The effects of particle size, fuel blending ratio, moisture content and excess air ratio on combustion efficiency and air emissions (CO2, CO, SO2 and NOx) from the co-combustion of white pine or peat with a Canadian lignite coal, were examined in a pilot-scale bubbling fluidised bed combustor. Pelletising was important for the efficient combustion of wood due to its high volatile content. Co-firing lignite and pine pellets gave a proportional reduction in SO2 and NOx emissions with blending ratio, while co-firing of peat and lignite resulted in increased SO2 emissions, but decreased NOx emissions. Moisture promotes combustion but with increased CO emissions, and results in increased NOx emissions, and decreased SO2 emissions. High excess air decreased CO, but moderately increased SO2 and NOx emissions. (c) 2011 Canadian Society for Chemical Engineering