Effect of freeboard extension on co-combustion of coal and olive cake in a fluidized bed combustor

In this study, flue gas emissions and combustion efficiencies during combustion and co-combustion of olive cake and coal were investigated in a bubbling fluidized bed. Temperature distributions along the combustion column and flue gas concentrations of O2, CO, SO2 and NOx were measured during combustion experiments. Two sets of experiments were performed to examine the effect of fuel composition, excess air ratio and freeboard extension on flue gas emissions and combustion efficiency.The results of the experiments showed that coal combustion occurs at lower parts of the combustion column whereas olive cake combustion takes place more in the freeboard region. As olive cake percentage in the fuel mixture increased, CO emissions increased, SO2 and NOx emissions decreased. Additionally, flue gas emissions could be lowered with the freeboard extension while burning biomass or biomass/coal mixtures. Noticeable decrease in CO emissions and slight increase in combustion efficiencies were observed with a column height of 1900 mm instead of 900 mm.