Method and system for preparing sodium bicarbonate and co-producing ammonium sulfate from mirabilite at low temperature

Abstract

The invention relates to preparation of sodium bicarbonate co-production ammonium sulfate, in particular to a method and a system for preparing sodium bicarbonate co-production ammonium sulfate from low-temperature mirabilite, and aims to overcome the defects that high-purity ammonium sulfate cannot be obtained or the technical route of twice freezing-high-temperature ammonia distillation is high in energy consumption and large in industrialization difficulty in the prior art. The method for preparing sodium bicarbonate and co-producing ammonium sulfate from mirabilite at low temperature comprises the steps of preparing sodium bicarbonate, preparing ammonium sodium solid salt, acidifying and crystallizing the ammonium sodium solid salt, cooling and crystallizing, and preparing ammonium sulfate, and the sodium sulfate and the ammonium sodium solid salt are removed to obtain a high-purity sodium bicarbonate product and an ammonium sulfate product. In the system for preparing sodium bicarbonate and co-producing ammonium sulfate from mirabilite at low temperature, a plurality of evaporation devices and recycling pipelines among the evaporation devices are reasonably arranged, so that full utilization and recovery of products in each step are realized.

Description

Technical Field

[0001] The invention relates to the preparation of sodium bicarbonate and ammonium sulfate, and in particular to a method and system for preparing sodium bicarbonate and ammonium sulfate by using low-temperature sodium sulfate. Background Art

[0002] With the acceleration of economic development and industrialization, the amount of industrial water and high-salt wastewater is increasing day by day. The amount of high-salt wastewater in the steel, petrochemical, coal chemical, printing and dyeing, dairy products, mining and other industries is particularly considerable. The composition of wastewater is gradually increasing, and the concentration is gradually increasing. At present, the quality separation and crystallization technology and resource utilization of high-salt wastewater have received extensive attention. Among them, nanofiltration separation, evaporation crystallization, cooling crystallization and other technologies have been maturely applied. After treatment, sodium sulfate and sodium chloride crystals are finally crystallized, and the purity of the dry product can reach more than 98.5%, with high yield and high quality.

[0003] The chlor-alkali industry uses sodium chloride as the main raw material to produce hydrogen, chlorine, caustic soda and other chemical products, and has achieved high-value resource utilization of industrial-grade sodium chloride; however, there are still relatively few ways to utilize industrial-grade sodium sulfate. The industrial-grade sodium sulfate obtained by enterprises from salt separation is piled up in large quantities and has poor sales. The price of industrial-grade sodium sulfate is relatively low, and the certification indicators and certification methods of its crystal products lack relevant standards, which hinders its true resource utilization as a commodity.

[0004] At present, my country's chemical metallurgical industry uses a large amount of sulfuric acid and sodium alkali, producing a large amount of waste sodium sulfate, with an annual production of more than 10 million tons. At present, only a small amount is used to produce sodium sulfate and sodium sulfide, with limited consumption capacity and a large amount of sodium sulfate stored. In order to solve the problem of resource utilization of waste sodium sulfate, domestic and foreign researchers have done a lot of work, but have not been able to make a breakthrough. At present, the use of sodium sulfate to make soda ash has always been the key research direction of the soda ash industry, and it is also an effective way to alleviate the pressure of by-product sodium sulfate storage. The method of preparing sodium bicarbonate and ammonium sulfate by double decomposition reaction of sodium sulfate and ammonium bicarbonate is the most ideal, but the bottleneck of this technology is that the conversion rate of sodium sulfate and ammonium bicarbonate is only 50-60%. After the precipitation of sodium bicarbonate, the phase point of the solution system is in the crystallization zone of sodium sulfate or complex salt, and high-purity ammonium sulfate cannot be obtained. Foreign researchers have adopted the technical route of twice freezing-high-temperature ammonia evaporation to prepare ammonium sulfate. The process is stable, but the energy consumption is high and the industrialization is difficult. After the expansion test, it stagnated. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art that high-purity ammonium sulfate cannot be obtained, or the technical route of twice freezing-high-temperature ammonia evaporation has high energy consumption and great difficulty in industrialization, and to provide a method and system for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate.

[0006] To achieve the above objectives, the technical solutions provided by the present invention are as follows:

[0007] A method for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate, which is special in that it comprises the following steps:

[0008] S1. Preparation of sodium bicarbonate: adding ammonium bicarbonate solid to low-temperature mirabilite slurry, reacting and crystallizing sodium bicarbonate, separating solid and liquid to obtain wet sodium bicarbonate and sodium bicarbonate mother liquor, and drying the wet sodium bicarbonate to obtain a sodium bicarbonate product; the temperature of the low-temperature mirabilite slurry is -5°C-35°C; the reaction time is 1-4 hours, the reaction temperature is 25-40°C, and the mass ratio of ammonium bicarbonate solid to sodium sulfate in the low-temperature mirabilite slurry is (1.5-3): 1;

[0009] S2. Preparation of sodium ammonium solid salt: adding sodium bicarbonate mother liquor to low-temperature mirabilite slurry, reacting and crystallizing, collecting the upper clear liquid and the lower crystal slurry, respectively, and performing solid-liquid separation on the lower crystal slurry to obtain sodium ammonia solid salt; the reaction time is 6-12 hours, the reaction temperature is 25-35 ° C, and the mass ratio of sodium bicarbonate mother liquor and low-temperature mirabilite slurry is 1: (0.8-1.2);

[0010] S3. Acidification and crystallization of sodium ammonia solid salt: dissolving and acidifying the sodium ammonia solid salt, then heating to precipitate sodium sulfate crystals, collecting the upper clear liquid and the lower crystal slurry, respectively, and performing solid-liquid separation on the lower crystal slurry to obtain sodium sulfate solid; the acidification is specifically to adjust the pH to 3-5 and heat to 80-90°C;

[0011] S4. Cooling crystallization: The supernatant obtained in step S3 is cooled to 20 to 30 ° C for crystallization, and the supernatant and the lower crystal slurry are collected, and the lower crystal slurry is subjected to solid-liquid separation to obtain a solid ammonium sodium salt, and the solid ammonium sodium salt is returned to step S3;

[0012] S5. Preparation of ammonium sulfate: The supernatant obtained in step S4 is evaporated and crystallized to obtain ammonium sulfate crystals, the supernatant and the lower crystal slurry are collected separately, the lower crystal slurry is solid-liquid separated to obtain ammonium sulfate solid, and the ammonium sulfate product is obtained after drying.

[0013] Furthermore, in step S1, the preparation method of the low-temperature mirabilite slurry is specifically as follows:

[0014] Mixing sodium sulfate and its solvent uniformly to obtain sodium sulfate slurry, and cooling to obtain low-temperature mirabilite slurry; the molar ratio of sodium sulfate to solvent is 1:(9-11), and the solvent is water and / or the supernatant of step S2;

[0015] Alternatively, the low temperature mirabilite slurry is made of Na 2 SO 4 10H 2 O cooling is obtained.

