The Rheology of a Bituminous Coal

Abstract

The fluidity of a rapidly heated, bituminous coal was studied with a capillary rheometer. Quantitative measurements of overall fluidity, of transition from no flow to flow, and of the effects of presence of the gaseous phase were the principal objectives. Separate measurements of the density of the coal indicated that the major changes in density with time were due to the production of gas by decomposition. The volume fraction of gas was calculated from the density measurements. The relationships between volumetric flow rate and pressure drop were expressed in terms of an overall, or effective, viscosity. The overall viscosity displayed values as low as thirty poise, and its rheological classification was Newtonian within the accuracy of the experimental equipment. The transition from no flow to flow was quite sudden, and it was independent of the volume of gas present in the reservoir. The multi-component, multi-phase flow of coal was considered to be a two-component, two-phase, liquid-gas system. Various correlations found in the literature were applied to the overall viscosity data, and estimates of the viscosity of the liquid phase were made. A constitutive relationship for the density as a function of temperature, time, and pressure was developed. Closed-form solutions of the simplified momentum equation were generated based on definitions of a mean viscosity as a function of the viscosities of the liquid and the gas, and the volume fractions of the liquid and the gas. Because of the magnitude of the volume fraction of gas, the viscosity of the liquid phase was greater than the overall viscosity of the mixture.