Mechanical vapor recompression and multi-effect evaporation coupling salt-making energy-saving technology

Abstract

The invention relates to the technical field of salt production, in particular to a mechanical vapor recompression and multi-effect evaporation coupled salt production energy-saving technology which comprises a first brine treatment unit, a second brine treatment unit and a third brine treatment unit, the first brine treatment unit comprises a first preheating device, an autoclave group, a flash tank group, a first salt slurry upgrading device, a salt production tank and a second salt thickener; the first brine treatment unit is used for treating first brine, the second brine treatment unit is used for treating second brine, and the nitrate preparation unit is used for preparing anhydrous sodium sulfate by utilizing nitrate liquid generated by the first brine treatment unit and the second brine treatment unit; the steam supply unit is used for providing steam for the first brine treatment unit, the second brine treatment unit and the saltpeter preparation unit, the steam supply unit is designed, gradient utilization of steam energy is achieved, the energy utilization rate is increased, the purposes of saving energy and reducing consumption are achieved, the overall energy consumption level reaches the most advanced international level, and the system is suitable for large-scale popularization and application. And meanwhile, the purposes of improving the product quality and packaging products in a centralized mode are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of salt production, and in particular to an energy-saving technology for salt production by coupling mechanical vapor recompression and multi-effect evaporation. Background Art

[0002] In China, the comprehensive energy consumption of industrial salt from well-mined salt in the salt production industry is on average 110 kg of standard coal per ton, and the comprehensive energy consumption of edible salt is on average 120 kg of standard coal per ton; the main technology is multi-effect evaporation for salt production (ME); currently abroad, it is 80 - 100 kg of standard coal per ton of salt, mainly using mechanical vapor recompression for salt production technology (MVR) and multi-effect evaporation for salt production technology (ME).

[0003] Traditional salt production processes mainly use multi-effect evaporation or mechanical vapor recompression for salt production, and the energy sources are single. For example, in multi-effect evaporation, live steam is used as the heat source; in mechanical vapor recompression, electric energy is used as the energy source; there is not much overlap or relationship between them. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to overcome the problem that traditional salt production processes in the prior art mainly use multi-effect evaporation or mechanical vapor recompression for salt production, and the energy sources are single. For example, in multi-effect evaporation, live steam is used as the heat source; in mechanical vapor recompression, electric energy is used as the energy source; there is not much overlap or relationship between them, and to provide an energy-saving technology for salt production by coupling mechanical vapor recompression and multi-effect evaporation.

[0005] The technical solution adopted by the present invention to solve its technical problem is: an energy-saving technology for salt production by coupling mechanical vapor recompression and multi-effect evaporation, including:

[0006] A first brine treatment unit for treating first brine. The first brine treatment unit includes a first preheating device, a heat compression tank group, a flash tank group, a first salt slurry quality improvement device, a salt production tank, and a second salt thickener. The input end of the first preheating device is used for inputting the first brine. The output end of the first preheating device is communicated with the input end of the heat compression tank group. The output end of the heat compression tank group is communicated with the input end of the flash tank group. The output end of the flash tank assembly is communicated with the input end of the salt production tank. The output end of the salt production tank is communicated with the input end of the second salt slurry quality improvement device. The output end of the heat compression tank group is communicated with the input end of the first salt slurry quality improvement device. The output end of the first salt slurry quality improvement device is communicated with the input end of the second salt thickener;

[0007] The second brine treatment unit is used to treat the second brine. The second brine treatment unit includes a second preheating device, an evaporation tank group, a first salt thickener, and a second salt slurry quality improvement device. The input end of the second preheating device is used for inputting the second brine. The output end of the second preheating device is connected to the input end of the evaporation tank group. The output end of the evaporation tank group is connected to the first salt thickener and the second salt slurry quality improvement device. The first salt thickener is used to treat the original liquid passing through the evaporation tank group and obtain packaged salt through salt centrifugal drying and packaging. The input end of the second salt slurry quality improvement device is used for inputting the third brine. The output end of the second salt slurry quality improvement device is connected to the second salt thickener.

[0008] The sodium nitrate production unit is used to prepare anhydrous sodium sulfate using the sodium nitrate solution generated by the first brine treatment unit and the second brine treatment unit. The salt production tank is connected to the sodium nitrate production unit. The sodium nitrate production unit is connected to the flash tank group. The evaporation tank group is connected to the sodium nitrate production unit.

[0009] And a steam supply unit is used to provide steam for the first brine treatment unit, the second brine treatment unit, and the sodium nitrate production unit. The steam supply unit is connected to the hot press tank group and the sodium nitrate production unit. The design of the steam supply unit in this system realizes the cascade utilization of steam energy, improves the energy utilization rate, achieves the purpose of energy conservation and consumption reduction, the overall energy consumption level reaches the international advanced level, and at the same time realizes the goals of improving product quality, product quality grading, and product centralized packaging.

[0010] It further includes that the steam supply unit includes a boiler, a steam turbine, and a steam compressor. The boiler is used to generate steam. The output end of the boiler is connected to the input end of the steam turbine. The steam turbine is used to generate backpressure steam and input the backpressure steam into the sodium nitrate production unit, the steam compressor, or for external sale. The output end of the steam turbine is connected to the sodium nitrate production unit and the steam compressor. The steam compressor is connected to the hot press tank group.

