Prediction of high-temperature rapid combustion behaviour of woody biomass particles.

Abstract

Biomass energy is becoming a promising option to reduce CO2 emissions, due to its renewability and carbon neutrality. Normally, biomass has high moisture and volatile contents, and thus its combustion behaviour is significantly different from that of coal, resulting in difficulties for large percentage biomass cofiring in coal-fired boilers. The biomass combustion behaviour at high temperatures and high heating rates is evaluated based on an updated single particle combustion model, considering the particle size changes and temperature gradients inside particle. And also the apparent kinetics determined by high temperature and high heating rate tests is employed to predict accurate biomass devolatilization and combustion performances. The time-scales of heating up, drying, devolatilization, and char oxidation at varying temperatures, oxygen concentrations, and particle sizes are studied. In addition, the uncertainties of swelling coefficient and heat fractions of volatile combustion absorbed by solid on the devolatilization time and total combustion time are discussed. And the characterised devolatilization time and total combustion time are finally employed to predict the biomass combustion behaviour. At the last, a biomass combustion/co-firing approach is recommended to achieve a better combustion performance towards large biomass substitution ratios in existing coal-fired boilers.