Influence of a CO2-enriched flue gas on mercury capture by activated carbons

The main environmental problem caused by the production of energy from coal combustion is the emission of CO2. One emerging technology designed for CO2 capture is oxy-combustion. Among other issues to be solved in oxy-combustion power plants is the presence of mercury as this may damage the CO2 compression unit. Hence the study of the behavior of mercury in oxy-combustion is of great interest both from an environmental and a technological point of view. The present study performed at laboratory scale evaluates the retention of mercury in a CO2-enriched flue gas using the same activated carbon before and after it has been impregnated with sulfur and proposes a mechanism to explain the interactions between mercury and activated carbons. The results show that carbonyl and quinone groups are responsible for mercury oxidation and retention in the carbons. Although the contact time between mercury and the activated carbon surface limits the amount of mercury that can be captured, high retention capacities can be achieved in an oxy-combustion atmosphere. The presence of water, in high concentrations in oxy-combustion, may compete for the same active sites (carbonyl groups) as mercury, thereby inhibiting mercury adsorption on the surface of the activated carbons. Moreover, the presence of sulfur in the impregnated material, which is the key to mercury capture in other atmospheres, does not modify mercury capture in oxy-combustion.