Separation and recovery system and method for polycrystalline silicon reduction tail gas

Abstract

The invention relates to the field of polycrystalline silicon, and discloses a polycrystalline silicon reduction tail gas separation and recovery system and method.The recovery system comprises a pretreatment unit, a desorption tower, a first cooling unit, a flash tank, a separation unit and the like. The content of the DCS in the trichlorosilane product is improved, the proportion of the DCS in the obtained trichlorosilane product is controlled by adjusting the pressure of the flash tank, and the yield and the economic benefit of the polycrystalline silicon product are improved; on the other hand, the one-time recovery rate of hydrogen chloride is improved, and the liquid-phase material from the flash tank directly enters the separation unit, so that the process is simplified, the energy consumption is reduced, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of polysilicon, and in particular to a system and method for separating and recovering polysilicon reduction tail gas. Background Art

[0002] The modified Siemens process is the mainstream process for polysilicon production, which is mainly achieved by reducing trichlorosilane (TCS) vapor-deposited silicon in a reduction furnace using hydrogen. Experiments and production practices have proved that introducing less than 5wt% of dichlorosilane (DCS) into the reduction furnace intake is conducive to reducing energy consumption and improving the primary conversion rate. The chlorosilane fed to the reduction furnace comes from the distillation process, including hydrogenated refined materials and reduced refined materials, wherein the hydrogenated refined materials come from the cold hydrogenation process, and the industrial silicon powder is converted into chlorosilane and then separated and purified to obtain pure TCS. The reduced refined material comes from the tail gas of the reduction furnace, which is purified by the distillation process after condensation, compression, absorption, and desorption, and includes TCS and DCS. At present, the DCS in the reduced refined material in polysilicon production enterprises is generally in the range of 2-5wt%, so it is necessary to introduce additional DCS and reduce refined materials before entering the reduction furnace, and the price of DCS is high, which is more than 10 times that of TCS, so it is necessary to recover DCS.

[0003] The utility model of CN217498694U discloses a chlorosilane recovery system for polysilicon reduction tail gas, wherein silicon powder is removed from the reduction tail gas in a silicon powder filter, and then the reduction tail gas enters a multi-stream heat exchanger for cooling, and then enters a circulating water cooler, a heat recovery heat exchanger, a chilled water heat exchanger and a Freon heat exchanger in sequence for four condensations, and the condensed chlorosilane directly enters a chlorosilane storage tank, and the reduction tail gas not containing chlorosilane re-enters a heat recovery heat exchanger to recover cold energy, and is finally discharged.

[0004] The utility model of CN206529298U discloses a polysilicon reduction tail gas energy-saving spraying chlorosilane recovery device, which replaces the low-temperature spraying equipment in the CDI tail gas recovery device with a normal-temperature spraying equipment, thereby saving equipment investment and reducing energy consumption.

[0005] However, the above-mentioned chlorosilane recovery system only separates and recovers chlorosilane, and does not further separate and recover DCS, so as to achieve the purpose of increasing the DCS ratio in the reducing refined material. In addition, the recovered chlorosilane contains HCl, which will cause tower pressure fluctuations when entering the subsequent distillation process, increase the difficulty of operation, and affect product quality.

[0006] Patent CN110240165A proposes a method and device for recovering dichlorosilane from polysilicon reduction tail gas. The reduction tail gas is subjected to low-pressure condensation treatment to separate gaseous hydrogen, hydrogen chloride and trace impurities and liquid chlorosilane; the gaseous hydrogen, hydrogen chloride and trace impurities are absorbed by an absorption liquid, and the unabsorbed hydrogen is separated and sent to the polysilicon production process, while the absorption liquid that absorbs hydrogen chloride and trace impurities is mixed with liquid chlorosilane as rich liquid chlorosilane to form a chlorosilane mixed liquid; the chlorosilane mixed liquid is gradually separated to gradually separate liquid silicon tetrachloride, liquid trichlorosilane, liquid dichlorosilane and gaseous hydrogen chloride, and at least a part of the liquid silicon tetrachloride is used as an absorption liquid. Thereby, the quality of the recovered hydrogen can be effectively improved and the system energy consumption and steam consumption can be reduced. Although the patent recovers DCS through a cryogenic device, the recovered DCS still contains a large amount of HCl.

[0007] The patent CN101357287A proposes a method for recovering hydrogen chloride from tail gas of polysilicon production. The method first converts trichlorosilane and silicon tetrachloride in the tail gas into liquid state, while hydrogen, hydrogen chloride and dichlorosilane in the tail gas remain in gaseous state, so that hydrogen, hydrogen chloride and dichlorosilane are separated, and then the gaseous hydrogen chloride and dichlorosilane are further dissolved in an absorbent to make them liquid, so as to separate them from the gaseous hydrogen, and then hydrogen chloride and dichlorosilane are resolved from the absorbent, and the gaseous dichlorosilane is converted into liquid state again so as to separate it from the gaseous hydrogen chloride, so as to achieve the purpose of recovering hydrogen chloride. Although the patent recovers hydrogen chloride in the tail gas, it does not further separate and recover dichlorosilane and trichlorosilane to achieve the purpose of increasing the proportion of dichlorosilane in trichlorosilane. Summary of the invention

[0008] The purpose of the present invention is to overcome the problem in the prior art that the DCS ratio in the refined material is insufficient and DCS needs to be additionally introduced, and to provide a separation and recovery system and method for polysilicon reduction tail gas. The recovery system and method can fully separate and recover HCl and DCS in the tail gas, so that the DCS content in the trichlorosilane product obtained thereby meets the subsequent feed requirements.

[0009] In order to achieve the above-mentioned object, the first aspect of the present invention provides a separation and recovery system for polysilicon reduction tail gas, which comprises:

[0010] A pre-treatment unit is used to treat the gaseous polysilicon reduction tail gas into liquid and separate and remove the hydrogen at the same time;

[0011] A desorption tower, whose feed inlet is connected to the liquid material outlet of the pre-treatment unit, the desorption tower has a first gaseous material outlet at the top and a first liquid material outlet at the bottom;

[0012] A first cooling unit connected to the first gaseous material outlet, the first cooling unit having a first part of HCL gas outlet and a second liquid material outlet;

[0013] A flash tank, whose feed port is connected to the second liquid material outlet, and the flash tank has a second portion of HCL gas outlet and a third liquid material outlet;

[0014] A separation unit, whose feed inlet is connected to the first liquid material outlet and the third liquid material outlet, and the separation unit has a dichlorosilane product outlet, a trichlorosilane product outlet and a silicon tetrachloride product outlet, wherein the separation unit is arranged so that the trichlorosilane product obtained at the trichlorosilane product outlet contains 8-10wt% of dichlorosilane.

