A method for recovering sodium sulfate and sodium chloride from mine water

Abstract

The invention relates to the technical field of high-salt mine water treatment, and discloses a method for recovering sodium sulfate and sodium chloride from mine water, comprising the following steps: passing the mine water to be treated into a sodium sulfate non-condensable gas preheater for heat exchange with non-condensable gas, and then passing the mine water into a sodium sulfate condensate preheater for heat exchange with steam condensate to obtain secondary preheating liquid; separating the non-condensable gas after heat exchange from gas and liquid, and passing the separated steam condensate into a sodium sulfate condensate preheater; heating and concentrating the secondary preheating liquid to obtain sodium sulfate slurry, non-condensable gas and steam condensate, passing the non-condensable gas into a sodium sulfate non-condensable gas preheater, and passing the steam condensate into a sodium sulfate condensate preheater; performing solid-liquid separation on the sodium sulfate slurry to obtain a sodium sulfate crude product and a sodium sulfate mother liquor; crystallizing the sodium sulfate mother liquor to obtain sodium sulfate and a crystallization mother liquor; and recovering sodium chloride from the crystallization mother liquor. The method can make full use of the heat in the non-condensable gas generated during the heating and concentration process, improve energy utilization, and reduce energy consumption of the entire process.

Description

Technical Field

[0001] The invention relates to the technical field of high-salt mine water treatment, in particular to a method for recovering sodium sulfate and sodium chloride from mine water. Background Art

[0002] A large amount of high-salt mine water is produced during coal mining, which contains pollutants such as suspended matter, salt, and special components. If not properly handled, it will cause great harm to the environment. To harmlessly treat and recycle high-salt mine water, it is necessary not only to reuse most of the treated water, but also to minimize the pollution to the surrounding environment. At present, the treatment process for high-salt mine water mainly includes three stages: pretreatment, membrane concentration, and salt separation crystallization. Among them, salt separation crystallization, as the last stage of the treatment process, plays an important role in the zero-discharge treatment of high-salt mine water. However, since the salt separation crystallization process requires a large amount of raw steam, cooling water, and electricity consumption, its operating cost is extremely high, which has become an important factor affecting the development of salt separation crystallization. Therefore, how to recover excess energy and reduce energy consumption is a major problem faced in the salt separation crystallization process.

[0003] Chinese patent CN112093966A discloses an energy-saving and consumption-reducing method based on the full process of zero discharge of mine water, which includes purification, membrane concentration and evaporation and crystallization of mine water. The method is to reuse the heat energy of mine water in the full process of zero discharge of mine water. According to the different content of temperature-sensitive substances in mine water, it is divided into direct flow type and mixed flow type. The process only recovers the high-grade heat generated by the evaporation and crystallization process, but does not pay attention to the energy in the non-condensable gas, and the energy utilization rate is not high. Summary of the invention

[0004] In order to solve the technical problem of low energy utilization rate of the existing mine water salt crystallization method, the present invention provides a method for recovering sodium sulfate and sodium chloride from mine water. The method can fully utilize the heat in the non-condensable gas generated during the heating and concentration process, improve the energy utilization rate, and reduce the energy consumption of the entire process.

[0005] The specific technical scheme of the present invention is:

[0006] A method for recovering sodium sulfate and sodium chloride from mine water comprises the following steps:

[0007] S1: passing the mine water to be treated into a sodium sulfate non-condensable gas preheater, exchanging heat with the non-condensable gas to obtain a primary preheated liquid; S2: passing the primary preheated liquid into a sodium sulfate condensate preheater, exchanging heat with steam condensate to obtain a secondary preheated liquid; S3: separating the non-condensable gas after heat exchange in step S1 from gas and liquid, and passing the separated steam condensate into the sodium sulfate condensate preheater;

[0008] S4: heating and concentrating the secondary preheated liquid to obtain sodium sulfate slurry, non-condensable gas and steam condensate, passing the obtained non-condensable gas into the sodium sulfate non-condensable gas preheater, and passing the steam condensate into the sodium sulfate condensate preheater;

[0009] S5: performing solid-liquid separation on the sodium sulfate slurry to obtain a crude sodium sulfate product and a sodium sulfate mother liquor;

[0010] S6: crystallizing the sodium sulfate mother liquor to obtain sodium sulfate and a crystallization mother liquor;

[0011] S7: recovering sodium chloride from the crystallization mother liquor.

[0012] The present invention separates sodium sulfate from the mine water by heating concentration, solid-liquid separation and crystallization, and processes the crystallization mother liquor after separating the sodium sulfate to recover the sodium chloride. In the process of recovering sodium sulfate, the present invention pays attention to the fact that the non-condensable gas generated during heating concentration contains more heat. On this basis, combined with the demand for heat in the heating concentration process, the heat in the non-condensable gas is transferred to the mine water to be treated by heat exchange, and the remaining heat in the steam condensed water formed after the non-condensable gas heat exchange is used to further preheat the mine water to be treated, so that the heat in the non-condensable gas can be fully recovered and utilized, and the energy consumption in the heating concentration process is reduced, and the equipment investment and operation cost are reduced.

[0013] Preferably, the specific process of step S6 includes the following steps:

[0014] S6.1: After precooling the sodium sulfate mother liquor, the mother liquor is passed into a crystallization mother liquor precooler to exchange cooling with the crystallization mother liquor to obtain a precooled feed liquid;

[0015] S6.2: freeze-crystallize the pre-cooled liquid to obtain frozen slurry; perform solid-liquid separation on the frozen slurry to obtain crystallization mother liquor and mirabilite; and pass the crystallization mother liquor into the crystallization mother liquor precooler.

[0016] In the process of crystallizing the sodium sulfate mother liquor, a cold source needs to be introduced to cool the sodium sulfate mother liquor. The present invention utilizes the crystallization mother liquor with a lower temperature after completing the freeze crystallization to cool the sodium sulfate mother liquor, which has the following two effects: on the one hand, the sodium sulfate mother liquor can be precooled to reduce the demand for a new cold source in the subsequent freeze crystallization process; on the other hand, the crystallization mother liquor can be preheated to reduce the demand for a new heat source in the subsequent process of recovering sodium chloride from the crystallization mother liquor.

[0017] Preferably, the specific process of step S7 includes the following steps:

[0018] S7.1: passing the crystallization mother liquor into the sodium chloride non-condensable gas preheater, exchanging heat with the non-condensable gas, and obtaining a preheated sodium chloride feed liquid;

[0019] S7.2: passing the primary preheated sodium chloride feed liquid into a sodium chloride condensate preheater to exchange heat with steam condensate to obtain a secondary preheated sodium chloride feed liquid;

[0020] S7.3: separating the non-condensable gas after heat exchange in step S7.1 into gas and liquid, and passing the separated steam condensate into the sodium chloride condensate preheater;

[0021] S7.4: heating and concentrating the secondary preheated sodium chloride liquid to obtain sodium chloride slurry, non-condensable gas and steam condensate, passing the obtained non-condensable gas into the sodium chloride non-condensable gas preheater, and passing the steam condensate into the sodium chloride condensate preheater;

[0022] S7.5: performing solid-liquid separation on the sodium chloride slurry to obtain a crude sodium chloride product and a sodium chloride mother liquor;

[0023] S7.6: Dry the sodium chloride mother liquor to obtain impure salt.

[0024] In the sodium chloride recovery process, the present invention adopts an energy recycling method similar to that of the sodium sulfate recovery process, that is, the non-condensable gas generated in the heating and concentration process is used to preheat the crystallization mother liquor, and then the remaining heat in the steam condensed water formed after the non-condensable gas heat exchange is used to further preheat the crystallization mother liquor, so that the heat in the non-condensable gas can be fully recycled and utilized, and the energy consumption in the heating and concentration process is reduced.

