Rd. Vidic et al., KINETICS OF VAPOR-PHASE MERCURY UPTAKE BY VIRGIN AND SULFUR-IMPREGNATED ACTIVATED CARBONS, Journal of the Air & Waste Management Association [1995], 48(3), 1998, pp. 247-255
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)).