阅读说明：本技术 一种从垃圾焚烧飞灰水洗液中提取钾盐的方法 (Method for extracting potassium salt from waste incineration fly ash water washing liquid ) 是由 陈侠 董建华 于 2021-09-24 设计创作，主要内容包括：本发明提供了一种从垃圾焚烧飞灰水洗液中提取钾盐的方法,包括将富钾母液泵入具有首级真空度的首级闪发结晶器内真空闪蒸获得首级闪蒸晶浆；将首级闪蒸晶浆泵入具有中间级真空度的中间级闪发结晶器内真空闪蒸获得中间级闪蒸晶浆；将中间级闪蒸晶浆泵入具有末级真空度的末级闪发结晶器内真空闪蒸获得末级闪蒸晶浆；将末级闪蒸晶浆进行增稠离心干燥,获得氯化钾晶体。本发明提供的一种从垃圾焚烧飞灰水洗液中提取钾盐的方法,采用逐级提高真空度的方式获得低温闪蒸晶浆,冷却过程中不存在实际换热面,因此能够避免富钾母液在降温结晶提取钾盐过程中的结壁现象,从而能够保证生产连续性,提高生产效率。(The invention provides a method for extracting sylvite from waste incineration fly ash water washing liquid, which comprises the steps of pumping potassium-rich mother liquid into a primary flash crystallizer with primary vacuum degree for vacuum flash evaporation to obtain primary flash crystal slurry; pumping the first-stage flash-evaporation crystal mush into an intermediate-stage flash-evaporation crystallizer with an intermediate-stage vacuum degree for vacuum flash evaporation to obtain intermediate-stage flash-evaporation crystal mush; pumping the intermediate-stage flash-evaporation crystal mush into a final-stage flash-evaporation crystallizer with a final-stage vacuum degree for vacuum flash evaporation to obtain final-stage flash-evaporation crystal mush; and thickening, centrifuging and drying the final-stage flash-evaporated crystal slurry to obtain potassium chloride crystals. According to the method for extracting the potassium salt from the waste incineration fly ash water washing liquid, provided by the invention, the low-temperature flash evaporation crystal slurry is obtained by gradually increasing the vacuum degree, and no actual heat exchange surface exists in the cooling process, so that the wall-forming phenomenon of potassium-rich mother liquid in the process of cooling, crystallizing and extracting the potassium salt can be avoided, the production continuity can be ensured, and the production efficiency can be improved.)

1. A method for extracting potassium salt from waste incineration fly ash water washing liquid is characterized by comprising the following steps:

step S10, separating and extracting sodium chloride crystals in the water washing liquid through a multi-effect crystallizer or MVR crystallizer to obtain potassium-rich mother liquor at the temperature of 90-120 ℃;

step S20, pumping the potassium-rich mother liquor at the temperature of 90-120 ℃ into a primary flash crystallizer for vacuum flash evaporation, introducing the obtained flash steam into a primary mixed condenser for mixing and condensing with cooling water, so as to promote the primary flash crystallizer to obtain a primary vacuum degree, and performing vacuum flash evaporation on the potassium-rich mother liquor at the primary vacuum degree to obtain primary flash crystal slurry at the temperature of 70-90 ℃;

step S30, pumping the primary flash evaporation crystal mush at the temperature of 70-90 ℃ into an intermediate stage flash evaporation crystallizer for vacuum flash evaporation, introducing the obtained flash evaporation steam into an intermediate stage mixing condenser for mixing and condensing with cooling water, so that an intermediate stage vacuum degree higher than the primary vacuum degree is obtained in the intermediate stage flash evaporation crystallizer, and performing vacuum flash evaporation on the primary flash evaporation crystal mush at the intermediate stage vacuum degree to obtain the intermediate stage flash evaporation crystal mush at the temperature of 50-70 ℃;

step S40, pumping the intermediate-stage flash evaporation crystal mush at the temperature of 50-70 ℃ into a final-stage flash evaporation crystallizer for vacuum flash evaporation, introducing obtained flash evaporation steam into a final-stage mixed condenser for mixing and condensing with cooling water, and extracting uncondensed flash evaporation steam and uncondensed gas in the final-stage mixed condenser by using a vacuum pump and a steam ejector to promote the final-stage flash evaporation crystallizer to obtain a final-stage vacuum degree higher than the intermediate-stage vacuum degree, wherein the intermediate-stage flash evaporation crystal mush is subjected to vacuum flash evaporation under the final-stage vacuum degree to obtain final-stage flash evaporation crystal mush at the temperature of 30-50 ℃;

and step S50, thickening, centrifuging and drying the final-stage flash-evaporated crystal slurry to obtain potassium chloride crystals.