[0025] Preferably, in step S5, after obtaining the crude sodium sulfate product, the crude sodium sulfate product is dried to obtain anhydrous sodium sulfate; in the process of drying the crude sodium sulfate product, air after heat exchange with live steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with live steam are used as boiler make-up water.

[0026] Preferably, in step S7.5, after obtaining the crude sodium chloride product, the crude sodium chloride product is dried to obtain industrial salt; in the process of drying the crude sodium chloride product, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler make-up water.

[0027] Preferably, in step S7.6, during the drying of the sodium chloride mother liquor, air after heat exchange with live steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with live steam are used as boiler feed water.

[0028] The raw steam generated by the boiler can be used as a heat source to supply the heating, concentration and drying processes in the entire process. In the process of the boiler generating raw steam, as the water vapor is continuously generated, the water level in the water supply tank gradually decreases, and water needs to be replenished. However, using water at room temperature for replenishment requires consuming other heat to heat it up to meet the boiler water inlet requirements. In this regard, the present invention uses the steam condensate formed after the raw steam heat exchange (heating the air) as boiler replenishment water, which can make full use of the heat in the steam condensate and reduce boiler energy consumption.

[0029] Preferably, in step S6.1, the method for precooling the sodium sulfate mother liquor is to use circulating cooling water at 25 to 35°C for cooling.

[0030] Preferably, in step S1, the mine water to be treated is mine water that has been pretreated and membrane concentrated.

[0031] Preferably, in step S5, the specific process of solid-liquid separation of the sodium sulfate slurry comprises the following steps: thickening and centrifuging the sodium sulfate slurry, the solid component separated during the centrifugation process is the crude sodium sulfate product, and the liquid components separated during the thickening and centrifugation process are combined to form the sodium sulfate mother liquor.

[0032] Preferably, in step S6.2, the method of solid-liquid separation of the frozen slurry is sedimentation and centrifugation.

[0033] Preferably, in step S7.5, the specific process of solid-liquid separation of the sodium chloride slurry comprises the following steps: thickening and centrifuging the sodium chloride slurry, the solid component separated during the centrifugation process is the crude sodium chloride product, and the liquid components separated during the thickening and centrifugation process are combined to form the sodium chloride mother liquor.

[0034] Preferably, the temperature of the non-condensable gas in step S1 and the steam condensate in step S2 is not less than 110°C; in step S2, the temperature of the secondary preheated liquid is 80-100°C.

[0035] Preferably, in step S6.1, the temperature of the crystallization mother liquor is -5 to 15°C, and the temperature of the pre-cooled liquid is 20 to 40°C.

[0036] Preferably, the temperature of the non-condensable gas in step S7.1 and the steam condensate in step S7.2 is not less than 110°C; in step S7.2, the temperature of the secondary preheated sodium chloride solution is 80-100°C.

[0037] Preferably, the inner wall and / or outer wall of the sodium sulfate non-condensable gas preheater and / or the sodium sulfate condensable water preheater are coated with a thermal insulation coating; the method for preparing the thermal insulation coating comprises the following steps: after coating a slurry containing hydrophobic cellulose aerogel on the inner wall and / or the outer wall to form a coating, irradiating the coating with ultraviolet light having a wavelength less than 300 nm; the crosslinking agent of the hydrophobic cellulose aerogel comprises the following components: a mercaptosilane coupling agent, a compound containing alkenyl and anthracene groups; the mercaptosilane coupling agent contains at least two silaneoxy groups (i.e., -SiOR groups).

[0038] By applying a thermal insulation coating on the inner or outer wall of the preheater, the heat loss in the preheater can be reduced, further improving the energy utilization rate of the entire salt separation crystallization process of the present invention and reducing energy consumption. Existing studies have shown that compared with hydrophobic silica aerogel, the use of hydrophobic cellulose aerogel as a thermal insulation material can give the thermal insulation coating better toughness and prevent it from cracking, but the thermal insulation performance is relatively insufficient. To this end, the present invention team has studied hydrophobic cellulose aerogel and provided a means to improve its thermal insulation performance.

[0039] Aerogels can play a role in thermal insulation by utilizing their high internal porosity. The thermal conductivity of aerogels is mainly composed of solid-state thermal conductivity, gaseous thermal conductivity, and radiation thermal conductivity. In hydrophobic cellulose aerogels, within a certain range, as the degree of cross-linking increases, the macropores inside the aerogels are divided into smaller holes, causing a significant decrease in gaseous thermal conductivity, while the increase in solid-state thermal conductivity is relatively small, so the overall thermal conductivity of the aerogels tends to decrease; after reaching a certain level, the degree of cross-linking continues to increase, the gaseous thermal conductivity inside the aerogels decreases less, while the increase in solid-state thermal conductivity is relatively large, so the overall thermal conductivity of the aerogels tends to increase.

[0040] The present invention adopts a mercaptosilane coupling agent and a compound containing alkenyl and anthracene as a crosslinking agent. In the preparation process of the hydrophobic cellulose aerogel, the mercaptosilane coupling agent forms crosslinks between cellulose molecular chains; at the same time, the compound containing alkenyl and anthracene can utilize the alkenyl therein to connect to the mercaptosilane coupling agent, and utilize the photodimerization reaction of two anthracene groups to further improve the degree of crosslinking between cellulose. The higher degree of crosslinking of the hydrophobic cellulose aerogel can give the aerogel a higher strength, play a better supporting role in the process of preparing the aerogel and the coating, and reduce the infiltration of the coating matrix material, so that the aerogel can better maintain its internal pores, so that it has a lower gaseous thermal conductivity after being made into the coating, and can maintain a better thermal insulation effect. After the coating is formed, under the irradiation of ultraviolet light with a wavelength less than 300nm, the dimer formed by the two anthracene groups is cracked, which can reduce the crosslinking in the aerogel, reduce the solid-state thermal conductivity inside it, and make the aerogel have a lower thermal conductivity as a whole, thereby improving the thermal insulation effect of the coating.

[0041] Preferably, the preparation method of the hydrophobic cellulose aerogel comprises the following steps: using nanocellulose, methyl silane coupling agent, mercapto silane coupling agent, alkenyl- and anthracene-containing compounds and solvent as raw materials, carrying out hydrolysis condensation reaction, and carrying out click reaction and anthracene dimerization reaction under ultraviolet light with a wavelength greater than 300 nm to prepare the hydrophobic cellulose aerogel.

[0042] In the above preparation process, the mercaptosilane coupling agent utilizes its multiple silaneoxy groups to undergo a hydrolysis and condensation reaction with the hydroxyl groups in cellulose, thereby forming covalent crosslinks between the cellulose molecular chains. At the same time, the methylsilane coupling agent undergoes a hydrolysis and condensation reaction with the cellulose, thereby playing the role of a hydrophobic modifier. Under the action of ultraviolet light with a wavelength greater than 300 nm, anthracene groups can undergo a dimerization reaction. At the same time, a click reaction can occur between the mercapto group in the mercaptosilane coupling agent and the alkenyl group in the compound containing alkenyl and anthracene groups, thereby further improving the degree of crosslinking in the hydrophobic cellulose aerogel.

[0043] Preferably, the molar ratio of the mercapto group in the mercaptosilane coupling agent to the alkenyl group in the compound containing alkenyl and anthracene groups is 1:1-5.

[0044] Preferably, the molar ratio of the methyl silane coupling agent to the mercapto silane coupling agent is 1:0.4-0.7.

[0045] Preferably, the weight average molecular weight of the nanocellulose is 40-60 kDa; the methyl silane coupling agent and the mercapto silane coupling agent both contain three siloxy groups; and the ratio of the molar amount of the nanocellulose to the total molar amount of the methyl silane coupling agent and the mercapto silane coupling agent is 1:420-630.

[0046] The molar amount of the nanocellulose is calculated as follows: molar amount = mass / weight average molecular weight.