[0016] Furthermore, step S2 is specifically as follows:

[0017] S2.1. Add low-temperature mirabilite slurry to the sodium bicarbonate mother liquor obtained in step S1, mix well, react and crystallize, and collect the lower crystal slurry and the upper clear liquid respectively;

[0018] S2.2. The lower crystal slurry obtained in step S2.1 is thickened to obtain a thickened slurry having a solid-liquid ratio of 30 wt% to 40 wt%. The thickened slurry is centrifuged to obtain a sodium ammonia solid salt and a centrifuged mother liquor, and the sodium ammonia solid salt is collected and entered into step S3; the centrifuged mother liquor and the thickened liquid are collected and returned to the system of step S2.1;

[0019] The supernatant obtained in step S2.1 is clarified to obtain a first clarified liquid and a solid precipitate. The first clarified liquid is collected and used to prepare low-temperature mirabilite slurry, and the solid precipitate is collected and returned to the system of step S2.1.

[0020] Furthermore, step S3 is specifically as follows:

[0021] S3.1. Dissolve all the solid sodium ammonia salt, add concentrated sulfuric acid to adjust the pH, then heat it to 80-90°C for crystallization, and collect the lower crystal slurry and the upper clear liquid respectively;

[0022] The mass ratio of sodium ammonia solid salt to water used for dissolution is (3-4):1; the concentration of concentrated sulfuric acid is 98wt%;

[0023] S3.2. The lower crystal slurry of step S3.1 is centrifuged to obtain sodium sulfate solid and centrifuged mother liquor, sodium sulfate solid is collected for preparing low-temperature mirabilite slurry, and the centrifuged mother liquor is returned to the system of step S3.1;

[0024] The supernatant in step S3.1 is clarified to obtain a solid precipitate and a second clarified liquid. The solid precipitate is collected and returned to the system of step S3.1, and the second clarified liquid enters step S4.

[0025] Furthermore, step S4 is specifically as follows:

[0026] S4.1. Cool the second clarified liquid to 20-30°C to precipitate crystals, and collect the lower crystal slurry and the upper clear liquid;

[0027] S4.2. The lower crystal slurry of step S4.1 is thickened to obtain a thickened slurry having a solid-liquid ratio of 30 wt% to 40 wt%. The thickened slurry is centrifuged to obtain a solid sodium ammonium salt and a centrifuged mother liquor thereof. The solid sodium ammonium salt is collected and returned to step S3.1 for treatment. The centrifuged mother liquor of the solid sodium ammonium salt and the thickened liquid are collected and returned to the system of step S4.1.

[0028] The supernatant liquid in step S4.1 is clarified to obtain a third clarified liquid and a solid precipitate. The third clarified liquid is collected and enters step S5, and the solid precipitate is returned to the system of step S4.1.

[0029] Furthermore, step S5 is specifically as follows:

[0030] S5.1. Evaporating and crystallizing the third clarified liquid, and collecting the lower crystal slurry and the upper clear liquid;

[0031] S5.2. The supernatant of step S5.1 is clarified to obtain a fourth clarified liquid and a solid precipitate, the fourth clarified liquid is returned to step S4.1 and mixed with the second clarified liquid for cooling and crystallization, and the solid precipitate is returned to step S5.1 and added to the third clarified liquid for evaporation and crystallization;

[0032] The lower layer crystal slurry of step S5.1 is thickened to obtain a thickened slurry with a solid-liquid ratio of 30wt% to 40wt%, which is centrifuged to obtain ammonium sulfate solid salt and its centrifugal mother liquor, the ammonium sulfate solid salt is collected, and dried to obtain an ammonium sulfate product; the thickened liquid and the centrifugal mother liquor of the ammonium sulfate solid salt are returned to step S5.1 and added to the third clarified liquid for evaporation and crystallization.

[0033] Further, in step S1, the mass ratio of ammonium bicarbonate solid to sodium sulfate in the low-temperature mirabilite slurry is 2:1;

[0034] In step S2, the mass ratio of the sodium bicarbonate mother liquor to the low-temperature sodium sulfate slurry is 1:1.

[0035] At the same time, the present invention also provides a system for preparing sodium bicarbonate and ammonium sulfate with low-temperature thenardite, which is used to realize the method for preparing sodium bicarbonate and ammonium sulfate with low-temperature thenardite, and the system is special in that it includes a sodium bicarbonate production unit, an ammonium sodium solid salt production unit, an acidification crystallization unit, a cooling crystallization unit and an ammonium sulfate production unit; the sodium bicarbonate production unit includes a sodium bicarbonate crystallizer, a first solid-liquid separation device and a sodium bicarbonate drying device, the first inlet of the sodium bicarbonate crystallizer is used to input low-temperature thenardite slurry, the second inlet is used to input ammonium bicarbonate solid, and the outlet of the sodium bicarbonate crystallizer is connected to the first solid-liquid separation device The solid outlet of the first solid-liquid separation device is connected to the sodium bicarbonate drying device; the sodium ammonium solid salt production unit includes a salting-out crystallizer and a second solid-liquid separation device, the first inlet of the salting-out crystallizer is connected to the liquid outlet of the first solid-liquid separation device, the upper and lower parts of the salting-out crystallizer are respectively provided with a first upper outlet and a first lower outlet, the first upper outlet is used to discharge the upper clear liquid, the first lower outlet is connected to the inlet of the second solid-liquid separation device, and the liquid outlet of the second solid-liquid separation device is connected to the second inlet of the salting-out crystallizer; the acidification crystallization unit includes a Glauber's salt crystallizer and a third solid-liquid separation device, the first inlet of the Glauber's salt crystallizer is connected to the The solid outlet of the second solid-liquid separation device is connected to the solid outlet of the second solid-liquid separation device, the upper and lower parts of the Glauber's salt crystallizer are respectively provided with a second upper outlet and a second lower outlet, the second lower outlet is connected to the inlet of the third solid-liquid separation device, the liquid outlet of the third solid-liquid separation device is connected to the second inlet of the Glauber's salt crystallizer, and the solid outlet is used to discharge sodium sulfate solid; the cooling crystallization unit includes a cooling crystallization device and a fourth solid-liquid separation device, the first inlet of the cooling crystallization device is connected to the second upper outlet of the Glauber's salt crystallizer, the upper and lower parts of the cooling crystallization device are respectively provided with a third upper outlet and a third lower outlet, the third lower outlet is connected to the inlet of the fourth solid-liquid separation device, and the fourth solid-liquid separation device is connected to the third solid-liquid separation device. The liquid outlet of the separation device is connected to the second inlet of the cooling crystallization device, and the solid outlet is connected to the third inlet of the mirabilite crystallizer; the ammonium sulfate production unit includes an evaporation crystallizer, a fifth solid-liquid separation device and an ammonium sulfate drying device, the first inlet of the evaporation crystallizer is connected to the third upper outlet of the cooling crystallization device, the upper part and the lower part of the evaporation crystallizer are respectively provided with a fourth upper outlet and a fourth lower outlet, the fourth upper outlet is connected to the third inlet of the cooling crystallization device, the fourth lower outlet is connected to the inlet of the fifth solid-liquid separation device, the liquid outlet of the fifth solid-liquid separation device is connected to the second inlet of the evaporation crystallizer, and the solid outlet is connected to the ammonium sulfate drying device.

