Distributed activation energy kinetic modeling of combustion of bagasse char, rice straw char and rice husk char blends

Utilizing lignocellulosic biomass agro-residues in the bioenergy sector is an effective way to manage the rising energy needs and minimize the carbon footprint, while significantly reducing the solid waste. This study provides a pathway for the use of lignocellulosic biomass, the biochars derived from them, and their blends for bioenergy generation. This research work investigates the combustion characteristics and kinetics of biochars derived from sugarcane bagasse (BG), rice straw (RS) and rice husk (RH), and binary blends of biochars. The combustion performance was assessed using key parameters such as ignition temperature, peak temperature, burnout temperature and maximum combustion rate. The combustion experiments were conducted in a thermogravimetric analyzer, and the kinetics was studied using distributed activation energy model. Three pseudocomponents, viz., cellulose, hemicellulose and lignin, were considered for biomass, while two pseudocomponents, viz., partially decomposed lignin and carbonaceous matter (char), were considered to model the combustion behaviour of biochars. The results signify that the combustion behaviour of biochars is similar to that of coal. During the combustion of individual biochars and their mixtures, the char decomposition exhibited the highest activation energy (247.6 kJ mol^-1), while combustion of partially decomposed lignin had the lowest activation energy. Notably, the activation energy for combustion of partially decomposed lignin differed significantly among the biochars and their blends. This was maximum for biochar derived from BG (175.5 kJ mol^-1) and minimum for biochar derived from RS (130.8 kJ mol^-1). Importantly, the activation energy of combustion of biochar blends was described by using a binary mixture rule, without fitting any kinetic parameters. Burning time, heat release rate, fuel consumption and ash generation analysis demonstrate that biochars and their blends can be utilized in the existing thermal utilities, and blending biochars derived from different biomass feedstocks is shown to enhance the energy potential of the mixtures.