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ISSN Online: 2377-424X

ISBN Print: 1-56032-797-9

International Heat Transfer Conference 11
August, 23-28, 1998, Kyongju, Korea

Numerical Simulation of Particle Motion and Combustion in a Packed Bed

Get access (open in a dialog) DOI: 10.1615/IHTC11.3810
pages 277-282

Abstract

Technical applications involving a packed bed of particles are frequently used in the processing industry, the energy-supplying industry and in waste incineration plants. Common to all these applications is that the entire flow and combustion process consists of several important ther-mo- and fluid dynamic processes, among which are the motion of the packed bed with its redistribution of particles and the chemical conversion processes of heterogeneous combustion. The objective of this paper is to present a numerical simulation method to model both the incineration of a packed bed and its motion taking place on a moving grate or in a rotary kiln.
The latter method is expressed in a Lagrangian frame of reference which uses as independent variables the position and orientation of particles. These are obtained by time integration of the three-dimensional dynamics equations, derived from the classical Newtonian approach for each particle. This includes keeping track of all the forces and moments acting on each particle at every time step. Contact forces include normal and tangential components with visco-elastic models for energy dissipation and friction. The equations are solved by a predictor/corrector sequence of 5th order accuracy.
The combustion of a packed bed consists of all the single particle processes, which form the entire incineration process. For this reason the method is based on the one-dimensional and transient conservation equations for species, energy and morphological parameters such as porosity and inner surface for each particle of the packed bed. The differential equations are written for spherical particles, because the effectiveness factor, which represents a measure for the reaction process in a porous particle, does not vary significantly for different particle shapes. Heat and mass transfer from the ambient gas phase as well as radiation between particles are taken into account. The solution yields the evolution of inner particle variables such as temperature, particle size, solid and gaseous concentrations in conjunction with porosity and inner surface.
As both methods for particle combustion and bed motion can deal with particles of different sizes and materials, the approach allows to describe conversion processes in technical applications. The implementation for either application is carried out with the proven software package TOSCA (Tools of Object-Oriented Software for Continuum Mechanic Applications) [1], [2]’, which allows for a high degree of flexibility and for a shortening the life-cycle of the software development process.