Method and system for absorbing hydrogen chloride in a reduction tail gas in a polysilicon production process

Abstract

This invention discloses a method and system for absorbing hydrogen chloride in the reduction tail gas during polycrystalline silicon production. The method includes: dividing an HCl absorption tower into a lean solution absorption section and a STC absorption section; in the lean solution absorption section, using lean solution to absorb and treat the reduction tail gas; passing the reduced tail gas after absorption by the lean solution into the STC absorption section; and sending the bottom liquid of the HCl absorption tower to an HCl desorption unit for desorption, obtaining HCl and the lean solution; in the STC absorption section, using silicon tetrachloride liquid to further absorb and treat the reduced tail gas after absorption by the lean solution; discharging the absorbed gas phase from the top of the HCl absorption tower to obtain high-purity hydrogen; and outputting the absorbed liquid phase and then returning it to the STC absorption section for further absorption and treatment of the reduced tail gas after absorption by the lean solution. Compared with traditional processes, this invention has lower absorption pressure, smaller absorption circulation volume, lower energy consumption, lower equipment investment and operating costs, and higher hydrogen purity, which can reduce the downstream hydrogen adsorption load.

Description

Technical Field

[0001] This invention belongs to the field of polycrystalline silicon technology, specifically relating to a method and system for absorbing hydrogen chloride in the reduction tail gas during polycrystalline silicon production. Background Technology

[0002] In the polysilicon production process, the tail gas generated by the reduction furnace mainly consists of hydrogen, hydrogen chloride, and chlorosilanes (dichlorosilane, trichlorosilane, and silicon tetrachloride). The tail gas is first separated by cryogenic separation of chlorosilanes. The uncondensed tail gas is pressurized and then hydrogen chloride is absorbed by silicon tetrachloride (STC) at low temperature to separate hydrogen. The absorbed liquid is then separated by a desorption tower. Part of the desorbed tower bottom liquid is recycled for hydrogen chloride absorption, and part is sent to the distillation section for purification.

[0003] Currently, most traditional processes use the bottom liquid (lean absorbent) of the desorption tower as the absorbent. This process is advantageous due to its short flow rate and simple operation. However, because the silicon tetrachloride (STC) content in the lean absorbent is only about 50 wt%, the absorption efficiency is low, requiring high absorption pressure and a large absorbent circulation volume. Simultaneously, the low purity of the hydrogen leads to a high downstream hydrogen adsorption load. Overall, the above processes suffer from high equipment investment, high power consumption for compression and refrigeration, and high operating costs. Some traditional processes use pure silicon tetrachloride as the absorbent. This process has the advantages of high absorption efficiency and low equipment investment; however, due to low utilization of cold and heat, and a large subsequent distillation volume, it results in high energy consumption and high operating costs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the above-mentioned shortcomings of the existing technology by providing a method and system for absorbing hydrogen chloride in the reduction tail gas during polysilicon production. Compared with traditional processes, the absorption pressure is low, the absorption cycle volume is small, the energy consumption is low, the equipment investment and operating costs are low, and the hydrogen purity is high, which can reduce the downstream hydrogen adsorption load.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is: According to one aspect of the present invention, a method for absorbing hydrogen chloride in the reduction tail gas during polysilicon production is provided, the technical solution of which is as follows: A method for absorbing hydrogen chloride in reduction tail gas during polysilicon production includes: The HCl absorption tower is divided into a lean solution absorption section and an STC absorption section. In the lean solution absorption section, the reduction tail gas is absorbed and treated by the lean solution. The reduction tail gas after absorption by the lean solution is introduced into the STC absorption section, and the bottom liquid of the HCl absorption tower is sent to the HCl desorption unit for desorption. HCl and the lean solution are obtained by desorption. In the STC absorption section, silicon tetrachloride liquid is used to re-absorb the reduction tail gas after absorption by the lean absorption solution. The absorbed gas phase is discharged from the top of the HCl absorption tower to obtain high-purity hydrogen. The absorbed liquid phase is output and then refluxed back to the STC absorption section for re-absorption of the reduction tail gas after absorption by the lean absorption solution.

[0006] Preferably, the HCl absorption tower operates at a pressure of 8–13 barg and an operating temperature of -45–-70°C.

[0007] Preferably, the theoretical number of plates in the HCl absorption tower is 45 to 120, wherein the theoretical number of plates in the STC absorption section is 15 to 40, the theoretical number of plates in the lean solution absorption section is 30 to 80, and the ratio of the theoretical number of plates in the STC absorption section to the theoretical number of plates in the lean solution absorption section is 0.5 to 1:1.

[0008] Preferably, the molar ratio of the reduction tail gas to the total of the absorption lean liquid and silicon tetrachloride liquid is 1:0.2 to 1:0.7, and the molar ratio of silicon tetrachloride liquid to absorption lean liquid is 1:20 to 1:200.

[0009] Preferably, before using the lean liquid to absorb and treat the reducing tail gas in the lean liquid absorption section, the process further includes pressurizing and pre-cooling the reducing tail gas.

[0010] Preferably, after pressurizing and precooling the reduction tail gas, and before using the lean liquid to absorb and treat the reduction tail gas in the lean liquid absorption section, the method further includes: exchanging heat between the pressurized and precooled reduction tail gas and the hydrogen gas discharged from the top of the HCl absorption tower for deep cooling.

