Method and system for recovery of reduction tail gas in polysilicon production

Abstract

The embodiment of the present application provides a method and system for recovering reduction tail gas in polysilicon production, which is used for reducing the recovery cost of the reduction tail gas. The method comprises the following steps: condensing the reduction tail gas to obtain liquid phase chlorosilane and gas phase tail gas; pressurizing the gas phase tail gas and sending it into an absorption tower; adding liquid phase trichlorosilane into a desorption tower to form a composite absorption liquid with a predetermined ratio in the desorption tower; cooling at least part of the composite absorption liquid and sending it into the absorption tower, the composite absorption liquid is countercurrently contacted with the gas phase tail gas, and the absorption tower outputs composite rich liquid containing hydrogen chloride and hydrogen-rich mixed gas; sending the composite rich liquid containing hydrogen chloride into the desorption tower for desorption, and the desorption tower outputs gas phase hydrogen chloride and the composite absorption liquid; and sending the hydrogen-rich mixed gas into an adsorption device to obtain high-purity hydrogen gas.

Description

Technical Field

[0001] This application relates to the field of polysilicon production technology, and in particular to a method and system for recovering reduction tail gas in polysilicon production. Background Technology

[0002] Polysilicon is a core raw material for the photovoltaic and semiconductor industries. Its production process requires the reduction of chlorosilanes into rod-shaped silicon at high temperatures using a reduction furnace. During operation, the reduction furnace releases high-temperature exhaust gas containing large amounts of hydrogen, hydrogen chloride, and chlorosilanes. Related technologies require the recovery and reuse of the hydrogen and hydrogen chloride in this high-temperature exhaust gas.

[0003] Existing processes typically use pure silicon tetrachloride as an absorbent to absorb hydrogen chloride in high-temperature exhaust gas and generate hydrogen-rich gas, thereby enabling the recovery and reuse of hydrogen and hydrogen chloride. However, using pure silicon tetrachloride as an absorbent requires a large absorbent circulation flow rate, resulting in high energy consumption during the exhaust gas recovery process and significantly increasing production costs. Summary of the Invention

[0004] This application provides a method and system for recovering reduction tail gas in polysilicon production, which aims to reduce production costs.

[0005] In a first aspect, embodiments of this application provide a method for recovering reduction tail gas from polysilicon production, comprising the steps of: condensing the reduction tail gas to obtain liquid-phase chlorosilane and gaseous tail gas; pressurizing the gaseous tail gas and sending it into an absorption tower; adding liquid-phase trichlorosilane into a stripping tower to form a composite absorbent with a predetermined ratio in the stripping tower; cooling at least a portion of the composite absorbent and sending it into the absorption tower, where the composite absorbent and gaseous tail gas are in countercurrent contact, and the absorption tower produces a hydrogen chloride-containing composite rich liquid and a hydrogen-rich mixed gas; sending the hydrogen chloride-containing composite rich liquid into a stripping tower for stripping, where the stripping tower produces gaseous hydrogen chloride and the composite absorbent; and sending the hydrogen-rich mixed gas into an adsorption device to obtain high-purity hydrogen.

[0006] In one possible implementation, the step further includes: feeding at least a portion of the liquid-phase chlorosilane into a distillation apparatus to obtain liquid-phase trichlorosilane.

[0007] In one possible implementation, at least a portion of the liquid-phase chlorosilane is fed into a distillation unit to obtain liquid-phase trichlorosilane; this includes: feeding the liquid-phase chlorosilane into a stripping column, where the liquid-phase chlorosilane participates in the formation of a composite absorbent; and feeding at least a portion of the composite absorbent into a distillation unit to obtain liquid-phase trichlorosilane.

[0008] In one possible implementation, the mass percentage of trichlorosilane in the composite absorbent is greater than or equal to 90%.

[0009] In one possible implementation, at least a portion of the composite absorbent is cooled and then fed into an absorption tower, where the composite absorbent comes into countercurrent contact with the gaseous tail gas, and the absorption tower produces a hydrogen chloride-containing composite rich liquid and a hydrogen-rich mixed gas; this includes: feeding at least a portion of the composite absorbent into a low-temperature heat exchanger to cool the composite absorbent to a first temperature; and feeding the cooled composite absorbent into the absorption tower; wherein the first temperature ranges from -70°C to -65°C.

[0010] In one possible implementation, the gas phase tail gas is pressurized and then sent into the absorption tower; including: sending the gas phase tail gas into a compression device to pressurize the gas phase tail gas to a first pressure value; and sending the pressurized gas phase tail gas into the absorption tower; wherein the first pressure value ranges from 0.9 MPa to 1 MPa.

[0011] In one possible implementation, in the step of feeding the hydrogen chloride-containing composite rich liquid into the stripping column for stripping, and the stripping column producing gaseous hydrogen chloride and composite absorbent, the bottom temperature of the stripping column is controlled at a second temperature; wherein the range of the second temperature is 85°C to 98°C.

[0012] In one possible implementation, the reduction tail gas is condensed to obtain liquid-phase chlorosilane and gaseous tail gas; including: sending the reduction tail gas into a condensation device to cool the reduction tail gas to a third temperature to obtain liquid-phase chlorosilane and gaseous tail gas; wherein the third temperature ranges from -10°C to -5°C.