[0036] Furthermore, it also includes a low-temperature thenardite unit, which includes a sodium sulfate silo, a sodium sulfate slurry tank and a sodium sulfate heat exchanger, wherein the outlet of the sodium sulfate silo is connected to the first inlet of the sodium sulfate slurry tank, the second inlet of the sodium sulfate slurry tank is used to input the solvent, and the sodium sulfate heat exchanger is connected to the sodium sulfate slurry tank for cooling it;

[0037] The first upper outlet is connected to the third inlet of the sodium sulfate slurry tank, and the solid outlet of the third solid-liquid separation device is connected to the inlet of the sodium sulfate silo;

[0038] A sodium ammonium solid salt clarification tank is arranged between the first upper outlet and the third inlet of the sodium sulfate slurry tank, the liquid outlet of the sodium ammonium solid salt clarification tank is connected to the third inlet of the sodium sulfate slurry tank, and the solid outlet is connected to the third inlet of the salting-out crystallizer;

[0039] A sodium sulfate clarification tank is arranged between the second upper outlet and the first inlet of the cooling crystallization device, the liquid outlet of the sodium sulfate clarification tank is connected to the first inlet of the cooling crystallization device, and the solid outlet is connected to the fourth inlet of the mirabilite crystallizer;

[0040] A cooling and clarifying tank is arranged between the third upper outlet and the first inlet of the evaporation crystallizer, the liquid outlet of the cooling and clarifying tank is connected to the first inlet of the evaporation crystallizer, and the solid outlet is connected to the fourth inlet of the temperature reduction crystallization device;

[0041] An ammonium sulfate clarification tank is arranged between the fourth upper outlet and the third inlet of the cooling crystallization device, the liquid outlet of the ammonium sulfate clarification tank is connected to the third inlet of the cooling crystallization device, and the solid outlet is connected to the third inlet of the evaporation crystallizer.

[0042] Furthermore, the mirabilite crystallizer comprises a primary crystallizer and a secondary crystallizer which are connected in sequence, the inlet of the primary crystallizer is connected to the solid outlet of the second solid-liquid separation device, the secondary crystallizer is connected to the inlet of the third solid-liquid separation device through the second lower outlet, the liquid outlet of the third solid-liquid separation device is connected to the secondary crystallizer, and the solid outlet of the fourth solid-liquid separation device is connected to the primary crystallizer;

[0043] The cooling crystallization device comprises a primary flash tank, a secondary flash tank and a tertiary flash tank which are connected in sequence, the inlet of the primary flash tank is connected to the second upper outlet, the tertiary flash tank is connected to the inlet of the fourth solid-liquid separation device through the third lower outlet, and the liquid outlet of the fourth solid-liquid separation device is connected to the primary flash tank;

[0044] The first inlet of the evaporation crystallizer is connected to the third-stage flash tank, and the fourth upper outlet of the evaporation crystallizer is connected to the first-stage flash tank;

[0045] The first solid-liquid separation device, the second solid-liquid separation device, the third solid-liquid separation device, the fourth solid-liquid separation device, and the fifth solid-liquid separation device are respectively a belt filter, a sodium ammonia solid salt centrifuge, a mirabilite centrifuge, a cooling centrifuge, and an ammonium sulfate centrifuge.

[0046] Beneficial effects of the present invention:

[0047] 1. The method for preparing sodium bicarbonate and ammonium sulfate from low-temperature sodium sulfate of the present invention mainly produces ammonium sulfate and sodium bicarbonate by double decomposition reaction of sodium sulfate and ammonium bicarbonate, and the reaction equation is as follows:

[0048] Na 2 SO 4 +(NH 4 )HCO 3 =2(NH 4 ) 2 SO 4 +NaHCO 3

[0049] Sodium sulfate and ammonium bicarbonate are used as raw materials to react to produce (NH 4 ) 2 SO 4 Afterwards, the solid salts of sodium sulfate and sodium ammonium are removed through multiple evaporation and crystallization, and the generated (NH 4 ) 2 SO 4 , reducing impurities in ammonium sulfate, the method has a simple process and low preparation cost, wherein, by recycling the mother liquor of sodium ammonium solid salt, the bicarbonate therein is fully reacted, so that the utilization rate of ammonium bicarbonate is greater than 85%, the purity of sodium bicarbonate in the obtained sodium bicarbonate product is greater than 90%, meeting the requirements of GB / T 1606-2008, and the purity of ammonium sulfate in the obtained ammonium sulfate product meets the requirements of GB535-1995.

[0050] 2. The present invention uses low-temperature sodium sulfate as a raw material. During the production process, the temperature of the reaction system can be controlled by adding low-temperature sodium sulfate to ensure the crystallization temperature. There is no need to set up an additional heat exchange device, thereby simplifying the production process and operation process.

[0051] 3. In the system for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate of the present invention, multiple evaporation devices and recycling pipelines between the multiple evaporation devices are reasonably arranged to achieve full utilization and recovery of the products of each step, so that the entire system achieves zero emission and fully utilizes the raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a flow chart of Example 1 of the method for preparing sodium bicarbonate and co-producing ammonium sulfate using low-temperature mirabilite of the present invention;

[0053] Figure 2 The present invention is a schematic diagram of the principle of a system for preparing sodium bicarbonate and co-producing ammonium sulfate using low-temperature sodium sulfate in accordance with a first embodiment of the present invention.

[0054] Description of reference numerals:

[0055] 1-sodium sulfate slurry tank, 101-screw conveyor, 2-sodium bicarbonate crystallizer, 201-ammonium bicarbonate silo, 202-belt filter, 203-sodium bicarbonate drying device, 3-salting out crystallizer, 301-sodium ammonia solid salt centrifuge, 4-glauber's salt crystallizer, 401-glauber's salt centrifuge, 402-sodium sulfate heat exchanger, 5-cooling crystallization device, 501-cooling centrifuge, 502-condenser, 6-evaporation crystallizer, 601-ammonium sulfate centrifuge, 602-ammonium sulfate drying device, 603-ammonium sulfate heat exchanger. DETAILED DESCRIPTION

[0056] Embodiment 1

[0057] The present invention provides a system for preparing sodium bicarbonate and co-producing ammonium sulfate using low-temperature sodium sulfate. Figure 2 As shown, it includes a low-temperature thenardite unit, a sodium bicarbonate production unit, a sodium ammonium solid salt production unit, an acidification crystallization unit, a cooling crystallization unit and an ammonium sulfate production unit; the low-temperature thenardite unit includes a sodium sulfate silo, a sodium sulfate slurry tank 1 and a sodium sulfate heat exchanger 402, the outlet of the sodium sulfate silo is connected to the first inlet of the sodium sulfate slurry tank 1, and the second inlet of the sodium sulfate slurry tank 1 is used to input a sodium sulfate solvent.

