Air emissions from co-firing woodwaste/peat and lignite in a fluidized bed combustor

The effects of the fuel blending ratios (0, 20%, 50%, 80% and 100% on a thermal basis), excess air, and moisture content on air emissions (CO ₂, CO, SO₂ and NOx) from co-combustion of woodwaste or peat and lignite were examined in a pilot-scale bubbling fluidized bed combustor. The results showed that there was no change in superficial CO ₂ emissions when lignite is co-fired with white pine or peat, while the emission of non-renewable CO₂ could be significantly reduced by co-firing, proportional to the fuel blending ratio if assuming the CO ₂ resulting from peat/white pine is renewable. The co-firing of white pine and lignite demonstrated significant drops in SO₂ and NO _x emissions, while the co-firing peat and lignite led to an increase in SO₂ and only slightly lower NO_x emissions. In co-combustion of lignite and pine or peat pellets, the SO₂ emission could be lowered considerably when as-received fuels (with a higher moisture content) were used in the combustion, and operated at a lower excess air ratio. In contrary, the NOx emission could be reduced when oven-dried fuels (with a lower moisture content) were used in the combustion, and operated at a higher excess air ratio.