[0013] Secondly, embodiments of this application provide a reduction tail gas recovery system for polysilicon production, including a condensation device, a compression device, an absorption tower, a stripping tower, and an adsorption device; the condensation device is used to condense the reduction tail gas into liquid-phase chlorosilane and gaseous tail gas; the compression device is connected between the gaseous outlet of the condensation device and the inlet of the absorption tower; the compression device is used to pressurize the gaseous tail gas; the inlet of the stripping tower is connected to the outlet of the absorption tower, and the inlet of the stripping tower is used to add liquid-phase trichlorosilane to form a composite absorbent with a predetermined ratio in the stripping tower; the outlet of the stripping tower is connected to the inlet of the absorption tower to provide the composite absorbent to the absorption tower; the absorption tower is used to make the pressurized gaseous tail gas and the composite absorbent come into countercurrent contact to form a hydrogen chloride-containing composite rich liquid and a hydrogen-rich mixed gas; the stripping tower is used to strip the hydrogen chloride in the hydrogen chloride-containing composite rich liquid into gaseous hydrogen chloride; the adsorption device is connected to the outlet of the absorption tower to purify the hydrogen-rich mixed gas.

[0014] In one possible implementation, the reduction tail gas recovery system further includes a distillation unit; the liquid outlet of the condensation unit is connected to the inlet of the stripping column; the distillation unit is connected to the outlet of the stripping column; and / or, the reduction tail gas recovery system further includes a circulation pump connected between the outlet of the stripping column and the inlet of the absorption column; and / or, the reduction tail gas recovery system further includes a cryogenic heat exchanger connected between the outlet of the stripping column and the inlet of the absorption column.

[0015] The polysilicon production reduction tail gas recovery method and system provided in this application involves adding liquid trichlorosilane into the desorption tower to form a composite absorbent with a predetermined ratio, which is then used to absorb hydrogen chloride. Compared to traditional processes, trichlorosilane has a higher solubility for HCl; therefore, the composite absorbent in this application has a higher solubility for HCl, reducing the amount of absorbent (i.e., the composite absorbent) used. This significantly reduces the circulating flow rate, thereby reducing the load and power consumption of the absorbent circulation device. Simultaneously, it reduces the amount of steam required for desorption heating and decreases the load on the refrigeration unit. As a result, the power consumption and steam consumption of the entire tail gas recovery process are significantly reduced, effectively lowering the overall energy consumption of the tail gas recovery process and thus substantially reducing the overall production cost of polysilicon production. Furthermore, the reduced absorbent circulation flow rate facilitates the stable operation of the tail gas recovery system, reduces the risk of inadequate hydrogen chloride removal due to insufficient absorbent supply, and improves the stability of the tail gas recovery process. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] Figure 1 A schematic flow diagram of the method for recovering reduction tail gas in polysilicon production provided in this application;

[0018] Figure 2 This is a schematic diagram of the overall structure of the polysilicon production reduction tail gas recovery system provided in this application.

[0019] Reference numerals: 1. Condensation unit; 2. Compression unit; 3. Absorption tower; 4. Desorption tower; 5. Adsorption unit; 6. Distillation unit; 7. Low-temperature heat exchanger; 8. Reduction furnace; 9. Cold hydrogenation unit.

[0020] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0021] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application.

[0022] Polysilicon is a core raw material for the photovoltaic and semiconductor industries. Its production process requires the reduction of chlorosilanes (such as trichlorosilane TCS and silicon tetrachloride STC) into silicon particles at high temperatures using a reduction furnace. During operation, the reduction furnace releases high-temperature exhaust gas containing large amounts of hydrogen (H2), hydrogen chloride (HCl), and chlorosilanes (such as TCS and STC). Direct emission of HCl from the exhaust gas would cause environmental pollution, while hydrogen and chlorosilanes, as high-value resources, need to be recycled and reused.

[0023] The current mainstream tail gas recovery process in the industry adopts a process of "condensation pretreatment + HCl removal in the absorption tower + regeneration of the absorbent in the desorption tower". In this process, the absorption tower selectively absorbs HCl using a low-temperature liquid absorbent, and the hydrogen-rich mixed gas produced at the top of the tower is returned to the reduction furnace. The rich liquid at the bottom of the tower is regenerated in the desorption tower and then recycled.

[0024] However, the existing process generally uses pure silicon tetrachloride (STC) as the absorbent. Its solubility in HCl at low temperatures is limited, and its high viscosity results in low gas-liquid mass transfer efficiency. Therefore, the absorbent circulation flow rate required in the tail gas recovery process is large, the desorption energy consumption is high, and the equipment size is large, resulting in high production costs for the tail gas recovery process.

[0025] To address the aforementioned technical problems, this application provides a method and system for recovering reduction tail gas during polysilicon production.

[0026] On the one hand, this application provides a method for recovering reduction tail gas in polysilicon production, such as... Figure 1 As shown, the specific implementation steps are as follows:

[0027] S1: The reduction tail gas is condensed to obtain liquid chlorosilane and gaseous tail gas.

[0028] S2: Pressurize the gas phase tail gas and send it into the absorption tower 3.

[0029] S3: Add liquid trichlorosilane into the stripping tower 4 to form a composite absorbent with a predetermined ratio in the stripping tower 4.

[0030] S4: After cooling at least part of the composite absorbent, it is sent to the absorption tower 3. The composite absorbent is in countercurrent contact with the gas phase tail gas. The absorption tower 3 produces a composite rich liquid containing hydrogen chloride and a hydrogen rich mixed gas.

[0031] S5: The hydrogen chloride-containing composite rich liquid is fed into the stripping tower 4 for stripping. The stripping tower 4 produces gaseous hydrogen chloride and composite absorbent.

[0032] S6: The hydrogen-rich mixed gas is fed into the adsorption unit 5 to obtain high-purity hydrogen.