[0058] The sodium bicarbonate production unit comprises a sodium bicarbonate crystallizer 2, a belt filter 202 and a sodium bicarbonate drying device 203, wherein the first inlet of the sodium bicarbonate crystallizer 2 is used to input low-temperature mirabilite slurry, the second inlet is used to input ammonium bicarbonate solid, the outlet of the sodium bicarbonate crystallizer 2 is connected to the inlet of the belt filter 202, and the solid outlet of the belt filter 202 is connected to the sodium bicarbonate drying device 203;

[0059] The sodium ammonium solid salt production unit includes a salting-out crystallizer 3 and a sodium ammonia solid salt centrifuge 301. The first inlet of the salting-out crystallizer 3 is connected to the liquid outlet of the belt filter 202. The upper part and the lower part of the salting-out crystallizer 3 are respectively provided with a first upper outlet and a first lower outlet. The first upper outlet is provided with a sodium ammonium solid salt clarification tank for discharging the upper clear liquid. The liquid outlet of the sodium ammonium solid salt clarification tank is connected to the third inlet of the sodium sulfate slurry tank 1, and the solid outlet of the sodium ammonium solid salt clarification tank is connected to the third inlet of the salting-out crystallizer 3; the first lower outlet is connected to the inlet of the sodium ammonia solid salt centrifuge 301, and the liquid outlet of the sodium ammonia solid salt centrifuge 301 is connected to the second inlet of the salting-out crystallizer 3.

[0060] The acidification crystallization unit includes a Glauber's salt crystallizer 4 and a Glauber's salt centrifuge 401. The first inlet of the Glauber's salt crystallizer 4 is connected to the solid outlet of the sodium ammonia solid salt centrifuge 301. The upper and lower parts of the Glauber's salt crystallizer 4 are respectively provided with a second upper outlet and a second lower outlet. The second lower outlet is connected to the inlet of the Glauber's salt centrifuge 401. The liquid outlet of the Glauber's salt centrifuge 401 is connected to the second inlet of the Glauber's salt crystallizer 4. The solid outlet of the Glauber's salt centrifuge 401 is connected to the inlet of the sodium sulfate silo for discharging sodium sulfate solid. The second upper outlet is provided with a sodium ammonium solid salt clarification tank.

[0061] The cooling crystallization unit includes a cooling crystallization device 5 and a cooling centrifuge 501. The first inlet of the cooling crystallization device 5 is connected to the liquid outlet of the ammonium sodium solid salt clarification tank. The upper part and the lower part of the cooling crystallization device 5 are respectively provided with a third upper outlet and a third lower outlet. The third lower outlet is connected to the inlet of the cooling centrifuge 501. The liquid outlet of the cooling centrifuge 501 is connected to the second inlet of the cooling crystallization device 5. The solid outlet is connected to the third inlet of the sodium ammonium solid salt clarification tank. The solid outlet of the sodium ammonium solid salt clarification tank is connected to the fourth inlet of the sodium ammonium solid salt crystallizer 4. The third upper outlet is provided with a cooling clarification tank.

[0062] The ammonium sulfate production unit includes an evaporation crystallizer 6, an ammonium sulfate centrifuge 601 and an ammonium sulfate drying device 602. The first inlet of the evaporation crystallizer 6 is connected to the liquid outlet of the cooling clarification tank. The upper part and the lower part of the evaporation crystallizer 6 are respectively provided with a fourth upper outlet and a fourth lower outlet. The fourth upper outlet is provided with an ammonium sulfate clarification tank. The liquid outlet of the ammonium sulfate clarification tank is connected to the third inlet of the cooling crystallization device 5. The solid outlet of the cooling clarification tank is connected to the fourth inlet of the cooling crystallization device 5. The fourth lower outlet is connected to the inlet of the ammonium sulfate centrifuge 601, the liquid outlet of the ammonium sulfate centrifuge 601 is connected to the second inlet of the evaporation crystallizer 6, the solid outlet of the ammonium sulfate centrifuge 601 is connected to the ammonium sulfate drying device 602, and the solid outlet of the ammonium sulfate clarification tank is connected to the third inlet of the evaporation crystallizer 6.

[0063] To facilitate production operations, a sodium bicarbonate mother liquor storage tank and a delivery pump are arranged between the liquid outlet of the belt filter 202 and the first inlet of the salting-out crystallizer 3, a sodium ammonia solid salt centrifugal mother liquor tank is arranged between the liquid outlet of the sodium ammonia solid salt centrifuge 301 and the second inlet of the salting-out crystallizer 3, a sodium sulfate centrifugal filtrate storage tank is arranged between the liquid outlet of the Glauber's salt centrifuge 401 and the second inlet of the Glauber's salt crystallizer 4, a cooling centrifugal filtrate storage tank is arranged between the liquid outlet of the cooling centrifuge 501 and the second inlet of the cooling crystallization device 5, and an ammonium sulfate centrifugal liquid tank is arranged between the liquid outlet of the ammonium sulfate centrifuge 601 and the second inlet of the evaporation crystallizer 6.

[0064] In order to improve the centrifugal efficiency, the present embodiment is further provided with a thickener before the belt filter 202, the sodium ammonia solid salt centrifuge 301, the mirabilite centrifuge 401, the cooling centrifuge 501 and the ammonium sulfate centrifuge 601. The material to be separated into solid and liquid is firstly thickened to make the solid-liquid ratio reach 30wt% to 40wt%. The liquid generated by the thickening is collected together with the liquid generated by the solid-liquid separation.

[0065] In order to improve the uniformity of the reaction materials, in this embodiment, a circulation pump is provided in the sodium sulfate slurry tank 1, the sodium bicarbonate crystallizer 2, the salting-out crystallizer 3, the mirabilite crystallizer 4, the cooling crystallization device 5 and the evaporation crystallizer 6.

[0066] To control the reaction temperature, in this embodiment, the mirabilite crystallizer 4 and the evaporation crystallizer 6 are respectively connected to the sodium sulfate heat exchanger 402 and the ammonium sulfate heat exchanger 603 to increase the temperature of the reaction materials. The cooling crystallization device 5 is also provided with a condenser 502 to condense and recover the evaporated steam.

[0067] Based on the above system, the present invention provides a method for preparing sodium bicarbonate and co-producing ammonium sulfate at low temperature. Figure 1 As shown, the following steps are included:

[0068] (1) Preparation of low-temperature sodium sulfate

[0069] Low-temperature mirabilite is obtained by mixing sodium sulfate and its solvent and then freezing and crystallizing. The temperature of the low-temperature mirabilite is -5°C-35°C; the molar ratio of sodium sulfate to the solvent is 1:(9-11).

[0070] In this embodiment, sodium sulfate is used as a raw material and is metered and transported from a sodium sulfate silo to a sodium sulfate slurry tank 1 through a screw conveyor 101, and a circulating pump is used to uniformly mix the sodium sulfate and its solvent to obtain a sodium sulfate slurry, and the uniformity of the sodium sulfate slurry is ensured, and the sodium sulfate heat exchanger 402 is used to cool it to obtain a low-temperature mirabilite slurry, wherein the molar ratio of sodium sulfate to the solvent is preferably 1:10, and the temperature of the low-temperature mirabilite is preferably 0° C. The solvent is one of water and the first clarified liquid, or a mixture of the two.

[0071] In other embodiments of the present invention, the sodium sulfate product (Na 2 SO 4 10H 2 O) cooling to obtain.

[0072] (2) Preparation of sodium bicarbonate

[0073] The ammonium bicarbonate solid is added to the prepared low-temperature mirabilite slurry in batches to react, and then the sodium bicarbonate is crystallized out by utilizing the difference in solubility, wet sodium bicarbonate and sodium bicarbonate mother liquor are obtained by solid-liquid separation, and the wet sodium bicarbonate is dried to obtain a sodium bicarbonate product.

