Method and system for utilizing waste heat of polysilicon reduction tail gas

Abstract

The invention provides a method for utilizing waste heat of polysilicon reduction tail gas, which comprises the following steps: using the cooling capacity of circulating water from the Liebig condensing tube in the first sleeve to cool the reduction tail gas output from the reduction furnace, and making the first set The reduced tail gas after the tube cooling enters the Liebig condensation tube; in the Liebig condensation tube, the cooling capacity of the feed gas from the static mixer and the circulating water from the circulating water system is used to control the reduction from the first sleeve. The tail gas is cooled again, and the feed gas whose cooling capacity has been utilized by the Liebig condensing tube enters the reduction furnace, and the circulating water whose cooling capacity has been utilized by the Liebig condensing tube enters the first casing. Correspondingly, a polysilicon reduction tail gas waste heat utilization system is also provided. The invention can not only reduce the unit power consumption of polysilicon production, improve the primary conversion rate of TCS, but also avoid appearance problems of products and effectively reduce the temperature of reduction tail gas.

Description

technical field [0001] The invention relates to the technical field of polysilicon production, in particular to a polysilicon reduction tail gas waste heat utilization method and a polysilicon reduction tail gas waste heat utilization system. Background technique [0002] Polysilicon is the building block material for the solar photovoltaic industry. At present, the production of polysilicon mainly adopts the improved Siemens method (that is, the reduction method of trichlorosilane), and the basic principle is to use SiHCl 3 (Trichlorosilane: trichlorosilane, referred to as TCS) and H 2 The vapor deposition reaction is carried out in a reduction furnace according to a certain ratio, and the reaction temperature is 1080°C to 1100°C, and the polysilicon crystal particles produced are deposited and grown on the silicon core to obtain rod-shaped polysilicon. [0003] The specific reaction equation is: [0004] 3SiHCl 3 +H 2 →2Si+5HCl+SiCl 4 [0005] In the process of prod...

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Problems solved by technology

[0007] However, the inventors have found that in the existing method, although a suitable process control can be found through long-term process exploration, the primary conversion rate of TCS and the unit power consumption of polysilicon production can reach a better level, wherein the primary conversion rate of TCS can reach 9.4 %-9.8%, the unit power consumption can reach 60-62kwh / TSi, but in the process of pursuing these indicators, due to the high temperature of the silicon rod surface, the polysilicon surface of the silicon rod in the furnace near the crossbeam changes, resulting in this The surface of the silicon rod is uneven and may contain some impurities, which is difficult to meet the customer's requirements for the appearance and purity of the silicon rod

Therefore, although the existing method can reduce the unit consumption of electricity and improve the primary conversion rate of TCS, the resulting problems of appearance and purity of silicon rods will lead to low prices when the products are sold, thereby indirectly increasing production. cost

[0008] In addition, energizing the silicon rods to increase the surface temperature of the silicon rods, thereby increasing the reaction temperature in the furnace, will also cause the temperature of the reduction tail gas output from the reduction furnace to be too high (500-550 ° C), and the reduction tail gas will be exhausted even if it passes through the existing However, due to the high temperature of the reduction tail gas and the limited heat transfer area, the temperature of the reduction tail gas after heat exchange is still very high (220-240 ° C), which leads to an increase in the cooling load of the downstream process, and then lead to an increase in production costs

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