2. The method for extracting potassium salt from waste incineration fly ash water washing liquid as claimed in claim 1, wherein the final stage mixing condenser has n and the steam ejector has n-1, wherein n is more than or equal to 2; the step S40 includes:

step S41, pumping the intermediate-stage flash evaporation crystal mush at the temperature of 50-70 ℃ into a final-stage flash evaporation crystallizer for vacuum flash evaporation, and introducing the obtained flash evaporation steam into a first final-stage mixing condenser for mixing and condensing with cooling water;

step S42, extracting uncondensed flash steam and uncondensed gas in the first final stage mixing condenser to the second final stage mixing condenser by using the high-pressure steam injected in the first steam injector, and mixing and condensing the flash steam and the cooling water in the second final stage mixing condenser;

step S43, if n is 2, extracting the uncondensed flash steam and the uncondensed gas in the second final-stage mixing condenser by using the vacuum pump; if n is more than 2, extracting uncondensed flash steam and uncondensed gas in a second final-stage mixing condenser to a next final-stage mixing condenser by using high-pressure steam injected in a second steam injector, mixing and condensing the flash steam and cooling water in the next final-stage mixing condenser, and extracting the flash steam and the uncondensed gas in the last final-stage mixing condenser by using the vacuum pump after the flash steam and the uncondensed gas are extracted in sequence to the last final-stage mixing condenser;

and S44, obtaining a final-stage vacuum degree of 85-95 kpa in the final-stage flash crystallizer under the coupling and extraction action of each final-stage mixing condenser, each steam ejector and the vacuum pump, and obtaining final-stage flash crystal slurry at 30-50 ℃ after vacuum flash evaporation of the intermediate-stage flash crystal slurry under the final-stage vacuum degree.

3. The method for extracting potassium salt from the waste incineration fly ash water washing liquid as claimed in claim 2, wherein the high pressure steam pressure is 0.4-1.2 Mpa.

4. The method for extracting potassium salt from waste incineration fly ash water washing liquid as claimed in claim 2, wherein the flash steam is mixed with cooling water in each final-stage mixing condenser and condensed and then introduced into the liquid seal tank.

5. The method for extracting potassium salt from waste incineration fly ash water washing liquid according to claim 1, wherein the step S20 includes:

pumping the potassium-rich mother liquor at the temperature of 90-120 ℃ into the primary flash crystallizer for vacuum flash evaporation;

introducing flash steam in the primary flash crystallizer into the primary mixed condenser to be mixed and condensed with cooling water, and introducing mixed condensed water into a liquid seal pool;

and forming saturated steam pressure difference by temperature difference between the primary mixed condenser and the primary flash crystallizer, so that the primary vacuum degree of 30-70 kpa is obtained in the primary flash crystallizer, and further the potassium-rich mother liquor is subjected to vacuum flash evaporation to obtain 70-90 ℃ primary flash crystal slurry.

6. The method for extracting potassium salt from waste incineration fly ash water washing liquid according to claim 1, wherein the step S30 includes:

pumping the primary flash evaporation crystal slurry at the temperature of 70-90 ℃ into the intermediate stage flash evaporation crystallizer for vacuum flash evaporation;

introducing flash steam in the intermediate-stage flash crystallizer into the intermediate-stage mixed condenser to be mixed and condensed with cooling water, and introducing mixed condensed water into a liquid seal pool;

and forming saturated steam pressure difference by temperature difference between the intermediate-stage mixing condenser and the intermediate-stage flash crystallizer, so that the intermediate-stage vacuum degree of 70-85 kpa is obtained in the intermediate-stage flash crystallizer, and the intermediate-stage flash crystal slurry of 50-70 ℃ is obtained after the first-stage flash crystal slurry is subjected to vacuum flash evaporation.

7. The method for extracting potassium salt from waste incineration fly ash water washing liquid according to claim 1, wherein in the steps S20 to S40, the first-stage flash evaporation crystal slurry with solid content of more than or equal to 10% and the intermediate-stage flash evaporation crystal slurry are directly transferred to a thickener, the first-stage flash evaporation crystal slurry with solid content of less than 10% is transferred to the intermediate-stage flash crystallizer, and the intermediate-stage flash evaporation crystal slurry with solid content of less than 10% is transferred to the final-stage flash crystallizer.

8. The method for extracting potassium salt from waste incineration fly ash water washing liquid according to claim 1, wherein the temperature of the cooling water is less than 36 ℃.

9. The method for extracting potassium salt from waste incineration fly ash water washing liquid according to claim 1, further comprising, in the steps S20 to S40: and periodically introducing cleaning water into the first-stage flash crystallizer, the middle-stage flash crystallizer and the last-stage flash crystallizer.

10. The method for extracting potassium salt from waste incineration fly ash water washing liquid according to any one of claims 1 to 9, wherein the first-stage flash crystallizer, the middle-stage flash crystallizer and the last-stage flash crystallizer are shielded crystallizers.

Technical Field

The invention belongs to the technical field of waste incineration fly ash water washing liquid treatment, and particularly relates to a method for extracting potassium salt from waste incineration fly ash water washing liquid.

