The detrimental health effects of mercury are well documented. Furthermore, it has been reported that U.S. coal-fired plants emit approximately 48 tons of mercury a year. To remedy this, the U.S. Environmental Protection Agency (EPA) released the Clean Air Mercury Rule (CAMR) on March 15, 2005. A promising method to achieve the mandated mercury reductions is activated carbon injection (ACI). While promising, the current cost of ACI for mercury capture is expensive, and ACI adversely impacts the use of the by-product fly-ash for concrete. Published prices for activated carbon are generally 0.5-1 $/lb and capital costs estimates are 2-55 $/KW. Because of the high costs of ACI, Praxair started feasibility studies on an alternative process to reduce the cost of mercury capture. The proposed process is composed of three steps. First, a hot oxidant mixture is created by using a proprietary Praxair burner. Next, the hot oxidant is allowed to react with pulverized coal and additives. The resulting sorbent product is separated from the resulting syngas. In a commercial installation, the resulting sorbent product would be injected between the air-preheater and the particulate control device.

To date, Praxair has generated mercury sorbents from bituminous, sub-bituminous, and lignite coals. Using EPRI's Pollution Control Test (PoCT) system, Apogee Scientific tested the sorbents at We Energies' Pleasant Prairie station and Xcel's Comanche station, which burn PRB coal. Mercury removals up to 94% at injection rates of 6 lb/MMacf, and 87% at injection rates of 2 lb/MMacf were achieved. The cost per pound of mercury removed is estimated to be less than 20% of the Department of Energy's baseline cost of $60,000 per pound of mercury removed. Because of these excellent preliminary technical and economic results, Praxair proposes to further develop the technology.

The objectives of the proposed study are:

• To produce carbon-based sorbents for mercury control that remove much greater than 70% of the inlet mercury.
• To test the sorbents on actual flue gas streams by using slip-stream tests.
• To analyze the properties of the sorbents to understand the relationship between processing conditions and fundamental properties.
• To evaluate the sorbents' impact on by-product characteristics for concrete use.
• To confirm the process economics.

Using its pilot-scale process, Praxair proposes to generate sorbents from sub-bituminous, bituminous, and lignite coals. These sorbents will be produced under various processing conditions to better understand and optimize the process for mercury control and to minimize the impact on fly-ash. After generation, the sorbents will be tested by Apogee for mercury capture on PRB and PRB/bituminous-blend flue gas streams. The sites planned for the slip-stream tests are the Xcel Comanche (PRB) station and the NRG Huntley (PRB/bituminous) station. The performance of the sorbents will be analyzed for BET surface area, particle size, ultimate/ proximate analysis, and by-product compatibility to further enhance the understanding of the sorbent manufacturing process. In addition to acting as host sites, NRG Energy, Xcel Energy, and Great River Energy have agreed to act as advisors to provide utility input to the program. EPRI has also agreed to act as an advisor.