March 15, 2005, will most likely go down in history as a significant day for U.S. electricity generators. It is the day that Steve Johnson, the Environmental Protection Agency's (EPA's) acting administrator, signed the Clean Air Mercury Rule. "This rule marks the first time the United States has regulated mercury emissions from power plants," Johnson said. "In so doing, we become the first nation in the world to address this remaining source of mercury pollution."

Electric utilities are the largest remaining source of human-generated mercury emissions, and although the Clean Air Mercury Rule will play an important part in reducing airborne mercury, it will not solve the issue. "Airborne mercury knows no boundaries; it is a global problem," Johnson said.

The rule limits mercury emissions from new and existing coal-fired plants, and creates a market-based cap-and-trade program that will permanently cap utility mercury emissions in two phases: the first phase cap is 38 tons beginning in 2010, with a final cap set at 15 tons beginning in 2018.

The rule's cap-and-trade program also creates incentives for continued development and testing of promising mercury control technologies that could later be used in other parts of the world. In addition, by making mercury emissions a tradable commodity, the system provides a strong motivation for some utilities to make early emission reductions and for continuous improvements in control technologies.

Several utilities have already joined other organizations and vendors to develop mercury control technologies. For example, Entergy's Independence Steam Electric Station (ISES), in partnership with the EPRI and ADA-ES Inc., has been selected as a site for the U.S. Department of Energy's (DOE's) mercury control technology field testing program to test EPRI's TOXECON II. TOXECON II is an experimental mercury control technology which uses sorbent materials that naturally adsorb mercury to remove it from coal plant flue gas. The field test is being conducted as part of a $5.5 million cooperative agreement awarded to ADA-ES by the DOE through its National Energy Technology Laboratory (NETL). The ISES portion of the project is $1.5 million. The DOE/NETL is providing more than 70 percent of the funding as part of a research program to advance the technical readiness of mercury control technology options for the nation's fleet of coal-fired power plants.

Under the cooperative agreement, tests will be conducted to evaluate the effectiveness of TOXECON II in reducing mercury emissions from plants that burn low-sulfur Western or high-sulfur Eastern coals. To date, mercury control technologies have achieved different reduction levels at plants firing these two types of fuels, presumably because of the differences in the coals' chemical composition. This means that tests need to be conducted on the flue gas from both fuels.

The test at ISES Unit 2, an 816 MW facility in northeast Arkansas, will begin later this year. Before the tests begin, an injection grid will be installed before the last two fields of the electrostatic precipitator (ESP) on the unit. A variety of sorbents - including activated carbon - will then be tested to determine: 1) how well each combines with the mercury in the flue gas, and 2) how effectively they are then removed by the last fields of the precipitator.

Each sorbent will be injected into the flue gas downstream of the ESP's initial particulate matter collecting fields. This technique avoids one important problem at facilities like ISES, which recycles more than 90 percent of its fly ash into commercial use. Previous activated carbon tests at power plants have injected the carbon in the flue gas upstream of the ESP. This contaminated the fly ash, rendering it unusable for recycling.

By injecting the carbon in the latter part of the ESP, it is possible to capture most of the fly ash upstream of the injection - before it mixes with the carbon. Entergy hopes this technique will allow facilities like ISES to meet two potentially conflicting goals - reduce mercury emissions and continue to recognize the benefits of recycling fly ash. Those benefits include the ability to: 1) maintain revenues from fly ash sales to offset plant operating costs; 2) reduce carbon dioxide emissions in the production of cement; and 3) reduce the need for on-site landfills for fly ash.

Finding an effective mercury control technology is a complicated matter. Not only are reduction levels influenced by the type of coal burned, but they're also affected by the configuration of the plant, existing emissions controls and operational variables. The ISES test will help determine if TOXECON II is a feasible long-term reduction technology for low-sulfur sub-bituminous generating units with a cold-side ESP.

"This project is an important component of NETL's overall program to develop advanced mercury control technologies and to evaluate their performance on actual coal-fired power plant flue gas," said Joseph Strakey, NETL's Office of Coal & Power R&D director. "It also demonstrates the kind of R&D (research and development) successes that can be achieved through government partnership with the private sector."

In October 2004, the DOE/NETL selected six projects through their Phase II, Round 2 Mercury Control Field Testing Program solicitation. Under the ADA-ES cooperative agreement, in addition to the tests at ISES, testing will be conducted at two MidAmerican Energy Facilities and one AEP facility. Entergy, EPRI, ADA-ES and the DOE/NETL are currently finalizing the details surrounding implementation of the project at ISES.