The combustion of oil sand fragments in hot low velocity streams

Abstract

The physical and chemical processes that occur typically within and around oil sand fragments of different shapes are examined when the fragments are subjected to hot, low-uniform velocity streams of air or the combustion products of very lean mixtures of hydrogen and air. The rate of mass loss due to bitumen volatilization at any constant stream temperature was established and then correlated with time on the basis of a characteristic length, defined as the ratio of the oil sand particle volume to its projected area normal to the direction of the surrounding stream. With increasing temperature, three regimes were identified in the behaviour of the fragments: volatilization, slow heterogenous combustion, and combustion of fuel as a diffusion flame. Combustion of the oil sand slabs and spheres in air at atmospheric pressure occurred when the surrounding air temperature was not less than about 530°C. The ignition delay time was obtained for oil sand slabs and spheres of the same mass or the same surface to volume ratio. These ignition delay times could be correlated with the stream temperature in an Arrhenius form when included in a non-dimensional time similar to Fourier number. A correlation for the rate of mass loss with time was then suggested in terms of a Fourier Number, temperature and the initial concentration of bitumen in the fragments.