Co-combustion characteristics of coal with invasive alien plant chars prepared by torrefaction or slow pyrolysis

Lignocellulosic samples of Lantana camara (LC) and Mimosa pigra (MP) were pre-treated by torrefaction (300 degrees C) or pyrolysis ( > 500 degrees C) in order to study their potential use as co-fuels with coal. Combustion of the resultant chars, three coals and some blends was investigated by thermogravimetric analysis (10 degrees C min(-1)). The effects of biomass composition, pre-treatment temperature of char and blending ratio, on combustibility parameters of ignition, burnout and combustion indices were determined. The addition of reactive char in the fuel mixture consistently resulted in the reduction of ignition temperature, while lowered burnout temperatures of the blends indicated interactions between char and coal during co-combustion. Blends up to 15% showed similar combustion characteristics as those of the parent coals, with co-combustion occurring within the coal combustion zone. Most of the lowest combustion indices were obtained at 30% blends, mainly due to combustion occurring over a wider temperature range, while for blends >= 60%, co-combustion took place in the char combustion zone, with better co-combustion efficiencies, by up to 244% for 90% blend when compared with parent coal. Comparatively, pyrolysed char blends recorded higher combustion indices than torrefied sample blends. The results also showed that lignocellulosic composition of the precursor influenced the combustion mechanisms.