System for recovering sodium sulfate, sodium carbonate and glaserite in alkali ash and removing chloride ions

Abstract

The utility model provides a system for recovering sodium sulfate, sodium carbonate and glaserite in alkali ash and removing chloride ions. The system comprises an alkali ash dissolving unit, a main crystallization unit, a glaserite crystallization unit, a nanofiltration unit and other elements. By means of the system, on one hand, sodium sulfate and sodium carbonate in the alkali ash solution can be extracted, glaserite can be extracted at the same time, chloride ions in the solution are removed at the same time, and the discharge amount of mother liquor is reduced.

Description

Technical Field

[0001] This application relates to the field of papermaking ash treatment, specifically to a system for recovering sodium sulfate, sodium carbonate, and potassium sulfate from ash and removing chloride ions. Background Technology

[0002] Alkali ash is the ash collected by dust collectors in the combustion section of the alkali furnace during the black liquor combustion process in the papermaking industry. Alkali recovery in the papermaking industry is a key environmental protection and energy-saving project promoted by the state. Alkali ash mainly contains sodium, potassium, sulfate, carbonate, and chloride ions. The recovery of sodium sulfate and sodium carbonate from alkali ash is a crucial component of alkali recovery in the papermaking industry. The recovery of process elements and other useful substances from alkali ash is of paramount importance to the sustainable development of the papermaking industry.

[0003] If non-processing elements from papermaking are not removed during the recycling of alkali ash, potassium and chloride ions will accumulate in the alkali furnace. Excessive levels of these non-processing elements will lower the adhesion temperature of the alkali ash, increase its adhesiveness, leading to ash accumulation, scaling, and a decrease in heat transfer coefficient in the alkali furnace, thus reducing furnace efficiency and capacity. Chloride ions will also accelerate the corrosion of the pipe walls.

[0004] In existing technologies, sodium sulfate and sodium carbonate are usually recovered from soda ash through simple evaporation and crystallization. A considerable amount of sodium sulfate and sodium carbonate are discharged from the system along with the mother liquor rich in potassium and chloride ions. This results in low recovery rates of sodium sulfate and sodium carbonate, and the high-value potassium ions are not recovered. At the same time, it also causes a large amount of mother liquor to be discharged.

[0005] Current research on soda ash recovery mainly focuses on the recovery of sodium sulfate and sodium carbonate, and does not provide an effective method for potassium recovery.

[0006] Potassium is actually an element with high economic value, used as potash fertilizer, but in current soda ash treatment, it is treated or discharged as a "pollutant," which not only pollutes the environment but also wastes resources. Furthermore, due to the limitations of potassium sulfate on crystallization endpoints, existing technologies typically have low recovery rates for sodium sulfate and sodium carbonate, resulting in large volumes of mother liquor discharge, loss of process elements, and the need for further treatment of large amounts of saturated brine.

[0007] Therefore, in order to address the shortcomings of existing technologies, it is of great significance to develop a system that can improve the recovery rate of sodium sulfate and sodium carbonate in soda ash, and recover potassium ions while removing potassium chloride ions in the soda ash recovery cycle, thereby reducing the amount of salt discharged from the soda ash recovery. Utility Model Content

[0008] This application provides a system for recovering sodium sulfate, sodium carbonate, and potassium sulfate from soda ash and removing chloride ions. The system includes a soda ash dissolution unit, a main crystallization unit, a potassium sulfate crystallization unit, and a nanofiltration unit. The soda ash dissolution unit dissolves the soda ash; the main crystallization unit extracts sodium sulfate and sodium carbonate crystals; the potassium sulfate crystallization unit extracts potassium sulfate crystals; and the nanofiltration unit separates sulfate and carbonate ions from chloride ions. The soda ash dissolution unit is connected to the main crystallization unit via pipeline, the main crystallization unit is connected to the potassium sulfate crystallization unit via pipeline, the potassium sulfate crystallization unit is connected to the nanofiltration unit via pipeline, and the nanofiltration unit is connected to the soda ash dissolution unit via pipeline.

[0009] In one embodiment, the alkali dissolving unit includes an alkali dissolving tank and an alkali dissolving agitator, with the agitator disposed inside the alkali dissolving tank.

[0010] The main crystallization unit includes a main crystallization device, a main crystallization dehydration device, a main crystallization filtrate stirring device, and a first condensate tank. The main crystallization device comprises a main crystallizer, a main crystallization circulation pump, a main crystallization heat exchanger, and a steam compression device. The main crystallizer, main crystallization circulation pump, and main crystallization heat exchanger are sequentially connected via pipelines. The steam outlet of the main crystallizer is connected to the steam compression device via a pipeline; the outlet of the steam compression device is connected to the steam inlet of the main crystallization heat exchanger; the first condensate outlet of the main crystallization heat exchanger is connected to the first condensate tank via a pipeline; the first mother liquor outlet of the main crystallizer is connected to the potassium sulfate crystallization unit via a pipeline; the discharge port of the main crystallizer is connected to the main crystallization dehydration device via a pipeline; the first filtrate outlet of the main crystallization dehydration device is connected to the main crystallization filtrate stirring device via a pipeline; the outlet of the main crystallization filtrate stirring device is connected to the main crystallization device; and the outlet of the alkali dissolution unit is connected to the main crystallizer via a pipeline.