[0011] Preferably, before using the lean absorber to absorb and treat the reduction tail gas in the lean absorber section, the process further includes: pre-cooling the lean absorber by exchanging heat with the bottom liquid output from the HCl absorption tower, then introducing it into the lean absorber cryocooler for deep cooling, and then introducing it into the lean absorber section.

[0012] Preferably, before the reduction tail gas after absorption by the lean absorber is re-absorbed using silicon tetrachloride liquid in the STC absorption section, the method further includes: introducing silicon tetrachloride liquid into the STC cryostat for deep cooling, and then introducing it into the STC absorption section.

[0013] Preferably, before the absorbed liquid phase is output and then returned to the STC absorption section for further absorption of the reduction tail gas after absorption by the lean absorber, the method further includes: pressurizing the absorbed liquid phase in the STC absorption section and then passing it into the STC cryostat for cryogenic cooling, and then returning it to the STC absorption section.

[0014] Preferably, the method further includes: outputting a portion of the liquid phase absorbed by the STC absorption section and then passing it into the lean liquid absorption section.

[0015] According to another aspect of the present invention, a system for absorbing hydrogen chloride in the reduction tail gas during polysilicon production is provided, the technical solution of which is as follows: A system for absorbing hydrogen chloride in the reduction tail gas during polysilicon production, used in the methods described above, includes an HCl absorption tower and an HCl desorption unit. The HCl absorption tower includes a lean solution absorption section and an STC absorption section, wherein: The lean liquor absorption section is located below the STC absorption section. The lean liquor absorption section is equipped with a feed pipeline for introducing the reduction tail gas from the polysilicon production process. The lean liquor absorption section is connected to the HCl desorption unit for introducing lean liquor from the HCl desorption unit to absorb and treat the reduction tail gas. The reduction tail gas after absorption by the lean liquor is then introduced into the STC absorption section, and the bottom liquid of the HCl absorption tower is transported to the HCl desorption unit for desorption, thereby obtaining HCl and the lean liquor. The STC absorption section is equipped with an STC replenishment pipeline and an STC circulation pipeline. The STC replenishment pipeline is used to introduce fresh silicon tetrachloride liquid to re-absorb the reduction tail gas after absorption by the lean absorber. The STC circulation pipeline is used to output the liquid phase after absorption by the silicon tetrachloride liquid and then return it to the STC absorption section for re-absorption of the reduction tail gas after absorption by the lean absorber. The gas phase after absorption by the STC absorption section is discharged from the top of the HCl absorption tower to obtain high-purity hydrogen.

[0016] Preferably, the system further includes a pressurizing device and a precooling device, both of which are connected to the feed pipeline and are used to pressurize and precool the reduction exhaust gas, respectively.

[0017] Preferably, the system further includes an absorption tower feed heat exchanger, which is connected to the feed pipeline, the lean liquor absorption section, and the STC absorption section, respectively, and is used to exchange heat between the pressurized and pre-cooled reduction tail gas and the hydrogen gas discharged from the top of the HCl absorption tower for deep cooling.

[0018] Preferably, the system further includes a lean-rich liquid heat exchanger and a lean liquid cryostat, wherein: The lean and rich liquid heat exchanger is connected to the lean liquid absorption section and the HCl desorption unit respectively, and is used to pre-cool the lean liquid obtained by the HCl desorption unit by using the bottom liquid output from the HCl absorption tower. The lean liquid cryostat is connected to the lean and rich liquid heat exchanger and the lean liquid absorption section, respectively, and is used to cryogenically cool the pre-cooled lean absorption liquid.

[0019] Preferably, the system further includes an STC reflux pump and an STC cryocooler, wherein: The STC reflux pump is located on the STC circulation pipeline. The STC cryostat is connected to the STC reflux pump, the STC replenishment pipeline, and the STC absorption section, respectively. The STC reflux pump is used to transport the liquid phase absorbed by the STC absorption section to the STC cryostat for cryogenic cooling. The STC cryostat is used to cryogenically cool the silicon tetrachloride liquid supplied through the STC replenishment line and the liquid phase delivered by the STC reflux pump.

[0020] Preferably, the STC absorption section is further provided with an STC delivery pipeline, which is connected to the lean liquid absorption section and is used to allow the liquid phase absorbed by the STC absorption section to flow by gravity into the lean liquid absorption section. Beneficial effects

[0021] The present invention relates to a method and system for absorbing hydrogen chloride in the reduction tail gas during the polysilicon production process. This method uses a lean absorption solution and fresh silicon tetrachloride liquid as the absorbent, performing a two-stage composite absorption of the reduction tail gas. Compared to traditional processes, this reduces harsh operating conditions, lowers absorption pressure, reduces absorption circulation volume, lowers energy consumption, and lowers equipment investment and operating costs. Simultaneously, it can fully absorb and separate hydrogen chloride gas and chlorosilanes from the reduction tail gas, ensuring the purity of the outlet hydrogen gas. The hydrogen purity can be increased from 97% in traditional processes to over 99%, reducing the downstream hydrogen adsorption load (approximately 60%) and significantly reducing the regeneration energy consumption of the downstream hydrogen adsorption tower. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the system for absorbing hydrogen chloride in the reduction tail gas during the polycrystalline silicon production process in an embodiment of the present invention.

