A process system for coordinated treatment of three wastes in the production process of granular silicon

Abstract

A process system for the coordinated treatment of three wastes in the production process of granular silicon utilizes a coupled process of adding chemicals for impurities removal, reuse of concentrated brine for waste treatment, evaporation and concentration of seed crystals for scale prevention, and fractional crystallization to treat the waste gas, wastewater, and waste residue generated in the production process of granular silicon and utilize them as resources. Lime milk, sodium sulfate, coagulants, coagulant aids, and other agents are added to the integrated wastewater obtained by homogenizing and adjusting multiple streams of production wastewater, and the wastewater passes through a high-density sedimentation tank and an air flotation filtration unit. Part of the concentrated brine is reused for waste treatment, and alkali liquor is added as a silicon slag slurry washing liquid and a process waste gas washing liquid. After alkali washing, hydrolysis, flocculation precipitation, and solid-liquid separation, the slag slurry wastewater and washing wastewater are returned to the wastewater treatment system. Another part of the concentrated brine enters the fractional crystallization system after seed crystals for scale prevention, evaporation, and concentration, and is centrifuged to obtain sodium chloride salt. The crystallization mother liquor is processed by a slicer to obtain miscellaneous salt. The environmental protection effect of the present invention is obvious.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection technology for waste gas, waste water and waste recycling, and in particular to a process for achieving coordinated waste gas, waste water and waste recycling in a granular silicon production process, and more specifically, to a coordinated waste gas, waste water and waste recycling process system in a granular silicon production process. Background Art

[0002] With the deepening implementation of the dual-carbon concept, the photovoltaic industry is experiencing a second wave of growth. Polysilicon, a key upstream raw material, has also become a highly sought-after commodity. However, polysilicon manufacturers are unable to shake off their high energy consumption, leading to widespread criticism of their development path. Currently, the modified Siemens process is mostly used to produce photovoltaic-grade and electronic-grade polysilicon. This process involves reducing high-purity trichlorosilane with high-purity hydrogen on a high-purity silicon core at approximately 1100°C. The resulting polysilicon is then grown on the core via chemical vapor deposition. Once the core has grown to a certain size, the furnace is shut down, cooled, and replaced, yielding rod-shaped polysilicon. The reaction conversion rate is relatively low, at only 5%-20%, and production is performed intermittently. This results in high energy consumption, reaching 60-70 kWh / kg.

[0003] In light of this, another polysilicon production process has recently gained renewed attention: the silane fluidized bed process (FBR). This process utilizes silane thermal decomposition to produce granular polysilicon. It primarily consists of silane production and separation, silane purification, silane thermal decomposition, silicon tetrachloride cold hydrogenation, silicon seed preparation, and waste treatment. The FBR process uses high-purity polysilicon fine particles as seeds, introduced into a fluidized bed reactor. A silane and hydrogen mixture is introduced from the bottom of the reactor, and the reaction proceeds at 600-800°C. Silane rapidly decomposes and deposits on the surface of the silicon seeds, causing the seeds to grow into larger granular silicon. This process boasts a high conversion rate of 60-70% and is capable of continuous production. It is estimated that compared to the modified Siemens process, its overall cost is approximately 30% lower, including a 70% reduction in electricity consumption, a 60% reduction in labor consumption, a 30% reduction in water consumption, and a 40% reduction in hydrogen consumption. Overall power consumption can be reduced to below 20 kWh / kg. Of course, granular silicon produced using a silane fluidized bed has its drawbacks. For example, its large surface area makes it susceptible to contamination, making it difficult to obtain high-purity granular silicon. Known impurity issues include hydrogen (adsorbed hydrogen), carbon (contamination from vessel wall wear), and metallic impurities. However, through continuous process improvements and optimization by the patent holder, the product's performance has reached the standards of modified Siemens process dense materials, and its industrialization is rapidly advancing.

[0004] Similar to the modified Siemens process, domestic granular silicon production companies, due to scale and cost constraints, have not yet achieved a fully closed-loop material circulation system. Consequently, the production process generates a certain amount of waste gas, wastewater, and waste residue requiring treatment. Waste gas is primarily generated from silane production and separation, silicon tetrachloride cold hydrogenation, and silane purification. Waste residue primarily consists of silicon slag slurry generated during the production process, an unavoidable byproduct that poses a significant environmental risk. Its main components include high-boiling substances, chlorosilane monomers, silicon powder, and catalysts. Wastewater is primarily generated during the waste gas and waste residue treatment process, including wastewater from chlorosilane waste gas scrubbing, wastewater from silane waste gas scrubbing, and slurry wastewater generated after hydrolysis and neutralization of silicon slag slurry. Tail gas scrubbing wastewater is the primary component of polysilicon production wastewater, generally accounting for over 90% of the total production wastewater. Small amounts of testing and analysis wastewater, as well as acid and alkaline wastewater, are also generated within the plant. Production process waste gas primarily contains chlorosilanes, silane, SiCl₄, HCl, H₂, and N₂. Since silane, chlorosilane and SiCl4 are easily hydrolyzed, alkaline solutions are often used for washing. For example, lime milk and sodium hydroxide solution, the concentration is generally selected to be 5%-15%. The chemical reactions involved in waste gas alkaline washing and silicon slag slurry hydrolysis reaction are mainly:

[0005] SiHCl3+H2O→SiO2+HCl+H2; HCl+NaOH→NaCl+H2O; HCl+Ca(OH)2→CaCl2+H2O

[0006] SiCl4+H2O→H2SiO3+HCl+H2; H2SiO3+NaOH→Na2SiO3+H2O; H2SiO3+Ca(OH)2→CaSiO3+H2O

[0007] SiH4+H2O→H2SiO3+H2; H2SiO3+NaOH→Na2SiO3+H2O; H2SiO3+Ca(OH)2→CaSiO3+H2O

[0008] SiH2Cl2+H2O→SiO2+H2+HCl; HCl+NaOH→NaCl+H2O; HCl+Ca(OH)2→CaCl2+H2O

[0009] The above reactions indicate that the wastewater generated after the treatment of process exhaust gas and silicon slag slurry is primarily saline wastewater composed of sodium chloride and calcium chloride, and contains large amounts of suspended particulate matter such as silicon powder and silicon dioxide, as well as colloidal impurities. Currently, the treatment of process exhaust gas and silicon slag slurry consumes large amounts of process water and generates corresponding saline wastewater. Typically, processes such as chemical mixing and multi-stage precipitation are used to remove insoluble salt pollutants from the wastewater, ensuring that it meets discharge standards. However, with the continuous improvement of national environmental standards for wastewater discharge, particularly regarding the concentration of soluble salts, this has necessitated the resource recovery of soluble salts in wastewater. Evaporative crystallization is currently one of the most widely used mainstream technologies for the enrichment and separation of salts in wastewater. However, scaling of equipment is a common problem, making long-term stable operation difficult. Furthermore, the evaporative crystallization process consumes significant energy and has high operating costs. At present, process waste gas washing water and silicon slag slurry washing liquid are directly prepared with process water, which consumes a lot of water and produces low concentration of salt wastewater, increases the treatment scale of wastewater treatment evaporation and crystallization equipment, and increases the investment cost of one-time environmental protection facilities of enterprises.