[0033] In the polysilicon production reduction tail gas recovery method of this application, liquid trichlorosilane is added to the desorption tower 4 to form a composite absorbent with a predetermined ratio, and hydrogen chloride is absorbed using this composite absorbent. Compared with traditional processes, trichlorosilane has a higher solubility for HCl. Therefore, the composite absorbent of this application has a higher solubility for HCl, which can reduce the amount of absorbent (i.e., composite absorbent) used. Its circulation flow rate is significantly reduced, thereby reducing the load and power consumption of the absorbent circulation device. At the same time, it simultaneously reduces the amount of steam required for desorption heating and reduces the load on the refrigeration unit. As a result, the power consumption and steam consumption of the entire tail gas recovery process are significantly reduced, effectively reducing the overall energy consumption of the tail gas recovery process, and thus significantly reducing the overall production cost of polysilicon production. At the same time, the reduced absorbent circulation flow rate required for tail gas recovery is conducive to the stable operation of the tail gas recovery system, reduces the risk of unqualified hydrogen chloride removal due to insufficient absorbent supply, and improves the stability of the tail gas recovery process.

[0034] Specifically, in some possible implementations, in step S1, the reduction tail gas is condensed to obtain liquid-phase chlorosilane and gaseous tail gas, which specifically includes: sending the reduction tail gas into the condensation device 1 and cooling the reduction tail gas to a third temperature to obtain liquid-phase chlorosilane and gaseous tail gas.

[0035] The third temperature range is -10℃ to -5℃. Understandably, the third temperature can be any specific temperature value between -10℃ and -5℃, or it can be any temperature range between -10℃ and -5℃. This application does not make any specific limitation in this regard.

[0036] In this step, the high-temperature reduction tail gas discharged from the reduction furnace 8 is sent to the condenser 1. Through continuous heat exchange via the heat exchange medium in the condenser 1, the overall temperature of the reduction tail gas is reduced to the third temperature range. The high-boiling-point chlorosilane components such as trichlorosilane and silicon tetrachloride in the reduction tail gas are liquefied, achieving gas-liquid two-phase separation, and producing a liquid chlorosilane mixture and a non-condensable gas tail gas, respectively.

[0037] More specifically, in some embodiments, the temperature of the reduction tail gas discharged from the reduction furnace 8 in the polysilicon production process is as high as 182°C to 188°C. After the high-temperature reduction tail gas enters the condenser 1 for two-stage shallow cooling, the cooling temperature is controlled at -10°C to -5°C. At this time, the liquefaction separation of the reduction tail gas can reach more than 91%, and the generated liquid chlorosilanes (including liquid TCS and STC) are at least partially sent to the subsequent distillation unit 6 for separation and purification. The generated gaseous tail gas is an uncondensed gaseous mixture (mainly H2, with trace amounts of chlorosilanes and HCl), which is sent to the absorption tower 3, specifically to the bottom of the absorption tower 3 or the bottom of the absorption tower 3.

[0038] In this embodiment, the boiling point of the chlorosilane component in the reduction tail gas is much higher than that of hydrogen and hydrogen chloride. Most of the chlorosilane can be liquefied and separated by shallow cooling, which reduces the gas phase chlorosilane load in the subsequent absorption tower 3, reduces the proportion of inert components in the composite absorbent, avoids excess chlorosilane occupying the absorbent's dissolution capacity, and ensures the long-term stability of the composite absorbent's HCl absorption capacity.

[0039] Furthermore, in some possible implementations, in step S2, the gaseous tail gas is pressurized and then sent into the absorption tower 3, specifically including:

[0040] S21: Send the gas phase tail gas into the compression device 2 to pressurize the gas phase tail gas to the first pressure value.

[0041] S22: The pressurized gas phase tail gas is sent into the absorption tower 3.

[0042] The first pressure value ranges from 0.9 MPa to 1 MPa. It can be understood that the first pressure value can be any specific pressure value within the range of 0.9 MPa to 1 MPa, or it can be any pressure range within the range of 0.9 MPa to 1 MPa. This application does not make any specific limitation in this regard.

[0043] In this step, the gas phase tail gas separated by the condenser 1 is fed into the compression device 2. Through multi-stage compression and pressurization, the gas phase tail gas is pressurized to the first pressure value. After the pressurization is completed, the gas phase tail gas is fed into the tower from the bottom air inlet of the absorption tower 3 and passes through the packing layer inside the tower from bottom to top.

[0044] In this embodiment, the pressurized gas phase tail gas is controlled at 0.9MPa~1MPa. After entering the absorption tower 3, the pressure at the top of the absorption tower 3 is maintained at 0.9MPa~1MPa, which helps to increase the upper limit of HCl solubility in the liquid-phase composite absorbent and improves the HCl removal efficiency under the same absorbent flow rate. This solution has a higher HCl solubility capacity in the composite absorbent, eliminating the need for further pressurization as in the pure STC system. This reduces the long-term pressurization energy consumption of the compressor, lowers compressor power consumption, and reduces production costs.

[0045] Furthermore, in step S3, liquid trichlorosilane is added into the stripping tower 4 to form a composite absorbent with a predetermined ratio in the stripping tower 4.

[0046] In some possible implementations, this step includes three liquid-phase trichlorosilane supply paths, which can be used individually or in combination:

[0047] Path 1: The liquid chlorosilane produced by condenser 1 is continuously fed into the inlet of stripping column 4. The liquid chlorosilane contains TCS and STC components, which can participate in the preparation of the composite absorbent. Simultaneously, a portion of the liquid phase from stripping column 4 is extracted and sent to distillation unit 6 for separation and purification to obtain high-purity liquid trichlorosilane.

[0048] Path 2: The high-purity liquid trichlorosilane produced by the distillation unit 6 is directly fed into the inlet of the stripping column 4, and liquid trichlorosilane is quantitatively supplied into the column to maintain the predetermined ratio of the composite absorbent in the column.

[0049] Path 3: The inlet of the hydrogen chloride-containing composite rich liquid produced by the absorption tower 3 to the stripping tower 4; the composite lean liquid produced after the hydrogen chloride-containing composite rich liquid is stripped in the stripping tower 4; and the composite absorbent liquid is mixed in the bottom of the stripping tower 4.

