| Summary: | Coal continues to be burned by direct combustion in packed or moving bed in
small size domestic furnaces, medium size industrial furnaces, as well as small power
stations. Recent stringent restrictions on exhaust emissions call for a better
understanding of the process of combustion of coal in beds.
The present study is a prelude to developing methods of analysis to obtain this
improved understanding. A one-dimensional steady-state computational model for
combustion of a bed of solid fuel particles with a counterflowing oxidant gas has
been developed. Air, with or without preheating, is supplied at the bottom of the bed.
Spherical solid fuel particles (composed of carbon and ash) are supplied at the top of
the bed. Upon sufficient heating in their downward descent, the carbon in particles
reacts with oxygen of the flowing gas.
The governing equations of conservation of mass, energy, and species are
integrated numerically to obtain the solid supply rate whose carbon content can be
completely consumed by a given gas supply rate. The distributions of solid and gas
temperatures, of concentrations of various gas species, of carbon content in solid, and
of velocity and density of gas mixture are also calculated along the bed length. The
dependence of these distributions on the solid and gas supply rates, the air supply
temperature, the size of solid fuel particle, and the initial carbon content in solid is
also investigated.
The calculated distributions are compared with the available measurements
from literature to find reasonable agreement. More gas supply is needed for complete
combustion at higher solid supply rate. At a given gas supply rate, more solid fuel
particles can be consumed at higher gas supply temperature, for larger particle size,
and for lower initial carbon content in solid. The temperature of the bed becomes
higher for higher solid supply rate, higher gas supply temperature, larger solid
particle diameter, or lower initial carbon content in solid. These reasonable results
lead one to encourage extension of the model presented here to more complex
problems involving combustion of coals in beds including the effects of drying and
pyrolysis. === Graduation date: 1994
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