[0011] In one embodiment, the potassium sulfate crystallization unit includes a potassium sulfate crystallization device, a potassium sulfate dehydration device, a potassium sulfate filtrate stirring device, and a second condensate tank. The potassium sulfate crystallization device includes a potassium sulfate crystallizer, a potassium sulfate circulation pump, a potassium sulfate heat exchanger, a condenser, and a vacuum device. The potassium sulfate crystallizer, circulation pump, and heat exchanger are sequentially connected via pipelines. The steam outlet of the potassium sulfate crystallizer is sequentially connected to the condenser and vacuum device via pipelines, and heating steam is connected to the potassium sulfate heat exchanger via pipelines. The second condensate outlet of the potassium sulfate heat exchanger is connected to the second condensate tank via a pipeline. The discharge port of the potassium sulfate crystallizer is connected to the potassium sulfate dehydration device via a pipeline. The second filtrate outlet of the potassium sulfate dehydration device is connected to the potassium sulfate filtrate stirring device via a pipeline. The outlet of the potassium sulfate filtrate stirring device is connected to the potassium sulfate crystallization device via a pipeline. The first mother liquor outlet of the main crystallizer is connected to the potassium sulfate crystallization device via a pipeline.

[0012] In one embodiment, the nanofiltration unit includes a pretreatment device, a dilution device, and a nanofiltration apparatus. The second mother liquor outlet of the potassium sulfate crystallizer is connected to the inlet of the pretreatment device via a pipeline. The dilution device includes a dilution water tank and a dilution water tank agitator, with the agitator disposed within the dilution water tank. The nanofiltration apparatus includes a nanofiltration feed pump, a nanofiltration security filter, a nanofiltration high-pressure pump, and a nanofiltration unit. The outlet of the pretreatment device is sequentially connected via pipeline to the dilution water tank, the nanofiltration feed pump, the nanofiltration security filter, the nanofiltration high-pressure pump, and the nanofiltration unit. The nanofiltration concentrate outlet of the nanofiltration unit is connected via pipeline to the inlet of the ash dissolution unit.

[0013] In one embodiment, the system further includes a reverse osmosis unit for concentrating the nanofiltration permeate from the nanofiltration unit, the reverse osmosis unit being connected to the nanofiltration unit via a pipeline.

[0014] In one embodiment, the reverse osmosis unit includes a reverse osmosis feed tank and a reverse osmosis device, wherein the reverse osmosis device includes a reverse osmosis feed pump, a reverse osmosis security filter, a reverse osmosis high-pressure pump, and a reverse osmosis apparatus. The reverse osmosis feed tank, the reverse osmosis feed pump, the reverse osmosis security filter, the reverse osmosis high-pressure pump, and the reverse osmosis apparatus are connected in sequence via pipelines, and the nanofiltration permeate port of the nanofiltration apparatus is connected to the reverse osmosis feed tank via a pipeline.

[0015] In one embodiment, the reverse osmosis permeate outlet of the reverse osmosis unit is connected to the dilution unit via a pipeline.

[0016] In one embodiment, the second mother liquor outlet of the potassium sulfate crystallizer is also connected to the inlet of the main crystallization filtrate stirring device via a pipeline.

[0017] The beneficial effects of this application are as follows:

[0018] This application achieves the technical effect of simultaneously extracting sodium sulfate, sodium carbonate, and potassium sulfate from soda ash by combining a main crystallization unit with a potassium sulfate crystallization unit. A nanofiltration unit is introduced into the system to remove chloride ions from the soda ash while extracting sodium sulfate, sodium carbonate, and potassium sulfate. A reverse osmosis unit is used to concentrate the chlorinated permeate, and the resulting demineralized water can be used as dilution water, maximizing water resource utilization and reducing the liquid discharge from the process and system. Furthermore, the system designed in this application can improve the extraction rates of sodium sulfate, sodium carbonate, and potassium sulfate from soda ash. The condensate and demineralized water generated in each unit can be returned to the system as dilution water, maximizing the use of limited resources, conserving water resources, and contributing to environmental protection and sustainable social development. Attached Figure Description

[0019] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0020] Figure 1 This is a flowchart of a method according to an embodiment of this application;

[0021] Figure 2 This is a process flow diagram of an embodiment of this application;

[0022] Figure 3 This is a process flow diagram of another embodiment of this application;

[0023] Figure 4 This is a schematic diagram of the system structure according to an embodiment of this application;

[0024] Figure 5 This is a schematic diagram of the system architecture of another embodiment of this application.