[0015] The liquid material coming out of the first liquid material outlet of the desorption tower mainly contains dichlorosilane, trichlorosilane and silicon tetrachloride, and the gas coming out of the first gaseous material outlet mainly contains HCl, dichlorosilane and trichlorosilane. A part of HCl is first separated out by the first cooling unit, and then the material liquid mainly containing HCl, dichlorosilane and trichlorosilane is flashed by the flash tank, so that the HCl is separated more thoroughly. The flash tank is arranged so that the HCl content in the liquid phase material coming out after the flashing does not exceed 0.35wt%. The flashed material is then separated into the separation unit together with the liquid material coming out of the first liquid material outlet. The trichlorosilane product obtained does not contain HCl, and the content of dichlorosilane meets the subsequent feeding requirements.

[0016] A second aspect of the present invention provides a method for separating and recovering polysilicon reduction tail gas, wherein the method comprises:

[0017] Pre-treating the gaseous polysilicon reduction tail gas to obtain a liquid material to be treated;

[0018] The liquid-phase material to be processed is subjected to a first separation treatment to obtain a first gaseous material and a first liquid material;

[0019] Cooling the first gaseous material to obtain a first portion of HCl gas and a second liquid material;

[0020] flashing the second liquid material to obtain a second portion of HCl gas and a third liquid material;

[0021] The first liquid material and the third liquid material are subjected to a second separation treatment to obtain a dichlorosilane product, a trichlorosilane product and a silicon tetrachloride product, wherein the trichlorosilane product contains 8-10 wt % of dichlorosilane.

[0022] Through the above technical scheme, on the one hand, the recovery of DCS in the tail gas of polysilicon reduction is realized, the content of DCS in the reduced refined material is increased, and the proportion of DCS in the obtained trichlorosilane product is controlled by adjusting the pressure of the flash tank, thereby improving the output and economic benefits of polysilicon products; on the other hand, the primary recovery rate of hydrogen chloride is improved, and the liquid phase material coming out of the flash tank is directly sent to the separation unit, which simplifies the process, saves energy consumption, and is conducive to reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of a separation and recovery system in which the separation unit includes a distillation tower;

[0024] Figure 2 It is a schematic diagram of the structure of the flash tank;

[0025] Figure 3 yes Figure 2 Sectional view of AA in the middle;

[0026] Figure 4 yes Figure 2 Cross-sectional view of the middle BB;

[0027] Figure 5 It is a schematic diagram of the structure when the separation unit contains two distillation towers;

[0028] Figure 6 It is a schematic diagram of the structure when the separation unit contains three distillation towers.

[0029] Description of Reference Numerals

[0030] 1-desorption tower; 101-lower tower; 102-upper tower; 1a-first gaseous material outlet; 1b-first liquid material outlet; 2-first heat exchanger; 2a-first part of HCL gas outlet; 3-first air cooler; 4-first water cooler; 5-first reflux tank; 5b-second liquid material outlet; 6-first pump; 7-first reboiler; 8-flash tank; 8a-second part of HCL gas outlet; 8b-third liquid material outlet; 9-cryogenic cooler; 10 -second pump; 11-distillation tower; 11a-gaseous dichlorosilane outlet; 11b-liquid reduced refined material outlet; 11c-liquid silicon tetrachloride outlet; 12-second air cooler; 13-second water cooler; 14-second reflux tank; 15-third pump; 16-second reboiler; 17-fourth pump; 18-liquid distributor; 19-demister; 20-condensing device; 21-absorption tower; 22-second heat exchanger; 23-third heat exchanger. DETAILED DESCRIPTION

[0031] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0032] In the description of the present application, it should be understood that the terms "upper", "lower", "vertical", "horizontal", "top", "bottom", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0033] The terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second", and "third" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0034] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0035] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0036] In order to achieve the above-mentioned object, the first aspect of the present invention provides a separation and recovery system for polysilicon reduction tail gas, which comprises:

[0037] A pre-treatment unit is used to treat the gaseous polysilicon reduction tail gas into liquid and separate and remove the hydrogen at the same time;

[0038] A desorption tower, whose feed inlet is connected to the liquid material outlet of the pre-treatment unit, the desorption tower has a first gaseous material outlet at the top and a first liquid material outlet at the bottom;

[0039] A first cooling unit connected to the first gaseous material outlet, the first cooling unit having a first part of HCL gas outlet and a second liquid material outlet;

[0040] A flash tank, whose feed port is connected to the second liquid material outlet, and the flash tank has a second portion of HCL gas outlet and a third liquid material outlet;

[0041] A separation unit, whose feed inlet is connected to the first liquid material outlet and the third liquid material outlet, and the separation unit has a dichlorosilane product outlet, a trichlorosilane product outlet and a silicon tetrachloride product outlet, wherein the separation unit is arranged so that the trichlorosilane product obtained at the trichlorosilane product outlet contains 8-10wt% of dichlorosilane.

[0042] There are no special requirements for the structure of the pre-treatment unit, as long as the gaseous polysilicon reduction tail gas can be processed into a liquid state. In the present invention, the pre-treatment unit includes a condensing device, an absorption tower, a second heat exchanger and a third heat exchanger, wherein the condensing device can be a plurality of condensers connected in series, and the reduction tail gas from the polysilicon production unit enters the condensing device and is condensed multiple times, and the gaseous part (mainly containing H2 and HCl) enters the absorption tower again, and after being absorbed by the absorption liquid, the gas discharged from the absorption tower mainly contains H2, which can be used as a production raw material, and the rich liquid containing HCl is heat exchanged in the second heat exchanger to recover heat, and then enters the third heat exchanger together with the liquid from the condensing device for heat exchange, wherein the liquid from the condensing device mainly contains DCS, TCS and STC, and after the third heat exchanger, the liquid from the condensing device enters the third heat exchanger for heat exchange. The liquid after heat exchange in the desorption tower is used as the raw material of the desorption tower and enters the desorption tower through its feed port. HCl, DCS and part of TCS are desorbed in the desorption tower and enter the first cooling unit through the first gaseous material outlet, while the liquid containing TCS and STC is discharged from the first liquid material outlet at the bottom of the desorption tower. After heat exchange with the third heat exchanger, a part of it can be sent to the second heat exchanger, and then sent to the absorption tower after heat exchange with the second heat exchanger. The amount of material sent to the absorption tower meets the liquid-gas ratio of 25-30 in the absorption tower. Therefore, the mass ratio of the first liquid material sent to the absorption tower and the first liquid material sent to the distillation tower is generally 1.5-2.5:1.

