Use of a Three Dimensional Network Model to Predict Equilibrium Desaturation Properties of Coal Filter Cakes

Abstract

A three dimensional bond-flow correlated network model has been successfully used to calculate equilibrium desaturation curves for coal filter cakes. A simple cubic lattice with the pore sizes correlated in the direction of macroscopic flow is used as the network. A new method of pore volume assignment is presented in which the pore volume occupied by the large pores (which give rise to capillary pressures less than a calculated critical value) is assigned to the nodes and the rest is distributed to the bonds according to an experimentally determined micrographic pore size distribution. Equilibrium desaturation curves for —32 mesh, —200 mesh and — 100 + 200 mesh coal cakes (Pittsburgh Seam coal), formed with distilled water have been calculated. A bond flow correlation factor, F,, is introduced to account for channeling of the displacing fluid through high volume, low resistance flow paths — a phenomenon which is displayed by many real systems. It is determined that a single value of 0.6 for Fc is required for — 32 mesh and — 200 mesh coals. However, for — 100 + 200 mesh coal, where all small as well as large particles have been removed, a value of 1.0 is required. The results for six — 32 mesh cakes formed with surfactants show that the effect of surfactants can be accounted for by modifying one of the model parameters, the entry diameter correction. A correlation is presented to estimate the modified correction using experimentally determined surface tension and contact angle values. Further, the predicted final saturations agree with the experimental values within an average absolute error of 5%.