Trichlorosilane primary rectification system

Abstract

A trichlorosilane primary rectification system comprises a rectification tower, an air cooler, a water cooling tower, a reflux tank and a plurality of parallel cryogenic towers, a top extraction outlet of the rectification tower is connected with hot air inlets of the air cooler and the water cooling tower through pipelines, so that light components are fed into the air cooler or the water cooling tower to be cooled; hot air outlets of the air cooler and the water cooling tower are connected with a feeding hole of the return tank through pipelines so as to feed cooled light components into the return tank, and the return tank is communicated with an air inlet of the deep cooling tower through a pipeline. According to the utility model, the air cooler and the water cooling tower are connected in parallel, so that the cooling capacity of the system is increased, the temperature of the dichlorosilane is lower, the liquefaction of the dichlorosilane is facilitated, and the safety risk of the dichlorosilane in the return tank is reduced. And meanwhile, when the air cooler or the water cooling tower breaks down or is usually maintained, production halt maintenance is not needed, and only the valve of the air cooler or the water cooling tower needs to be temporarily closed.

Description

Technical Field

[0001] The utility model relates to the technical field of polysilicon production, in particular to a primary distillation system of trichlorosilane. Background Art

[0002] At present, the production of polysilicon generally adopts the modified Siemens method. The overall technical route is to synthesize trichlorosilane (TCS) from silicon powder (purity requirement is above 99.5%) and hydrogen chloride (HCl), and then convert high-purity trichlorosilane into high-purity polysilicon through reduction reaction and chemical vapor deposition (CVD). Silicon powder and hydrogen chloride will also produce by-products such as silicon tetrachloride (STC) and dichlorosilane (DCS) when they react. There are many by-product components and the boiling points are not much different, so multi-stage distillation is required to gradually improve the purity of trichlorosilane. Among them, in the primary distillation, the content of dichlorosilane in the light components of the top mining is relatively high. Dichlorosilane and silicon tetrachloride can generate trichlorosilane through anti-disproportionation reaction. Dichlorosilane is usually liquefied and recovered by a reflux tank. Dichlorosilane has a low boiling point, only 8.3°C under normal pressure. The high pressure in the distillation tower and reflux tank can increase the boiling point of dichlorosilane. For example, at 0.29MPa, the boiling point can be raised to more than 50 degrees Celsius. An air cooler is installed between the distillation tower and the reflux tank, and dichlorosilane can be liquefied by cooling the air. The reflux tank is a pressure vessel. Under normal circumstances, dynamic equilibrium can be achieved in the reflux tank, making the liquefaction of dichlorosilane stable. That is, the pressure of the reflux tank decreases, the gas phase dichlorosilane increases, the pressure of the reflux tank increases again, and the liquid phase dichlorosilane increases. However, when the reflux tank fails, such as valve damage causing leakage, the pressure in the reflux tank will suddenly decrease, and a large amount of liquid dichlorosilane will quickly vaporize, causing a very large impact on the leak, which may damage the equipment at the least, or even cause a safety accident. Summary of the invention

[0003] In view of this, it is necessary to provide a trichlorosilane primary distillation system for safely recovering dichlorosilane.

[0004] A primary distillation system of trichlorosilane comprises a distillation tower, an air cooler, a water cooling tower, a reflux tank, and several parallel cryogenic towers. The top extraction outlet of the distillation tower is connected with the hot gas inlet of the air cooler and the water cooling tower through a pipeline so that the light component is sent to the air cooler or the water cooling tower for cooling. The hot gas outlet of the air cooler and the water cooling tower is connected with the feed port of the reflux tank through a pipeline so that the light component after cooling is sent to the reflux tank. The reflux tank is connected with the air inlet of the cryogenic tower through a pipeline.

[0005] Preferably, the top outlet of the distillation tower is also connected to the air inlet of the cryogenic tower through a pipeline.

[0006] Preferably, the trichlorosilane primary distillation system also includes a flow control unit to control the gas flow entering the air cooler or the water cooling tower. The flow control unit includes a temperature sensor, a flow sensor, a controller, and an electrically controlled valve. The temperature sensor and the flow sensor are arranged at the top extraction outlet to collect the gas temperature information and flow information of the top extraction outlet. The temperature sensor is also arranged at the hot gas outlet of the air cooler and the water cooling tower to collect the temperature information of the cooled gas. The temperature sensor and the flow sensor are electrically connected to the controller to transmit the temperature information and the flow information to the controller. The controller is also electrically connected to the electrically controlled valve. The electrically controlled valve is arranged on the pipeline between the distillation tower and the air cooler and the water cooling tower to distribute the hot gas flowing out of the top extraction outlet.