[0010] In response to the above problems, the present invention provides a new process for the coordinated treatment of three wastes in the granular silicon production process, which effectively reduces the overall investment and operating costs of the three wastes treatment, improves the comprehensive efficiency of the three wastes treatment, and simultaneously achieves the resource utilization of salt and water in the wastewater. Summary of the Invention

[0011] The purpose of this invention is to address the problems of high water consumption and high treatment costs in the existing wastewater treatment process of granular silicon production, and to provide a process system for the coordinated treatment of three wastes in the granular silicon production process. This system achieves the goals of low cost, high efficiency and resource utilization of the coordinated treatment of three wastes.

[0012] The technical solution of the present invention is:

[0013] A process system for the coordinated treatment of three wastes in the production process of granular silicon, characterized in that it consists of a concentrated brine recycling and waste treatment system 1, a dosing and impurity removal system 2, a seed anti-scaling evaporation and concentration system 3 and a fractionation crystallization system 4; the concentrated brine recycling and waste treatment system 1 consists of a slurry / waste gas washing liquid preparation tank 101, a slurry alkali washing and hydrolysis unit 102, a flocculation and precipitation unit 103, a solid-liquid separation unit 104, and a waste gas washing device 105. The slurry / waste gas washing liquid preparation tank 101 is provided with an alkali solution addition port, one output of the slurry / waste gas washing liquid preparation tank 101 is connected to the slurry alkali washing and hydrolysis unit 102, and the other is connected to the waste gas washing device 105, and the slurry alkali washing and hydrolysis unit 102 is connected to the silicon slurry output port. The inlet, its output is connected to the input end of the flocculation sedimentation unit 103, the output end of the flocculation sedimentation unit 103 is connected to the input end of the solid-liquid separation unit 104, the solid separated by the solid-liquid separation unit 104 is directly transported out for disposal, and the separated liquid and the waste liquid generated by the exhaust gas washing equipment 105 are input into the regulating tank 201 in the dosing and impurity removal system 2; the dosing and impurity removal system 2 consists of a regulating tank 201, a dosing tank 202, a high-density sedimentation tank 203, an air flotation filtration unit 204, a sludge thickening tank 205, and a filter press 206. The waste liquid from the regulating tank 201 is sent to the dosing tank 202 to add lime milk and sodium sulfate, and then sent to the high-density sedimentation tank 203 to add flocculants and The sludge produced after the coagulant reaction is sent to the sludge thickening tank 205 and then filtered by the filter press 206 before being transported for disposal. The wastewater after precipitation in the high-density sedimentation tank 203 is discharged into the flotation filtration unit 204 for further treatment. Part of the wastewater treated by the flotation filtration unit 204 is returned to the slurry / waste gas washing liquid preparation tank 101 for further treatment, and the other part is sent to the feed tank 301 of the seed anti-scaling evaporation and concentration system 3 for further treatment; the seed anti-scaling evaporation and concentration system 3 is composed of a feed tank 301, a degasser 302, and an evaporator 303. The concentrated salt wastewater entering the feed tank 301 from the flotation filtration unit 204 enters the degasser 302 after adding a pH regulator and is then discharged. After the oxygen, carbon dioxide and non-condensable gas are discharged, the condensate enters the evaporator 303 for evaporation. The secondary steam generated by evaporation is condensed into liquid water for recycling. After the seed crystal circulation operation, a certain seed crystal concentration in the evaporation system is maintained. The evaporated concentrated liquid is sent to the fractionation crystallization system (4) to obtain crystallized salt; the fractionation crystallization system 4 is composed of a crystallizer 401, a centrifugal dehydrator 402, a dryer 403 and a slicer 404; the secondary steam condensate generated by the crystallizer 401 is sent to the water recovery system, the suspension generated by the crystallization is sent to the centrifugal dehydrator 402 for dehydration, the wet solid salt is sent to the dryer 403 for drying to obtain sodium chloride salt, and the crystallization mother liquor is sent to the slicer 404 for treatment to obtain miscellaneous salt.

[0014] The new process and system provided by this invention targets the three wastes generated during the granular silicon production process, including silicon slag slurry, process waste gases from various stages (chlorosilane waste gas, silane waste gas), and wastewater discharged from various stages (waste gas scrubbing wastewater, slag wastewater, testing and analysis wastewater, and acid and alkaline wastewater). Process waste gas scrubbing wastewater is the primary component of production wastewater, generally accounting for over 90% of the total production wastewater. The combined wastewater, formed after homogenization and equalization of the various wastewater streams in the equalization tank 201, has a salinity of 2%-6%, primarily sodium chloride and calcium chloride. The combined wastewater has a high suspended solids content exceeding 5000 mg / L, is alkaline with a pH of 8-10, and has a COD content of less than 1000 mg / L. The main components of the process waste gases are nitrogen, hydrogen, chlorosilanes, silanes, and hydrogen chloride, of which chlorosilanes and silanes account for 25%-35% by weight. Silicon slag slurry is primarily composed of high-boiling substances, accompanied by small amounts of chlorosilanes, silicon powder, and catalysts. Silicon slag slurry is an inevitable by-product in production and poses a great threat to the environment.

