Tail gas treatment system for cold hydrogenation in polysilicon production

Abstract

Disclosed in the present patent is a tail gas treatment system for cold hydrogenation in polysilicon production, said system comprising a cold hydrogenation reactor, a quench tower, a generator, a circulating water heat exchanger, a gas-liquid separation tank, a heat exchanger, a hydrogen compressor, an evaporator, a mixer, a distillation column, a condenser, an expansion valve, an absorber and a solution pump, wherein a tail gas outlet of the quench tower is in communication with a tail gas inlet of the generator via piping, a tail gas outlet of the generator is in communication with a hot medium inlet of the circulating water heat exchanger via piping, a hot medium outlet of the circulating water heat exchanger is in communication with an inlet of the gas-liquid separation tank via piping, a gas phase outlet of the gas-liquid separation tank is in communication with a hot medium inlet of the heat exchanger via piping, and a hot medium outlet of the heat exchanger is in communication with a medium gas inlet of the evaporator via piping. The advantage lies in: there is no need to provide an air cooler and a refrigeration unit, thereby reducing capital and operating costs of the system, while also preventing the release of a large amount of heat into the atmosphere, and thereby mitigating thermal pollution.

Description

A tail gas treatment system for the cold hydrogenation production process of polysilicon Technical Field

[0001] This patent relates to an exhaust gas treatment system, and more particularly to an exhaust gas treatment system for a polycrystalline silicon cold hydrogenation production process. Background Technology

[0002] During the cold hydrogenation reaction, the tail gas contains hydrogen, chlorosilanes, and solid silicon powder. It needs to enter a quench tower to remove the solid silicon powder. The tail gas temperature at the top outlet of the quench tower reaches 140-150℃, requiring further cooling to 60-80℃ in an air cooler. The tail gas then undergoes a three-stage cryogenic heat exchange to further condense the chlorosilanes into a liquid state, achieving gas-liquid separation of hydrogen and chlorosilanes (including trichlorosilane and silicon tetrachloride). The gas phase, mainly composed of hydrogen, can re-enter the system to participate in the cold hydrogenation synthesis reaction. The liquid phase, consisting of chlorosilanes, is sent to a crude distillation column for preliminary separation.

[0003] In the above process flow, the exhaust gas discharged from the top of the quench tower is cooled by an air cooler, dissipating a large amount of heat energy into the atmosphere, resulting in significant waste of heat energy. Furthermore, the exhaust gas needs to be further cooled and condensed through a cryogenic system, requiring the addition of a refrigeration unit on-site, thus increasing investment and operating costs. Summary of the Invention

[0004] In order to solve the above problems, the purpose of this utility model is to provide a tail gas treatment system in the cold hydrogenation production process of polycrystalline silicon.

[0005] This patent is implemented using the following technical solution:

[0006] A tail gas treatment system for a polycrystalline silicon cold hydrogenation production process includes a cold hydrogenation reactor, a quench tower, a generator, a circulating water heat exchanger, a gas-liquid separator, a heat exchanger, a hydrogen compressor, an evaporator, a mixer, a distillation tower, a condenser, an expansion valve, an absorber, and a solution pump.

[0007] The tail gas outlet of the cold hydrogenation reactor is connected to the tail gas inlet of the quench tower via a pipeline. The tail gas outlet of the quench tower is connected to the tail gas inlet of the generator via a pipeline. The tail gas outlet of the generator is connected to the heat medium inlet of the circulating water heat exchanger via a pipeline. The heat medium outlet of the circulating water heat exchanger is connected to the inlet of the gas-liquid separator via a pipeline. The gas phase outlet of the gas-liquid separator is connected to the heat medium inlet of the heat exchanger via a pipeline. The heat medium outlet of the heat exchanger is connected to the medium gas inlet of the evaporator via a pipeline. The medium gas phase outlet of the evaporator is connected to the cold medium inlet of the heat exchanger via a pipeline. The cold medium outlet of the heat exchanger is connected to the inlet of the hydrogen compressor via a pipeline. The outlet of the hydrogen compressor is connected to the hydrogen inlet of the mixer via a pipeline. The medium liquid phase outlet of the evaporator is connected to the inlet of the chlorosilane storage tank via a pipeline. The outlet of the chlorosilane storage tank is connected to the inlet of the transfer pump via a pipeline. The outlet of the transfer pump is connected to the spray liquid inlet of the quench tower via a pipeline.

[0008] The condensate outlet of the generator is connected to the inlet of the condenser via a pipeline. The outlet of the condenser is connected to the inlet of the expansion valve via a pipeline. The outlet of the expansion valve is connected to the condensate inlet of the evaporator. The condensate outlet of the evaporator is connected to the condensate inlet of the absorber. The condensate outlet of the absorber is connected to the inlet of the solution pump. The outlet of the solution pump is connected to the condensate inlet of the generator via a pipeline.

