Production technology of polycrystalline silicon
Hydrogen preparation and purify processes, through electric desalted water to obtain hydrogen in electrolyzer. Electrolysis of hydrogen after cooling, separating the liquid, enter into the deaerator, under the role of catalyst, trace oxygen in the hydrogen react with hydrogen to generate water and being removed.
The hydrogen through a group of adsorptive dryer to be dried after removed oxygen. The purification and after drying hydrogen gas fed to the hydrogen storage tank, and then sent to the hydrogen chloride synthesis, hydrogen reduction of trichlorosilane, silicon tetrachloride hydrogenation step.
The hydrogen from hydrogen preparation and purification process and the recycle hydrogen returns from syngas dry separation process respectively enter into hydrogen buffer tank and mixed in the tank. The hydrogen out from hydrogen buffer tank was introduced at the bottom of the combustion of hydrogen chloride synthesis furnace gun. The chlorine from liquid chlorine vaporization process through chlorine buffer tank, also introduced to bottom hydrogen chloride synthesis furnace combustion gun. The mixed gas of hydrogen and chlorine is ignited in the outlet of the combustion gun, the combustion reaction was generated the hydrogen chloride gas. The hydrogen chloride gas out of the synthesis furnace through air cooler, water cooler, deep cooler mist separator was sent to trichlorosilane synthesis process.
To guarantee security hydrogen chloride gas absorption system is mainly composed of two hydrogen chloride falling film absorber and two sets of hydrochloric acid circulation tank, the hydrogen chloride gas composed by hydrochloric acid circulation pump, can use water to absorb hydrogen chloride discharged by the plant load adjustment or emergency reliefgas. The system maintains continuous operation, can receive and absorb the hydrogen chloride gas discharged by the device.
The device is a set of chlorine gas treatment system mainly composed by the exhaust gas treatment tower, lye circulation tank, lye circulation pump and lye cycle cooler. When necessary, the chlorine in the chlorine gas buffer tank can be fed into the exhaust gas treating tower, washed with aqueous sodium hydroxide to remove. The exhaust gas treatment system maintains continuous operation, to ensure that can be received and processed the chlorine-containing gas at any time. According to metal powder supplier, the polycrystalline silicon production should use silicon powder as the raw materials, raw silicon powder by lifted, through silica fume hopper discharged into the silica fume receiving hopper. Silica fume from the receiving hopper into the middle of the hopper, the silicon powder in supply hopper sent to trichlorosilane synthesis furnace feed tube.
In the trichlorosilane synthesis furnace, silicon powder and hydrogen chloride gas form a fluidized bed and react, generate trichlorosilane, silicon tetrachloride, dichloro dihydro silicon, metal chloride, polychloroprene silane, hydrogen etc. is generated at the same time, this mixed gas is referred to as the trichlorosilane synthesis gas. This reaction was giving off a lot of heat. The outer wall of the synthesis furnace is provided with a water jacket, through the jacket water take away the heat to maintain the temperature of the furnace wall. Out of the top of the synthesis furnace entrained synthesis gas which contains silicon powder, through the dry dust removal system to remove silicon powder, which composed by three cyclone dry dust removal system, sent to wet dust removal system, washed by liquid silicon tetrachloride, portion fine silica dust in the gas was washed down; while washing, inject wet hydrogen to contact with the gas, part of the metal oxide contained in the gas will be removed by hydrolysis. The synthesis gas removed silicon powder and be purified, sent to mixed gas dry separating step.
In the reduction furnace, get the polycrystalline silicon rod from furnace, cut, broken into lumps of polycrystalline silicon. Use hydrofluoric acid and nitric acid treating polycrystalline silicon, and then use ultrapure water washing polysilicon block, then dry the polysilicon block. In acid etching process will have hydrogen fluoride and nitrogen oxide gases escape to the air, so use the fan through the hood at the top of the wind shield in the acid etching treatment tank to absorb the containing hydrogen fluoride and nitrogen oxides air, then sent the gas to an exhaust gas processing apparatus for processing, discharge in the standard. Through tested the block polysilicon products which meet the required quality indicators were sent to be packing.
Article Tags: Hydrogen Chloride Synthesis, Dust Removal System, Polycrystalline Silicon, Hydrogen Chloride, Chloride Synthesis, Silicon Tetrachloride, Buffer Tank, Synthesis Furnace, Trichlorosilane Synthesis, Silicon Powder, Silica Fume, Dust Removal, Removal System
Source: Free Articles from ArticlesFactory.com
ABOUT THE AUTHOR