[0047] Preferably, the mass ratio of the nanocellulose to the solvent is 1:20-40.

[0048] Preferably, the preparation method of the hydrophobic cellulose aerogel specifically comprises the following steps: adding a methylsilane coupling agent and a mercaptosilane coupling agent to a solvent A, hydrolyzing them to obtain a modifier solution; dissolving an olefinic and anthracene-containing compound into a solvent B, adding nanocellulose and the modifier solution thereto, mixing them, reacting them under ultraviolet light with a wavelength greater than 300 nm for 0.5 to 1 h, and then aging and drying them to obtain a hydrophobic cellulose aerogel.

[0049] Preferably, the aging temperature is 15-25° C. and the aging time is 24-48 hours.

[0050] Preferably, the solvent A is a mixed solvent of water and acetone; and the solvent B is acetone.

[0051] Compared with the prior art, the present invention has the following advantages:

[0052] (1) The present invention adopts corresponding energy recycling according to the temperature requirements of the feed in different process stages, and fully utilizes the energy generated by non-condensable gas, crystallization mother liquor and salt drying steam condensation water for heating or cooling, which can achieve a higher energy utilization rate, reduce the introduction of new heat sources or cold sources, achieve the purpose of energy saving and consumption reduction, and reduce equipment investment and operating costs;

[0053] (2) In the thermal insulation coating used in the present invention, mercaptosilane coupling agents and compounds containing alkenyl and anthracene groups are used as crosslinking agents in the hydrophobic cellulose aerogel, and the dimerization and cleavage reactions of anthracene groups under ultraviolet light of different wavelengths are utilized, so that the aerogel can maintain a good pore structure after being made into a coating and has a low solid-state thermal conductivity, thereby improving the thermal insulation effect of the coating, improving the energy utilization rate in the process of water salt crystallization in the mine, and reducing energy consumption. DETAILED DESCRIPTION

[0054] The present invention will be further described below in conjunction with the embodiments.

[0055] Overall embodiment

[0056] A method for recovering sodium sulfate and sodium chloride from mine water comprises the following steps:

[0057] S1: passing the mine water to be treated into a sodium sulfate non-condensable gas preheater, exchanging heat with the non-condensable gas to obtain a primary preheated liquid; S2: passing the primary preheated liquid into a sodium sulfate condensate preheater, exchanging heat with steam condensate to obtain a secondary preheated liquid; S3: separating the non-condensable gas after heat exchange in step S1 from gas and liquid, and passing the separated steam condensate into the sodium sulfate condensate preheater;

[0058] S4: heating and concentrating the secondary preheated liquid to obtain sodium sulfate slurry, non-condensable gas and steam condensate, passing the obtained non-condensable gas into the sodium sulfate non-condensable gas preheater, and passing the steam condensate into the sodium sulfate condensate preheater;

[0059] S5: performing solid-liquid separation on the sodium sulfate slurry to obtain a crude sodium sulfate product and a sodium sulfate mother liquor;

[0060] S6: After cooling the sodium sulfate mother liquor with circulating cooling water at 25-35° C., the sodium sulfate mother liquor is passed into a crystallization mother liquor precooler to exchange cooling with the crystallization mother liquor to obtain a precooled feed liquid;

[0061] S7: freeze-crystallize the pre-cooled liquid to obtain a frozen slurry; perform solid-liquid separation on the frozen slurry to obtain a crystallization mother liquor and mirabilite; and pass the crystallization mother liquor into the crystallization mother liquor precooler;

[0062] S8: passing the crystallization mother liquor after cooling in step S6 into a sodium chloride non-condensable gas preheater, exchanging heat with the non-condensable gas, and obtaining a preheated sodium chloride feed liquid;

[0063] S9: passing the primary preheated sodium chloride feed liquid into a sodium chloride condensate preheater to exchange heat with steam condensate to obtain a secondary preheated sodium chloride feed liquid;

[0064] S10: separating the non-condensable gas after heat exchange in step S8 into gas and liquid, and passing the separated steam condensate into the sodium chloride condensate preheater;

[0065] S11: heating and concentrating the secondary preheated sodium chloride liquid to obtain sodium chloride slurry, non-condensable gas and steam condensate, passing the obtained non-condensable gas into the sodium chloride non-condensable gas preheater, and passing the steam condensate into the sodium chloride condensate preheater;

[0066] S12: performing solid-liquid separation on the sodium chloride slurry to obtain a crude sodium chloride product and a sodium chloride mother liquor;

[0067] S13: drying the sodium chloride mother liquor to obtain mixed salt.

[0068] As a specific implementation, in step S1, the mine water to be treated is mine water that has been pretreated and membrane concentrated.

[0069] As a specific implementation, in step S5, the specific process of solid-liquid separation of the sodium sulfate slurry includes the following steps: thickening and centrifuging the sodium sulfate slurry, the solid component separated during the centrifugation process is the crude sodium sulfate, and the liquid components separated during the thickening and centrifugation process are combined to form the sodium sulfate mother liquor.

[0070] As a specific implementation, in step S5, after obtaining the crude sodium sulfate, the crude sodium sulfate is dried to obtain anhydrous sodium sulfate; in the process of drying the crude sodium sulfate, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler make-up water.

[0071] As a specific implementation, in step S7, the method of solid-liquid separation of the frozen slurry is sedimentation and centrifugation.

[0072] As a specific implementation, in step S12, the specific process of solid-liquid separation of the sodium chloride slurry includes the following steps: thickening and centrifuging the sodium chloride slurry, the solid component separated during the centrifugation process is the crude sodium chloride product, and the liquid components separated during the thickening and centrifugation process are combined to form the sodium chloride mother liquor.

[0073] As a specific implementation, in step S12, after obtaining the crude sodium chloride product, the crude sodium chloride product is dried to obtain industrial salt; in the process of drying the crude sodium chloride product, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler make-up water.

[0074] As a specific implementation, in step S13, during the drying of the sodium chloride mother liquor, the air after heat exchange with the raw steam is used as the heat source, and the steam and steam condensate obtained after heat exchange with the raw steam are used as boiler feed water.

[0075] As a specific implementation manner, the temperature of the non-condensable gas in step S1 and the steam condensate in step S2 is not less than 110°C; in step S2, the temperature of the secondary preheating liquid is 80-100°C; in step S6, the temperature of the crystallization mother liquor is -5-15°C, and the temperature of the precooling liquid is 20-40°C; the temperature of the non-condensable gas in step S8 and the steam condensate in step S9 is not less than 110°C; in step S9, the temperature of the secondary preheating sodium chloride liquid is 80-100°C.

[0076] As a specific embodiment, the inner wall and / or outer wall of one or more of the sodium sulfate non-condensable gas preheater, the sodium sulfate condensate preheater, the sodium chloride non-condensable gas preheater, and the sodium chloride condensate preheater are coated with a thermal insulation coating; the preparation method of the thermal insulation coating comprises the following steps: after coating a slurry containing hydrophobic cellulose aerogel on the inner wall and / or the outer wall to form a coating, irradiating the coating with ultraviolet light having a wavelength less than 300nm; the crosslinking agent of the hydrophobic cellulose aerogel comprises the following components: a mercaptosilane coupling agent, a compound containing alkenyl and anthracene groups; the mercaptosilane coupling agent contains at least two silaneoxy groups.

[0077] As a specific embodiment, the preparation method of the hydrophobic cellulose aerogel comprises the following steps: using nanocellulose, methyl silane coupling agent, mercapto silane coupling agent, alkenyl and anthracene-containing compounds and solvent as raw materials, carrying out hydrolysis condensation reaction, and carrying out click reaction and anthracene dimerization reaction under ultraviolet light with a wavelength greater than 300nm to prepare hydrophobic cellulose aerogel.

