through a two-stage circulation pipeline to form a circulation loop. The two-stage condensed water tank is connected to the two-stage heating chamber.

[0007] In the above technical solution, the outlet of the first stage evaporation tank is connected to the first stage salt discharge tank, and the outlet of the second stage evaporation tank is connected to the heat preservation settler.

[0008] In the above technical solution, the first-stage evaporation device and the second-stage evaporation device share a scrubbing tower, and the first-stage evaporation device and the second-stage evaporation device each correspond to an evaporation compressor, namely a first-stage evaporation compressor and a second-stage evaporation compressor, wherein: The input end of the scrubbing tower is connected to the secondary steam outlets of the first-stage evaporation tank and the second-stage evaporation tank, the output section is connected to the first-stage evaporation compressor and the second-stage evaporation compressor, the output end of the first-stage evaporation compressor is connected to the steam inlet of the first-stage heating chamber, and the output end of the second-stage evaporation compressor is connected to the steam inlet of the second-stage heating chamber.

[0009] In the above technical scheme, the non-condensable gas outlet on the steam outlet pipe of the scrubbing tower, the non-condensable gas outlet of the first-stage heating chamber, and the non-condensable gas outlet of the second-stage heating chamber are all connected to the vacuum cooler, the vacuum cooler is connected to the vacuum buffer tank, the vacuum buffer tank is connected to the water ring vacuum pump, and the water ring vacuum pump is connected to the condensed water storage tank.

[0010] In the above technical solution, a steam superheat elimination device is provided on the steam pipeline between the first stage evaporation compressor and the first stage heating chamber, and on the steam pipeline between the second stage evaporation compressor and the second stage heating chamber.

[0011] In the above technical solution, the air supply mechanism includes a first-stage supplementary steam pipeline and a second-stage supplementary steam pipeline, the first-stage supplementary steam pipeline is connected to the steam pipeline of a first heating chamber, and the second-stage supplementary steam pipeline is connected to the steam pipeline of a second heating chamber.

[0012] The second invention object of the present invention is to provide a process for producing potassium chloride by two-stage negative pressure evaporation using MVR technology, which is completed by continuous production through the following steps, including: 1) Raw material brine mixing process The concentrated brine is preheated to 60-90℃ according to a certain proportion of the bittern feed amount and then enters the first evaporation tank. The byproduct brine is mixed and preheated to 60-90℃ and then enters the first evaporation tank evenly and stably. 2) One-stage evaporation and two-stage evaporation process The bittern is preheated to 60-90℃ and enters the first stage evaporator for evaporation. The mother liquor of the first stage evaporation is transferred to the second stage evaporator through a transfer pump for further evaporation and concentration. The evaporated liquid undergoes heat preservation sedimentation, cooling crystallization and decomposition washing in the traditional potassium chloride production process to prepare potassium chloride. Compressor heating process The secondary steam evaporated from the first and second evaporation tanks is collected together, containing a small amount of hydrochloric acid gas and droplets. After being neutralized and washed with alkali solution in the steam washing tower, it enters the first and second steam compressors. The clean secondary steam enters the first and second steam compressors for compression, pressure increase and temperature increase. After the secondary steam becomes saturated steam through the steam superheat elimination device on the steam pipeline, it enters the first and second heating chambers respectively. 4) Negative pressure process At the beginning of production, the non-condensable gas in the evaporation system is pumped out by the water ring vacuum pump to form a vacuum, so that the absolute pressure in the first stage evaporator and the second stage evaporator is controlled at 47-58kPa. During normal production, the vacuum in the first stage evaporator and the second stage evaporator is maintained by the negative pressure of the suction port of the first stage evaporator compressor and the second stage evaporator compressor. The non-condensable gas generated during the production process passes through the vacuum cooler, and the steam brought out by the non-condensable gas is condensed into liquid water. After the liquid water is separated by the vacuum buffer tank, it is pumped out by the water ring vacuum pump; 5) Gas replenishment process Because the calorific value required for material evaporation is greater than the calorific value released by the secondary steam generated by evaporation after recompression and condensation into water in the heating chamber, in order to maintain the thermal balance of the production system, it is necessary to supplement raw steam to the evaporation system.

