Engineering Computational Technology
Chapter 11 A.C. Benim
Department of Mechanical and Process Engineering, Düsseldorf University of Applied Sciences, Germany Keywords: pulverized coal combustion, two-phase flow, equilibrium Euler-Euler vs. Euler-Lagrange modelling.
This paper demonstrates the application of an equilibrium Euler-Euler model of two- phase flow for modelling pulverized coal combustion. The state-of-the art two-phase flow models, being used for pulverized coal flames are majorly based on an Euler- Lagrange description. An alternative approach is the equilibrium Euler-Euler description of the two-phase flow. The latter offers the advantage of being potentially more economical due to the reduced number of momentum and energy transport equations and the missing problem of inter-phase coupling. The present paper shows that the equilibrium Euler-Euler model is able to deliver results with a similar degree of accuracy compared to the Euler-Lagrange model for the investigated configurations. This designates the equilibrium Euler-Euler model as a potentially attractive alternative especially for large-scale industrial applications. In the modelling, we assume that gas and solid phases behave as interpenetrating continua and can both be described using an Eulerian frame of reference. The additional assumption introduced here is that the phases are in fluid dynamical and thermodynamical equilibrium. This assumption simplifies the problem in such a way that only a single set of momentum and energy transport equations needs to be solved, where the particle phase appears as a ``component" of the ``mixture". What remains is a convenient description of the relevant transport equations of the mixture, which is discussed in the full paper. Results for a two-dimensional flame have been compared with experiments and predictions of other authors using an Euler-Lagrange approach. This comparison indicates that the degree of accuracy obtained by the present model is comparable to that of the principally more expensive Euler-Lagrange modelling. The reduced computer costs by the present approach become important, especially for large scale applications. An application of the model to a large utility boiler is also demonstrated.
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