[0078] Furthermore, the preparation method of the hydrophobic cellulose aerogel specifically includes the following steps: adding a methylsilane coupling agent and a mercaptosilane coupling agent to a solvent A, hydrolyzing them to obtain a modifier solution; dissolving a compound containing an olefinic group and an anthracene group into a solvent B, adding nanocellulose and the modifier solution thereto, mixing them, reacting them under ultraviolet light with a wavelength greater than 300 nm for 0.5 to 1 h, and then aging them at 15 to 25° C. for 24 to 48 h, and drying them to obtain a hydrophobic cellulose aerogel.

[0079] As a specific embodiment, in the preparation process of hydrophobic cellulose aerogel, the weight average molecular weight of the nanocellulose is 40-60 kDa; the methylsilane coupling agent and the mercaptosilane coupling agent both contain three siloxy groups; the ratio of the molar amount of the nanocellulose to the total molar amount of the methylsilane coupling agent and the mercaptosilane coupling agent is 1:420-630; the molar ratio of the mercapto group in the mercaptosilane coupling agent to the alkenyl group in the compound containing alkenyl and anthracene is 1:1-5; the molar ratio of the methylsilane coupling agent to the mercaptosilane coupling agent is 1:0.4-0.7; the mass ratio of the nanocellulose to the solvent is 1:20-40.

[0080] As a specific implementation, in the preparation process of the thermal insulation coating, the slurry containing the hydrophobic cellulose aerogel includes the following components in parts by weight: 100 parts of styrene acrylic emulsion, 5 to 15 parts of propylene glycol methyl ether, 200 to 600 parts of hydrophobic cellulose aerogel, 100 to 200 parts of glass microspheres, 0 to 3 parts of polyether siloxane copolymer, and 150 to 250 parts of water.

[0081] Preparation Example 1

[0082] The steps of applying a thermal insulation coating on the outer walls of a sodium sulfate non-condensable gas preheater, a sodium sulfate condensate preheater, a sodium chloride non-condensable gas preheater and a sodium chloride condensate preheater are as follows:

[0083] (1) Preparation of hydrophobic cellulose aerogel:

[0084] 27.2 kg of methyltrimethoxysilane and 27.5 kg of 3-mercaptopropyltrimethoxysilane were added to 300 kg of acetone-water mixture (volume ratio of acetone to water was 3:1), pH was adjusted to 4.0 with hydrochloric acid, and stirred for 30 min to obtain a modifier solution for later use. 110.5 kg of 9-anthracenemethyl methacrylate was dissolved in 600 kg of acetone, and 30.0 kg of nanocellulose (M w =44 kDa), after ultrasonic dispersion for 15 min, add the modifier solution, stir at room temperature for 30 min, and then continue stirring for 0.5 h under ultraviolet light irradiation of λ=365 nm, stand and age at room temperature for 48 h, freeze-dry, crush, grind, and sieve to obtain a hydrophobic cellulose aerogel with a particle size of 10-20 μm for use.

[0085] (2) Preparation of thermal insulation slurry:

[0086] The following raw materials were weighed: 10 kg styrene acrylic emulsion (solid content 47.5 wt%), 1.5 kg propylene glycol methyl ether, 60 kg hydrophobic cellulose aerogel, 10 kg glass microspheres, 0.1 kg polyether siloxane copolymer, 20 kg water, and all the raw materials were mixed and stirred to obtain a thermal insulation slurry.

[0087] (3) Apply thermal insulation coating:

[0088] The thermal insulation slurry was evenly coated on the outer wall of the preheater, dried, and irradiated with ultraviolet light of λ=254nm for 40min to obtain a thermal insulation coating with a thickness of about 1mm.

[0089] According to the test, the thermal conductivity of the thermal insulation coating in this preparation example is 0.021 W / (m·K).

[0090] Preparation Example 2

[0091] The steps of applying a thermal insulation coating on the outer walls of a sodium sulfate non-condensable gas preheater, a sodium sulfate condensate preheater, a sodium chloride non-condensable gas preheater and a sodium chloride condensate preheater are as follows:

[0092] (1) Preparation of hydrophobic cellulose aerogel:

[0093] 36.6 kg of methyltrimethoxysilane and 31.6 kg of 3-mercaptopropyltrimethoxysilane were added to 600 kg of acetone-water mixture (the volume ratio of acetone to water was 3:1), the pH was adjusted to 5.0 with hydrochloric acid, and the mixture was stirred for 20 min to obtain a modifier solution for later use. 44.5 kg of 9-anthracenemethyl methacrylate was dissolved in 600 kg of acetone, and 30.0 kg of nanocellulose (M w =44 kDa), after ultrasonic dispersion for 15 min, add the modifier solution, stir at room temperature for 40 min, and then continue stirring for 1 h under ultraviolet light irradiation of λ=365 nm, stand and age at room temperature for 48 h, freeze-dry, crush, grind, and sieve to obtain hydrophobic cellulose aerogel with a particle size of 10-20 μm for use.

[0094] (2) Preparation of thermal insulation slurry:

[0095] The following raw materials were weighed: 10 kg styrene acrylic emulsion (solid content 47.5 wt%), 1 kg propylene glycol methyl ether, 40 kg hydrophobic cellulose aerogel, 15 kg glass microspheres, 0.3 kg polyether siloxane copolymer, and 20 kg water. All the raw materials were mixed and stirred to obtain a thermal insulation slurry.

[0096] (3) Apply thermal insulation coating:

[0097] The thermal insulation slurry was evenly coated on the outer wall of the preheater, dried, and irradiated with ultraviolet light of λ=254nm for 30min to obtain a thermal insulation coating with a thickness of about 1mm.

[0098] According to the test, the thermal conductivity of the thermal insulation coating in this preparation example is 0.020 W / (m·K).

[0099] Preparation Example 3

[0100] The steps of applying a thermal insulation coating on the outer walls of a sodium sulfate non-condensable gas preheater, a sodium sulfate condensate preheater, a sodium chloride non-condensable gas preheater and a sodium chloride condensate preheater are as follows:

[0101] (1) Preparation of hydrophobic cellulose aerogel:

[0102] 27.9 kg of methyltrimethoxysilane and 16.1 kg of 3-mercaptopropyltrimethoxysilane were added to 100 kg of acetone-water mixture (volume ratio of acetone to water was 3:1), pH was adjusted to 4.5 with hydrochloric acid, and stirred for 40 min to obtain a modifier solution for later use. 113.0 kg of 9-anthracenemethyl methacrylate was dissolved in 500 kg of acetone, and 30.0 kg of nanocellulose (M w=44 kDa), after ultrasonic dispersion for 20 min, add the modifier solution, stir at room temperature for 20 min, and then continue stirring for 0.5 h under ultraviolet light irradiation of λ=365 nm, stand and age at room temperature for 24 h, freeze-dry, crush, grind, and sieve to obtain hydrophobic cellulose aerogel with a particle size of 10-20 μm for use.

[0103] (2) Preparation of thermal insulation slurry:

[0104] The following raw materials were weighed: 10 kg styrene acrylic emulsion (solid content 47.5 wt%), 0.5 kg propylene glycol methyl ether, 20 kg hydrophobic cellulose aerogel, 20 kg glass microspheres, 0.2 kg polyether siloxane copolymer, 20 kg water, and all the raw materials were mixed and stirred to obtain a thermal insulation slurry.

[0105] (3) Apply thermal insulation coating:

[0106] The thermal insulation slurry was evenly coated on the outer wall of the preheater, dried, and irradiated with ultraviolet light of λ=254nm for 20min to obtain a thermal insulation coating with a thickness of about 1mm.

[0107] According to the test, the thermal conductivity of the thermal insulation coating in this preparation example is 0.023 W / (m·K).

