Compositional factors affecting NOx emissions from Ohio coals

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 NOx emission levels for each coal were determined and compared to the coalsʹ composition, including their volatile matter, fixed carbon, and nitrogen content. A relationship was developed based on the coalʹs compositional factors and defined asFF=αFCVM−β(No)where FF is the coalʹs fuel factor, α and β are constants, FC is the coalʹs fixed carbon, VM is the volatile matter, and No is the nitrogen percentage, all on a dry, ash-free (daf) basis. This relationship was shown to predict the relative NOx emission values of the 10 coals (relative NOx emissions were determined by normalizing the actual NOx emissions for each coal to the concentration of the coal with the lowest measured NOx 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 NOx emission levels and the coalʹs 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 NOx emissions.