Low chlorine loss process for producing polycrystalline silicon by GCL silane fluidized bed method

Abstract

The invention provides a low chlorine loss process for producing polycrystalline silicon by a GCL silane fluidized bed method, which comprises the following steps: step 1, enabling chlorosilane waste liquid generated in the polycrystalline silicon production process to pass through a rotary drum filtering unit to obtain a chlorosilane liquid phase and waste residue; 2, recycling the chlorosilane liquid phase, feeding the waste residues into a waste residue drying unit, and evaporating residual chlorosilane and metal chloride in the waste residues to obtain dried waste residues; 3, the dried waste residues are input into a reaction etching unit to be reused, and recoverable chlorosilane and tail gas to be treated are obtained. According to the technical scheme provided by the invention, the recovery rate and the utilization efficiency of chlorine resources are improved, and the emission pollution of chlorine elements is reduced.

Description

Technical Field

[0001] This invention relates to a low-chlorine-loss process for producing polycrystalline silicon, and more particularly to a low-chlorine-loss process for producing polycrystalline silicon using a GCL silane fluidized bed method. Background Technology

[0002] This section provides only background information relevant to this disclosure and is not necessarily prior art.

[0003] In the polycrystalline silicon production process, SiHCl3 is prepared using SiCl4, H2, and Si powder. SiHCl3 then undergoes further reactions to convert into polycrystalline silicon. Throughout this process, Cl... - It circulates within the system, but there will be some losses due to the exhaust gas, with chlorine consumption around 5%, leading to an imbalance of chloride ions. Therefore, it is necessary to purchase SiCl4 or HCl externally to replenish chloride ions.

[0004] The vented exhaust gases (N2, H2, chlorosilanes, and Si powder) from the entire plant are collected in the main vent pipe and sent to the waste gas treatment unit. After spraying, the silicon powder is removed, and the chlorosilanes react with Ca(OH)2 solution to produce CaSiO3, CaCl2, HCl, etc. The exhaust gases are discharged into the atmosphere, while the solid residue-containing waste liquid is sent to the wastewater treatment unit. After solid-liquid separation by a filter press, the waste residue is transported off-site for disposal, and the waste liquid is sent to a wastewater treatment plant for treatment. From a material balance perspective, the treatment of the exhaust gases results in significant losses of chlorine and silicon atoms. Chlorine atoms are absorbed by alkaline solution and converted into calcium chloride, which precipitates after the addition of precipitating agents such as Na2SO4. Silicon atoms are hydrolyzed into substances such as silicon dioxide, and these substances are not recovered and are wasted. Furthermore, the exhaust gas treatment process consumes a large amount of alkaline solution and water, resulting in high treatment costs for the waste gas and waste liquid.

[0005] In summary, the existing technology has the following drawbacks in the polysilicon production process:

[0006] 1. Chlorosilanes cannot be effectively condensed and recovered. The hydrolysis of chlorosilanes requires a large amount of alkaline solution (such as Ca(OH)2), and the saline wastewater needs further treatment, which is costly.

[0007] 2. The HCl produced by hydrochloric acid desorption cannot be used efficiently, and a large amount of HCl is not effectively utilized.

[0008] 3. A large amount of waste salt generated by the sewage treatment plant cannot be effectively recovered.

[0009] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0010] Purpose of the invention: The technical problem to be solved by the present invention is to provide a low chlorine loss process for producing polycrystalline silicon using the GCL silane fluidized bed method, which addresses the shortcomings of the existing technology.

[0011] To address the aforementioned technical problems, this invention discloses a low-chlorine-loss process for producing polycrystalline silicon using a GCL silane fluidized bed method, comprising the following steps:

[0012] Step 1: The chlorosilane waste liquid generated during the polysilicon production process is passed through a rotary drum filter unit to obtain chlorosilane liquid phase and waste residue;

[0013] Step 2: The chlorosilane liquid phase is recovered, and the waste residue is sent to the waste residue drying unit to evaporate the residual chlorosilane and metal chloride in the waste residue to obtain the dried waste residue;

[0014] Step 3: The dried waste residue is fed into the reactive etching unit for reuse to obtain recyclable chlorosilane and tail gas to be treated.