[0108] Comparative Preparation Example 1

[0109] The thermal insulation coating is applied on the outer walls of the sodium sulfate non-condensable gas preheater, the sodium sulfate condensate preheater, the sodium chloride non-condensable gas preheater and the sodium chloride condensate preheater. The only difference from Preparation Example 1 is that no ultraviolet light irradiation treatment is performed during the preparation of the hydrophobic cellulose aerogel. The specific steps are as follows:

[0110] (1) Preparation of hydrophobic cellulose aerogel:

[0111] 27.2 kg of methyltrimethoxysilane and 27.5 kg of 3-mercaptopropyltrimethoxysilane were added to 300 kg of acetone-water mixture (volume ratio of acetone to water was 3:1), pH was adjusted to 4.0 with hydrochloric acid, and stirred for 30 min to obtain a modifier solution for later use. 110.5 kg of 9-anthracenemethyl methacrylate was dissolved in 600 kg of acetone, and 30.0 kg of nanocellulose (M w =44 kDa), after ultrasonic dispersion for 15 min, add the modifier solution, stir at room temperature for 1 h, stand and age at room temperature for 48 h, freeze-dry, crush, grind, and sieve to obtain a hydrophobic cellulose aerogel with a particle size of 10 to 20 μm for later use.

[0112] (2) Preparation of thermal insulation slurry:

[0113] The following raw materials were weighed: 10 kg styrene acrylic emulsion (solid content 47.5 wt%), 1.5 kg propylene glycol methyl ether, 60 kg hydrophobic cellulose aerogel, 10 kg glass microspheres, 0.1 kg polyether siloxane copolymer, 20 kg water, and all the raw materials were mixed and stirred to obtain a thermal insulation slurry.

[0114] (3) Apply thermal insulation coating:

[0115] The thermal insulation slurry was evenly coated on the outer wall of the preheater, dried, and irradiated with ultraviolet light of λ=254nm for 40min to obtain a thermal insulation coating with a thickness of about 1mm.

[0116] After testing, the thermal conductivity of the thermal insulation coating in this comparative preparation example is 0.034 W / (m·K).

[0117] Comparative Preparation Example 2

[0118] The thermal insulation coating is applied on the outer walls of the sodium sulfate non-condensable gas preheater, the sodium sulfate condensate preheater, the sodium chloride non-condensable gas preheater and the sodium chloride condensate preheater. The only difference from Preparation Example 1 is that no ultraviolet light irradiation treatment is performed after the coating is dried. The specific steps are as follows:

[0119] (1) Preparation of hydrophobic cellulose aerogel:

[0120] 27.2 kg of methyltrimethoxysilane and 27.5 kg of 3-mercaptopropyltrimethoxysilane were added to 300 kg of acetone-water mixture (volume ratio of acetone to water was 3:1), pH was adjusted to 4.0 with hydrochloric acid, and stirred for 30 min to obtain a modifier solution for later use. 110.5 kg of 9-anthracenemethyl methacrylate was dissolved in 600 kg of acetone, and 30.0 kg of nanocellulose (M w =44 kDa), after ultrasonic dispersion for 15 min, add the modifier solution, stir at room temperature for 30 min, and then continue stirring for 0.5 h under ultraviolet light irradiation of λ=365 nm, stand and age at room temperature for 48 h, freeze-dry, crush, grind, and sieve to obtain a hydrophobic cellulose aerogel with a particle size of 10-20 μm for use.

[0121] (2) Preparation of thermal insulation slurry:

[0122] The following raw materials were weighed: 10 kg styrene acrylic emulsion (solid content 47.5 wt%), 1.5 kg propylene glycol methyl ether, 60 kg hydrophobic cellulose aerogel, 10 kg glass microspheres, 0.1 kg polyether siloxane copolymer, 20 kg water, and all the raw materials were mixed and stirred to obtain a thermal insulation slurry.

[0123] (3) Apply thermal insulation coating:

[0124] The thermal insulation slurry is evenly coated on the outer wall of the preheater and dried to obtain a thermal insulation coating with a thickness of about 1 mm.

[0125] According to the test, the thermal conductivity of the thermal insulation coating in this preparation example is 0.037 W / (m·K).

[0126] Example 1

[0127] The sodium sulfate non-condensable gas preheater, sodium sulfate condensate preheater, sodium chloride non-condensable gas preheater and sodium chloride condensate preheater to which the thermal insulation coating is applied in Preparation Example 1 are used to recover sodium sulfate and sodium chloride from mine water that has been pretreated by conventional methods (coagulation and precipitation, filtration, reagent softening, tubular microfiltration, high-density clarifier, sand filtration, ultrafiltration, ion exchange and decarbonization tower to remove CO2) and membrane concentrated, and the steps are as follows:

[0128] S1: The mine water to be treated is passed into the sodium sulfate non-condensable gas preheater, with the inlet water temperature of 25°C and the mass flow rate of 12520 kg / h, and heat is exchanged with the non-condensable gas, and the non-condensable gas temperature is 110°C to obtain a primary preheated liquid;

[0129] S2: passing the primary preheated liquid into the sodium sulfate condensate preheater to exchange heat with the steam condensate, the steam condensate temperature is 110°C, and obtaining the secondary preheated liquid with a temperature of 88°C;

[0130] S3: separating the non-condensable gas after heat exchange in step S1 into gas and liquid, and passing the separated steam condensate into the sodium sulfate condensate preheater in step S2;

[0131] S4: Circulating heating and concentrating the secondary preheated liquid, the heating and concentrating temperature is 105°C, to obtain sodium sulfate slurry, non-condensable gas and steam condensate, the obtained non-condensable gas is passed into the sodium sulfate non-condensable gas preheater in step S1, and the steam condensate is passed into the sodium sulfate condensate preheater in step S2;

[0132] S5: thickening and centrifuging the sodium sulfate slurry, the solid component separated in the centrifugal process is the crude sodium sulfate product, and the liquid component separated in the thickening and centrifugal process is the sodium sulfate mother liquor; the crude sodium sulfate product is dried to obtain anhydrous sodium sulfate, and in the drying process, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water;

[0133] S6: After cooling the sodium sulfate mother liquor with 30°C circulating cooling water, the mother liquor is passed into the crystallization mother liquor precooler to exchange cooling with the crystallization mother liquor. The crystallization mother liquor temperature is -5°C, and a precooled feed liquid is obtained with a temperature of 22.5°C. The temperature of the crystallization mother liquor after cooling is 25°C;

[0134] S7: performing cyclic freezing and crystallization on the pre-cooled liquid to obtain a frozen slurry; performing sedimentation and centrifugation on the frozen slurry to obtain a crystallization mother liquor and mirabilite; and passing the crystallization mother liquor into the crystallization mother liquor precooler in step S6;

[0135] S8: passing the crystallization mother liquor after cooling in step S6 into a sodium chloride non-condensable gas preheater, exchanging heat with the non-condensable gas, the non-condensable gas temperature is 110° C., and obtaining a preheated sodium chloride feed liquid;

[0136] S9: passing the primary preheated sodium chloride feed liquid into a sodium chloride condensate preheater to exchange heat with steam condensate, the steam condensate temperature is 110° C., and obtaining a secondary preheated sodium chloride feed liquid, the temperature of which is 82° C.;

[0137] S10: separating the non-condensable gas after heat exchange in step S8 into gas and liquid, and passing the separated steam condensate into the sodium chloride condensate preheater in step S9;

[0138] S11: Circulating heating and concentrating the secondary preheated sodium chloride liquid, the heating and concentrating temperature is 106°C, to obtain sodium chloride slurry, non-condensable gas and steam condensate, the obtained non-condensable gas is passed into the sodium chloride non-condensable gas preheater in step S8, and the steam condensate is passed into the sodium chloride condensate preheater in step S9;

[0139] S12: thickening and centrifuging the sodium chloride slurry, wherein the solid component separated in the centrifugal process is the crude sodium chloride product, and the liquid component separated in the thickening and centrifugal process is the sodium chloride mother liquor; the crude sodium chloride product is dried to obtain industrial salt, and in the drying process, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water;

[0140] S13: drying the sodium chloride mother liquor to obtain impure salt; in the process of drying the sodium chloride mother liquor, using the air after heat exchange with the raw steam as the heat source, and the steam and steam condensate obtained after heat exchange with the raw steam are used as boiler make-up water.