[0074] In this embodiment, the low-temperature mirabilite slurry obtained in step (1) is transported to the sodium bicarbonate crystallizer 2 by a slurry delivery pump, and the ammonium bicarbonate solid is measured and delivered to the sodium bicarbonate crystallizer 2 from the ammonium bicarbonate silo 201 in batches, the two are mixed to react and crystallize to obtain a sodium bicarbonate slurry liquid, which is delivered to a thickener by a delivery pump for thickening to obtain a thickened slurry with a solid-liquid ratio of 30wt%, and then flows into a belt filter 202 for filtration to obtain a sodium bicarbonate mother liquor and wet sodium bicarbonate, and the wet sodium bicarbonate is added to a sodium bicarbonate drying device 203 for drying to obtain a sodium bicarbonate product, which is packaged by a sodium bicarbonate ton bag packaging machine and then transported to a product warehouse for storage and standby use.

[0075] The sodium bicarbonate mother liquor is collected in a sodium bicarbonate mother liquor storage tank and pumped to the salting-out crystallizer 3 of the next stage.

[0076] Among them, the reaction time in the sodium bicarbonate crystallizer 2 is 1-4 hours, the reaction temperature is 25-40°C, and the mass ratio of ammonium bicarbonate solid to sodium sulfate in the reaction material is (1.5-3):1. In this embodiment, the reaction time is 2 hours, the reaction temperature is 25°C, and the mass ratio is 2:1.

[0077] (3) Preparation of sodium ammonium solid salt

[0078] The low-temperature mirabilite slurry prepared in step (1) is added to the sodium bicarbonate mother liquor obtained in step (2), and the mixture is mixed. The temperature of the material in the salting-out crystallizer 3 is controlled by the amount of the low-temperature mirabilite slurry added. The two react and crystallize. The upper clear liquid and the lower crystal slurry are collected respectively. The lower crystal slurry is subjected to solid-liquid separation to obtain sodium ammonia solid salt.

[0079] In this embodiment, the sodium bicarbonate mother liquor obtained in step (2) is pumped to the salting-out crystallizer 3, and then the low-temperature mirabilite slurry is added thereto for uniform mixing, reaction and crystallization, and the upper clear liquid and the lower crystal slurry are collected through the first upper outlet and the first lower outlet, respectively.

[0080] The lower layer of crystal slurry is pumped to a thickener for thickening, and the thickened slurry enters a sodium ammonia solid salt centrifuge 301 for centrifugation to obtain sodium ammonia solid salt, which enters a sodium ammonium salt crystallizer 4 in the next step, and the thickened slurry has a solid-liquid ratio of 30wt%. The upper clear liquid of the salting-out crystallizer 3 enters a sodium ammonium solid salt clarification tank for clarification to obtain a first clarified liquid, and the first clarified liquid is sent to a sodium sulfate slurry tank 1 in step (1) as a solvent for mixing with sodium sulfate for slurrying. The bicarbonate contained in the first clarified liquid is used in step (2) to prepare sodium bicarbonate, thereby improving the utilization rate of the bicarbonate.

[0081] The centrifugal mother liquor produced by the sodium ammonia solid salt centrifuge 301 is collected in the sodium ammonia solid salt centrifugal mother liquor tank, and the liquid separated by the thickener is also collected in the sodium ammonia solid salt centrifugal mother liquor tank, and then sent back to the salting-out crystallizer 3, and the treatment is repeated to precipitate sodium ammonium solid salt. The solid precipitate produced by the clarification separation is also returned to the salting-out crystallizer 3, and the recovery rate of sodium ammonium solid salt is improved by multi-stage reflux.

[0082] The reaction time in the salting-out crystallizer 3 is 6-12 hours, the reaction temperature is 25-35°C, the mass ratio of the sodium bicarbonate mother liquor to the low-temperature mirabilite slurry is 1:(0.8-1.2), and in this embodiment, the reaction time is 8 hours, the reaction temperature is 25°C, and the mass is 1:1. If the mass ratio of the sodium bicarbonate mother liquor to the low-temperature mirabilite slurry is less than 1:0.8, the ammonium salt separation will not be complete, so that the ammonium sodium salt content in the centrifuged mother liquor of the sodium ammonia solid salt is too high, which will affect the reaction in the salting-out crystallizer 3 when it returns; if the mass ratio of the sodium bicarbonate mother liquor to the low-temperature mirabilite slurry is greater than 1:1.2, it is necessary to add an excessive amount of low-temperature mirabilite slurry, resulting in a large load on the back-end process, in which sodium sulfate is an invalid cycle, wasting energy consumption.

[0083] (4) Sodium ammonia solid hydrochloride crystallization

[0084] The solid sodium ammonia salt obtained in step (3) is acidified and heated. Due to the different solubilities of the two salts, sodium sulfate in the solution is precipitated after the temperature is raised, while ammonium sulfate is not precipitated, thereby obtaining sodium sulfate crystals. The upper clear liquid and the lower crystal slurry are collected separately, and the lower crystal slurry is subjected to solid-liquid separation to obtain sodium sulfate solid. The sodium sulfate solid is continuously returned to step (1) to prepare low-temperature mirabilite slurry;

[0085] In this embodiment, this step is carried out in a Glauber's salt crystallizer 4, which includes a primary crystallizer and a secondary crystallizer. The sodium ammonia solid salt and water obtained in step (3) are added to the primary crystallizer and mixed evenly. The mass ratio of the sodium ammonia solid salt to the water is (3-4):1. Then, concentrated sulfuric acid with a concentration of 98wt% is added to adjust the pH to 3-5, and the temperature is raised to 80-90°C. In this embodiment, the mass ratio is 3:1, the pH is 3, the temperature is raised to 80°C, and the crystal slurry is crystallized in the secondary crystallizer. The lower crystal slurry and the upper clear liquid are collected respectively. The lower crystal slurry enters the Glauber's salt centrifuge 401 for centrifugation to obtain sodium sulfate solid. The sodium sulfate solid is collected and returned to the sodium sulfate silo of step (1) for preparing low-temperature Glauber's salt slurry; the centrifugal mother liquor generated by the centrifugation is collected in a sodium sulfate centrifugal filtrate storage tank and returned to the secondary crystallizer.

[0086] The supernatant enters a sodium sulfate clarification tank for clarification to obtain a solid precipitate and a second clarified liquid. The solid precipitate mainly includes sodium sulfate, which is returned to the secondary crystallizer. The second clarified liquid enters step (5).

[0087] (5) Vacuum flash crystallization

[0088] The supernatant in step (4) is cooled and crystallized, and the supernatant and the lower crystal slurry are collected respectively, and the lower crystal slurry is subjected to solid-liquid separation to obtain ammonium sodium solid salt, and the process is returned to step (3);

[0089] In this embodiment, the cooling crystallization device 5 is a vacuum flash crystallizer, which realizes crystallization by flash cooling. The vacuum flash crystallizer includes a primary flash tank, a secondary flash tank and a tertiary flash tank. The second clarified liquid is added to the primary flash tank, flash cooled, and then pumped to the secondary flash tank through the transfer material. After the secondary flash cooling, the material is transferred to the tertiary flash tank through the transfer material, and the temperature is flashed to 20-30 ° C for three times. In this embodiment, the temperature is reduced to 25 ° C, and crystals are precipitated. The lower layer crystal slurry and the upper layer clear liquid of the third-stage flash tank are collected, and the lower layer crystal slurry is taken out and pumped to a thickener for thickening to obtain a thickened slurry with a solid-liquid ratio of 30wt%. The thickened slurry is added to a cooling centrifuge 501 for centrifugation to obtain ammonium sodium solid salt and its centrifugal mother liquor, and the ammonium sodium solid salt is returned to step (4) and combined with the ammonium sodium solid salt of step (3) for treatment. The centrifugal mother liquor and the overflow liquid of the thickener are collected in a cooling centrifugal filtrate storage tank and returned to the third-stage flash tank.