[0013] In the above technical solution, in the one-stage evaporation and the two-stage evaporation process, the boiling point temperature at the end of the first-stage evaporation is controlled at 101-106°C, and the boiling point temperature at the end of the second-stage evaporation is controlled at 108-113°C.

[0014] In the above technical solution, in the compressor heating process, the saturation temperature of the first stage compressor rises to 28-30°C, and the saturation temperature of the second stage compressor rises to 35-37°C.

[0015] Combining all the above technical solutions, the advantages and positive effects of the present invention are as follows: 1. The present invention utilizes heat pump technology to optimize and upgrade the existing bittern-based potassium chloride production process, and replaces steam with electricity, which can reduce production costs and achieve loss reduction or even loss-making in the bittern-based potassium chloride production process.

[0016] 2. Compared with the traditional potassium chloride multi-effect evaporation, the present invention can flexibly adjust the amount of evaporated water between the first and second stages according to the quality change of the raw bittern, control the amount of salt discharged in the first stage, and improve the evaporation efficiency.

[0017] 3. The two stages of the present invention both adopt negative pressure evaporation, which reduces the temperature of the boiling point of the material and slows down the scaling of the heating chamber, thereby extending the tank cleaning cycle and improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings herein are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the description, serve to explain the principles of the present disclosure; Figure 1 It is a structural schematic diagram of a device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology in the present invention.

[0019] In the figure: 1-first stage evaporation tank; 2-second stage evaporation tank; 3-first stage heating chamber; 4-second stage heating chamber; 5-first stage circulation pump; 6-second stage circulation pump; 7-first stage condensate tank; 8-second stage condensate tank; 9-washing tower; 10-first stage evaporation compressor; 11-second stage evaporation compressor; 12-first stage desalination tank; 13-vacuum cooler; 14-vacuum buffer tank; 15-condensate storage tank; 16-water ring vacuum pump; 17-transfer pump; 18-first stage supplementary steam pipeline; 19-second stage supplementary steam pipeline. DETAILED DESCRIPTION

[0020] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific implementation disclosed below.

[0021] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Example 1

[0022] A device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology, comprising an evaporation system, a compression and heating system, a negative pressure system and an air supply system, wherein: An evaporation system, comprising at least two groups of evaporation devices for continuous production, wherein the evaporation devices include an evaporation tank, a heating chamber, a circulation pump and a condensed water tank; The compression and heating system includes a scrubbing tower, an evaporation compressor and a steam superheat elimination device. The secondary steam evaporated from the evaporation tanks of each group of evaporation devices is collected together, and after being neutralized and washed in the scrubbing tower, it enters the evaporation compressor. After being compressed and pressurized by the evaporation compressor and heated, the secondary steam is made into saturated steam by the steam superheat elimination device and then enters the heating chamber of each group of evaporation devices respectively. Negative pressure system, which includes a water ring vacuum pump, an evaporation compressor and a vacuum cooler, is used to maintain negative pressure in each group of evaporation tanks and heating chambers; The air supplement system is used to supplement the raw steam to each section of the evaporation device.

[0023] Furthermore, in this embodiment, it can also be considered that the evaporation device includes a first-stage evaporation device and a second-stage evaporation device, and the first-stage evaporation device transfers the feed liquid to the second-stage evaporation device through a transfer pump 17, wherein: The first stage evaporation device comprises a first stage evaporation tank 1, a first stage heating chamber 3, a first stage circulation pump 5 and a first stage condensation water tank 7, wherein the first stage evaporation tank 1, the first stage heating chamber 3 and the first stage circulation pump 5 are connected through a first stage circulation pipeline to form a circulation loop, and the first stage condensation water tank 7 is connected to the first stage heating chamber 3; The two-stage evaporation device includes a two-stage evaporation tank 2, a two-stage heating chamber 4, a two-stage circulation pump 6 and a two-stage condensed water tank 8. The two-stage evaporation tank 2, the two-stage heating chamber 4 and the two-stage circulation pump 6 are connected through a two-stage circulation pipeline to form a circulation loop, and the two-stage condensed water tank 8 is connected to the two-stage heating chamber 4.