[0043] The liquid material coming out of the first liquid material outlet of the desorption tower mainly contains dichlorosilane, trichlorosilane and silicon tetrachloride, and the gas coming out of the first gaseous material outlet mainly contains HCl, dichlorosilane and trichlorosilane. A part of HCl is first separated by the first cooling unit, and then the material liquid mainly containing HCl, dichlorosilane and trichlorosilane is flashed by the flash tank, so as to separate HCl more thoroughly. The flashed material enters the separation unit together with the liquid material coming out of the first liquid material outlet for separation, so that the trichlorosilane product obtained does not contain HCl, and the DCS content meets the subsequent feeding requirements.

[0044] After pretreatment by the pretreatment unit, a liquid phase material to be treated is obtained, and the liquid phase material to be treated will be sent to the analysis tower for the first separation treatment. The liquid phase material to be treated mainly contains HCl, dichlorosilane (DCS), trichlorosilane (TCS) and silicon tetrachloride (STC). Based on the total amount of the liquid phase material to be treated, the amount of HCl can be 0.2-0.5wt%, the amount of DCS can be 2-6wt%, the amount of TCS can be 45-50wt%, the amount of STC can be 45-55wt%, and their total amount is 100wt%.

[0045] In some embodiments, preferably, the first cooling unit comprises: a first heat exchanger, a first air cooler, a first water cooler and a first reflux tank connected in sequence;

[0046] wherein the first heat exchanger is configured to allow the first gaseous material from the first gaseous material outlet to perform a first heat exchange with the gas from the first reflux drum, so as to cool the first gaseous material with the gas from the first reflux drum, and the first heat exchanger has an outlet for the first portion of HCl gas;

[0047] The first air cooler and the first water cooler are configured to gradually cool the first gaseous material into a mixture of liquid and gas;

[0048] The first reflux drum is configured to separate the gas phase and the liquid phase in the liquid and gas mixture, and the liquid outlet of the first reflux drum forms the second liquid material outlet.

[0049] With this structure, the produced gas from the desorption tower mainly containing HCl, dichlorosilane and trichlorosilane can be cooled by the first cooling unit, thereby achieving the effect of preliminarily separating the HCl gas.

[0050] The specific connection relationship between the various parts of the first cooling unit is as follows:

[0051] A first heat exchanger, a first air cooler, a first water cooler and a first reflux tank, the first gaseous material outlet is connected to the first fluid inlet of the first heat exchanger, the first fluid outlet of the first heat exchanger is connected to the first air cooler, the first water cooler and the first reflux tank in sequence, the liquid outlet of the first reflux tank forms the second liquid material outlet, the gas outlet of the first reflux tank is connected to the second fluid inlet of the first heat exchanger, and the second fluid outlet of the first heat exchanger forms the first part of HCL gas outlet.

[0052] In some embodiments, preferably, the liquid outlet of the first reflux tank is also connected to the reflux inlet of the desorption tower. With this solution, part of the liquid in the first reflux tank is refluxed to the desorption tower, so that enough liquid phase contacts the gas phase in the tower.

[0053] In some embodiments, preferably, the desorption tower comprises a lower tower and an upper tower, the upper tower is stacked on the lower tower, the two are connected, the lower tower has a height of 14-18m and an inner diameter of 3.5-5m, and the upper tower has a height of 6-16m and an inner diameter of 2-3m. With this structure, the height and inner diameter of the upper and lower sections of the desorption tower are different, which is conducive to ensuring the gas-liquid exchange efficiency.

[0054] In some embodiments, preferably, the outlet of the second portion of HCl gas is connected to a cryocooler, and the liquid outlet of the cryocooler is connected to the reflux inlet of the flash tank. With this solution, the gas separated from the flash tank is further cooled by the cryocooler to separate the small amount of dichlorosilane remaining therein, and refluxes into the flash tank, which is conducive to improving the recovery rate of DCS.

[0055] In some embodiments, preferably, the flash tank includes a tank body, a liquid distributor is arranged in the tank body, the feed port of the flash tank is connected to the liquid distributor, and a demister is arranged in the tank body above the liquid distributor. With this structure, the liquid can be distributed more evenly through the liquid distributor, and the demister can remove the mist entrained in the gas to ensure the mass transfer efficiency, which is conducive to improving the flash evaporation effect. The demister is generally a standard wire mesh, which is funnel-shaped, and the angle is generally about 120°, and is used to remove mist with a droplet diameter greater than 3-5 μm.

[0056] An online ICP (inductively coupled plasma atomic emission spectrometer) can also be installed at the outlet of the trichlorosilane product to achieve real-time monitoring of the DCS concentration in the trichlorosilane product, and the pressure of the flash tank can be adjusted according to the monitoring results to adjust the material ratio in the reduced refined material.

[0057] In some embodiments, preferably, the separation unit comprises a distillation tower, the top of the distillation tower is provided with the dichlorosilane product outlet, the side wall thereof has the trichlorosilane product outlet, and the side wall of the distillation tower below the trichlorosilane product outlet has the silicon tetrachloride product outlet.

[0058] With the above structure, the separation unit may consist of only one distillation tower or 2-3 distillation towers connected in series.

[0059] In some embodiments, preferably, the separation unit is connected to a second cooling unit, and the second cooling unit includes a second air cooler, a second water cooler, and a second reflux tank connected in sequence;

[0060] The second air cooler and the second water cooler are configured to gradually cool the dichlorosilane product from the dichlorosilane product outlet from a gaseous state to a liquid state, and to separate and discharge the remaining gaseous impurities;

[0061] The second reflux tank is used to store the liquid dichlorosilane product and reflux part of the liquid dichlorosilane product into the distillation tower.