[0050] For example, the bottom of the stripping column 4 may be provided with a stripping column inlet, through which liquid substances from the three paths mentioned above can be introduced into the stripping column 4. For example, the bottom of the stripping column 4 may also be provided with two or three stripping column inlets, through which liquid substances from the three paths mentioned above can be introduced into the stripping column 4.

[0051] In this step, liquid trichlorosilane is used as the core component of the composite absorbent. TCS molecules have a stronger affinity for HCl molecules. Under low-temperature conditions, the saturated solubility of HCl in TCS is much higher than that of the pure STC system, thereby improving the hydrogen chloride absorption capacity of the entire absorption system.

[0052] Furthermore, in some possible implementations, in step S3, the mass percentage of trichlorosilane in the predetermined ratio of the composite absorbent is greater than or equal to 90% to improve the solubility of HCl.

[0053] The pre-mixed composite absorbent of this embodiment, relying on the high HCl solubility of TCS, can significantly reduce the absorbent circulation flow rate under the same tail gas treatment load, directly reducing the power consumption of the circulation pump. At the same time, the system produces its own chlorosilane in a closed-loop formulation of the composite absorbent, without introducing external impurities, and will not disrupt the purity balance of materials in reduction furnace 8 and the cold hydrogenation system.

[0054] Furthermore, in some possible implementations, in step S3, liquid trichlorosilane is added to the analytical column 4 at a predetermined flow rate to maintain a predetermined ratio of composite absorbent. The predetermined flow rate can range from 1 t / h to 5 t / h (tons per hour).

[0055] Furthermore, in some possible implementations, in step S4, at least a portion of the composite absorbent is cooled and then fed into the absorption tower 3. The composite absorbent is in countercurrent contact with the gaseous tail gas, and the absorption tower 3 produces a hydrogen chloride-containing composite rich liquid and a hydrogen-rich mixed gas, specifically including:

[0056] S41: At least a portion of the composite absorbent is fed into the cryogenic heat exchanger 7 to cool the composite absorbent to a first temperature.

[0057] S42: Send the cooled composite absorbent liquid into absorption tower 3.

[0058] The first temperature range is -70℃ to -65℃. Understandably, the first temperature can be any specific temperature value within -70℃ to -65℃, or it can be any temperature range within -70℃ to -65℃, and this application does not make any specific limitation in this regard.

[0059] In this step, the composite absorbent is cooled to -70℃ to -65℃ before being fed into absorption tower 3, which can further increase the upper limit of HCl solubility in the composite absorbent. In this scheme, the composite absorbent is mainly composed of TCS. Under cryogenic conditions of -70℃ to -65℃, the increase in refrigeration unit load is limited, but the HCl absorption capacity is significantly increased. The gas-liquid countercurrent contact mode maximizes the gas-liquid mass transfer contact time, ensuring complete HCl removal.

[0060] More specifically, in some possible implementations, a circulation pump is provided at the outlet of the analytical column 4. The specific operation process of the above steps is as follows:

[0061] Start the circulating pump to extract the composite absorbent liquid that has been regenerated in the bottom of the analytical tower 4, and send at least a portion of the composite absorbent liquid into the low-temperature heat exchanger 7.

[0062] The composite absorbent is cooled to the first temperature by exchanging heat through the cryogenic heat exchange medium in the low-temperature heat exchanger 7.

[0063] The low-temperature composite absorbent liquid, after undergoing deep cooling, is sprayed into the tower from the top of absorber tower 3 and flows slowly from top to bottom along the packing layer; the pressurized gas phase tail gas flows upward from the bottom of the tower, and the gas and liquid phases fully come into countercurrent contact on the surface of the packing.

[0064] The hydrogen chloride component in the gas phase tail gas is selectively dissolved by the low-temperature composite absorbent, and the liquid phase is enriched with HCl to form a hydrogen chloride-containing composite rich liquid, which is collected at the bottom of absorber 3; the gas phase after the removal of hydrogen chloride is a hydrogen-rich mixed gas, which is discharged from the top of absorber 3.

[0065] Furthermore, in some possible implementations, in step S5, the hydrogen chloride-containing composite rich liquid is fed into the stripping tower 4 for stripping, and the stripping tower 4 produces gaseous hydrogen chloride and composite absorbent liquid. Specifically, the temperature of the bottom of the stripping tower 4 is controlled at a second temperature.

[0066] The second temperature ranges from 85°C to 98°C. Understandably, the second temperature can be any specific temperature value within the range of 85°C to 98°C, or it can be any temperature range within the range of 85°C to 98°C; this application does not impose any specific limitation on it.

[0067] The boiling point of TCS at atmospheric pressure is only 31.8℃, far lower than that of STC at 57.6℃. The composite absorbent of this application uses TCS as the main component, therefore the heating temperature required for removing dissolved HCl in the stripping column 4 is lower. Stripping column 4 does not need to maintain the high-temperature operating conditions of the existing pure STC system, significantly reducing low-pressure steam consumption. Simultaneously, the low-temperature stripping condition reduces the high-temperature decomposition side reactions of chlorosilanes, lowering material loss.

[0068] More specifically, in some implementations, this step is performed as follows:

[0069] The hydrogen chloride-containing composite rich solution produced at the bottom of absorber 3 is transported to the interior of stripping tower 4.

[0070] Start the heating unit of the bottom of the stripping column 4 to stabilize the liquid phase temperature of the bottom of the stripping column 4 at the second temperature.

[0071] Inside the stripping tower 4, the hydrogen chloride dissolved in the composite rich liquid is desorbed and released by heating. It is then extracted from the top of the stripping tower 4 in the form of gaseous hydrogen chloride and transported to the cold hydrogenation unit 9 for recycling as raw material.