Background

At present, when waste incineration fly ash water washing liquid is treated, the idea of separating sodium chloride and potassium chloride salt is to separate and extract sodium chloride by adopting an evaporative crystallization mode, obtain potassium-rich mother liquid after sodium chloride is separated, cool the potassium-rich mother liquid by a jacketed cooling kettle so as to crystallize and extract potassium chloride products, wherein the potassium-rich mother liquid in the cooling kettle is cooled by cooling liquid of internal circulation or external circulation in the cooling kettle, but the temperature of general sodium salt evaporative mother liquid is about 100 ℃, the temperature of cooling liquid is 20-35 ℃, the final temperature of the evaporative mother liquid after the potassium chloride and the cooling kettle exchange heat through a ceramic jacket is about 40 ℃, potassium chloride can be crystallized and separated out at a heat exchange surface after being cooled, and the potassium chloride can be formed on the heat exchange wall (namely the heat exchange surface) by carrying out high-strength heat exchange in the cooling kettle, Scabbing, it is huge to consume energy moreover, though can alleviate potassium chloride crystal wall-forming speed to a certain extent through set up agitating unit in the cauldron, still can't fundamentally eliminate the wall-forming problem of heat-transfer surface department to cause equipment to block up and cause the unable outer row of mother liquor and then lead to intermittent type nature to shut down, influence production, the crystallized potassium chloride of wall built-up simultaneously not only is difficult to discharge the cooling cauldron smoothly, still can cause heat transfer efficiency to descend, thereby influences cooling heat transfer effect.

Disclosure of Invention

The embodiment of the invention provides a method for extracting potassium salt from waste incineration fly ash water washing liquid, and aims to solve the wall forming problem in the potassium salt extraction process by cooling and crystallizing potassium-rich mother liquid.

In order to achieve the purpose, the invention adopts the technical scheme that: provides a method for extracting potassium salt from waste incineration fly ash water washing liquid, which comprises the following steps:

step S10, separating and extracting sodium chloride crystals in the water washing liquid through a multi-effect crystallizer or an MVR (Mechanical Vapor Recompression) crystallizer to obtain potassium-rich mother liquid at 90-120 ℃;

step S20, pumping the potassium-rich mother liquor at the temperature of 90-120 ℃ into a primary flash crystallizer for vacuum flash evaporation, introducing the obtained flash steam into a primary mixed condenser for mixing and condensing with cooling water, so that a primary vacuum degree is obtained in the primary flash crystallizer, and the potassium-rich mother liquor is subjected to vacuum flash evaporation at the primary vacuum degree to obtain primary flash crystal slurry at the temperature of 70-90 ℃;

step S30, pumping the primary flash evaporation crystal mush at the temperature of 70-90 ℃ into an intermediate-stage flash evaporation crystallizer for vacuum flash evaporation, introducing the obtained flash evaporation steam into an intermediate-stage mixing condenser for mixing and condensing with cooling water, so that an intermediate-stage vacuum degree higher than the primary vacuum degree is obtained in the intermediate-stage flash evaporation crystallizer, and performing vacuum flash evaporation on the primary flash evaporation crystal mush at the intermediate-stage vacuum degree to obtain the intermediate-stage flash evaporation crystal mush at the temperature of 50-70 ℃;

step S40, pumping the intermediate-stage flash evaporation crystal mush at the temperature of 50-70 ℃ into a final-stage flash evaporation crystallizer for vacuum flash evaporation, introducing the obtained flash evaporation steam into a final-stage mixed condenser for mixing and condensing with cooling water, and pumping out the uncondensed flash evaporation steam and uncondensed gas in the final-stage mixed condenser by using a vacuum pump and a steam ejector to promote the final-stage vacuum degree higher than the intermediate-stage vacuum degree in the final-stage flash evaporation crystallizer, wherein the intermediate-stage flash evaporation crystal mush is subjected to vacuum flash evaporation at the final-stage vacuum degree to obtain final-stage flash evaporation crystal mush at the temperature of 30-50 ℃;

and step S50, thickening, centrifuging and drying the final-stage flash-evaporated crystal slurry to obtain potassium chloride crystals.

In one possible implementation, the final mixing condenser has n, the steam ejector has n-1, wherein n is more than or equal to 2; step S40 includes:

step S41, pumping the intermediate-stage flash evaporation crystal slurry at the temperature of 50-70 ℃ into a final-stage flash evaporation crystallizer for vacuum flash evaporation, and introducing the obtained flash evaporation steam into a first final-stage mixing condenser for mixing and condensing with cooling water;

step S42, extracting the uncondensed flash steam and the uncondensed gas in the first final stage mixing condenser to a second final stage mixing condenser by using the high-pressure steam injected in the first steam ejector, and mixing and condensing the flash steam and the cooling water in the second final stage mixing condenser;

step S43, if n is 2, extracting the uncondensed flash steam and the uncondensed gas in the second final-stage mixing condenser by using a vacuum pump; if n is more than 2, extracting the uncondensed flash steam and the uncondensed gas in the second final-stage mixing condenser to the next final-stage mixing condenser by using the high-pressure steam injected in the second steam ejector, mixing and condensing the flash steam and the cooling water in the next final-stage mixing condenser, extracting the mixture in sequence until the last final-stage mixing condenser, and extracting the uncondensed flash steam and the uncondensed gas in the last final-stage mixing condenser by using a vacuum pump;

and S44, obtaining a final-stage vacuum degree of 85-95 kpa in the final-stage flash crystallizer under the coupling and extraction action of each final-stage mixing condenser, each steam ejector and a vacuum pump, and obtaining final-stage flash crystal mush at 30-50 ℃ after vacuum flash evaporation of intermediate-stage flash crystal mush under the final-stage vacuum degree.

