Separation method and separation system for tail gas in polycrystalline silicon production

Abstract

The invention provides a separation method and a separation system for tail gas in polycrystalline silicon production. The method for separating the tail gas in polycrystalline silicon production comprises the following steps: carrying out first absorption treatment on to-be-treated hydrogen by using a chlorosilane solution to obtain a chlorosilane rich solution and intermediate hydrogen; carrying out second absorption treatment on the intermediate hydrogen by using a chlorosilane barren solution to obtain a chlorosilane intermediate solution and recovered hydrogen; the chlorosilane rich solution comprises a first chlorosilane rich solution, and the first chlorosilane rich solution is returned to participate in the first absorption treatment. According to the separation method, high-efficiency separation of hydrogen chloride in hydrogen to be treated in polycrystalline silicon production can be realized under the condition of saving circulating liquid.

Description

Technical Field

[0001] The present invention relates to a method and a system for separating tail gas in polysilicon production, belonging to the technical field of chemical separation. Background Art

[0002] Polysilicon is a key material for manufacturing integrated circuits, photovoltaic solar cells and high-purity silicon products. With the rapid development of the electronic information industry and the solar photovoltaic industry, the market demand for polysilicon is increasing continuously. At present, the mainstream process for preparing polysilicon is the improved Siemens process. Trichlorosilane is generated by reacting metallurgical grade silicon with silicon tetrachloride, hydrogen chloride and hydrogen recovered from reduction tail gas. The mixed gas after dust removal is separated by condensation and recovery to obtain hydrogen and a mixed liquid composed of trichlorosilane generated by the reaction, unreacted silicon tetrachloride, etc. The hydrogen returns to the system to participate in the reaction again. The mixed liquid is separated by distillation to obtain high-purity trichlorosilane (silicon tetrachloride is purified and then recycled by hydrogenation). Then, the vaporized trichlorosilane and hydrogen are mixed in a certain proportion and introduced into a polysilicon reduction furnace. A voltage is applied across the two ends of the rod-shaped silicon core placed in the reduction furnace to generate high temperature. On the surface of the high-temperature silicon core, trichlorosilane is reduced by hydrogen to elemental silicon and deposited on the surface of the silicon core, gradually forming a polysilicon rod of the required specification. Only about 8-10% of the trichlorosilane entering the reduction furnace is converted into polysilicon. The reduction tail gas contains a large amount of unreacted production raw materials hydrogen (H2), trichlorosilane (SiHCL3) and reaction by-products silicon tetrachloride (SiCl4), hydrogen chloride (HCL), dichlorosilane (SiH2Cl2), etc. Through the tail gas recovery device, after "dry" separation and recovery, the separated chlorosilane is sent to distillation and purification, the hydrogen returns to the reduction furnace for recycling, and the hydrogen chloride is sent to the cold hydrogenation device. This process realizes fully closed-loop production.

[0003] The existing tail gas recovery process adopts dry recovery technology, which can basically separate and recover all components in the reduction tail gas, does not introduce new pollution sources, and the quality of the recovered products is stable and directly returns to the polysilicon production system for reuse. With the development of polysilicon technology, the tail gas recovery process has been continuously optimized and improved, but there is still a contradiction between improving the quality of the recovered products and increasing energy consumption. Figure 1 FIG. is a schematic diagram of the polysilicon tail gas recovery process in the prior art, as Figure 1As shown in the figure, the existing polysilicon tail gas recovery system includes processes such as tail gas condensation, hydrogen compression, hydrogen chloride absorption, hydrogen chloride desorption, and hydrogen adsorption. The reduction tail gas is initially subjected to gas-liquid separation of hydrogen (containing hydrogen chloride and a small amount of chlorosilane) and chlorosilane (mainly trichlorosilane and tetrachlorosilane) through tail gas condensation; the condensed chlorosilane and the chlorosilane rich in hydrogen chloride (rich liquid) from the bottom of the hydrogen chloride absorption tower enter the hydrogen chloride desorption tower together, and hydrogen chloride is desorbed by heating and reducing pressure in the hydrogen chloride desorption tower. The recovered hydrogen chloride produced at the top of the tower is sent to processes such as cold hydrogenation or trichlorosilane synthesis, and a part of the chlorosilane (lean liquid) discharged from the bottom of the tower is sent to the hydrogen chloride absorption tower as a hydrogen chloride absorbent, and a part is sent to the polysilicon rectification device as a recovered product; the non-condensable hydrogen after tail gas condensation is sent to the hydrogen chloride absorption tower after being pressurized by a hydrogen compressor, and hydrogen chloride in the hydrogen is absorbed by chlorosilane in a low-temperature and high-pressure environment. The hydrogen produced at the top of the hydrogen chloride absorption tower is further purified through a hydrogen adsorption tower to obtain recovered hydrogen with a purity of up to 99.9999% for use in reduction and other devices; the by-product chlorosilane waste liquid during the regeneration process of the hydrogen adsorption tower is sent to the rectification device for further treatment, and the regenerated hydrogen is sent to the cold hydrogenation device as supplementary hydrogen.