[0025] Explanation of reference numerals in the attached figures:

[0026] 1. Alkali dissolving unit; 101. Alkali dissolving tank; 102. Alkali dissolving agitator;

[0027] 2. Main crystallization unit; 201. Main crystallization device; 2011. Main crystallizer; 2012. Main crystallization circulation pump; 2013. Main crystallization heat exchanger; 2014. Steam compression device; 202. Main crystallization dehydration device; 203. Main crystallization filtrate stirring device; 2031. Main crystallization filtrate tank; 2032. Main crystallization filtrate agitator; 204. First condensate tank; 205. Heat exchanger; 206. Main crystallization feed pump; 207. First mother liquor pump; 208. First condensate pump; 209. Main crystallization filtrate pump;

[0028] 3. Potassium sulfate crystallization unit; 301. Potassium sulfate crystallization device; 3011. Potassium sulfate crystallizer; 3012. Potassium sulfate circulating pump; 3013. Potassium sulfate heat exchanger; 3014. Condenser; 3015. Vacuum device; 302. Thickening device; 3021. Thickener; 3022. Thickener scraper; 303. Potassium sulfate dehydration device; 304. Potassium sulfate filtrate stirring device; 3041. Potassium sulfate filtrate tank; 3042. Potassium sulfate filtrate agitator; 305. Second condensate tank; 306. Discharge pump; 307. Second mother liquor pump; 308. Second condensate pump; 309. Potassium sulfate filtrate pump.

[0029] 4. Nanofiltration unit; 401. Pretreatment device; 402. Dilution device; 4021. Dilution water tank; 4022. Dilution water tank agitator; 403. Nanofiltration equipment; 4031. Nanofiltration inlet pump; 4032. Nanofiltration security filter; 4033. Nanofiltration high-pressure pump; 4034. Nanofiltration unit;

[0030] 5. Reverse osmosis unit; 501. Reverse osmosis feed tank; 502. Reverse osmosis equipment; 5021. Reverse osmosis feed pump; 5022. Reverse osmosis security filter; 5023. Reverse osmosis high-pressure pump; 5024. Reverse osmosis device. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this application.

[0032] It should also be noted that, for ease of description, the accompanying drawings show only the parts relevant to this application, not the entire structure. Throughout this specification, the same or similar reference numerals represent the same or similar structures, elements, or processes. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0033] The terms “first” and “second” as used in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as “first” and “second” may explicitly or implicitly include one or more of that feature. Furthermore, the term “comprising” and any derivative thereof are intended to cover non-exclusive inclusion.

[0034] Unless otherwise defined, in this disclosure, when an element is referred to as being “connected to / fixed to” another element, it may be directly connected to / fixed to the other element or may be interposed in an intermediate element.

[0035] like Figure 1 and Figure 2 , Figure 1 A flowchart of a method according to an embodiment of this application is shown. Figure 2 A process flow diagram of one embodiment is shown. This embodiment provides a process for recovering sodium sulfate, sodium carbonate, and potassium sulfate from soda ash while simultaneously removing chloride ions, specifically including the following steps.

[0036] S1, Soda Ash Dissolution: Soda ash is passed into the soda ash dissolution unit, and a solvent is used to dissolve the soda ash to obtain a soda ash solution. The solvent is demineralized water.

[0037] S2 involves thermal crystallization to separate sodium sulfate and sodium carbonate from the soda ash solution. The soda ash solution from S1 is passed into the main crystallization unit, where it is evaporated and concentrated. Soda sulfate and sodium carbonate crystals are then crystallized at a target crystallization temperature of 70-120°C, producing a first mother liquor and a first condensate. The sodium sulfate and sodium carbonate crystals, along with a portion of the first mother liquor, are separated into sodium sulfate and sodium carbonate crystals by the main crystallization dehydration unit within the main crystallization unit, producing a first filtrate. In this paper, the first mother liquor refers to the remaining solution after evaporation, concentration, and crystallization in the main crystallization unit. The first filtrate refers to the remaining solution after the sodium sulfate and sodium carbonate crystal slurry has been separated into sodium sulfate and sodium carbonate crystals by the main crystallization dehydration unit.

[0038] S3 involves cooling and crystallizing the potassium sulfate solution to separate it from the soda ash solution. The first mother liquor from S2 is passed into the potassium sulfate crystallization device within the potassium sulfate crystallization unit. Evaporation and concentration are carried out at 30-60°C, crystallizing potassium sulfate crystals and producing a second mother liquor and a second condensate. The potassium sulfate crystals, along with a portion of the second mother liquor, are separated from the potassium sulfate crystals by the potassium sulfate dehydration device within the potassium sulfate crystallization unit, producing a second filtrate. In this paper, the second mother liquor refers to the remaining solution after evaporation, concentration, and crystallization of the solution in the potassium sulfate device. The second filtrate refers to the remaining solution after the potassium sulfate crystal slurry has been separated from the potassium sulfate crystals by the potassium sulfate dehydration device.