In the embodiment, the high-pressure steam pressure is 0.4-1.2 MPa; the flash steam is mixed and condensed with cooling water in each final-stage mixing condenser and then is introduced into the liquid seal pool.

In one possible implementation, step S20 includes:

pumping the potassium-rich mother liquor at the temperature of 90-120 ℃ into a primary flash crystallizer for vacuum flash evaporation;

introducing flash steam in the primary flash crystallizer into a primary mixed condenser to be mixed and condensed with cooling water, and introducing mixed condensed water into a liquid seal pool;

and the temperature difference between the primary mixed condenser and the primary flash crystallizer forms saturated steam pressure difference, so that a primary vacuum degree of 30-70 kpa is obtained in the primary flash crystallizer, and further, a primary flash crystal slurry at 70-90 ℃ is obtained after the potassium-rich mother liquor is subjected to vacuum flash evaporation.

In one possible implementation, step S30 includes:

pumping the primary flash evaporation crystal slurry at the temperature of 70-90 ℃ into an intermediate flash evaporation crystallizer for vacuum flash evaporation;

introducing flash steam in the intermediate-stage flash crystallizer into an intermediate-stage mixing condenser to be mixed and condensed with cooling water, and introducing mixed condensed water into a liquid seal pool;

and the temperature difference between the intermediate-stage mixing condenser and the intermediate-stage flash crystallizer forms saturated steam pressure difference, so that the intermediate-stage vacuum degree of 70-85 kpa is obtained in the intermediate-stage flash crystallizer, and the intermediate-stage flash crystal slurry at 50-70 ℃ is obtained after the first-stage flash crystal slurry is subjected to vacuum flash evaporation.

In some embodiments, in steps S20 to S40, the first-stage flash slurry and the intermediate-stage flash slurry with solid content of more than or equal to 10% are directly transferred to the thickener, the first-stage flash slurry with solid content of less than 10% is transferred to the intermediate-stage flash crystallizer, and the intermediate-stage flash slurry with solid content of less than 10% is transferred to the final-stage flash crystallizer.

Specifically, the temperature of the cooling water is less than 36 ℃.

Further, the steps S20 to S40 further include: and periodically introducing cleaning water into the primary flash crystallizer, the intermediate flash crystallizer and the final flash crystallizer.

Illustratively, the first-stage flash crystallizer, the middle-stage flash crystallizer and the last-stage flash crystallizer are shielding crystallizers.

The method for extracting the potassium salt from the waste incineration fly ash water washing liquid has the beneficial effects that: compared with the prior art, the method for extracting potassium salt from the waste incineration fly ash water washing liquid is characterized in that the potassium-rich mother liquid obtained after sodium chloride crystallization is separated from the waste incineration fly ash water washing liquid through evaporation crystallization is subjected to physical property, the temperature of flash steam and cooling water in a mixing condenser is reduced after mixing and condensation, so that saturated steam pressure difference is generated between the mixing condenser and a flash crystallizer, the vacuum degree is formed in the flash crystallizer, the flash evaporation effect is generated on the potassium-rich mother liquid higher than 70-90 ℃ under the first vacuum degree, the temperature of the first flash evaporation crystal mush obtained after vacuum flash evaporation in the first flash crystallizer is reduced to 70-90 ℃, similarly, the flash evaporation effect is generated on the first flash evaporation crystal mush higher than 50-70 ℃ under the intermediate vacuum degree, the temperature of the intermediate flash evaporation crystal mush obtained after vacuum flash evaporation in the intermediate flash crystallizer is reduced to 50-70 ℃, the vacuum pump and the steam ejector are utilized to perform coupling extraction on uncondensed flash steam and uncondensed gas in the final-stage mixing condenser, so that a higher final-stage vacuum degree can be obtained in the final-stage flash crystallizer, the intermediate-stage flash crystal slurry generates a flash evaporation effect at 30-50 ℃, the temperature of the finally obtained final-stage flash crystal slurry is reduced to 30-50 ℃, and a potassium chloride salt product can be obtained after the final-stage flash crystal slurry is thickened and centrifugally dried; because the cooling process of the potassium-rich mother liquor adopts a mode of gradually improving the vacuum degree, compared with a mode of directly cooling in a cooling kettle to a large extent, the energy consumption can be greatly reduced, and in the whole process, the potassium-rich mother liquor realizes the crystallization and precipitation of potassium chloride by utilizing a vacuum cooling mode in a system of the potassium-rich mother liquor, so that no heat exchange surface exists, and the wall-forming phenomenon in the potassium salt extraction process of the potassium-rich mother liquor through cooling crystallization can be naturally avoided, thereby ensuring the production continuity and improving the production efficiency.

