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Show result. This is clearly of major importance for fuel use in real pulverized burner applications, since the ASTM maximum for US coals is about 45 percent, while high heating rate yields can exceed 80 percent. For the case chosen, representing a wall fired water wall boiler, low volatile coals are not acceptable and a real volatile content in excess of 35 percent is desirable for good stability. Low volatile coals, notably anthracite, are used in combustor-boiler systems specifically designed to provide both a high temperature radiation environment and staged air introduction. Table II shows the result of calculations in which the furnace wall temperature was varied, while holding other parameters constant, for a 20 percent volatile coal. There results a very strong effect of wall radiator temperature on flame stability, consistent with current boiler practice. A. CONCLUSIONS The modelling approach used appears to be an effective tool for analysis of the interaction of major effects in real combustion systems. Use of a simplified fluid dynamic description, coupled with a more detailed particle distribution based heat release model allows treatment of a wide range of fuels in well characterized burner geometries. Also, the results can be used to infer the most useful directions of burner development for specific fuels. Application of the model to a simple swirl burner case has shown that high volatile coal of nominal power plant grind gives a high recirculation zone temperature, and stable combustion over a wide range of operating parameters. Similarly, the residence time required for a stable flame to exist is relatively small, indicating the potential for high throughput. The model allows exploration of burner optimization, including such effects as -17- ^ A V C O EVERETT |