[0062] By adopting the above structure, the gas collected from the upper side of the separation unit mainly containing dichlorosilane can be cooled and liquefied by the second cooling unit, so that the dichlorosilane is liquefied into liquid, and the uncondensed HCl is discharged through the exhaust port when cooled in the second water cooler, and the remaining liquid dichlorosilane product enters the second reflux tank for buffering, thereby ensuring that the liquid dichlorosilane product finally obtained does not contain HCl.

[0063] A second aspect of the present invention provides a method for separating and recovering polysilicon reduction tail gas, wherein the method comprises:

[0064] Pre-treating the gaseous polysilicon reduction tail gas to obtain a liquid material to be treated;

[0065] The liquid-phase material to be processed is subjected to a first separation treatment to obtain a first gaseous material and a first liquid material;

[0066] Cooling the first gaseous material to obtain a first portion of HCl gas and a second liquid material;

[0067] flashing the second liquid material to obtain a second portion of HCl gas and a third liquid material;

[0068] The first liquid material and the third liquid material are subjected to a second separation treatment to obtain a dichlorosilane product, a trichlorosilane product and a silicon tetrachloride product, wherein the trichlorosilane product contains 8-10 wt % of dichlorosilane.

[0069] By adopting the above technical scheme, the gaseous polysilicon tail gas is converted into a liquid phase material to be treated, and HCl, dichlorosilane product, silicon tetrachloride product and trichlorosilane product containing DCS are gradually separated through the first separation treatment, flash evaporation, second separation treatment, etc. The content of DCS in the trichlorosilane product can be any value within the numerical range consisting of any two numbers of 8wt%, 8.5wt%, 9wt%, 9.5wt% and 10wt%.

[0070] In some embodiments, preferably, the flash evaporation pressure is 0.12-0.25 MPaG.

[0071] In some embodiments, preferably, the flash evaporation pressure is 0.17-0.19 MPaG.

[0072] By controlling the flash pressure, the DCS content in the trichlorosilane product can be adjusted. The pressure of the flash tank can be any value within the numerical range consisting of any two numbers among 0.12 MPaG, 0.15 MPaG, 0.17 MPaG, 0.18 MPaG, 0.19 MPaG, 0.2 MPaG, 0.23 MPaG, and 0.25 MPaG.

[0073] In some embodiments, preferably, the mass ratio of the first liquid material to the third liquid material is 0.05-0.07: 1. The mass ratio of the first liquid material to the third liquid material can be any value within a numerical range consisting of any two numbers of 0.05: 1, 0.06: 1, and 0.07: 1.

[0074] In some embodiments, preferably, the method further comprises: returning a portion of the second liquid material to the first separation treatment step, wherein the mass ratio of the returned second liquid material to the liquid material to be treated is 0.1-1: 1. With this solution, part of the liquid in the first reflux tank is refluxed to the desorption tower, so that there is enough liquid phase to contact the gas phase in the tower.

[0075] In some embodiments, preferably, the pressure of the first separation treatment is 0.6-0.8 MPaG. The desorption pressure can be any value within the numerical range of any two numbers of 0.6 MPaG, 0.7 MPaG, and 0.8 MPaG, and the pressure drop during desorption does not exceed 8-10 kPa.

[0076] In some embodiments, preferably, the pressure of the second separation treatment is 0.3-0.65 MPaG. The pressure of the distillation can be any value within the numerical range consisting of any two numbers of 0.3 MPaG, 0.4 MPaG, 0.5 MPaG, and 0.65 MPaG.

[0077] In some embodiments, preferably, the method further comprises: cooling the gaseous dichlorosilane product to obtain a liquid dichlorosilane product, and refluxing a portion of the liquid dichlorosilane product to the second separation step, wherein the temperature of the refluxing liquid dichlorosilane product is 5-15°C lower than the temperature of the gaseous dichlorosilane product obtained in the second separation step. By adopting the above method, the gaseous dichlorosilane is liquefied into liquid, and a small amount of HCl in this process remains in gaseous state and can be separated and sent to a subsequent treatment unit, wherein a small portion of the liquid dichlorosilane can be sent to a subsequent anti-disproportionation fixed bed, and a large portion of the liquid dichlorosilane can be returned to the second separation step, so that there is enough liquid phase to contact the gas phase in the second separation step, to ensure gas-liquid mass transfer and improve the separation effect.

[0078] In some embodiments, preferably, the method further comprises: cooling the second portion of HCl gas to obtain purified HCl gas and a fourth liquid material, and returning the fourth liquid material to the flash evaporation step. With this solution, the gas separated from the flash tank is further cooled by a cryogenic chiller to separate a small amount of dichlorosilane remaining therein, and refluxes into the flash tank, which is beneficial to improving the recovery rate of DCS.

[0079] The present invention will be described in detail below through examples.

[0080] Chlorosilane recovery rate = mass of DCS+TCS+STC in the third liquid material per unit time / mass of DCS+TCS+STC in the second liquid material per unit time × 100%;

[0081] HCL removal rate = (1-the mass of HCL in the third liquid material per unit time / the mass of HCL in the second liquid material per unit time) × 100%;

[0082] DCS recovery rate = the mass of DCS in the third liquid material per unit time / the mass of DCS in the second liquid material per unit time × 100%.

[0083] The following examples or some comparative examples adopt Figure 1-4 The separation and recovery system shown specifically comprises:

[0084] A pre-treatment unit, used to treat the gaseous polysilicon reduction tail gas into liquid, and to separate and remove hydrogen at the same time;

[0085] A desorption tower 1, whose feed inlet is connected to the liquid material outlet of the pre-treatment unit, the desorption tower 1 has a first gaseous material outlet 1a at the top and a first liquid material outlet 1b at the bottom;

[0086] A first cooling unit connected to the first gaseous material outlet, the first cooling unit having a first HCl gas outlet 2a and a second liquid material outlet 5b;

[0087] A flash tank 8, whose feed port is connected to the second liquid material outlet 5b, and the flash tank 8 has a second part of HCl gas outlet 8a and a third liquid material outlet 8b;

[0088] A separation unit, whose feed port is connected to the first liquid material outlet 1b and the third liquid material outlet 8b, and the separation unit has a dichlorosilane product outlet 11a, a trichlorosilane product outlet 11b and a silicon tetrachloride product outlet 11c, wherein the separation unit is arranged so that the trichlorosilane product obtained at the trichlorosilane product outlet 11b contains 8-10wt% of dichlorosilane.