Drawings

FIG. 1 is a schematic diagram of a method for extracting potassium salt from waste incineration fly ash water washing liquid according to an embodiment of the present invention.

In the figure: 100. a multi-effect crystallizer or MVR crystallizer; 201. a primary flash crystallizer; 202. a middle stage flash crystallizer; 203. a last stage flash crystallizer; 301. a first-stage mixing condenser; 302. an intermediate stage mixing condenser; 303. a final stage mixing condenser; 400. a steam ejector; 401. a high pressure steam main; 500. a vacuum pump; 600. a thickener; 700. a liquid seal pool; 701. a circulating cooling water line; 800. and cleaning the pipeline.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Referring to fig. 1, a method for extracting potassium salt from a waste incineration fly ash water washing solution according to the present invention will now be described. The method for extracting the potassium salt from the waste incineration fly ash water washing liquid comprises the following steps:

step S10, separating sodium chloride crystals in the extraction water washing liquid through a multi-effect crystallizer or MVR crystallizer 100 to obtain potassium-rich mother liquid at the temperature of 90-120 ℃;

step S20, pumping the potassium-rich mother liquor at the temperature of 90-120 ℃ into a primary flash crystallizer 201 for vacuum flash evaporation, introducing the obtained flash steam into a primary mixed condenser 301 for mixing and condensing with cooling water, so as to promote the primary flash crystallizer 201 to obtain a primary vacuum degree, and carrying out vacuum flash evaporation on the potassium-rich mother liquor at the primary vacuum degree to obtain primary flash crystal slurry at the temperature of 70-90 ℃;

step S30, pumping the primary flash evaporation crystal mush at the temperature of 70-90 ℃ into the intermediate stage flash evaporation crystallizer 202 for vacuum flash evaporation, introducing the obtained flash evaporation steam into the intermediate stage mixed condenser 302 for mixing and condensing with cooling water, so that the intermediate stage flash evaporation crystallizer 202 is promoted to obtain an intermediate stage vacuum degree higher than the primary vacuum degree, and the primary flash evaporation crystal mush is subjected to vacuum flash evaporation at the intermediate stage vacuum degree to obtain the intermediate stage flash evaporation crystal mush at the temperature of 50-70 ℃;

step S40, pumping the intermediate-stage flash evaporation crystal mush at the temperature of 50-70 ℃ into a final-stage flash evaporation crystallizer 203 for vacuum flash evaporation, introducing the obtained flash evaporation steam into a final-stage mixed condenser 303 to mix and condense with cooling water, and pumping out the uncondensed flash evaporation steam and non-condensable gas in the final-stage mixed condenser 303 by using a vacuum pump 500 and a steam ejector 400 to promote the final-stage vacuum degree higher than the intermediate-stage vacuum degree to be obtained in the final-stage flash evaporation crystallizer 203, and carrying out vacuum flash evaporation on the intermediate-stage flash evaporation crystal mush at the final-stage vacuum degree to obtain final-stage flash evaporation crystal mush at the temperature of 30-50 ℃;

and step S50, thickening, centrifuging and drying the final-stage flash-evaporated crystal slurry to obtain potassium chloride crystals.

It should be noted that the process of separating and extracting sodium chloride crystals in the water washing solution by using the multi-effect crystallizer or the MVR crystallizer 100 is a mature prior art, and is not described herein again; the technological process of thickening, centrifuging and drying the potassium chloride crystal mush at about 40 ℃ (30-50 ℃) is also a mature prior art, specifically, the final-stage flash evaporation crystal mush is deposited by a thickener 600, then the mother liquor at the middle upper part of the thickener 600 is collected to a mother liquor tank (used for secondary extraction of sodium chloride crystals), the potassium chloride crystal mush deposited at the lower part is subjected to solid-liquid separation by a centrifuge to obtain a potassium chloride product with the water content lower than 5%, and the potassium chloride product with high purity can be further prepared by drying treatment, and the mature engineering technology is not described again; the cooling water introduced into each mixing condenser is supplied through a circulating cooling water line 701.

