A Study of Two Chemical Reaction Models in Turbulent Coal Combustion

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Abstract
Research efforts with comprehensive computer models that have tried to predict the performance of coal combustors have either neglected the effect of the turbulence on the mean chemical properties or have used one of two approximate methods. This paper focuses on the impact of the turbulence on the chemical reactions of the volatile products of coal combusion processes. It is shown that by ignoring the effect of the turbulence on mean combustion properties significant differences occur as compared to experimental data and as predicted hy both of the more rigorous models. The first method (Lockwood, Salooja and Syed, 1980), the volatile reacted ness model, is an extension of an approach for premixed gaseous combustion presented by Magnussen and Hjertager (1976). The second method (Smoot, Hedman and Smith, 1984), the statistical. coal-gas mixture-fraction model, is an extension of gaseous diffusion flame approaches. These two methods are examined.analyzed and evaluated by comparing predictions from each method with experimental data from three laboratory furnaces. It is shown that while the first method takes only half as much computational time,the second method is required if species and temperatures in zones containing other than mixtures of pure fuel, pure oxidant and pure stoichiometric product are needed. The distribution of eddy mixtures as formulated in the second method is shown to bemore consistent with existing limited experimental data.

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