[0004] However, in order to improve the purity of the recovered hydrogen in the existing tail gas recovery process, a large amount of chlorosilane lean liquid is used to reduce the content of chlorosilane, hydrogen chloride, and trace impurities in the hydrogen to be treated. However, using a large amount of chlorosilane lean liquid will increase the energy consumption during chlorosilane desorption and cyclic pressurization. Summary of the Invention

[0005] The present invention provides a method for separating tail gas in polysilicon production, which can efficiently separate hydrogen chloride in the hydrogen to be treated in polysilicon production while saving chlorosilane lean liquid.

[0006] The present invention provides a tail gas separation system in polysilicon production for implementing the above separation method, which can save the usage amount of circulating liquid and reduce material and energy consumption during the separation process.

[0007] The present invention provides a method for separating tail gas in polysilicon production, which includes:

[0008] Performing a first absorption treatment on the hydrogen to be treated using a chlorosilane solution to obtain a chlorosilane rich liquid and intermediate hydrogen;

[0009] Performing a second absorption treatment on the intermediate hydrogen using a chlorosilane lean liquid to obtain a chlorosilane intermediate liquid and recovered hydrogen;

[0010] The chlorosilane rich liquid includes a first chlorosilane rich liquid, and the first chlorosilane rich liquid is returned to participate in the first absorption treatment.

[0011] In the separation method as described above, the chlorosilane intermediate liquid is returned to participate in the first absorption treatment.

[0012] The separation method as described above, wherein before the rich chlorosilane liquid of the first stage returns to participate in the first absorption treatment, it further includes: performing cryogenic treatment on the rich chlorosilane liquid of the first stage.

[0013] The separation method as described above, wherein the rich chlorosilane liquid further includes a second rich chlorosilane liquid, and the second rich chlorosilane liquid is subjected to desorption treatment.

[0014] The separation method as described above, wherein in the first absorption treatment, the temperature is -70 to -45 °C, and the pressure is 0.8 to 1.5 MpaG; and / or,

[0015] In the second absorption treatment, the temperature is -70 to -50 °C, and the pressure is 0.8 to 1.5 MpaG; and / or,

[0016] The mass ratio of the rich chlorosilane liquid of the first stage to the rich chlorosilane liquid of the second stage is 1:(1 - 10).

[0017] The present invention provides a separation system for tail gas in polysilicon production for implementing the separation method as described above, which includes a first absorption unit and a second absorption unit;

[0018] The first absorption unit has a chlorosilane solution inlet and a hydrogen to be treated inlet, and the second absorption unit has a lean chlorosilane liquid inlet;

[0019] The intermediate hydrogen outlet of the first absorption unit is communicated with the intermediate hydrogen inlet of the second absorption unit, and the rich chlorosilane liquid outlet of the first absorption unit is communicated with the chlorosilane solution inlet.

[0020] The separation system as described above, wherein the intermediate chlorosilane liquid outlet of the second absorption unit is communicated with the chlorosilane solution inlet.

[0021] The separation system as described above, which further includes a cryogenic cooler, the rich chlorosilane liquid outlet is communicated with the heat source inlet of the cryogenic cooler, and the heat source outlet of the cryogenic cooler is communicated with the chlorosilane solution inlet.

