How should waste gases from polysilicon production be treated?
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The process of polysilicon production is becoming more and more mature. However, the treatment of waste gases caused by polysilicon production has become a headache for most manufacturers. With the expansion of polysilicon production, the problem of polysilicon pollution is becoming more and more serious. Many manufacturers focus on profits and ignore environmental issues. So how should the waste gases generated during the polysilicon production process be treated? Please actively participate in the discussion, thank you!
There are special waste gas and liquid treatments, and the solids are buried or incinerated after treatment.
Use a specialized waste gas and waste water treatment manufacturer. Generally, waste gas and waste water are treated together. Neutral water spray is used to treat the waste gas. Alkaline spray is used to treat the silicon core acid mist. Sodium hydroxide or return water is used to treat the waste water. The water can be recycled and discharged regularly.
There are too many types and sources of exhaust gases in the polysilicon production process. Generally, the exhaust gas from reduction furnaces and hydrogenation furnaces needs to be recycled. At present, most domestic polysilicon manufacturers use American CDI technology. It seems that no domestic technology is used yet (I hope that domestic technology will speed up research and development and catch up with international standards. It is actually not difficult). Acid cleaning is required during the cleaning process of silicon rods, especially hydrofluoric acid, which requires special treatment because * * There are strict requirements for fluorine-containing emissions. According to reports, some use calcium oxide and HF to react to generate Ca2F. The solids are then processed separately. There is also the tail gas from rectification or some replacement, which of course needs to be treated with a elution tower. The wastewater is then neutralized and discharged.
The waste gas of chlorosilane is treated with alkali solution and hydrofluoric acid is treated with calcium ions.
The waste gas generated is mainly acidic gases such as chlorosilane and hydrogen chloride. Milk of lime can be used to spray and neutralize these waste gases in the elution tower. The large amount of hydrolyzate produced is cleaned regularly.
The reduced exhaust gas is recycled and reused through the Siemens method. The tail gas generated during the production process is generally processed through the tail gas elution tower. The main components such as chlorosilane and hydrogen chloride generally maintain a pressure of no more than 20kpa and a rinse water flow rate of 40 to 60 m3. Of course, it can be calculated specifically that the pickling tail gas is mainly NOx, HF, etc. generated by the reaction of polycrystalline silicon blocks, silicon cores, HF, and HNO3. It is mainly treated by NaOH entering the alkali pool for neutralization reaction and acid mist elution tower treatment. The liquid chlorine tail gas is mainly replaced by liquid chlorine cylinder replacement gas and processed through an alkaline pool (about 25% NaOH).
The exhaust gas generated in polysilicon production has a special recovery system. Reduction furnace exhaust gas: There is CDI to separate hydrogen, chlorosilanes, and HCl. Hydrogen: sent back for reduction and continued use ； Chlorosilane: sent to distillation section for purification ； HCl: Send trichlorosilane synthesis. Hydrogenation furnace tail gas: mainly trichlorosilane, hydrogen, silicon tetrachloride, and other small amounts of chlorosilanes. There is also CDI separation and reuse. The specifics are similar to the treatment of exhaust gas from the reduction furnace. There are also synthetic exhaust gas treatments, all of which are treated by CDI.