[0015] Furthermore, step 3, which involves feeding the dried waste residue into the reactive etching unit for reuse, includes:

[0016] Step 3-1: Using a catalytic cracking unit, the high-boiling-point substance Si2Cl6 is introduced with hydrogen chloride gas under the action of a cracking agent. After catalytic cracking, SiHCl3 and SiCl4 are obtained and condensed to obtain a chlorosilane liquid phase, which is then recovered.

[0017] In step 3-2, unreacted hydrogen chloride gas is introduced into the reactive etching unit and reacts with the silicon block and the dried waste residue obtained in step 2 to obtain gaseous chlorosilane. After condensation, the liquid phase of chlorosilane is recovered and the tail gas is discharged.

[0018] Furthermore, the process also includes:

[0019] Step 4: The exhaust gas to be treated generated after reuse in Step 3, as well as the exhaust gas from other production units, are sent to the exhaust gas emission unit for preliminary condensation and regulation, and then sent to the pressurized cryogenic unit.

[0020] Step 5: The pressurized cryogenic unit recovers the residual chlorosilane components in the exhaust gas by pressurizing and then condensing it. The uncondensed exhaust gas is sent to the exhaust gas scrubbing unit.

[0021] Step 6: The exhaust gas scrubbing unit scrubs the uncondensed exhaust gas to obtain wastewater containing solid residue and exhaust gas that can be discharged.

[0022] Furthermore, the process also includes:

[0023] Step 7: The wastewater containing solid residue is pretreated by a chemical pretreatment unit;

[0024] Step 8: The pretreated mixture is subjected to solid-liquid separation by a mechanical filter press unit. The separated solid waste is directly transported off-site for treatment, while the waste liquid is processed in an MVR evaporation and crystallization unit.

[0025] Step 9: The waste liquid is concentrated and purified by MVR evaporation and crystallization unit to obtain NaCl, CaCl2 and condensate.

[0026] Furthermore, the hydrogen chloride gas mentioned in step 3-1 is obtained by desorbing the externally input hydrochloric acid using a hydrochloric acid desorption unit.

[0027] Furthermore, the exhaust gas emission unit includes a main exhaust gas pipe connected to the exhaust gas discharge pipes of each production unit, for collecting all exhaust gases.

[0028] Furthermore, the exhaust gas mentioned in step 6 is exhaust gas that meets emission standards and is directly emitted into the atmosphere.

[0029] Furthermore, the preprocessing described in step 7 includes:

[0030] Add Ca(OH)2 to control pH value; add flocculation and precipitation of metal ions.

[0031] Furthermore, the MVR evaporation crystallization unit described in step 8 is a three-level thermally coupled architecture.

[0032] Furthermore, the MVR evaporation crystallization unit described in step 8 includes:

[0033] Preheater, evaporator and compressor.

[0034] Beneficial effects:

[0035] The technical solution proposed in this invention improves the recovery rate and utilization efficiency of chlorine resources and reduces chlorine emission pollution. Attached Figure Description

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0037] Figure 1 This is a schematic diagram of the overall process of the present invention. Detailed Implementation

[0038] This invention proposes a low-chlorine-loss production process for polycrystalline silicon using the GCL silane fluidized bed method, comprising: a drum filtration unit, a waste residue drying unit, a hydrochloric acid desorption unit, a catalytic cracking unit, a reactive etching unit, a tail gas emission unit, a pressurized cryogenic unit, a tail gas scrubbing unit, a chemical pretreatment unit, a mechanical pressure filtration unit, and an MVR evaporation and crystallization unit.

[0039] The rotary drum filter unit is used to receive chlorosilane waste liquid generated during polysilicon production, filter solid waste residue, and recover chlorosilane clear liquid.

[0040] The waste residue drying unit is used to evaporate the residual chlorosilanes and metal chlorides in the filtered waste residue; the hydrochloric acid desorption unit desorbs 30-35% hydrochloric acid into hydrogen chloride gas;

[0041] The catalytic cracking unit causes the high-boiling-point substance (Si2Cl6) to be catalytically cracked into SiHCl3 and SiCl4 under the action of a cracking agent and the introduction of HCl.

[0042] In the reactive etching unit, waste silicon blocks and silicon powder are reacted with HCl at a certain temperature to generate chlorosilanes for recycling.

[0043] The exhaust gas emission unit first condenses the exhaust gas from each device and then collects the exhaust gas into the vent pipe.

