Modelling co-combustion of wood and coal in circulating fluidised beds

In this work carbon combustion efficiencies in circulating fluidised bed combustors (CFBC) when cofiring biomass and coal mixtures were studied. Experimental results were obtained from the combustion of two kinds of coals with forest residue (pine bark) in two pilot plants (0.1 and 0.3 MW). The effect of operating conditions such as percentage of biomass in feed, temperature, excess air, air velocity, coal particle size distribution and percentage of secondary air on carbon combustion efficiency was analysed. A mathematical model to predict the behaviour of the co-combustion of coal and biomass in a CFBC has been developed. The developed model can predict the different gas concentrations along the riser (O2, CO, CH4, etc.) and the carbon combustion efficiency. The experimental results of carbon combustion efficiencies and gas emissions were compares with those predicted by the model and a good correlation was found for all the conditions tested