Compared with the prior art, the method for extracting potassium salt from the waste incineration fly ash water washing liquid provided by the embodiment has the advantages that aiming at the physical property characteristics of the potassium-rich mother liquid obtained after sodium chloride crystallization is separated from the waste incineration fly ash water washing liquid through evaporation crystallization, flash steam enters the mixing condenser to be mixed and condensed with cooling water, the temperature is reduced, so that saturated steam pressure difference is generated between the mixing condenser and the flash crystallizer, the vacuum degree is formed in the flash crystallizer, the flash evaporation effect is generated on the potassium-rich mother liquid higher than 70-90 ℃ under the first vacuum degree, the temperature of the first flash evaporation crystal slurry obtained after vacuum flash evaporation in the first-stage flash crystallizer 201 is reduced to 70-90 ℃, similarly, the flash evaporation effect is generated on the first flash evaporation crystal slurry higher than 50-70 ℃ under the intermediate vacuum degree, the temperature of the intermediate flash evaporation crystal slurry obtained after vacuum flash evaporation in the intermediate-stage flash crystallizer 202 is reduced to 50-70 ℃, due to the coupling and extraction effect of the vacuum pump 500 and the steam ejector 400 on the uncondensed flash steam and the uncondensed gas in the final-stage mixing condenser 303, a higher final-stage vacuum degree can be obtained in the final-stage flash crystallizer 203, so that the intermediate-stage flash crystal mush generates a flash evaporation effect at 30-50 ℃, the temperature of the finally obtained final-stage flash crystal mush is reduced to 30-50 ℃, and a potassium chloride salt product can be obtained after the final-stage flash crystal mush is thickened and centrifugally dried; because the cooling process of the potassium-rich mother liquor adopts a mode of gradually improving the vacuum degree, compared with a mode of directly cooling in a cooling kettle to a large extent, the energy consumption can be greatly reduced, and in the whole process, the potassium-rich mother liquor realizes the crystallization and precipitation of potassium chloride by utilizing a vacuum cooling mode in a system of the potassium-rich mother liquor, so that no heat exchange surface exists, and the wall-forming phenomenon in the potassium salt extraction process of the potassium-rich mother liquor through cooling crystallization can be naturally avoided, thereby ensuring the production continuity and improving the production efficiency.

In one possible implementation, referring to FIG. 1, the final mixing condenser 303 has n, and the steam ejector 400 has n-1, where n ≧ 2; step S40 includes:

step S41, pumping the intermediate-stage flash evaporation crystal slurry at the temperature of 50-70 ℃ into a final-stage flash evaporation crystallizer 203 for vacuum flash evaporation, and introducing the obtained flash evaporation steam into a first final-stage mixing condenser 303 for mixing and condensing with cooling water;

step S42, extracting the uncondensed flash steam and the uncondensed gas in the first final stage mixing condenser 303 to the second final stage mixing condenser 303 by using the high-pressure steam injected in the first steam injector 400, and mixing and condensing the flash steam and the cooling water in the second final stage mixing condenser 303;

in step S43, if n is 2, the vacuum pump 500 is used to remove the uncondensed flash steam and the uncondensed gas in the second final-stage mixing condenser 303; if n is more than 2, the high-pressure steam injected in the second steam injector 400 is utilized to pump the uncondensed flash steam and the uncondensed gas in the second final-stage mixing condenser 303 to the next final-stage mixing condenser 303, so that the flash steam and the cooling water in the next final-stage mixing condenser 303 are mixed and condensed, and after the flash steam and the uncondensed gas in the last final-stage mixing condenser 303 are pumped out in sequence until the last final-stage mixing condenser 303 is reached, the vacuum pump 500 pumps the uncondensed flash steam and the uncondensed gas in the last final-stage mixing condenser 303 out;

and step S44, obtaining a final-stage vacuum degree of 85-95 kpa in the final-stage flash crystallizer 203 under the coupling and extraction action of each final-stage mixing condenser 303, each steam ejector 400 and the vacuum pump 500, and obtaining final-stage flash crystal slurry at 30-50 ℃ after vacuum flash evaporation of the intermediate-stage flash crystal slurry under the final-stage vacuum degree.

The specific working principle of the process is as follows: the method comprises the following steps that (1) intermediate-stage flash evaporation crystal slurry at 50-70 ℃ enters a final-stage flash evaporation crystallizer 203 to be subjected to vacuum flash evaporation in a vacuum environment, flash evaporation steam enters a first final-stage mixing condenser 303 to be mixed and condensed with cooling water and then is temporarily retained and discharged, wherein the flash evaporation steam enters from the bottom of the final-stage mixing condenser 303, the cooling water passes through the final-stage mixing condenser 303 in an up-down and down-down mode, so that mixed heat exchange and condensation of the flash evaporation steam are realized in a counter-current process with the cooling water, high-pressure steam (provided by a high-pressure steam header pipe 401) sprayed by a first steam sprayer 400 is sucked into a chamber to generate strong negative pressure, and thus flash evaporation steam and non-condensable gas which are not subjected to mixed and condensation in the first final-stage mixing condenser 303 are pumped out to a second final-stage mixing condenser 303;