[0023] In the diagram: T1 - HCl absorption tower; T2 - HCl desorption unit; E1 - Absorption tower feed heat exchanger; E2 - Lean and rich liquor heat exchanger; E3 - Lean liquor cryocooler; E4 - STC cryocooler; P1 - STC reflux pump; S1 - Feed line; S2 - Hydrogen line; S3 - Lean liquor absorption line; S4 - STC replenishment line; S5 - STC rich liquor absorption line; S6 - STC circulation line; S7 - STC external delivery line; S8 - Rich liquor absorption line. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0025] In the description of this invention, it should be noted that the terms "above" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience and simplification of the description and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0026] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0027] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connection," "setting," "installation," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection, an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] To address the problems of low absorption pressure, small absorption cycle volume, high energy consumption, high equipment investment and operating costs in traditional processes, and the high hydrogen adsorption load downstream due to low hydrogen purity, this invention provides a method for absorbing hydrogen chloride from the reduction tail gas during polysilicon production, comprising: The HCl absorption tower is divided into a lean solution absorption section and an STC absorption section. In the lean solution absorption section, the reduction tail gas is absorbed and treated by the lean solution. The reduction tail gas after absorption by the lean solution is introduced into the STC absorption section, and the bottom liquid of the HCl absorption tower is sent to the HCl desorption unit for desorption. HCl and the lean solution are obtained by desorption. In the STC absorption section, silicon tetrachloride liquid is used to re-absorb the reduction tail gas after absorption by the lean absorption solution. The absorbed gas phase is discharged from the top of the HCl absorption tower to obtain high-purity hydrogen. The absorbed liquid phase is output and then refluxed back to the STC absorption section for re-absorption of the reduction tail gas after absorption by the lean absorption solution.

[0029] Accordingly, the present invention also provides a system for absorbing hydrogen chloride in the reduction tail gas during polysilicon production, used in the above-described method, comprising an HCl absorption tower and an HCl desorption unit, wherein the HCl absorption tower comprises a lean solution absorption section and an STC absorption section, wherein: The lean liquor absorption section is located below the STC absorption section. The lean liquor absorption section is equipped with a feed pipeline for introducing the reduction tail gas from the polysilicon production process. The lean liquor absorption section is connected to the HCl desorption unit for introducing lean liquor from the HCl desorption unit to absorb and treat the reduction tail gas. The reduction tail gas after absorption by the lean liquor is then introduced into the STC absorption section, and the bottom liquid of the HCl absorption tower is transported to the HCl desorption unit for desorption, thereby obtaining HCl and the lean liquor. The STC absorption section is equipped with an STC replenishment pipeline and an STC circulation pipeline. The STC replenishment pipeline is used to introduce fresh silicon tetrachloride liquid to re-absorb the reduction tail gas after absorption by the lean absorber. The STC circulation pipeline is used to output the liquid phase after absorption by the silicon tetrachloride liquid and then return it to the STC absorption section for re-absorption of the reduction tail gas after absorption by the lean absorber. The gas phase after absorption by the STC absorption section is discharged from the top of the HCl absorption tower to obtain high-purity hydrogen. Example 1

[0030] like Figure 1 As shown in the figure, this embodiment discloses a method for absorbing hydrogen chloride in the reduction tail gas during polycrystalline silicon production, including: The HCl absorption tower T1 is divided into a lean solution absorption section in the lower half and an STC absorption section in the upper half. In the lean solution absorption section, the reducing tail gas (including hydrogen, hydrogen chloride, and chlorosilane) is absorbed and treated using the lean solution. Most of the hydrogen chloride (HCl) in the hydrogen is absorbed. The reducing tail gas after absorption by the lean solution is passed into the STC (silicon tetrachloride) absorption section, and the bottom liquid of the HCl absorption tower T1 is sent to the HCl desorption unit for desorption. HCl and the lean solution are obtained by desorption. In the STC absorption section, silicon tetrachloride liquid is used to re-absorb the reduction tail gas after absorption by the lean absorption solution, further absorbing the remaining hydrogen chloride in the hydrogen gas. The absorbed gas phase is discharged from the top of the HCl absorption tower T1 to obtain high-purity hydrogen gas (pure hydrogen). The absorbed liquid phase is output and then refluxed to the STC absorption section for re-absorption of the reduction tail gas after absorption by the lean absorption solution.

[0031] Specifically, the preferred operating pressure of the HCl absorption tower T1 is 8–13 barg, and the preferred operating temperature is -45–-70°C. Compared to the traditional process that requires increasing the absorption pressure to 15–17 MPa, this method uses a lower absorption pressure, which reduces the power consumption of the upstream circulating hydrogen compressor by 20–30%, resulting in lower equipment investment, lower compression energy consumption, and lower costs.

[0032] Specifically, the HCl absorption tower T1 can be a packed tower, a plate tower, or a combination of packed and plate towers.

[0033] The theoretical plate number of the HCl absorption tower T1 is preferably 45 to 120, wherein the theoretical plate number of the STC absorption section is preferably 15 to 40, the theoretical plate number of the lean solution absorption section is preferably 30 to 80, and the ratio of the theoretical plate number of the STC absorption section to the theoretical plate number of the lean solution absorption section is 0.5 to 1:1.

