MODELING THE SPONTANEOUS IGNITION OF COAL STOCKPILES

The spontaneous ignition of coal stockpiles is a serious economic and safety problem. This phenomenon is analyzed using the approach of mode rn reaction engineering, which is made challenging by the nonlinear in teractions of chemical reaction, heat transfer, and buoyancy-driven fl ows within and around the stockpile. A model developed represents reac tion and transport within a realistically-shaped stockpile and transpo rt and flow in the surrounding air. A new methodology based on the Gal erkin finite-element method (Salinger, 1993b) allows for efficient sol ution of flows in both porous and open domains. Bifurcation analysis i s used to track steady-state model solutions of relevant parameters, s uch as the Damkohler number (dimensionless reaction rate), Rayleigh nu mber (dimensionless driving force for buoyant flow), and dimensionless permeability of the stockpile. The solutions provide an understanding of the roles of various transport mechanisms on the ignition behavior and nonlinear coupling between these mechanisms. Results clearly demo nstrate the need for incorporating realistic descriptions of flow and transport in the surrounding air into the model.