Polycrystalline silicon reduction furnace raw material gas feeding amount controller

Abstract

The invention discloses a polycrystalline silicon reduction furnace raw material gas feeding amount controller. A polycrystalline silicon reduction furnace comprises an air inlet and a gas outlet. The fed raw material gas comprises tail gas discharged by the polycrystalline silicon reduction furnace, newly fed trichlorosilane and newly fed hydrogen. The tail gas comprises tail gas trichlorosilane, tail gas hydrogen chloride and tail gas hydrogen. The controller comprises a detection mechanism for detecting mole content of hydrogen chloride in tail gas, a raw material gas feeding mechanism and a master controller. The detection mechanism for detecting mole content of hydrogen chloride in tail gas is electrically connected to the master controller. The raw material gas feeding mechanism is electrically connected to the master controller. The controller realizes on-line automatic control of a mole amount of tail gas fed into the reduction furnace, is free of personnel monitoring, keeps a ratio of trichlorosilane to hydrogen chloride in the reduction furnace in a normal high efficiency production reasonable scope by timely change of a used tail gas amount in polycrystalline silicon reduction furnace production so that the tail gas is reasonably used to a highest degree.

Description

technical field [0001] The invention belongs to the field of polysilicon production, in particular to a polysilicon reduction furnace [0002] The control device of raw material gas feeding amount. Background technique [0003] Polysilicon is the basic material of the solar photovoltaic industry, and its main production process is the improved Siemens method (ie trichlorosilane reduction method, SiHCl 3 +H 2 →Si+3HCl). The large-scale application of this process in my country has a history of nearly 10 years. Since the core technology has not yet broken through, the circulation volume of refined trichlorosilane (TCS) used as raw material gas reaches 55-60 tons for every ton of polysilicon produced. , while producing about 16 tons of silicon tetrachloride (45% SiCl 4 From thermal decomposition of TCS, 4SiHCl 3 →Si+3SiCl 4 +2H 2 , the reason for thermal decomposition is due to the low amount of hydrogen); in addition, when the silicon rod grows to 135-150 mm, the diamete...

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Problems solved by technology

The large-scale application of this process in my country has a history of nearly 10 years. Since the core technology has not yet broken through, the circulation volume of refined trichlorosilane (TCS) used as raw material gas reaches 55-60 tons for every ton of polysilicon produced. , while producing about 16 tons of silicon tetrachloride (45% SiCl 4 From thermal decomposition of TCS, 4SiHCl 3 →Si+3SiCl 4 +2H 2 , the reason for thermal decomposition is due to the low amount of hydrogen); in addition, when the silicon rod grows to 135-150mm, the diameter of the silicon rod needs about 100 hours of deposition time; thus, the current situation of high energy consumption in polysilicon production

The main reason is that during the growth of polycrystalline silicon rods, there is an over-thick gas interface layer (the Boundary Layer) on the surface of the hot silicon rods, resulting in TCS and H 2 The speed of diffusion (rather than convection) to the hot silicon rod surface is greatly reduced (the mass transfer coefficient in the interface layer is proportional to the square root of the average linear velocity of the raw material gas), and the HCl produced on the hot silicon rod surface cannot diffuse rapidly through the interface layer The silicon rods are corroded, resulting in a very slow deposition rate of polysilicon, a very low TCS conversion rate (Single-Pass Conversion Efficiency), a large number of TCS and H that do not pass through the diffusion layer and are short-circuited at the exhaust gas outlet. 2 As the tail gas enters the recovery unit, a large amount of unconverted TCS in the tail gas enters the recovery system, resulting in a large increase in the circulation of refined trichlorosilane and a heavier load on the recovery unit

[0004] Through the unremitting efforts of colleagues in the industry, although there has been some technological progress compared with 10 years ago, there has been no substantial breakthrough. The tail gas composition of the polysilicon reduction furnace in the production process is uncontrollable, resulting in the content of TCS entering the recovery system ( 55~60mole%) is much higher than the standard value of 31mole%, which increases the circulation of refined TCS in the whole production process, and the primary conversion rate of trichlorosilane entering the polysilicon reduction furnace is only 8~11%, resulting in polysilicon The production energy consumption remains high, and the production cost has not dropped much.

[0005] The polysilicon deposition reactors currently used by all polysilicon production enterprises in my country are mass transfer limited or diffusion limited chemical vapor deposition reactors. For various pairs (12, 18, 24, 36, 48) The deposition rate is very low. Although they are all chemical vapor deposition reactors (polysilicon reduction furnaces) designed for the design concept of increasing the deposition area and low deposition rate, the chemical vapor deposition reactors have not fundamentally effectively solved the problem of polysilicon reduction. The uniform distribution of the gas field and temperature field in the furnace did not eliminate the problem of the laminar layer on the surface of the silicon rods. The deposition rate of polysilicon was still very slow, and a large amount of unreacted trichlorosilane entered the recovery unit with the tail gas, resulting in three A lot of waste of chlorosilane

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