the flash steam and the cooling water entering the second final-stage mixing condenser 303 are mixed and condensed in a counter-current manner and are discharged after being temporarily retained, the high-pressure steam (provided by a high-pressure steam header pipe 401) injected by the second steam ejector 400 causes the high-pressure steam to be sucked into a chamber to generate strong negative pressure, so that the flash steam and the non-condensable gas which are not mixed and condensed in the second final-stage mixing condenser 303 are sucked to the third final-stage mixing condenser 303 (it should be noted here that the number of the final-stage mixing condensers 303 and the steam ejectors 400 is related to the final-stage vacuum value and the energy consumption which are finally required to be obtained, the higher the number of the final-stage vacuum degrees is, the corresponding energy consumption is higher, but the equipment cost is also considered here, and therefore, three final-stage mixing condensers 303 and two steam ejectors 400 which are relatively high in cost performance are selected here);

the flash steam and cooling water entering the third final-stage mixing condenser 303 are subjected to countercurrent mixing condensation and are discharged after being temporarily retained, and the flash steam (extremely small amount) and non-condensable gas which are not obtained by mixing condensation in the third final-stage mixing condenser 303 are extracted and discharged outside by using a vacuum pump 500 (particularly a water ring vacuum pump 500) connected to the exhaust end of the third final-stage mixing condenser 303;

because the final stage vacuum degree condition higher than the intermediate stage vacuum degree is difficult to achieve simply by the vacuum pump 500 or the saturated vapor pressure difference between the mixing condenser and the flash crystallizer, the vacuum flash evaporation condition with the final stage vacuum degree of 85-95 kpa can be obtained in the final stage flash crystallizer 203 by selecting and utilizing the combined coupling effect of the three final stage mixing condensers 303, the two vapor ejectors 400 and the vacuum pump 500, and the temperature of the final stage flash evaporation crystal slurry obtained after the final stage flash evaporation crystal slurry is subjected to vacuum flash evaporation in the final stage flash crystallizer 203 is reduced to 30-50 ℃ due to the fact that the temperature of the final stage flash evaporation crystal slurry is higher than that of the original intermediate stage flash evaporation crystal slurry due to the fact that the temperature of the final stage flash evaporation crystal slurry is 50-70 ℃, compared with a mode of simply adopting the vacuum pump 500 or the saturated vapor pressure difference to generate the vacuum degree, the vacuum degree can be achieved is higher, and the energy consumption is lower.

In some embodiments, referring to fig. 1, the high pressure steam pressure is 0.4 to 1.2Mpa, and the flash steam is mixed with cooling water and condensed in each final-stage mixing condenser 303 and then introduced into the liquid seal tank 700. The specific required high-pressure steam pressure is related to the final stage vacuum degree required by the final stage flash crystallizer 203, the higher the high-pressure steam pressure is, the higher the obtained final stage vacuum degree is, and the specific requirement is met by adopting the high-pressure steam pressure of 0.6MPa when the final stage flash crystallizer 203 needs the vacuum degree of 90kpa in the flash process; in addition, the liquid seal pool 700 should be located below each mixing condenser to ensure that the height difference between the liquid level in the liquid seal pool 700 and the liquid level in each mixing condenser is kept about ten meters, the bottom drainage end of each mixing condenser is connected with a pipeline and is introduced below the liquid level of the liquid seal pool 700, on one hand, the liquid seal pool 700 can be used for forming air-tight seal on the whole system to ensure the vacuum degree of the system, and on the other hand, the pressure generated by the height difference between the liquid levels can be used for preventing the water in the liquid seal pool 700 from flowing back under the action of atmospheric pressure.

In one possible implementation, referring to fig. 1, step S20 includes: pumping the potassium-rich mother liquor at the temperature of 90-120 ℃ into a primary flash crystallizer 201 for vacuum flash evaporation; introducing flash steam in the primary flash crystallizer 201 into a primary mixed condenser 301 to be mixed and condensed with cooling water, and introducing mixed condensed water into a liquid seal pool 700; the temperature difference between the primary mixing condenser 301 and the primary flash crystallizer 201 forms a saturated steam pressure difference, so that a primary vacuum degree of 30-70 kpa is obtained inside the primary flash crystallizer 201, and further, a primary flash crystal slurry of 70-90 ℃ is obtained after the potassium-rich mother liquor is subjected to vacuum flash evaporation.

The specific working principle of the process is as follows: pumping the potassium-rich mother liquor at 90-120 ℃ into the primary flash crystallizer 201 to carry out vacuum flash evaporation to form flash steam, feeding the flash steam into the primary mixing condenser 301 from the top position of the primary mixing condenser 301, flows with the cooling water of upper, lower and lower rows in the first-stage mixing condenser 301 in parallel, is mixed and condensed in the lower process and then is discharged into the liquid seal tank 700, due to the temperature difference between the primary hybrid condenser 301 and the primary flash crystallizer 201, and the temperature difference can enable a saturated steam pressure difference to be formed between the primary mixing condenser 301 and the primary flash crystallizer 201, the saturated steam pressure difference promotes the interior of the primary flash crystallizer 201 to form a primary vacuum degree of 30-70 kpa, because the higher the vacuum degree is, the lower the flash evaporation temperature is, the temperature of the first-stage flash evaporation crystal slurry obtained after the potassium-rich mother liquor is subjected to vacuum flash evaporation in the first-stage flash evaporation crystallizer 201 is reduced to 70-90 ℃ due to the fact that the temperature of 90-120 ℃ of the original potassium-rich mother liquor is reduced.

