Adsorption Model Equation for Multi-Component Gas on Coalbed and Its Assessment

Abstract

The Langmuir isothermal model is most widely used model in Enhanced Coalbed Methane Recovery (ECBMR) simulation because of its simplicity and a certain level of its accuracy. But the model is literally applicable only to the isothermal condition. And the extended Langmuir model to binary or ternary gases does not necessarily correspond to experimental data.The Dubinin-Astakhov (D-A) model and the Doong-Yang (D-Y) model applies to the non-isothermal condition, maintaining its simplicity. The former is the equation for a single component adsorbate gas and the latter is the equation for multi-component adsorbate gases. These models are containing parameters of the saturated vapor pressure in the equation. However, as methane and carbon dioxide in coalbed reservoir are in the supercritical state, the saturated vapor pressure of these gases is indefinable. In this study, the modification of the D-Y model which is sometimes made in the D-A model to enable it to apply to the supercritical state was made.The comparison was made between the modified D-Y model and the experimental data which was obtained by displacement experiments for binary and ternary gases. Theoretical values calculated from the modified D-Y model gave close agreement with the experimental values and, especially in components less adsorbed. As a result, the modified D-Y model was promising model to predict amount of adsorbed and desorbed gas on coal matrix.