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| We use a modified Siemens process to produce polysilicon. The modified Siemens process results in higher utilization of TCS, requires less electricity and is also more environmentally friendly as less pollutants are produced than the original Siemens reactor process. The process includes four distinct steps: (1) hydrochlorination; (2) distillation; (3) poly deposition; and (4) vent gas recovery. |
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| Hydrochlorination Facility in Xuzhou |
Hydrochlorination
This process is used to recycle the silicon tetrachlorosilane (“STC”) produced as a by-product from the poly deposition process, combining the STC with hydrogen gas, to produce TCS. HCl, a by-product of this process, will be mixed with metallurgical silicon simultaneously, to further produce TCS. |
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| Distillation Tower in Xuzhou |
Distillation
This process involves separating the unused HCl and STC from the TCS through distillation and condensation, that is, pressure and temperature separation. The TCS will then undergo further distillation and results in high purity TCS feedstock to be used in the poly deposition process. |
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| Phase II Deposition Hall in Xuzhou |
Poly Deposition
The resulting purified TCS is mixed with hydrogen and vaporized into a gas. The resulting gas is then released into the reactor with heated silicon rods inside the cooled bell jar of the reactor. The silicon contained in the gas is deposited on the heated rods, which gradually grow until the desired diameter has been reached. The reactor must then be shut down, and the rods cooled before being broken into chunks. |
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| CDI Vent Gas Recovery System in Xuzhou |
Vent Gas Recovery
The manufacturing of silicon crystals generates a vent gas comprised primarily of hydrogen, chlorosilanes and hydrogen chloride. The vent gas is separately recovered using a low temperature absorption method. We use the CDI vent gas recovery system which combines compression, cryogenic condensation, catalytic reaction, distillation, ambient absorption and cryogenic absorption, to separate the vent stream into components that are readily recycled. Mixed chlorosilanes are recovered as a liquid stream suitable for distillation to TCS for reuse, and STC, which can be converted to TCS through the hydrochlorination process. |
| Anhydrous hydrogen chloride is recovered with high purity, suitable for use in TCS production. Recovered hydrogen typically contains contaminants of less than 10 parts per million (“ppm”) in total and can be recycled to the TCS vaporizer without further treatment. For some applications, CDI has achieved less than 1 ppm total contaminants (99.9999% pure hydrogen). The Siemens reactor recovers and utilizes the vent gas, which enhances the quality of the polysilicon produced and reduces the need to store or dispose of by-products. |
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