Compositional factors affecting NO x emissions from Ohio coals

Abstract

A series of controlled combustion experiments has been performed on nine bituminous coals that represent the types of coals typically used from the State of Ohio, and one bituminous coal from Kentucky with a high percentage nitrogen content. The coals were combusted in a drop tube reactor at 1200 °C, a gas residence time of 0.5 s, and an air/fuel ratio (A/F) of 1.1. The steady-state NO x emission levels for each coal were determined and compared to the coals' composition, including their volatile matter, fixed carbon, and nitrogen content. A relationship was developed based on the coal's compositional factors and defined as FF=α FC VM −β(N o ) where FF is the coal's fuel factor, α and β are constants, FC is the coal's fixed carbon, VM is the volatile matter, and N o is the nitrogen percentage, all on a dry, ash-free (daf) basis. This relationship was shown to predict the relative NO x emission values of the 10 coals (relative NO x emissions were determined by normalizing the actual NO x emissions for each coal to the concentration of the coal with the lowest measured NO x concentration) when the values of α and β are 550 and 92, respectively. In addition, when the heat content of the coals was considered, a linear relationship still exists between the relative NO x emission levels and the coal's chemical properties. Possible explanations for this behavior are given in the text. These results may be useful in determining the type of similar-rank coals to burn in a particular combustor to reduce NO x emissions.