co-firing of lignite with peat and white pine in a pilot scale bubbling fluidized bed air - emissions and feedstock reactivity
abstract
the increasing awareness of the environmental impact of fossil fuels (mainly coal) combustion, which leads to high levels of co 2 , no x , so 2 , mercury and particulate emissions, has motivated research for potential alternatives such as switching from fossil fuels to biomass, or co-firing of both fuels. co-firing proved to be a promising technology for large scale use of biomass for energy production, as it makes use of the extensive infrastructure associated with the existing coal-based power systems, and requires only relatively modest additional capital investment to achieve a significant co 2 reduction. the research objectives of the present work were to: (1) investigate on combustion/cofiring lignite and woodwaste/peat in a 16.19 kw pilot-scale fluidized-bed combustor, and effects of fuel-blending ratios, excess air, particle size and moisture contents on co 2 , co, so 2 , and no x emissions in the combustion/co-combustion; and (2) study the combustion reactivity of lignite, woodwaste, peat, and the blended fuels using thermogravimetric analysis (tga). the combustion/co-combustion behaviour and kinetics of lignite, peat and woodwaste (white pine sawdust) and their blends were investigated using non-isothermal thermogravimetric analysis (tga) technique. the tga experiments were performed for pure fuels and compared to blended fuels with respect to their performance in air over a temperature range of 25-700 °c and at a heating rate of 20°c/min. the overall kinetic de-volatilization-combustion reactions for these fuels and their blends were evaluated using the power law model. using the differential thermal analysis (dta) data and applying the least square multi-linear regression method, kinetic parameters for the overall devolatilization/combustion reactions including the apparent activation energy ( e a ) , reaction order ( n ) and the pre-exponential ( a ) factor were calculated for each homogeneous fuel and the lignite-peat or lignite-pine sawdust blended fuels (50 wt%-50 wt%%). the wood waste and peat demonstrated a higher reactivity when compared to lignite. the activation energies for lignite, peat, and white pine were determined to be 124.10 kj/mol, 83.95 kj/mol, and 98.23 kj/mol, respectively. compared with the devolatilization/combustion of homogenous solid fuels, blending peat/white pine with lignite resulted in synergistic effects, enhancing the combustion reactivity of each component fuel.