CFD-based engineering models can be cost-effective tools in determining technical feasibility of clean coal-fired power generation technologies like NOx mitigation strategies targeting the reduction of acid rain and smog. Their actual effectiveness depends on their capability to provide realistic engineering estimates without arbitrary adjustment of model parameters. This investigation focused on testing a CFD based NOx model over a variety of coal type, firing configuration and boiler size ranging from 200MW(e) sub-critical to most modern 1000 MWe ultra supercritical. In most cases, the NOx estimates based on input data readily available from power plants were found within the range of measured data (with the worst estimate being 22% higher than the maximum measured NOx level). The CFD results also indicated some sensitivity of the NOx estimates to the ratio of volatile nitrogen to char nitrogen and the importance of NO reduction by char. However, this study showed that the locations of fuel-bound nitrogen evolution with respect to the stoichiometric condition within the boiler actually governed the overall NO emissions. Crown Copyright (c) 2010 Published by Elsevier Ltd. All rights reserved.