[0015] The three wastes coordinated treatment process and system provided by the present invention adopts alkaline solution washing and hydrolysis treatment for the treatment of waste gas and waste residue, and finally exists in the form of waste water. The waste water is then treated as a resource to realize the recycling of salt and water. The specific process includes a dosing and impurity removal system 2, a concentrated brine recycling and waste treatment system 1, a seed anti-scaling evaporation and concentration system 3, and a fractionation crystallization system 4. The comprehensive wastewater first enters the dosing and impurity removal system 2, that is, the comprehensive wastewater is pumped into the dosing tank 202, and lime milk and sodium sulfate are added to the dosing tank 202. The addition of lime milk is used to remove magnesium hardness and alkalinity in the wastewater, and the addition of sodium sulfate is required for the subsequent seed anti-scaling process in the seed anti-scaling evaporation and concentration system 3. The calcium ion concentration of the concentrated brine after dosing and impurity removal is 5000mg / L-8000mg / L, and the sulfate ion concentration is 500mg / L-2000mg / L. A mechanical stirring device is provided in the dosing tank 202 to ensure that the added reagents are mixed evenly and the reaction is rapid and thorough. The inner wall of dosing tank 202 is protected against corrosion, such as by coating with anti-corrosion paint. Dosing tank 202 is equipped with a fully automatic dosing device. Wastewater discharged from dosing tank 202 is pumped into high-density sedimentation tank 203, where a coagulant and flocculant are added. Coagulants such as polyferric sulfate or polyferric chloride can be used, with a dosage of 10ppm-100ppm; coagulants such as polyacrylamide can be used, with a dosage of 1mg / L-10mg / L. Suspended particles, colloids, and some organic matter in the wastewater aggregate and combine under the action of the coagulant and coagulant aid, forming floccules. These floccules settle into sludge thickening tank 205, where they are processed in filter press 206 as a sludge cake and then discharged to the disposal system. Filter press 206 can be a plate and frame filter press 2061, with the moisture content of the sludge cake controlled to below 20%. The supernatant enters flotation filtration unit 204, further reducing the suspended solids content in the wastewater. A dissolved air flotation machine 2041 equipped with a micro-nano bubble generator can be used; a media filter 2042 can be used, using a stack of one or more filter media such as quartz sand, ceramic sheets, and activated carbon as the filter layer, with a filter media particle size of 0.5mm-4mm. After adding drugs and removing impurities, the concentrated brine should have a suspended solids content of less than 5mg / L, a magnesium ion concentration of less than 50mg / L, a combined carbonate and bicarbonate concentration of less than 50mg / L, a COD content of less than 300mg / L, and a pH of 9-10.

[0016] After adding chemicals and removing impurities, the concentrated brine is divided into two streams. One stream is recycled for waste treatment, namely for the treatment of silicon slag slurry and process exhaust gas. Specifically, this concentrated brine accounts for 20%-50% by weight. Alkali is added to the concentrated brine and prepared in the slurry / exhaust gas washing liquid preparation tank to form silicon slag slurry washing liquid and process exhaust gas washing liquid. The alkaline liquid can be selected from lime milk with a concentration of 10%-15% or sodium hydroxide solution with a concentration of 5%-15%, or a mixture of the two. The selection principle is that lime milk is weakly alkaline, has a moderate washing effect, low corrosiveness, a wide range of equipment selection, and relatively low cost. Sodium hydroxide solution is a strong base with good washing effect, but it is highly corrosive, requiring high-grade equipment and pipelines to meet process requirements. The silicon slag slurry generated during the production process is mixed and reacted with the prepared washing liquid in the slurry alkaline washing and hydrolysis unit 102. It is equipped with a mechanical agitator, and under the stirring action, the two undergo a thorough hydrolysis and neutralization reaction. The discharged slurry wastewater is then treated in the flocculation and sedimentation unit 103 and the solid-liquid separation unit 104, and then returned to the regulating tank 201. The silicon slurry residue is transported out for disposal as solid waste. The process waste gas is contacted and reacted with the prepared washing liquid in the waste gas washing equipment 105. The waste gas washing equipment 105 can be in the form of a packed tower scrubber or a venturi scrubber 1051. The elution temperature is controlled at 40°C-50°C, and an electric heater can be set at the same time to balance the system temperature. After the washing liquid has become ineffective after multiple circulation reactions, it is returned to the regulating tank 201 as washing wastewater. The tail gas after elution is discharged through a liquid seal tank. After the concentrated brine is reused for waste gas and waste residue treatment, the salinity of the wastewater returning to the system is further increased, achieving the effect of "internal circulation concentration" of saline wastewater, reducing the treatment scale of the evaporation crystallization section, and reducing investment and operating costs.

[0017] Another stream of concentrated brine, after dosing and impurity removal, is acidified in feed tank 301 to adjust the pH to 5-6. The residual carbonate alkalinity in the wastewater reacts with the acid to produce carbon dioxide. The wastewater is then pumped into deaerator 302, where carbon dioxide, dissolved oxygen, and non-condensable gases are thermally removed. Removing dissolved oxygen helps prevent corrosion in the evaporation and crystallization system, while removing non-condensable gases helps maintain high heat transfer efficiency in the evaporation and crystallization equipment. Concentrated sulfuric acid or hydrochloric acid can be used for acid adjustment. Deaerator 302 can be a plate tower or a packed tower, operating at a temperature of 90°C-95°C. The degassed concentrated brine enters evaporator 303 for evaporation and concentration. Evaporator 303 utilizes a vertical tube falling film system, with the concentrated brine flowing through the tubes. The seeded anti-scaling evaporation and concentration system 3 incorporates a seeded anti-scaling process, which involves adding calcium sulfate as seeds and maintaining an effective seed concentration within the system between 10g / L and 15g / L. An internal seed recovery process is also included to ensure efficient seed utilization. The principle of seed crystal anti-scaling is that the concentrated brine is continuously concentrated in the evaporator. When the concentration of scaling particles reaches supersaturation, they are preferentially precipitated on the surface of the seed crystals, reducing their tendency to scale on the heated surface of the heat exchanger, thereby achieving scale-free, long-term, and stable operation of the evaporation and concentration system. The seed crystal anti-scaling evaporation and concentration system 3 combines high-efficiency energy-saving technologies to further reduce costs and increase efficiency, such as the use of TVR, MVR, or multi-effect evaporation. The energy-saving principle lies in the full utilization of the latent heat enthalpy of secondary steam. High temperature and high salt operating conditions place high demands on the equipment material. That is, the flow-through equipment of the seed crystal anti-scaling evaporation and concentration system 3 that comes into contact with the brine is made of high-grade materials. For example, titanium can be used for heat exchange tubes, 2205 and 2507 duplex steel can be used for the evaporator 303 body, and titanium composite plates can be used for the tube sheets.

