Polysilicon production process and system

Abstract

The application provides a polysilicon production process and system, and relates to the technical field of polysilicon production. H2 produced by chlor-alkali electrolysis is used as hydrogen gas raw material of a hydrogen chloride synthesis process, a polysilicon reduction process and a cold hydrogenation process; Cl2 produced by chlor-alkali electrolysis is used as chlorine raw material of the hydrogen chloride synthesis process; hydrogen chloride produced by the hydrogen chloride synthesis process is provided to the cold hydrogenation process; silicon powder, SiCl4, HCl and H2 are reacted in a cold hydrogenation reactor; crude trichlorosilane produced by the cold hydrogenation process is provided to rectification for fractionation; intermediate product dichlorodisilane is produced by a fixed bed to generate silane; intermediate product silicon tetrachloride and hydrogen gas are used as raw materials of the cold hydrogenation process to generate trichlorosilane; and the trichlorosilane is used as one of raw materials of the polysilicon reduction process to generate polysilicon. The application can fully utilize raw materials and by-products, reduce the dependence of the production system on the outside world, and effectively reduce the amount of three wastes.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polycrystalline silicon production, in particular to a polycrystalline silicon production process and system. BACKGROUND

[0002] Polycrystalline silicon is a main raw material for manufacturing integrated circuits, photovoltaic components and other products, and single crystal silicon has been widely used in the semiconductor industry. At the same time, with the increasing tension of global energy situation, the use of clean and safe solar energy resources has attracted more and more attention, and one important way is to use the photoelectric effect of semiconductor polycrystalline silicon for photovoltaic power generation. In recent years, the electronic information industry and the photovoltaic industry are in a stage of rapid development, and the demand for polycrystalline silicon raw materials continues to increase.

[0003] The production process route of polycrystalline silicon by improved Siemens method is to synthesize trichlorosilane by using hydrogen chloride and industrial silicon powder at a certain temperature, then to purify trichlorosilane by rectification, and to generate high-purity polycrystalline silicon by gas-phase chemical deposition of the purified trichlorosilane with hydrogen in a reduction furnace. The reduction tail gas is treated by a recovery system, and the separated hydrogen and hydrogen chloride are returned to the production system for reuse, and the separated liquid chlorosilane is recycled to the production system after separation and purification. Trichlorosilane is transported to the reduction process, and silicon tetrachloride is transported to the cold hydrogenation process as reaction raw materials for continuous recycling.

[0004] In the existing improved Siemens method, important by-products such as dichlorodihydrogen silicon generated by the reduction reaction have not been well utilized. The common practice is to treat them as waste or use them as special gases for the electronic industry after purification. The former wastes resources and increases treatment costs, and the latter has the problem of low added value. In addition, as a trichlorosilane synthesis system, the recovered hydrogen chloride needs to react with industrial silicon powder to generate trichlorosilane, which also requires the addition of a separate production device, which accordingly increases the investment scale and operating cost of the device. Therefore, the common practice is to directly purchase trichlorosilane, which brings uncertainty in raw material supply and problems in hydrogen chloride treatment. The treatment of waste gas and waste liquid in the process is generally carried out by using lime milk, which produces a large amount of waste solid after treatment, and there are problems in waste solid treatment and transportation. The current improved Siemens method cycle system is not perfect, and there is a problem of insufficient utilization of materials. SUMMARY

[0005] The present application provides a polycrystalline silicon production process and system, which can fully utilize raw materials and by-products, reduce the dependence on the outside world of the production system, and effectively reduce the amount of three wastes.

[0006] The present application is implemented as follows:

[0007] In a first aspect, the present application provides a polycrystalline silicon production process, characterized by comprising the following steps:

[0008] Chlor-alkali process step: the NaCl concentrated solution from the waste treatment process step is treated to remove impurities, and after electrolysis, Cl2, H2 and NaOH solution are obtained, and H2 is provided to the hydrogen chloride synthesis process, the cold hydrogenation process and the polysilicon reduction process;

[0009] Hydrogen chloride synthesis process: Cl2 and H2 from the chlor-alkali process step are synthesized to generate HCl, which is provided to the cold hydrogenation process;

[0010] Cold hydrogenation process: silicon powder, SiCl4 provided by the fixed bed polysilane production process, HCl and H2 are reacted in a cold hydrogenation reactor to produce chlorosilane mixed gas, which is separated by a crude fraction column to obtain crude trichlorosilane, which is fed into the rectification process; the waste after reaction is settled and stripped to obtain waste chlorosilane containing silicon powder, high-boiling and metal impurities;

[0011] Rectification process: crude trichlorosilane produced by the cold hydrogenation process and chlorosilane mixed liquid produced by the reduction tail gas recovery process are separated by rectification into SiCl4, SiH2Cl2 and SiHCl3, and SiCl4 is provided to the cold hydrogenation process, SiHCl3 is provided to the polysilicon reduction process, and SiH2Cl2 is provided to the fixed bed polysilane production process;