[0044] The pressurized cryogenic unit uses pressurization to increase the boiling point of chlorosilanes before deep condensation of the chlorosilanes.

[0045] The exhaust gas scrubbing unit scrubs the deeply cooled exhaust gas.

[0046] The chemical pretreatment unit pretreats the wastewater;

[0047] The mechanical filter press unit efficiently separates solids and liquids;

[0048] The MVR evaporation and crystallization unit concentrates and purifies NaCl and CaCl2 for sale.

[0049] like Figure 1 As shown, the specific technical solution is as follows:

[0050] The hydrochloric acid analysis unit outlet is connected to the catalytic cracking unit inlet, which in turn is connected to the reaction etching unit inlet. The reaction etching unit outlet is connected to the plant-wide chlorosilane tail gas emission unit. The venting tail gas main pipe is connected to the chlorosilane venting tail gas outlets of each production unit (the venting tail gas main pipe belongs to the tail gas emission unit, and the tail gas emission ports of each production unit (other units) are connected to the main pipe). The tail gas emission unit outlet is connected to the pressurized cryogenic unit inlet, which is connected to the tail gas scrubbing unit inlet. The gas phase outlet of the tail gas scrubbing unit goes to the atmosphere, and the liquid outlet containing waste residue goes to the chemical pretreatment unit. After treatment, it is sent to the mechanical filter press unit. The liquid phase outlet of the mechanical filter press unit is connected to the MVR process unit inlet. The MVR unit evaporates, concentrates, and purifies NaCl and CaCl2 for sale.

[0051] Example 1:

[0052] In one specific embodiment, a low-chlorine-loss process for producing polycrystalline silicon using the GCL silane fluidized bed method includes an efficient recycling method for chlorosilane waste liquid. Specifically, the externally input chlorosilane waste liquid passes through a drum filter unit to obtain a chlorosilane liquid phase and waste residue. The chlorosilane liquid is then recycled, and the waste residue enters a waste residue drying unit. The dried waste residue is then fed into a reaction etching unit for reuse.

[0053] Among them, the chlorosilane waste liquid (SiCl4, Si2Cl6, silicon powder, metal chlorides, etc.) comes from the cold hydrogenation unit.

[0054] The rotary drum filtration unit includes a chlorosilane waste liquid storage tank, a waste liquid transfer pump, a rotary drum filtration device, a vacuum device, and a clarified liquid tank. It receives upstream chlorosilane waste liquid into a slurry storage tank equipped with a stirring device to prevent silica powder deposition. The waste liquid is then pumped (diaphragm pump) to the rotary drum filtration system for filtration. The rotary drum filtration system creates negative pressure through the vacuum device, forcing the liquid to pass through a porous ceramic drum (with an outer filter element, the material of which can be carbon fiber or other types of filter cloth). The filter cloth is pre-coated with diatomaceous earth, separating the liquid and solid phases. Si powder and solid metal chlorides are separated by a scraper beside the drum. The waste residue falls into a waste residue drying unit, while the chlorosilane liquid phase is recovered after entering the clarified liquid tank.

[0055] The waste residue drying unit includes a drying device, a tail gas condensation device, and a sublimation device. In the drying device, the waste residue enters dryer 1 for preliminary drying. Dryer 1 uses the device's steam condensate as a heat source (120℃) for drying. The dryer's tail gas vent has a silicon powder settling zone. The settling zone is a wide-diameter cylinder with a certain length to prevent silicon powder from clogging the tail gas vent pipe. The dryer is heated by stirring. The rotating shaft is controlled by a motor to drive the silicon powder stirrer. After the chlorosilane is vaporized, it enters the tail gas condensation device from the chlorosilane gas phase outlet for recovery. The waste residue after the first step of drying is sent to dryer 2. The dryer 2 uses an electric heater as a heat source (350℃) for drying. The exhaust gas venting pipeline of the dryer 2 is insulated. Metal chlorides and high-boiling-point substances enter the sublimation device. The sublimation device consists of a stirrer with a scraper and a condensate cooling device (cooling the gaseous material to 140-150℃). The high-boiling-point gaseous substances are sent to the downstream high-boiling-point cracking unit. Low-boiling-point metal chlorides such as AlCl3 are condensed on the cylinder and then separated by the scraper and sent to the metal chloride storage tank for recovery. The waste residue after drying in the dryer 2 contains a large amount of silicon powder. After drying, it enters the silicon powder transfer tank and is sent to the etching reactor for further reaction.