[0089] There are no special requirements for the structure of the pre-treatment unit, as long as the gaseous polysilicon reduction tail gas can be processed into liquid. In this example, the pre-treatment unit includes a condensing device 20, an absorption tower 21, a second heat exchanger 22 and a third heat exchanger 23, wherein the condensing device 20 can be a plurality of condensers connected in series, and the reduction tail gas from the polysilicon production unit enters the condensing device 20 and is condensed multiple times, and the gaseous part (mainly containing H2 and HCl) enters the absorption tower 21 again, and after being absorbed by the absorption liquid, the gas discharged from the absorption tower 21 mainly contains H2, which can be used as a production raw material, and the rich liquid containing HCl is heat exchanged in the second heat exchanger 22 to recover heat, and then enters the third heat exchanger 23 together with the liquid from the condensing device 20 for heat exchange, wherein the liquid from the condensing device 20 mainly contains DCS, TCS and STC, the liquid after heat exchange in the third heat exchanger 23 is used as the raw material of the desorption tower 1 and enters the desorption tower 1 through its feed port. HCl and DCS are desorbed in the desorption tower 1 and enter the first cooling unit through the first gaseous material outlet 1a, while the liquid containing TCS and STC is discharged from the first liquid material outlet 1b at the bottom of the desorption tower 1. After heat exchange with the third heat exchanger 23, a part of it can be sent to the second heat exchanger 22, and after heat exchange with the second heat exchanger 22, it is sent to the absorption tower 21, and the other part is sent to the distillation tower 11, wherein the weight ratio of the part sent to the second heat exchanger 22 to the part sent to the distillation tower 11 is 2.

[0090] The desorption tower 1 includes a lower tower 101 and an upper tower 102, wherein the upper tower 102 is stacked on the lower tower 101, and the two are connected. The height of the lower tower 101 is 14-18m, and the inner diameter is 3.5-5m. The height of the upper tower 102 is 6-16m, and the inner diameter is 2-3m. The lower tower 101 and the upper tower 102 are both filled with fillers, and the fillers can be BX type wire mesh corrugated fillers. The pressure drop in the tower is generally controlled within 8-10kPa. The material from the third heat exchanger 23 can be distributed through the liquid distributor, and it enters the upper part of the lower tower 101. A part of the liquid coming out from the bottom of the desorption tower 1 enters the desorption tower 1 again through the first reboiler 7 to provide sufficient heat to the desorption tower 1.

[0091] The first cooling unit comprises: a first heat exchanger 2, a first air cooler 3, a first water cooler 4 and a first reflux drum 5 which are connected in sequence, wherein the first heat exchanger 2 is configured to allow the first gaseous material from the first gaseous material outlet 1a to perform a first heat exchange with the gas from the first reflux drum 5, so as to cool the first gaseous material using the gas from the first reflux drum 5, the first heat exchanger has the first part of HCl gas outlet 2a, the first air cooler 3 and the first water cooler 4 are configured to allow the first gaseous material to be gradually cooled into a mixture of liquid and gas, the first reflux drum 5 is configured to allow the gas phase and the liquid phase in the mixture of liquid and gas to be separated, and the liquid outlet of the first reflux drum 5 forms the second liquid material outlet 5b, and their specific connection relationship is as follows:

[0092] The first gaseous material outlet 1a is connected to the first fluid inlet of the first heat exchanger 2, the first fluid outlet of the first heat exchanger 2 is connected to the first air cooler 3, the first water cooler 4 and the first reflux tank 5 in sequence, the liquid outlet of the first reflux tank 5 forms the second liquid material outlet 5b, the gas outlet of the first reflux tank 5 is connected to the second fluid inlet of the first heat exchanger 2, the second fluid outlet of the first heat exchanger 2 forms the first part of HCl gas outlet 2a, the liquid outlet of the first reflux tank 5 is connected to the feed port of the flash tank 3 through the first pump 6, and the liquid outlet of the first reflux tank 5 is also connected to the reflux material inlet of the desorption tower 1.

[0093] The gas containing HCl, dichlorosilane and trichlorosilane in the first cooling unit is cooled step by step through the first heat exchanger 2, the first air cooler 3 and the first water cooler 4, and part of the HCl gas and dichlorosilane and trichlorosilane are cooled into liquids, and the gaseous HCl and the liquid dichlorosilane and trichlorosilane+liquid HCl are separated in the first reflux tank 5, wherein the gaseous HCl is discharged in the form of gas after heat exchange and cooling with the first heat exchanger 2, i.e., the first part of HCl gas is obtained, which can be used in other units, and the liquid dichlorosilane and trichlorosilane+liquid HCl further enters the flash tank 8.

[0094] The flash tank 8 comprises a tank body, in which a liquid distributor 18 is arranged, the feed port of the flash tank 8 is connected to the liquid distributor 18, and a demister 19 is arranged in the tank body above the liquid distributor 18, and the demister 19 is funnel-shaped, and its angle is generally 120°. The top of the flash tank 8 has the second part of HCl gas outlet 8a, which is further connected to the cryogenic refrigerator 9, and the circulating water used for cooling in the cryogenic refrigerator 9 is pipe-passed, and the gas material from the top of the flash tank 8 is shell-passed, and the shell side of the cryogenic refrigerator 9 has a liquid outlet and a gas outlet, wherein the gas outlet mainly outputs HCl gas, which can enter other units, and the liquid outlet is connected to the reflux material inlet of the flash tank 8, so that the liquid after deep cooling can be refluxed to improve the recovery rate of DCS, and the material at the bottom of the flash tank 8 is sent to the separation unit through the second pump 10.

[0095] In this example, the separation unit includes a distillation tower 11, the top of the distillation tower 11 has a gaseous dichlorosilane product outlet 11a, the side wall has a liquid trichlorosilane product outlet 11b, and the side wall of the distillation tower 11 below the trichlorosilane product outlet 11b has a liquid silicon tetrachloride product outlet 11c.

[0096] Furthermore, the dichlorosilane product outlet 11a can also be connected to a second cooling unit, which includes a second air cooler 12, a second water cooler 13, and a second reflux tank 14 connected in sequence. The second air cooler 12 and the second water cooler 13 are configured to gradually cool the dichlorosilane product from the dichlorosilane product outlet 11a from a gaseous state to a liquid state. The second reflux tank 14 is used to store the liquid dichlorosilane product and reflux most of the liquid dichlorosilane product into the distillation tower 11, and the other small part is mainly sent to other units, such as a deproportionation fixed bed, through a third pump 15. The slurry deposited at the bottom of the distillation tower 11 can be pumped out by a fourth pump 17, and part of the material at the bottom of the distillation tower 11 is sent back to the lower part of the distillation tower 11 through a second reboiler 16 to provide sufficient heat to the distillation tower 11.

