Feasibility of CO2 Sequestration as a Closure Option for Underground Coal Mine

Abstract

The Kyoto Protocol, 1998, was signed by member countries to reduce greenhouse gas (GHG) emissions to a minimum acceptable level. India agreed to Kyoto Protocol since 2002 and started its research on GHG mitigation. Few researchers have carried out research work on CO2 sequestration in different rock formations. However, CO2 sequestration in abandoned mines has yet not drawn its attention largely. In the past few years or decades, a significant amount of research and development has been done on Carbon Capture and Storage (CCS) technologies, since it is a possible solution for assuring less emission of CO2 to the atmosphere from power plants and some other major industrial plants. CCS mainly involves three steps: (a) capture and compression of CO2 from source (power plants and industrial areas), (b) transportation of captured CO2 to the storage mine and (c) injecting CO2 into underground mine. CO2 is stored at an underground mine mainly in three forms: (1) adsorbed in the coals left as pillars of the mine, (2) absorbed in water through a chemical process and (3) filled in void with compressed CO2. Adsorption isotherm is a graph developed between the amounts of adsorbate adsorbed on the surface of adsorbent and the pressure at constant temperature. Various types of adsorption isotherms are available, namely, Freundlich, Langmuir and BET theory. Indian coal is different in origin from most of the international coal deposits and thus demands isotherm experiments of the same to arrive at the right adsorption isotherm. To carry out these experiments, adsorption isotherm set up is fabricated in the laboratory with a capacity to measure the adsorbed volume up to a pressure level of 100 bar. The coal samples are collected from the pillars and walls of the underground coal seam using a portable drill machine. The adsorption isotherm experiments have been carried out for the samples taken from a mine. From the adsorption isotherm experiments, Langmuir Equation is found to be more acceptable as compared to Freundlich’s and BET adsorption isotherm models. CO2 is soluble in water and is reversibly formed carbonic acid. It is a weak acid since its ionization in water is incomplete. The CO2 solubility in water is estimated from the experimental results published by Wiebe and Gaddy. In most of the cases of abandoned mines, the chances of available air filled void space is limited as the level of operation is below the water table. So it is expected that the void would be completely filled with water. During this research investigation, the practical experimentation for CO2 sequestration was not within the scope. Thus, one operating mine was considered for the feasibility study. The sequestrated quantities of CO2 in terms of adsorbed volume and soluble volume were quantified. The cost of the CO2 was taken from the standard international literature. The sealing cost of the shaft was also considered. Costs of CO2 sequestration for different pressure were estimated for the mine.