Discussion on CDI in polysilicon production

CDI dry exhaust recovery; basic principle of dry recovery: The components such as H2, HCl, and SiCl4 in the exhaust gas are reduced, followed by bubbling and scrubbing with chlorosilane. The mixture is then pressurized and cooled to a certain temperature, at which point SiCl4 and SiCl3 can be almost completely condensed. The condensed chlorosilane mixture, after being separated in a separation tower, yields SiHC12 and SiHC11 respectively. SiHC13 is sent directly back to the reduction process for the production of polycrystalline silicon, while SiHC11 is partially converted into SiHC12 in a hydrogenation unit; after further separation and purification, it is also sent back to the reduction process for polycrystalline silicon production. The compressed and condensed non-condensable gases are H2 and HCl. Under high pressure and low temperature conditions, HCl is dissolved in SiHCl3 using SiHCl3 as an absorbent; in other words, HCl is absorbed by SiHCl3, thereby allowing H2 to be separated. The H2 obtained after separation still contains trace amounts of HCl. To prevent HCl from affecting the deposition rate of polycrystalline silicon, the H2 is passed through an adsorption tower again to remove these trace amounts of HCl, resulting in pure H2 free of moisture and other impurities, which can then be reused in the reduction process. HCl absorbed by SiCl4 can be desorbed from SiHCl4 under conditions of increased temperature and reduced pressure. The desorbed HCl is cooled to a certain temperature under a specific pressure, so that the residual SiHCl3 content in it reaches an acceptable level; thereafter, it is sent to the chlorination process to produce SiHCl3. The desorbed SiHCl4 is used for recirculation in the absorption tower.

I am involved in the design of dry-process recovery for polysilicon. Given the large fluctuations in exhaust gas flow rates, I’m looking for suggestions on how to ensure that the entire processing system can continue to operate properly even under such drastic changes in flow rate. I would appreciate any advice from experts in this field.

If the self-regulating valve becomes clogged or some other fault occurs that requires local shutdown for maintenance, the flow rate and voltage must be kept constant. The control of voltage and flow rate is crucial.

At the beginning, the traffic volume is low and the voltage is relatively low compared to later stages. As the rod grows thicker, more flow is required, and the voltage also increases slightly. The pressure remains constant. The amount of exhaust gas is also higher. The flow rate control in the heat exchange section should also be increased accordingly.

The difficulties lie in determining the time and the process flow!

The difficulty lies in the fact that the conversion rate cannot be increased.

The difficulty lies in how to continuously feed the material that has condensed.

CDI-chemical design institute is just a design company; they merely carried out the complete engineering design for exhaust gas recovery and sold it as a packaged solution

The importance of CDI in the polysilicon industry lies not only in the issue of recovering exhaust gases and recycling them, but more importantly, and in the long term, in environmental concerns

In terms of recycling, the dry recycling technology developed by CDI is capable of recovering all the exhaust gases generated during reduction and other processes and separating them individually, which creates highly favorable conditions for their subsequent separate utilization；