[0090] The supernatant collected in this step enters a cooling clarification tank for clarification to obtain a third clarified liquid and a solid precipitate. The third clarified liquid enters step (6), and the solid precipitate returns to the third-stage flash tank.

[0091] (6) Preparation of ammonium sulfate

[0092] The third clarified liquid obtained in step (5) is evaporated and crystallized to obtain ammonium sulfate crystals, and the upper clear liquid and the lower crystal slurry are collected separately. The lower crystal slurry is subjected to solid-liquid separation to obtain ammonium sulfate solid salt, which is then dried to obtain an ammonium sulfate product.

[0093] In this embodiment, the evaporation crystallizer 6 adopts an MVR evaporation crystallizer. After the third clarified liquid of step (5) is preheated by a preheater, it is added to the MVR evaporation crystallizer for evaporation crystallization, and the lower layer crystal slurry and the upper layer clear liquid produced by the evaporation crystallization are collected. The lower layer crystal slurry is added to a thickener for thickening to obtain a thickened slurry with a solid-liquid ratio of 35wt%. The thickened slurry is added to an ammonium sulfate centrifuge 601 to produce ammonium sulfate solid salt. After drying by an ammonium sulfate drying device 602, a finished ammonium sulfate product is obtained, which is packaged by an ammonium sulfate ton bag packaging machine and transported to a product warehouse for storage and standby use. The centrifuge produced by the ammonium sulfate centrifuge 601 and the liquid overflowing from the thickener are collected in an ammonium sulfate centrifuge tank and returned to the MVR evaporation crystallizer.

[0094] The supernatant produced by evaporation and crystallization is added to the ammonium sulfate clarification tank for clarification to obtain the fourth clarified liquid and solid precipitate. The fourth clarified liquid is collected and returned to the primary flash tank to reduce the ammonium sodium solid salt content therein, and the solid precipitate is returned to the MVR evaporation crystallizer.

[0095] Embodiment 2

[0096] A method for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate specifically comprises the following steps:

[0097] S0. Preparation of low temperature Glauber's salt

[0098] The preparation method is the same as step (1) of Example 1, wherein the molar ratio of sodium sulfate to solvent is 1:10, and the temperature of the low-temperature mirabilite slurry is 5°C.

[0099] S1. Preparation of sodium bicarbonate

[0100] Adding ammonium bicarbonate solid into low-temperature mirabilite slurry, reacting and crystallizing sodium bicarbonate, separating solid and liquid to obtain wet sodium bicarbonate and sodium bicarbonate mother liquor, and drying the wet sodium bicarbonate to obtain a sodium bicarbonate product; wherein, the reaction time is 4 hours, the reaction temperature is 35°C, and the mass ratio of ammonium bicarbonate solid to sodium sulfate in the low-temperature mirabilite slurry is 3:1.

[0101] S2. Preparation of solid sodium ammonium salt

[0102] S2.1. Add low-temperature mirabilite slurry to the sodium bicarbonate mother liquor obtained in step S1, mix evenly, react and crystallize, and collect the lower layer of crystal slurry and the upper layer of clear liquid respectively; wherein, the reaction time is 10 hours, the reaction temperature is 35°C, and the mass ratio of the sodium bicarbonate mother liquor to the low-temperature mirabilite slurry is 1:0.8.

[0103] S2.2. The lower layer of crystal slurry in step S2.1 is thickened, and the solid-liquid ratio of the thickened slurry is 33wt%. It is centrifuged to obtain sodium ammonia solid salt and centrifuged mother liquor, and the sodium ammonia solid salt is collected and enters step S3; the centrifuged mother liquor and the liquid produced by thickening are collected and returned to the system of step S2.1.

[0104] The supernatant in step S2.1 is clarified to obtain a first clarified liquid and a solid precipitate. The first clarified liquid is collected and returned to step S0 for preparing low-temperature mirabilite slurry. The solid precipitate is collected and returned to the system of step S2.1.

[0105] S3. Sodium ammonia solid hydrochloric acid crystallization

[0106] S3.1. Dissolve all the sodium ammonia solid salt, add concentrated sulfuric acid to adjust the pH to 5, heat it to 90°C for crystallization, and collect the lower layer of crystal slurry and the upper layer of clear liquid respectively; the mass ratio of sodium ammonia solid salt to the water used for dissolution is 4:1.

[0107] S3.2. The lower layer crystal slurry of step S3.1 is centrifuged to obtain sodium sulfate solid and centrifugal mother liquor, and the sodium sulfate solid is collected for preparing low-temperature mirabilite slurry, and the centrifugal mother liquor is returned to the system of step S3.1.

[0108] The supernatant in step S3.1 is clarified to obtain a solid precipitate and a second clarified liquid. The solid precipitate is collected and returned to the system of step S3.1, and the second clarified liquid enters step S4.

[0109] S4. Vacuum Flash Crystallization

[0110] S4.1. The second clarified liquid is subjected to vacuum flash evaporation to precipitate crystals, and the lower crystal slurry and the upper clear liquid are collected respectively; the vacuum flash evaporation device is the same as that in Example 1, wherein the temperature of the third-stage flash tank is reduced to 30°C;

[0111] S4.2. The lower layer crystal slurry of step S4.1 is thickened to obtain a thickened slurry having a solid-liquid ratio of 36 wt %. The thickened slurry is centrifuged to obtain ammonium sodium solid salt and its centrifuged mother liquor. The ammonium sodium solid salt is collected and returned to the system of step S3.1. The centrifuged mother liquor of the ammonium sodium solid salt and the liquid produced by the thickening are collected and returned to the third-stage flash tank to continue the vacuum flash evaporation.

[0112] The supernatant in step S4.1 is clarified to obtain a third clarified liquid and a solid precipitate. The third clarified liquid is collected and transferred to the next step. The solid precipitate is returned to the system in step S4.1 for vacuum flash evaporation.

[0113] S5. Preparation of ammonium sulfate

[0114] S5.1. Evaporate and crystallize the third clarified liquid, and collect the lower layer of crystal slurry and the upper layer of clear liquid respectively.

[0115] S5.2. The supernatant of step S5.1 is clarified to obtain a fourth clarified liquid and a solid precipitate. The fourth clarified liquid is returned to the system of step S4.1, mixed with the second clarified liquid for vacuum flash evaporation, and the solid precipitate is returned to step S5.1 and the third clarified liquid is added for evaporation and crystallization;

[0116] The lower layer crystal slurry of step S5.1 is thickened to obtain a thickened slurry with a solid-liquid ratio of 40wt%, and solid ammonium sulfate salt and its centrifugal mother liquor are obtained by centrifugal separation, and the solid ammonium sulfate salt is collected and dried to obtain an ammonium sulfate product; the thickened liquid and the centrifugal mother liquor of the solid ammonium sulfate salt are returned to step S5.1, and the third clarified liquid is added for evaporation and crystallization.

