Effects of Coal Properties on Recycled-NO sub(x) Reduction in Coal Combustion with O sub(2)/Recycled Flue Gas

The emission of NO sub(x) and the reduction of recycled-NO sub(x) in coal combustion with O sub(2)/recycled flue gas were experimentally studied in an electrically heated up flow combustor under low recycling ratio with three kinds of coal: a high volatile bituminous, a medium volatile bituminous and a semi-anthracite. The recycled flue gas was simulated with the mixture of CO sub(2) and NO sub(x). NO sub(x) emissions from the combustion of the three coals were firstly investigated under the recycling ratio ranging from 0 to 0.4 but without recycled-NO sub(x). The results show that the relative release rate of fuel-nitrogen to volatile matter and the partitioning of volatile-N and char-N are more critical than volatile matter content and nitrogen content in coal for NO sub(x) emissions, especially in the fuel lean combustion. The experimental data on recycled-NO reduction indicate that the reduction efficiency increased with fuel equivalence ratio and recycling ratio. In the fuel rich region, the reduction efficiency reached as high as 80% at a fuel equivalence ratio of 1.4. The experiments on the replacement of NO recycle by NO sub(2) recycle indicated that the same reduction efficiencies of recycled-NO sub(2) as those of recycled-NO were reached for the high volatile bituminous, while the reduction efficiencies of recycled-NO sub(2) were always lower than those of recycled-NO for the semi-anthracite coal.