[0056] Example 2:

[0057] A low-chlorine-loss process for producing polycrystalline silicon using GCL silane fluidized bed method includes a hydrochloric acid desorption unit, a catalytic cracking unit, and a reactive etching unit for efficient utilization of HCl.

[0058] The process involves converting 25-40% concentration hydrochloric acid, sourced externally, into HCl gas via a hydrochloric acid desorption unit. This unit includes a desorption apparatus, a dehydration and drying apparatus, and a compression apparatus. The HCl produced from the 25-40% concentration hydrochloric acid desorption process contains a large amount of water. This water is condensed in a condenser, and the HCl temperature is lowered to room temperature. After passing through a demister, the HCl is further dried in a concentrated sulfuric acid tower to achieve a water content of 5-20 ppm. The subsequent HCl gas is pressurized from 0.13-0.15 MPa to 0.5-0.6 MPa by a compressor.

[0059] The catalytic cracking unit includes a reactor, condenser, waste recovery tank, hydrolysis tank, and absorption tower. The equipment is preferably made of corrosion-resistant materials. Pressurized HCl gas is introduced into the reactor. Si2Cl6 in the high-boiling-point components (containing 40-60% SiCl4, 15-25% Si2OCl6, and 25-35% Si2Cl6) from the upstream distillation column bottoms is cracked into SiHCl3 and SiCl4 under the action of a catalyst. The SiCl4 is then condensed and enters the chlorosilane collection tank. Unreacted HCl is introduced into the reactive etching unit. Since Si2OCl6 is relatively stable and difficult to react, the waste from the reactor is discharged to the waste recovery tank after a certain period. After being pressurized, the waste from the waste recovery tank is sent to the hydrolysis tank via pressure conveying. The hydrolysis tank treats the waste liquid using a two-step hydrolysis process. The hydrolysis tank is equipped with a stirrer and nozzles at the bottom. It has two outlets: one to the absorption tower and the other to the tail gas scrubbing tower (programmable switching is possible). In the first stage of hydrolysis, water enters the tank as a mist through the bottom nozzles and reacts with Si₂OCl₆ to produce HCl and SiO₂. Continuous stirring and controlled H₂O generation are crucial. The generated HCl gas is fed into the absorption tower, where a bottom pump provides circulating spraying. Once the absorption tower absorbs the HCl gas to form 20-35% hydrochloric acid, it is sent to a hydrochloric acid storage tank for use in the hydrochloric acid desorption unit. The waste liquid formed after neutralizing the waste acid with Ca(OH)₂ solution following the first stage of hydrolysis is sent to the wastewater treatment unit, while the gas phase is simultaneously switched to the tail gas scrubbing unit.

[0060] The reactive etching unit includes an etching reactor and a condenser. Unreacted HCl from the pyrolysis unit and HCl from the hydrochloric acid desorption unit are fed into the etching reactor together. The etching reactor is electrically heated to reach an internal temperature of 450-550℃. Silicon blocks and waste silicon powder are placed inside the etching reactor. HCl reacts with Si to generate gaseous chlorosilanes, which are condensed to -10℃ to -20℃ by a two-stage condenser and then sent to a chlorosilane collection tank. The tail gas is then connected to the tail gas main.

[0061] Example 3:

[0062] A low-chlorine-loss production process for polycrystalline silicon using the GCL silane fluidized bed method includes an exhaust gas emission unit, a pressurized cryogenic unit, and an exhaust gas scrubbing unit for efficient recovery and treatment of exhaust gas.

[0063] Among them, the process vent gas (SiCl4, SiHCl3, HCl, N2, etc.) from the whole plant is initially condensed into chlorosilane by the Freon condenser of its respective unit. The uncondensed vent gas is then merged into the vent main pipe. The vent main pipe includes multiple branch pipes, each of which is connected to the vent outlet of a different production unit. A control valve is installed before the gas merges into the main pipe to regulate the flow and pressure entering the vent main pipe. After regulation, the gas is sent to the pressurized cryogenic unit.

