Coal Pyrolysis in a Fluidized Bed for Adapting to a Two-Stage Gasification Process

Coal pyrolysis is generally performed in atmospheres without oxygen and at temperatures below 650 degrees C for producing pyrolysis liquid and gas. To support the development of a new two-stage gasification process integrating a fluidized-bed pyrolysis and a downdraft fixed-bed gasifier, this paper investigated the Coal pyrolysis in atmospheres containing oxygen and steam and at temperatures up to 900 degrees C to understand the viable pyrolysis conditions in view of process adaptation. The examined pyrolysis characteristics include the product distribution, char gasification reactivity, and tar composition The pyrolysis gas yield, especially the yields of H(2) and CO, increased with elevating the temperature and mass ratio of steam/coal (S/C). Additing O(2) to the reaction atmosphere promoted the formation of CO and CO(2) but decreased that of H(2). the inclusion of O(2) and steam in the atmosphere resulted in chars with a larger surface area and more micropores. At 900 degrees C in N(2) atmosphere or at 850 degrees C with oxygen in the atmosphere (e.g.; at an excessive air ratio of 0.22), graphitization was observed in the produced char, which lowered the char gasification reactivity. Analyzing the produced tar via thermogravimetry,coupled with Fourier, transform infrared (TG-FTIR) spectroscopy clarified that the presence of steam significantly affected the tar composition by leading to more aliphatic hydrocarbons and lowering the contents of single-ring aromatics, phenols, and ketonic species. Thus, the pyrolysis gas product from a steamcontaining reaction atmosphere would be easier to crack and be reformed in the downstream char gasifier.