[0011] It further includes that the hot press tank group includes a first hot press tank and a second hot press tank. The first preheating device is connected to the first hot press tank. The first hot press tank is connected to the second hot press tank. The steam compressor is connected to the first hot press tank and the second hot press tank. The second hot press tank is connected to the flash tank group. The first hot press tank and the second hot press tank are connected through the second salt slurry quality improvement device and the second salt thickener. The first hot press tank is connected to the first salt thickener.

[0012] It further includes that the flash tank group includes a first flash tank, a second flash tank, and a third flash tank. The second hot press tank is connected to the first flash tank. The first flash tank is connected to the second flash tank. The second flash tank is connected to the third flash tank. The third flash tank is connected to the salt production tank.

[0013] Further comprising an evaporation tank group including a first-effect evaporation tank, a second-effect evaporation tank, a third-effect evaporation tank, and a fourth-effect evaporation tank, a second preheating device is connected to the first-effect evaporation tank, the first-effect evaporation tank is connected to the second-effect evaporation tank, the second-effect evaporation tank is connected to the third-effect evaporation tank, the third-effect evaporation tank is connected to the fourth-effect evaporation tank, the fourth-effect evaporation tank is connected to the salt production unit, the first-effect evaporation tank, the second-effect evaporation tank, and the third-effect evaporation tank are all connected to the first salt thickener, and the steam turbine is connected to the first-effect evaporation tank.

[0014] Further comprising that the salt production system further includes a brine purification device, and the salt production tank and the fourth-effect evaporation tank are both connected to the brine purification device.

[0015] Further comprising that the salt production unit includes a first salt production tank, a second salt production tank, a first heat exchanger group, a second heat exchanger group, a salt thickener, and a fourth flash evaporation tank, the salt production tank is connected to the first salt production tank through the first heat exchanger group, the first salt production tank is connected to the salt thickener, and the first salt production tank is connected to the flash evaporation tank group;

[0016] The fourth-effect evaporation tank is connected to the second salt production tank through the second heat exchanger group, the second salt production tank is connected to the salt thickener, the steam turbine is connected to the first salt production tank and the second salt production tank, and the second salt production tank is connected to the fourth-effect evaporation tank through the fourth flash evaporation tank.

[0017] Further comprising that the first heat exchanger group includes a first heat exchanger, a second heat exchanger, and a third heat exchanger, the salt production tank is connected to the first heat exchanger, the first heat exchanger is connected to the second heat exchanger, the second heat exchanger is connected to the third heat exchanger, and the third heat exchanger is connected to the first salt production tank;

[0018] The second heat exchanger assembly includes a fourth heat exchanger and a fifth heat exchanger, the fourth-effect evaporation tank is connected to the fourth heat exchanger, the fourth heat exchanger is connected to the fifth heat exchanger, and the fifth heat exchanger is connected to the second salt production tank.

[0019] The beneficial effects of the present invention are as follows: The present invention provides an energy-saving technology for salt production by coupling mechanical vapor recompression and multi-effect evaporation.

[0020] (1) The design of the steam supply unit in this system realizes the cascade utilization of steam energy, improves the energy utilization rate, achieves the purpose of energy conservation and consumption reduction, the overall energy consumption level reaches the international most advanced level, and at the same time realizes the goals of improving product quality, product quality grading, and centralized product packaging;

[0021] (2) The brine in this system is used according to the brine quality. According to the different treatment capabilities of different devices for sodium sulfate, high-sodium-sulfate refined brine enters the multi-effect evaporation (ME) device for salt production, low-sodium-sulfate refined brine enters the mechanical heat compression (MVR) device for salt production, and at the same time, the low-nitrate refined brine generated by nanofiltration is used for salt leg elutriation and salt slurry quality improvement, saving energy and improving product quality;

[0022] (3) The system realizes the coupled classification of salt products in the MVR and ME coupled salt production devices. For the first-effect evaporation tank, the II evaporation tank, and the III evaporation tank of the multi-effect evaporation (ME) device, the salt quality is good and the salt particle size is large, which can be used to prepare high-quality salt. For the IV evaporation tank of the mother liquor recovery system of the multi-effect evaporation (ME) device and the first heat compression tank, the second heat compression tank, and the salt production tank of the mechanical vapor recompression (MVR) device, the salt particle size distribution range is relatively wide, and it can enter the salt slurry quality improvement device for hydraulic screening and classification. The screened mother liquor enters the refined brine bucket, making the refined brine components change from unsaturated to saturated, achieving the purpose of controlling the particle uniformity, improving the salt quality, and meeting the customer requirements;

[0023] (4) The mother liquor of the MVR and ME coupled salt production evaporation device of this system is discharged to the brine purification system. The impurities enriched in the mother liquor can be further removed in the brine purification system. The mother liquor after removing impurities can enter the coupled salt production device again along with the first brine and the second brine, realizing full-process controllability, maximizing the utilization of resources and energy, and not causing pollution to the environment, being energy-saving and environmentally friendly;

[0024] (5) The system realizes the centralized centrifugal dehydration, storage and transportation of wet salt and the centralized dehydration, drying and packaging of edible packaged salt in the MVR and ME coupled salt production devices, and a set of dehydration, drying and packaging devices is shared by the coupled device and the anhydrous nitrate device, realizing the intensive treatment of drying and packaging. Compared with the traditional method of separate centrifugal dehydration and drying for the MVR and ME devices, the process improvement measures of this patent not only reduce the consumption of drying steam, reduce the equipment maintenance cost, but also improve the labor efficiency of packaging workers, and greatly reduce the production cost. Brief Description of the Drawings

[0025] The present invention will be further described below with reference to the drawings and embodiments.

