Kinetics based on two-stage scheme for co-combustion of herbaceous biomass and bituminous coal

Abstract

The kinetics of co-combustion of two herbaceous biomass species (beetroot and switchgrass) with bituminous coal was evaluated using a non-isothermal thermogravimetric method (TGA). The effects of heating rates, sample kinds and blend ratios on the kinetics of co-combustion were revealed based on two-stage scheme, which referred to the two stages before and after the maximum combustion rate. The kinetic parameters and combustion reaction mechanisms were tested by combining the isoconversional method (Ozawa–Flynn–Wall) and the Coats–Redfern method in order to find out the kinetics characteristics responsible for the combustion of the samples. There were significant difference between combustion kinetics of bituminous coal and biomass. The blending ratios and the heating rates had have certain effect on the mechanisms of switchgrass/coal blends at pre-peak. The dominant mechanisms associated with co-combustion kinetics for beetroot/coal at pre-peak and post-peak were described by the Avrami–Erofeev equations. The mechanisms of co-combustion for switchgrass/coal samples at pre-peak were described by the Avrami–Erofeev equation, Z–L–T equation or Anti-Jander equation; however, at post-peak, their mechanisms were described by the Avrami–Erofeev equation. The general kinetic compensation effect correlations were deduced for all samples within the heating rates of 10–90°C/min.