[0024] Furthermore, in this embodiment, it can also be considered that the outlet of the first-stage evaporation tank 1 is connected to the first-stage salt removal tank 12, and the outlet of the second-stage evaporation tank 2 is connected to the heat preservation settler.

[0025] Furthermore, in this embodiment, it can also be considered that the first-stage evaporation device and the second-stage evaporation device share a scrubbing tower, and the first-stage evaporation device and the second-stage evaporation device each correspond to an evaporation compressor, namely, a first-stage evaporation compressor 10 and a second-stage evaporation compressor 11, wherein: The input end of the scrubbing tower 9 is connected to the secondary steam outlets of the first-stage evaporation tank 1 and the second-stage evaporation tank 2, and the output section is connected to the first-stage evaporation compressor 10 and the second-stage evaporation compressor 11. The output end of the first-stage evaporation compressor 10 is connected to the steam inlet of the first-stage heating chamber 3, and the output end of the second-stage evaporation compressor 11 is connected to the steam inlet of the second-stage heating chamber 4.

[0026] Furthermore, in the present embodiment, it can also be considered that the non-condensable gas outlet on the steam outlet pipe of the scrubbing tower 9, the non-condensable gas outlet of the first-stage heating chamber 3, and the non-condensable gas outlet of the second-stage heating chamber 4 are all connected to the vacuum cooler 13, the vacuum cooler 13 is connected to the vacuum buffer tank 14, the vacuum buffer tank 14 is connected to the water ring vacuum pump 16, and the water ring vacuum pump 16 is connected to the condensed water storage tank 15.

[0027] Furthermore, in this embodiment, it can also be considered that a steam superheat elimination device is provided on the steam pipeline between the first stage evaporation compressor 10 and the first stage heating chamber 3 and on the steam pipeline between the second stage evaporation compressor 11 and the second stage heating chamber 4.

[0028] Furthermore, in this embodiment, it can also be considered that the air supply mechanism includes a first-stage supplementary steam pipe 18 and a second-stage supplementary steam pipe 19, the first-stage supplementary steam pipe 18 is connected to the steam pipe of a first-stage heating chamber 3, and the second-stage supplementary steam pipe 19 is connected to the steam pipe of a second-stage heating chamber 4.