[0026] Figure 1 It is a structural schematic diagram of the present invention.

[0027] In the figure: 1. First brine treatment unit, 11. First preheating device, 12. Heat compression tank group, 121. First heat compression tank, 122. Second heat compression tank, 13. Flash evaporation tank group, 131. First flash evaporation tank, 132. Second flash evaporation tank, 133. Third flash evaporation tank, 14. First salt slurry quality improvement device, 15. Salt production tank, 16. Second salt thickener

[0028] 2. Second brine treatment unit, 21. Second preheating device, 22. Evaporation tank group, 221. First-effect evaporation tank, 222. II-effect evaporation tank, 223. III-effect evaporation tank, 224. IV-effect evaporation tank, 23. First salt thickener, 24. Second salt slurry quality improvement device,

[0029] 3. Nitrate production unit, 31. First nitrate production tank, 32. Second nitrate production tank, 33. First heat exchanger group, 331. First heat exchanger, 332. Second heat exchanger, 333. Third heat exchanger, 34. Second heat exchanger group, 341. Fourth heat exchanger, 342. Fifth heat exchanger, 35. Nitrate thickener, 36. Fourth flash tank;

[0030] 4. Steam supply unit, 41. Boiler, 42. Steam turbine, 43. Steam compressor;

[0031] 5. Brine purification device. Detailed implementation manners

[0032] Now, the present invention will be further described in detail with reference to the accompanying drawings. These drawings are all simplified schematic diagrams, only illustrating the basic structure of the present invention in a schematic manner, so they only show the components related to the present invention.

[0033] As Figure 1 is the structural schematic diagram of the present invention, a salt production energy-saving technology coupling mechanical vapor recompression and multi-effect evaporation, including:

[0034] The first brine treatment unit 1, which is used for treating the first brine. The first brine treatment unit 1 includes a first preheating device 11, a thermocompression tank group 12, a flash tank group 13, a first salt slurry quality improvement device 14, a salt production tank 15, and a second salt thickener 16.

[0035] The input end of the first preheating device 11 is used for inputting the first brine, and the first brine is low-sodium-sulfate refined brine with a sulfate radical content less than or equal to 8 g / L.

[0036] The output end of the first preheating device 11 is connected to the input end of the autoclave group 12, and the output end of the autoclave group 12 is connected to the input end of the flash tank group 13. The autoclave group 12 includes a first autoclave 121 and a second autoclave 122. The first preheating device 11 is connected to the first autoclave 121, the first autoclave 121 is connected to the second autoclave 122, the steam compressor 43 is connected to the first autoclave 121 and the second autoclave 122, the second autoclave 122 is connected to the first flash tank 131 of the flash tank group 13, the first autoclave 121 and the second autoclave 122 are connected through the first salt slurry upgrading device 14 and the second salt thickener 16, the first autoclave 121 is connected to the first salt thickener 23, the first autoclave 121 is connected to the steam compressor 43 to realize steam rotation and can recycle the residual steam. The second autoclave 122 is connected to the steam compressor 43 to realize steam rotation and can recycle the residual steam. An autoclave is a high-temperature and high-pressure container mainly used for heating, high-pressure treatment and sealing materials. The first brine is nearly saturated brine. After evaporation and crystallization in the autoclave, the crystallized salt crystals (salt slurry) enter the first salt slurry upgrading device 14, and the generated mother liquor is transferred to the first flash tank 131 for heat recovery.

[0037] The output end of the flash tank group 13 is connected to the input end of the salt production tank 15. The flash tank group 13 includes a first flash tank 131, a second flash tank 132 and a third flash tank 133. The second autoclave 122 is connected to the first flash tank 131, the first flash tank 131 is connected to the second flash tank 132, the second flash tank 132 is connected to the third flash tank 133, and the third flash tank 133 is connected to the salt production tank 15. A flash tank is a device widely used in specific industrial fields. Its main function is to quickly vaporize the liquid under high temperature and high pressure by reducing the pressure, so as to realize the concentration or separation of materials.

[0038] The output end of the salt production tank 15 is connected to the input end of the second salt slurry upgrading device 24. The second salt thickener 16 is used to process the raw liquid and obtain wet salt after salt centrifugal dehydration. The output end of the autoclave group 12 is connected to the input end of the first salt slurry upgrading device 14, and the output end of the first salt slurry upgrading device 14 is connected to the input end of the second salt thickener 16. The salt production tank 15 is connected to the first heat exchanger 331; the materials processed by the salt production tank 15 are all salt-making mother liquor. Part of the mother liquor generated by the salt production tank 15 goes to the first heat exchanger 331, and part goes to the brine purification.

[0039] The second brine treatment unit 2 is used to treat the second brine. The second brine treatment unit 2 includes a second preheating device 21, an evaporation tank group 22, a first salt thickener 23 and a second salt slurry upgrading device 24.

[0040] The input end of the second preheating device 21 is used for the input of the second brine, and the second brine is high-sodium sulfate refined brine with a sulfate radical content higher than 12 g / L.