[0097] Example 1

[0098] This embodiment is implemented based on the above structure, wherein the lower tower 101 has a height of 14.1 m and an inner diameter of 5 m, and the upper tower 102 has a height of 15.6 m and an inner diameter of 2.3 m. The specific separation and recovery method is as follows:

[0099] S1: First, the gaseous polysilicon reduction tail gas is treated into liquid through the pre-treatment unit. At this time, the liquid polysilicon reduction tail gas mainly contains HCL, DCS, TCS and STC. Based on the total amount of liquid polysilicon reduction tail gas, HCl is 0.248wt%, DCS is 4wt%, TCS is 46.4wt%, STC is 49.4wt%, and the total material flow rate entering the analysis tower 1 is 875953kg / hr.

[0100] S2: sending the liquid polysilicon reduction tail gas (liquid phase material to be processed) into the desorption tower 1 for desorption separation, controlling the pressure of the desorption tower 1 to 0.8 MPaG, and obtaining a first gaseous material and a first liquid material;

[0101] S3: sending the first gaseous material to a first cooling unit for cooling, wherein the cooling water outlet temperature of the first water cooler 4 in the first cooling unit is controlled to be 42° C., so that most of the dichlorosilane, trichlorosilane and part of the HCl are cooled to liquid, while the other part of the HCl exists in the form of gas, and the gas-liquid separation is carried out through the first reflux tank 5 to obtain a first part of HCl gas and a second liquid material, wherein the second liquid material mainly contains DSC, TCS and part of HCl, and the first part of the HCl gas can be further sent to other units.

[0102] A portion of the second liquid material is returned to the desorption tower 1, and the mass ratio of the returned second liquid material to the liquid polysilicon reduction tail gas is controlled to be 0.1:1. The other small portion of the second liquid material is sent to the flash tank 8. The total flow rate of the second liquid material entering the flash tank 8 is 16058 kg / hr, and its specific components are: DCS 31.8wt%, TCS 64.9wt%, and HCl 3.3wt%.

[0103] S4: Flash the second liquid material and control the flash pressure to 0.182 MPaG to obtain a second portion of HCL gas and a third liquid material. The content of chlorosilane recovered in the obtained third liquid material is as high as 99.7 wt%. Specifically, the total flow rate of the third liquid material is 14901.3 kg / hr, and its specific components are: 31.2 wt% of DCS, 68.4 wt% of TCS, and 0.3 wt% of HCl.

[0104] Compared with the material composition before flash evaporation, the removal rate of HCL was as high as 90.9%, the overall recovery rate of chlorosilane was 95.6%, of which the recovery rate of DCS was 91.1%.

[0105] The second part of HCl gas is further sent to the cryogenic refrigerator 9, which is cooled by water at 7°C. The outlet temperature of the cooling water is 12°C. The outlet temperature of the material in the cryogenic refrigerator 9 is controlled to be 15°C by adjusting the flow rate of the cooling water, so that a small amount of dichlorosilane mixed in the HCl is cooled to a liquid phase, and the liquid phase is returned to the flash tank 8.

[0106] S5: sending the first liquid material and the third liquid material into a distillation tower 11 for distillation separation, controlling the mass ratio of the first liquid material and the third liquid material to be 0.06:1, controlling the pressure of the distillation tower 11 to be 0.35 MPaG, and obtaining a gaseous dichlorosilane product, a liquid trichlorosilane product, and a liquid silicon tetrachloride product, wherein the trichlorosilane product includes TCS and DCS, based on the total amount of the trichlorosilane product, wherein the amount of DCS is 9.5wt%, and the amount of TCS is 90.5wt% (the contents of other impurities such as HCl and STC are both below 0.0001ppm); the liquid silicon tetrachloride product has high purity (wherein the contents of HCl and DCS are both below 0.0001ppm, and the content of TCS is below 0.5wt%).

[0107] The gaseous dichlorosilane product can also be further sent to the second cooling unit for cooling to obtain a liquid dichlorosilane product (wherein the content of HCl is below 0.6wt%, and the contents of TCS and STC are both below 40ppm) and gaseous HCl (wherein the contents of DCS, TCS and STC are all below 10ppm). The gaseous HCl can be sent to other units, a part of the liquid dichlorosilane product can be sent to the subsequent anti-disproportionation fixed bed, and another part of the liquid dichlorosilane product is refluxed to the top of the distillation tower 11, and the temperature of the refluxed liquid dichlorosilane product is controlled to be 10°C lower than the temperature at the top of the distillation tower 11 to ensure the gas-liquid mass transfer effect.

[0108] Example 2

[0109] The structure of the separation system on which this embodiment is based is the same as that of Example 1, with the only difference being that the total flow rate of materials entering the analytical tower 1 is 728243 kg / hr, including 4 wt% DCS, 46.4 wt% TCS, 49.4 wt% STC, and 0.25 wt% HCl.

[0110] The pressure of the analytical tower 1 is 0.7 MPa, and the mass ratio of the second liquid material returned to the material entering the analytical tower 1 is 0.122:1. Therefore, the height of the lower tower 101 is 17.1 m, the inner diameter is 4.2 m, and the height of the upper tower 102 is 8 m, and the inner diameter is 2.8 m.

[0111] The recovery method adopted is the same as that in Example 1, and the total flow rate of the second liquid material obtained in step S3 is 16058 kg / hr, and its specific composition is: DCS 67.3 wt%, TCS 31.1 wt%, HCl 1.6 wt%.

[0112] The total flow rate of the third liquid material obtained in step S4 is 15363 kg / hr, and its specific composition is: DCS 67.6 wt%, TCS 32.2 wt%, HCl 0.11 wt%.

[0113] Compared with the material composition before flash evaporation, the removal rate of HCl was as high as 93.4%, and the overall recovery rate of chlorosilane was 95.6%, of which the recovery rate of DCS was 96.1%.