[0039] In step S4, sulfate, carbonate, and chloride ions in the soda ash solution are separated. The second mother liquor generated in step S3 is pretreated to remove suspended solids and diluted to the target concentration before being passed into a nanofiltration unit. The nanofiltration unit separates monovalent and divalent ions from chloride ions in the second mother liquor, resulting in nanofiltration concentrate rich in sulfate and carbonate ions and nanofiltration permeate rich in chloride ions, thus achieving the removal of chloride ions from the soda ash solution.

[0040] In one embodiment, the target concentration for dilution is 1% to 10%.

[0041] S5, further separate sodium sulfate, sodium carbonate and potassium sulfate from the soda ash solution. The nanofiltration concentrate obtained in S4 is returned to the soda ash dissolution unit as a replenishment solution for the solvent in S1 to dissolve the soda ash. Steps S1-S5 are repeated to further extract sodium sulfate, sodium carbonate and potassium sulfate from the soda ash solution, thereby improving the extraction rate of sodium sulfate, sodium carbonate and potassium sulfate from the soda ash.

[0042] like Figure 3The diagram illustrates a process flow chart of another embodiment of this application. This embodiment includes the same steps as the embodiments described above, but also includes passing the nanofiltration permeate obtained in step S4 into a reverse osmosis unit for concentration, resulting in reverse osmosis permeate (demineralized water) and concentrated chlorine water. The reverse osmosis permeate is returned to the nanofiltration unit in step S4 to dilute the second mother liquor, while the concentrated chlorine water is discharged from the system. This process design maximizes water resource utilization while minimizing the amount of mother liquor discharged.

[0043] like Figure 2 and Figure 3 In one embodiment, the second mother liquor generated in S3, after being heated by heat exchange, is simultaneously returned to the main crystallization device in S2 to perform subsequent steps together with the solution in the main crystallization device. This process design aims to improve the extraction rates of sodium sulfate, sodium carbonate, and potassium sulfate from soda ash, while also increasing the chloride ion content of the discharged mother liquor.

[0044] like Figure 2 and Figure 3 As shown, in one embodiment, the first condensate obtained in S2 and the second condensate obtained in S3 are passed into the soda ash dissolving unit in S1 as replenishment of the solvent to dissolve the soda ash. This maximizes resource utilization while reducing the amount of liquid discharged from the system, which is beneficial for energy conservation and environmental protection.

[0045] In one embodiment, the first filtrate produced in S2 is returned to the main crystallization device in the main crystallization unit, where it undergoes S2-S5 together with the solution in the main crystallization device. The second filtrate produced in S3 is returned to the potassium sulfate crystallization device in the potassium sulfate crystallization unit, where it undergoes S3-S5 together with the solution in the potassium sulfate crystallization device. This arrangement maximizes the extraction of sodium sulfate, sodium carbonate, and potassium sulfate crystals from the soda ash solution while simultaneously reducing the discharge of mother liquor.

[0046] In one embodiment, before the potassium sulfate crystals enter the potassium sulfate dehydration unit along with the second mother liquor, the potassium sulfate crystals are first concentrated in a thickening device before entering the potassium sulfate dehydration unit. This arrangement can improve the stability of the potassium sulfate dehydration unit.

[0047] The sodium sulfate and sodium carbonate crystals obtained through the above process can be introduced into the black liquor concentration section of the paper mill along with the black liquor from papermaking. Sodium sulfide and alkali can be recovered through the black liquor concentration section, alkali furnace combustion section, and causticizing section of the paper mill. The recovered sodium sulfide and alkali can be used in the cooking section of the paper mill for plant fiber raw materials.

[0048] Potassium sulfate crystals are obtained through the above process and can ultimately be used as raw materials for the production of potassium sulfate fertilizer.

[0049] like Figure 4As shown, this application also provides a system for performing the above-described method. The system includes a soda ash dissolution unit 1, a main crystallization unit 2, a potassium sulfate crystallization unit 3, and a nanofiltration unit 4. The soda ash dissolution unit 1 is used to dissolve soda ash; the main crystallization unit 2 is used to extract sodium sulfate and sodium carbonate crystals; the potassium sulfate crystallization unit 3 is used to extract potassium sulfate crystals; and the nanofiltration unit 4 is used to separate sulfate and carbonate ions from chloride ions. The outlet of the soda ash dissolution unit 1 is connected to the main crystallization unit 2 via a pipeline; the first mother liquor outlet of the main crystallization unit 2 is connected to the potassium sulfate crystallization unit 3 via a pipeline; the second mother liquor outlet of the potassium sulfate crystallization unit 3 is connected to the nanofiltration unit 4 via a pipeline; and the nanofiltration concentrate outlet of the nanofiltration unit 4 is connected to the soda ash dissolution unit 1 via a pipeline.

[0050] Specifically, the alkali dissolving unit 1 includes an alkali dissolving tank 101 and an alkali dissolving stirrer 102, with the alkali dissolving stirrer 102 disposed inside the alkali dissolving tank 101.