[0041] The output end of the second preheating device 21 is communicated with the input end of the evaporation tank group 22. The output end of the evaporation tank group 22 is communicated with the first salt thickener 23 and the second salt slurry quality-improving device 24. The evaporation tank group 22 includes a first-effect evaporation tank 221, a second-effect evaporation tank 222, a third-effect evaporation tank 223, and a fourth-effect evaporation tank 224. The second preheating device 21 is communicated with the first-effect evaporation tank 221. The first-effect evaporation tank 221 is communicated with the second-effect evaporation tank 222. The second-effect evaporation tank 222 is communicated with the third-effect evaporation tank 223. The third-effect evaporation tank 223 is communicated with the fourth-effect evaporation tank 224. The fourth-effect evaporation tank 224 is communicated with the sodium nitrate production unit 3. The first-effect evaporation tank 221, the second-effect evaporation tank 222, and the third-effect evaporation tank 223 are all communicated with the first salt thickener 23. The steam turbine 42 is communicated with the first-effect evaporation tank 221. After evaporation and crystallization in the evaporation tank, the salt slurry is transferred to the salt thickener, and the mother liquor is transferred to the next-level evaporation tank for continuous evaporation and crystallization. Since the sodium chloride in the brine also contains sodium sulfate, during the process of step-by-step evaporation and crystallization, the sodium sulfate content in the mother liquor will continuously accumulate. When it reaches the fourth-effect evaporation tank 224, the solid salt produced by crystallization contains a high content of sodium sulfate impurities and needs quality-improving treatment.

[0042] The first salt thickener 23 is used to process the original liquid passing through the evaporation tank group 22 and obtain packaged salt through salt centrifugal drying and packaging. The input end of the second salt slurry quality-improving device 24 is used for the input of the third brine, and the third brine is low-nitrate refined brine with a sulfate radical content lower than 1 g / L. The output end of the second salt slurry quality-improving device 24 is communicated with the second salt thickener 16.

[0043] The salt production system further includes a brine purification device 5. The salt production tank 15 and the fourth-effect evaporation tank 224 are both communicated with the brine purification device 5. The brine purification device 5 can specifically be an original brine tank, a primary reaction tank, a secondary reaction tank, and a refined brine tank, as well as relevant brine transfer pumps and mud pumps, etc.

[0044] The sodium nitrate production unit 3 is used to prepare anhydrous sodium sulfate by using the nitrate solution generated by the first brine treatment unit 1 and the second brine treatment unit 2. The salt production tank 15 is communicated with the sodium nitrate production unit 3. The sodium nitrate production unit 3 is communicated with the flash evaporation tank group 13. The evaporation tank group 22 is communicated with the sodium nitrate production unit 3.

[0045] The nitrate production unit 3 includes a first nitrate production tank 31, a second nitrate production tank 32, a first heat exchanger group 33, a second heat exchanger group 34, a nitrate thickener 35, and a fourth flash tank 36. The salt production tank 15 is connected to the first nitrate production tank 31 through the first heat exchanger group 33. The first nitrate production tank 31 is connected to the nitrate thickener 35 and the second flash tank 132 of the flash tank group 13. The first nitrate production tank 31 produces nitrate slurry and mother liquor for salt production. The nitrate slurry (sodium sulfate nitrate slurry) enters the nitrate thickener 35, and the mother liquor for salt production enters the second flash tank 132.

[0046] The IV-effect evaporation tank 224 is connected to the second nitrate production tank 32 through the second heat exchanger group 34. The second nitrate production tank 32 is connected to the nitrate thickener 35. The steam turbine 42 is connected to the first nitrate production tank 31 and the second nitrate production tank 32. The second nitrate production tank 32 is connected to the IV-effect evaporation tank 224 through the fourth flash tank 36. The nitrate slurry (sodium sulfate nitrate slurry) enters the nitrate thickener 35, and the mother liquor for salt production enters the fourth flash tank 36.

[0047] The first heat exchanger group 33 includes a first heat exchanger 331, a second heat exchanger 332, and a third heat exchanger 333. The salt production tank 15 is connected to the first heat exchanger 331. The first heat exchanger 331 is connected to the second heat exchanger 332. The second heat exchanger 332 is connected to the third heat exchanger 333. The third heat exchanger 333 is connected to the first nitrate production tank 31.

[0048] To increase the temperature of the mother liquor for salt production entering the first nitrate production tank 31, the second heat exchanger group 34 includes a fourth heat exchanger 341 and a fifth heat exchanger 342. The IV-effect evaporation tank 224 is connected to the fourth heat exchanger 341. The fourth heat exchanger 341 is connected to the fifth heat exchanger 342. The fifth heat exchanger 342 is connected to the second nitrate production tank 32, increasing the temperature of the mother liquor for salt production entering the second nitrate production tank 32 to be close to the boiling point temperature of the liquid in the tank.

[0049] The steam supply unit 4 is used to supply steam to the first brine treatment unit 1, the second brine treatment unit 2, and the nitrate production unit 3. The steam supply unit 4 is connected to the heat press tank group 12 and the nitrate production unit 3.