[0117] In this embodiment, 200 g of ammonium bicarbonate solid and 294 g of low-temperature thenardite slurry are added, and the low-temperature thenardite slurry is prepared from 180 g of sodium sulfate and 114 g of water. Step S1 obtains 191.88 g of sodium bicarbonate product, wherein the utilization rate of ammonium bicarbonate solid reaches 90.23%, and the alkalinity of sodium bicarbonate in the sodium bicarbonate product is 100.43. Step S5.2 obtains 149.23 g of ammonium sulfate product, wherein the nitrogen content of the ammonium sulfate is 20.79%.

Claims

1. A method for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate, characterized in that: The following steps are involved: S1. Preparation of sodium bicarbonate: adding ammonium bicarbonate solid to low-temperature mirabilite slurry, reacting and crystallizing sodium bicarbonate, separating solid and liquid to obtain wet sodium bicarbonate and sodium bicarbonate mother liquor, and drying the wet sodium bicarbonate to obtain a sodium bicarbonate product; the temperature of the low-temperature mirabilite slurry is -5°C-35°C; the reaction time is 1-4 hours, the reaction temperature is 25-40°C, and the mass ratio of ammonium bicarbonate solid to sodium sulfate in the low-temperature mirabilite slurry is (1.5-3): 1; S2. Preparation of sodium ammonium solid salt: adding sodium bicarbonate mother liquor to low-temperature mirabilite slurry, reacting and crystallizing, collecting the upper clear liquid and the lower crystal slurry, respectively, and performing solid-liquid separation on the lower crystal slurry to obtain sodium ammonia solid salt; the reaction time is 6-12 hours, the reaction temperature is 25-35 ° C, and the mass ratio of sodium bicarbonate mother liquor and low-temperature mirabilite slurry is 1: (0.8-1.2); S3. Acidification and crystallization of sodium ammonia solid salt: dissolving and acidifying the sodium ammonia solid salt, then heating to precipitate sodium sulfate crystals, collecting the upper clear liquid and the lower crystal slurry, respectively, and performing solid-liquid separation on the lower crystal slurry to obtain sodium sulfate solid; the acidification is specifically to adjust the pH to 3-5 and heat to 80-90°C; S4. Cooling crystallization: The supernatant obtained in step S3 is cooled to 20 to 30 ° C for crystallization, and the supernatant and the lower crystal slurry are collected, and the lower crystal slurry is subjected to solid-liquid separation to obtain a solid ammonium sodium salt, and the solid ammonium sodium salt is returned to step S3; S5. Preparation of ammonium sulfate: The supernatant obtained in step S4 is evaporated and crystallized to obtain ammonium sulfate crystals, the supernatant and the lower crystal slurry are collected separately, the lower crystal slurry is solid-liquid separated to obtain ammonium sulfate solid, and the ammonium sulfate product is obtained after drying.

2. The method for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate according to claim 1, characterized in that: In step S1, the preparation method of the low-temperature mirabilite slurry is specifically as follows: Mixing sodium sulfate and its solvent uniformly to obtain sodium sulfate slurry, and cooling to obtain low-temperature mirabilite slurry; the molar ratio of sodium sulfate to solvent is 1:(9-11), and the solvent is water and / or the supernatant of step S2; Alternatively, the low-temperature mirabilite slurry is obtained by cooling Na2SO4·10H2O.

3. The method for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate according to claim 1 or 2, characterized in that: Step S2 is specifically as follows: S2.

1. Add low-temperature mirabilite slurry to the sodium bicarbonate mother liquor obtained in step S1, mix well, react and crystallize, and collect the lower crystal slurry and the upper clear liquid respectively; S2.

2. The lower crystal slurry obtained in step S2.1 is thickened to obtain a thickened slurry having a solid-liquid ratio of 30wt% to 40wt%. The thickened slurry is centrifuged to obtain a sodium ammonia solid salt and a centrifuged mother liquor, and the sodium ammonia solid salt is collected and entered into step S3; Collect the centrifuged mother liquor and the liquid produced by thickening, and return them to the system of step S2.1; The supernatant obtained in step S2.1 is clarified to obtain a first clarified liquid and a solid precipitate. The first clarified liquid is collected and used to prepare low-temperature mirabilite slurry, and the solid precipitate is collected and returned to the system of step S2.

1.

4. The method for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate according to claim 1 or 2, characterized in that: Step S3 is specifically as follows: S3.

1. Dissolve all the solid sodium ammonia salt, add concentrated sulfuric acid to adjust the pH, then heat it to 80-90°C for crystallization, and collect the lower crystal slurry and the upper clear liquid respectively; The mass ratio of sodium ammonia solid salt to water used for dissolution is (3-4):1; the concentration of concentrated sulfuric acid is 98wt%; S3.

2. The lower crystal slurry of step S3.1 is centrifuged to obtain sodium sulfate solid and centrifuged mother liquor, sodium sulfate solid is collected for preparing low-temperature mirabilite slurry, and the centrifuged mother liquor is returned to the system of step S3.1; The supernatant in step S3.1 is clarified to obtain a solid precipitate and a second clarified liquid. The solid precipitate is collected and returned to the system of step S3.1, and the second clarified liquid enters step S4.

5. The method for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate according to claim 4, characterized in that: Step S4 is specifically as follows: S4.

1. Cool the second clarified liquid to 20-30°C to precipitate crystals, and collect the lower crystal slurry and the upper clear liquid; S4.

2. The lower crystal slurry of step S4.1 is thickened to obtain a thickened slurry having a solid-liquid ratio of 30 wt% to 40 wt%. The thickened slurry is centrifuged to obtain a solid sodium ammonium salt and a centrifuged mother liquor thereof. The solid sodium ammonium salt is collected and returned to step S3.1 for treatment. The centrifuged mother liquor of the solid sodium ammonium salt and the thickened liquid are collected and returned to the system of step S4.

1. The supernatant liquid in step S4.1 is clarified to obtain a third clarified liquid and a solid precipitate. The third clarified liquid is collected and enters step S5, and the solid precipitate is returned to the system of step S4.

1.

6. The method for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate according to claim 5, characterized in that: Step S5 is specifically as follows: S5.

1. Evaporating and crystallizing the third clarified liquid, and collecting the lower crystal slurry and the upper clear liquid; S5.

2. The supernatant of step S5.1 is clarified to obtain a fourth clarified liquid and a solid precipitate, the fourth clarified liquid is returned to step S4.1 and mixed with the second clarified liquid for cooling and crystallization, and the solid precipitate is returned to step S5.1 and added to the third clarified liquid for evaporation and crystallization; The lower layer crystal slurry of step S5.1 is thickened to obtain a thickened slurry with a solid-liquid ratio of 30wt% to 40wt%, which is centrifuged to obtain ammonium sulfate solid salt and its centrifugal mother liquor, the ammonium sulfate solid salt is collected, and dried to obtain an ammonium sulfate product; the thickened liquid and the centrifugal mother liquor of the ammonium sulfate solid salt are returned to step S5.1 and added to the third clarified liquid for evaporation and crystallization.

