Influence of potassium carbonate catalysis and pre-treatment atmosphere on the textural, structural, and chemical properties of high and low rank coals blended with biomass and their reactivity under conventional and oxy-combustion processes

Abstract

The structural, textural, and chemical properties of coal/biomass char blends obtained under N2 and CO2 atmospheres at 700 °C were evaluated when potassium carbonate (K2CO3) catalyst was added at 2, 5 and, 10 wt%. Char blend properties were investigated by N2 adsorption, Raman spectroscopy, and X-ray photoelectron spectroscopy. Reactivity under oxy-combustion (21% O2 + 79% CO2) and conventional combustion (21% O2 + 79% N2) conditions was studied by thermogravimetry. Significant differences in characteristics and reactivity were evident between blends containing high rank anthracite coal (AC/B) and low rank lignite coal (LC/B). For AC/B chars, K2CO3 loading up to 10 wt% raised the combustion rate and decreased the activation energy over the entire conversion range under both combustion processes. However, for LC/B chars, K2CO3 loading above 2 wt% resulted in lower combustion rate and higher activation energy. The oxy-combustion process facilitated lower activation energies for both char blends compared with conventional combustion. When CO2 was used during the devolatilization process, activation energies were lower than with a N2 atmosphere, which is attributed to the gasification reaction in the blends favoring the subsequent combustion process. These results demonstrate the positive role of CO2 (the balance gas during oxy-combustion) in the thermochemical transformation of char blends.