[0050] The steam supply unit 4 includes a boiler 41, a steam turbine 42, and a steam compressor 43. The boiler 41 is used to generate steam. The output end of the boiler 41 is connected to the input end of the steam turbine 42. The steam turbine 42 is used to generate backpressure steam and input the backpressure steam into the nitrate production unit 3, the steam compressor 43, or for external sale. The output end of the steam turbine 42 is connected to the nitrate production unit 3 and the steam compressor 43. The steam compressor 43 is connected to the hot pressing tank group 12. In this application, self-produced steam is used to replace grid power to drive the start of the steam compressor 43, which can effectively reduce the electricity operation cost of the workshop. Research and technological innovation are carried out on the drive device motor of the compressor. The steam turbine is used to replace the motor for the cascade utilization of steam energy, improving the energy utilization rate. At the same time, the output power directly drives the steam compressor 43. The backpressure steam of the steam turbine 42 is used as the heat source for the system mother liquor recovery system device and the multi-effect evaporation (ME) device, and the remaining steam is used as the heat source power for external sale.

[0051] The steam produced by the sub-high-pressure boiler (4.8 MPa(a), 450 °C) enters the backpressure steam turbine 42 to drive the MVR compressor, sucks in the secondary steam generated by the evaporation of the evaporation tank group after defoaming and steam washing, continuously pressurizes and increases the steam temperature, enters the heating chamber, provides heat to the second brine, and performs evaporation; the constant-pressure medium-temperature backpressure steam discharged from the steam turbine 42 (outlet 0.45 MPa(a), steam temperature 209 °C) enters the mother liquor recovery system to heat and evaporate for nitrate production and the multi-effect evaporation (ME) device as the heat source for the first-effect evaporation tank for salt and nitrate production.

[0052] The brine of this system is used according to its quality. According to the different treatment capabilities of different devices for sodium sulfate, the high-sodium-sulfate refined brine enters the multi-effect evaporation (ME) device for salt production, and the low-sodium-sulfate refined brine enters the mechanical vapor recompression (MVR) device for salt production. At the same time, the low-nitrate refined brine generated by nanofiltration is used for salt leg flushing and salt slurry quality improvement, saving energy and improving product quality;

[0053] This system realizes the coupling grading of salt products in the MVR and ME coupling salt production devices. The salt quality of the first-effect evaporation tank, the II evaporation tank, and the III evaporation tank in the multi-effect evaporation (ME) device is better, and the salt particle size is larger, which can be used to prepare high-quality salt. The salt particle size distribution range of the mother liquor recovery system IV evaporation tank in the multi-effect evaporation (ME) device and the first hot pressing tank 121, the second hot pressing tank 122, and the salt production tank 15 in the mechanical vapor recompression (MVR) device is relatively wide, and it can enter the second salt slurry quality improvement device 24 for hydraulic screening and grading. The screened mother liquor enters the refined brine bucket, converting the refined brine component from unsaturated to saturated, achieving the purpose of controlling the particle uniformity, improving the salt quality, and meeting customer requirements;

[0054] The mother liquor of the salt-making evaporation device with MVR and ME coupling in this system is discharged to the brine purification system. The impurities enriched in the mother liquor can be further removed in the brine purification system. The mother liquor after impurity removal can enter the coupled salt-making device again along with the first brine and the second brine, realizing full-process controllability, maximizing the utilization of resources and energy, and causing no environmental pollution, thus being energy-saving and environment-friendly.

[0055] This system realizes the centralized centrifugal dehydration, storage and transportation of wet salt and the centralized dehydration, drying and packaging of edible packaged salt in the MVR and ME coupling salt-making device, and a set of dehydration, drying and packaging device is shared by the anhydrous nitrate device of the coupling device, realizing the intensive treatment of drying and packaging. Compared with the traditional method of separating centrifugal dehydration and drying for MVR and ME devices, the process improvement measures of this patent not only reduce the consumption of drying steam and the equipment maintenance cost, but also improve the labor efficiency of packaging workers, and greatly reduce the production cost.

[0056] Examples:

[0057] Example 1:

[0058] The first brine contains 300 - 310 g / L of sodium chloride, ≤5 g / L of sodium sulfate, and ≤5 mg / L of total calcium and magnesium. The first brine is preheated to 130°C by the first preheating device and enters the first hot pressing tank. The slurry in the first hot pressing tank is transferred to the second hot pressing tank for evaporation. After the slurry in the circulation pipe of the second hot pressing tank undergoes solid-liquid separation, the clear liquid is transferred to the first flash tank to flash and recover heat. The slurry in the first flash tank is transferred to the second flash tank, the slurry in the second flash tank is transferred to the third flash tank, and the slurry in the third flash tank is transferred to the salt production tank. After the salt slurry in the salt production tank undergoes solid-liquid separation, a part of the clear liquid is heated by the first heat exchanger, the second heat exchanger, and the third heat exchanger and then transported to the first nitrate production tank. After the slurry in the first nitrate production tank undergoes solid-liquid separation, the liquid is transferred to the second flash tank. The second brine contains 290 - 300 g / L of sodium chloride, ≤20 g / L of sodium sulfate, and ≤5 mg / L of total calcium and magnesium. The second brine is heated by the second preheating device and then transported to the first-effect evaporation tank. The clear liquid is transferred to the second-effect evaporation tank, the clear liquid is transferred to the third-effect evaporation tank, the clear liquid is transferred to the fourth-effect evaporation tank. The mother liquor in the fourth-effect evaporation tank is heat-exchanged by the fourth heat exchanger and the fifth heat exchanger and then transported to the second nitrate production tank. After the slurry in the nitrate production tank undergoes solid-liquid separation, it is transported to the fourth flash tank, and the slurry after flashing is transported to the fourth evaporation tank.