[0022] The separation system as described above, which further includes a desorption tower, and the rich chlorosilane liquid outlet is communicated with the chlorosilane inlet of the desorption tower.

[0023] The separation system as described above, wherein the first absorption unit and the second absorption unit are respectively absorption towers; or,

[0024] The separation system includes an absorption tower, the absorption tower includes a first absorption unit and a second absorption unit which are communicated with each other, and the second absorption unit is located on top of the first absorption unit.

[0025] The method for separating tail gas in polysilicon production of the present invention enables a part of the rich chlorosilane liquid obtained from the first absorption treatment to return and participate in the first absorption treatment, which can not only achieve efficient separation of hydrogen chloride in the hydrogen to be treated in polysilicon production, but also reduce the circulation liquid volume of the absorption treatment and relieve the pressure of the tail gas separation system.

[0026] The tail gas separation system in polysilicon production of the present invention is used to implement the above separation method. The separation system has a simple structure and is suitable for wide popularization and application. Brief Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention or related technologies. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0028] Figure 1 It is a schematic diagram of the polysilicon tail gas recovery process in the prior art;

[0029] Figure 2 It is a schematic diagram of the separation process of hydrogen to be treated in polysilicon production in some embodiments of the present invention;

[0030] Figure 3 It is a schematic diagram of the separation process of hydrogen to be treated in polysilicon production in the comparative example of the present invention.

[0031] Explanation of the reference numerals in the drawings:

[0032] 1: Absorption tower;

[0033] 3: Pressure pump;

[0034] 4: Cryogenic cooler;

[0035] 11: First absorption unit;

[0036] 12: Second absorption unit. Detailed Embodiments

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0038] Figure 2This is a schematic diagram of the separation process of hydrogen to be treated in polysilicon production in some embodiments of the present invention. As Figure 2 shown, a first aspect of the present invention provides a method for separating tail gas in polysilicon production, including:

[0039] Performing a first absorption treatment on the hydrogen to be treated with a chlorosilane solution to obtain a chlorosilane-rich solution and intermediate hydrogen;

[0040] Performing a second absorption treatment on the intermediate hydrogen with a chlorosilane lean solution to obtain a chlorosilane intermediate solution and recovered hydrogen.

[0041] The chlorosilane-rich solution includes a first chlorosilane-rich solution, and the first chlorosilane-rich solution is returned to participate in the first absorption treatment.

[0042] In the present invention, the hydrogen to be treated refers to the tail gas after condensation treatment, which includes, by mass percentage: 60-80% hydrogen, 5-15% hydrogen chloride, and 10-25% chlorosilane; the chlorosilane lean solution does not include hydrogen chloride and includes, by mass percentage: 35-60% trichlorosilane, 35-60% silicon tetrachloride, and 4-8% dichlorodihydrogen silane; the chlorosilane-rich solution includes hydrogen chloride and includes, by mass percentage: 35-60% trichlorosilane, 35-60% silicon tetrachloride, 4-8% dichlorodihydrogen silane, and 0.4-0.6% hydrogen chloride.

[0043] The separation method of the present invention specifically includes: performing a first absorption treatment on the hydrogen to be treated with a chlorosilane solution to absorb hydrogen chloride and chlorosilane in the hydrogen to be treated, obtaining a chlorosilane-rich solution including hydrogen chloride, trichlorosilane, tetrachlorosilane, and dichlorodihydrogen silane, and intermediate hydrogen from which part of the hydrogen chloride has been removed; then returning part of the chlorosilane-rich solution (the first chlorosilane-rich solution) to continue to participate in the first absorption treatment; performing a second absorption treatment on the intermediate hydrogen with a chlorosilane lean solution to absorb the hydrogen chloride and chlorosilane not completely removed in the first absorption treatment, obtaining recovered hydrogen with a lower chlorosilane content and a lower hydrogen chloride content, and a chlorosilane intermediate solution including hydrogen chloride, trichlorosilane, tetrachlorosilane, and dichlorodihydrogen silane.

[0044] By returning part of the chlorosilane-rich solution to participate in the first absorption treatment again, the present invention can reduce the usage amount of the chlorosilane lean solution in the entire separation process, relieve the treatment pressure of the subsequent hydrogen chloride analysis system, thereby saving the energy consumption of this part and the investment in the expansion of the corresponding equipment and pipelines.