[0034] Specifically, the molar ratio of the reduction tail gas to the absorbent (including the lean absorbent solution introduced into the HCl absorber and the fresh silicon tetrachloride liquid supplemented by the STC replenishment pipeline T4) is preferably 1:0.2 to 1:0.7, wherein the molar ratio of the supplemented fresh silicon tetrachloride liquid to the lean absorbent solution is preferably 1:20 to 1:200.

[0035] Specifically, the STC content in the absorbent solution is 50 mas % ± 2%, the trichlorosilane content is 48 mas % ± 2%, and the dichlorosilane content is < 3 mas %; the STC content in the silicon tetrachloride liquid is > 99 mas, and the operating pressure is preferably 18 to 24 barg.

[0036] Specifically, in the liquid phase output after absorption in the STC absorption section, the STC content is 98.5 mas%±0.5%, the trichlorosilane content is 1.3 mas %±0.5%, the dichlorosilane content is 0.2 mas %±0.1%, and the HCl content is <0.01 mas.

[0037] Specifically, the hydrogen content in the gas phase discharged from the top of the HCl absorption tower T1 is >99 mas% (mass fraction, the same below), the hydrogen chloride content is <0.1 mas%, and the total chlorosilane content is <1 mas.

[0038] In some embodiments, before the reduction tail gas is absorbed and treated by the lean liquid in the lean liquid absorption section, the process further includes pressurizing and pre-cooling the reduction tail gas.

[0039] In the reduced tail gas after pressurization and precooling, the hydrogen content was 81.7 mas %±1.0% (mas fraction, the same below), the hydrogen chloride content was 9.8 mas %±0.5%, the dichlorosilane content was 5.3 mas %±0.5%, and the total content of trichlorosilane and silicon tetrachloride was 3.2 mas %±0.5%.

[0040] In some embodiments, after pressurizing and precooling the reduction tail gas, and before using the lean liquid to absorb and treat the reduction tail gas in the lean liquid absorption section, the process further includes: exchanging heat between the pressurized and precooled reduction tail gas and the hydrogen gas discharged from the top of the low-temperature HCl absorption tower T1 in the absorption tower feed heat exchanger E1 for deep cooling, and then introducing it into the bottom of the lean liquid absorption section.

[0041] In this embodiment, by cryogenically cooling the reduction tail gas, the cooling capacity of the hydrogen gas at the top of the HCl absorber can be fully recovered, allowing for efficient utilization of the cooling capacity and effectively reducing energy consumption. The temperature of the cryogenically cooled reduction tail gas can reach -50℃±5℃.

[0042] In some embodiments, before the absorption treatment of the reduction tail gas by the absorption lean liquid in the lean liquid absorption section, the process further includes: pre-cooling the absorption lean liquid and the bottom liquid (i.e., the absorption rich liquid, -40~-60℃) output from the HCl absorption tower T1 by exchanging heat in the lean-rich liquid heat exchanger E2, then passing it into the lean liquid deep cooler E3 for deep cooling, and then passing it into the top of the lean liquid absorption section.

[0043] In this embodiment, it is preferable to further reduce the temperature of the lean absorption solution to match the temperature at the top of the HCl absorption tower T1, i.e., the temperature of the deep-cooled lean absorption solution is -45~-70℃. By pre-cooling the lean absorption solution, the cold energy of the rich absorption solution can be recovered, allowing the cold energy to be fully utilized and effectively reducing energy consumption.

[0044] In some embodiments, before the reduction tail gas after absorption by the lean absorber is re-absorbed using silicon tetrachloride liquid in the STC absorption section, the method further includes: introducing silicon tetrachloride liquid into the STC cryostat E4 for cryogenic cooling, and then introducing it into the top of the STC absorption section.

[0045] In this embodiment, the temperature of the cryogenic silicon tetrachloride liquid is preferably the same as the temperature at the top of the HCl absorption tower, i.e., -45 to -70°C.

[0046] In some embodiments, before the absorbed liquid phase is output and then returned to the STC absorption section for re-absorption treatment of the reduction tail gas after absorption by the lean liquid, the method further includes: pressurizing the absorbed liquid phase in the STC absorption section through the STC reflux pump P1 and then introducing it into the STC cryocooler E4 for cryogenic cooling, and then returning it to the top of the STC absorption section.

[0047] In this embodiment, the pressure after being pressurized by the STC reflux pump P1 is preferably 18-24 barg. The temperature of the liquid phase after absorption in the STC absorption section after cryogenic treatment is the same as the top temperature of the HCl absorption tower T1, i.e., -45 to -70°C.

[0048] In some embodiments, the method further includes: outputting a portion of the liquid phase absorbed by the STC absorption section and then passing it into the top of the lean liquid absorption section. This portion of the liquid phase enters the HCl absorption tower T1 from the top of the lean liquid absorption section, and its flow rate is equal to the flow rate of the fresh silicon tetrachloride liquid replenished from outside.

[0049] In other words, the liquid phase output after absorption by the STC absorption section is divided into two parts. One part is used as the absorbent for circulation in the STC absorption section, and the remaining part enters the lean liquid absorption section in the HCl absorption tower T1 from the top of the lean liquid absorption section. The preferred molar ratio of the two liquid phases is 20:1 to 200:1.