[0029] In this embodiment, a device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology includes a first-stage evaporation tank 1, a second-stage evaporation tank 2, a first-stage heating chamber 3, a second-stage heating chamber 4, a first-stage circulating pump 5, a second-stage circulating pump 6, a first-stage condensed water tank 7, a second-stage condensed water tank 8, a scrubber 9, a first-stage evaporation compressor 10, a second-stage evaporation compressor 11, a first-stage salt removal tank 12, a vacuum cooler 13, a vacuum buffer tank 14, a condensed water storage tank 15, a water ring vacuum pump 16, a transfer pump 17, a first-stage regeneration steam pipeline 18, and a second-stage regeneration steam pipeline 19. The first stage evaporation tank 1, the first stage heating chamber 3, the first stage circulation pump 5 and the first stage condensed water tank 7 are connected to form a first stage evaporation device, the second stage evaporation tank 2, the second stage heating chamber 4, the second stage circulation pump 6 and the second stage condensed water tank 8 form a second stage evaporation device, the material transfer pump 17 transfers the material liquid of the first stage evaporation device to the second stage evaporation device, the scrubbing tower 9 is connected to the secondary steam outlet of the first stage evaporation tank 1 and the second stage evaporation tank 2, the first stage evaporation compressor 10 and the second stage evaporation compressor 11 are connected to the scrubbing tower 9, the first stage evaporation compressor 10 is connected to the steam inlet of the first stage heating chamber 3, and the second stage evaporation compressor 1 1 is connected to the steam inlet of the second-stage heating chamber 4, the first-stage evaporation tank outlet is connected to the first-stage salt removal tank 12, the non-condensable gas outlet on the steam outlet pipeline of the scrubber 9, the non-condensable gas outlet of the first-stage heating chamber 3 and the second-stage heating chamber 4 are connected to the vacuum cooler 13, the vacuum cooler 13 is connected to the vacuum buffer tank 14, the vacuum buffer tank 14 is connected to the water ring vacuum pump 16, the water ring vacuum pump 16 is connected to the condensed water storage tank 15, the first-stage supplementary steam pipeline 18 is connected to the first-stage heating chamber 3 steam pipeline, and the second-stage supplementary steam pipeline 19 is connected to the second-stage heating chamber 4 steam pipeline.

[0030] Working principle: After the raw brine is preheated and brine is added, it enters the first stage of evaporation, and a stage of salt is discharged after evaporation and concentration. The feed liquid enters the second stage of evaporation, and the evaporation completed liquid is discharged after evaporation and concentration. Potassium chloride is prepared by heat preservation sedimentation, cooling crystallization and decomposition washing in the traditional potassium chloride production process. The device and method provided by the present invention can continuously produce potassium chloride. During this period, both evaporation systems maintain negative pressure, and the secondary steam generated by the first and second stage evaporation is washed by the steam washing tower and enters the first and second stage steam compression and pressure increase and temperature increase respectively. Then, the secondary steam is made into saturated steam through the steam superheat elimination device on the steam pipeline, and then enters the first and second stage heating chambers for reheating. In order to maintain the thermal balance of the production system, it is also necessary to supplement raw steam. It should be noted that the above-mentioned components are all sealed. Example 2

[0031] A process for preparing potassium chloride using the device described in Example 1, comprising: 1) Adding brine to raw materials The concentrated brine is preheated to 60-90℃ according to a certain proportion of the bitter brine feed and then enters the first evaporation tank. The by-product brine is mixed and preheated to 60-90℃ and then enters the first evaporation tank evenly and stably.

[0032] 2) One-stage evaporation and two-stage evaporation The bittern is preheated to 60-90℃ and enters the first evaporator for evaporation. The boiling point temperature of the first evaporation is controlled at 101-106℃. The mother liquor of the first evaporation is transferred to the second evaporator through a transfer pump for further evaporation and concentration. The boiling point temperature of the second evaporation is controlled at 108-113℃. The evaporated liquid is subjected to the traditional potassium chloride production process of heat preservation sedimentation, cooling crystallization and decomposition washing to prepare potassium chloride.

[0033] 3) Compressor temperature rise The secondary steam evaporated from the first and second stages is collected together, containing a small amount of hydrochloric acid gas and foam. After being neutralized and washed with alkali solution in the steam washing tower, it enters the first and second stage steam compressors. The clean secondary steam enters the compressor for compression and pressure increase, and after the temperature is increased, it passes through the steam superheat elimination device on the steam pipeline to make the secondary steam saturated steam and then enters the first and second stage heating chambers respectively. The saturated temperature rise of the first stage compressor is 28-30℃, and the saturated temperature rise of the second stage compressor is 35-37℃.

[0034] 4) Negative pressure process At the beginning of production, the non-condensable gas in the evaporation system is pumped out by the water ring vacuum pump to form a vacuum, so that the absolute pressure in the first and second evaporation tanks is controlled at 47-58kPa. During normal production, the vacuum in the first and second evaporation tanks is maintained by the negative pressure of the suction port of the first and second evaporation compressors. The non-condensable gas generated during the production process passes through the vacuum cooler, and the steam brought out by the non-condensable gas is condensed into liquid water. After the liquid water is separated by the vacuum buffer tank, it is pumped out by the water ring vacuum pump.

