NO and SO2 emissions from combustion of raw and torrefied biomasses and their blends with lignite

Abstract

The impact of torrefaction on the NO and SO2 emissions from combustion of biomass was investigated. Combustion experiments were carried out with two torrefied biomass fuels, i.e., poultry litter and olive tree pruning and their blends with lignite using a bench scale single particle reactor. For comparison, NO and SO2 emissions from tests with untorrefied biomasses and their blends with lignite were also investigated. The total release of SO2 and NO for each fuel was determined at three different temperatures: 900, 1000, and 1100 °C. The NO release from the untorrefied biomasses was found to be lower than those from torrefied biomasses, despite their higher fuel- N content. In case of co-combustion of both raw and torrefied biomass with lignite, the NO release was lower than the anticipated one. On the other hand, in the co-combustion experiments, blends with torrefied biomass showed a larger reduction in SO2 release than the blends with raw biomass.The study revealed that the SO2 emissions from blends are not proportional to the mixing ratio of the fuels and to the emissions properties of the respective fuels. No clear correlation was detected between the NOx emissions and fuel-N content. In addition to the NO and SO2 emissions, the sintering propensity of the ash residue were investigated using scanning electron microscopy (SEM).