[0114] like Figure 5 As shown, the separation unit includes: two distillation towers 11, the feed condition of the first distillation tower 11 and the pressure of the two distillation towers 11 are the same as those in Example 1, the feed port of the first distillation tower 11 is connected to the first liquid material outlet 1b and the third liquid material outlet 8b, the first distillation tower 11 has the liquid silicon tetrachloride outlet 11c on the side wall, and the discharge port at the top is connected to the feed port of the second distillation tower 11, the second distillation tower 11 has the gaseous dichlorosilane outlet 11a at the top, and has the liquid reduced refined material outlet 11b on the side wall.

[0115] The amount of DCS in the trichlorosilane product obtained in step S5 is 8.3 wt% (the rest is trichlorosilane), and the contents of HCl and other components in the dichlorodihydrosilane product, trichlorosilane product and silicon tetrachloride product are all below 3 ppm.

[0116] Example 3

[0117] The structure of the separation system based on this embodiment is the same as that of Example 1, and the material flow rate and composition entering the analytical column are also the same as those of Example 1, with the only difference being:

[0118] like Figure 6As shown, the separation unit includes three distillation towers 11, the feed condition of the first distillation tower 11 and the pressure of the three distillation towers 11 are the same as those in Example 1, the feed port of the first distillation tower 11 is connected to the first liquid material outlet 1b and the third liquid material outlet 8b, the side wall of the first distillation tower 11 is provided with the liquid silicon tetrachloride outlet 11c, and the discharge port at the top is connected to the feed port of the second distillation tower 11, the top of the second distillation tower 11 is provided with the gaseous dichlorosilane outlet 11a, and the discharge port at the bottom is connected to the feed port of the third distillation tower 11, the top of the third distillation tower 11 is provided with the liquid reduced refined material outlet 11b, and the materials coming out of the tops of the three distillation towers 11 can be partially returned to the present distillation tower 11 in addition to entering the next structure / unit, so as to ensure sufficient contact between the gas-liquid two phases.

[0119] The only difference between the separation and recovery methods is that the flash evaporation pressure is 0.25 MPaG.

[0120] The total flow rate of the second liquid material obtained in step S3 is 16058 kg / hr, and its specific composition is: DCS 31.8 wt%, TCS 64.9 wt%, HCl 3.3 wt%.

[0121] The total flow rate of the third liquid material obtained in step S4 is 15174.4 kg / hr, and its specific composition is: DCS 31.7 wt%, TCS 67.6 wt%, HCl 0.65 wt%.

[0122] Compared with the material composition before flash evaporation, the removal rate of HCl was as high as 81.4%, and the overall recovery rate of chlorosilanes was 97%, of which the recovery rate of DCS was 94.2%.

[0123] In the trichlorosilane product obtained in step S5, the amount of DCS is 9.44 wt% (the rest is TCS), and the contents of HCl and other components in the liquid dichlorosilane product, trichlorosilane product and silicon tetrachloride product are all below 8 ppm.

[0124] Example 4

[0125] This implementation is carried out in the manner of Example 1, and the material flow rate and composition entering the analytical tower are also the same as those in Example 1, with the only difference being that the flash evaporation pressure is 0.15 MPaG.

[0126] The total flow rate of the second liquid material obtained in step S3 is 16058 kg / hr, and its specific composition is: DCS 31.8 wt%, TCS 64.9 wt%, HCl 3.3 wt%.

[0127] The total flow rate of the third liquid material obtained in step S4 is 14672.7 kg / hr, and its specific composition is: DCS 30.8 wt%, TCS 69.0 wt%, HCl 0.21 wt%.

[0128] Compared with the material composition before flash evaporation, the removal rate of HCl was as high as 94.2%, and the overall recovery rate of chlorosilanes was 94.3%, of which the recovery rate of DCS was 88.5%.

[0129] In the trichlorosilane product obtained in step S5, the amount of DCS is 9.55 wt% (the rest is TCS), and the contents of HCl and other components in the liquid dichlorosilane product, trichlorosilane product and silicon tetrachloride product are all below 3 ppm.

[0130] Example 5

[0131] The process was carried out in the same manner as in Example 1, except that the flash evaporation pressure was 0.12 MPaG.

[0132] The total flow rate of the second liquid material obtained in step S3 is 16058 kg / hr, and the specific composition is DCS 31.8 wt%, TCS 64.9 wt%, HCl 3.3 wt% (the same as Example 1).

[0133] The total flow rate of the third liquid material obtained in step S4 is 14420.2 kg / hr, and its specific composition is: DCS 30.1 wt%, TCS 69.8 wt%, HCl 0.08 wt%.

[0134] Compared with the material composition before flash evaporation, the removal rate of HCl was as high as 97.8%, and the overall recovery rate of chlorosilane was 92.8%, of which the recovery rate of DCS was 85.0%.

[0135] The liquid dichlorosilane product obtained in step S5 has an HCl content of less than 0.6 wt%, and TCS and DCS contents of less than 0.01 ppm respectively;

[0136] The amount of DCS in the trichlorosilane product is 9.6wt% (the remainder is TCS), the HCl content is 1ppm, and the STC content does not exceed 0.0001ppm;

[0137] The HCl content in silicon tetrachloride products is essentially 0.

[0138] Comparative Example 1

[0139] The method of Example 1 is followed, except that the second liquid material does not enter the flash tank 8 because the large amount of HCl in the second liquid material will cause the tower pressure of the distillation tower to be unstable and therefore cannot enter the distillation tower 11. Instead, the second liquid material directly enters the subsequent anti-disproportionation fixed bed, and the distillation tower 11 is only used to separate the liquid material from the analytical tower 1. The amount of DCS in the reduced refined material obtained thereby is 5.6 wt%.

[0140] It can be seen that the amount of DCS in the reduced refined material obtained in Example 1 in which a flash tank is added increases by 69.6% compared with Comparative Example 1.

[0141] Comparative Example 2

[0142] The process was carried out in the same manner as in Example 1, except that the flash evaporation pressure was 0.4 MPaG.

[0143] The total flow rate of the second liquid material obtained in step S3 is 16058 kg / hr, and the specific composition is: DCS 31.8 wt%, TCS 64.9 wt%, HCl 3.3 wt%.

[0144] The total flow rate of the third liquid material obtained in step S4 is 15497.5 kg / hr, and the specific composition is: DCS 32.1 wt%, TCS 66.6 wt%, HCl 1.33 wt%.

