Combustion behaviour of biochars thermally pretreated via torrefaction, slow pyrolysis, or hydrothermal carbonisation and co-fired with pulverised coal

The combustion characteristics and kinetics of straw biochars thermally pretreated via torrefaction, slow pyrolysis, or hydrothermal carbonisation (HTC) and co-combusted with bituminous coal were examined in this study to explore the effects of various pretreatment methods and blending ratios on the combustion characteristics of biochars to assess potential practical applications. Non-isothermal experiments were performed using a thermogravimetry analyser. The results showed that the thermogravimetric curve of biochar obtained after HTC was similar to that of raw straw, thereby indicating similar combustion characteristics and reactivity. The average reactivity (R-m) index of hydrochar and straw was 1.648 and 2.082, respectively. By contrast, the biochars produced after torrefaction or pyrolysis were more similar to bituminous coal, with the Rm index of 0.696, 0.78 and 0.773, respectively. A positive interaction was observed during the char combustion stage of co-firing, with the activation energy of the blends tending towards the lower side. The catalytic effect of biomass ash was likely the predominant reason for the better interaction of pyrolytic biochar with coal. (C) 2020 Elsevier Ltd. All rights reserved.