Date of Graduation

1981

Document Type

Dissertation/Thesis

Abstract

A comprehensive one-dimensional model for the simulation of combustion of wet coal has been developed taking into account (i) the vaporization of coal moisture and the existence of a moving evaporation front, (ii) pyrolysis and char/gas reactions occurring in the dry coal zone, (iii) molecular diffusion and Darcy flow through the coal, (iv) variation in porosity and permeability of the coal, (v) temperature dependence of the physical properties of the coal, (vi) transpiration cooling effect of the water vapor and pyrolysis gases, (vii) multi-component diffusion in the ash and gas film, and (viii) oxidation reactions in the ash. The model is capable of predicting the flame position, the combustion rate, the temperatures at the coal face and on the edge of the ash, the flame temperature, the thickness of the semi-coking and coking zones of the coal and the fraction of the coal moisture that is reacted in the coal. The performance of the model is compared with the data obtained from several laboratory experiments. Agreement between the computed results and observed data is good. The global rates, the mode of combustion, the steady state multiplicities and flame extinction points are discussed as a function of ambient gas temperature, ash layer thickness, coal moisture content and film transport coefficients. The model describes the heat and mass transfer through the gas film by parameterizing the transport coefficients. However, an experimental system has been designed and constructed for future evaluation of the values of these coefficients. The system has been used to determine the flow pattern in the entrance region of the cavity.

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