The effect of operating conditions on emissions from a two-stage lump coal combustor
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Residential coal stoves emit various pollutants such as CO, NOx, SOx, and smoke. The emissions can be reduced by varying the burning conditions in the stove. This investigation studied the effect of various burning conditions on the emissions from a two-stage lump coal combustor burning Wyoming bituminous coal. The parameters that were varied include primary air mass flow rate, secondary air mass flow rate, secondary air temperature, secondary air inlet velocity, and secondary air swirl. Each parameter was varied independently to attempt to isolate its effect on emissions. In addition, radial and axial probe sampling was conducted in the combustor's secondary combustion zone to determine the CO concentrations. A chemical kinetic model of CO oxidation was formulated and compared to the measured CO concentrations. A wide range of emission factors can be achieved for the various pollutants by varying the burning conditions. The CO, NOx, SOx, and smoke emission factors range from 7.0 to 159, 0.67 to 3.1, 0.98 to 2.0, and 0.16 to 3.7 g/kg respectively. The emissions tests appear to be reasonably repeatable with emission factors and coal burning rates agreeing within 15% in most cases. The various tests indicate that increasing the primary zone equivalence ratio decreases the CO emission factor. The smoke emissions from the test combustor are quite low compared to those from typical commercial coal stoves. The amount of swirl has a large effect on mixing in the secondary combustion zone, and highly stratified flows are created by certain burning conditions. The CO oxidation model does not correlate well with the experimental results since possible CO formation from hydrocarbons, and stratified flow effects are not considered.
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