[0072] The liquid phase after HCl removal is retained in the bottom of the stripping tower 4 and used to participate in the formation of a composite absorbent with a predetermined ratio, which is continuously circulated and supplied to the absorption tower 3.

[0073] Furthermore, in some possible embodiments, in step S6, the hydrogen-rich mixed gas is fed into the adsorption device 5 to obtain high-purity hydrogen. Since the composite absorbent in this scheme has no external impurities and its HCl solubility is high, HCl removal is more thorough, resulting in fewer impurities in the hydrogen-rich mixed gas. Therefore, there is no need to add an adsorption protective bed to the adsorption device 5, simplifying the equipment and saving costs. Simultaneously, fewer impurities in the hydrogen-rich mixed gas reduce the adsorption load on the adsorption device 5, reducing the use of adsorbent and extending the service life of the adsorption device 5.

[0074] In some possible implementations, this step specifically includes the following operations:

[0075] The hydrogen-rich mixed gas discharged from the top of the absorption tower 3 is introduced into the adsorption device 5, trace chlorosilane impurities in the mixed gas are selectively adsorbed through the activated carbon adsorption column, and high-purity hydrogen is produced after impurity removal; the high-purity hydrogen is delivered to the reduction furnace 8 to participate in the polysilicon deposition reaction in circulation, or delivered to the cold hydrogenation unit 9 for recycling.

[0076] Further, in some embodiments, the method further comprises the step:

[0077] S7: at least part of the liquid-phase chlorosilane is fed into the rectification device 6 to obtain liquid-phase trichlorosilane.

[0078] This step is a supporting closed-loop material purification process for the entire recovery process, takes over the liquid-phase chlorosilane mixture produced by condensation in step S1, and relies on the boiling point separation characteristic of the rectification device 6 to purify high-purity liquid-phase trichlorosilane. The purified TCS is refluxed to the desorption tower 4 in step S3, and is continuously supplied as the core raw material for preparing the composite absorbent.

[0079] This embodiment can realize a self-sufficient closed loop of materials inside the system, no need to purchase external trichlorosilane, avoid the risk of introducing external impurities, and the material components of the entire recovery system, reduction furnace 8 and cold hydrogenation unit are always kept balanced, without damaging the material purity system of the whole polysilicon process. Meanwhile, the silicon tetrachloride by-produced from rectification can be directly delivered to the cold hydrogenation unit 9 for reuse, so as to maximize the recovery of all valuable components in the condensed liquid-phase chlorosilane and improve the comprehensive material utilization rate of the entire tail gas recovery process.

[0080] Further, in some possible embodiments, step S7 specifically comprises:

[0081] S71: the liquid-phase chlorosilane is fed into the desorption tower 4, and the liquid-phase chlorosilane participates in forming the composite absorbent.

[0082] S7: at least part of the composite absorbent is fed into the rectification device 6 to obtain liquid-phase trichlorosilane.

[0083] In step S71, the liquid-phase chlorosilane mixture produced by the condensing unit 1 in step S1 is delivered to the liquid inlet of the desorption tower 4 through an independent pipeline. The mixture naturally contains TCS and STC components, which are directly mixed into the circulating liquid phase at the bottom of the desorption tower 4 to initially participate in the proportioning adjustment of the composite absorbent, buffer the short-term supply fluctuation of TCS in the rectification device 6, and avoid a transient drop in the TCS proportion of the composite absorbent.

[0084] In step S72, a branch line can be drawn from the reboiler circulation line of the stripping column 4, and a fixed proportion of the composite absorbent can be drawn into the feed inlet of the distillation unit 6 through a flow control valve. Inside the distillation unit 6, the chlorosilane components are separated by controlling temperature, pressure, and reflux ratio. High-purity liquid trichlorosilane is collected from the top side line of the distillation column, while the silicon tetrachloride-enriched heavy component at the bottom is collected and sent to the cooling hydrogenation unit 9 for reuse. The high-purity liquid trichlorosilane purified at the top of the column is returned to the feed inlet of the stripping column 4 through the reflux line, precisely replenishing the TCS consumed by the composite absorbent and stably maintaining the predetermined ratio of the composite absorbent in the stripping column 4.

[0085] On the other hand, this application provides a reduction tail gas recovery system for polysilicon production, such as... Figure 2 As shown, it includes a condensation device 1, a compression device 2, an absorption tower 3, a desorption tower 4, and an adsorption device 5.

[0086] The condensing unit 1 is used to receive the high-temperature reduction tail gas discharged from the reduction furnace 8, cool and condense the reduction tail gas, and separate it into two materials: liquid chlorosilane and gaseous tail gas. The condensing unit 1 is equipped with a gaseous outlet and a liquid outlet. The gaseous outlet delivers non-condensable gaseous tail gas, and the liquid outlet delivers the liquefied chlorosilane mixture.

[0087] The compression device 2 is connected between the gas phase outlet of the condensation device 1 and the air inlet of the absorption tower 3. The compression device 2 is used to receive the condensed gas phase tail gas and pressurize it, then deliver the pressurized gas phase tail gas to the bottom air inlet of the absorption tower 3, so that the gas phase tail gas enters the absorption tower 3 from bottom to top.

[0088] The inlet of the stripping tower 4 is connected to the outlet of the absorption tower 3, and the inlet of the stripping tower 4 is used to add liquid trichlorosilane to form a composite absorbent with a predetermined ratio within the stripping tower 4. The outlet of the stripping tower 4 is connected to the inlet of the absorption tower 3 to supply the composite absorbent to the absorption tower 3. The absorption tower 3 is used to bring the pressurized gaseous tail gas into countercurrent contact with the composite absorbent to form a hydrogen chloride-containing composite rich liquid and a hydrogen-rich mixed gas. The stripping tower 4 is used to strip the hydrogen chloride in the hydrogen chloride-containing composite rich liquid into gaseous hydrogen chloride.

