CN109603329B - Reduction furnace tail gas treatment system - Google Patents

Abstract

The application discloses a reducing furnace tail gas treatment system, which comprises a filtering device arranged at a reducing furnace tail gas outlet, wherein the filtering device is sequentially connected with a tail gas cooler, a hydrogen preheater, a silica powder filter and a silica powder collector.

Description

A reduction furnace tail gas treatment system

Technical Field

The invention relates to the field of tail gas treatment in a reduction section during polysilicon production, and in particular to a reduction furnace tail gas treatment system.

Background technique

At present, the main process technology for producing polysilicon at home and abroad is the "Siemens Improved Method", in which high-purity trichlorosilane and hydrogen are mixed in a certain proportion and deposited in a reduction furnace to form polysilicon. The reaction temperature of the reduction process is around 1080-1100 degrees Celsius, and the tail gas generated in the reduction furnace section carries a large amount of heat and amorphous silicon powder.

In the conventional production process, the tail gas is recycled to preheat the raw materials. However, when recycling the tail gas, a large amount of amorphous silicon powder will enter the pipeline and heat exchanger, causing pipeline blockage. In order to make full use of the waste heat of the tail gas, the tail gas treatment method of the traditional reduction furnace is to cool the tail gas through the cooling coil first, and then filter the amorphous silicon powder contained in the tail gas through the tail gas filter before entering the tail gas recovery. The filtered tail gas enters the recovery system for treatment.

However, if the temperature of the reduction furnace exhaust is too low during the transportation of the exhaust gas cooling coil and subsequent pipelines, amorphous silicon powder will be deposited on the walls of the coil and pipeline. Over time, the cooling effect of the coil will decrease and the energy consumption of the system will increase.

Summary of the invention

In view of this, the present application provides a reduction furnace exhaust gas treatment system, which first filters the amorphous silicon powder in the reduction furnace exhaust gas, then utilizes the waste heat step by step, and then filters the residual silicon powder in the reduction section exhaust gas, so as to maximize the utilization of the waste heat of the exhaust gas, while ensuring that the amorphous silicon powder in the exhaust gas is deposited in the pipeline and equipment as little as possible, thereby extending the equipment cleaning and maintenance cycle and reducing system energy consumption.

In order to solve the above technical problems, the technical solution provided by the present invention is based on this. The present application provides a reduction furnace exhaust gas treatment system, including a filtering device arranged at the reduction furnace exhaust gas outlet, and the filtering device is connected to the exhaust gas cooler, hydrogen preheater, silicon powder filter and silicon powder collector in sequence.

Preferably, it includes a metal filter located in the inner layer and a metal tube mounted on the outer periphery of the metal filter, the top of the metal filter is provided with an opening, the opening is connected to the exhaust gas outlet of the reduction furnace, the opening of the metal filter is provided with a circle of fixed edges folded outward, the fixed edges can be installed and fixed in the reduction furnace so that the metal filter passes through the exhaust gas outlet of the reduction furnace.

Preferably, the cross-sectional area of the upper end of the metal tube is larger than that of the lower end.

Preferably, the first tube side of the exhaust gas cooler is connected to the filtering device, and the first shell side of the exhaust gas cooler is used for introducing heat exchange medium.

Preferably, the first shell side of the exhaust gas cooler is divided into several cavities, the cavity is connected to an electrically controlled switching valve, and a first temperature detection device is arranged at the outlet of the first tube side of the exhaust gas cooler, the first temperature detection device is connected to the electrically controlled switching valve, and the temperature detection device is used to detect the exhaust gas temperature at the outlet of the first tube side of the exhaust gas cooler to control the electrically controlled switching valve, and adjust the number of cavities participating in heat exchange in the shell side to adjust the heat exchange efficiency.

Preferably, the second tube side of the hydrogen preheater is connected to the first tube side of the tail gas cooler, and the second shell side of the hydrogen preheater is used for introducing hydrogen.

Preferably, a second temperature detection device is provided at the outlet of the second tube side of the hydrogen preheater, and a flow control device is provided at the inlet of the second shell side of the hydrogen preheater. The second temperature detection device is electrically connected to the flow control device and is used to adjust the flow rate of hydrogen according to the exhaust gas temperature at the outlet of the second tube side.

Preferably, a plurality of filter elements are distributed vertically in the silicon powder filter, and the filter elements are ceramic filter elements or silicon nitride filter elements.

Preferably, a buffer cavity is provided on the pipeline between the silicon powder filter and the silicon powder collector, and the cross-sectional area of the buffer cavity is larger than the cross-sectional area of the pipeline.