7. The method for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate according to claim 6, characterized in that: In step S1, the mass ratio of ammonium bicarbonate solid to sodium sulfate in the low-temperature mirabilite slurry is 2:1; In step S2, the mass ratio of the sodium bicarbonate mother liquor to the low-temperature sodium sulfate slurry is 1:

1.

8. A system for preparing sodium bicarbonate and ammonium sulfate from low-temperature sodium sulfate, used to implement the method for preparing sodium bicarbonate and ammonium sulfate from low-temperature sodium sulfate according to any one of claims 1 to 8, characterized in that: It includes a sodium bicarbonate production unit, a sodium ammonium solid salt production unit, an acidification crystallization unit, a cooling crystallization unit and an ammonium sulfate production unit; The sodium bicarbonate production unit comprises a sodium bicarbonate crystallizer (2), a first solid-liquid separation device and a sodium bicarbonate drying device (203); the first inlet of the sodium bicarbonate crystallizer (2) is used to input low-temperature mirabilite slurry, the second inlet is used to input ammonium bicarbonate solid, the outlet of the sodium bicarbonate crystallizer (2) is connected to the inlet of the first solid-liquid separation device, and the solid outlet of the first solid-liquid separation device is connected to the sodium bicarbonate drying device (203); The sodium ammonium solid salt production unit comprises a salting-out crystallizer (3) and a second solid-liquid separation device, wherein a first inlet of the salting-out crystallizer (3) is connected to a liquid outlet of the first solid-liquid separation device, a first upper outlet and a first lower outlet are respectively arranged at the upper part and the lower part of the salting-out crystallizer (3), the first upper outlet is used to discharge the upper clear liquid, the first lower outlet is connected to an inlet of the second solid-liquid separation device, and the liquid outlet of the second solid-liquid separation device is connected to a second inlet of the salting-out crystallizer (3); The acidification crystallization unit comprises a Glauber's salt crystallizer (4) and a third solid-liquid separation device, wherein a first inlet of the Glauber's salt crystallizer (4) is connected to a solid outlet of the second solid-liquid separation device, a second upper outlet and a second lower outlet are respectively arranged at the upper and lower parts of the Glauber's salt crystallizer (4), the second lower outlet is connected to an inlet of the third solid-liquid separation device, the liquid outlet of the third solid-liquid separation device is connected to a second inlet of the Glauber's salt crystallizer (4), and the solid outlet is used to discharge sodium sulfate solid; The cooling crystallization unit comprises a cooling crystallization device (5) and a fourth solid-liquid separation device, wherein a first inlet of the cooling crystallization device (5) is connected to a second upper outlet of the mirabilite crystallizer (4), a third upper outlet and a third lower outlet are respectively arranged at the upper and lower parts of the cooling crystallization device (5), the third lower outlet is connected to an inlet of the fourth solid-liquid separation device, a liquid outlet of the fourth solid-liquid separation device is connected to the second inlet of the cooling crystallization device (5), and a solid outlet is connected to a third inlet of the mirabilite crystallizer (4); The ammonium sulfate production unit comprises an evaporation crystallizer (6), a fifth solid-liquid separation device and an ammonium sulfate drying device (602); a first inlet of the evaporation crystallizer (6) is connected to a third upper outlet of the cooling crystallization device (5); a fourth upper outlet and a fourth lower outlet are respectively arranged at the upper and lower parts of the evaporation crystallizer (6); the fourth upper outlet is connected to the third inlet of the cooling crystallization device (5); the fourth lower outlet is connected to the inlet of the fifth solid-liquid separation device; the liquid outlet of the fifth solid-liquid separation device is connected to the second inlet of the evaporation crystallizer (6); and the solid outlet is connected to the ammonium sulfate drying device (602).

9. A system for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate according to claim 8, characterized in that: The invention also comprises a low-temperature sodium sulfate unit, which comprises a sodium sulfate silo, a sodium sulfate slurry tank (1) and a sodium sulfate heat exchanger (402), wherein the outlet of the sodium sulfate silo is connected to the first inlet of the sodium sulfate slurry tank (1), the second inlet of the sodium sulfate slurry tank (1) is used to input a solvent, and the sodium sulfate heat exchanger (402) is connected to the sodium sulfate slurry tank (1) for cooling the sodium sulfate slurry tank; The first upper outlet is connected to the third inlet of the sodium sulfate slurry tank (1), and the solid outlet of the third solid-liquid separation device is connected to the inlet of the sodium sulfate silo; A sodium ammonium solid salt clarification tank is arranged between the first upper outlet and the third inlet of the sodium sulfate slurry tank (1), the liquid outlet of the sodium ammonium solid salt clarification tank is connected to the third inlet of the sodium sulfate slurry tank (1), and the solid outlet is connected to the third inlet of the salting-out crystallizer (3); A sodium sulfate clarification tank is arranged between the second upper outlet and the first inlet of the cooling crystallization device (5); the liquid outlet of the sodium sulfate clarification tank is connected to the first inlet of the cooling crystallization device (5), and the solid outlet is connected to the fourth inlet of the mirabilite crystallizer (4); A cooling clarification tank is arranged between the third upper outlet and the first inlet of the evaporation crystallizer (6), the liquid outlet of the cooling clarification tank is connected to the first inlet of the evaporation crystallizer (6), and the solid outlet is connected to the fourth inlet of the temperature reduction crystallization device (5); An ammonium sulfate clarification tank is arranged between the fourth upper outlet and the third inlet of the cooling crystallization device (5); the liquid outlet of the ammonium sulfate clarification tank is connected to the third inlet of the cooling crystallization device (5); and the solid outlet is connected to the third inlet of the evaporation crystallizer (6).

10. The system for preparing sodium bicarbonate and co-producing ammonium sulfate from low-temperature sodium sulfate according to claim 8, characterized in that: The mirabilite crystallizer (4) comprises a primary crystallizer and a secondary crystallizer which are connected in sequence, the inlet of the primary crystallizer is connected to the solid outlet of the second solid-liquid separation device, the secondary crystallizer is connected to the inlet of the third solid-liquid separation device through the second lower outlet, the liquid outlet of the third solid-liquid separation device is connected to the secondary crystallizer, and the solid outlet of the fourth solid-liquid separation device is connected to the primary crystallizer; The temperature reduction crystallization device (5) comprises a primary flash tank, a secondary flash tank and a tertiary flash tank which are connected in sequence, the inlet of the primary flash tank is connected to the second upper outlet, the tertiary flash tank is connected to the inlet of the fourth solid-liquid separation device through the third lower outlet, and the liquid outlet of the fourth solid-liquid separation device is connected to the primary flash tank; The first inlet of the evaporation crystallizer (6) is connected to the third-stage flash tank, and the fourth upper outlet of the evaporation crystallizer (6) is connected to the first-stage flash tank; The first solid-liquid separation device, the second solid-liquid separation device, the third solid-liquid separation device, the fourth solid-liquid separation device, and the fifth solid-liquid separation device are respectively a belt filter (202), a sodium ammonia solid salt centrifuge (301), a mirabilite centrifuge (401), a cooling centrifuge (501), and an ammonium sulfate centrifuge (601).

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