[0012] Fixed bed polysilane production process: SiH2Cl2 provided by the rectification process is used as raw material to produce SiCl4 and SiCl4, which is provided to the cold hydrogenation process;

[0013] Polysilicon reduction process: H2 and SiHCl3 from the rectification process are used as raw materials to produce polysilicon and obtain by-product reduction tail gas;

[0014] Reduction tail gas recovery process: the reduction tail gas is preliminarily separated into H2, HCl and chlorosilane mixed liquid, and H2 is provided to the cold hydrogenation process and the polysilicon reduction process, HCl is provided to the cold hydrogenation process, and the chlorosilane mixed liquid is provided to the rectification process; and

[0015] Waste treatment process: waste gas, waste liquid and solid waste from each process are subjected to leaching treatment, and the generated chlorion-containing acidic wastewater is subjected to acid-base neutralization reaction using NaOH solution produced by the chlor-alkali process as neutralizing liquid, and NaCl solution is obtained after concentration treatment, which is provided to the chlor-alkali process step.

[0016] In a second aspect, the present application provides a polysilicon production system, which comprises a chlor-alkali system, a hydrogen chloride synthesis system, a cold hydrogenation system, a rectification system, a fixed bed polysilane production system, a polysilicon reduction system and a reduction tail gas recovery system, which carries out the polysilicon production process according to the first aspect when producing polysilicon.

[0017] The embodiments of the present application have at least the following beneficial effects:

[0018] The polycrystalline silicon production process and system of the present application, the raw material required for chlor-alkali is from the NaCl concentrated solution of the waste treatment process, the NaOH solution produced by chlor-alkali electrolysis is supplied to the waste treatment process as neutralizing liquid, replacing the lime milk in the prior art, thereby avoiding the generation of waste solid and reducing the treatment cost. The H2 produced by chlor-alkali electrolysis can be used as hydrogen raw material for the hydrogen chloride synthesis process, the polycrystalline silicon reduction process and the cold hydrogenation process, the Cl2 produced by chlor-alkali electrolysis can be used as chlorine raw material for the hydrogen chloride synthesis process, the hydrogen chloride produced by the hydrogen chloride synthesis process can be supplied to the cold hydrogenation process, the silicon powder used in the cold hydrogenation process only needs to be purchased, and the crude trichlorosilane (containing dichlorosilane, trichlorosilane and silicon tetrachloride) produced can be supplied to the rectification process for fractionation, the intermediate product dichlorosilane is produced by fixed bed, and the subsequent step of producing granular silicon by silane method generates finished product granular silicon; meanwhile, the intermediate product silicon tetrachloride and hydrogen are also used as raw materials for the cold hydrogenation step to generate trichlorosilane, and the trichlorosilane is further used as one of the raw materials for the polycrystalline silicon reduction process to generate polycrystalline silicon, thereby not only solving the comprehensive utilization problem of these by-products, but also the trichlorosilane generated can be reused as polycrystalline silicon production raw material, thereby effectively realizing the recycling utilization of each intermediate product (also including hydrogen and hydrogen chloride involved in production), thereby significantly reducing the three waste emissions of the production method. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0020] Figure 1 The polycrystalline silicon production process flow chart of the embodiments of the present application;

[0021] Figure 2 The waste heat utilization system diagram of the reduction tail gas recovery process of the embodiments of the present application;

[0022] Figure 3 The waste heat utilization system diagram of the polycrystalline silicon reduction process of the embodiments of the present application;

[0023] Figure 4 The waste heat utilization system diagram of the cold hydrogenation process of the embodiments of the present application;

[0024] Figure 5 The waste heat utilization system diagram of the rectification process of the embodiments of the present application.

[0025] Figure: 11 - tail gas water cooler; 12 - seven-degree water heat exchanger; 13 - tail gas No. 1 gas-gas heat exchanger; 14 - tail gas cryogenic cooler; 15 - second chlorosilane separation tank; 16 - tail gas No. 2 gas-gas heat exchanger; 17 - tail gas five-stage cooler; 18 - first chlorosilane separation tank; 19 - lean-rich liquid two-stage heat exchanger; 20 - compressed gas No. 1 gas-gas heat exchanger; 21 - compressed gas No. 2 gas-gas heat exchanger; 22 - HCL absorption tower; 23 - compressed gas cryogenic cooler; 24 - lean-rich liquid one-stage heat exchanger; 25 - tower kettle cooler; 26 - waste heat heat exchanger; 27 - HCL stripping tower; 28 - HCL stripping tower reboiler; 29 - absorption liquid cryogenic cooler; 31 - TCS preheater; 32 - TCS vaporizer; 33 - reduction furnace bell jar; 34 - high-temperature water tank; 35 - waste heat utilization conversion device; 36 - medium-temperature water tank; 37 - hydrogen heater; 38 - tail gas heat exchanger; 39 - ultra-high-temperature water flash tank; 41 - reactor outlet heat exchanger; 42 - cold hydrogenation reactor; 43 - H2 preheater; 44 - STC vaporizer; 45 - third condensate storage tank; 46 - STC preheater; 47 - waste heat conversion device; 48 - second condensate storage tank; 49 - quench tower cooler; 50 - circulating hydrogen two-stage heat exchanger; 51 - circulating hydrogen condenser; 52 - first condensate storage tank; 53 - circulating hydrogen one-stage heat exchanger; 54 - terminal condenser; 61 - first rectifying tower; 62 - second rectifying tower; 63 - third rectifying tower; 64 - first reboiler; 65 - second reboiler; 66 - third reboiler; 67 - first condenser; 68 - second condenser; 69 - third condenser; 70 - first reflux tank; 71 - second reflux tank; 72 - third reflux tank. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0027] EMBODIMENT