[0007] Preferably, the controller is also electrically connected to a fan of the air cooler to control the air flow entering the air cooler.

[0008] Preferably, the controller is also electrically connected to a circulation pump of the water cooling tower to control the flow rate of cooling water in the water cooling tower.

[0009] Preferably, the hot gas outlet of the air cooler is also connected to the air inlet of the cryogenic tower through a pipeline, and an electrically controlled three-way valve is provided at the hot gas outlet of the air cooler to control the flow of hot gas to the reflux tank or the cryogenic tower.

[0010] Preferably, the refrigerant temperature of the cryogenic tower is less than or equal to 7 degrees Celsius.

[0011] Beneficial effects: The utility model increases the cooling capacity of the system by connecting an air cooler and a water cooling tower in parallel, making the temperature of dichlorosilane lower, which is beneficial to the liquefaction of dichlorosilane and reduces the safety risk of dichlorosilane in the reflux tank. At the same time, when the air cooler or the water cooling tower fails or is required for routine maintenance, there is no need to stop production for maintenance. It is only necessary to temporarily close the valve of the air cooler or the water cooling tower. By connecting several cryogenic towers in parallel on the top of the reflux tank, the gaseous dichlorosilane will be further cooled to below 8 degrees Celsius in the cryogenic tower, and then refluxed to the reflux tank. This is more conducive to the liquefaction of dichlorosilane under normal circumstances. When the valve leaks and causes the air pressure in the reflux tank to drop sharply, the amount of dichlorosilane that becomes gaseous is also less, thereby avoiding safety accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a structural schematic diagram of the primary distillation system of trichlorosilane of the utility model.

[0013] Figure 2 This is a control flow chart of the trichlorosilane primary distillation system of the utility model.

[0014] In the figure: trichlorosilane primary distillation system 10, distillation tower 20, air cooler 30, water cooling tower 40, reflux tank 50, cryogenic tower 60, flow control unit 70, temperature sensor 701, flow sensor 702, controller 703, and electric control valve 704. DETAILED DESCRIPTION

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the utility model, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Please see Figure 1 A trichlorosilane primary distillation system 10 includes a distillation tower 20, an air cooler 30, a water cooling tower 40, a reflux tank 50, and a plurality of parallel cryogenic towers 60. The top extraction outlet of the distillation tower 20 is connected to the hot gas inlet of the air cooler 30 and the water cooling tower 40 through a pipeline to send the light component into the air cooler 30 or the water cooling tower 40 for cooling. The hot gas outlet of the air cooler 30 and the water cooling tower 40 is connected to the feed port of the reflux tank 50 through a pipeline to send the cooled light component into the reflux tank 50. The reflux tank 50 is connected to the air inlet of the cryogenic tower 60 through a pipeline.

[0017] The distillation tower 20 of the utility model is used to distill trichlorosilane generated by the reaction of hydrogen chloride and silicon at high temperature. The high-temperature and high-pressure gas of the light component is discharged from the top of the distillation tower 20, and the main component is dichlorosilane. Under the cooling effect of the air cooler 30 or the water cooler, dichlorosilane changes from gas phase to liquid phase and condenses into the reflux tank 50. In order to achieve a better cooling effect, a three-way valve is set between the distillation tower 20, the air cooler 30, and the water cooling tower 40. If the temperature in the distillation tower 20 is high or the flow rate is large, then more flow is allocated in the water cooling tower 40 so that more dichlorosilane can be liquefied; if the temperature in the distillation tower 20 is low or the flow rate is small, then more flow is allocated in the air cooler 30 to save energy consumption.

[0018] In a preferred embodiment, the air cooler 30 and the water cooling tower 40 are both similar shell-and-tube structures, that is, the pipes are bent in a serpentine shape or arranged in parallel in a bundle shape. The side wall of the air cooler 30 is provided with a ventilation window and a fan, and the air is used to cool the pipes and indirectly cool the hot air flow in the pipes; the top of the water cooling tower 40 is provided with spray water to cool the pipes and indirectly cool the hot air flow in the pipes. The spray water can be recycled, and a cooling pool is provided at the bottom or outside of the water cooling tower 40 to cool the heated water.