[0045] In some embodiments of the present invention, the chlorosilane intermediate solution can be returned to participate in the first absorption treatment. That is, after the first chlorosilane-rich solution and the chlorosilane intermediate solution are mixed, they are used as the chlorosilane solution to perform the first absorption treatment on the hydrogen to be treated. By this operation, the usage amount of the chlorosilane lean solution can be further reduced, and the energy consumption can be saved.

[0046] In some embodiments of the present invention, before the first rich chlorosilane liquid returns to participate in the first absorption treatment, it further includes: performing cryogenic treatment on the first rich chlorosilane liquid to make the temperature of the first rich chlorosilane liquid more matched with the temperature of the first absorption treatment, thereby improving the efficiency of the first absorption treatment.

[0047] In some embodiments of the present invention, the rich chlorosilane liquid further includes a second rich chlorosilane liquid, and the second rich chlorosilane liquid is subjected to an analysis treatment to separate hydrogen chloride and chlorosilane.

[0048] The inventors found in the research that when the mass ratio of the first rich chlorosilane liquid to the second rich chlorosilane liquid is 1:(1-10), more hydrogen chloride can be separated while reducing the circulating liquid volume of the absorption treatment and relieving the pressure of the tail gas separation system, further improving the separation efficiency of the tail gas in polysilicon production.

[0049] The present invention can also select the specific parameters of the absorption treatment in order to improve the efficiency of the absorption treatment and achieve the efficient separation of the tail gas in polysilicon production. Exemplarily, in the first absorption treatment, the temperature is -70 to -45 °C and the pressure is 0.8 to 1.5 MpaG; and / or, in the second absorption treatment, the temperature is -70 to -50 °C and the pressure is 0.8 to 1.5 MpaG.

[0050] As Figure 2 shown, the second aspect of the present invention provides a separation system for implementing the separation method of the first aspect, including a first absorption unit 11 and a second absorption unit 12;

[0051] The first absorption unit 11 has a chlorosilane solution inlet and a hydrogen to be treated inlet, and the second absorption unit 12 has a lean chlorosilane liquid inlet;

[0052] The intermediate hydrogen outlet of the first absorption unit 11 is communicated with the intermediate hydrogen inlet of the second absorption unit 12, and the rich chlorosilane liquid outlet of the first absorption unit 11 is communicated with the chlorosilane solution inlet.

[0053] Specifically, the hydrogen to be processed enters the first absorption unit 11 through the hydrogen to be processed inlet. In the first absorption unit 11, the chlorosilane solution absorbs hydrogen chloride and chlorosilane in the hydrogen to be processed, obtaining a chlorosilane-rich liquid including hydrogen chloride, trichlorosilane, silicon tetrachloride, and dichlorosilane dihydride, and intermediate hydrogen with part of the hydrogen chloride removed; the chlorosilane-rich liquid is output through the outlet of the chlorosilane-rich liquid of the first absorption unit 11. Part of the chlorosilane-rich liquid (the first chlorosilane-rich liquid) enters the first absorption unit 11 through the chlorosilane solution inlet of the first absorption unit 11 to participate in the first absorption treatment, absorbing hydrogen chloride and chlorosilane in the hydrogen to be processed; the intermediate hydrogen is output through the intermediate hydrogen outlet of the first absorption unit 11 and enters the second absorption unit 12 through the intermediate hydrogen inlet of the second absorption unit 12. In the second absorption unit 12, the chlorosilane lean liquid absorbs hydrogen chloride and chlorosilane in the intermediate hydrogen, obtaining a chlorosilane intermediate liquid and recovered hydrogen.

[0054] The separation system of the present invention is used to implement the above separation method. The separation system has a simple structure and is suitable for wide promotion and application.

[0055] In some embodiments of the present invention, the chlorosilane intermediate liquid outlet of the second absorption unit 12 is communicated with the chlorosilane solution inlet.

[0056] Specifically, the chlorosilane intermediate liquid is output through the chlorosilane intermediate liquid outlet and enters the first absorption unit 11 through the chlorosilane solution inlet to participate in the first absorption treatment. By setting it in this way, the consumption of the chlorosilane lean liquid in the separation process can be further reduced, and the energy consumption can be saved.

