KINETICS OF VAPOR-PHASE MERCURY UPTAKE BY VIRGIN AND SULFUR-IMPREGNATED ACTIVATED CARBONS

The injection of powdered activated carbon (PAC) into combustion flue gas, with subsequent collection in a particulate control device, and g ranular activated carbon (GAG) fixed-bed adsorption offer new promise for achieving high-quality air emissions with respect to elemental mer cury concentrations. One of the key parameters that governs the applic ability of adsorption technology to flue gas cleanup is the rate of va por-phase mercury removal, which was the main focus of this study. The kinetics of vapor-phase mercury uptake by a virgin bituminous coal-ba sed activated carbon (BPL), a commercially available sulfur impregnate d activated carbon (HGR), and a BPL carbon impregnated with sulfur at 600 degrees C (BPL-S) was evaluated as a function of temperature and e lemental mercury concentration For all three carbons, an increase in m ercury concentration and a decrease in temperature resulted in an incr eased overall mercury uptake. The rate of mercury uptake by HGR carbon was slower at higher temperatures due to the change in sulfur structu re, which induced a decreased number of terminal sulfur atoms availabl e to react with mercury. For a given flue gas temperature, an increase in mercury concentration resulted in slower mercury uptake kinetics, which suggests that the rate of mercuric sulfide (HgS) diffusion into the sulfur mass is the rate-limiting step. The rate of mercury uptake by BPL-S carbon deteriorated with an increase in temperature, which in dicates that the rate of HgS formation is the rate-limiting step in th e overall mercury removal process. BPL-S carbon displayed faster uptak e kinetics and higher total mercury uptake than HGR carbon, except for very high initial mercury concentrations (e.g., >1,000 mu g/m(3)).