[0018] The 15%-25% concentrated brine discharged from the seed crystal anti-scaling evaporation and concentration system 3 is pumped into the fractionation crystallization system 4. The brine continues to evaporate and concentrate in the crystallizer 401 to a concentration of 40%-65%, forming sodium chloride crystals with a solids content of 10%-30%. The concentrated slurry at the outlet of the crystallizer 401 enters the centrifugal dehydrator 402. The separated wet salt is conveyed via a conveyor belt to the dryer 403 for dehydration and drying, resulting in sodium chloride byproduct salt of a quality that meets first-class industrial salt standards. The crystallizer 401 can be a forced circulation type or a DTB type. The salt leg of the crystallizer 401 features a special flow channel design that facilitates material remixing and the growth and elutriation of the crystallized salt. The centrifugal dehydrator 402 is equipped with an elutriation line to further enhance the quality of the crystallized salt. A demister, either wire mesh or folded plate, is installed at the secondary steam outlet of the evaporation crystallization system to reduce mist entrainment and improve the quality of the product water. The mother liquor is centrifuged and enters the slicer 404 for processing to obtain miscellaneous salts.

[0019] The beneficial effects of the present invention are:

[0020] The present invention achieves the treatment of waste gas and waste residue generated in the granular silicon production process, and simultaneously realizes the resource disposal and utilization of wastewater, that is, achieves the purpose of efficient coordinated treatment of three wastes. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the overall flow chart of the three wastes coordinated treatment process in the granular silicon production process of the present invention.

[0022] Figure 2 This is a process flow chart for the treatment of three wastes in the granular silicon production process according to an embodiment of the present invention.

[0023] Among them, 1- concentrated brine recycling and waste treatment system, 2- dosing and impurity removal system, 3- seed anti-scaling evaporation and concentration system, 4- fractionation crystallization system, 101- slurry / waste gas washing liquid preparation tank, 1011- slurry washing liquid preparation tank, 102- slurry alkaline washing and hydrolysis unit, 103- flocculation and sedimentation unit, 104- solid-liquid separation unit, 105- waste gas washing equipment, 1051- Venturi scrubber, 201- regulating tank, 202- dosing tank, 203- high-density sedimentation tank, 204- gas Floating filtration unit, 2041-dissolved air flotation machine, 2042-media filter, 205-sludge thickening tank, 206-filter press, 2061-plate and frame filter press, 301-feed tank, 302-degasser, 303-evaporator, 3031-MVR evaporator, 304-plate heat exchanger, 401-crystallizer, 4011-forced circulation crystallizer, 402-centrifugal dehydrator, 403-dryer, 4031-vibrating fluidized bed dryer, 404-slicer. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings and examples.

[0025] like Figure 1 shown.

[0026] A process system for the coordinated treatment of three wastes in the production process of granular silicon, characterized in that it consists of a concentrated brine recycling and waste treatment system 1, a dosing and impurity removal system 2, a seed anti-scaling evaporation and concentration system 3 and a fractionation crystallization system 4; the concentrated brine recycling and waste treatment system 1 consists of a slurry / waste gas washing liquid preparation tank 101, a slurry alkali washing and hydrolysis unit 102, a flocculation and precipitation unit 103, a solid-liquid separation unit 104, and a waste gas washing device 105. The slurry / waste gas washing liquid preparation tank 101 is provided with an alkali liquid addition port, and the output of the slurry / waste gas washing liquid preparation tank 101 is connected to the slurry alkali washing and hydrolysis unit 102 on one side and to the waste gas washing device 105 on the other side. The slurry alkali washing and hydrolysis unit 102 is connected to the silicon slag. The slurry input port, its output is connected to the input end of the flocculation sedimentation unit 103, the output end of the flocculation sedimentation unit 103 is connected to the input end of the solid-liquid separation unit 104, the solid separated by the solid-liquid separation unit 104 is directly transported out for disposal, and the separated liquid and the waste liquid generated by the waste gas washing equipment 105 are input into the regulating tank 201 in the dosing and impurity removal system 2; the dosing and impurity removal system 2 consists of a regulating tank 201, a dosing tank 202, a high-density sedimentation tank 203, a flotation filtration unit 204, a sludge thickening tank 205, and a filter press 206. The waste liquid from the regulating tank 201 is sent to the dosing tank 202, where lime milk and sodium sulfate are added, and then sent to the high-density sedimentation tank 203 to add flocculants. The sludge produced after the reaction of the coagulant and the coagulant is sent to the sludge thickening tank 205 and then filtered by the filter press 206 before being transported for disposal. The wastewater after precipitation in the high-density sedimentation tank 203 is discharged into the flotation filtration unit 204 for further treatment. Part of the wastewater treated by the flotation filtration unit 204 is returned to the slurry / waste gas washing liquid preparation tank 101 for further treatment, and the other part is sent to the feed tank 301 of the seed anti-scaling evaporation and concentration system 3 for further treatment; the seed anti-scaling evaporation and concentration system 3 is composed of a feed tank 301, a degasser 302, and an evaporator 303. The concentrated salt wastewater entering the feed tank 301 from the flotation filtration unit is adjusted by adding a pH regulator and then enters the degasser 302. After the oxygen, carbon dioxide and non-condensable gas are discharged, they enter the evaporator 303 for evaporation. The secondary steam generated by evaporation is condensed into liquid water for recycling. After the seed crystal circulation operation, a certain seed crystal concentration in the evaporation system is maintained, and the evaporated concentrate is sent to the fractionation crystallization system 4 to obtain crystalline salt; the fractionation crystallization system 4 is composed of a crystallizer 401, a centrifugal dehydrator 402, a dryer 403 and a slicer 404; the secondary steam condensate generated by the crystallizer 401 is sent to the water recovery system, the suspension generated by the crystallization is sent to the centrifugal dehydrator 402 for dehydration, the wet solid salt is sent to the dryer 403 for drying to obtain sodium chloride salt, and the crystallization mother liquor is sent to the slicer 404 for treatment to obtain miscellaneous salt.