[0064] The pressurized cryogenic unit includes an exhaust gas buffer tank, a compressor, a post-compressor buffer tank, and a condenser. The 0-20 kPa vented exhaust gas enters the pre-buffer tank for pressure stabilization, then is pressurized to 0.55-0.65 MPa by a corrosion-resistant three-stage reciprocating compressor (compression ratio ≈ 3.2 per stage) before entering the condenser. The condenser uses Freon as refrigerant and maintains a temperature of -40 to -30°C to condense chlorosilanes, achieving efficient condensation and recovery of chlorosilane components in the exhaust gas (recovery rate > 95%). Uncondensed exhaust gas (HCl, a small amount of chlorosilanes) enters the exhaust gas scrubbing unit, which includes an exhaust gas scrubbing tower, an exhaust gas water scrubbing tower, and a wastewater external pump. The exhaust gas is introduced into an alkaline scrubbing device for scrubbing and neutralization. The alkaline scrubbing device is equipped with Ca(OH)2 solution spray to remove chlorosilanes and other acidic gases from the exhaust gas. The scrubbed exhaust gas is further purified by a water scrubbing tower, which has a packing layer inside to enhance the gas-liquid contact area and improve purification efficiency. The treated exhaust gas is eventually discharged into the atmosphere, meeting emission standards, while the wastewater containing solid residue after rinsing is sent to the chemical pretreatment unit.

[0065] Example 4:

[0066] A low-chlorine-loss production process for polycrystalline silicon using the GCL silane fluidized bed method includes a chemical pretreatment unit, a mechanical pressure filtration unit, and an MVR evaporation crystallization unit for chloride ion reuse. The process employs a three-stage combined process of "chemical pretreatment-mechanical pressure filtration-MVR evaporation crystallization" to form a complete chloride ion recovery and zero wastewater discharge system.

[0067] In the chemical pretreatment unit, wastewater containing CaCl2, CaSiO3, SiO2, and HCl first enters the pretreatment tank. Through precise addition of Ca(OH)2 and intelligent pH control within the alkaline range of 10-11 (using an online pH monitoring and automatic dosing linkage system), auxiliaries such as Na2SO4, polyacrylamide, and coagulants (polyferric sulfate) are added to flocculate and precipitate metal ions. For example, CaCl2 reacts with Na2SO4 to form NaCl and CaSO4 precipitates, and MgCl2 reacts with Na2SO4 to form NaCl and MgSO4 precipitates.

[0068] The pretreated mixture is pumped to the filter press unit via a waste liquid pump. This unit uses a specially designed plate and frame filter press (equipped with a composite filter plate structure with high-pressure elastic membranes) to achieve efficient solid-liquid separation under a gradient pressure of 0.1-0.8MPa (constant pressure filtration is achieved through pressure sensor and frequency conversion speed regulation of feed pump). The separated solid waste residue (mainly containing CaSO4, CaSiO3, and SiO2) with a moisture content of <40% can be directly transported off-site, while the filtrate enters the core MVR process unit.

[0069] The MVR system achieves cascaded energy utilization through a three-stage thermal coupling design (preheater-evaporator-compressor integrated thermal energy cycle architecture): First, the waste heat of secondary steam generated in the evaporator is used to raise the temperature of the filtrate to 90-100℃ in the preheater. Then, low-temperature evaporation at 80-90℃ is achieved in the vacuum evaporator (operating pressure -0.07~-0.09MPa) (vacuum degree adaptive control technology based on boiling point rise prediction model). The generated secondary steam is pressurized and heated to 100-110℃ by a Roots compressor and then reused as a system heat source; concentration... The supersaturated NaCl solution is then separated in a centrifuge (the feed concentration is adjusted by linking an online densitometer and a crystallization particle size analyzer), ultimately obtaining an industrial-grade NaCl product with a water content of <5%. The mother liquor (the solution after sodium chloride crystallization) is sliced ​​in a drum dryer (CaCl2·2H2O is dried and crystallized on the drum surface) to recover the CaCl2·2H2O product, while the condensate meets the reuse standard. This achieves a chloride ion recovery rate of >99% and reduces energy consumption by 70% compared to traditional processes, perfectly achieving the goals of efficient chloride ion recovery and utilization and zero wastewater discharge.