[0035] 5) Gas replenishment process Because the calorific value required for material evaporation is greater than the calorific value released by the secondary steam generated by evaporation and condensed into water in the heating chamber after recompression, raw steam needs to be supplemented to maintain the thermal balance of the production system.

[0036] The above is only a preferred embodiment of the present invention. It should be understood that the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The present invention is not limited to the form disclosed herein, and should not be regarded as an exclusion of other embodiments, but can be used in various other combinations, modifications and environments. The changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should all be within the scope of protection of the claims attached to the present invention.

Claims

1. A device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology, characterized in that: It includes: An evaporation system, comprising at least two groups of evaporation devices for continuous production, wherein the evaporation devices include an evaporation tank, a heating chamber, a circulation pump and a condensed water tank; The compression and heating system includes a scrubbing tower, an evaporation compressor and a steam superheat elimination device. The secondary steam evaporated from the evaporation tanks of each group of evaporation devices is collected together, and after being neutralized and washed in the scrubbing tower, it enters the evaporation compressor. After being compressed and pressurized by the evaporation compressor and heated, the secondary steam is made into saturated steam by the steam superheat elimination device and then enters the heating chamber of each group of evaporation devices respectively. Negative pressure system, which includes a water ring vacuum pump, an evaporation compressor and a vacuum cooler, is used to maintain negative pressure in each group of evaporation tanks and heating chambers; The air supplement system is used to supplement the raw steam to each section of the evaporation device.

2. A device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology according to claim 1, characterized in that: The evaporation device comprises a first-stage evaporation device and a second-stage evaporation device, wherein the first-stage evaporation device transfers the feed liquid to the second-stage evaporation device through a transfer pump (17), wherein: The one-stage evaporation device comprises an evaporation tank (1), a heating chamber (3), a circulation pump (5) and a condensation water tank (7); the one-stage evaporation tank (1), the one-stage heating chamber (3) and the circulation pump (5) are connected via a circulation pipeline to form a circulation loop; the one-stage condensation water tank (7) is connected to the one-stage heating chamber (3); The two-stage evaporation device comprises a two-stage evaporation tank (2), a two-stage heating chamber (4), a two-stage circulation pump (6) and a two-stage condensed water tank (8); the two-stage evaporation tank (2), the two-stage heating chamber (4) and the two-stage circulation pump (6) are connected via a two-stage circulation pipeline to form a circulation loop; the two-stage condensed water tank (8) is connected to the two-stage heating chamber (4).

3. A device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology according to claim 2, characterized in that: The outlet of the first-stage evaporation tank (1) is connected to the first-stage salt removal tank (12), and the outlet of the second-stage evaporation tank (2) is connected to the heat preservation settler.

4. A device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology according to claim 2, characterized in that: The first stage evaporation device and the second stage evaporation device share a scrubbing tower, and the first stage evaporation device and the second stage evaporation device each correspond to an evaporation compressor, namely a first stage evaporation compressor (10) and a second stage evaporation compressor (11), wherein: The input end of the scrubbing tower (9) is connected to the secondary steam outlets of the first-stage evaporation tank (1) and the second-stage evaporation tank (2), and the output section is connected to the first-stage evaporation compressor (10) and the second-stage evaporation compressor (11). The output end of the first-stage evaporation compressor (10) is connected to the steam inlet of the first-stage heating chamber (3), and the output end of the second-stage evaporation compressor (11) is connected to the steam inlet of the second-stage heating chamber (4).