[0027] After conditioning, the combined wastewater from multiple streams of production wastewater, including exhaust gas scrubbing wastewater, slurry wastewater, and other wastewater, has a salinity of 2%-6%, primarily composed of sodium chloride and calcium chloride. The COD content is less than 1000 mg / L, the suspended solids content is greater than 5000 mg / L, and the pH is 8-10. This combined wastewater passes through the dosing and impurity removal system 2, where lime milk, sodium sulfate, coagulants, and flocculants are added. After treatment in the high-density sedimentation tank 203 and flotation filtration unit 204, a concentrated brine is obtained, removing magnesium hardness, alkalinity, and impurity particles (suspended particles, colloids, and some organic matter). This concentrated brine enters the waste recycling system 1 for use in silicon slurry hydrolysis and process waste gas scrubbing. This involves adding alkaline solution to the concentrated brine and preparing it in the slurry / waste gas scrubbing solution preparation tank 101 to create the wash solution required for silicon slurry hydrolysis and process waste gas scrubbing. After treatment in the slurry alkaline washing and hydrolysis unit 102, the flocculation and sedimentation unit 103, and the solid-liquid separation unit 104, the slurry wastewater and exhaust gas scrubbing wastewater are returned to the regulating tank 201, and the silicon slurry residue is transported and disposed of as solid waste. Another portion of the concentrated brine enters the seed crystal anti-scaling evaporation and concentration system 3, which is equipped with an internal seed crystal recycling process to ensure efficient seed crystal utilization. The highly concentrated brine discharged from the seed crystal anti-scaling evaporation and concentration system 3 enters the fractionation crystallization system 4. The highly concentrated brine is further dehydrated and concentrated in the crystallizer 401 to form a sodium chloride crystal product. The crystal suspension is then processed in the centrifugal dehydrator 402 and dryer 403 to obtain solid sodium chloride salt. The crystallization mother liquor is processed in the slicer 404 to obtain solid miscellaneous salts. The secondary steam produced by the seed crystal anti-scaling evaporation and concentration system 3 and the fractionation crystallization system 4 is condensed and deeply purified before being recycled as high-quality water. The present invention treats the combined wastewater generated by the multiple wastewater streams in the granular silicon production process after homogenization and equalization in the regulating tank. Multiple wastewater streams include chlorosilane waste gas washing wastewater, silane waste gas washing wastewater, slurry wastewater and other wastewater, such as a small amount of detection and analysis wastewater, acid and alkaline wastewater, etc. In the dosing tank 202, lime milk and sodium sulfate are added to the comprehensive wastewater to reduce the magnesium hardness and alkalinity of the wastewater while maintaining a certain concentration of calcium ions and sulfate ions in the system to meet the requirements of the subsequent seed anti-scaling evaporation and concentration system 3. The effluent suspension from the dosing tank 202 enters the high-density sedimentation tank 203, where coagulants and flocculants are added. After stirring and settling, the suspended particles, colloids and some organic matter in the wastewater are aggregated and combined into alum flocs. After being treated in the sludge thickening tank 205 and the filter press 206, they are discharged from the system in the form of mud cakes for disposal. The outlet clear liquid enters the flotation filtration unit 204 to further reduce the suspended matter content of the wastewater and obtain concentrated brine after dosing and impurity removal. In order to meet the requirements of the seed crystal anti-scaling process in the seed crystal anti-scaling evaporation concentration system 3, the calcium ion concentration in the concentrated brine after adding medicine and removing impurities is 5000mg / L-8000mg / L, and the sulfate ion concentration is 500mg / L-2000mg / L.After adding drugs and removing impurities, the concentrated brine satisfies the requirements of suspended solids content less than 5 mg / L, magnesium ion concentration less than 50 mg / L, the sum of carbonate and bicarbonate concentrations less than 50 mg / L, COD content less than 300 mg / L, and pH 9-10. The coagulant added to the high-density sedimentation tank 203 can be polyferric sulfate or polyferric chloride, etc., with a dosage of 10ppm-100ppm; the coagulant aid can be polyacrylamide, etc., with a dosage of 1mg / L-10mg / L. The flotation filtration unit 204 can be equipped with a dissolved air flotation machine 2041, a medium filter 2042, etc. The dissolved air flotation machine 2041 uses a micro-nano bubble generator, and the diameter of the microbubbles is less than 50um. The medium filter 2042 can use one or more filter media such as quartz sand, ceramic sheets, activated carbon, etc. as the filter layer, and the filter media particle size is 0.5mm-4mm. A portion of the concentrated brine treated by the dosing and impurity removal system 2 enters the concentrated brine reuse and waste treatment system 1. After the treatment, the brine is divided into two streams. Alkali is added to one of the streams and mixed into silicon slag slurry and process waste gas washing liquid in the slurry / waste gas washing liquid preparation tank 101. Under the action of the washing liquid, the silicon slag slurry undergoes hydrolysis and neutralization in the slurry alkaline washing and hydrolysis unit 102, removing the chlorosilanes entrained in the slurry and the hydrogen chloride gas produced by the hydrolysis. The resulting slurry wastewater contains calcium silicate, calcium chloride, silicon powder, and residual high-boiling materials in the slurry. After treatment in the flocculation and sedimentation unit 103 and the solid-liquid separation unit 104, it flows back to the equalization tank 201, and the silicon slurry residue is transported and disposed of as solid waste. Process waste gases containing chlorosilane, silane, and hydrogen chloride, generated during the granular silicon production process, react with alkaline scrubbing liquid in the waste gas scrubbing equipment 105 and are then vented through a liquid seal tank. The ineffective scrubbing liquid is returned to the equalization tank 201 as scrubbing wastewater. The mass fraction of the concentrated brine reused for waste treatment is 20%-50%. Lime milk or sodium hydroxide solution can be used as the added alkaline solution. The concentration of lime milk is 10%-15%, and the concentration of sodium hydroxide solution is 5%-15%. The silicon slag slurry and the prepared scrubbing liquid are conveyed to the slurry alkaline washing and hydrolysis unit 102, which is equipped with a mechanical agitator. The agitation allows for thorough hydrolysis and neutralization. The waste gas scrubbing equipment 105 can be a packed tower scrubber or a Venturi scrubber 1051. The scrubbing temperature is 40°C-50°C, and an electric heater can be installed to balance the system temperature. The coupled seed crystal anti-scaling process in the concentrated salt crystal seed anti-scaling evaporation concentration system 3 involves adding calcium sulfate as a seed crystal to the system. The concentrated brine is continuously concentrated in the evaporator 303. When the concentration of scale-forming particles reaches supersaturation, they preferentially precipitate on the surface of the seed crystals, reducing their tendency to scale on the heat exchanger surface. A seed crystal internal recovery process section is provided to maintain the effective seed crystal concentration in the system at 10g / L-15g / L, while reducing the amount of seed crystals added during the process. Before entering the evaporator 303, the concentrated brine needs to be acidified in the feed tank 301 for pH adjustment and degassed in the degasser 302 to remove carbonate alkalinity, dissolved oxygen, carbon dioxide, and non-condensable gases.Evaporator 303 in the seed crystal anti-scaling evaporation and concentration system 3 utilizes a vertical tube falling film system, with the concentrated brine flowing through the tubes. Energy-saving technologies, such as TVR, MVR, or multi-effect technologies, are used to reduce costs and increase efficiency. The flow-through equipment in contact with the brine in the seed crystal anti-scaling evaporation and concentration system 3 is constructed from high-grade materials, such as 2205 and 2507 duplex steels, titanium, and titanium composite plates. The brine is acidified to adjust its pH to 5-6, and the concentration of the concentrated brine at the outlet of evaporator 303 is maintained at 15%-25%. The concentrated brine continues to evaporate and concentrate in crystallizer 401 of fractional crystallization system 4 to a concentration of 40%-60% and a solids content of 10%-30%. The concentrated slurry at the outlet of crystallizer 401 enters centrifugal dehydrator 402, and the discharged wet-solid salt enters dryer 403 for dehydration and drying, producing sodium chloride as a byproduct. The mother liquor from the centrifuge enters slicer 404 for processing, producing miscellaneous salts. Crystallizer 401 can be a forced circulation (FC) or DTB type. It features a special salt leg design for material backmixing and elutriation. Centrifugal dehydrator 402 is equipped with an elutriation line to improve the quality of the byproduct sodium chloride salt, bringing it up to Grade 1 industrial salt standards. A demister, either wire mesh or folded plate, is installed at the secondary steam outlet of crystallizer 401.