[0050] This embodiment describes a method for absorbing hydrogen chloride from the reduction tail gas during polysilicon production. It employs a lean absorption solution and fresh silicon tetrachloride liquid as the absorbent, performing a two-stage composite absorption of the reduction tail gas. Compared to traditional processes, this method reduces harsh operating conditions, lowers absorption pressure, reduces absorption circulation volume, lowers energy consumption, and lowers equipment investment and operating costs. Simultaneously, it effectively absorbs and separates hydrogen chloride gas and chlorosilanes from the reduction tail gas, ensuring the purity of the outlet hydrogen. Hydrogen purity can be increased from 97% in traditional processes to over 99%, reducing the downstream hydrogen adsorption load (approximately 60%) and significantly lowering the regeneration energy consumption of the downstream hydrogen adsorption tower. Furthermore, compared to most traditional processes that use lean absorbent as the absorbent in the HCl absorption tower, this method, although supplementing with some silicon tetrachloride liquid, can appropriately reduce the circulating volume of absorbent in the lean absorbent absorption section. Therefore, it not only does not increase the heat exchange load, but also reduces the load on some heat exchangers such as the lean absorbent cryocooler. Compared to some traditional processes that use pure silicon tetrachloride liquid as the absorbent in the HCl absorption tower, resulting in a large waste of cold and heat and an increased load on downstream distillation processes, this method can make full use of the heat exchange gradient, reduce the frequency of heating and cooling, and reduce energy consumption and the load on downstream purification processes. Example 2

[0051] like Figure 1 As shown, this embodiment discloses a system for absorbing hydrogen chloride in the reduction tail gas during polysilicon production, used in the method described in Embodiment 1. It includes an HCl absorption tower T1, an HCl desorption unit T2, and related pipelines. The HCl absorption tower T1 includes a lean liquor absorption section and an STC absorption section, wherein: The lean liquid absorption section is located below the STC absorption section. The lean liquid absorption section is equipped with a feed pipeline S1 for introducing the reduction tail gas from the polysilicon production process. The lean liquid absorption section is connected to the HCl desorption unit T2 for introducing lean absorption liquid from the HCl desorption unit T2 to absorb and treat the reduction tail gas. The reduction tail gas after absorption by the lean liquid is then introduced into the STC absorption section as the absorbent. The bottom liquid of the HCl absorption tower T1 is transported to the HCl desorption unit T2 for desorption, and HCl and the lean absorption liquid are obtained by desorption. The top of the STC absorption section is equipped with an STC replenishment pipeline S4 and an STC circulation pipeline S6. The STC replenishment pipeline S4 is used to introduce fresh silicon tetrachloride liquid from outside the interface to re-absorb the reduction tail gas after absorption by the lean absorption solution. The STC circulation pipeline S6 is used to output the liquid phase after absorption by silicon tetrachloride liquid and then return it to the STC absorption section for re-absorption of the reduction tail gas after absorption by the lean absorption solution. The gas phase after absorption by the STC absorption section is discharged from the top of the HCl absorption tower T1 to obtain high-purity hydrogen.

[0052] Specifically, the feed line S1 is positioned above the liquid level in the bottom of the HCl absorber T1, meaning the reduction tail gas enters from above the liquid level in the bottom of the HCl absorber T1. The preferred operating pressure of the HCl absorber T1 is 8–13 barg, and the preferred operating temperature is -45–-70℃. Compared to traditional processes that require pressurizing the absorption pressure to 15–17 MPa, this system has a lower absorption pressure, resulting in lower equipment investment, reduced compression energy consumption, and lower costs.

[0053] The HCl absorption tower T1 can be a packed tower, a plate tower, or a combination of packed and plate towers. The theoretical plate number of the HCl absorption tower T1 is preferably 45–120, wherein the theoretical plate number of the STC absorption section is preferably 15–40, and the theoretical plate number of the lean solution absorption section is preferably 30–80. The ratio of the theoretical plate number of the STC absorption section to the theoretical plate number of the lean solution absorption section is 0.5–1:1.

[0054] The molar ratio of the reduction tail gas to the absorbent (including the lean absorbent solution introduced into the HCl absorber and the fresh silicon tetrachloride liquid supplemented by the STC replenishment pipeline S4) is preferably 1:0.2 to 1:0.7, wherein the molar ratio of the supplemented fresh silicon tetrachloride liquid to the lean absorbent solution is preferably 1:20 to 1:200.

[0055] The HCl desorption unit T2 can be a desorption tower or similar equipment. The absorption lean liquid is the upper layer liquid obtained after desorption in the desorption tower, also called the desorption lean liquid. The lower layer liquid mainly consists of chlorosilanes and is collected from the bottom of the desorption tower. The STC content in the absorption lean liquid is 50 mas % ± 2%, the trichlorosilane content is 48 mas % ± 2%, and the dichlorosilane content is < 3 mas %. The STC content in the silicon tetrachloride liquid is > 99 mas, and the preferred operating pressure is 18–24 barg.

[0056] One end of the STC circulation pipeline S6 is connected to the outlet of the liquid collection tray at the bottom of the STC absorption section to discharge the liquid phase output after absorption by the STC absorption section. The other end of the STC circulation pipeline S6 is connected to the top of the STC absorption section, and the liquid phase output after absorption by the STC absorption section then enters the HCl absorption tower T1 from the top of the STC absorption section to achieve circulation. In the liquid phase output after absorption by the STC absorption section, the STC content is 98.5 mas%±0.5%, the trichlorosilane content is 1.3 mas %±0.5%, the dichlorosilane content is 0.2 mas %±0.1%, and the HCl content is <0.01 mas %. In this embodiment, the STC replenishment pipeline is connected to the STC circulation pipeline. The silicon tetrachloride liquid replenished from outside the boundary first merges with the reflux liquid phase before entering the top of the STC absorption section.