[0019] After the temperature is reduced, the dichlorosilane in the hot air flow is liquefied and enters the reflux tank 50. The reflux tank 50 is also in a high-pressure state, which can liquefy the dichlorosilane at a higher temperature. At the same time, the gas in the reflux tank 50 further enters the cryogenic tower 60 to be cooled. The cryogenic tower 60 also cools the pipeline through the refrigerant, thereby indirectly cooling the gas. The refrigerant of the cryogenic tower 60 generally uses the same refrigerant as the air conditioner, which can reduce the gas temperature to below 8 degrees Celsius, so that the dichlorosilane can be liquefied at room temperature. In this way, when an accident occurs and causes a large amount of dichlorosilane in the reflux tank 50 to be gasified, the cryogenic tower 60 can liquefy it in time to avoid the occurrence of accidents. The liquid dichlorosilane in the reflux tank 50 will subsequently react with silicon tetrachloride to generate trichlorosilane. The reaction needs to be carried out at a certain temperature, so it does not need to be cooled by the cryogenic tower 60. The cryogenic tower 60 does not cool the liquid dichlorosilane in the reflux tank 50, which can reduce the energy consumption of the cryogenic tower 60. At the same time, it can also reduce energy consumption in the subsequent reaction with silicon tetrachloride.

[0020] When an accident occurs in the distillation tower 20, resulting in a very large flow of light components at the top, a very large burden will be placed on the subsequent system. In a preferred embodiment, the top outlet of the distillation tower 20 is also connected to the air inlet of the cryogenic tower 60 through a pipeline. Rapidly cooling the large flow of gas through the cryogenic tower 60 helps to liquefy it quickly, thereby reducing the system pressure and avoiding accidents. It can also quickly liquefy dichlorosilane and adapt to the efficient distillation of the distillation tower 20.

[0021] In order to save more energy, in a preferred embodiment, the trichlorosilane primary distillation system 10 further includes a flow control unit 70 to control the gas flow entering the air cooler 30 or the water cooling tower 40. Figure 2 The flow control unit 70 includes a temperature sensor 701, a flow sensor 702, a controller 703, and an electric control valve 704. The temperature sensor 701 and the flow sensor 702 are arranged at the top extraction outlet to collect the gas temperature information and flow information of the top extraction outlet. The temperature sensor 701 is also arranged at the hot gas outlet of the air cooler 30 and the water cooling tower 40 to collect the temperature information of the cooled gas. The temperature sensor 701 and the flow sensor 702 are electrically connected to the controller 703 to transmit the temperature information and the flow information to the controller 703. The controller 703 is also electrically connected to the electric control valve 704. The electric control valve 704 is arranged on the pipeline between the distillation tower 20 and the air cooler 30 and the water cooling tower 40 to distribute the hot gas flowing out from the top extraction outlet.

[0022] The controller 703 is provided with a plurality of gradient top extraction outlet temperature thresholds and flow thresholds. Accordingly, each set temperature also corresponds to the flow value entering the air cooler 30 and the water cooler. When the temperature sensor 701 and the flow sensor 702 at the top extraction outlet detect that the actual temperature and flow meet the set temperature threshold and flow threshold, the controller controls the electric control valve 704 to open to a predetermined position so that the flow entering the air cooler 30 and the water cooler meets the set flow value. For example, the set temperature threshold of the controller 703 is [90,95] degrees Celsius, the flow threshold is [9,11] L / min, the corresponding set flow value of the air cooler 30 is 4L / min, and the rest are set flow values ​​entering the water cooler. The actual temperature of the top extraction outlet is 92 degrees Celsius, and the flow is 10L / min. Then the controller 703 controls the electric control valve 704 so that the flow entering the air cooler 30 is 4L / min and the flow entering the water cooler is 6L / min.

[0023] Affected by various factors, the temperature of the air flow out of the air cooler 30 or the water cooler fluctuates. When the temperature after refrigeration is high, dichlorosilane may not be liquefied, which puts a burden on the reflux tank 50. Therefore, a temperature sensor 701 is set at the hot air outlet of the air cooler 30 and the water cooling tower 40 to collect the temperature information of the outlet in time. When the temperature of the hot air flow is high, the hot air flow can be introduced into the cryogenic tower 60 through a valve for rapid cooling.