[0051] The main crystallization unit 2 includes a main crystallization device 201, a main crystallization dehydration device 202, a main crystallization filtrate stirring device 203, and a first condensate tank 204. The main crystallization device 201 includes a main crystallizer 2011, a main crystallization circulation pump 2012, a main crystallization heat exchanger 2013, and a steam compression device 2014. The main crystallizer 2011, the main crystallization circulation pump 2012, and the main crystallization heat exchanger 2013 are sequentially connected via pipelines. The steam outlet of the main crystallizer 2011 is connected to the steam compression device 2014 via a pipeline, and the outlet of the steam compression device 2014 is connected to the steam inlet of the main crystallization heat exchanger 2013. The first condensate outlet of the main crystallizer heat exchanger 2013 is connected to the first condensate tank 204 via a pipeline. The first mother liquor outlet of the main crystallizer 2011 is connected to the potassium sulfate crystallization unit 3 via a pipeline through a first mother liquor pump 207. The outlet of the main crystallizer 2011 is connected to the main crystallization dehydration device 202 via a pipeline. The first filtrate outlet of the main crystallization dehydration device 202 is connected to the main crystallization filtrate stirring device 203 via a pipeline. The main crystallization filtrate stirring device 203 includes a main crystallization filtrate tank 2031 and a main crystallization filtrate stirrer 2032, which is disposed inside the main crystallization filtrate tank 2031. The outlet of the main crystallization filtrate stirring device 203 is connected to the main crystallization device 201 via a pipeline through the main crystallization filtrate pump 209. The outlet of the soda ash dissolving unit 1 is connected to the main crystallizer 2011 via a pipeline through the main crystallization feed pump 206.

[0052] In one embodiment, the outlet of the soda ash dissolving unit 1 is connected to the main crystallization filtrate stirring device 203 via a pipeline.

[0053] Further, the potassium sulfate crystallization unit 3 includes a potassium sulfate crystallization device 301, a potassium sulfate dehydration device 303, a potassium sulfate filtrate stirring device 304, and a second condensate tank 305. The potassium sulfate crystallization device 301 includes a potassium sulfate crystallizer 3011, a potassium sulfate circulation pump 3012, a potassium sulfate heat exchanger 3013, a condenser 3014, and a vacuum device 3015. The potassium sulfate crystallizer 3011, the potassium sulfate circulation pump 3012, and the potassium sulfate heat exchanger 3013 are sequentially connected via pipelines. The steam outlet of the potassium sulfate crystallizer 3011 is sequentially connected to the condenser 3014 and the vacuum device 3015 via pipelines, and heating steam is connected to the potassium sulfate heat exchanger 3013 via pipelines. The second condensate outlet of the potassium sulfate heat exchanger 3013 is connected to the second condensate tank 305 via a pipeline. The outlet of the potassium sulfate crystallizer 3011 is connected to the potassium sulfate dehydration device 303 via a pipeline and a discharge pump 306. The second filtrate outlet of the potassium sulfate dehydration device 303 is connected to the potassium sulfate filtrate stirring device 304 via a pipeline. The potassium sulfate filtrate stirring device 304 includes a potassium sulfate filtrate tank 3041 and a potassium sulfate filtrate stirrer 3042, which is located inside the potassium sulfate filtrate tank 3041. The outlet of the potassium sulfate filtrate stirring device is connected to the potassium sulfate crystallizer 301 via a pipeline and a potassium sulfate filtrate pump 309. The first mother liquor outlet of the main crystallizer 2011 is connected to the potassium sulfate crystallizer 301 via a pipeline and a first mother liquor pump 207.

[0054] In one embodiment, the potassium sulfate crystallization unit 3 further includes a thickening device 302. The outlet of the potassium sulfate crystallizer 3011 can be connected to the thickening device 302 via a pipeline and a discharge pump 306. Then, the thickening device 302 is connected to the potassium sulfate dewatering device 303 via a pipeline. The thickening device 302 includes a thickener 3021 and a thickening scraper 3022.

[0055] In one embodiment, the supernatant outlet of the thickening device 302 is also directly connected to the potassium sulfate filtrate stirring device 304 to concentrate the potassium sulfate crystal slurry in the thickener.

[0056] Further, the nanofiltration unit 4 includes a pretreatment device 401, a dilution device 402, and a nanofiltration apparatus 403. The second mother liquor outlet of the potassium sulfate crystallizer 3011 is connected to the inlet of the pretreatment device 401 via a pipeline and a second mother liquor pump 307. The dilution device 402 includes a dilution water tank 4021 and a dilution water tank agitator 4022, with the agitator 4022 housed within the dilution water tank 4021. The nanofiltration apparatus includes a nanofiltration inlet pump 4031, a nanofiltration security filter 4032, a nanofiltration high-pressure pump 4033, and a nanofiltration unit 4034. The outlet of the pretreatment device 401 is sequentially connected to the dilution water tank 4021, the nanofiltration inlet pump 4031, the nanofiltration security filter 4032, the nanofiltration high-pressure pump 4033, and the nanofiltration unit 4034 via pipelines. The nanofiltration concentrate outlet of the nanofiltration unit is connected to the inlet of the ash dissolution unit 1 via a pipeline.