[0089] For example, the analytical tower 4 can be provided with multiple liquid inlets, such as a rich liquid inlet and a supplementary liquid inlet.

[0090] Specifically, the rich liquid inlet of the stripping tower 4 is connected to the bottom outlet of the absorption tower 3 via a pipeline. The hydrogen chloride-containing composite rich liquid produced at the bottom of the absorption tower 3 can be pumped into the stripping tower 4 by differential pressure or a transfer pump. The supplementary inlet of the stripping tower 4 is used to introduce liquid trichlorosilane. After entering the stripping tower 4, the liquid trichlorosilane mixes with the circulating liquid phase inside the tower to form a composite absorbent with a predetermined ratio. An absorbent outlet is provided at the bottom of the stripping tower 4, which is connected to the top inlet of the absorption tower 3 via a pipeline, allowing for the continuous delivery of the regenerated composite absorbent to the top of the absorption tower 3, achieving top-down spraying of the composite absorbent.

[0091] In this process, a countercurrent gas-liquid contact condition is formed inside absorber 3. The pressurized gas phase tail gas and the low-temperature composite absorbent are in full countercurrent contact, and the hydrogen chloride component in the gas phase is selectively dissolved by the composite absorbent. The bottom of absorber 3 produces a hydrogen chloride-rich composite liquid containing dissolved HCl, and the top of absorber 3 produces a hydrogen-rich mixed gas after the removal of hydrogen chloride.

[0092] Furthermore, in some embodiments, the stripping tower 4 is equipped with a reboiler heating unit. Before entering the reboiler of the stripping tower 4, the hydrogen chloride-containing composite rich liquid first flows through the heating unit to raise its temperature and reach the operating temperature for stripping. In some more specific embodiments, the reboiler heating unit can be a heat exchange device. This heat exchange device includes a first heat exchange channel and a second heat exchange channel. The first heat exchange channel can be connected between the liquid outlet of the stripping tower 4 and the liquid inlet of the absorption tower 3, and the second heat exchange channel can be connected between the liquid outlet of the absorption tower 3 and the liquid inlet of the stripping tower 4. This configuration enables heat exchange between the low-temperature material in the absorption tower 3 and the high-temperature material in the stripping tower 4, achieving heat energy recovery and utilization.

[0093] Specifically, the hydrogen chloride-containing composite rich solution entering the stripping tower 4 undergoes a stripping reaction under heating conditions in the tower bottom. The hydrogen chloride dissolved in the liquid phase is separated into gaseous hydrogen chloride, which is collected from the top of the stripping tower 4 and can be transported to the polycrystalline silicon cold hydrogenation unit 9 for recycling as raw material. The liquid phase after HCl removal in the bottom of the stripping tower 4 is the regenerated composite absorbent, which is continuously circulated to the absorption tower 3.

[0094] Furthermore, the adsorption device 5 is connected to the outlet of the absorption tower 3 for purifying the hydrogen-rich mixed gas. Specifically, the adsorption device 5 is connected to the top outlet of the absorption tower 3 to receive the hydrogen-rich mixed gas produced by the absorption tower 3. An activated carbon adsorption column is installed inside the adsorption device 5. The hydrogen-rich mixed gas flows through the activated carbon adsorption column to remove trace amounts of chlorosilane impurities from the mixed gas, purifying it to obtain high-purity hydrogen that meets the reuse standards of the reduction furnace 8 or the cold hydrogenation unit 9.

[0095] In one optional embodiment, the reduction tail gas recovery system is further equipped with a distillation unit 6. The liquid phase outlet pipe of the condenser 1 is connected to the inlet of the stripping tower 4, as described above, and the liquid chlorosilane mixture obtained by condensation and separation can be sent to the stripping tower 4 to participate in the preparation of the composite absorbent. The feed pipe of the distillation unit 6 is connected to the outlet branch of the stripping tower 4, as described above, and a portion of the composite absorbent can be drawn and sent to the distillation unit 6 for high-purity liquid trichlorosilane separation and purification through distillation. The purified liquid trichlorosilane can be refluxed to the inlet of the stripping tower 4, as described above, to continuously and stably supply the TCS material required for constructing the composite absorbent.

[0096] In one alternative embodiment, the reduction tail gas recovery system is further equipped with a circulation pump, which is installed between the liquid outlet of the stripping tower 4 and the liquid inlet of the absorption tower 3. For example, the circulation pump is installed on the circulation pipeline between the absorbent liquid outlet and the liquid inlet at the top of the absorption tower 3. The circulation pump provides power for the circulation and transportation of the composite absorbent liquid, ensuring that the composite absorbent liquid is stably and continuously transported to the top of the absorption tower 3 for spraying.

[0097] In one optional embodiment, the reduction tail gas recovery system is further equipped with a cryogenic heat exchanger 7, which is arranged in series in the circulation pipeline between the outlet of the desorption tower 4 and the inlet of the absorption tower 3. More specifically, the cryogenic heat exchanger 7 can be arranged between the pump outlet of the aforementioned circulation pump and the inlet of the absorption tower 3, with the pump inlet of the circulation pump connected to the outlet of the desorption tower 4. The high-temperature composite absorbent discharged from the desorption tower 4 is first passed into the cryogenic heat exchanger 7 for deep cooling, and then sent into the absorption tower 3 for hydrogen chloride absorption reaction.

[0098] For example, the condensing device 1 may be a shell-and-tube type two-stage shallow cooling condenser, and the heat exchange medium may be circulating chilled water.

