We have considerable experience in mercury control processes including process evaluation, developmental research, speciated mercury testing, and mercury data analysis.
For many utilities, mercury control has become a major issue for coal-fired plants, and in fact mercury control has moved to the forefront of the long-term environmental controls planning for some utilities. Mercury control is a complicated issue due partly to the very low levels of mercury present in flue gas, and the difficulty in measuring both the absolute level of mercury and the relative amounts of the various mercury species that are present. Mercury speciation is an important factor with all mercury control technologies because of the difference in the physical and chemical behavior of the various mercury species.
A number of technologies are available for mercury control, each with its own specific capabilities and problems. Technologies that either capture mercury, or impact mercury speciation, include; SCR (for mercury oxidation), wet scrubbers, dry and wet ESPs, activated carbon injection, sorbent injection, dry scrubbers, and other novel technologies. In addition, various operations in the flue gas train can affect mercury behavior, such as the air preheater. The myriad technologies available for capturing mercury, along with their highly variable performance and applicability, make choosing the right technology for a particular application very difficult.
In particular, we have a great deal of experience related to the oxidation of mercury using SCR. SCR catalysts are known to oxidize mercury, but the actual oxidation efficiency is dependent on many factors including the SCR operating condition (flow rate, temperature, deNOx level, etc.) as well as the catalyst formulation, and especially the flue gas composition. Flue gas levels of chlorine and bromine, in particular, strongly influence the level of mercury oxidation that occurs across SCRs. We have been involved with several SCR-related projects associated with mercury oxidation and capture at the Mercury Research Center, located at Gulf Power’s Plant Crist, in Pensacola, Florida, as well as slip-stream facilities and laboratory test reactors.
These projects have made significant headway in evaluating the mercury oxidation performance of a number of catalysts with respect to various flue gas parameters, and have evaluated the resulting capture efficiency of mercury across devices, such as ESPs and wet scrubbers. Other similar work has examined the relative mercury oxidation performance of new, aged, and regenerated catalysts, as well as advanced catalysts designed to optimize mercury oxidation.