[0070] This invention provides a low-chlorine-loss process and method for producing polycrystalline silicon using a GCL silane fluidized bed method. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A low-chlorine-loss process for producing polycrystalline silicon using a GCL silane fluidized bed method, characterized in that, Includes the following steps: Step 1: The chlorosilane waste liquid generated during the polysilicon production process is passed through a rotary drum filter unit to obtain chlorosilane liquid phase and waste residue; Step 2: The chlorosilane liquid phase is recovered, and the waste residue is sent to the waste residue drying unit to evaporate the residual chlorosilane and metal chloride in the waste residue to obtain the dried waste residue; Step 3: The dried waste residue is fed into the reactive etching unit for reuse to obtain recyclable chlorosilane and tail gas to be treated.

2. The low chlorine loss process for producing polycrystalline silicon using the GCL silane fluidized bed method according to claim 1, characterized in that, Step 3, which involves feeding the dried waste residue into the reactive etching unit for reuse, includes: Step 3-1: Using a catalytic cracking unit, the high-boiling-point substance Si2Cl6 is introduced with hydrogen chloride gas under the action of a cracking agent. After catalytic cracking, SiHCl3 and SiCl4 are obtained and condensed to obtain a chlorosilane liquid phase, which is then recovered. In step 3-2, unreacted hydrogen chloride gas is introduced into the reactive etching unit and reacts with the silicon block and the dried waste residue obtained in step 2 to obtain gaseous chlorosilane. After condensation, the liquid phase of chlorosilane is recovered and the tail gas is discharged.

3. The low-chlorine-loss process for producing polycrystalline silicon using a GCL silane fluidized bed method according to claim 1, characterized in that, The process also includes: Step 4: The exhaust gas to be treated generated after reuse in Step 3, as well as the exhaust gas from other production units, are sent to the exhaust gas emission unit for preliminary condensation and regulation, and then sent to the pressurized cryogenic unit. Step 5: The pressurized cryogenic unit recovers the residual chlorosilane components in the exhaust gas by pressurizing and then condensing it. The uncondensed exhaust gas is sent to the exhaust gas scrubbing unit. Step 6: The exhaust gas scrubbing unit scrubs the uncondensed exhaust gas to obtain wastewater containing solid residue and exhaust gas that can be discharged.

4. The low-chlorine-loss process for producing polycrystalline silicon using the GCL silane fluidized bed method according to claim 3, characterized in that, The process also includes: Step 7: The wastewater containing solid residue is pretreated by a chemical pretreatment unit; Step 8: The pretreated mixture is subjected to solid-liquid separation by a mechanical filter press unit. The separated solid waste is directly transported off-site for treatment, while the waste liquid is processed in an MVR evaporation and crystallization unit. Step 9: The waste liquid is concentrated and purified by MVR evaporation and crystallization unit to obtain NaCl, CaCl2 and condensate.

5. The low-chlorine-loss process for producing polycrystalline silicon using a GCL silane fluidized bed method according to claim 2, characterized in that, The hydrogen chloride gas mentioned in step 3-1 is obtained by desorbing the externally input hydrochloric acid using a hydrochloric acid desorption unit.

6. The low-chlorine-loss process for producing polycrystalline silicon using a GCL silane fluidized bed method according to claim 3, characterized in that, The exhaust gas emission unit includes a main exhaust gas pipe connected to the exhaust gas discharge pipes of each production unit, for collecting all exhaust gases.

7. The low-chlorine-loss process for producing polycrystalline silicon using the GCL silane fluidized bed method according to claim 3, characterized in that, The exhaust gas mentioned in step 6 is exhaust gas that meets emission standards and is directly emitted into the atmosphere.

8. The low chlorine loss process for producing polycrystalline silicon using the GCL silane fluidized bed method according to claim 4, characterized in that, The preprocessing described in step 7 includes: Add Ca(OH)2 to control pH value; add flocculation and precipitation of metal ions.

9. A low-chlorine-loss process for producing polycrystalline silicon using a GCL silane fluidized bed method according to claim 4, characterized in that, The MVR evaporation crystallization unit described in step 8 is a three-level thermally coupled architecture.

10. A low-chlorine-loss process for producing polycrystalline silicon using a GCL silane fluidized bed method according to claim 9, characterized in that, The MVR evaporation crystallization unit described in step 8 includes: Preheater, evaporator and compressor.

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