Adsorption measurement and dual-site Langmuir model II: Modeling and prediction of carbon dioxide storage in coal seam

Abstract

Accurate estimation of carbon dioxide adsorption capacity in coal seam is very important for planning the carbon dioxide storage efforts of carbon capture and storage technology; however, an appropriate model is needed to convert the measured adsorption quantity to absolute adsorption quantity. In this work, carbon dioxide adsorption behavior is demonstrated and accurately predicted under a wide range of temperature and pressure using the dual-site Langmuir model. This model sufficiently explains the laboratory measurements of carbon dioxide adsorption equilibrium data across critical points in coal. The results show that the isotherms crossover beyond the Gibbs excess maximum and higher temperatures now result in higher excess uptake at equivalent pressures. Adsorbed phase volume and gas phase density of carbon dioxide change with equilibrium temperature and pressure, and the contribution of the volume–density term for the absolute adsorption gradually becomes less pronounced as the temperature increases. If only the excess adsorption quantity is taken, the result is a very large underestimation of the contribution of adsorbed carbon dioxide to the total content. As the coal seam depth increases, the contribution rates of actual adsorbed carbon dioxide quantity to total carbon dioxide storage quantity gradually decrease; however, the contribution rates of free carbon dioxide phase content gradually increase. The method used herein, with limited formulas and fast computing solutions, provides accurate estimations of the true carbon dioxide storage, which will lay the foundation for the research and development of carbon capture and storage technology.