Combustion of the Pellets of Sewage Sludge and Woody Biomass Blend in a Circulating Fluidized Bed Combustor: Effect of Oxidant Conditions on the Reduction of Pollutant Emissions

Combustion experiment for pellets of sewage sludge and woody biomass blend was conducted in a pilot-scale circulating fluidized bed combustor (CFBC) consisting of the riser, two hot cyclones and a loop-seal to reduce pollutant emission in exhausted flue gas. To achieve them, the effect of the oxidant variations, such as superficial velocity, equivalence ratio(ER: 1.2, 1.3, 1.4) and combustion atmosphere (air-fired and oxy-fired) was evaluated. As pollutant emissions in flue gas, SO2, NO, CO, CO2, HCl, odor contaminants and leaching behavior of heavy metals were analyzed. As a result, to stably operate combustion of pellet mixed with sewage sludge and woody biomass as alternative renewable fuel in a CFBC system, the superficial velocity in the riser had to be kept under 6 m/s and the equivalence ratio was proper around 1.3-1.4. All odor contaminants formed at these operating conditions met the domestic air pollutant standards. Heavy metals in fly ash met the environment ministry's standard. Additionally, compared to air-firing, SO2, NO and CO as precursors of fine particles during oxy-firing were reduced by 70.8, 77.1 and 38.2%, respectively.