[0028] The present embodiment provides a polysilicon production process, which refers to Figure 1 and includes the following steps:

[0029] Chlor-alkali process step: the NaCl concentrated solution from the waste treatment process step is treated to remove impurities, electrolyzed to obtain Cl2, H2, and NaOH solution, and H2 is provided to the hydrogen chloride synthesis process, cold hydrogenation process, and polysilicon reduction process;

[0030] Hydrogen chloride synthesis process: Cl2 and H2 from the chlor-alkali process step are synthesized to generate HCl, which is provided to the cold hydrogenation process;

[0031] Cold hydrogenation process: silicon powder, SiCl4 provided by the fixed-bed production of silane process, HCl, and H2 are reacted in the cold hydrogenation reactor 42 to produce chlorosilane mixed gas, which is separated by a crude fraction column to obtain crude trichlorosilane, which is fed to the rectification process; the waste material after reaction is settled and stripped to obtain waste chlorosilane containing silicon powder, high-boiling, and metal impurities;

[0032] Slurry treatment process: the waste chlorosilane obtained from the cold hydrogenation step is first subjected to flash evaporation, drying, and gas-phase condensation to obtain chlorosilane, which is fed to the cold hydrogenation process for crude separation, and the remaining sewage is discharged to the sewage treatment for treatment.

[0033] Rectification process: crude trichlorosilane produced by the cold hydrogenation process and chlorosilane mixed liquid produced by the reduction tail gas recovery process are separated by rectification into SiCl4, SiH2Cl2, and SiHCl3, and SiCl4 is provided to the cold hydrogenation process, SiHCl3 is provided to the polysilicon reduction process, and SiH2Cl2 is provided to the fixed-bed production of silane process;

[0034] Fixed-bed production of silane process: SiH2Cl2 provided by the rectification process is used as raw material to produce silane and SiCl4, and SiCl4 is provided to the cold hydrogenation process;

[0035] Silane method production of granular silicon process: silane produced by the fixed-bed production of silane process is used as raw material to produce granular silicon and H2 in a fluidized bed, and H2 is provided to the cold hydrogenation process.

[0036] Polysilicon reduction process: H2 and SiHCl3 from the rectification process are used as raw materials to produce polysilicon and obtain by-product reduction tail gas;

[0037] Reduction tail gas recovery process: the reduction tail gas is preliminarily separated into H2, HCl, and chlorosilane mixed liquid, and H2 is provided to the cold hydrogenation process and the polysilicon reduction process, HCl is provided to the cold hydrogenation process, and the chlorosilane mixed liquid is provided to the rectification process; and

[0038] Waste treatment process: waste gas, waste liquid, and solid waste from each process are subjected to leaching treatment, and the generated chlorion-containing acidic wastewater is subjected to acid-base neutralization reaction using NaOH solution produced by the chlor-alkali process as neutralizing liquid, and NaCl solution is obtained after concentration treatment, which is provided to the chlor-alkali process step.

[0039] The polysilicon production process and system of the present application, the raw material needed for chlor-alkali is from the NaCl concentrated solution of waste treatment process, the NaOH solution produced by chlor-alkali electrolysis is supplied to the waste treatment process as neutralizing liquid, replacing the lime milk in the prior art, thereby avoiding the generation of waste solid and reducing the treatment cost. The produced sodium chloride solution is concentrated and then provides raw material for the chlor-alkali process, which is beneficial to reduce the comprehensive energy consumption, reduce the waste solid discharge treatment, and thus reduce the production cost.

[0040] The H2 produced by chlor-alkali electrolysis can be used as hydrogen raw material for hydrogen chloride synthesis process, polysilicon reduction process and cold hydrogenation process, the Cl2 produced by chlor-alkali electrolysis can be used as chlorine raw material for hydrogen chloride synthesis process, the hydrogen chloride produced by hydrogen chloride synthesis process can be provided for cold hydrogenation process, and the silicon powder used in cold hydrogenation process only needs to be purchased, and the produced crude trichlorosilane (containing dichlorodihydrogen silicon, trichlorosilane and silicon tetrachloride) can be provided for rectification and fractionation, the intermediate product dichlorodihydrogen silicon is produced by fixed bed, and the finished product granular silicon is generated by the step of producing granular silicon by using silane method. The accumulation of dichlorodihydrogen silicon in the system is effectively eliminated, the real balance of system materials is realized, which is beneficial to reduce the comprehensive energy consumption, and thus reduce the production cost.