Compared with the prior art, the present application is described in detail as follows:

The present application discloses a reduction furnace exhaust gas treatment system, in which the exhaust gas is first preliminarily filtered by a filtering device before heat exchange is performed, which can effectively prevent excessive amorphous silicon powder in the exhaust gas from entering the pipeline and causing blockage. At the same time, a filtering device is arranged at the exhaust gas outlet of the reduction furnace, which can minimize the heat waste caused by filtering silicon powder. Filtering is performed before heat exchange, ensuring full utilization of the exhaust gas heat.

The cross-sectional area of the upper end of the metal tube is larger than that of the lower end. The diameter of the upper end of the metal tube is relatively large, which can increase the diameter of the reduction furnace exhaust gas outlet and increase the flow rate while also serving as a variable diameter transfer pipe section. The reduced cross-sectional area of the metal tube can cause the amorphous silicon powder entering between the upper end of the metal tube and the metal filter to accumulate in the variable diameter area, thereby preventing excessive amorphous silicon powder from entering the pipeline through the filtering device, thereby serving as a second filtration.

The electrically controlled switching valve adjusts the number of cavities participating in heat exchange in the first shell side according to the temperature of the delivered exhaust gas, and further adjusts the ratio of the first tube side to the cavity area participating in heat exchange, so as to achieve the balance of heat exchange efficiency and avoid the adhesion and deposition of amorphous silicon powder in the exhaust gas cooler due to excessive temperature drop of the exhaust gas due to heat exchange. At the same time, the actual flow rate of the heat exchange medium in the first shell side of the exhaust gas cooler will not be reduced due to the adjustment of the heat exchange efficiency, which can fully meet the actual production needs of the reduction furnace.

The second temperature detection device detects the temperature of the tail gas at the outlet of the second tube side of the hydrogen preheater, and adjusts the flow rate of hydrogen introduced into the second shell side of the hydrogen preheater according to the temperature of the tail gas. After preheating, the hydrogen can be mixed with trichlorosilane in the mixed gas and then fed into the reduction furnace. Therefore, the fluctuation of the flow rate will not affect the demand for the raw gas of the reduction furnace.

The ceramic filter element or the silicon nitride filter element can effectively prevent silicon powder from adhering to or depositing on the filter element of the silicon powder filter.

Buffering the silicon powder in the buffer chamber can prevent the silicon powder from flowing back into the silicon powder filter due to impact, and can further prevent the silicon powder from being discharged with the exhaust gas in the silicon powder filter, thereby improving the effect of exhaust gas filtration and purification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a system of the present invention;

FIG. 2 is a schematic structural diagram of the filtering device 1 of the present invention.

Detailed ways

In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in the figure, a reduction furnace tail gas treatment system includes a filter device 1, which is arranged at the reduction furnace tail gas outlet 6. After being filtered by the filter device 1, the tail gas enters the tail gas cooler 2, the hydrogen preheater 3, the silicon powder filter 4 and the silicon powder collector 5 in sequence; the tail gas exchanges heat with the heat exchange medium in the tail gas cooler 2 and then preheats the hydrogen through the hydrogen preheater 3. By adjusting the heat exchange area of the tail gas cooler 2 and the hydrogen flow rate entering the hydrogen preheater 3, the temperature of the tail gas is ensured to be appropriate when it is sent to the silicon powder filter 4, and the amorphous silicon powder mixed in the tail gas is prevented from being deposited on the pipe wall of the pipeline too early. The silicon powder filter 4 further filters the remaining amorphous silicon powder in the tail gas, and the tail gas with solid particles removed is sent to the silicon powder filter 4 for separation and treatment, and the silicon powder obtained by the silicon powder filter 4 is sent to the silicon powder collector 5 for storage.

Specifically, the filtering device 1 described in the present application includes a metal filter 11 located in the inner layer and a metal tube 12 mounted on the outer periphery of the metal filter 11. The top of the metal filter 11 is provided with an opening, and the opening is connected to the exhaust gas outlet 6 of the reduction furnace. The opening of the metal filter 11 is provided with a circle of fixed edges 13 folded outward, and the fixed edges 13 are installed and fixed in the reduction furnace so that the metal filter 11 passes through the exhaust gas outlet 6 of the reduction furnace.

The heavy metal filter 11 of the present application is preferably a columnar metal filter 11 with a sealed bottom, and the metal filter 11 is made of austenitic steel. When the filtering effect of the metal filter 11 decreases and affects the exhaust gas flow rate, the metal filter 11 can be disassembled, cleaned and then reinstalled.

