Regasification properties of industrial CFB-gasified semi-char

Abstract

Fluidized bed (FB) gasification provides a promising way for the clean and effective utilization of low-rank coal. However, massive amounts of high-carbon-containing gasified semi-chars are produced, which greatly reduces its total carbon conversion. The disposal of the semi-char has become an intractable problem. Regasification of the semi-char is a possible way to realize further utilization of the residual carbon and achieve higher carbon conversion of coal gasification. In this paper, the regasification properties of the ultrafine semi-char, obtained from an industrial circulating fluidized bed gasifier, were investigated via thermogravimetric analysis and bench-scale study in a FB reactor. The kinetic parameters are derived by four different reaction models, namely homogeneous model (HM), shrinking core model, random pore model and modified random pore model (MRPM). Both non-isothermal and isothermal tests show that the chemical reactivity of the semi-char is poorer than the coal char. A higher temperature greatly favors regasification of the semi-char. For the studied reaction models, MRPM is the most favorable one for both coal char and semi-char. The activation energy of the semi-char is slightly higher than that of the coal char. Stable regasification of the semi-char in a FB reactor is achieved, and the residual carbon is further utilized. Increasing oxygen concentration could largely improve the heat value of the fuel gas, but slightly decrease the carbon conversion. Higher temperature operation greatly benefits the conversion of the residual carbon in the semi-char. Consequently, it will be considered feasible that the semi-chars are reclaimed and reused as feedstocks for gasification.