[0059] The salt slurries from the first autoclave and the second autoclave enter the first salt slurry upgrading device. After hydraulic screening, they are transported to the second salt thickener for thickening and concentration. At the same time, the salt slurry from the IV-effect evaporator and the salt slurry from the salt production tank together pass through the third brine with a sodium chloride content of 250 - 300 g / L, a sodium sulfate content of less than or equal to 1 g / L, and a total calcium and magnesium content of less than or equal to 1 mg / L. After washing and flotation of the third brine, it is transported to the second salt thickener for thickening and concentration. The salt slurry after concentration by the second salt thickener is centrifugally dewatered to obtain wet salt. The characteristics of the wet salt are that NaCl (dry basis) is greater than or equal to 97.5%, moisture is less than or equal to 2.0%, and the sulfate content is less than or equal to 0.10%. The original particle size distribution was relatively wide, with 85% in the particle size range of 0.075 - 0.85 mm. After hydraulic classification for salt slurry upgrading, the particle size distribution of the product becomes 85% in the range of 0.25 - 0.60 mm, improving the particle size uniformity of the product. Part of the salt slurry from the first autoclave and the salt slurries from the first-effect evaporator, the II-effect evaporator, and the III-effect evaporator are transported to the first salt thickener for concentration. The concentrated salt slurry is centrifugally dried and packaged to obtain packaged salt. This packaged salt has good quality, significantly improved particle uniformity, extended the caking probability between crystals, increased the storage time of the salt product, and does not require the addition of anti-caking agents. The particle size distribution is shown in Table 1. The high-quality salt produced can be used for sodium metal salts, casing salts, salts for butter processing, and high-quality edible salts.

[0060] The nitre slurries generated by evaporation and crystallization in the first nitre production tank and the second nitre production tank are discharged to the nitre thickener for thickening and concentration, and then centrifugally dried and packaged after nitre centrifugation to obtain anhydrous sodium sulfate products.

[0061] The mother liquor generated by the salt production tank and the mother liquor generated by the III-effect evaporator are discharged to the brine purification device for impurity removal, and sodium chloride, sodium sulfate, caustic soda, and soda ash inside are recovered.

[0062] The high-pressure live steam generated by the boiler, 4.8 MPa(a), 450 °C, is used as the driving steam for the steam turbine to drive the steam turbine to do work. The steam turbine converts thermal energy into mechanical energy, and the mechanical energy generated by the steam turbine then drives the steam compressor to compress the steam; after the high-pressure steam driving the steam turbine is converted from thermal energy into mechanical energy, the low-pressure steam with a back pressure of 0.45 MPa(a) and a steam temperature of 209 °C is partially transported to the first-effect evaporator, the first nitre production tank, and the second nitre production tank, and the remaining low-pressure steam is transported to other users for external sale through pipelines; realizing the recovery and utilization of the entire thermal energy. The secondary steam generated by evaporation and crystallization in the first autoclave and the second autoclave is compressed by the steam compressor and then returned to the first autoclave and the second autoclave to heat the brine, realizing the recovery and utilization of the heat of the secondary steam, and repeating the cycle. Calculated based on an annual output of 1 million tons of products, the combined use of single-stage mechanical heat compression and multi-effect vacuum evaporation saves 10,000 - 15,000 tons of standard coal per year compared to using single-stage mechanical heat compression for salt production alone, and saves 30,000 - 35,000 tons of standard coal per year compared to multi-effect evaporation for salt production.

[0063] Example Two:

[0064] The composition of the first brine is 300 - 310 g / L of sodium chloride, ≤8 g / L of sodium sulfate, ≤5 mg / L of total calcium and magnesium. The first brine is preheated to 128°C by the first preheating device and enters the first hot pressing tank. The slurry in the first hot pressing tank is transferred to the second hot pressing tank for evaporation. After the slurry in the circulation pipe of the second hot pressing tank undergoes solid-liquid separation, the clear liquid is transferred to the first flash tank for flash heat recovery. The slurry in the first flash tank is transferred to the second flash tank, the slurry in the second flash tank is transferred to the third flash tank, and the slurry in the third flash tank is transferred to the salt production tank. After the salt slurry in the salt production tank undergoes solid-liquid separation, part of the clear liquid is heated by the first heat exchanger, the second heat exchanger, and the third heat exchanger and then transported to the first nitrate production tank. After the slurry in the first nitrate production tank undergoes solid-liquid separation, the liquid is transferred to the second flash tank. The composition of the second brine is 290 - 300 g / L of sodium chloride, ≤25 g / L of sodium sulfate, ≤5 mg / L of total calcium and magnesium. The second brine is heated by the second preheating device and then transported to the first-effect evaporation tank. The clear liquid is transferred to the second-effect evaporation tank, the clear liquid is transferred to the third-effect evaporation tank, the clear liquid is transferred to the fourth-effect evaporation tank. The mother liquor in the fourth-effect evaporation tank is heat-exchanged by the fourth heat exchanger and the fifth heat exchanger and then transported to the second nitrate production tank. After the slurry in the nitrate production tank undergoes solid-liquid separation, it is transported to the fourth flash tank, and the slurry after flashing is transported to the fourth evaporation tank.