[0141] Example 2

[0142] The sodium sulfate non-condensable gas preheater, sodium sulfate condensate preheater, sodium chloride non-condensable gas preheater and sodium chloride condensate preheater after applying the thermal insulation coating in Preparation Example 2 are used to recover sodium sulfate and sodium chloride from mine water pretreated by conventional methods (same as Example 1) and membrane concentrated, and the steps are as follows:

[0143] S1: The mine water to be treated is passed into the sodium sulfate non-condensable gas preheater, with the inlet water temperature of 25°C and the mass flow rate of 12520 kg / h, and heat is exchanged with the non-condensable gas, and the non-condensable gas temperature is 110°C to obtain a primary preheated liquid;

[0144] S2: passing the primary preheated liquid into the sodium sulfate condensate preheater to exchange heat with the steam condensate, the steam condensate temperature is 110°C, and obtaining the secondary preheated liquid with a temperature of 86°C;

[0145] S3: separating the non-condensable gas after heat exchange in step S1 into gas and liquid, and passing the separated steam condensate into the sodium sulfate condensate preheater in step S2;

[0146] S4: Circulating heating and concentrating the secondary preheated liquid, the heating and concentrating temperature is 105°C, to obtain sodium sulfate slurry, non-condensable gas and steam condensate, the obtained non-condensable gas is passed into the sodium sulfate non-condensable gas preheater in step S1, and the steam condensate is passed into the sodium sulfate condensate preheater in step S2;

[0147] S5: thickening and centrifuging the sodium sulfate slurry, the solid component separated in the centrifugal process is the crude sodium sulfate product, and the liquid component separated in the thickening and centrifugal process is the sodium sulfate mother liquor; the crude sodium sulfate product is dried to obtain anhydrous sodium sulfate, and in the drying process, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water;

[0148] S6: After cooling the sodium sulfate mother liquor with 30°C circulating cooling water, the mother liquor is passed into the crystallization mother liquor precooler to exchange cooling with the crystallization mother liquor. The crystallization mother liquor temperature is -5°C, and a precooled feed liquid is obtained with a temperature of 21°C. The temperature of the crystallization mother liquor after cooling is 25°C;

[0149] S7: performing cyclic freezing and crystallization on the pre-cooled liquid to obtain a frozen slurry; performing sedimentation and centrifugation on the frozen slurry to obtain a crystallization mother liquor and mirabilite; and passing the crystallization mother liquor into the crystallization mother liquor precooler in step S6;

[0150] S8: passing the crystallization mother liquor after cooling in step S6 into the sodium chloride non-condensable gas preheater, exchanging heat with the non-condensable gas, the non-condensable gas temperature is 112° C., and obtaining a preheated sodium chloride feed liquid;

[0151] S9: passing the primary preheated sodium chloride feed liquid into a sodium chloride condensate preheater to exchange heat with steam condensate, the steam condensate temperature is 112° C., and obtaining a secondary preheated sodium chloride feed liquid, the temperature of which is 85° C.;

[0152] S10: separating the non-condensable gas after heat exchange in step S8 into gas and liquid, and passing the separated steam condensate into the sodium chloride condensate preheater in step S9;

[0153] S11: Circulating heating and concentrating the secondary preheated sodium chloride liquid, the heating and concentrating temperature is 106°C, to obtain sodium chloride slurry, non-condensable gas and steam condensate, the obtained non-condensable gas is passed into the sodium chloride non-condensable gas preheater in step S8, and the steam condensate is passed into the sodium chloride condensate preheater in step S9;

[0154] S12: thickening and centrifuging the sodium chloride slurry, wherein the solid component separated in the centrifugal process is the crude sodium chloride product, and the liquid component separated in the thickening and centrifugal process is the sodium chloride mother liquor; the crude sodium chloride product is dried to obtain industrial salt, and in the drying process, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water;

[0155] S13: drying the sodium chloride mother liquor to obtain impure salt; in the process of drying the sodium chloride mother liquor, using the air after heat exchange with the raw steam as the heat source, and the steam and steam condensate obtained after heat exchange with the raw steam are used as boiler make-up water.

[0156] Example 3

[0157] The sodium sulfate non-condensable gas preheater, sodium sulfate condensate preheater, sodium chloride non-condensable gas preheater and sodium chloride condensate preheater after applying the thermal insulation coating in Preparation Example 3 are used to recover sodium sulfate and sodium chloride from mine water pretreated by conventional methods (same as Example 1) and membrane concentrated, and the steps are as follows:

[0158] S1: The mine water to be treated is passed into the sodium sulfate non-condensable gas preheater, with the inlet water temperature of 25°C and the mass flow rate of 12520 kg / h, and heat is exchanged with the non-condensable gas, and the non-condensable gas temperature is 113°C to obtain a primary preheated liquid;

[0159] S2: passing the primary preheated liquid into the sodium sulfate condensate preheater to exchange heat with the steam condensate, the steam condensate temperature is 113°C, and obtaining the secondary preheated liquid with a temperature of 84°C;

[0160] S3: separating the non-condensable gas after heat exchange in step S1 into gas and liquid, and passing the separated steam condensate into the sodium sulfate condensate preheater in step S2;

[0161] S4: Circulating heating and concentrating the secondary preheated liquid, the heating and concentrating temperature is 105°C, to obtain sodium sulfate slurry, non-condensable gas and steam condensate, the obtained non-condensable gas is passed into the sodium sulfate non-condensable gas preheater in step S1, and the steam condensate is passed into the sodium sulfate condensate preheater in step S2;

[0162] S5: thickening and centrifuging the sodium sulfate slurry, the solid component separated in the centrifugal process is the crude sodium sulfate product, and the liquid component separated in the thickening and centrifugal process is the sodium sulfate mother liquor; the crude sodium sulfate product is dried to obtain anhydrous sodium sulfate, and in the drying process, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water;

[0163] S6: After cooling the sodium sulfate mother liquor with 30°C circulating cooling water, the mother liquor is passed into the crystallization mother liquor precooler to exchange cooling with the crystallization mother liquor. The crystallization mother liquor temperature is -5°C, and a precooled feed liquid is obtained with a temperature of 21.5°C. The temperature of the crystallization mother liquor after cooling is 28.5°C;

[0164] S7: performing cyclic freezing and crystallization on the pre-cooled liquid to obtain a frozen slurry; performing sedimentation and centrifugation on the frozen slurry to obtain a crystallization mother liquor and mirabilite; and passing the crystallization mother liquor into the crystallization mother liquor precooler in step S6;

[0165] S8: passing the crystallization mother liquor after cooling in step S6 into the sodium chloride non-condensable gas preheater, exchanging heat with the non-condensable gas, the non-condensable gas temperature is 115° C., and obtaining a preheated sodium chloride feed liquid;

[0166] S9: passing the primary preheated sodium chloride feed liquid into a sodium chloride condensate preheater to exchange heat with steam condensate, the steam condensate temperature is 115° C., and obtaining a secondary preheated sodium chloride feed liquid, the temperature of which is 82° C.;

[0167] S10: separating the non-condensable gas after heat exchange in step S8 into gas and liquid, and passing the separated steam condensate into the sodium chloride condensate preheater in step S9;

[0168] S11: Circulating heating and concentrating the secondary preheated sodium chloride liquid, the heating and concentrating temperature is 106°C, to obtain sodium chloride slurry, non-condensable gas and steam condensate, the obtained non-condensable gas is passed into the sodium chloride non-condensable gas preheater in step S8, and the steam condensate is passed into the sodium chloride condensate preheater in step S9;

[0169] S12: thickening and centrifuging the sodium chloride slurry, wherein the solid component separated in the centrifugal process is the crude sodium chloride product, and the liquid component separated in the thickening and centrifugal process is the sodium chloride mother liquor; the crude sodium chloride product is dried to obtain industrial salt, and in the drying process, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water;

[0170] S13: drying the sodium chloride mother liquor to obtain impure salt; in the process of drying the sodium chloride mother liquor, using the air after heat exchange with the raw steam as the heat source, and the steam and steam condensate obtained after heat exchange with the raw steam are used as boiler make-up water.