[0041] Meanwhile, the intermediate product silicon tetrachloride and hydrogen are also used as raw materials for the step of cold hydrogenation to generate trichlorosilane, and the trichlorosilane is further used as one of the raw materials for polysilicon reduction process to generate polysilicon, thereby not only solving the comprehensive utilization problem of these by-products, but also the generated trichlorosilane can be reused as polysilicon production raw material, thereby effectively realizing the recycling utilization of each intermediate product (also including hydrogen and hydrogen chloride involved in production), thereby significantly reducing the three-waste discharge amount of the production method. The polysilicon production process of the present application can produce polysilicon rods and granular silicon, which can not only eliminate the accumulation of intermediate product dichlorodihydrogen silicon in the system, but also make the intermediate products generated in the closed loop system realize the maximum recycling utilization as much as possible, and also meet the different needs of customers for products.

[0042] The polysilicon production process of the present application basically uses industrial silicon powder as the only purchased raw material, and the rest of the raw materials are basically from the product materials of each process, thereby effectively avoiding the fluctuations of various factors (such as purity, supply amount changes, etc.) when purchasing raw materials, which may adversely or uncontrollably affect the production method, thereby facilitating the comprehensive management and overall control of the production method of the present application, and further reducing the management and control costs of the production method. The production process uses a basically completely closed-loop production system to produce polysilicon, with a raw material utilization rate of more than 99wt% (of which the conversion rate of industrial silicon powder to polysilicon is more than 90wt%), greatly reducing the degree of dependence on the outside world of the production system, not only significantly reducing the comprehensive production cost of polysilicon and energy consumption, but also fundamentally realizing truly green and clean production.

[0043] Further, the polysilicon production process of the present application also includes the utilization of waste heat of each process, which includes a waste heat utilization step of the reduction tail gas recovery process. The waste heat of the reduction tail gas recovery process is used for the HCL desorption tower 27 after multi-stage heat exchange treatment, and the heat source of the HCL desorption tower 27 comes from the 0.4MPa steam generated in the waste heat utilization step of the polysilicon reduction process.

[0044] Please refer to Figure 2 The waste heat utilization step of the reduction tail gas recovery process specifically includes the following steps:

[0045] The reduction tail gas is cooled in the tail gas water cooler 11, then enters the seven-degree water heat exchanger 12 for cooling, and then is cooled in the tail gas No. 1 gas heat exchanger 13 and the tail gas low-temperature cooler 14, and then is separated in the second chlorosilane separation tank 15, and then is cooled in the tail gas No. 2 gas heat exchanger 16, and then enters the tail gas No. 1 gas heat exchanger 13; the material from the tail gas No. 2 gas heat exchanger 16 is cooled in the tail gas five-stage cooler 17, and then enters the first chlorosilane separation tank 18 for separation, and then enters the lean-liquid two-stage heat exchanger 19; the reduction tail gas cooled in the tail gas No. 1 gas heat exchanger 13 enters the compressed gas No. 1 gas heat exchanger 20 for treatment, and then enters the HCL absorption tower 22 after passing through the compressed gas No. 2 gas heat exchanger 21; the compressed gas No. 2 gas heat exchanger 21 provides a cold source for the compressed gas No. 1 gas heat exchanger 20, and the cold source required by the compressed gas No. 2 gas heat exchanger 21 is provided by the compressed gas deep cooler 23;

[0046] The liquid treated by the HCL absorption tower 22 enters the lean-liquid one-stage heat exchanger 24, and then enters the HCL absorption tower 22 after being treated by the absorption liquid deep cooler 29; the lean-liquid two-stage heat exchanger 19 provides a cold source for the lean-liquid one-stage heat exchanger 24, and the cold source of the lean-liquid two-stage heat exchanger 19 is provided by the tower kettle cooler 25; the waste heat heat exchanger 26 provides a heat source for the tower kettle cooler 25;

[0047] The lean-rich liquid secondary heat exchanger 19 discharges into the HCL absorption tower 27 through the waste heat exchanger 26. The heat source for the HCL absorption tower 27 is the 0.4 MPa steam generated in the polysilicon reduction process. After the HCL absorption tower 27 discharges, part of it is discharged, and part of it is reabsorbed into the HCL absorption tower 27 through the HCL absorption tower reboiler 28.

[0048] The waste heat utilization step recovers the cold and heat energy of the HCL absorption tower 22 and the HCL absorption tower 27 through multi-stage heat exchange, maximally recovers the cold and heat energy of the HCL absorption tower 22 and the HCL absorption tower 27, improves the utilization rate of cold and heat energy, and reduces the amount of circulating water used for cooling the HCL absorption tower 27.