[0009] Furthermore, there are two evaporators, namely a primary evaporator and a secondary evaporator. The hot medium outlet of the heat exchanger is connected to the medium gas inlet of the primary evaporator through a pipeline. The medium gas phase outlet of the primary evaporator is connected to the medium gas inlet of the secondary evaporator through a pipeline. The medium gas phase outlet of the secondary evaporator is connected to the cold medium inlet of the heat exchanger through a pipeline.

[0010] The liquid phase outlets of both the primary evaporator and the secondary evaporator are connected to the inlet of the chlorosilane storage tank via pipelines.

[0011] The expansion valve has two outlets, which are connected to the condensate inlets of the first-stage evaporator and the second-stage evaporator via pipelines, respectively. The condensate outlets of the first-stage evaporator and the second-stage evaporator are both connected to the condensate inlet of the absorber via pipelines.

[0012] Furthermore, the liquid phase outlet of the gas-liquid separator is connected to the inlet of the condensate storage tank via a pipeline, and the outlet of the condensate storage tank is connected to the inlet of the distillation column via a pipeline.

[0013] Furthermore, the outlet of the mixer is connected to the inlet of the vaporizer via a pipeline, the outlet of the vaporizer is connected to the inlet of the superheater via a pipeline, the outlet of the superheater is connected to the cold medium inlet of the heat exchanger via a pipeline, the cold medium outlet of the heat exchanger is connected to the inlet of the electric heater via a pipeline, and the outlet of the electric heater is connected to the raw material inlet of the cold hydrogenation reactor via a pipeline.

[0014] Advantages of this patent:

[0015] This patent introduces a process for generating cryogenic energy from low-grade heat energy into the cold hydrogenation production of polycrystalline silicon, replacing the air cooler in the original process. It recovers and utilizes low-grade heat of 140-160℃, converting it into cold energy of approximately -40℃, thus replacing the refrigeration unit. Since there is no need to configure air coolers and refrigeration units, it can save on system investment and operating costs. At the same time, it avoids the dissipation of large amounts of heat energy into the atmosphere, reducing thermal pollution and achieving efficient energy utilization and environmentally friendly protection. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this patent or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this patent. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 is a schematic diagram of the system connection in this embodiment.

[0018] In the diagram: 1. Cold hydrogenation reactor; 2. Quenching tower; 3. Generator; 4. Circulating water heat exchanger; 5. Gas-liquid separator; 6. Heat exchanger; 7. Hydrogen compressor; 8. Primary evaporator; 9. Secondary evaporator; 10. Mixer; 11. Distillation column; 12. Condenser; 13. Expansion valve; 14. Absorber; 15. Solution pump; 16. Vaporizer; 17. Superheater; 18. Electric heater; 19. Condensate storage tank; 20. Chlorosilane storage tank; 21. Transfer pump; 22. Heat exchanger. Detailed Implementation

[0019] The technical solutions of this patent embodiment will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this patent, and not all of them. Based on the embodiments of this patent, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this patent.

[0020] Example 1:

[0021] Figure 1 shows a tail gas treatment system in a cold hydrogenation production process, including a cold hydrogenation reactor 1, a quench tower 2, a generator 3, a circulating water heat exchanger 4, a gas-liquid separator 5, a heat exchanger 6, a hydrogen compressor 7, an evaporator, a mixer 9, a distillation column 11, a condenser 12, an expansion valve 13, an absorber 14, and a solution pump 15.

[0022] The tail gas outlet of the cold hydrogenation reactor 1 is connected to the tail gas inlet of the quench tower 2 via a pipeline. The tail gas outlet of the quench tower 2 is connected to the tail gas inlet of the generator 3 via a pipeline. The tail gas outlet of the generator 3 is connected to the hot medium inlet of the circulating water heat exchanger 4 via a pipeline. The hot medium outlet of the circulating water heat exchanger 4 is connected to the inlet of the gas-liquid separator 5 via a pipeline. The gas phase outlet of the gas-liquid separator 5 is connected to the hot medium inlet of the heat exchanger 6 via a pipeline. The hot medium outlet of the heat exchanger 6 is connected to the medium gas inlet of the evaporator via a pipeline. The medium gas phase outlet of the evaporator is connected to the cold medium inlet of the heat exchanger 6 via a pipeline. The cold medium outlet of the heat exchanger 6 is connected to the inlet of the hydrogen compressor 7 via a pipeline. The outlet of the hydrogen compressor 7 is connected to the hydrogen inlet of the mixer 10 via a pipeline.