[0171] Comparative Example 1

[0172] The sodium sulfate non-condensable gas preheater, sodium sulfate condensate preheater, sodium chloride non-condensable gas preheater and sodium chloride condensate preheater after applying the thermal insulation coating in Comparative Preparation Example 1 are used to recover sodium sulfate and sodium chloride from mine water pretreated by conventional methods (same as Example 1) and membrane concentrated, and the steps are as follows:

[0173] S1: The mine water to be treated is passed into the sodium sulfate non-condensable gas preheater, with the inlet water temperature of 25°C and the mass flow rate of 12520 kg / h, and heat is exchanged with the non-condensable gas, and the non-condensable gas temperature is 112°C to obtain a primary preheated liquid;

[0174] S2: passing the primary preheated liquid into the sodium sulfate condensate preheater to exchange heat with the steam condensate, the steam condensate temperature is 112°C, and obtaining the secondary preheated liquid with a temperature of 78°C;

[0175] S3: separating the non-condensable gas after heat exchange in step S1 into gas and liquid, and passing the separated steam condensate into the sodium sulfate condensate preheater in step S2;

[0176] S4: Circulating heating and concentrating the secondary preheated liquid, the heating and concentrating temperature is 105°C, to obtain sodium sulfate slurry, non-condensable gas and steam condensate, the obtained non-condensable gas is passed into the sodium sulfate non-condensable gas preheater in step S1, and the steam condensate is passed into the sodium sulfate condensate preheater in step S2;

[0177] S5: thickening and centrifuging the sodium sulfate slurry, the solid component separated in the centrifugal process is the crude sodium sulfate product, and the liquid component separated in the thickening and centrifugal process is the sodium sulfate mother liquor; the crude sodium sulfate product is dried to obtain anhydrous sodium sulfate, and in the drying process, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water;

[0178] S6: After cooling the sodium sulfate mother liquor with circulating cooling water at 30°C, the mother liquor is passed into a crystallization mother liquor precooler to exchange cooling with the crystallization mother liquor. The temperature of the crystallization mother liquor is -5°C, and a precooled feed liquid is obtained with a temperature of 21°C. The temperature of the crystallization mother liquor after cooling is 26°C;

[0179] S7: performing cyclic freezing and crystallization on the pre-cooled liquid to obtain a frozen slurry; performing sedimentation and centrifugation on the frozen slurry to obtain a crystallization mother liquor and mirabilite; and passing the crystallization mother liquor into the crystallization mother liquor precooler in step S6;

[0180] S8: passing the crystallization mother liquor after cooling in step S6 into a sodium chloride non-condensable gas preheater, exchanging heat with the non-condensable gas, the non-condensable gas temperature is 110° C., and obtaining a preheated sodium chloride feed liquid;

[0181] S9: passing the primary preheated sodium chloride feed liquid into a sodium chloride condensate preheater to exchange heat with steam condensate, the steam condensate temperature is 110° C., and obtaining a secondary preheated sodium chloride feed liquid, the temperature of which is 74° C.;

[0182] S10: separating the non-condensable gas after heat exchange in step S8 into gas and liquid, and passing the separated steam condensate into the sodium chloride condensate preheater in step S9;

[0183] S11: Circulating heating and concentrating the secondary preheated sodium chloride liquid, the heating and concentrating temperature is 106°C, to obtain sodium chloride slurry, non-condensable gas and steam condensate, the obtained non-condensable gas is passed into the sodium chloride non-condensable gas preheater in step S8, and the steam condensate is passed into the sodium chloride condensate preheater in step S9;

[0184] S12: thickening and centrifuging the sodium chloride slurry, wherein the solid component separated in the centrifugal process is the crude sodium chloride product, and the liquid component separated in the thickening and centrifugal process is the sodium chloride mother liquor; the crude sodium chloride product is dried to obtain industrial salt, and in the drying process, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water;

[0185] S13: drying the sodium chloride mother liquor to obtain impure salt; in the process of drying the sodium chloride mother liquor, using the air after heat exchange with the raw steam as the heat source, and the steam and steam condensate obtained after heat exchange with the raw steam are used as boiler make-up water.

[0186] Data analysis: Compared with Preparation Example 1, the thermal conductivity of the thermal insulation coating of Comparative Preparation Example 1 is significantly higher; and when the preheater with the thermal insulation coating applied is used to recover sodium sulfate and sodium chloride from mine water, the preheating effect of Comparative Example 1 on the treated mine water and crystallization mother liquor is poorer than that of Example 1. This is because the comparative preparation example 1 did not perform ultraviolet light irradiation treatment to dimerize the anthracene groups during the preparation of the aerogel, and the degree of cross-linking between cellulose was low, so the skeleton support effect was low during the preparation of the aerogel and the coating, and the coating matrix (styrene-acrylic emulsion) easily penetrated into the pores, causing the pore structure to be easily destroyed, which led to the poor thermal insulation effect of the aerogel in the coating.

[0187] Comparative Example 2

[0188] The sodium sulfate non-condensable gas preheater, sodium sulfate condensate preheater, sodium chloride non-condensable gas preheater and sodium chloride condensate preheater after applying the thermal insulation coating in Comparative Preparation Example 2 are used to recover sodium sulfate and sodium chloride from mine water pretreated by conventional methods (same as Example 1) and membrane concentrated, and the steps are as follows:

[0189] S1: The mine water to be treated is passed into the sodium sulfate non-condensable gas preheater, with the inlet water temperature of 25°C and the mass flow rate of 12520 kg / h, and heat is exchanged with the non-condensable gas, and the non-condensable gas temperature is 113°C to obtain a primary preheated liquid;

[0190] S2: passing the primary preheated liquid into the sodium sulfate condensate preheater to exchange heat with the steam condensate, the steam condensate temperature is 113°C, and obtaining the secondary preheated liquid with a temperature of 76°C;

[0191] S3: separating the non-condensable gas after heat exchange in step S1 into gas and liquid, and passing the separated steam condensate into the sodium sulfate condensate preheater in step S2;

[0192] S4: Circulating heating and concentrating the secondary preheated liquid, the heating and concentrating temperature is 105°C, to obtain sodium sulfate slurry, non-condensable gas and steam condensate, the obtained non-condensable gas is passed into the sodium sulfate non-condensable gas preheater in step S1, and the steam condensate is passed into the sodium sulfate condensate preheater in step S2;

[0193] S5: thickening and centrifuging the sodium sulfate slurry, the solid component separated in the centrifugal process is the crude sodium sulfate product, and the liquid component separated in the thickening and centrifugal process is the sodium sulfate mother liquor; the crude sodium sulfate product is dried to obtain anhydrous sodium sulfate, and in the drying process, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water;

[0194] S6: After cooling the sodium sulfate mother liquor with 30°C circulating cooling water, the mother liquor is passed into the crystallization mother liquor precooler to exchange cooling with the crystallization mother liquor. The crystallization mother liquor temperature is -5°C, and a precooled feed liquid is obtained with a temperature of 21.5°C. The temperature of the crystallization mother liquor after cooling is 28°C;

[0195] S7: performing cyclic freezing and crystallization on the pre-cooled liquid to obtain a frozen slurry; performing sedimentation and centrifugation on the frozen slurry to obtain a crystallization mother liquor and mirabilite; and passing the crystallization mother liquor into the crystallization mother liquor precooler in step S6;

