Thermodynamic optimisation and computational analysis of irreversibilities in a small-scale wood-fired circulating fluidised bed adiabatic combustor

An analysis of irreversibilities generated due to combustion in an adiabatic combustor burning wood was conducted. This was done for a reactant mixture varying from a rich to a lean mixture. A non-adiabatic non-premixed combustion model of a numerical code was used to simulate the combustion process where the solid fuel was modelled by using the ultimate analysis data. The entropy generation rates due to the combustion and frictional pressure drop processes were computed to eventually arrive at the irreversibilities generated. It was found that the entropy generation rate due to frictional pressure drop was negligible when compared to that due to combustion. It was also found that a minimum in irreversibilities generated was achieved when the Air–Fuel mass ratio was 4.9, which corresponds to an equivalence ratio of 1.64, which are lower than the respective Air–Fuel mass ratio and equivalence ratio for complete combustion with theoretical amount of air of 8.02 and 1. - Highlights: • Entropy generation rate in an adiabatic combustor firing pine wood was investigated. • Most entropy generation rate due to combustion process. • Minimum entropy generation rate was found to occur for an Air–Fuel mass ratio of 4.9. • Molar fractions of species H2 and H2O are equal at minimum entropy generation rate