[0023] The liquid outlet of the evaporator is connected to the inlet of the chlorosilane storage tank 20 via a pipeline. The outlet of the chlorosilane storage tank 20 is connected to the inlet of the transfer pump 21 via a pipeline. The outlet of the transfer pump 21 is connected to the spray liquid inlet of the quench tower 2 via a pipeline. The liquid outlet of the gas-liquid separator 5 is connected to the inlet of the condensate storage tank 19 via a pipeline. The outlet of the condensate storage tank 19 is connected to the inlet of the distillation column 11 via a pipeline. The outlet of the mixer 10 is connected to the inlet of the vaporizer 16 via a pipeline. The outlet of the vaporizer 16 is connected to the inlet of the superheater 17 via a pipeline. The outlet of the superheater 17 is connected to the cold medium inlet of the heat exchanger 23 via a pipeline. The cold medium outlet of the heat exchanger 23 is connected to the inlet of the electric heater 18 via a pipeline. The outlet of the electric heater 18 is connected to the raw material inlet of the cold hydrogenation reactor 1 via a pipeline.

[0024] The refrigerant outlet of generator 3 is connected to the inlet of condenser 12 via a pipeline. The outlet of condenser 12 is connected to the inlet of expansion valve 13 via a pipeline. The outlet of expansion valve 13 is connected to the refrigerant inlet of evaporator. The refrigerant outlet of evaporator is connected to the refrigerant inlet of absorber 14. The refrigerant outlet of absorber 14 is connected to the inlet of solution pump 15. The outlet of solution pump 15 is connected to the refrigerant inlet of generator 3 via a pipeline.

[0025] In this embodiment, there are two evaporators: a primary evaporator 8 and a secondary evaporator 9. The hot medium outlet of the heat exchanger 6 is connected to the medium gas inlet of the primary evaporator 8 via a pipeline. The medium gas phase outlet of the primary evaporator 8 is connected to the medium gas inlet of the secondary evaporator 9 via a pipeline. The medium gas phase outlet of the secondary evaporator 9 is connected to the cold medium inlet of the heat exchanger 6 via a pipeline. The medium liquid phase outlets of both the primary evaporator 8 and the secondary evaporator 9 are connected to the inlet of the chlorosilane storage tank 20 via pipelines. The outlet of the expansion valve 13 is divided into two paths, which are connected to the refrigerant inlets of the primary evaporator 8 and the secondary evaporator 9 via pipelines, respectively. The refrigerant outlets of both the primary evaporator 8 and the secondary evaporator 9 are connected to the refrigerant inlet of the absorber 14 via pipelines.

[0026] Job Description:

[0027] The reactants (hydrogen and silicon tetrachloride) for cold hydrogenation enter the mixer 10 in proportion, then enter the vaporizer 16 to vaporize the liquid silicon tetrachloride, then enter the superheater 17 to heat the mixed gas raw material, then enter the heat exchanger 23 for further heating, and finally are heated to 540-560°C by the electric heater 18 before being sent to the cold hydrogenation reactor 1 to carry out the cold hydrogenation reaction. After the cold hydrogenation reaction, the tail gas contains hydrogen, chlorosilanes, and solid silicon powder. It first enters quench tower 2, where wet dust removal removes the solid silicon powder. The tail gas temperature at the top outlet of quench tower 2 is approximately 140-150℃. It then enters generator 3, where the waste heat from the tail gas heats the low-boiling-point working fluid (the condenser) within generator 3. In this embodiment, ammonia is used as the condenser, resulting in a high-pressure gaseous refrigerant. After passing through generator 3, the tail gas enters circulating water heat exchanger 4 for further cooling. It then enters gas-liquid separator 5, where the condensed chlorosilanes enter condensate storage tank 19. Next, it enters distillation column 11, where the boiling point differences of the substances in the chlorosilane mixture are used to separate and purify the product. The uncondensed gas in gas-liquid separator 5 contains hydrogen and a small amount of chlorosilanes. After further heat exchange and cooling in heat exchanger 6, it sequentially enters primary evaporator 8 and secondary evaporator 9. Simultaneously, the gas... The high-pressure gaseous refrigerant in the generator 3 is condensed by the condenser 12 to obtain high-pressure liquid refrigerant. It is then depressurized by thermal expansion through the expansion valve 13 to a saturated liquid state and undergo flash vaporization to provide sufficient cooling energy. After that, it enters the first-stage evaporator 8 and the second-stage evaporator 9 to deeply cool the exhaust gas. The chlorosilane liquid that is condensed after cooling enters the chlorosilane storage tank 20 and is transported to the quench tower 2 by the transfer pump 21 for use as a spray liquid. The gas that is still not condensed after cooling is mainly composed of hydrogen. After being heated by the heat exchanger 6, it is used as a raw material and pressurized by the hydrogen compressor 22 before returning to the mixer 10 to participate in the cold hydrogenation reaction again. The low-pressure gaseous refrigerant in the first-stage evaporator 8 and the second-stage evaporator 8 enters the absorber 14 and is absorbed again by the lean working liquid to make a low-pressure rich liquid. It is then turned into a high-pressure rich liquid by the solution pump 15 and enters the generator 3 for recycling.

