SBIR-STTR Award

The health and environmental effects of trace mercury emissions from coal combustion are increasingly under scrutiny. In response to a recent U.S. Environmental Protection Agency (EPA) Information Collection Request, utilities currently are sampling their coal for mercury and many are sampling their stacks. By the end of the year 2000, the Agency is to decide whether to require mercury reductions from coal-fired power plants. The Phase I objective is to learn how to effectively prepare and use the new mercury sorbents to establish the technology's feasibility, so that a pilot- or full-scale Phase II demonstration can be carried out successfully at a power plant site later. Unfortunately, if utilities must reduce mercury, it could be very expensive. As the Executive Summary of the EPA's recent Report to Congress on Hazardous Air Pollutants from Utilities stated: "Regarding potential methods for reducing mercury emissions, the EPA has not identified any demonstrated add-on control technologies currently in use in the United States that effectively remove mercury from utility emissions." However, an inexpensive material was discovered recently that appears to effectively capture elemental mercury from simulated coal-fired flue gases when injected into ductwork at modest rates. When the powdered sorbent is then removed by the electrostatic precipitator, the mercury is separated from the gas stream as well. Importantly, the new sorbents appear to be effective at high temperatures (300 F to 400 F). This means that expensive gas-cooling or fabric-filter retrofits are not required and that fly ash sales can remain unaffected. Consequently, preliminary estimates of their cost effectiveness suggest that costs are one-tenth of those estimated by the EPA for other technologies. An existing duct-injection test system will be used in Phase I to parametrically examine the new sorbent's performance, rather than just a simple fixed-bed system, which would not accurately simulate actual sorbent conditions. This project's ambitious performance and cost goals are the demonstration of in-duct elemental mercury removal of 80 percent from a simulated, representative flue gas at 350 F with an estimated cost of less than $3,000 per-lb-of-Hg removed, one-tenth that of current technologies.

The results of the Phase I project increase the likelihood that the project's new technology will make a major contribution to a healthier world environment. First, the U.S. EPA is introducing mercury-control standards on power plants requiring significant emission reductions from over 1,000 utility coal-fired boilers. A regulatory timetable has now been set, which will lead to the installation of mercury control technologies on these units. Second, an analysis of the measurements supplied in response to EPA's mercury Information Collection Request reveals that the biggest part of the U.S. utility problem is the emission of the elemental form of mercury, which current controls do not capture. During the Phase I project, two discoveries were made that help demonstrate the feasibility of Sorbent Technologies' new duct-injection sorbent approach. First, the new elemental-mercury sorbents were found to work through a chemisorption process. Project experiments showed this to be responsible for high sorbent stability and surprisingly good high-temperature performance. Powdered activated carbons (PACs), the best sorbents currently available, capture mercury primarily through a weak physical adsorption. In fixed-bed experiments at representative utility flue-gas temperatures, the new sorbents demonstrated elemental-mercury capacities ten (10) times higher than typical PACs. With the new technology, it may be possible to achieve net mercury-removal costs that are one-tenth that of current technologies. The second discovery was that the sorbents can be made from commercially available substrate many times smaller than PACs. This would relieve the bulk-gas mass-transfer limitations that many believe inherently constrain PACs from achieving high performance under economical conditions. The stage is now set for continued Phase II laboratory and duct-injection pilot-plant testing on simulated coal-combustion gases at Sorbent Technologies' existing facilities. Also in Phase II, materials scientists at The Pennsylvania State University will join the effort to better understand and exploit the increased performance of the new sorbents. In addition, an excellent site has been located that will allow inexpensive duct-injection testing on actual flue gases from a number of problem coals. Outside equity investments for the Phase II Commercialization Option have already been received, enabling the addition of this last task to the Phase II project. Production of the new sorbent has already been scaled up to 40-lb quantities for such testing. Supplemental

Keywords:
small business, SBIR, air pollution, mercury, coal-fired boilers, powdered activated carbon, PAC, flue gases, EPA