[0196] S8: passing the crystallization mother liquor after cooling in step S6 into the sodium chloride non-condensable gas preheater, exchanging heat with the non-condensable gas, the non-condensable gas temperature is 112° C., and obtaining a preheated sodium chloride feed liquid;

[0197] S9: passing the primary preheated sodium chloride feed liquid into a sodium chloride condensate preheater to exchange heat with steam condensate, the steam condensate temperature is 112° C., and obtaining a secondary preheated sodium chloride feed liquid, the temperature of which is 70° C.;

[0198] S10: separating the non-condensable gas after heat exchange in step S8 into gas and liquid, and passing the separated steam condensate into the sodium chloride condensate preheater in step S9;

[0199] S11: Circulating heating and concentrating the secondary preheated sodium chloride liquid, the heating and concentrating temperature is 106°C, to obtain sodium chloride slurry, non-condensable gas and steam condensate, the obtained non-condensable gas is passed into the sodium chloride non-condensable gas preheater in step S8, and the steam condensate is passed into the sodium chloride condensate preheater in step S9;

[0200] S12: thickening and centrifuging the sodium chloride slurry, wherein the solid component separated in the centrifugal process is the crude sodium chloride product, and the liquid component separated in the thickening and centrifugal process is the sodium chloride mother liquor; the crude sodium chloride product is dried to obtain industrial salt, and in the drying process, air after heat exchange with raw steam is used as a heat source, and the steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water;

[0201] S13: drying the sodium chloride mother liquor to obtain impure salt; in the process of drying the sodium chloride mother liquor, using the air after heat exchange with the raw steam as the heat source, and the steam and steam condensate obtained after heat exchange with the raw steam are used as boiler make-up water.

[0202] Data analysis: Compared with Preparation Example 1, the thermal conductivity of the thermal insulation coating of Comparative Preparation Example 2 is significantly higher; and when the preheater with the thermal insulation coating applied is used to recover sodium sulfate and sodium chloride from mine water, the preheating effect of Comparative Example 2 on the treated mine water and crystallization mother liquor is poorer than that of Example 1. This is because after the coating is made, Comparative Preparation Example 2 is not subjected to ultraviolet irradiation treatment to decompose the anthracene dimer, the degree of cross-linking between cellulose is high, and the solid-state thermal conductivity inside is large, which leads to poor thermal insulation effect of the aerogel in the coating.

[0203] The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art.

[0204] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for recovering sodium sulfate and sodium chloride from mine water, characterized in that: The following steps are involved: S1: passing the mine water to be treated into a sodium sulfate non-condensable gas preheater, exchanging heat with the non-condensable gas to obtain a primary preheated liquid; S2: passing the primary preheated liquid into a sodium sulfate condensate preheater to exchange heat with steam condensate to obtain a secondary preheated liquid; S3: separating the non-condensable gas after heat exchange in step S1 into gas and liquid, and passing the separated steam condensate into the sodium sulfate condensate preheater; S4: heating and concentrating the secondary preheated liquid to obtain sodium sulfate slurry, non-condensable gas and steam condensate, passing the obtained non-condensable gas into the sodium sulfate non-condensable gas preheater, and passing the steam condensate into the sodium sulfate condensate preheater; S5: performing solid-liquid separation on the sodium sulfate slurry to obtain a crude sodium sulfate product and a sodium sulfate mother liquor; S6: crystallizing the sodium sulfate mother liquor to obtain sodium sulfate and a crystallization mother liquor; S7: recovering sodium chloride from the crystallization mother liquor; The inner wall and / or outer wall of the sodium sulfate non-condensable gas preheater and / or the sodium sulfate condensable water preheater are coated with a thermal insulation coating; The preparation method of the thermal insulation coating comprises the following steps: coating a slurry containing hydrophobic cellulose aerogel on the inner wall and / or the outer wall to form a coating, and then irradiating the coating with ultraviolet light having a wavelength less than 300 nm; the crosslinking agent of the hydrophobic cellulose aerogel comprises the following components: a mercaptosilane coupling agent, and a compound containing alkenyl and anthracene groups; the mercaptosilane coupling agent contains at least two siloxy groups.

2. The method according to claim 1, characterized in that The specific process of step S6 includes the following steps: S6.1: After precooling the sodium sulfate mother liquor, the mother liquor is passed into a crystallization mother liquor precooler to exchange cooling with the crystallization mother liquor to obtain a precooled feed liquid; S6.2: freeze-crystallize the pre-cooled liquid to obtain frozen slurry; perform solid-liquid separation on the frozen slurry to obtain crystallization mother liquor and mirabilite; and pass the crystallization mother liquor into the crystallization mother liquor precooler.

3. The method according to claim 1, characterized in that The specific process of step S7 includes the following steps: S7.1: passing the crystallization mother liquor into the sodium chloride non-condensable gas preheater, exchanging heat with the non-condensable gas, and obtaining a preheated sodium chloride feed liquid; S7.2: passing the primary preheated sodium chloride feed liquid into a sodium chloride condensate preheater to exchange heat with steam condensate to obtain a secondary preheated sodium chloride feed liquid; S7.3: separating the non-condensable gas after heat exchange in step S7.1 into gas and liquid, and passing the separated steam condensate into the sodium chloride condensate preheater; S7.4: heating and concentrating the secondary preheated sodium chloride liquid to obtain sodium chloride slurry, non-condensable gas and steam condensate, passing the obtained non-condensable gas into the sodium chloride non-condensable gas preheater, and passing the steam condensate into the sodium chloride condensate preheater; S7.5: performing solid-liquid separation on the sodium chloride slurry to obtain a crude sodium chloride product and a sodium chloride mother liquor; S7.6: Dry the sodium chloride mother liquor to obtain impure salt.

4. The method according to claim 1, characterized in that In step S5, after obtaining the crude sodium sulfate product, the crude sodium sulfate product is dried to obtain anhydrous sodium sulfate; in the process of drying the crude sodium sulfate product, air after heat exchange with raw steam is used as a heat source, and steam and steam condensate obtained after heat exchange with raw steam are used as boiler make-up water.

5. The method according to claim 3, characterized in that: In step S7.5, after obtaining the crude sodium chloride product, the crude sodium chloride product is dried to obtain industrial salt; in the process of drying the crude sodium chloride product, air after heat exchange with raw steam is used as a heat source, and steam and steam condensate obtained after heat exchange with raw steam are used as boiler feed water; and / or In step S7.6, during the drying process of the sodium chloride mother liquor, the air after heat exchange with the raw steam is used as the heat source, and the steam and steam condensate obtained after heat exchange with the raw steam are used as boiler make-up water.

6. The method according to claim 2, characterized in that In step S6.1, the method for precooling the sodium sulfate mother liquor is to use circulating cooling water at 25-35°C for cooling.

7. The method according to claim 1, characterized in that The preparation method of the hydrophobic cellulose aerogel comprises the following steps: using nanocellulose, a methyl silane coupling agent, a mercapto silane coupling agent, a compound containing alkenyl and anthracene groups and a solvent as raw materials, performing a hydrolysis condensation reaction, and performing a click reaction and anthracene dimerization reaction under ultraviolet light with a wavelength greater than 300 nm to prepare the hydrophobic cellulose aerogel.

8. The method according to claim 1 or 7, characterized in that The molar ratio of the mercapto group in the mercaptosilane coupling agent to the alkenyl group in the compound containing alkenyl and anthracene groups is 1:1-5.

9. The method according to claim 7, characterized in that The weight average molecular weight of the nanocellulose is 40-60 kDa; the methyl silane coupling agent and the mercapto silane coupling agent both contain three siloxy groups; and the ratio of the molar amount of the nanocellulose to the total molar amount of the methyl silane coupling agent and the mercapto silane coupling agent is 1:420-630.