[0057] like Figure 5 As shown, the system also includes a reverse osmosis unit 5, which is used to concentrate the nanofiltration permeate from the nanofiltration unit 4. The reverse osmosis unit is connected to the nanofiltration unit 4 via a pipeline. Specifically, the reverse osmosis unit 5 includes a reverse osmosis feed tank 501 and a reverse osmosis device 502. The reverse osmosis device 502 includes a reverse osmosis feed pump 5021, a reverse osmosis security filter 5022, a reverse osmosis high-pressure pump 5023, and a reverse osmosis unit 5024. The reverse osmosis feed tank 501, reverse osmosis feed pump 5021, reverse osmosis security filter 5022, reverse osmosis high-pressure pump 5023, and reverse osmosis unit 5024 are sequentially connected via pipelines. The nanofiltration permeate outlet of the nanofiltration unit 4034 is connected to the reverse osmosis feed tank 501 via a pipeline.

[0058] In one embodiment, the reverse osmosis permeate outlet of the reverse osmosis unit 5024 is connected to the dilution unit 402 via a pipeline.

[0059] In one embodiment, the outlet of the first condensate tank 204 is connected to the heat exchanger 205 and the ash dissolving tank 101 in sequence via a pipeline and a first condensate pump 208, and the outlet of the second condensate tank 305 is connected to the ash dissolving tank 101 via a pipeline and a second condensate pump 308.

[0060] In one embodiment, the second mother liquor outlet of the potassium sulfate crystallizer 3011 is also connected to the inlet of the main crystallization filtrate stirring device 203 via a pipeline through the second mother liquor pump 307.

[0061] This application also illustrates an embodiment, detailing the process proposed in this application for recovering sodium sulfate, sodium carbonate, and potassium sulfate from soda ash while simultaneously removing chloride ions, as follows:

[0062] A paper mill produces 300 tons of soda ash per day (12.5 tons per hour). The composition of this soda ash is as follows:

[0063] <![CDATA[Na2SO4]]> kg / h 7,672 <![CDATA[Na2CO3]]> kg / h 3,591 NaCl kg / h 340 <![CDATA[K2SO4]]> kg / h 599 <![CDATA[K2CO3]]> kg / h 298

[0064] Based on the above components, the content of each ion is calculated as follows:

[0065] <![CDATA[Na + ]]> kg / h 4177 <![CDATA[K + ]]> kg / h 437 <![CDATA[SO4 2- ]]> kg / h 5517 <![CDATA[CO3 2- ]]> kg / h 2162 <![CDATA[Cl - ]]> kg / h 206

[0066] First, alkali ash and deionized water are introduced into the alkali ash dissolving tank 101. At the same time, the alkali ash is stirred and dissolved using the alkali ash dissolving stirrer 102, and the concentration of the alkali ash solution is dissolved to 20% to 30%.

[0067] Then, using the main crystallization feed pump 206, the soda ash solution is pumped into the main crystallizer 2011 in the main crystallization device 201. The soda ash solution is evaporated and concentrated using the main crystallization circulation pump 2012, the main crystallization heat exchanger 2013 and the vapor compression device 2014, and sodium sulfate and sodium carbonate crystals are crystallized at a crystallization temperature of 100~110℃, generating a first mother liquor and a first condensate. The sodium sulfate and sodium carbonate crystals are passed into the main crystallization dehydration device 202 along with part of the first mother liquor. The sodium sulfate and sodium carbonate crystals are separated by the main crystallization dehydration device 202 and a first filtrate is generated. The first filtrate is passed into the main crystallization filtrate stirring device 203.

[0068] The first condensate generated by the main crystallizer heat exchanger 2013 flows into the first condensate tank 204 and is pumped into the heat exchanger 205 by the first condensate pump 208. After being cooled, it flows into the alkali ash dissolving tank 101 to dissolve alkali ash.

[0069] Next, the first mother liquor generated by the main crystallizer 2011 is pumped into the potassium sulfate crystallization device 301 in the potassium sulfate crystallization unit via the first mother liquor pump 207. Using the potassium sulfate crystallizer 3011, potassium sulfate circulation pump 3012, potassium sulfate heat exchanger 3013, condenser 3014, and vacuum device 3015, evaporation, concentration, and crystallization of potassium sulfate are carried out at 30-60°C, producing a second mother liquor and a second condensate. The potassium sulfate crystals, along with a portion of the second mother liquor, are passed into the thickening device 302 for concentration and then into the potassium sulfate dehydration device 303. The potassium sulfate crystals are separated in the dehydration device 303, producing a second filtrate, which is then passed into the potassium sulfate filtrate stirring device 304.

[0070] The second condensate generated by the potassium sulfate heat exchanger 3013 flows into the second condensate tank 305 and is pumped into the alkali ash dissolving tank 101 by the second condensate pump 308 for dissolving alkali ash.