The cross-sectional area of the upper end of the metal tube 12 is larger than that of the lower end, and the gap between the upper end of the metal tube 12 and the metal filter 11 is larger, so that the flux of the metal tube 12 can be increased while ensuring that the diameter of the pipe connected to the reduction furnace exhaust gas outlet 6 does not need to be changed. Increasing the diameter of the reduction furnace exhaust gas outlet 6 increases the flow rate while also playing the role of a diameter-changing transfer pipe section. In addition, since the exhaust gas has a high flow rate just after entering the metal filter 11, the fine amorphous silicon powder attached to the metal filter 11 is easily impacted by the exhaust gas and enters the gap between the metal tube 12 and the metal filter 11. Therefore, the reduction in the cross-sectional area of the metal tube 12 can cause the amorphous silicon powder entering between the upper end of the metal tube 12 and the metal filter 11 to accumulate in the diameter-changing area, thereby preventing excessive amorphous silicon powder from entering the pipeline through the filter device 1 and causing pipeline blockage.

The first tube side 21 of the exhaust gas cooler 2 is connected to the filtering device 1, and the filtered exhaust gas is heat exchanged with the heat exchange medium introduced into the first shell side 22 through the exhaust gas cooler 2. The heat exchange medium described in the present application can be the raw gas used in the polysilicon reduction section, or other media such as water or air for heat exchange with the exhaust gas. When it is raw gas, the raw gas can fully absorb the heat of the exhaust gas through heat exchange with the exhaust gas, so that the raw gas is preheated and heated before being sent to the reduction furnace, saving the energy consumed by heating the raw gas and saving production costs.

The first shell side 22 of the exhaust gas cooler 2 is divided into a plurality of cavities 23, and the cavities 23 evenly divide the exhaust gas cooler 2 into a plurality of spaces. The inlets of the cavities 23 are connected to an electrically controlled switching valve 24. A first temperature detection device 25 is provided at the outlet of the first tube side 21 of the exhaust gas cooler 2. The first temperature detection device 25 is connected to the electrically controlled switching valve 24. The first temperature detection device 25 is used to detect the exhaust gas temperature at the outlet of the first tube side 21 of the exhaust gas cooler 2 to control the electrically controlled switching valve 24 and adjust the number of cavities 23 participating in heat exchange in the first shell side 22. When the number of cavities 23 participating in heat exchange changes, , the ratio of the area of the first tube side 21 to the area of the cavity 23 involved in the heat exchange has changed, thereby realizing the linkage adjustment of the heat exchange efficiency, avoiding the adhesion and deposition of amorphous silicon powder in the exhaust gas cooler 2 due to excessive temperature reduction of the exhaust gas due to heat exchange, and at the same time, the actual flow rate of the heat exchange medium in the first shell side 22 of the exhaust gas cooler 2 will not be reduced due to the adjustment of the heat exchange efficiency. When the exhaust gas cooler 2 is used to preheat the raw gas, it can effectively adjust the exhaust gas heat exchange efficiency to avoid the adhesion of amorphous silicon powder due to temperature reduction, and can also effectively ensure the flow rate of the raw gas. The raw gas flow rate will not be reduced due to the adjustment of the heat exchange efficiency, and the actual production needs of the reduction furnace cannot be met.

The second tube side 31 of the hydrogen preheater 3 is connected to the first tube side 21 of the exhaust gas cooler 2. The exhaust gas after heat exchange and cooling in the exhaust gas cooler 2 is sent to the hydrogen preheater 3, and the hydrogen in the second shell side 32 of the hydrogen preheater 3 is preheated. After preheating, the hydrogen can be mixed with trichlorosilane to form a raw gas, and the raw gas is then sent to the exhaust gas cooler 2 for step-by-step preheating, so as to make full use of the heat entrained in the exhaust gas.

In summary, this system can effectively avoid the drop in exhaust gas temperature due to excessive heat exchange, thereby avoiding the adhesion of amorphous silicon powder to subsequent equipment and pipelines, avoiding blockage caused by the adhesion of amorphous silicon powder and reducing heat exchange efficiency, thereby reducing investment costs and operating costs.

The inlet of the second shell side 32 of the hydrogen preheater 3 is provided with a flow control device 34, and the outlet of the second tube side 31 of the hydrogen preheater 3 is provided with a second temperature detection device 33, the second temperature detection device 33 is electrically connected to the flow control device 34, and the second temperature detection device 33 detects the temperature of the tail gas at the outlet of the second tube side 31 of the hydrogen preheater 3, and adjusts the hydrogen flow rate introduced into the second shell side 32 of the hydrogen preheater 3 according to the temperature of the tail gas. Hydrogen can be mixed with trichlorosilane in the mixed gas after preheating and then sent to the reduction furnace, so the fluctuation of the flow rate will not affect the demand and use of the raw gas of the reduction furnace.