[0057] The hydrogen content in the gas phase discharged from the top of the HCl absorption tower T1 is >99 mas% (mass fraction, the same below), the hydrogen chloride content is <0.1 mas%, and the total chlorosilane content is <1 mas.

[0058] In some embodiments, the system further includes a pressurizing device and a precooling device (not shown in the figure), both of which are connected to the feed line S1 and are used to pressurize and precool the reduction tail gas, respectively.

[0059] Specifically, the pressurizing device can be a compressor or similar equipment, and the precooling device can be a heat exchanger or similar equipment. The pressure of the reduction tail gas after treatment by the pressurizing and precooling devices is 8–13 barg, the temperature is -20℃±5℃, and the hydrogen content in the reduction tail gas is 81.7 mas %±1.0% (mass fraction, the same below), the hydrogen chloride content is 9.8 mas %±0.5%, the dichlorosilane content is 5.3 mas %±0.5%, and the total content of trichlorosilane and silicon tetrachloride is 3.2 mas %±0.5%.

[0060] In some embodiments, the system further includes an absorption tower feed heat exchanger E1, which is connected to the feed pipeline S1 and the top gas phase outlet of the STC absorption section, respectively, for exchanging heat between the pressurized and pre-cooled reduction tail gas and the hydrogen gas discharged from the top of the HCl absorption tower for deep cooling. Specifically, the absorption tower feed heat exchanger E1 is connected to the top gas phase outlet of the STC absorption section via the hydrogen pipeline S2.

[0061] The low-temperature hydrogen gas discharged from the top of the HCl absorption tower T1 is used to deeply cool the reduction tail gas through the feed heat exchanger E1 of the absorption tower. This can fully recover the cold energy carried away by the hydrogen gas discharged from the top of the tower, making full use of the cold energy and effectively reducing energy consumption. The temperature of the reduction tail gas after deep cooling can reach -50℃±5℃. The hydrogen gas discharged from the top of the HCl absorption tower T1 is reheated by the feed heat exchanger E1 and then fed into the downstream hydrogen adsorption unit for further treatment, which will not be described in detail here.

[0062] In some embodiments, the system further includes a lean-rich liquid heat exchanger E2 and a lean liquid cryotherm E3, wherein: the lean-rich liquid heat exchanger E2 is connected to the bottom of the lean liquid absorption section and the HCl desorption unit T2, respectively, for utilizing the bottom liquid output from the HCl absorption tower T1 (i.e., the rich absorption liquid, with a temperature of -40~-60℃, wherein the STC content is 49.6 mas %±2% (mass fraction, the same below), the trichlorosilane content is 47.6 mas %±2%, the dichlorosilane content is 2.4 mas %±0.1%, and the HCl content is 0.4 mas The lean absorbent obtained from the HCl desorption unit T2 (±0.1%) is pre-cooled by heat exchange. The rich absorbent after heat exchange is then introduced into the HCl desorption unit T2 for desorption. Specifically, the lean-rich absorbent heat exchanger E2 is connected to the bottom of the lean absorbent absorption section through the lean absorbent pipeline S3, and to the bottom of the HCl desorption unit T2 through the rich absorbent pipeline S8 to introduce the rich absorbent. The lean absorbent is also connected to the bottom of the HCl desorption unit T2 through the lean absorbent pipeline S3 to discharge the lean absorbent obtained after desorption. The lean absorbent cryostat E3 is connected to the lean-rich absorbent heat exchanger E2 and the top of the lean absorbent absorption section, respectively, and is used to cryogenically cool the pre-cooled lean absorbent. The cryogenically cooled lean absorbent enters the HCl absorption tower T1 from the top of the lean absorbent absorption section and is counter-current with the reduction tail gas to achieve hydrogen chloride absorption.

[0063] In this embodiment, it is preferable to further reduce the temperature of the lean absorption solution to match the temperature at the top of the HCl absorption tower T1, i.e., the temperature of the deep-cooled lean absorption solution is -45~-70℃. By pre-cooling the lean absorption solution, the cold energy of the rich absorption solution can be recovered, allowing the cold energy to be fully utilized and effectively reducing energy consumption.

[0064] In some embodiments, the system further includes an STC reflux pump P1 and an STC cryostat E4. The STC reflux pump P1 is located on the STC circulation line S6 and is connected to the outlet of the liquid accumulation pan at the bottom of the STC absorption section via the STC absorption rich liquid line S5. The STC cryostat E4 is connected to the STC reflux pump P1, the STC replenishment line S4, and the top of the STC absorption section, respectively. The STC reflux pump P1 is used to transport the liquid phase absorbed by the STC absorption section to the STC cryostat E4 for cryogenic cooling. The STC cryostat E4 is used to cryogenically cool the silicon tetrachloride liquid introduced into the STC replenishment line S4 and the liquid phase transported by the STC reflux pump P1.

[0065] In this embodiment, the pressure after being pressurized by the STC reflux pump is preferably 18-24 barg. The temperature of the liquid phase and silicon tetrachloride liquid after absorption in the STC absorption section after cryogenic treatment is preferably the same as the top temperature of the HCl absorption tower T1, i.e., -45 to -70°C.

