A comparative performance evaluation of co-combustion of coal and biomass in drop tube furnace

Abstract

The combustion and co-combustion of coal and agricultural residues were investigated in a 0.4 kW electrically heated Drop Tube Furnace (DTF). Pure samples and their blends were studied in terms of carbon burnout percentage, NOx, SO₂ and CO emissions. It was found that Dukki Coal (DC) had higher carbon burnout compared to Chamalang Coal (CC) due to its higher Volatile Matter (VM) to Fixed Carbon (FC) ratio, VM/FC. Among the four agricultural residues namely, Rice Husk (RH), Corn Husk (CH), Sunflower Disc (SD) and Falsa Sticks (FS), CH was found to have the highest percentage of carbon burnout whereas SD had the lowest. Addition of agricultural residues into coal reduced the emission of NOx and the reduction was more with increase in proportion of biomass in the blended fuel. For NOx reduction potential, the blends of agricultural resides with coal samples could be arranged in following order, FS > RH > CH > SD at same Biomass Blending Ratio (BBR) on thermal basis. The co-firing was found to have a positive impact on the emission reduction of SO₂. Among the four biomass fuels, the RH was found to have highest reduction in SO₂. The fuel blends could be arranged in following order for SO₂ reduction potential RH > FS > CH > SD. Among the two coal samples, blends of DC with all agricultural residues were found to have higher emissions of SO₂ due to the inherently large sulfur content in DC. The co-firing was found to have lower emissions of CO and higher carbon burnout for all blends compared to combustion of coal only. It was noticed that with an increase in BBR, the emission of CO reduced drastically for all fuels. The highest reduction was observed for blends of coal with Corn Husk (CH).