The silicon powder filter 4 is provided with a plurality of filter elements 41 placed in a vertical direction, and the filter element 41 is a hollow cylindrical ceramic filter element or a hollow silicon nitride filter element, and the silicon powder filter 4 is used to filter the fine silicon powder mixed in the tail gas. The ceramic filter element or the silicon nitride filter element can effectively prevent silicon powder from adhering to or depositing on the filter element 41 of the silicon powder filter 4, thereby ensuring the filtering efficiency of the silicon powder filter 4. The bottom of the silicon powder filter 4 is connected to a silicon powder collector 5 through an electric control valve 42.

A buffer chamber 7 is provided on the pipeline between the silicon powder collector 5 and the silicon powder filter 4. When the silicon powder accumulated in the silicon powder filter 4 needs to be sent to the silicon powder collector 5, the silicon powder is buffered in the buffer chamber 7 to prevent the silicon powder from flowing back into the silicon powder filter 4 due to impact, and can further prevent the silicon powder from being discharged along with the exhaust gas in the silicon powder filter 4, thereby ensuring the filtering effect of the silicon powder filter 4.

The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims (7)

1. A reduction furnace tail gas treatment system, comprising a filtering device (1) arranged at a reduction furnace tail gas outlet (6), wherein the filtering device (1) is sequentially connected to a tail gas cooler (2), a hydrogen preheater (3), a silicon powder filter (4) and a silicon powder collector (5); The filtering device (1) comprises a metal filter (11) located in an inner layer and a metal tube (12) sleeved on the outer periphery of the metal filter (11); the top of the metal filter (11) is provided with an opening, the opening is connected to the exhaust gas outlet (6) of the reduction furnace; the opening of the metal filter (11) is provided with a circle of fixed edges (13) folded outwards; the fixed edges (13) are installed and fixed in the reduction furnace so that the metal filter (11) passes through the exhaust gas outlet (6) of the reduction furnace; the metal filter (11) is a columnar metal filter with a sealed bottom; The cross-sectional area of the upper end of the metal tube (12) is larger than that of the lower end, and the gap between the upper end of the metal tube (12) and the metal filter (11) is relatively large. The reduction in the cross-sectional area of the metal tube (12) can cause the amorphous silicon powder that enters between the upper end of the metal tube (12) and the metal filter (11) to accumulate in the diameter-changing area, thereby preventing excessive amorphous silicon powder from entering the pipeline through the filtering device (1). 2. A reduction furnace exhaust gas treatment system according to claim 1, characterized in that the first tube side (21) of the exhaust gas cooler (2) is connected to the filtering device (1), and the first shell side (22) of the exhaust gas cooler (2) is used to pass a heat exchange medium. 3. A reduction furnace exhaust gas treatment system according to claim 2, characterized in that the first shell side (22) of the exhaust gas cooler (2) is divided into a plurality of cavities (23), the cavity (23) is connected to an electrically controlled switching valve (24), and a first temperature detection device (25) is provided at the outlet of the first tube side (21) of the exhaust gas cooler (2), the first temperature detection device (25) is connected to the electrically controlled switching valve (24), and the first temperature detection device (25) is used to detect the exhaust gas temperature at the outlet of the first tube side (21) of the exhaust gas cooler (2), control the electrically controlled switching valve (24), and adjust the number of cavities (23) participating in heat exchange in the first shell side (22) to adjust the heat exchange efficiency. 4. A reduction furnace tail gas treatment system according to claim 1, characterized in that the second tube side (31) of the hydrogen preheater (3) is connected to the first tube side (21) of the tail gas cooler (2), and the second shell side (32) of the hydrogen preheater (3) is used to introduce hydrogen. 5. A reduction furnace tail gas treatment system according to claim 4, characterized in that a second temperature detection device (33) is provided at the outlet of the second tube side (31) of the hydrogen preheater (3), and a flow control device (34) is provided at the inlet of the second shell side (32) of the hydrogen preheater (3), and the second temperature detection device (33) is electrically connected to the flow control device (34) for adjusting the flow of hydrogen according to the tail gas temperature at the outlet of the second tube side (31). 6. A reduction furnace tail gas treatment system according to claim 1, characterized in that a plurality of filter elements (41) are distributed in the silicon powder filter (4) along the vertical direction, and the filter element (41) is a ceramic filter element. 7. A reduction furnace exhaust gas treatment system according to claim 1, characterized in that a buffer chamber (7) is provided on the pipeline between the silicon powder filter (4) and the silicon powder collector (5), and the cross-sectional area of the buffer chamber (7) is larger than the cross-sectional area of the pipeline.