[0145] Compared with the material composition before flash evaporation, the removal rate of HCl is as high as 61.1%, the overall recovery rate of chlorosilane is 98.5%, and the recovery rate of DCS is 97.42%. It can be seen that the change of flash evaporation pressure will lead to a decrease in the removal rate of HCl, which may affect the tower pressure stability of the distillation tower.

[0146] The content of HCl in the dichlorodihydrogen silicon product obtained in step S5 is 0.6wt%, and the contents of TCS and DCS are respectively less than 0.01ppm;

[0147] The amount of DCS in the trichlorosilane product is 8.55wt% (TCS is 91.4wt%), the HCl content is 18ppm, the STC content is no more than 0.0001ppm, and the silicon tetrachloride product does not contain HCl.

[0148] Comparative Example 3

[0149] According to the method in CN110240165A, the liquid phase dichlorosilane obtained contains 0.55 wt% HCl, and the liquid phase trichlorosilane contains 2.86 wt% HCl.

[0150] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A separation and recovery system for polysilicon reduction tail gas, It is characterized in that The system includes: A pre-treatment unit is used to treat the gaseous polysilicon reduction tail gas into liquid and separate and remove the hydrogen at the same time; A desorption tower, whose feed inlet is connected to the liquid material outlet of the pre-treatment unit, the desorption tower has a first gaseous material outlet at the top and a first liquid material outlet at the bottom; A first cooling unit connected to the first gaseous material outlet, the first cooling unit having a first portion of HCl gas outlet and a second liquid material outlet; A flash tank, whose feed inlet is connected to the second liquid material outlet, and the flash tank has a second portion of HCl gas outlet and a third liquid material outlet; A separation unit, whose feed inlet is connected to the first liquid material outlet and the third liquid material outlet, and the separation unit has a dichlorosilane product outlet, a trichlorosilane product outlet and a silicon tetrachloride product outlet, wherein the separation unit is arranged so that the trichlorosilane product obtained at the trichlorosilane product outlet contains 8-10wt% of dichlorosilane.

2. The separation and recovery system according to claim 1, in, The first cooling unit comprises: a first heat exchanger, a first air cooler, a first water cooler and a first reflux tank connected in sequence; wherein the first heat exchanger is configured to allow the first gaseous material from the first gaseous material outlet to perform a first heat exchange with the gas from the first reflux drum, so as to cool the first gaseous material with the gas from the first reflux drum, and the first heat exchanger has an outlet for the first portion of HCl gas; The first air cooler and the first water cooler are configured to gradually cool the first gaseous material into a mixture of liquid and gas; The first reflux drum is configured to separate the gas phase and the liquid phase in the liquid and gas mixture, and the liquid outlet of the first reflux drum forms the second liquid material outlet; Preferably, the liquid outlet of the first reflux tank is also connected to the reflux material inlet of the desorption tower.

3. The separation and recovery system according to claim 1 or 2, in, The desorption tower comprises a lower tower and an upper tower, wherein the upper tower is stacked on the lower tower and the two are connected, the lower tower has a height of 14-18m and an inner diameter of 3.5-5m, and the upper tower has a height of 6-16m and an inner diameter of 2-3m.

4. The separation and recovery system according to any one of claims 1 to 3, in, The outlet of the second part of HCl gas is connected to a cryogenic refrigerator, and the liquid outlet of the cryogenic refrigerator is connected to the reflux inlet of the flash tank; And / or, the flash tank comprises a tank body, a liquid distributor is arranged in the tank body, a feed inlet of the flash tank is connected to the liquid distributor, and a defoamer is arranged in the tank body above the liquid distributor.

5. The separation and recovery system according to any one of claims 1 to 4, in, The separation unit comprises a distillation tower, the top of which is provided with the dichlorosilane product outlet, the side wall of which is provided with the trichlorosilane product outlet, and the side wall of the distillation tower below the trichlorosilane product outlet is provided with the silicon tetrachloride product outlet; Preferably, the dichlorosilane product outlet is connected to a second cooling unit, and the second cooling unit comprises a second air cooler, a second water cooler and a second reflux tank connected in sequence; The second air cooler and the second water cooler are configured to gradually cool the dichlorosilane product from the dichlorosilane product outlet from a gaseous state to a liquid state, and to separate and discharge the remaining gaseous impurities; The second reflux tank is used to store the liquid dichlorosilane product and reflux part of the liquid dichlorosilane product into the distillation tower.

6. A method for separating and recovering dichlorosilane from polysilicon reduction tail gas, It is characterized in that The method comprises: Pre-treating the gaseous polysilicon reduction tail gas to obtain a liquid material to be treated; The liquid-phase material to be processed is subjected to a first separation treatment to obtain a first gaseous material and a first liquid material; Cooling the first gaseous material to obtain a first portion of HCL gas and a second liquid material; Flashing the second liquid material to obtain a second portion of HCL gas and a third liquid material; The first liquid material and the third liquid material are subjected to a second separation treatment to obtain a dichlorosilane product, a trichlorosilane product and a silicon tetrachloride product, wherein the trichlorosilane product contains 8-10 wt % of dichlorosilane.

7. The separation and recovery method according to claim 6, in, The flash evaporation pressure is 0.12-0.25 MPaG, preferably 0.17-0.19 MPaG; And / or, the mass ratio of the first liquid material to the third liquid material is 0.05-0.07:

1.

8. The separation and recovery method according to claim 6 or 7, in, The method further includes: returning a portion of the second liquid material to the first separation treatment step, wherein the mass ratio of the returned second liquid material to the liquid phase material to be treated is 0.1-1:

1.

9. The separation and recovery method according to any one of claims 6 to 8, in, The pressure of the first separation treatment is 0.6-0.8 MPaG; And / or, the pressure of the second separation treatment is 0.3-0.65 MPaG.

10. The separation and recovery method according to any one of claims 6 to 9, in, The method further comprises: cooling the gaseous dichlorosilane product to obtain a liquid dichlorosilane product, and refluxing a portion of the liquid dichlorosilane product to the second separation step, wherein the temperature of the refluxing liquid dichlorosilane product is 5-15° C. lower than the temperature of the gaseous dichlorosilane product obtained in the second separation step; And or, the method further comprises: cooling the second portion of HCl gas to obtain purified HCl gas and a fourth liquid material, and returning the fourth liquid material to the flash evaporation step.

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