[0049] In addition, the waste heat utilization of the reduction tail gas recovery process first uses the circulating water as a cold source through the tail gas water cooler 11 to preliminarily condense and separate the reduction tail gas, cools the reduction tail gas from about 100°C to about 30°C, and the tail gas cooled by the circulating water can reduce the cooling load by 7°C. After being cooled by the circulating water, the 7°C water and the -20°C ethylene glycol produced by the polysilicon reduction process waste heat utilization conversion device 35 are used as cold sources, and the tail gas is processed through the seven-degree water heat exchanger 12 and the tail gas low-temperature cooler 14. After the tail gas is preliminarily condensed and separated by the circulating water, the seven-degree water heat exchanger 12 can reduce the load of the tail gas low-temperature cooler 14 by 68%. The reduction tail gas is cooled by the circulating water, 7°C water, -20°C ethylene glycol, and -50R23, which can effectively reduce energy consumption.

[0050] Exemplarily, the waste heat treatment of the reduction tail gas recovery process is optimized based on the traditional process, and the absorption liquid flow is automatically adjusted according to the system load to reduce the heat consumption of the HCL absorption tower 27 when the system is running at low load.

[0051] In the waste heat utilization step of the polysilicon reduction process, the waste heat utilization efficiency can be improved to 85%, and the waste heat utilization step of the polysilicon reduction process specifically includes the following steps:

[0052] The high-purity SiHCl3 generated in the polysilicon reduction process is heated through the TCS preheater 31 and the reduction tail gas, and the SiHCl3 is preheated, and then vaporized through the TCS vaporizer 32 and enters the reduction furnace bell 33 for reaction;

[0053] The high-temperature water tank 34 discharges high-temperature water to cool the reduction furnace bell 33, and forms medium-temperature return water and high-temperature return water. The high-temperature return water is flashed in the high-temperature water tank 34 to generate 0.4 MPa steam for use in the HCL absorption tower 27, and high-temperature water is supplied to the reduction furnace bell 33;

[0054] The medium temperature return water is converted by the waste heat utilization conversion device 35 to generate 7℃ water and -20℃ glycol cold source to supply to the seven-degree water heat exchanger 12 and the tail gas low-temperature cooler 14 respectively, and the used medium temperature return water is collected into the medium temperature water tank 36 to cool the bottom plate of the reduction furnace;

[0055] The hydrogen heater 37 preheats the hydrogen, and the reduction tail gas generated in the reduction furnace bell jar 33 is exchanged with the super-high temperature upper water in the tail gas heat exchanger 38, and then exchanged with the hydrogen in the hydrogen heater 37, and the exchanged hydrogen provides heat source for the TCS preheater 31;

[0056] The super-high temperature upper water is exchanged in the tail gas heat exchanger 38, and then the super-high temperature return water is returned to the super-high temperature water flash tank 39 for flashing to generate 1.0MPa steam and super-high temperature upper water, and the 1.0MPa steam condensate is supplied to the high temperature water tank 34 to flash 0.4MPa steam.

[0057] Further, the waste heat utilization step of the cold hydrogenation process is further included:

[0058] The chlorosilane mixed gas generated in the cold hydrogenation process is preheated by the reactor outlet heat exchanger 41 to the raw material entering the cold hydrogenation reactor 42, the chlorosilane mixed gas out of the reactor outlet heat exchanger 41 is preheated by the H2 preheater 43 to the H2 entering the STC vaporizer 44, part of the chlorosilane mixed gas out of the H2 preheater 43 enters the third condensate storage tank 45, part of the chlorosilane mixed gas is preheated by the STC preheater 46 to the STC, and the condensed chlorosilane mixed liquid is discharged into the third condensate storage tank 45, and the chlorosilane mixed gas generates -20℃ glycol cold source by the waste heat conversion device 47 to utilize the waste heat again, and the mixed liquid is discharged into the second condensate storage tank 48;

[0059] The chlorosilane mixed gas in the second condensate storage tank 48 is cooled by the quenching tower cooler 49 and then discharged into the second condensate storage tank 48 again, the chlorosilane mixed gas is heated by the circulating hydrogen secondary heat exchanger 50 to the circulating hydrogen gas again, the liquid phase is discharged into the second condensate storage tank 48, the chlorosilane mixed gas is cooled by the circulating hydrogen condenser 51, and the cold source of the circulating hydrogen condenser 51 is -20℃ glycol generated by the waste heat conversion device 47;

[0060] The chlorosilane mixed gas is cooled by the circulating hydrogen condenser 51, and the liquid phase is discharged into the first condensate storage tank 52, the chlorosilane mixed gas is cooled by the circulating hydrogen primary heat exchanger 53, and the cold source is H2 provided by the first condensate storage tank 52; the chlorosilane mixed gas is cooled by the terminal condenser 54, and the liquid phase is discharged into the first condensate storage tank 52, and H2 in the first condensate storage tank 52 is precipitated to provide cold source for the circulating hydrogen primary heat exchanger 53.