[0024] Due to the different flow rates entering the air cooler 30, the temperature of the hot air flow is also different, and the outside air temperature is also different. In order to achieve the expected cooling effect, the hot air flow is cooled to a predetermined temperature so that dichlorosilane can be liquefied. In a preferred embodiment, the controller 703 is also electrically connected to the fan of the air cooler 30 to control the air flow entering the air cooler 30. When the hot air flow temperature is high and the flow rate is large, the controller 703 increases the fan power so that more cold air passes through the air cooler 30 to cool the hot air flow.

[0025] Likewise, in a preferred embodiment, the controller 703 is also electrically connected to the circulation pump of the water cooling tower 40 to control the flow rate of cooling water in the water cooling tower 40 .

[0026] In a preferred embodiment, the hot gas outlet of the air cooler 30 is also connected to the air inlet of the cryogenic tower 60 through a pipeline, and an electrically controlled three-way valve is provided at the hot gas outlet of the air cooler 30 to control the hot gas flow to the reflux tank 50 or the cryogenic tower 60. When the temperature of the hot gas flow cooled by the air cooler 30 does not reach the predetermined temperature, it can be further cooled in the cryogenic tower 60. Or when the reflux tank 50 fails, the hot gas flow cooled by the air cooler 30 is further cooled to below 8 degrees Celsius, and the dichlorosilane can be turned into liquid and enter the reflux tank 50 at normal pressure, which will not affect the safety hazard of the reflux tank 50.

[0027] In a preferred embodiment, the refrigerant temperature of the cryogenic tower 60 is less than or equal to 7 degrees Celsius.

[0028] The above disclosure is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims

1. A trichlorosilane primary distillation system, characterized in that: It includes a distillation tower, an air cooler, a water cooling tower, a reflux tank, and several parallel cryogenic towers. The top extraction outlet of the distillation tower is connected to the hot gas inlet of the air cooler and the water cooling tower through a pipeline to send the light component to the air cooler or the water cooling tower for cooling. The hot gas outlet of the air cooler and the water cooling tower is connected to the feed port of the reflux tank through a pipeline to send the cooled light component to the reflux tank. The reflux tank is connected to the air inlet of the cryogenic tower through a pipeline.

2. The trichlorosilane primary distillation system according to claim 1, characterized in that: The top outlet of the distillation tower is also connected to the air inlet of the cryogenic tower through a pipeline.

3. The trichlorosilane primary distillation system according to claim 1, characterized in that: The trichlorosilane primary distillation system also includes a flow control unit to control the gas flow entering the air cooler or the water cooling tower. The flow control unit includes a temperature sensor, a flow sensor, a controller, and an electrically controlled valve. The temperature sensor and the flow sensor are arranged at the top extraction outlet to collect the gas temperature information and flow information of the top extraction outlet. The temperature sensor is also arranged at the hot gas outlet of the air cooler and the water cooling tower to collect the temperature information of the cooled gas. The temperature sensor and the flow sensor are electrically connected to the controller to transmit the temperature information and the flow information to the controller. The controller is also electrically connected to the electrically controlled valve. The electrically controlled valve is arranged on the pipeline between the distillation tower and the air cooler and the water cooling tower to distribute the hot gas flowing out of the top extraction outlet.

4. The trichlorosilane primary distillation system according to claim 3, characterized in that: The controller is also electrically connected to the fan of the air cooler to control the air flow entering the air cooler.

5. The trichlorosilane primary distillation system according to claim 3, characterized in that: The controller is also electrically connected to a circulating pump of the water cooling tower to control the flow of cooling water in the water cooling tower.

6. The trichlorosilane primary distillation system according to claim 1, characterized in that: The hot gas outlet of the air cooler is also connected to the air inlet of the cryogenic tower through a pipeline. An electrically controlled three-way valve is provided at the hot gas outlet of the air cooler to control the hot gas flow to the reflux tank or the cryogenic tower.

7. The trichlorosilane primary distillation system according to claim 1, characterized in that: The refrigerant temperature of the cryogenic tower is less than or equal to 7 degrees Celsius.

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