Model for drying during fluidized-bed combustion of wet low-rank coals

Pradeep, K. Agarwal; William, E. Genetti; Yam Yee Lee; Shyam, N. Prasad

Fuel 63(7): 1020-1027

1984


ISSN/ISBN: 0016-2361
DOI: 10.1016/0016-2361(84)90328-4
Accession: 061777297

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Abstract
An unsteady state heat conduction model with a convective boundary condition is proposed for the drying of low-rank, high-porosity coals, such as lignites, during fluidized-bed combustion. The drying front is assumed to be the receding surface of a wet core. The solution technique for this moving boundary problem is based on the heat balance integral approach with immobilization of the moving boundary by a change in space variable. The governing cubic equation describing the drying curve in dimensionless form may be solved easily by the Newton- Raphson method. The model predictions are compared with experimental data for Mississippi lignite with excellent agreement. A correlation for estimation of total drying time is proposed. The temperature profiles obtained may be used for the study of the coupled drying and devolatilization in fluidized-bed combustors. The profiles could also be of importance in the study of formation of fissures/cracks in lignites subjected to intense heating conditions encountered during fluidized-bed combustion.