[0061] The waste heat utilization step of the cold hydrogenation process of the embodiment increases the waste heat utilization rate of the system by 30% by adding a heat exchanger; the heat after the quenching tower is used to preheat silicon tetrachloride and hydrogen by increasing the heat exchanger, thereby increasing the waste heat utilization rate of the cold hydrogenation process by 20%. The above two energy-saving measures can increase the waste heat utilization rate by 50%. In addition, the cold hydrogenation process uses the H2 provided by the first condensate storage tank 52 to mix with the chlorosilane mixed gas, and the mixed gas is heated through the first-stage circulating hydrogen heat exchanger 53 and the second-stage circulating hydrogen heat exchanger 50 to increase the temperature of the hydrogen gas. The cold energy utilization rate of the system can be increased to 76.5%.

[0062] Further, the waste heat utilization step of the rectification process is also included:

[0063] The rectification process uses the first rectification tower 61, the second rectification tower 62, and the third rectification tower 63 for rectification treatment.

[0064] The liquid discharged from the bottom of the second rectification tower 62 enters the third rectification tower 63 for distillation. The bottom of the third rectification tower 63 is provided with a third reboiler 66. The third reboiler 66 uses the 0.4 MPa flash steam generated in the waste heat treatment step of the polysilicon reduction process to provide heat for heating. After the distillation of the third rectification tower 63, high-temperature gas is discharged from the top.

[0065] The bottom of the second rectification tower 62 is provided with a second reboiler 65. The second reboiler 65 is heated by the high-temperature gas discharged from the top of the third rectification tower 63. The temperature of the high-temperature gas from the top of the third rectification tower 63 is reduced after passing through the second reboiler 65, and then discharged to the third reflux tank 72 after passing through the third condenser 69 for reflux and recovery of tower feed. After the distillation of the second rectification tower 62, high-temperature gas is discharged from the top.

[0066] The bottom of the first rectification tower 61 is provided with a first reboiler 64. The first reboiler 64 is heated by the high-temperature gas discharged from the top of the second rectification tower 62. The temperature of the high-temperature gas from the top of the second rectification tower 62 is reduced after passing through the first reboiler 64, and then discharged to the second reflux tank 71 after passing through the second condenser 68 for reflux and recovery of tower feed. After the distillation of the first rectification tower 61, high-temperature gas is discharged from the top. The high-temperature gas from the top of the first rectification tower 61 is condensed after passing through the first condenser 67, and then discharged to the first reflux tank 70 for reflux and recovery of tower feed.

[0067] The embodiment adopts a differential pressure coupled rectification method, which can reduce the energy consumption required by the conventional rectification process by more than 50%.

[0068] The main methods for waste heat utilization of each process in the embodiment are:

[0069] (1) The high-temperature equipment in production needs to maintain temperature. The high-temperature equipment is cooled by circulating water, and the waste heat of the exhaust gas after cooling is used to increase the temperature of the raw materials;

[0070] (2) The high-temperature product gas or high-temperature tail gas generated is used for waste heat utilization, and the high-temperature tail gas is used for generating high-grade steam through heat exchange flash evaporation for utilization of other raw materials needing to be heated;

[0071] (3) Stepwise heating, a multi-stage heating process is adopted to heat the raw materials entering the reactor step by step using product gas or tail gas at different temperatures;

[0072] (4) The waste heat conversion device 47 is used to convert the waste heat into a cold source for cooling;

[0073] (5) Utilization of the cold source, the low-temperature cold source or tail gas generated provides a cold source for the heat exchange of the front part, through the above-mentioned various types of waste heat utilization methods, the waste heat is utilized as much as possible, the production cost is reduced, the energy is saved, and the competitiveness of the enterprise is increased.

[0074] The embodiment also provides a polysilicon production system, which comprises a chlor-alkali system, a hydrogen chloride synthesis system, a cold hydrogenation system, a rectification system, a fixed-bed polysilane production system, a polysilicon reduction system and a reduction tail gas recovery system, and the polysilicon production system is used for producing polysilicon according to the above-mentioned polysilicon production process.

[0075] In summary, the polysilicon production process and system provided by the embodiment of the application can make full use of raw materials, by-products and waste heat, reduce the dependence of the production system on the outside world, and effectively reduce the three-waste discharge amount, thereby significantly reducing the production cost of polysilicon and reducing the production energy consumption and material consumption.