[0028] like Figure 2 shown.

[0029] A granular silicon production company is implementing a coordinated three-waste treatment process. Process waste gas, primarily composed of chlorosilanes and silanes, is treated in a Venturi scrubber 1051. The scrubbing liquid is a 5% sodium hydroxide solution prepared from caustic soda and process water. The scrubbing liquid and waste gas first react in the throat, accelerating the reaction. Then, the waste gas and scrubbing liquid undergo a countercurrent reaction in a spray tower equipped with a packing layer, consuming the chlorosilanes and silanes in the waste gas. The remaining purified gas, primarily composed of nitrogen, hydrogen, and water vapor, is discharged from the chimney. The wastewater from the scrubbing process has a salinity of 4%-6% and a pH of approximately 9. Silicon slag slurry is treated by adding recycled concentrated brine to a 10% lime milk solution prepared in the slag slurry washing solution preparation tank 1011. The silicon slag slurry and washing solution react in the slag alkali washing and hydrolysis unit 102. An internal mechanical agitator ensures a more thorough hydrolysis and neutralization reaction, completely hydrolyzing any remaining chlorosilanes. The slag wastewater at the outlet of the slag alkali washing and hydrolysis unit 102 contains some high-boiling substances, silicon powder, silicon oxide, catalyst, and other substances, with a high suspended solids content. After treatment in the flocculation and sedimentation unit 103 and the solid-liquid separation unit 104, the outlet slag wastewater has a salt content of 5%-6% and is returned to the equalization tank 201. The silicon slag is then transported for disposal as solid waste.

[0030] Waste gas washing wastewater, slurry wastewater and other small amounts of production wastewater such as testing center wastewater, hydrochloric acid analysis wastewater, etc. are homogenized and equalized in the regulating tank 201 to form comprehensive wastewater. The comprehensive wastewater is pumped into the dosing tank 202, and the automatic dosing device is used to add lime milk and sodium sulfate with a concentration of 10% into the dosing tank. The built-in stirring device is used to make the added agents and wastewater evenly mixed and react thoroughly. The inner wall of the dosing tank 202 is painted with anti-corrosion paint. The wastewater discharged from the dosing tank 202 is pumped into the high-density sedimentation tank 203, and 60ppm-80ppm polyferric sulfate is added in the coagulation stirring zone, and 5-8mg / L polyacrylamide is added in the flocculation stirring zone. Under the action of coagulants, flocculants, and agitation, suspended particles, colloids, and some organic matter in the wastewater aggregate and combine into large-sized flocs. These particles slowly settle in the sedimentation zone, are then scraped by a bottom scraper and transported to the sludge thickening tank 205. After treatment in the plate and frame filter press 2061, the sludge cake, with a moisture content of less than 20%, is transported for disposal. The filtrate is returned to the high-density sedimentation tank 203. The clear liquid at the upper outlet of the high-density sedimentation tank 203 enters the dissolved air flotation machine 2041, which is equipped with a micro-nano bubble generator that produces microbubbles with a diameter of less than 50 μm. The wastewater at the outlet of the dissolved air flotation machine 2041 enters the media filter 2042, which uses a mixture of quartz sand and activated carbon with a particle size of 2-4 mm as the filter layer. The suspended solids content of the concentrated brine at the outlet of the media filter 2042 is less than 5 mg / L, the magnesium ion concentration is less than 30 mg / L, the sum of the carbonate and bicarbonate concentrations is less than 30 mg / L, the COD content is less than 200 mg / L, and the pH is 9.5-10.

[0031] 20%-30% of the brine mass at the outlet of media filter 2042 is recycled as brine for treating silicon slag slurry. The remaining brine is pumped into feed tank 301, where concentrated sulfuric acid is added to adjust the pH to 5-6. The brine is heated to 90°C-95°C in plate heat exchanger 304 and pumped into deaerator 302, where carbon dioxide, dissolved oxygen, and non-condensable gases are discharged. The liquid at the outlet of deaerator 302 is pumped into the inlet of MVR evaporator 3031, where it circulates through evaporation and concentration to a concentration of 20%-25%. Calcium sulfate seeds are added to the MVR evaporator 3031 to maintain a seed concentration of 10g / L-15g / L in the evaporation system. The evaporation and concentration system is equipped with an internal seed recovery process to ensure efficient seed utilization and reduce seeding reagent costs. The MVR 3031 evaporator utilizes a vertical tube falling film system, with titanium heat exchange tubes, 2205 duplex steel for the body, and titanium composite plate for the tubesheet. The application of seed crystal technology allows scaling ions in the slurry to preferentially precipitate on the seed crystal surface when they reach supersaturation during the concentration process, reducing their tendency to scale on the heat exchanger's heating surfaces and achieving scale-free, long-term, and stable operation of the evaporation and concentration system.

