Effects of coal properties on recycled-NO x reduction in coal combustion with O 2/recycled flue gas

Abstract

The emission of NO x and the reduction of recycled-NO x in coal combustion with O 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 2 and NO x . NO 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 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 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 2 recycle indicated that the same reduction efficiencies of recycled-NO 2 as those of recycled-NO were reached for the high volatile bituminous, while the reduction efficiencies of recycled-NO 2 were always lower than those of recycled-NO for the semi-anthracite coal.