Evaluation of the structural changes of a char produced by slow pyrolysis of biomass and of a high-ash coal during its combustion and their role in the reactivity and flue gas emissions

Abstract

One way to increase the share of biomass in the energy matrix, and reduce the greenhouse gas and emissions of SOx from fossil-fuel combustion, would be through its co-combustion with mineral coal. However, biomass has very distinct properties from mineral coal, and pyrolysis is a technique that has been studied to improve the performance of biomass in existing coal-fired power stations. A detailed investigation was conducted about the structural changes of a char produced from slow pyrolysis of biomass and of a high-ash coal throughout its combustion process, being assessed its role on reactivity. The kinetics and reactivity were investigated by thermal analysis (TGA/DTG), while structural changes were evaluated in a drop tube furnace (DTF). The biomass char was obtained from slow pyrolysis of Pinus elliottii in a fixed bed reactor at 400 °C with heating rate of 5 °C⋅min−1. Biomass char reactivity was higher than that of coal at low heating rates, and maximum reactivity was observed for both fuels around a conversion of 0.9. A burnout above 90% was obtained for biomass char at 330 ms, while for coal and a biomass char and coal blend (50/50 %wt) such burnout was observed only at 430 ms.