Volatility Model for Coal Dust Flame Propagation and Extinguishment.
Hertzberg-M; Zlochower-IA; Cashdollar-KL
21st Symp International on Combustion the Combustion Institute 1986 :325-333
This paper presents a theoretical analysis for thepropagation and extinguishment of coal dust flames and of dust and gas flames containing inhibitor powders. The analysis is based on the established mechanisms for homogeneous flame propagation and the well known concept of a constant limit flame temperature for a given class of homogeneous fuels. The analysis is expanded to phase- heterogeneous systems such as coal dust by means of a volatility model. The analysis includes the singly heterogeneous system of a solid fuel dust in air; the singly heterogeneous solid inhibitor dust in a homogeneous fuel-air flame; and the doubly heterogeneous system consisting of a solid fuel and inhibitor dust mixture in air. The data for measured explosion pressures, flammability limits, and extinguishant requirements for heterogeneous systems are shown to be consistent with the established mechanisms and processes for homogeneous flame propagation provided that one adds an additional process: the heating and devolatilization of the solid fuel or inhibitor. The limitations on the rates of devolatilization of the solid particles become rate controlling at high burning velocities, at high dust loadings, and for large particle sizes. Devolatilization rates are controlled by the intrinsic devolatilization rate constant for the solid fuel or inhibitor and the effective heating flux of the approaching flame front. The effective yield of volatiles is a function of those factors, the decomposition chemistry, and the time available for devolatilization. The fraction of the total volatiles that
21st Symp. (International) on Combustion. The Combustion Institute, 1986, PP. 325-333