[0071] Next, a portion of the second mother liquor is pumped through the second mother liquor pump 307 and heated by heat exchange with the first condensate through the heat exchanger 205 before being fed into the main crystallization filtrate stirring device 203. After mixing and stirring with the solution in the main crystallization filtrate stirring device 203, it is returned to the main crystallization device 201. After mixing with the solution in the main crystallization device 201, it is used together to perform subsequent steps to further extract sodium sulfate, sodium carbonate, and potassium sulfate from the soda ash solution, while further removing chloride ions. Meanwhile, the remaining second mother liquor is pumped into the pretreatment device 401 of the nanofiltration unit through the second mother liquor pump 307. The pretreatment device 401 removes suspended solids and then flows into the dilution tank 4021. At the same time, demineralized water is introduced into the dilution tank 4021 and diluted by the dilution tank agitator 4022. The diluted second mother liquor is then pumped into the nanofiltration security filter 4032 through the nanofiltration inlet pump 4031, and then into the nanofiltration device 4034 through the nanofiltration high-pressure pump 4033. The nanofiltration device separates monovalent and divalent ions, separating sulfate and carbonate ions from chloride ions, producing nanofiltration concentrate rich in sulfate and carbonate ions and nanofiltration permeate containing chloride ions.

[0072] The nanofiltration concentrate, rich in sulfate and carbonate ions, is returned to the soda ash dissolving tank 101 to dissolve the soda ash, thereby increasing the extraction rates of sodium sulfate, sodium carbonate, and potassium sulfate in the soda ash solution, and simultaneously increasing the concentration of chloride ions removed.

[0073] Finally, the chloride-containing nanofiltration permeate is further concentrated by the reverse osmosis unit 5 to produce reverse osmosis permeate, namely demineralized water and chloride-containing concentrate. The reverse osmosis permeate is returned to the dilution tank 4021 in the nanofiltration unit to dilute the second mother liquor, while the chloride-containing concentrate is discharged from the system, thus achieving the removal of chloride ions from the soda ash solution.

[0074] The parameters involved in this embodiment are shown in the table below.

[0075] project unit Soda Ash External reverse osmosis concentrate salinity Recovery rate <![CDATA[Na + ]]> kg / h 4177 110 97.37% <![CDATA[K + ]]> kg / h 437 101 76.94% <![CDATA[SO4 2- ]]> kg / h 5517 6 99.88% <![CDATA[CO3 2- ]]> kg / h 2162 45 97.92% <![CDATA[Cl - ]]> kg / h 206 203 Total kg / h 12500 466 96.27%

[0076] The data above shows that, after processing by this system for recovering and removing potassium chloride ions from alkali ash, a total of 12034 (12500-466) kg / h of process elements and potassium ions are recovered from the alkali ash. The recovery rates of sodium ions, sulfate ions, and carbonate ions in the alkali ash are over 90%, and the total salt recovery rate reaches over 90%, far exceeding the total salt recovery rate of conventional alkali ash recovery systems. The potassium ion recovery rate is over 70%. At the same time, the removal of potassium chloride ions is achieved during the alkali ash recovery cycle.

[0077] The above description is merely a preferred embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application. For example, multiple nanofiltration high-pressure pumps and nanofiltration devices can be operated in series, and the diluted mother liquor can be passed sequentially through the multiple nanofiltration devices connected in series to further separate sulfate, carbonate, and chloride ions. These improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A system for recovering sodium sulfate, sodium carbonate and potassium mirabilite from a caustic ash and removing chloride ions, characterized in that, It includes a soda ash dissolution unit (1), a main crystallization unit (2), a potassium sulfate crystallization unit (3), and a nanofiltration unit (4), wherein, The soda ash dissolving unit (1) is used to dissolve soda ash, the main crystallization unit (2) is used to extract sodium sulfate and sodium carbonate crystals, the potassium sulfate crystallization unit (3) is used to extract potassium sulfate crystals, and the nanofiltration unit (4) is used to separate sulfate ions and carbonate ions from chloride ions. The soda ash dissolution unit (1) is connected to the main crystallization unit (2) through a pipeline, the main crystallization unit (2) is connected to the potassium mirabilite crystallization unit (3) through a pipeline, the potassium mirabilite crystallization unit (3) is connected to the nanofiltration unit (4) through a pipeline, and the nanofiltration unit (4) is connected to the soda ash dissolution unit (1) through a pipeline.