[0032] MVR evaporator 3031 discharges highly concentrated brine with a concentration of 20%-25%, which is pumped into the fractional crystallization system. This brine continues to evaporate and concentrate in the forced circulation crystallizer 4011 to a concentration of 50%-60%. Sodium chloride crystals are formed in the system, and the solids content of the crystalline suspension is controlled to 15%-20%. The salt legs of forced circulation crystallizer 4011 utilize a special flow channel design that facilitates back-mixing of materials in the legs, aiding the growth and washing of the crystallized salt. The concentrated slurry at the outlet of forced circulation crystallizer 4011 enters centrifugal dehydrator 402, where wet solid salt with a moisture content of less than 20% is separated. The wet solid salt is conveyed via a conveyor belt to vibrating fluidized bed dryer 4031 for dehydration and drying, resulting in sodium chloride byproduct salt, which meets first-class industrial salt standards. The centrifuged mother liquor enters slicer 404 for processing, yielding impurity salt.

[0033] Wire mesh demisters are installed at the outlets of the secondary steam generated by the MVR evaporator 3031 and the forced circulation crystallizer 4011 to reduce mist entrainment and improve product water quality. The product water is treated by a reverse osmosis system to produce desalted water for reuse in process systems, such as in the preparation of exhaust gas scrubbing fluid.

[0034] The parts not involved in the present invention are the same as the existing technology or can be implemented by using the existing technology.

Claims

1. A process system for the coordinated treatment of three wastes in the production process of granular silicon, characterized in that: It consists of a brine recycling and waste treatment system (1), a dosing and impurity removal system (2), a seed crystal anti-scaling evaporation and concentration system (3) and a fractionation crystallization system (4); The concentrated brine recycling waste treatment system (1) is composed of a slurry / waste gas washing liquid preparation tank (101), a slurry alkali washing and hydrolysis unit (102), a flocculation sedimentation unit (103), a solid-liquid separation unit (104), and a waste gas washing device (105). The slurry / waste gas washing liquid preparation tank (101) is provided with an alkali liquid addition port. One output of the slurry / waste gas washing liquid preparation tank (101) is connected to the slurry alkali washing and hydrolysis unit (102), and the other output is connected to the waste gas washing device (105). The slurry alkali washing and hydrolysis unit (102) is connected to the silicon slurry input port, and its output is connected to the input end of the flocculation and sedimentation unit (103). The output end of the flocculation and sedimentation unit (103) is connected to the input end of the solid-liquid separation unit (104). The solid separated by the solid-liquid separation unit (104) is directly transported to the outside for disposal, and the separated liquid is input into the regulating tank (201) in the dosing and impurity removal system (2) together with the waste liquid generated by the waste gas washing equipment (105); The dosing and impurity removal system (2) consists of a regulating tank (201), a dosing tank (202), a high-density sedimentation tank (203), an air flotation filtration unit (204), a sludge thickening tank (205), and a filter press (206). The waste liquid from the regulating tank (201) is sent to the dosing tank (202) to be added with lime milk and sodium sulfate, and then sent to the high-density sedimentation tank (203). The sludge generated after the reaction of the flocculant and the coagulant is sent to the sludge thickening tank (205) and then passed through the filter press ( 206) After filtration, the wastewater is transported for disposal. After sedimentation in the high-density sedimentation tank (203), it is discharged into the flotation filtration unit (204) for further treatment. A portion of the wastewater treated by the flotation filtration unit (204) is returned to the slurry / waste gas washing liquid preparation tank (101) for further treatment, wherein the mass proportion of the concentrated brine used for waste treatment is 20%-50%; the other portion is sent to the feed tank (301) of the seed anti-scaling evaporation concentration system (3) for further treatment; The seed anti-scaling evaporation and concentration system (3) is composed of a feed tank (301), a degasser (302), and an evaporator (303). The concentrated salt wastewater entering the feed tank (301) from the flotation filtration unit (204) is adjusted with a pH regulator and then enters the degasser (302). After the oxygen, carbon dioxide and non-condensable gas are discharged, the wastewater enters the evaporator (303) for evaporation. The secondary steam generated by evaporation is condensed into liquid water for recycling. After the seed circulation operation, a certain seed concentration is maintained in the evaporation system. The evaporated concentrated liquid is sent to the fractionation crystallization system (4) to obtain crystalline salt. The fractionation crystallization system (4) consists of a crystallizer (401), a centrifugal dehydrator (402), a dryer (403) and a slicer (404); the secondary steam condensate generated by the crystallizer (401) is sent to the water recovery system, the suspension generated by the crystallization is sent to the centrifugal dehydrator (402) for dehydration, the wet solid salt is sent to the dryer (403) for drying to obtain sodium chloride salt, and the crystallization mother liquor is sent to the slicer (404) for treatment to obtain miscellaneous salt.

2. The process system according to claim 1, characterized in that: The waste gas washing wastewater generated by the waste gas washing equipment (105), the slurry wastewater generated by the solid-liquid separation unit (104) and other multiple production wastewaters have a salt content of 2%-6% after conditioning, and the salt is composed of sodium chloride and calcium chloride; the COD content is less than 1000 mg / L, the suspended solids content of the wastewater is greater than 5000 mg / L, and the pH is 8-10; The comprehensive wastewater is treated by the dosing and impurity removal system (2), after lime milk, sodium sulfate, coagulant and flocculant are added, and then the wastewater is treated by the high-density sedimentation tank (203) and the flotation filtration unit (204) to obtain concentrated brine after removing magnesium hardness, alkalinity and impurity particles; part of the concentrated brine is reused for waste treatment and used for silicon slag slurry hydrolysis and process waste gas washing treatment, that is, alkali solution is added to a stream of concentrated brine to prepare the washing solution required for silicon slag slurry hydrolysis and process waste gas washing; the slag slurry wastewater and waste gas washing wastewater treated by the slurry alkali washing and hydrolysis unit (102), the flocculation and sedimentation unit (103) and the solid-liquid separation unit (104) are returned to the wastewater treatment system, and the silicon slurry slag is transported out for disposal as solid waste; the other part of the concentrated brine enters the crystal seed anti-scaling evaporation concentration system (3), which is equipped with a crystal seed internal circulation recovery process section to ensure efficient use of the crystal seed; The seed crystal anti-scaling evaporation concentration system (3) discharges highly concentrated brine and enters the fractionation crystallization system (4); The highly concentrated brine is further dehydrated and concentrated in the crystallizer (401) to form a sodium chloride crystal product. The crystal suspension is centrifugally dehydrated and dried in a centrifugal dehydrator (402) and a dryer (403) to obtain solid sodium chloride salt. The crystallization mother liquor is processed by a slicer (404) to obtain solid miscellaneous salts. The secondary steam produced by the evaporation crystallization system is condensed and deeply purified before being recycled as high-quality water.