[0076] The above is only a preferred embodiment of the application and is not used to limit the application, and the application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A polycrystalline silicon production process, characterized in that, Includes the following steps: Chlor-alkali process steps: The NaCl concentrate from the waste treatment process is treated to remove impurities, and then electrolyzed to obtain Cl2, H2 and NaOH solution. The H2 is then provided to the hydrogen chloride synthesis process, the cold hydrogenation process and the polysilicon reduction process. Hydrogen chloride synthesis process: Cl2 and H2 from the chlor-alkali process step are synthesized to produce HCl, which is then supplied to the cold hydrogenation process; Cold hydrogenation process: Silicon powder, SiCl4, HCl and H2 provided by the fixed-bed silane production process are reacted in a cold hydrogenation reactor. The resulting chlorosilane mixture is separated by a coarse separator to obtain crude trichlorosilane, which then enters the distillation process. The waste material after the reaction is settled and stripped to obtain waste chlorosilane containing silicon powder, high boiling point and metal impurities. Distillation process: The crude trichlorosilane produced in the cold hydrogenation process and the chlorosilane mixture produced in the reduction tail gas recovery process are separated into SiCl4, SiH2Cl2 and SiHCl3 by distillation. The SiCl4 is provided to the cold hydrogenation process, the SiHCl3 is provided to the polycrystalline silicon reduction process, and the SiH2Cl2 is provided to the fixed bed silane production process. Fixed-bed silane production process: using SiH2Cl2 provided by the distillation process as raw material to produce silane and SiCl4, and providing the SiCl4 to the cold hydrogenation process; The silane process for producing granular silicon involves using silane produced in the fixed-bed silane production process as a raw material to react in a fluidized bed to produce granular silicon and H2. The H2 is then supplied to the cold hydrogenation process. Polycrystalline silicon reduction process: Using H2 and SiHCl3 from the distillation process as raw materials, polycrystalline silicon is manufactured and reduction tail gas is obtained as a byproduct; Reduction tail gas recovery process: The reduction tail gas is initially separated into a mixture of H2, HCl and chlorosilane, and the H2 is provided to the cold hydrogenation process and the polysilicon reduction process, the HCl is provided to the cold hydrogenation process, and the chlorosilane mixture is provided to the distillation process; as well as Waste treatment process: The waste gas, waste liquid and solid waste from each process are washed. The resulting acidic wastewater containing chloride ions is neutralized by the NaOH solution produced in the chlor-alkali process. The resulting NaCl solution is concentrated to obtain the NaCl concentrate, which is then provided to the chlor-alkali process step.

2. The polycrystalline silicon production process according to claim 1, characterized in that, It also includes a slurry treatment process: the waste chlorosilane obtained from the cold hydrogenation step is first flashed, dried, and condensed in the gas phase to obtain chlorosilane, which is then entered into the cold hydrogenation process for coarse separation. The resulting solid waste is then hydrolyzed and entered into the waste treatment process.

3. The polycrystalline silicon production process according to claim 1 or 2, characterized in that, It includes a waste heat utilization step in the reduction tail gas recovery process, wherein the waste heat from the reduction tail gas recovery process is used in the HCl desorption tower after being treated by multiple heat exchange stages, and the heat source of the HCl desorption tower comes from the 0.4MPa steam generated in the waste heat utilization step of the polycrystalline silicon reduction process.

4. The polycrystalline silicon production process according to claim 3, characterized in that, The step of using the waste heat from the reduction tail gas recovery process for the HCl desorption tower after multi-stage heat exchange treatment includes: The reduction tail gas is cooled in a tail gas water cooler, then further cooled in a 7-degree water heat exchanger, then cooled by a tail gas No. 1 gas-to-gas heat exchanger and a tail gas cryogenic cooler before being separated in a second chlorosilane separator. It then undergoes further cooling in a tail gas No. 2 gas-to-gas heat exchanger, and the cooled material re-enters the tail gas No. 1 gas-to-gas heat exchanger. The material exiting the tail gas No. 2 gas-to-gas heat exchanger is cooled by a tail gas five-stage cooler before entering the first chlorosilane separator for further separation, and then proceeds to a lean-rich liquid two-stage heat exchanger. The reduction tail gas, cooled by the tail gas No. 1 gas-to-gas heat exchanger, enters the compressed gas No. 1 gas-to-gas heat exchanger for treatment, and after passing through the compressed gas No. 2 gas-to-gas heat exchanger, it enters the HCl absorption tower. The compressed gas No. 2 gas-to-gas heat exchanger provides a cooling source for the compressed gas No. 1 gas-to-gas heat exchanger. The cooling source required for the second gas-to-gas heat exchanger of the compressed gas is provided by the compressed gas cryocooler; the liquid after treatment in the HCl absorption tower enters the first-stage lean-rich liquid heat exchanger, and after being treated by the absorbent cryocooler, it enters the HCl absorption tower. The second-stage lean-rich liquid heat exchanger provides the cooling source for the first-stage lean-rich liquid heat exchanger, and the cooling source for the second-stage lean-rich liquid heat exchanger is provided by the tower bottom cooler; the waste heat heat exchanger provides the heat source for the tower bottom cooler; the output of the second-stage lean-rich liquid heat exchanger enters the HCl desorption tower through the waste heat heat exchanger, and the heat source required for the HCl desorption tower to desorb HCl comes from the 0.4MPa steam generated in the polycrystalline silicon reduction process; after the output of the HCl desorption tower, part of it is discharged, and part of it passes through the HCl desorption tower reboiler and re-enters the HCl desorption tower.