2. A system as claimed in claim 1, characterized in that The soda ash dissolving unit (1) includes a soda ash dissolving tank (101) and a soda ash dissolving agitator (102), wherein the soda ash dissolving agitator (102) is disposed inside the soda ash dissolving tank (101); The main crystallization unit (2) includes a main crystallization device (201), a main crystallization dehydration device (202), a main crystallization filtrate stirring device (203), and a first condensate tank (204). The main crystallization device (201) includes a main crystallizer (2011), a main crystallization circulation pump (2012), a main crystallization heat exchanger (2013), and a steam compression device (2014). The main crystallizer (2011), the main crystallization circulation pump (2012), and the main crystallization heat exchanger (2013) are sequentially connected via pipelines. The steam outlet of the main crystallizer (2011) is connected to the steam compression device (2014) via a pipeline. The outlet of the steam compression device (2014) is connected to the main crystallization heat exchanger (2014). 2013) Steam inlet connection, the first condensate outlet of the main crystallizer (2013) is connected to the first condensate tank (204) through a pipeline, the first mother liquor outlet of the main crystallizer (2011) is connected to the potassium Glauber's salt crystallization unit (3) through a pipeline, the discharge port of the main crystallizer (2011) is connected to the main crystallization dehydration device (202) through a pipeline, the first filtrate outlet of the main crystallization dehydration device (202) is connected to the main crystallization filtrate stirring device (203) through a pipeline, the outlet of the main crystallization filtrate stirring device (203) is connected to the main crystallizer (201), and the outlet of the soda ash dissolving unit (1) is connected to the main crystallizer (2011) through a pipeline.

3. The system of claim 2, wherein, The potassium sulfate crystallization unit (3) includes a potassium sulfate crystallization device (301), a potassium sulfate dehydration device (303), a potassium sulfate filtrate stirring device (304), and a second condensate tank (305). The potassium sulfate crystallization device (301) includes a potassium sulfate crystallizer (3011), a potassium sulfate circulation pump (3012), a potassium sulfate heat exchanger (3013), a condenser (3014), and a vacuum device (3015). The potassium sulfate crystallizer (3011), the potassium sulfate circulation pump (3012), and the potassium sulfate heat exchanger (3013) are sequentially connected via pipelines. The steam outlet of the potassium sulfate crystallizer (3011) is connected via pipelines to the condenser (3014) and the vacuum device (3015). 3015) are connected in sequence. Heating steam is connected to the potassium mirabilite heat exchanger (3013) through a pipeline. The second condensate outlet of the potassium mirabilite heat exchanger (3013) is connected to the second condensate tank (305) through a pipeline. The outlet of the potassium mirabilite crystallizer (3011) is connected to the potassium mirabilite dehydration device (303) through a pipeline. The second filtrate outlet of the potassium mirabilite dehydration device (303) is connected to the potassium mirabilite filtrate stirring device (304) through a pipeline. The outlet of the potassium mirabilite filtrate stirring device is connected to the potassium mirabilite crystallizer (301) through a pipeline. The first mother liquor outlet of the main crystallizer (2011) is connected to the potassium mirabilite crystallizer (301) through a pipeline.

4. A system as claimed in claim 2 or 3, characterised in that, The nanofiltration unit (4) includes a pretreatment device (401), a dilution device (402), and a nanofiltration apparatus (403). The second mother liquor outlet of the potassium sulfate crystallizer (3011) is connected to the inlet of the pretreatment device (401) via a pipeline. The dilution device (402) includes a dilution tank (4021) and a dilution tank agitator (4022), with the agitator (4022) located within the dilution tank (4021). The nanofiltration apparatus includes a nanofiltration inlet pump. 4031), nanofiltration security filter (4032), nanofiltration high-pressure pump (4033) and nanofiltration device (4034), the outlet of the pretreatment device (401) is connected in sequence to the dilution water tank (4021), the nanofiltration inlet pump (4031), the nanofiltration security filter (4032), the nanofiltration high-pressure pump (4033) and the nanofiltration device (4034) through pipelines, and the nanofiltration concentrate outlet of the nanofiltration device is connected to the feed port of the ash dissolution unit (1) through pipelines.

5. A system as claimed in claim 4, characterized in that The system also includes a reverse osmosis unit (5), which is used to concentrate the nanofiltration permeate from the nanofiltration unit (4). The reverse osmosis unit (5) is connected to the nanofiltration unit (4) via a pipeline.

6. A system as claimed in claim 5, characterized in that The reverse osmosis unit (5) includes a reverse osmosis feed tank (501) and a reverse osmosis device (502). The reverse osmosis device (502) includes a reverse osmosis feed pump (5021), a reverse osmosis security filter (5022), a reverse osmosis high-pressure pump (5023), and a reverse osmosis unit (5024). The reverse osmosis feed tank (501), the reverse osmosis feed pump (5021), the reverse osmosis security filter (5022), the reverse osmosis high-pressure pump (5023), and the reverse osmosis unit (5024) are connected in sequence through pipelines. The nanofiltration permeate port of the nanofiltration unit (4034) is connected to the reverse osmosis feed tank (501) through a pipeline.

7. A system as claimed in claim 6, characterised in that, The reverse osmosis permeate outlet of the reverse osmosis unit (5024) is connected to the dilution unit (402) via a pipeline.

8. The system of claim 3, wherein, The second mother liquor outlet of the potassium mirabilite crystallizer (3011) is also connected to the inlet of the main crystallization filtrate stirring device (203) via a pipeline.

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