Emissions of nitrogen oxides from coal combustion are a major environmental problem because they have been shown to contribute to the formation of acid rain and photochemical smog. Air staging and the application of low-NOx burners are effective in reducing the In-furnace-formed NOx. Fuel staging, or reburning, is another effective method to reduce NOx emissions in the combustion chamber. For a successful application of these processes on industrial scale, the governing parameters must be evaluated very carefully. Computer modeling is an efficient tool for acquiring a better knowledge of the optimum process parameters. In order to predict NO emissions from furnaces operated with advanced combustion technologies, a knowledge of the fare of coal nitrogen during the combustion process is paramount. An advanced NOx model for staged combustion of pulverized coal is presented. It is closely connected to a coal combustion model that includes primary pyrolysis and secondary reactions of tars formed during primary pyrolysis. The present NOx model takes into account the different pathways of coal nitrogen release during primary and secondary pyrolysis, char, and soot combustion. The subsequent conversions of nitrogen-containing species comprise formation of NO from fuel nitrogen and air nitrogen (thermal NO) as well as reduction of NO by hydrocarbon and NHi radicals, char, and soot. The interaction between turbulence and chemistry is modeled by an advanced eddy dissipation concept (EDC). The NOx model is used to predict NO profiles that are compared to measurements obtained from combustion tests carried out at a bench-scale entrained-flow reactor. Comparisons are made for air-staged and fuel-staged combustion of pulverized coal using methane and coal as reburn fuel.     «

Emissions of nitrogen oxides from coal combustion are a major environmental problem because they have been shown to contribute to the formation of acid rain and photochemical smog. Air staging and the application of low-NOx burners are effective in reducing the In-furnace-formed NOx. Fuel staging, or reburning, is another effective method to reduce NOx emissions in the combustion chamber. For a successful application of these processes on industrial scale, the governing parameters must be evalua...     »