Compositional factors affecting NOx emissions from Ohio coals

A series of controlled combustion experiments has been performed on nine bi tuminous coals that represent the types of coals typically used from the St ate of Ohio, and one bituminous coal from Kentucky with a high percentage n itrogen content. The coals were combusted in a drop tube reactor at 1200 de greesC, a gas residence time of 0.5 s, and an air/fuel ratio (A/F) of 1.1. The steady-state NO, emission levels for each coal were determined and comp ared to the coals' composition, including their volatile matter, fixed carb on, and nitrogen content. A relationship was developed based on the coal's compositional factors and defined as FF = alpha (FC/VM) - beta (N-o) where FF is the coal's fuel factor, alpha and beta are constants, FC is the coal's fixed carbon, VM is the volatile matter, and N-o is the nitrogen pe rcentage, all on a dry, ash-free (daf) basis. This relationship was shown t o predict the relative NOx emission values of the 10 coals (relative NO, em issions were determined by normalizing the actual NOx emissions for each co al to the concentration of the coal with the lowest measured NOx concentrat ion) when the values of alpha and beta are 550 and 92, respectively. In add ition, when the heat content of the coals was considered, a linear relation ship still exists between the relative NOx emission levels and the coal's c hemical properties. Possible explanations for this behavior are given in th e text. These results may be useful in determining the type of similar-rank coals to burn in a particular combustor to reduce NOo emissions. (C) 2001 Elsevier Science B.V. All rights reserved.