[0066] In some embodiments, the STC absorption section is further provided with an STC external supply pipeline S7, which is connected to the top of the lean solution absorption section. This pipeline allows the liquid phase absorbed by the STC absorption section to flow by gravity into the lean solution absorption section. The flow rate of the liquid phase delivered to the lean solution absorption section is preferably equal to the flow rate of the externally replenished silicon tetrachloride liquid. In other words, the liquid phase output from the STC absorption section is divided into two parts: one part is used as the absorbent for circulation within the STC absorption section, and the remaining part enters the HCl absorption tower T1 from the top of the lean solution absorption section. The molar ratio of the two liquid phases is preferably 20:1 to 200:1.

[0067] In this embodiment, the STC delivery pipeline S7 is first connected to the lean liquid absorption pipeline S3, and then connected to the lean liquid absorption section through the lean liquid absorption pipeline S3. That is to say, the liquid phase absorbed by part of the STC absorption section is first collected into the lean liquid absorption section, and then introduced into the lean liquid absorption section.

[0068] The system for absorbing hydrogen chloride in the reduction tail gas during the polysilicon production process in this embodiment uses both lean absorbent solution and fresh silicon tetrachloride liquid as absorbents for two-stage composite absorption of the reduction tail gas. Compared with traditional processes, this reduces harsh operating conditions, lowers absorption pressure, reduces absorption circulation volume, lowers energy consumption, and lowers equipment investment and operating costs. Simultaneously, it can effectively absorb and separate hydrogen chloride gas and chlorosilanes from the reduction tail gas, ensuring the purity of the outlet hydrogen. The hydrogen purity can be increased from 97% in traditional processes to over 99%, reducing the downstream hydrogen adsorption load (approximately 60%) and significantly reducing the regeneration energy consumption of the downstream hydrogen adsorption tower. Furthermore, compared to most traditional processes that use lean absorbent as the absorbent in the HCl absorption tower, this method, although supplementing with some silicon tetrachloride liquid, can appropriately reduce the circulating volume of absorbent in the lean absorbent absorption section. Therefore, it not only does not increase the heat exchange load, but also reduces the load on some heat exchangers such as the lean absorbent cryocooler. Compared to some traditional processes that use pure silicon tetrachloride liquid as the absorbent in the HCl absorption tower, resulting in a large waste of cold and heat and an increased load on downstream distillation processes, this method can make full use of the heat exchange gradient, reduce the frequency of heating and cooling, and reduce energy consumption and the load on downstream purification processes.

[0069] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for absorbing hydrogen chloride in reduction tail gas during polysilicon production, comprising: The HCl absorption tower (T1) is divided into a lean solution absorption section and an STC absorption section; In the lean liquid absorption section, the reduction tail gas is absorbed and treated by the lean liquid. The reduction tail gas after absorption by the lean liquid is passed into the STC absorption section, and the bottom liquid of the HCl absorption tower is sent to the HCl desorption unit (T2) for desorption. HCl and the lean liquid are obtained by desorption. In the STC absorption section, silicon tetrachloride liquid is used to re-absorb the reduction tail gas after absorption by the lean solution. The absorbed gas phase is discharged from the top of the HCl absorption tower to obtain high-purity hydrogen. After the absorbed liquid phase is output, part of it is returned to the STC absorption section for re-absorption of the reduction tail gas after absorption by the lean solution, and the other part is introduced into the lean solution absorption section. The molar ratio of the two liquid phases is 20:1 to 200:1, and the flow rate of the liquid phase introduced into the lean solution absorption section is equal to the flow rate of the fresh silicon tetrachloride liquid replenished from outside. Specifically, in the liquid phase output after absorption by the STC absorption section, the STC content is 98.5 mas% ± 0.5%, the trichlorosilane content is 1.3 mas% ± 0.5%, the dichlorosilane content is 0.2 mas% ± 0.1%, and the HCl content is < 0.01 mas%; The hydrogen content in the gas phase discharged from the top of the HCl absorber is >99 mas, the hydrogen chloride content is <0.1 mas, and the total chlorosilane content is <1 mas.

2. The method of claim 1, wherein the hydrogen chloride absorption in the reduction tail gas in the polysilicon production process is characterized by, The HCl absorption tower operates at a pressure of 8–13 barg and a temperature of -45–-70°C.

3. The method of absorbing hydrogen chloride in a reduction tail gas in a polysilicon production process according to claim 1, characterized by, The theoretical number of plates in the HCl absorption tower is 45 to 120, of which the theoretical number of plates in the STC absorption section is 15 to 40, the theoretical number of plates in the lean solution absorption section is 30 to 80, and the ratio of the theoretical number of plates in the STC absorption section to the theoretical number of plates in the lean solution absorption section is 0.5 to 1:

1.

4. The method of claim 1, wherein the hydrogen chloride absorption is performed in a process for producing polycrystalline silicon. The molar ratio of the reduction tail gas to the total of the absorption lean solution and silicon tetrachloride liquid is 1:0.2 to 1:0.7, and the molar ratio of silicon tetrachloride liquid to absorption lean solution is 1:20 to 1:

200.

5. The method for absorbing hydrogen chloride in a reduction tail gas in a polysilicon production process according to any one of claims 1 to 4, characterized in that, Before the absorption treatment of the reducing tail gas using the lean solution in the lean solution absorption section, the process also includes: The exhaust gas from the reduction process is pressurized and pre-cooled.

