Abstract: An initial coal is cleaned to reduce ash content by ?20% and yield refined coal that optimizes combustion air flow through a coal burner. This permits conveyance of pulverized refined coal in suspended condition through feeder pipes of the coal burner using reduced air flow compared to the quantity of air required to convey pulverized initial coal in suspended condition through the feeder pipes. This reduces oxygen in the primary combustion zone, lowering conversion of fuel nitrogen into NOx and instead converting it into N2 using the refined coal product. Reduced primary combustion air also reduces core flame temperature, reducing thermal NOx formation using the refined coal product. Increasing secondary and/or tertiary combustion air compensates for reduced primary combustion air and result in overall decrease in NOx formation (e.g., thermal NOx formation is reduced when combustion completed in cooler secondary and/or tertiary combustion zones).

Abstract: An initial coal feedstock comprised of primary or second coal is cleaned so as to reduce its ash content by at least about 20% in order to yield a refined coal product that produces fewer NOx emissions. The reduced NOx emissions result primarily from the ability to use less primary combustion air in order to maintain the pulverized refined coal in a suspended condition within the feeder pipes of a coal burner compared to the minimum quantity of air required to maintain pulverized coal from the initial coal feedstock in a suspended condition within the feeder pipes. Reducing the primary combustion air reduces the amount of oxygen in the primary combustion zone that would otherwise be available for converting fuel nitrogen into NOx. Instead, more of the fuel nitrogen is converted into N2. Reducing the primary combustion air also reduces the temperature of the core flame, reducing thermal NOx formation.