Co-pyrolysis of lignocellulosic biomass with low-quality coal: Optimal design and synergistic effect from gaseous products distribution

Co-pyrolysis of lignocellulosic biomass and low-quality coal can alternate fossil fuel partially and utilize biomass on a commercial scale. Gaseous products from co-pyrolysis process can be widely applied in industries due to the advantage in transportation and compression. Thus, investigation of synergistic effect and optimal design about gas products is essential for efficiently and comprehensively design of the process. In this research, three model compounds of lignocellulosic biomass (cellulose, hemicellulose, lignin) and wheat straw were co-pyrolyzed with a kind of low-quality coal via a drop tube furnace. Based on the component insight of biomass and response surface methodology, synergetic effects from gas distribution were investigated. The influence of reaction condition (biomass ratio and pyrolysis temperature) on the yield and high heat value (HHV) of gaseous products were explored. Optimal result for the objective of the highest effective gas yield during co-pyrolysis were obtained. Results revealed that both positive and negative synergic effects on yields and composition of pyrolysis gas were presented. When pyrolysis temperature was 600 °C, both wheat straw and three model compounds promoted the formation of H2 and CO. Negative effects on CO2 were observed when co-pyrolysis of cellulose/wheat straw with coal at the temperature of 600 °C to 800 °C. Whether positive or negative synergy existed depended on the mixing ratio, temperature and combined action of lignin, hemicellulose, and cellulose. For coal and hemicellulose mixtures, the mixing ratio of 0.03 and temperature of 936 °C can get the highest yield of H2 (20.56 mmol/g). Moreover, the maximum yield of CO and CO2 was obtained at cellulose mixing ratio of 0.99 and 0.98 at 787 °C and 626 °C, respectively. Based on the view of biomass composition, the results can be used to optimize the gaseous products distribution during co-pyrolysis of coal and biomass.