Small-scale co-utilisation of coal and biomass

Abstract

Co-utilisation of coal and biomass for energy production results in pollutant reduction. Most notable is the impact on NOx, SOx, volatile organic compounds (VOC) and polyaromatic hydrocarbons (PAH). The aim of this study is to improve our understanding of the synergy in toxic organic emission reduction from co-firing or co-gasifying coal and biomass. Co-combustion was studied by TGA and by burning briquettes supported on a needle in a methane air flame. A range of coals of varying rank, different biomass, as well as model compounds were used. Results show that non-additive combustion behaviour is not easily explained by studying devolatilisation because of the difficulty in replicating the conditions of temperature profile and residence time experienced by the volatiles. Thus, conflicting behaviour is exhibited depending upon pyrolysis technique. However, the atmosphere during experiments appears to be more important. Non-additive combustion for both powdered and pelletised fuels was seen by TGA and studies in a methane–air burner. The coal ignites and burns at a lower temperature because of the interaction with the biomass volatile combustion region. Thus it is proposed that the reduction in emissions from co-combustion arises from enhanced reaction of the coal volatiles by mixing with biomass volatiles in a hot oxidising atmosphere.