[0057] Furthermore, the separation system further includes a cryogenic cooler 4. The chlorosilane-rich liquid outlet is communicated with the heat source inlet of the cryogenic cooler 4, and the heat source outlet of the cryogenic cooler 4 is communicated with the chlorosilane solution inlet.

[0058] Specifically, part of the chlorosilane-rich liquid (the first chlorosilane-rich liquid) enters the cryogenic cooler 4 through the heat source inlet of the cryogenic cooler 4. After being cooled in the cryogenic cooler 4, it is output through the heat source outlet of the cryogenic cooler 4 and enters the first absorption unit 11 through the chlorosilane solution inlet for the first absorption treatment.

[0059] The present invention uses the cryogenic cooler 4 to perform cryogenic treatment on the first chlorosilane-rich liquid, and a chlorosilane solution with a suitable temperature can be obtained, improving the solubility, promoting the first absorption treatment, thereby dissolving and absorbing more hydrogen chloride and chlorosilane, improving the hydrogen purity in the intermediate hydrogen, and reducing the load of the second absorption treatment and the circulation amount of the chlorosilane lean liquid.

[0060] In some embodiments of the present invention, the separation system further includes an analytical tower. The chlorosilane-rich liquid outlet is communicated with the chlorosilane inlet of the analytical tower.

[0061] Specifically, a part of the rich chlorosilane liquid is output through the rich chlorosilane liquid outlet and enters the stripping tower through the chlorosilane inlet of the stripping tower. In the stripping tower, hydrogen chloride in the rich chlorosilane liquid is stripped to obtain hydrogen chloride and chlorosilane by separation.

[0062] In the present invention, hydrogen chloride in the rich chlorosilane liquid is stripped by the stripping tower to obtain hydrogen chloride and chlorosilane, which can further realize the efficient recycling and utilization of resources.

[0063] The present invention does not particularly limit the specific structures of the first absorption unit 11 and the second absorption unit 12, as long as the above functions can be achieved. In some embodiments of the present invention, the first absorption unit 11 and the second absorption unit 12 are respectively absorption towers.

[0064] In some embodiments of the present invention, as Figure 2 shown, the separation system includes an absorption tower, and the absorption tower includes a first absorption unit 11 and a second absorption unit 12 that are interconnected. The second absorption unit 12 is located on top of the first absorption unit 11. By this arrangement, the floor area can be saved and the cost can be further reduced.

[0065] Hereinafter, the technical solution of the present invention will be further described in conjunction with specific embodiments.

[0066] Example 1

[0067] The separation system for tail gas in polysilicon production in this embodiment is as Figure 2 shown, and includes: a stripping tower, an absorption tower, a pressure pump 3, and a cryogenic cooler 4;

[0068] The absorption tower includes a first absorption unit 11 and a second absorption unit 12 that are interconnected. The second absorption unit 12 is located on top of the first absorption unit 11;

[0069] The first absorption unit 11 has a chlorosilane solution inlet and an inlet for hydrogen to be treated, and the second absorption unit 12 has a lean chlorosilane liquid inlet;

[0070] The intermediate hydrogen outlet of the first absorption unit 11 is connected to the intermediate hydrogen inlet of the second absorption unit 12. The rich chlorosilane liquid outlet of the first absorption unit 11 is connected to the inlet of the pressure pump 3. The outlet of the pressure pump 3 is connected to the heat source inlet of the cryogenic cooler 4. The heat source outlet of the cryogenic cooler 4 is connected to the chlorosilane solution inlet;

[0071] The intermediate chlorosilane liquid outlet of the second absorption unit 12 is connected to the chlorosilane solution inlet; the rich chlorosilane liquid outlet is connected to the chlorosilane inlet of the stripping tower.

