Development of criteria for extension of applicability of low-emission, high-efficiency coal burners

A program to develop criteria for extending the applicability of low emission, high efficiency coal burners is described. For the small scale fuel studies, 28 coals covering all ranks were tested under a wide variety of conditions to ascertain the impact of coal properties on the fate of fuel nitrogen (N). Significant accomplishments in this part of the program include: (1) bench scale test results confirm the pilot scale concept that decreasing the initial air/fuel ratio decreases fuel NOx formation; (2) detailed studies on optimizing a staged combustion system suggest that the stoichiometry producing minimum NOx emissions is a function of both fuel composition and primary zone conditions; (3) distribution of the total fixed nitrogen (TFN) species--NO, NH3, and HCN--leaving the first stage strongly dependent on coal composition; (4) distribution of the first stage fuel N emissions has a significant impact on second stage exhaust NO emissions (minimum second stage NO emissions depend on competition between first stage NO and increased gas and solid phase N species); and (5) during staged combustion, increasing the rate of heat extraction from the first stage (fuel rich zone) decreases the decay of TFN species, but dramatically decreases TFN conversion in the second stage (first stage extraction reduces exhaust NO emissions).