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Model and experimental results of temperature distribution within coal particle during pyrolysis in fluidized bed

DOI: 10.1615/ICHMT.2004.IntThermSciSemin.470
pages 407-410

Mirko S. Komatina
Mechanical Engineering Faculty, Belgrade University, 27. marta 80, 11000 Belgrade, Serbia and Montenegro

Stevan Dj. Nemoda
Laboratory for Thermal Engineering and Energy, Institute for nuclear sciencies "Vinca", P.O. Box 522, 11001, Belgrade, Yugoslavia

Milijana J. Paprika
Laboratory for Thermal Engineering and Energy, Institute for nuclear sciencies "Vinca", P.O. Box 522, 11001, Belgrade, Yugoslavia


During combustion in fluidized bed (FB) a coal particle passes through different phases: heating, drying, devolatilization and char combustion. Temperature of coal particle is a very important data for modelling all of these processes and in application of FB combustion.
The large influence on different phases of combustion process has a temperature inside the coal particle. Some of assumptions in models were not realistic. For these reasons new theoretical and experimental investigations were done whose results are presented in this paper.
The original physical and mathematical model was made to describe unsteady behaviour of the coal particle during heating and pyrolysis in fluidized bed. It was supposed that the shape of coal particles is spherical with constant diameter during drying and pyrolysis, without particle fragmentation. The mathematical model enables analysis of the particle temperature profile using different relations for thermal conductivity and specific heat capacity.
Temperature changes in the coal particle were determined numerically solving differential equations for heat and mass conservation. The boundary conditions of third kind took into account fluidized bed conditions. Convective heat transfer coefficient between the coal particle surface and the fluidized bed is described with correlation obtained on the basis of our prior experimental investigations.
Parameter analysis of model showed remarkable temperature gradient within a large particle during processes of drying and devolatilization. The thermal properties that were used in model and compared with experimental results were determined on the basis of separate experimental measurement with dried off coal particles and their comparison with the devolatilization model.

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