AVAILABLE FOR IMMEDIATE SALE
Various units with technology package from a 2000 tons/year Polysilicon facility (solar cell grade N6 and N7) based on hydrochlorination (using hydrogenation reactors) and fluid bed technology (in TCS Decomposition reactors)
Equipment modules ready to relocate and reinstall
Plant new in 2008, shut down due to adverse market conditions and global financial crisis.
Raw Material: Metallurgical grade Silicon (MGS)
Impurities are removed from MGS by producing a silicon containing compound that can be refined to a very high purity. This compound is then decomposed under controlled conditions to deposit silicon in a form that can be used in the Photovoltaic or Semiconductor industries.
Major Units available:
Unit 100: TCS Production
This area converts the MG-silicon solids into the TCS liquid. Pre-ground MGS is mixed with a copper catalyst. The mix is dried and fed into the fluid-bed synthesis reactor. The mix is reacted with STC and Hydrogen to produce TCS. The hot gas leaving the synthesis reactor passes through a separator before being condensed and fed into a high-pressure degasser column. The hydrogen gas exits from the top of degasser then goes to the hydrogen compression station (Area 500) being recycled back to the reactor. The liquid from the degasser is reduced in pressure then further cooled by heat exchange with cool STC being pumped back to the reactor. Two synthesis reactor trains are implemented in the current design. The resulting cooled TCS/STC liquid is mixed with the stream from the other train and fed to Area 200.
Unit 200: TCS/STC Purification and Recovery
This area separates and purifies the TCS stream to a high purity suitable for deposition of high purity silicon and purifies the STC to a purity suitable for recycle. In this area, several distillation columns equipped with condensers and re-boilers are used to separate the TCS from the TCS/STC mix stream. Furthermore, TCS stream is purified to remove the impurities before it is sent to the 300 Area for decomposition. The STC stream is also purified before it is recycled back into the Area 100 reactor.
Unit 300: TCS Decomposition and Polysilicon Production
This area contains the fluidized-bed TCS decomposition reactors and auxiliary equipments. Area 300 consists mostly of the decomposition reactors and distillation columns with re-boilers and condensers. In the fluidized-bed reactors, the pure TCS is decomposed into pure silicon, STC, and hydrogen. The silicon is collected and sold to our customers. The STC is separated and purified from the unreacted TCS and then recycled to hydrogen reactor. The unreacted TCS is recycled to the decomposition reactor.
Polysilicon Process Details
MGS is reacted with Silicon Tetrachloride (SiCl4) and Hydrogen at a high temperature and high pressure in a hydrogenation reactor to produce Trichlorosilane (SiHCl3). Many of the impurities in the MGS are converted into compounds that contain hydrogen and/or chlorine.
Hydrogen that has not been reacted in the reactor and gaseous materials produced in the hydrogenation reactor, such as methane (CH4), are separated from the reactor effluent. These gaseous contaminants are removed from the hydrogen, concentrated, neutralized, and scrubbed. The effluent from this scrubber will be discharged into the atmosphere in compliance with the requested permit. The purified hydrogen is recycled to the hydrogenation reactor.
Next, solid contaminants are removed from the process stream and held for further processing. The solid contaminants stream contains some Silicon Tetrachloride (STC) and Trichlorosilane (TCS) in the liquid state.
The Trichlorosilane that was produced in the hydrogenation reactor is then separated from the Silicon Tetrachloride that was not consumed in the hydrogenation reactor.
The Trichlorosilane undergoes further distillation to remove additional impurities. The small impurity stream which contains Dichlorosilane, Trichlorosilane, and Boron Trichloride, is mixed with the waste stream in item 3 above.
The Silicon Tetrachloride stream is distilled to remove a small amount of solid and higher boiling liquid materials. This small stream contains Silicon Tetrachloride, Titanium Tetrachloride, and a small amount of solids. The stream is mixed with the waste stream in items 3 and 5 above.
The purified Silicon Tetrachloride is recycled to the hydrogenation reactor.
The waste stream is reacted with water to render it harmless. Chloride containing materials are oxidized, and the resulting hydrochloric acid is neutralized with Sodium Hydroxide to produce common salt (NaCl). The small amount of Hydrogen that is produced is processed through the scrubber.
The pure Trichlorosilane (from 5 above) is directed to a high temperature, low pressure reactor where it decomposes into pure Silicon and Silicon Tetrachloride. The Silicon is collected and sold to our customers. The Silicon Tetrachloride is separated from the unreacted Trichlorosilane and recycled to the hydrogenation reactor. The unreacted Trichlorosilane is recycled to the decomposition reactor.