6. The method of claim 5, wherein the hydrogen chloride absorption is performed in the presence of a catalyst. After pressurizing and precooling the reduction tail gas, and before using the lean absorption solution to absorb and treat the reduction tail gas in the lean absorption section, the process also includes: The pressurized and pre-cooled reduction tail gas is exchanged with the hydrogen gas discharged from the top of the HCl absorption tower for deep cooling.

7. The method of claim 6, wherein the hydrogen chloride absorption is performed by using a hydrogen chloride absorption tower. Before the absorption treatment of the reducing tail gas using the lean solution in the lean solution absorption section, the process also includes: The lean absorber solution is pre-cooled by heat exchange with the bottom liquid output from the HCl absorption tower, and then introduced into the lean absorber (E3) for deep cooling. After that, it is introduced into the lean absorber section.

8. The method of claim 6, wherein the hydrogen chloride absorption is performed in a process for producing polycrystalline silicon. Before the re-absorption treatment of the reduction tail gas after absorption by the lean absorber using silicon tetrachloride liquid in the STC absorption section, the method further includes: Liquid silicon tetrachloride is introduced into the STC cryostat (E4) for cryogenic cooling, and then introduced into the STC absorption section.

9. The method of claim 6, wherein the hydrogen chloride absorption is performed in a process for producing polycrystalline silicon. Before the absorbed liquid phase is output and then returned to the STC absorption section for further absorption treatment of the reduction tail gas after absorption with lean solution, the process also includes: After the liquid phase absorbed by the STC absorption section is pressurized, it is fed into the STC cryocooler (E4) for cryogenic cooling, and then returned to the STC absorption section.

10. A system for absorbing hydrogen chloride in a reduction tail gas in a polysilicon production process, characterized by, The method for use in any one of claims 1-9 includes an HCl absorption tower (T1) and an HCl desorption unit (T2), said HCl absorption tower comprising a lean solution absorption section and an STC absorption section. The lean liquor absorption section is located below the STC absorption section. The lean liquor absorption section is equipped with a feed pipeline (S1) for introducing the reduction tail gas from the polysilicon production process. The lean liquor absorption section is connected to the HCl desorption unit for introducing the absorption lean liquor from the HCl desorption unit to absorb and treat the reduction tail gas. The reduction tail gas after absorption by the absorption lean liquor is then introduced into the STC absorption section, and the bottom liquid of the HCl absorption tower is transported to the HCl desorption unit for desorption, thereby obtaining HCl and the absorption lean liquor. The STC absorption section is equipped with an STC replenishment pipeline (S4) and an STC circulation pipeline (S6). The STC replenishment pipeline is used to introduce fresh silicon tetrachloride liquid to re-absorb the reduction tail gas after absorption by the lean absorption solution. The STC circulation pipeline is used to output the liquid phase after absorption by silicon tetrachloride liquid and then return it to the STC absorption section for re-absorption of the reduction tail gas after absorption by the lean absorption solution. The gas phase after absorption by the STC absorption section is discharged from the top of the HCl absorption tower to obtain high-purity hydrogen. The STC absorption section is also equipped with an STC delivery pipeline (S7), which is connected to the lean liquid absorption section and is used to allow a portion of the liquid phase absorbed by the STC absorption section to flow into the lean liquid absorption section by gravity.

11. The system for absorbing hydrogen chloride in a polysilicon production process reduction tail gas according to claim 10, wherein The system also includes a pressurization device and a precooling device. The pressurizing device and the precooling device are both connected to the feed pipeline and are used to pressurize and precool the reduction tail gas, respectively.

12. The system for absorbing hydrogen chloride in a polysilicon production process reduction tail gas according to claim 11, wherein The system also includes an absorption tower feed heat exchanger (E1). The absorber feed heat exchanger is connected to the feed pipeline, the lean liquid absorption section, and the STC absorption section, respectively, and is used to exchange heat between the pressurized and pre-cooled reduction tail gas and the hydrogen gas discharged from the top of the HCl absorber for deep cooling.

13. The system for absorbing hydrogen chloride in a polysilicon production process reduction tail gas according to claim 12, wherein The system also includes a lean-rich liquid heat exchanger (E2) and a lean liquid cryocooler (E3). The lean and rich liquid heat exchanger is connected to the lean liquid absorption section and the HCl desorption unit respectively, and is used to pre-cool the lean liquid obtained by the HCl desorption unit by using the bottom liquid output from the HCl absorption tower. The lean liquid cryostat is connected to the lean and rich liquid heat exchanger and the lean liquid absorption section, respectively, and is used to cryogenically cool the pre-cooled lean absorption liquid.

14. The system for absorbing hydrogen chloride in the reduction tail gas during polycrystalline silicon production according to claim 13, characterized in that, The system also includes an STC reflux pump (P1) and an STC cryocooler (E4). The STC reflux pump is located on the STC circulation pipeline, and the STC cryocooler is connected to the STC reflux pump, the STC replenishment pipeline, and the STC absorption section, respectively. The STC reflux pump is used to transport the liquid phase absorbed by the STC absorption section to the STC cryostat for cryogenic cooling. The STC cryostat is used to cryogenically cool the silicon tetrachloride liquid supplied through the STC replenishment line and the liquid phase delivered by the STC reflux pump.

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