Mercury capture by regenerable sorbents under oxycoal combustion conditions

The largest source of mercury to the atmosphere in the world is the burning of fossil fuels, primarily coal. Electrical power plants are estimated to account for about 25% of the global anthropogenic mercury emissions to the atmosphere and industrial and residential heating for another 20% [1]. According to the European Environmental Agency (EEA), Spain is the third country among EU27 in mercury emissions, mainly due to coal-fired plants [4]. Mercury is found in coal in the form of sulphides or associated to them, interchanged on clays and associated to the organic matter in low rank coals. During the combustion processes, these forms evaporate, giving rise to Hg(0), HgO and HgCl2, which proportions in gas phase depend on the concentration and mode of occurrence in the coal and on the compounds present in the gaseous stream, especially particulates and HCl. The environmental implications of mercury do not correspond only to the emissions to the atmosphere; the quality of CO2 to be transported and sequestered has been subject of research, concerning trace quantities of heavy metals participating in mineralization and precipitation reactions in sequestration conditions. However, for coal oxycombustion mercury is not an environmental issue alone but also an operational issue, particularly about where mercury could accumulate within the CO2 processing unit. The removal of Hg is necessary to prevent Hg attack on the aluminium heat exchangers. Because of this, an activated carbon bed guard is placed downstream the dryers. Once exhausted, this activated carbon must be treated as a toxic residue. Regenerable sorbents can accomplish high mercury retention that can be recovered as well as balance cost because of its regenerability. Recognizing reversible characteristics of mercury amalgamate with gold have been widely used to pre-concentrate low concentration of elemental mercury for its detection. The gold-mercury amalgam is extremely stable at room temperature. However, the amalgam decomposes to release mercury to a gas phase at