NITROUS-OXIDE EMISSIONS IN COMBUSTION OF COAL POSSIBILITIES OF THEIR REDUCTION AND RELATION TO EMISSIONS OF OTHER GASEOUS-POLLUTANTS

Nitrous oxide concentrations in atmosphere increase at an estimated rate of about 0,7 ppb per year. Potential anthropogenic sources of N2O include fertilization, ground water release through irrigation and combustion of fossil solid fuels. Fluidized bed combustion of coal (FBC) has been recognized lately to emit significant concentration of N2O in flue gas. From the FBC process variables, the combustion temperature, excess of combustion air with the air splitting, fuel type and pressure have a decisive influence on N2O emissions. The optimization of FBC conditions to attain the lowest N2O emission is limited by elevation of emissions of other gaseous pollutants and by complex relations among emission levels of individual pollutants. Nitrous oxide concentrations in flue gas of FBC of bituminous ''black'' coals are several times higher than the corresponding concentrations in FBC of lignite and brown coals. The main practical methods of N2O reduction in FBC systems, their effect on overal emission situation and other possible additional catalytic methods, based on zeolites or perovskites, are reviewed.