CO2 Adsorption Inside the Pore Structure of Different Rank Coals during Low Temperature Oxidation of Open Air Coal Stockpiles

Steam coals are used in utilities worldwide for electrical power production. During monitoring of gases evolved via the weathering processes of large coal piles under open air storage and laboratory simulations, it has been observed that large amounts of carbon dioxide are adsorbed by the coal. Thus, one should take into account that appreciable amounts of CO2 formed by the low temperature oxidation (LTO) of the coal are trapped inside the pore structure of the coal as well as when studying LTO processes and performing kinetic evaluations of CO2 production, the amounts of CO2 released and adsorbed should be calculated. As the coals used for power production are often stored in large piles (> 100 000 tons) for long periods, these piles are prone to undergo weathering which might result in self-heating of the coal piles and, in extreme cases, can spontaneously combust. Furthermore, the adsorption is also rank dependent and deviates from coal to coal. The effect of coal rank has been characterized with a South African bituminous coal and with Indonesian sub-bituminous coal which are currently in use in Israeli utilities as well as two German lignites which are consumed in German utilities. The results indicate that only the higher rank coals (bituminous and sub-bituminous) exhibit significant adsorption of CO2.