3. The process system according to claim 1, characterized in that: The treatment object is the comprehensive wastewater generated by multiple wastewaters in the granular silicon production process after homogenization and equalization in the regulating tank; the multiple wastewaters include chlorosilane waste gas washing wastewater, silane waste gas washing wastewater, slurry wastewater and a small amount of detection and analysis wastewater, acid and alkali wastewater; The comprehensive wastewater is added with lime milk and sodium sulfate in the dosing tank (202) to reduce the magnesium hardness and alkalinity of the wastewater while maintaining a certain concentration of calcium ions and sulfate ions in the system to meet the requirements of the seed anti-scaling process in the subsequent seed anti-scaling evaporation concentration system (3); The effluent suspension from the dosing tank (202) enters the high-density sedimentation tank (203), where coagulants and flocculants are added. After stirring and settling, the suspended particles, colloids and some organic matter in the wastewater aggregate and combine to form alum flocs. After being treated in the sludge thickening tank (205) and the filter press (206), the effluent is discharged into the system in the form of mud cakes for disposal; the outlet clear liquid enters the flotation filtration unit (204) to further reduce the suspended matter content of the wastewater, thereby obtaining concentrated brine after dosing and impurity removal.

4. The process system according to claim 1, characterized in that The calcium ion concentration in the brine after adding the drug and removing impurities is 5000mg / L-8000mg / L, and the sulfate ion concentration is 500mg / L-2000mg / L; the brine after adding the drug and removing impurities meets the requirements of suspended solids content less than 5mg / L, magnesium ion concentration less than 50mg / L, the sum of carbonate and bicarbonate concentrations less than 50mg / L, COD content less than 300mg / L, and pH 9-10; The high-density sedimentation tank (203) is added with a coagulant of polyferric sulfate or polyferric chloride at a dosage of 10ppm-100ppm; the coagulant aid is polyacrylamide at a dosage of 1mg / L-10mg / L; The flotation filtration unit (204) uses a dissolved air flotation machine (2041) and a medium filter (2042); wherein the dissolved air flotation machine (2041) uses a micro-nano bubble generator, and the diameter of the microbubbles is less than 50 μm; the medium filter (2042) uses a stack of one or more filter materials selected from quartz sand, ceramic sheets, and activated carbon as a filter layer, and the filter material particle size is 0.5 mm-4 mm.

5. The process system according to claim 1, characterized in that: After adding chemicals and removing impurities, the brine is divided into two streams. Alkali solution is added to one of the brine streams to prepare silicon slag slurry washing liquid and process waste gas washing liquid. The silicon slag slurry undergoes hydrolysis and neutralization reaction under the action of the washing liquid, removing the chlorosilanes entrained in the slurry and the hydrogen chloride gas generated by hydrolysis. The resulting slurry wastewater contains calcium silicate, calcium chloride, silicon powder and residual slurry high-boiling substances. After being processed in the flocculation and sedimentation unit (103) and the solid-liquid separation unit (104), the silicon slurry is returned to the regulating tank (201), and the silicon slurry residue is transported out for disposal as solid waste; The process waste gas containing chlorosilane, silane and hydrogen chloride generated during the preparation of granular silicon is discharged through a liquid seal tank after contact reaction with alkaline washing liquid in the waste gas washing equipment (105). The washing liquid that fails in the circulation reaction is returned to the regulating tank (201) as washing wastewater.

6. The process system according to claim 2, characterized in that: Lime milk or sodium hydroxide solution should be used for adding alkali solution; the concentration of lime milk is 10%-15%, and the concentration of sodium hydroxide solution is 5%-15%; The silicon slag slurry and the prepared washing liquid are transported to the slag alkali washing and hydrolysis unit (102), which is equipped with a mechanical stirrer. Under the stirring action, the two undergo a full hydrolysis and neutralization reaction; the exhaust gas washing equipment (105) adopts a packed tower scrubber or a Venturi scrubber (1051), the elution temperature is 40℃-50℃, and an electric heater is provided to balance the system temperature.

7. The process system according to claim 1, characterized in that: A seed anti-scaling process is coupled to the seed anti-scaling evaporation concentration system (3), i.e., calcium sulfate is added as a seed in the system, and the concentrated brine is continuously concentrated in the evaporator (303). When the concentration of scaling particles reaches supersaturation, they are preferentially precipitated on the surface of the seed, thereby reducing their scaling tendency on the surface of the heat exchanger. A seed internal recovery process section is provided to maintain the effective seed concentration in the system at 10 g / L-15 g / L, while reducing the amount of seed added during the process. Before the concentrated brine enters the evaporator (303), it needs to be acidified to adjust the pH and degassed to remove carbonate alkalinity, dissolved oxygen, carbon dioxide and non-condensable gas.

8. The process system according to claim 7, characterized in that: The evaporator (303) adopts a vertical tube falling film type, and the concentrated brine flows through the tubes; the pH of the concentrated brine is adjusted to 5-6 by adding acid, and the concentration of the high-concentration brine at the outlet of the seed anti-scaling evaporation concentration system (3) is 15%-25%.

9. The process system according to claim 1, characterized in that: The high-concentration brine at the outlet of the seed anti-scaling evaporation crystallization system (3) enters the crystallizer (401) for further evaporation and concentration to a concentration of 40%-65% and a solid content of 10%-30%; the concentrated slurry at the outlet of the crystallizer (401) enters the centrifugal dehydrator (402), and the discharged wet solid salt enters the dryer (403) for dehydration and drying to obtain sodium chloride as a by-product salt; the centrifuged mother liquor enters the slicer (404) for treatment to obtain miscellaneous salt.

10. The process system according to claim 9, characterized in that: A forced circulation (FC) type or DTB type crystallizer is used. The crystallizer (401) has a salt leg design, and the salt leg is used for material back-mixing and washing. The centrifugal dehydrator (402) is provided with an elutriation pipeline for improving the quality of the by-product sodium chloride salt to meet the first-class industrial salt standard. The secondary steam outlet of the crystallizer (401) is provided with a demister in the form of a wire mesh or a folded plate.

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