[0072] The separation method for tail gas in polysilicon production in this embodiment is carried out using the above separation system, and specifically includes:

[0073] The hydrogen to be processed enters the first absorption unit 11 through the hydrogen to be processed inlet, and undergoes a first absorption treatment in the first absorption unit 11 to obtain a chlorosilane-rich liquid including hydrogen chloride, trichlorosilane, tetrachlorosilane, and dichlorosilane, as well as intermediate hydrogen with part of the hydrogen chloride removed; the chlorosilane-rich liquid is output through the outlet of the chlorosilane-rich liquid of the first absorption unit 11. Part of the chlorosilane-rich liquid (the first chlorosilane-rich liquid) is output through the chlorosilane-rich liquid outlet of the first absorption unit 11, enters the cryogenic cooler 4 through the heat source inlet of the cryogenic cooler 4, and after being cooled by the cryogenic cooler 4, enters the first absorption unit 11 through the chlorosilane solution inlet of the first absorption unit 11 to participate in the first absorption treatment to absorb hydrogen chloride and chlorosilane in the hydrogen to be processed;

[0074] The intermediate hydrogen is output through the intermediate hydrogen outlet of the first absorption unit 11, enters the second absorption unit 12 through the intermediate hydrogen inlet of the second absorption unit 12. In the second absorption unit 12, the chlorosilane lean liquid absorbs hydrogen chloride and chlorosilane in the intermediate hydrogen to obtain a chlorosilane intermediate liquid and recycled hydrogen. The chlorosilane intermediate liquid is output through the chlorosilane intermediate liquid outlet of the second absorption unit 12 and enters the first absorption unit 11 through the chlorosilane solution inlet of the first absorption unit 11 to participate in the first absorption treatment;

[0075] Part of the chlorosilane-rich liquid is output through the chlorosilane-rich liquid outlet, enters the stripping column through the chlorosilane inlet of the stripping column for stripping treatment to obtain hydrogen chloride and chlorosilane.

[0076] Among them, the hydrogen to be processed, by mass percentage, includes: hydrogen 75.94%, hydrogen chloride 12.10%, dichlorosilane 7.61%, trichlorosilane 4.33%, tetrachlorosilane 0.02%;

[0077] The chlorosilane lean liquid, by mass percentage, includes: dichlorosilane 4.15%, trichlorosilane 52.76%, tetrachlorosilane 43.09%;

[0078] In the first absorption unit 11, the temperature is -65.1 °C (top) to -57.1 °C (bottom), and the pressure is 0.9 MPaG; the intermediate hydrogen, by mass percentage, includes: hydrogen 91.04%, hydrogen chloride 5.77%, dichlorosilane 0.84%, trichlorosilane 1.97%, tetrachlorosilane 0.37%;

[0079] The chlorosilane-rich liquid, by mass percentage, includes: hydrogen 38 PPM, hydrogen chloride 0.57%, dichlorosilane 4.43%, trichlorosilane 52.35%, tetrachlorosilane 42.64%;

[0080] The mass ratio of the first chlorosilane-rich liquid to the second chlorosilane-rich liquid is 1:3.37;

[0081] In the second absorption unit 12, the temperature is -65°C (top) to -63.8°C (bottom), and the pressure is 0.9 MPaG; the mass ratio of the hydrogen to be treated to the lean chlorosilane liquid is 1:21;

[0082] The recovered hydrogen by mass percentage includes: hydrogen 96.57%, hydrogen chloride <10 PPB, dichlorosilane 0.89%, trichlorosilane 2.14%, and silicon tetrachloride 0.40%;

[0083] The cooling consumption of the cryogenic cooler 4 is 0.017 kW·h / kg of the hydrogen to be treated; this part of the cooling reduces the second rich chlorosilane liquid to -57.1°C, and 80% of the cooling can be recovered through the subsequent heat exchanger; the steam consumption is 12.56 kW·h / t of the lean chlorosilane liquid, and the consumption of the low-temperature refrigerant is 2.87 kW·h / t of the lean chlorosilane liquid; the total specific consumption for the hydrogen to be treated is: steam 263.4 kW·h / t of the hydrogen to be treated, and the low-temperature refrigerant 77.2 kW·h / t of the hydrogen to be treated.