5. A device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology according to claim 4, characterized in that: The non-condensable gas outlet on the steam outlet pipe of the scrubbing tower (9), the non-condensable gas outlet of the first-stage heating chamber (3), and the non-condensable gas outlet of the second-stage heating chamber (4) are all connected to a vacuum cooler (13), the vacuum cooler (13) is connected to a vacuum buffer tank (14), the vacuum buffer tank (14) is connected to a water ring vacuum pump (16), and the water ring vacuum pump (16) is connected to a condensed water storage tank (15).

6. A device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology according to claim 4, characterized in that: A steam superheat elimination device is provided on the steam pipeline between the first-stage evaporation compressor (10) and the first-stage heating chamber (3), and on the steam pipeline between the second-stage evaporation compressor (11) and the second-stage heating chamber (4).

7. A device for producing potassium chloride by two-stage negative pressure evaporation using MVR technology according to claim 2, characterized in that: The air supply mechanism comprises a first-stage supplementary steam pipeline (18) and a second-stage supplementary steam pipeline (19), wherein the first-stage supplementary steam pipeline (18) is connected to a steam pipeline of a first-stage heating chamber (3), and the second-stage supplementary steam pipeline (19) is connected to a steam pipeline of a second-stage heating chamber (4).

8. A process for producing potassium chloride by two-stage negative pressure evaporation using MVR technology, characterized in that: The production is completed by the following continuous processes, including: 1) Raw material brine mixing process The concentrated brine is preheated to 60-90℃ according to a certain proportion of the bittern feed amount and then enters the first evaporation tank. The by-product brine is mixed and preheated to 60-90℃ and then enters the first evaporation tank evenly and stably. 2) One-stage evaporation and two-stage evaporation process The bittern is preheated to 60-90℃ and enters the first stage evaporator for evaporation. The mother liquor of the first stage evaporation is transferred to the second stage evaporator through a transfer pump for further evaporation and concentration. The evaporated liquid undergoes heat preservation sedimentation, cooling crystallization and decomposition washing in the traditional potassium chloride production process to prepare potassium chloride. 3) Compressor heating process The secondary steam evaporated from the first and second evaporation tanks is collected together, containing a small amount of hydrochloric acid gas and droplets. After being neutralized and washed with alkali solution in the steam washing tower, it enters the first and second steam compressors. The clean secondary steam enters the first and second steam compressors for compression, pressure increase and temperature increase. After the secondary steam becomes saturated steam through the steam superheat elimination device on the steam pipeline, it enters the first and second heating chambers respectively. 4) Negative pressure process At the beginning of production, the non-condensable gas in the evaporation system is pumped out by the water ring vacuum pump to form a vacuum, so that the absolute pressure in the first stage evaporator and the second stage evaporator is controlled at 47-58kPa. During normal production, the vacuum in the first stage evaporator and the second stage evaporator is maintained by the negative pressure of the suction port of the first stage evaporator compressor and the second stage evaporator compressor. The non-condensable gas generated during the production process passes through the vacuum cooler, and the steam brought out by the non-condensable gas is condensed into liquid water. After the liquid water is separated by the vacuum buffer tank, it is pumped out by the water ring vacuum pump; 5) Gas replenishment process Because the calorific value required for material evaporation is greater than the calorific value released by the secondary steam generated by evaporation after recompression and condensation into water in the heating chamber, in order to maintain the thermal balance of the production system, it is necessary to supplement raw steam to the evaporation system.

9. A process for producing potassium chloride by two-stage negative pressure evaporation using MVR technology according to claim 8, characterized in that: In the one-stage evaporation and two-stage evaporation processes, the boiling point temperature at the end of the first-stage evaporation is controlled at 101-106°C, and the boiling point temperature at the end of the second-stage evaporation is controlled at 108-113°C.

10. A process for producing potassium chloride by two-stage negative pressure evaporation using MVR technology according to claim 8, characterized in that: In the compressor heating process, the saturation temperature of the first stage compressor rises to 28-30°C, and the saturation temperature of the second stage compressor rises to 35-37°C.

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