[0099] For example, the compression device 2 can be a multi-stage reciprocating hydrogen compressor, equipped with a buffer tank and an oil-gas separation unit.

[0100] For example, both the absorption tower 3 and the desorption tower 4 are packed towers, filled with regular metal corrugated packing to increase the gas-liquid mass transfer contact area.

[0101] For example, the reboiler heating unit of analytical column 4 can employ a low-pressure steam coil heat exchanger.

[0102] For example, the adsorption device 5 can be a PSA pressure swing adsorption purification device, which is filled with molecular sieve adsorbent.

[0103] For example, the low-temperature heat exchanger 7 can be a shell-and-tube cryogenic heat exchanger, and the heat exchange medium can be ethylene glycol refrigerant at -70°C.

[0104] For example, the circulating pump can be a corrosion-resistant magnetic centrifugal pump, which is suitable for conveying chlorosilane media.

[0105] For example, the distillation apparatus 6 can be a trichlorosilane purification distillation column, equipped with a reboiler and a top condenser.

[0106] The operating logic of the recovery system in this embodiment is as follows: High-temperature tail gas from the reduction furnace 8 enters the condenser 1 for cooling and liquefaction, separating the liquid phase chlorosilane from the gaseous tail gas. The gaseous tail gas is pressurized by the compressor 2 and then sent to the bottom of the absorption tower 3. Liquid trichlorosilane is continuously replenished in the desorption tower 4 to form a composite absorbent. The composite absorbent is pumped to the low-temperature heat exchanger 7 for deep cooling, and then sprayed downwards from the top of the absorption tower 3, contacting the pressurized gaseous tail gas from bottom to top in a countercurrent flow. The hydrogen chloride in the gaseous phase is dissolved by the composite absorbent. The hydrogen chloride-rich composite solution at the bottom of the absorption tower 3 is sent to the desorption tower 4 for heating and desorption. The gaseous hydrogen chloride is collected from the top of the tower for reuse, and the composite absorbent is recycled from the bottom of the tower. The hydrogen-rich mixed gas at the top of the absorption tower 3 is sent to the adsorption unit 5 for purification to obtain high-purity hydrogen.

[0107] The polysilicon reduction tail gas recovery system provided in this application adds liquid trichlorosilane to the desorption tower 4 to form a composite absorbent with a predetermined ratio, and uses this composite absorbent to absorb hydrogen chloride. Compared with traditional processes, trichlorosilane has a higher solubility for HCl. Therefore, the composite absorbent of this application has a higher solubility for HCl, which can reduce the amount of absorbent (i.e., composite absorbent) used. Its circulation flow rate is significantly reduced, thereby reducing the load and power consumption of the absorbent circulation device. At the same time, it simultaneously reduces the amount of steam required for desorption heating and reduces the load on the refrigeration unit. In this way, the power consumption and steam consumption of the entire tail gas recovery process are significantly reduced, effectively reducing the overall energy consumption of the tail gas recovery process, and thus significantly reducing the overall production cost of polysilicon production. At the same time, the reduced absorbent circulation flow rate required for tail gas recovery is conducive to the stable operation of the tail gas recovery system, reduces the risk of unqualified hydrogen chloride removal due to insufficient absorbent supply, and improves the stability of the tail gas recovery process.

[0108] Example: A 3000-ton / month polysilicon plant was used. Liquid trichlorosilane was added to the stripping tower 4 to form a composite absorbent with a predetermined ratio. The initial temperature of the composite absorbent after cooling was -65℃. The pressure inside the absorption tower 3 was 0.9 MPa. The bottom temperature of the stripping tower 4 was 98℃. Test results: HCl solubility was 14.9%, and the circulation flow rate was 210 m³ / s. 3 / h; steam consumption is 2.1t / h, and HCl removal rate is consistently above 99.9%.

[0109] Comparative Example: A 3000-ton / month polysilicon plant was used, with STC as the absorbent. The absorbent was cooled to -65℃ before entering absorption tower 3; the pressure inside absorption tower 3 was 1.2 MPa; the reactor temperature of desorption tower 4 was 120℃. Test Results: HCl solubility was 8.2%, and the circulation flow rate was 270 m³ / h. 3 / h; Steam consumption is 4.2t / h, the packing volume of absorber 3 is large, and the HCl at the outlet of absorber 3 exceeds the standard when the cold hydrogenation STC is reduced.

[0110] Practical verification has shown that the method and system for recovering reduction tail gas in polysilicon production of this application have at least the following advantages:

[0111] 1. Benefits in power consumption during transportation: The saturated solubility of HCl is increased to 15.7%, the absorbent circulation flow rate is reduced by 25% under the same load, the power consumption of the circulation pump is reduced by 52%, and the annual power saving is 960,000 kWh for a production capacity of 10,000 tons.

[0112] 2. Steam energy consumption benefits: With the operating temperature of stripper tower 4 reduced, the steam consumption per stripper unit of the pure TCS system is 0.35~0.5t steam / SI, compared with 0.7~1.0t steam / SI of the pure STC system, resulting in a significant reduction in steam consumption.

[0113] 3. Benefits from reduced refrigeration power consumption: The load on the refrigeration unit was reduced by 300kW, and the power consumption related to refrigeration decreased by 14% year-on-year, resulting in an annual power saving of 2.35 million kWh for a production capacity of 10,000 tons.

[0114] 4. Load adaptation benefits: No longer relying solely on silicon tetrachloride supply, alleviating the supply pressure of cold hydrogenation STC production, the HCl removal qualification rate of absorption tower 3 is stable at 100%, and the unit operates at 0~100% load without process fluctuations.

[0115] 5. Closed-loop material synergy benefits: The absorbent is all self-produced chlorosilane, with no external impurities entering, reducing the content of trace impurities in the hydrogen at the top of the tower, extending the regeneration cycle of the downstream PSA adsorbent by 40%, and reducing the cost of adsorbent replacement and maintenance.