In one possible implementation, referring to fig. 1, step S30 includes: pumping the primary flash evaporation crystal slurry at the temperature of 70-90 ℃ into an intermediate flash evaporation crystallizer 202 for vacuum flash evaporation; introducing the flash steam in the intermediate-stage flash crystallizer 202 into an intermediate-stage mixing condenser 302 to be mixed and condensed with cooling water, and introducing the mixed condensed water into a liquid seal pool 700; the temperature difference between the intermediate-stage mixing condenser 302 and the intermediate-stage flash crystallizer 202 forms a saturated steam pressure difference, so that the intermediate-stage vacuum degree of 70-85 kpa is obtained in the intermediate-stage flash crystallizer 202, and the intermediate-stage flash crystal slurry at 50-70 ℃ is obtained after the first-stage flash crystal slurry is subjected to vacuum flash evaporation.

The specific working principle of the process is as follows: pumping the primary flash evaporation crystal slurry at the temperature of 70-90 ℃ into the intermediate-stage flash evaporation crystallizer 202 for vacuum flash evaporation to form flash evaporation steam, wherein the flash evaporation steam enters the intermediate-stage mixing condenser 302 from the top position of the intermediate-stage mixing condenser 302, the cooling water flows in parallel with the upper and lower rows of cooling water in the intermediate-stage mixing condenser 302, is mixed and condensed in the lower process and then is discharged into the liquid seal tank 700, because of the temperature differential between the mid-stage hybrid condenser 302 and the mid-stage flash crystallizer 202, and this temperature differential enables a saturated vapor pressure differential to develop between the mid-stage hybrid condenser 302 and the mid-stage flash crystallizer 202, the pressure difference of the saturated steam promotes the interior of the intermediate-stage flash crystallizer 202 to form an intermediate-stage vacuum degree of 70-85 kpa, because the higher the vacuum degree is, the lower the flash evaporation temperature is, the temperature of the intermediate-stage flash evaporation crystal slurry obtained after the potassium-rich mother liquor is subjected to vacuum flash evaporation in the intermediate-stage flash evaporation crystallizer 202 is reduced to 50-70 ℃ due to the temperature of 70-90 ℃ of the original primary flash evaporation crystal slurry.

In some embodiments, referring to fig. 1, in steps S20 to S40, the first-stage flash slurry and the intermediate-stage flash slurry with solid content of more than or equal to 10% are directly transferred to the thickener 600, the first-stage flash slurry with solid content of less than 10% is transferred to the intermediate-stage flash crystallizer 202, and the intermediate-stage flash slurry with solid content of less than 10% is transferred to the final-stage flash crystallizer 203. Because the flash evaporation crystal mush discharged by the flash evaporation crystallizer of each stage is separated out along with the potassium chloride crystals, the crystal mush with the solid content of more than or equal to 10 percent can be directly discharged into the thickener 600, and the crystal mush part with the lower solid content is discharged into the flash evaporation crystallizer of the next stage for further cooling and crystallization, thereby improving the production efficiency and avoiding the phenomenon of energy consumption waste caused by repeated flash evaporation of the separated potassium chloride crystals.

Specifically, the temperature of the cooling water is less than 36 ℃. In the actual production process, cooling water with the temperature of about 30 ℃ can be preferably adopted, namely, the cooling effect can be ensured, and the power consumption of equipment for circularly cooling the cooling water can be reduced to a reasonable range.

Further, referring to fig. 1, the steps S20 to S40 further include: and periodically introducing cleaning water into the first-stage flash crystallizer 201, the middle-stage flash crystallizer 202 and the last-stage flash crystallizer 203. Generally, in the case of continuous operation, the evaporation condition inside the flash crystallizer deteriorates in a cycle of three to six months, and at this time, the flash crystallizer is scrubbed and cleaned by introducing cleaning water (supplied from a cleaning line 800) into the flash crystallizer, so that the evaporation environment is ensured, and the product quality is ensured.

For example, referring to fig. 1, the first-stage flash crystallizer 201, the middle-stage flash crystallizer 202, and the last-stage flash crystallizer 203 are shielding crystallizers. The shielded Crystallizer is a DTB Crystallizer (abbreviation of Drabt Tube Babbed crystallized), the outside of the DTB Crystallizer is provided with a circulating pump which can promote the flash evaporation crystal slurry to circulate between shielding plates in the DTB Crystallizer, so that potassium chloride crystals in the flash evaporation crystal slurry continuously circulate and continue to grow, new potassium chloride crystals are formed, the new potassium chloride crystals can also circulate in the flash evaporation Crystallizer and continue to grow, large-size potassium chloride crystals are deposited and collected to salt feet at the bottom of the potassium chloride crystals to be discharged outside, and the obtained large-size potassium chloride crystals can improve the quality of potassium chloride products.

The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.