5. The polycrystalline silicon production process according to claim 4, characterized in that, The waste heat utilization step of the polysilicon reduction process includes: The high-purity SiHCl3 produced in the polycrystalline silicon reduction process is preheated by exchanging heat with the reduction tail gas through a TCS preheater, and then vaporized by a TCS vaporizer before entering the bell jar of the reduction furnace for reaction. The high-temperature water discharged from the high-temperature water tank cools the bell jar of the reduction furnace and forms medium-temperature return water and high-temperature return water. The high-temperature return water is flash-evaporated in the high-temperature water tank to generate 0.4MPa steam for use by the HCl stripping tower and to generate the high-temperature water supplied to the bell jar of the reduction furnace. The medium-temperature return water is converted into 7°C water and -20°C ethylene glycol cold source through a waste heat utilization conversion device, which are then supplied to the 7°C water heat exchanger and the tail gas low-temperature cooler, respectively. The medium-temperature return water after utilization is collected in a medium-temperature water tank to cool the chassis of the reduction furnace. The hydrogen heater preheats the hydrogen. The reduction tail gas generated in the bell jar of the reduction furnace exchanges heat with the ultra-high temperature water in the tail gas heat exchanger, and then exchanges heat with the hydrogen in the hydrogen heater. After the heat exchange, it provides a heat source for the TCS preheater. The ultra-high temperature feed water, after heat exchange in the exhaust gas heat exchanger, becomes ultra-high temperature return water and returns to the ultra-high temperature water flash tank for flash evaporation, generating 1.0 MPa steam and the ultra-high temperature feed water. The 1.0 MPa steam condensate is supplied to the high temperature water tank to flash evaporate 0.4 MPa steam.

6. The polycrystalline silicon production process according to claim 1 or 2, characterized in that, It includes a waste heat utilization step in the aforementioned cold hydrogenation process: The chlorosilane mixture generated in the cold hydrogenation process preheats the raw materials entering the cold hydrogenation reactor via a reactor outlet heat exchanger. The chlorosilane mixture exiting the reactor outlet heat exchanger preheats the H2 entering the STC vaporizer via an H2 preheater. Part of the chlorosilane mixture exiting the H2 preheater enters the third condensate storage tank, and part of the chlorosilane mixture preheats the STC via the STC preheater. After condensation, the chlorosilane mixture is discharged into the third condensate storage tank. The chlorosilane mixture then generates a -20°C ethylene glycol cold source through a waste heat conversion device for further waste heat utilization. The mixture is then discharged into the second condensate storage tank.

7. The polycrystalline silicon production process according to claim 6, characterized in that, After being cooled by the quench tower cooler, the chlorosilane mixture in the second condensate storage tank is discharged back into the second condensate storage tank. The chlorosilane mixture is then heated by the circulating hydrogen secondary heat exchanger, and the liquid phase is discharged into the second condensate storage tank. The chlorosilane mixture is then cooled by the circulating hydrogen condenser. The cold source for the circulating hydrogen condenser is -20°C ethylene glycol generated by the waste heat conversion device. After the chlorosilane mixture is cooled by the circulating hydrogen condenser, the liquid phase is discharged into the first condensate storage tank. The chlorosilane mixture continues to be cooled by the circulating hydrogen primary heat exchanger, with the H2 provided by the first condensate storage tank as the cold source. After the chlorosilane mixture is cooled again by the terminal condenser, the liquid phase is discharged into the first condensate storage tank, and the H2 in the first condensate storage tank is released, providing a cold source for the circulating hydrogen primary heat exchanger.

8. The polycrystalline silicon production process according to claim 1 or 2, characterized in that, It includes a waste heat utilization step in the distillation process: The distillation process employs a first distillation column, a second distillation column, and a third distillation column for distillation treatment; The liquid discharged from the bottom of the second distillation column enters the third distillation column for distillation. The bottom of the third distillation column is equipped with a third reboiler. The third reboiler is heated by the 0.4MPa steam generated by the flash heat treatment step of the polycrystalline silicon reduction process. After distillation, high-temperature gas is discharged from the top of the third distillation column. The second distillation column is equipped with a second reboiler at the bottom. The second reboiler is heated by the high-temperature gas exiting from the top of the third distillation column. The high-temperature gas from the third distillation column is cooled down after passing through the second reboiler, and then discharged to the third reflux tank after passing through the third condenser for reflux and recovery column feed. After distillation, the second distillation column produces high-temperature gas at the top. The first distillation column is equipped with a first reboiler at the bottom. The first reboiler is heated by the high-temperature gas exiting from the top of the second distillation column. After passing through the first reboiler, the temperature of the high-temperature gas from the second distillation column decreases. Then, after passing through the second condenser, it goes to the second reflux tank for reflux and recovery column feed. After distillation in the first distillation column, high-temperature gas exits from the top of the column. After being condensed by the first condenser, the high-temperature gas goes to the first reflux tank for reflux and recovery column feed.

9. A polycrystalline silicon production system, characterized in that, It includes a chlor-alkali system, a hydrogen chloride synthesis system, a cold hydrogenation system, a distillation system, a fixed-bed silane production system, a polysilicon reduction system, and a reduction tail gas recovery system, and the production of polysilicon is carried out in accordance with the polysilicon production process of any one of claims 1 to 8.

Images