[0116] 6. Core production cost benefits: Simultaneous reduction of consumption in multiple dimensions such as absorbent circulation flow, desorption steam, refrigeration power consumption, and absorbent operation and maintenance, resulting in a significant reduction in the overall energy consumption of the entire reduction tail gas recovery process, thereby reducing the overall production cost of polysilicon production from the source of the process.

[0117] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A method for recovering reduction tail gas in polycrystalline silicon production, characterized in that, Including the following steps: The reduction tail gas was condensed to obtain liquid chlorosilane and gaseous tail gas. The gaseous tail gas is pressurized and then sent into the absorption tower; Liquid trichlorosilane is added to the stripping column to form a composite absorbent with a predetermined ratio inside the stripping column; At least a portion of the composite absorbent is cooled and then fed into the absorption tower, where the composite absorbent is in countercurrent contact with the gas phase tail gas, and the absorption tower produces a hydrogen chloride-containing composite rich liquid and a hydrogen-rich mixed gas. The hydrogen chloride-containing composite rich liquid is fed into the desorption tower for desorption, and the desorption tower produces gaseous hydrogen chloride and the composite absorbent liquid. The hydrogen-rich mixed gas is fed into an adsorption device to obtain high-purity hydrogen.

2. The method for recovering reduction tail gas in polycrystalline silicon production according to claim 1, characterized in that, It also includes the following steps: At least a portion of the liquid-phase chlorosilane is fed into a distillation apparatus to obtain the liquid-phase trichlorosilane.

3. The method for recovering reduction tail gas in polycrystalline silicon production according to claim 2, characterized in that, At least a portion of the liquid-phase chlorosilane is fed into a distillation unit to obtain the liquid-phase trichlorosilane; comprising: The liquid chlorosilane is fed into the stripping column, where it participates in the formation of the composite absorbent. At least a portion of the composite absorbent is fed into the distillation apparatus to obtain the liquid trichlorosilane.

4. The method for recovering reduction tail gas in polycrystalline silicon production according to any one of claims 1-3, characterized in that, The mass percentage of trichlorosilane in the composite absorbent is greater than or equal to 90%.

5. The method for recovering reduction tail gas in polycrystalline silicon production according to any one of claims 1-3, characterized in that, At least a portion of the composite absorbent is cooled and then fed into the absorption tower, where it comes into countercurrent contact with the gaseous tail gas. The absorption tower produces a hydrogen chloride-containing composite rich liquid and a hydrogen-rich mixed gas; comprising: At least a portion of the composite absorbent is fed into a cryogenic heat exchanger to cool the composite absorbent to a first temperature. The cooled composite absorbent is fed into the absorption tower; The first temperature range is -70℃ to -65℃.

6. The method for recovering reduction tail gas in polycrystalline silicon production according to any one of claims 1-3, characterized in that, The gaseous tail gas is pressurized and then sent into an absorption tower; including: The gas phase exhaust gas is fed into a compression device to pressurize the gas phase exhaust gas to a first pressure value; The pressurized gaseous tail gas is sent into the absorption tower; The first pressure value ranges from 0.9 MPa to 1 MPa.

7. The method for recovering reduction tail gas in polycrystalline silicon production according to any one of claims 1-3, characterized in that, In the step of feeding the hydrogen chloride-containing composite rich liquid into the desorption tower for desorption, and the desorption tower producing gaseous hydrogen chloride and the composite absorbent liquid, the bottom temperature of the desorption tower is controlled at a second temperature. The second temperature range is 85℃~98℃.

8. The method for recovering reduction tail gas in polycrystalline silicon production according to any one of claims 1-3, characterized in that, The reduction tail gas is condensed to obtain liquid-phase chlorosilane and gaseous tail gas; including: The reduction tail gas is sent to a condenser to cool it to a third temperature to obtain the liquid chlorosilane and the gaseous tail gas. The third temperature range is -10℃ to -5℃.

9. A reduction tail gas recovery system for polycrystalline silicon production, characterized in that, It includes condensation units, compression units, absorption towers, desorption towers, and adsorption units; The condensation device is used to condense the reduction tail gas into liquid-phase chlorosilane and gas-phase tail gas. The compression device is connected between the gas phase outlet of the condensation device and the gas inlet of the absorption tower; the compression device is used to pressurize the gas phase tail gas. The inlet of the analytical tower is connected to the outlet of the absorption tower, and the inlet of the analytical tower is used to add liquid trichlorosilane to form a composite absorbent with a predetermined ratio in the analytical tower; the outlet of the analytical tower is connected to the inlet of the absorption tower to provide the composite absorbent to the absorption tower. The absorption tower is used to bring the pressurized gaseous tail gas into countercurrent contact with the composite absorption liquid to form a hydrogen chloride-containing composite rich liquid and a hydrogen-rich mixed gas; the desorption tower is used to desorb the hydrogen chloride in the hydrogen chloride-containing composite rich liquid into gaseous hydrogen chloride. The adsorption device is connected to the outlet of the absorption tower and is used to purify the hydrogen-rich mixed gas.

10. The polycrystalline silicon production reduction tail gas recovery system according to claim 9, characterized in that, The reduction tail gas recovery system further includes a distillation unit; the liquid outlet of the condensation unit is connected to the inlet of the stripping column; the distillation unit is connected to the outlet of the stripping column; and / or, The reduction tail gas recovery system further includes a circulation pump connected between the outlet of the desorption tower and the inlet of the absorption tower; and / or, The reduction tail gas recovery system also includes a low-temperature heat exchanger; the low-temperature heat exchanger is connected between the liquid outlet of the desorption tower and the liquid inlet of the absorption tower.

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