[0065] Part of the salt slurry in the first hot pressing tank and the second hot pressing tank enters the first salt slurry quality improvement device. After being improved by grinding balls and eliminating fine crystals, it is transported to the second salt thickener for thickening and concentration. At the same time, the salt slurry in the fourth-effect evaporation tank and the salt slurry in the salt production tank together pass through the third brine with a composition of 250 - 300 g / L of sodium chloride, ≤1 g / L of sodium sulfate, ≤1 mg / L of total calcium and magnesium. After being washed, floated, and then transported to the second salt thickener for thickening and concentration. The salt slurry concentrated by the second salt thickener is centrifugally dehydrated to produce wet salt. The characteristics of the wet salt are that NaCl (dry basis) ≥97.5%, moisture ≤2.0%, sulfate content ≤0.05%. The original particle size distribution range of 0.075 - 0.85 mm accounts for 75%. After hydraulic classification by the salt slurry quality improvement device, the particle size distribution of the product becomes 0.30 - 0.60 mm accounting for 75%, improving the particle size uniformity of the product. Part of the salt slurry in the first hot pressing tank and the salt slurry in the first-effect evaporation tank, the second-effect evaporation tank, and the third-effect evaporation tank are transported to the first salt thickener for concentration. The concentrated salt slurry is centrifugally dried and packaged to produce packaged salt. The composition of the packaged dry salt is: NaCl ≥99.7%, moisture ≤0.002%, sulfate content ≤0.02%. This packaged salt has good quality, extends the caking probability between crystals, improves the storage time of the salt product, does not require the addition of anti-caking agents, and the high-quality salt produced can be used for high-quality edible salt, daily chemical salt, and food processing salt, etc.

[0066] The nitre slurry generated by evaporation crystallization in the first nitre production tank and the second nitre production tank is discharged to the nitre thickener for thickening and concentration, and then packaged after nitre centrifugal drying to obtain anhydrous sodium sulfate products.

[0067] The mother liquor generated by the salt production tank and the mother liquor generated by the third-effect evaporation tank are discharged to the brine purification device for impurity removal, and sodium chloride, sodium sulfate, caustic soda, and soda ash inside are recovered.

[0068] The high-pressure live steam generated by the boiler is 4.8 MPa(a), 450 °C, which is used as the driving steam of the steam turbine to drive the steam turbine to do work. The steam turbine converts thermal energy into mechanical energy, and the mechanical energy generated by the steam turbine then drives the steam compressor to compress the steam; after the high-pressure steam driving the steam turbine is converted from thermal energy into mechanical energy, the low-pressure steam generated by the back pressure is 0.45 MPa(a), and the steam temperature is 209 °C. The steam temperature refers to the steam temperature and is transported to the first-effect evaporation tank, the first nitre production tank, and the second nitre production tank; the recovery and utilization of the entire thermal energy are realized. At the same time, by controlling the steam consumption of the first-effect evaporation tank and the circulation volume of the circulation pumps of each effect evaporation tank, the evaporation amount is controlled, and the particle size of the salt crystals is regulated to realize the production of salts with different particle sizes. The secondary steam generated by evaporation crystallization in the first hot pressing tank and the second hot pressing tank is compressed by the steam compressor and then returned to the first hot pressing tank and the second hot pressing tank to heat the brine, realizing the recovery and utilization of the heat of the secondary steam, and repeating in a cycle. Calculated based on an annual output of 1 million tons of products, the combination of single-stage mechanical heat compression and multi-effect vacuum evaporation saves 13,000 - 17,000 tons of standard coal per year compared to using single-stage mechanical heat compression alone for salt production, and saves 35,000 - 40,000 tons of standard coal per year compared to multi-effect evaporation for salt production.

[0069] Inspired by the ideal embodiments of the present invention described above, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. An energy-saving technology for salt production by coupling mechanical vapor recompression and multi-effect evaporation, characterized in that, Comprising: A first brine treatment unit (1) for treating first brine, the first brine treatment unit (1) including a first preheating device (11), a heat press tank group (12), a flash tank group (13), a first salt slurry upgrading device (14), a salt production tank (15), and a second salt thickener (16). The input end of the first preheating device (11) is for inputting the first brine. The output end of the first preheating device (11) is communicated with the input end of the heat press tank group (12). The output end of the heat press tank group (12) is communicated with the input end of the flash tank group (13). The output end of the flash tank group (13) is communicated with the input end of the salt production tank (15). The output end of the salt production tank (15) is communicated with the input end of the second salt slurry upgrading device (24). The output end of the heat press tank group (12) is communicated with the input end of the first salt slurry upgrading device (14). The output end of the first salt slurry upgrading device (14) is communicated with the input end of the second salt thickener (16); A second brine treatment unit (2) for treating second brine, the second brine treatment unit (2) including a second preheating device (21), an evaporation tank group (22), a first salt thickener (23), and a second salt slurry upgrading device (24). The input end of the second preheating device (21) is for inputting the second brine. The output end of the second preheating device (21) is communicated with the input end of the evaporation tank group (22). The output end of the evaporation tank group (22) is communicated with the first salt thickener (23) and the second salt slurry upgrading device (24). The first salt thickener (23) is used for treating the original liquid passing through the evaporation tank group (22) and obtaining packaged salt through salt centrifugal drying and packaging. The input end of the second salt slurry upgrading device (24) is for inputting third brine. The output end of the second salt slurry upgrading device (24) is communicated with the second salt thickener (16); A sodium nitrate production unit (3) for preparing anhydrous sodium sulfate by using the sodium nitrate solution generated by the first brine treatment unit (1) and the second brine treatment unit (2). The salt production tank (15) is communicated with the sodium nitrate production unit (3). The sodium nitrate production unit (3) is communicated with the flash tank group (13). The evaporation tank group (22) is communicated with the sodium nitrate production unit (3); And a steam supply unit (4) for providing steam for the first brine treatment unit (1), the second brine treatment unit (2), and the sodium nitrate production unit (3). The steam supply unit (4) is communicated with the heat press tank group (12) and the sodium nitrate production unit (3).