[0084] Example 2

[0085] The separation method of the tail gas in the polysilicon production of this example is carried out using the separation system of Example 1. The difference between the separation method of the tail gas in the polysilicon production of this example and that of Example 1 is as follows:

[0086] In the first absorption unit 11, the temperature is -62.0°C (top) to -55.5°C (bottom), and the pressure is 0.9 MPaG; the intermediate hydrogen by mass percentage includes: hydrogen 89.62%, hydrogen chloride 6.38%, dichlorosilane 1.01%, trichlorosilane 2.50%, and silicon tetrachloride 0.49%;

[0087] The rich chlorosilane liquid by mass percentage includes: hydrogen 39 PPM, hydrogen chloride 0.56%, dichlorosilane 4.42%, trichlorosilane 52.36%, and silicon tetrachloride 42.65%;

[0088] The mass ratio of the first rich chlorosilane liquid to the second rich chlorosilane liquid is 1:6.05;

[0089] In the second absorption unit 12, the temperature is -65°C (top) to -61.5°C (bottom), and the pressure is 0.9 MPaG; the mass ratio of the hydrogen to be treated to the lean chlorosilane liquid is 1:21.5;

[0090] The cold consumption of the cryogenic cooler 4 is 0.009 kW·h / kg of the hydrogen to be treated; this part of the cold reduces the rich dichlorosilane liquid to -55.5 °C, and 80% of the cold can be recovered through the subsequent heat exchanger; the steam consumption is 12.56 kW·h / t of the lean dichlorosilane liquid, and the low-temperature refrigerant consumption is 3.19 kW·h / t of the lean dichlorosilane liquid; the total unit consumption for the hydrogen to be treated is: 269.9 kW·h / t of steam for the hydrogen to be treated, and 77.5 kW·h / t of low-temperature refrigerant for the hydrogen to be treated.

[0091] Comparative example

[0092] The separation system of the tail gas in the polysilicon production of this comparative example is as Figure 3 shown, including: an absorption tower 1,

[0093] The absorption tower 1 has an inlet for lean dichlorosilane liquid and an inlet for hydrogen to be treated. The hydrogen recovery outlet of the absorption tower 1 is connected to a hydrogen adsorption tower, and the rich dichlorosilane liquid outlet of the absorption tower 1 is connected to a hydrogen chloride stripping tower.

[0094] The separation method of the tail gas in the polysilicon production of this comparative example is carried out using the above separation system, including:

[0095] The hydrogen to be treated enters the absorption tower 1 through the inlet for hydrogen to be treated, and the lean dichlorosilane liquid enters the absorption tower 1 through the inlet for lean dichlorosilane liquid of the absorption tower 1. In the absorption tower 1, the lean dichlorosilane liquid absorbs hydrogen chloride and dichlorosilane in the hydrogen to be treated to obtain a rich dichlorosilane liquid including hydrogen chloride, trichlorosilane, silicon tetrachloride, and dichlorodihydrogen silane, and recovered hydrogen with lower contents of hydrogen chloride and dichlorosilane. The rich dichlorosilane liquid all enters the stripping tower for stripping treatment, and the recovered hydrogen enters the hydrogen adsorption tower for hydrogen adsorption treatment;

[0096] Among them, the hydrogen to be treated includes by mass percentage: 75.94% hydrogen, 12.10% hydrogen chloride, 7.61% dichlorodihydrogen silane, 4.33% trichlorosilane, and 0.02% silicon tetrachloride;

[0097] The lean dichlorosilane liquid includes by mass percentage: 4.15% dichlorodihydrogen silane, 52.76% trichlorosilane, and 43.09% silicon tetrachloride;

[0098] In the absorption tower 1, the temperature is -64.4 °C (top) to -54.5 °C (bottom), and the pressure is 0.9 MPaG;

[0099] The rich dichlorosilane liquid includes by mass percentage: 39 PPM hydrogen, 0.51% hydrogen chloride, 4.40% dichlorodihydrogen silane, 52.39% trichlorosilane, and 42.69% silicon tetrachloride;

[0100] The mass ratio of the hydrogen to be treated to the lean dichlorosilane liquid is 1:23.53;

[0101] The recycled hydrogen, by mass percentage, includes: hydrogen 96.42%, hydrogen chloride <10 PPB, dichlorosilane 0.92%, trichlorosilane 2.23%, and silicon tetrachloride 0.42%.

