Catalytic effects of key compositions in biomass ashes on coal gasification reactivity and structural evolution characteristic during gasification process

Co-gasification of biomass and coal is featured by decreasing demand for coal resource and allowing alkali and alkaline earth metals in biomass ashes to catalyze gasification reactions. However, due to diverse compositions of biomass ash, catalytic mechanisms of biomass ash and structural evolution characteristic remains ambiguous. In this work, an in-depth investigation into catalytic effects of biomass ash on coal gasification was conducted using simulated ashes and the catalytic mechanisms of key compositions in biomass ash on coal gasification were elucidated in detail. The results show that K and Fe is proved to have synergistic catalytic effects on coal gasification reactivity, which is ascribed to that Fe addition lowers melting temperature of sample, thereby enhancing mobility of K. Moreover, the silicon content and temperature are closely related with gasification efficiency. When temperature was 900 degrees C, carbon conversion of all samples achieved 100 % within 16.7 mins, of which the shortest time was just 7.2 mins. Kinetic analyses indicated that random pore model better described reaction process compared with the others. Gas product distribution verifies that when Si/K ratio was constant, H2 content increased proportionally with the Fe ratio. When introduced with additives, all sample surfaces became rougher with cracks and pores emerging, which could account for that gasification efficiency of samples with additives was markedly improved. Scanning electron microscope (SEM) images showed K and Fe could expand pore structure and high temperature enhanced this effect. The incorporation of K and Fe was also proved to enhance the conversion of microcyclic aromatic structures to macrocyclic ones during coal gasification process, corresponding to the increase of gasification efficiency.