![]() A number of companies delayed or suspended their UMG-silicon operations as a result of low prices and lack of demand for UMG material for solar cells. Upgraded metallurgical grade (UMG) silicon was seen as one option to produce cheaper solar grade silicon with 5- or 6-nines purity, but the support for this technology is waning in an environment where higher-purity methods are cost-competitive. Several major players in the polysilicon industry, including Wacker Chemie and Hemlock, are developing FB processes, while at the same time continuing to produce silicon using the Siemens process as well. Several new facilities will also feature variations of the FB. MEMC Electronic Materials, a silicon wafer manufacturer, has been producing granular silicon from silane feedstock, using a fluidised bed approach for over a decade. The growing seed crystals fall to the bottom of the reactor where they are continuously removed. At the operating temperatures of 750 ☌, the silane gas is reduced to elemental silicon and deposits on the surface of the silicon seeds. ![]() At a continuous rate, high-purity silicon seeds are inserted from the top and are suspended by the upward flow of gases. In this process, tetrahydrosilane or trichlorosilane and hydrogen gases are continuously introduced onto the bottom of the FB reactor at moderately elevated temperatures and pressures. The motivation to use the FB approach is the potentially lower energy consumption and a continuous production, compared to the Siemens batch process. Arnulf Jäger-Waldau, in Solar Cells (Second Edition), 2013 3.1.2 Fluidised Bed ProcessĪ number of companies develop polysilicon production processes based on fluidised bed (FB) reactors. ![]()
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