2. The mechanical vapor recompression and multi-effect evaporation coupled salt production energy-saving technology according to claim 1, characterized in that: The steam supply unit (4) includes a boiler (41), a steam turbine (42), and a steam compressor (43). The boiler (41) is used for generating steam. The output end of the boiler (41) is communicated with the input end of the steam turbine (42). The steam turbine (42) is used for generating backpressure steam and inputting the backpressure steam into the sodium nitrate production unit (3), the steam compressor (43), or for external sale. The output end of the steam turbine (42) is communicated with the sodium nitrate production unit (3) and the steam compressor (43). The steam compressor (43) is communicated with the heat press tank group (12).

3. A mechanical vapor recompression and multi-effect evaporation coupled salt production energy-saving technology as described in claim 2, characterized in that: The autoclave group (12) includes a first autoclave (121) and a second autoclave (122). The first preheating device (11) is communicated with the first autoclave (121), the first autoclave (121) is communicated with the second autoclave (122), the steam compressor (43) is communicated with the first autoclave (121) and the second autoclave (122), the second autoclave (122) is communicated with the flash tank group (13), the first autoclave (121) and the second autoclave (122) are communicated through the first salt slurry upgrading device (14) and the second salt thickener (16), and the first autoclave (121) is communicated with the first salt thickener (23).

4. A mechanical vapor recompression and multi-effect evaporation coupled salt production energy-saving technology according to claim 3, characterized in that: The flash tank group (13) includes a first flash tank (131), a second flash tank (132) and a third flash tank (133). The second autoclave (122) is communicated with the first flash tank (131), the first flash tank (131) is communicated with the second flash tank (132), the second flash tank (132) is communicated with the third flash tank (133), and the third flash tank (133) is communicated with the salt production tank (15).

5. The energy-saving technology for salt production by coupling mechanical vapor recompression and multi-effect evaporation according to claim 2, wherein: The evaporation tank group (22) includes a first-effect evaporation tank (221), a second-effect evaporation tank (222), a third-effect evaporation tank (223) and a fourth-effect evaporation tank (224). The second preheating device (21) is communicated with the first-effect evaporation tank (221), the first-effect evaporation tank (221) is communicated with the second-effect evaporation tank (222), the second-effect evaporation tank (222) is communicated with the third-effect evaporation tank (223), the third-effect evaporation tank (223) is communicated with the fourth-effect evaporation tank (224), the fourth-effect evaporation tank (224) is communicated with the nitrate production unit (3), the first-effect evaporation tank (221), the second-effect evaporation tank (222) and the third-effect evaporation tank (223) are all communicated with the first salt thickener (23), and the steam turbine (42) is communicated with the first-effect evaporation tank (221).

6. A mechanical vapor recompression and multi-effect evaporation coupled salt production energy-saving technology according to claim 5, characterized in that: The salt production system further includes a brine purification device (5), and the salt production tank (15) and the fourth-effect evaporation tank (224) are both communicated with the brine purification device (5).

7. A mechanical vapor recompression and multiple-effect evaporation coupled salt production energy-saving technology according to claim 5, characterized in that: The nitrate production unit (3) includes a first nitrate production tank (31), a second nitrate production tank (32), a first heat exchanger group (33), a second heat exchanger group (34), a nitrate thickener (35) and a fourth flash tank (36). The salt production tank (15) is communicated with the first nitrate production tank (31) through the first heat exchanger group (33), the first nitrate production tank (31) is communicated with the nitrate thickener (35), and the first nitrate production tank (31) is communicated with the flash tank group (13); The fourth-effect evaporation tank (224) is communicated with the second nitrate production tank (32) through the second heat exchanger group (34), the second nitrate production tank (32) is communicated with the nitrate thickener (35), the steam turbine (42) is communicated with the first nitrate production tank (31) and the second nitrate production tank (32), and the second nitrate production tank (32) is communicated with the fourth-effect evaporation tank (224) through the fourth flash tank (36).

8. A mechanical vapor recompression and multi-effect evaporation coupled salt production energy-saving technology according to claim 7, characterized in that: The first heat exchanger group (33) includes a first heat exchanger (331), a second heat exchanger (332), and a third heat exchanger (333). The salt production tank (15) is communicated with the first heat exchanger (331), the first heat exchanger (331) is communicated with the second heat exchanger (332), the second heat exchanger (332) is communicated with the third heat exchanger (333), and the third heat exchanger (333) is communicated with the first nitrate production tank (31). The second heat exchanger group (34) includes a fourth heat exchanger (341) and a fifth heat exchanger (342). The IV-effect evaporation tank (224) is communicated with the fourth heat exchanger (341), the fourth heat exchanger (341) is communicated with the fifth heat exchanger (342), and the fifth heat exchanger (342) is communicated with the second nitrate production tank (32).

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