Where is high-purity hydrogen used in polysilicon production?
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Since I don’t understand this industry, I’m asking. Which step requires high-purity hydrogen? Is it usually hydrogen produced by electrolyzing water? What are the standards for hydrogen? I heard someone say that hydrogen also needs to be recovered and purified – what does that mean?
Both reduction and hydrogenation require high-purity hydrogen, which is generally produced by electrolysis, with a dew point of below -65 degrees and an impurity content of less than 3 PPM. Due to the relatively low conversion rate, most of the hydrogen is wasted; therefore, to reduce costs, CDI recovery technology is now widely used.
In addition to reduction and hydrogenation, hydrogen displacement in the exhaust gas recovery unit equipment as well as the regeneration of adsorption tower equipment also require high-purity hydrogen; therefore, a large amount of high-purity hydrogen is needed before the exhaust gas recovery unit is put into operation.
Specifications for hydrogen: Electrolytic hydrogen: purity of 99.8%. Recycled hydrogen: purity of 99.9%; impurity levels – N2 < 10 vppm, HCl < 1 vppm, SiH2Cl2 < 1 vppm, SiHCl3 < 1 vppm, SiCl4 < 1 vppm. The hydrogen used in the reduction workshop is utilized not only in combination with trichlorosilane but also for cleaning the viewports, thereby preventing silicon oil from obscuring the lenses； The hydrogenation unit uses hydrogen, which is mixed with silicon tetrachloride, as well as hydrogen used for purging when the furnace is shut down ； It will also be needed on the CDI side. The data wasn’t easy to obtain; please give it some extra points. Thank you.