Fluidized bed chemical looping gasification of sewage sludge with bituminous coal to produce H2 rich syngas: An examination on fuel synergy and reaction conditions

Abstract

Chemical looping gasification (CLG) is an efficient and economical solution to convert organic solid waste into hydrogen-rich syngas for fossil fuel substitution. In this work, chemical looping co-gasification (CLCG) of sewage sludge (SS) and bituminous coal (BC) with hematite as the oxygen carrier was examined in a fluidized bed. The SS-BC CLCG exhibited significant fuel synergy compared to the SS/BC CLG, enhancing the gasification efficiency and carbon conversion. The effects of several key operating variables including SS blending ratio, reaction temperature, and steam mass flow rate on CLCG performance were investigated and the optimum conditions were 20 wt% SS, 900 °C with a steam mass flow rate of 0.6 g/min. Moreover, a cyclic CLCG test was also performed to evaluate the stability of oxygen carrier reactivity and gasification performance at optimized operating conditions. After 13 cycles, the hematite still presented good or even improved performance with gasification efficiency of 80.94 %, syngas yield of 2.10 Nm3/kgfuel, and carbon conversion of 93.73 %. The improved porous structure and the ash catalyst effect were responsible for the promoted performance of the natural hematite oxygen carrier with increasing cycles. It is concluded that CLG is a promising technology to provide high-quality hydrogen-rich syngas from SS and BC mixtures.