[0028] The above description is merely a preferred embodiment of this patent and is not intended to limit this patent. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this patent shall be included within the scope of protection of this patent.

Claims

1. A tail gas treatment system for the cold hydrogenation production process of polycrystalline silicon, characterized in that, It includes a cold hydrogenation reactor, a quench tower, a generator, a circulating water heat exchanger, a gas-liquid separator, a heat exchanger, a hydrogen compressor, an evaporator, a mixer, a distillation column, a condenser, an expansion valve, an absorber, and a solution pump; The tail gas outlet of the cold hydrogenation reactor is connected to the tail gas inlet of the quench tower via a pipeline. The tail gas outlet of the quench tower is connected to the tail gas inlet of the generator via a pipeline. The tail gas outlet of the generator is connected to the heat medium inlet of the circulating water heat exchanger via a pipeline. The heat medium outlet of the circulating water heat exchanger is connected to the inlet of the gas-liquid separator via a pipeline. The gas phase outlet of the gas-liquid separator is connected to the heat medium inlet of the heat exchanger via a pipeline. The heat medium outlet of the heat exchanger is connected to the medium gas inlet of the evaporator via a pipeline. The medium gas phase outlet of the evaporator is connected to the cold medium inlet of the heat exchanger via a pipeline. The cold medium outlet of the heat exchanger is connected to the inlet of the hydrogen compressor via a pipeline. The outlet of the hydrogen compressor is connected to the hydrogen inlet of the mixer via a pipeline. The medium liquid phase outlet of the evaporator is connected to the inlet of the chlorosilane storage tank via a pipeline. The outlet of the chlorosilane storage tank is connected to the inlet of the transfer pump via a pipeline. The outlet of the transfer pump is connected to the spray liquid inlet of the quench tower via a pipeline. The condensate outlet of the generator is connected to the inlet of the condenser via a pipeline. The outlet of the condenser is connected to the inlet of the expansion valve via a pipeline. The outlet of the expansion valve is connected to the condensate inlet of the evaporator. The condensate outlet of the evaporator is connected to the condensate inlet of the absorber. The condensate outlet of the absorber is connected to the inlet of the solution pump. The outlet of the solution pump is connected to the condensate inlet of the generator via a pipeline.

2. The tail gas treatment system in the polycrystalline silicon cold hydrogenation production process according to claim 1, characterized in that, The evaporator consists of two units: a primary evaporator and a secondary evaporator. The hot medium outlet of the heat exchanger is connected to the medium gas inlet of the primary evaporator via a pipeline. The medium gas phase outlet of the primary evaporator is connected to the medium gas inlet of the secondary evaporator via a pipeline. The medium gas phase outlet of the secondary evaporator is connected to the cold medium inlet of the heat exchanger via a pipeline. The liquid phase outlets of both the primary evaporator and the secondary evaporator are connected to the inlet of the chlorosilane storage tank via pipelines. The expansion valve has two outlets, which are connected to the condensate inlets of the first-stage evaporator and the second-stage evaporator via pipelines, respectively. The condensate outlets of the first-stage evaporator and the second-stage evaporator are both connected to the condensate inlet of the absorber via pipelines.

3. The tail gas treatment system in the polycrystalline silicon cold hydrogenation production process according to claim 1, characterized in that, The liquid phase outlet of the gas-liquid separator is connected to the inlet of the condensate storage tank via a pipeline, and the outlet of the condensate storage tank is connected to the inlet of the distillation column via a pipeline.

4. The tail gas treatment system in the polycrystalline silicon cold hydrogenation production process according to claim 1, characterized in that, The outlet of the mixer is connected to the inlet of the vaporizer via a pipeline, the outlet of the vaporizer is connected to the inlet of the superheater via a pipeline, the outlet of the superheater is connected to the cold medium inlet of the heat exchanger via a pipeline, the cold medium outlet of the heat exchanger is connected to the inlet of the electric heater via a pipeline, and the outlet of the electric heater is connected to the raw material inlet of the cold hydrogenation reactor via a pipeline.

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