[0102] To obtain the lean chlorosilane solution by separation, steam and low-temperature refrigerant are consumed. The steam consumption for the lean chlorosilane solution is 12.56 kW·h / t of the lean chlorosilane solution, and the low-temperature refrigerant consumption is 3.52 kW·h / t of the lean chlorosilane solution. The total specific consumption for the hydrogen to be treated is: steam 295.6 kW·h / t of the hydrogen to be treated, and low-temperature refrigerant 82.8 kW·h / t of the hydrogen to be treated.

[0103] It can be seen from Example 1, Example 2 and the comparative example that, on the premise of achieving the same separation requirements, compared with the comparative example, in Example 1, the circulation volume of the lean chlorosilane solution is reduced by 10.87%, the steam consumption is saved by 10.89%, and the low-temperature refrigerant consumption is saved by 6.76%; in Example 2, the circulation volume of the lean chlorosilane solution is reduced by 8.70%, the steam consumption is saved by 8.70%, and the low-temperature refrigerant consumption is saved by 6.40%. At the same time, since the circulation volume of the lean chlorosilane solution is reduced in the embodiments of the present invention, the corresponding equipment and pipelines will be reduced proportionally, saving the corresponding investment, maintenance and operation costs.

[0104] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. The above is only a preferred embodiment of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for separating tail gas in polysilicon production, characterized in that, Comprising: Performing a first absorption treatment on the hydrogen to be treated using a chlorosilane solution to obtain a chlorosilane-rich liquid and intermediate hydrogen; Performing a second absorption treatment on the intermediate hydrogen using a chlorosilane-lean liquid to obtain a chlorosilane intermediate liquid and recovered hydrogen; The chlorosilane-rich liquid includes a first chlorosilane-rich liquid, and the first chlorosilane-rich liquid is returned to participate in the first absorption treatment.

2. The separation method according to claim 1, wherein Returning the chlorosilane intermediate liquid to participate in the first absorption treatment.

3. The separation method according to any one of claims 1-2, characterized in that, Before the first chlorosilane-rich liquid is returned to participate in the first absorption treatment, it further includes: performing cryogenic treatment on the first chlorosilane-rich liquid.

4. The separation method according to any one of claims 1 to 3, characterized in that, The chlorosilane-rich liquid further includes a second chlorosilane-rich liquid, and the second chlorosilane-rich liquid is subjected to stripping treatment.

5. The separation method according to claim 4, characterized in that In the first absorption treatment, the temperature is -70 to -45 °C, and the pressure is 0.8 to 1.5 MpaG; and / or, In the second absorption treatment, the temperature is -70 to -50 °C, and the pressure is 0.8 to 1.5 MpaG; and / or, The mass ratio of the first chlorosilane-rich liquid to the second chlorosilane-rich liquid is 1:(1 - 10).

6. A separation system for tail gas in polysilicon production for implementing the separation method according to any one of claims 1-5, characterized in that, Including a first absorption unit and a second absorption unit; The first absorption unit has a chlorosilane solution inlet and a hydrogen-to-be-treated inlet, and the second absorption unit has a chlorosilane-lean liquid inlet; The intermediate hydrogen outlet of the first absorption unit is communicated with the intermediate hydrogen inlet of the second absorption unit, and the chlorosilane-rich liquid outlet of the first absorption unit is communicated with the chlorosilane solution inlet.

7. The separation system according to claim 6, wherein The chlorosilane intermediate liquid outlet of the second absorption unit is communicated with the chlorosilane solution inlet.

8. The separation system according to claim 6 or 7, characterized in that It further includes a cryogenic cooler, the chlorosilane-rich liquid outlet is communicated with the heat source inlet of the cryogenic cooler, and the heat source outlet of the cryogenic cooler is communicated with the chlorosilane solution inlet.

9. The separation system according to claim 8, wherein It further includes a stripping tower, and the chlorosilane-rich liquid outlet is communicated with the chlorosilane inlet of the stripping tower.

10. The separation system according to any one of claims 6-9, characterized in that, The first absorption unit and the second absorption unit are respectively absorption towers; or, The separation system includes an absorption tower, the absorption tower includes a first absorption unit and a second absorption unit that are communicated with each other, and the second absorption unit is located on top of the first absorption unit.

Images