July 8, 2002 — Great River Energy on Monday announced that test results at its Stanton Station power plant to control power plant mercury emissions fell short of the expectation of 90 per cent removal.
The technology tested at Stanton Station removed only half the expected amount. The research is part of an effort to find a cost-efficient way to remove mercury from power plant emissions.
“Our test results show that 90 per cent removal in power plants such as ours may not be readily achievable with current approaches such as activated carbon injection. They also indicate that the economics of the technology are not in line with earlier expectations,” said Mark Strohfus, Great River Energy mercury reduction project leader. “Further testing is warranted to better define the total costs of the technology.”
The full-scale emission tests were conducted at Great River Energy’s Stanton Station in Stanton, North Dakota. The research is a joint effort of EPRI and Great River Energy, a generation and transmission cooperative, together with a team from URS Corporation and Apogee Scientific who conducted the fieldwork and data analyses.
“Great River Energy volunteered to participate in this study because nearly 1,300 megawatts of our power plant capacity is lignite-based, so the study results directly affect us,” said Strohfus. “It also supports our promise to the state of Minnesota, through our Voluntary Mercury Reduction Agreement, to support research in mercury reduction technologies.”
Stanton Station was considered a nearly ideal site because of its smaller size and the absence of any other tests on this type of power plant, which is equipped with a spray dryer flue gas desulfurization system and a baghouse for controlling particulate matter and which burns lignite coal. Lignite and other Western coals contain less chloride than bituminous coal, making mercury removal more difficult.
The Stanton Station tests showed that the injection of activated carbon to control mercury emissions is adversely affected by the presence of a spray dryer. Prior to these tests, some believed that carbon injection ahead of a baghouse would remove up to 90 per cent of the mercury emissions, whether or not the unit also has a spray dryer. Tests at other plants with a baghouse but no spray dryer were able to reduce mercury emissions by up to 90 per cent over a short period of time.
Chemical addition tests also were conducted in an effort to convert the mercury to a form believed to be more easily removed by existing, conventional air pollution controls. EPRI and Great River Energy researchers thought the chemical additives would promote the production of oxidized mercury compounds, which could then be removed by the plant’s existing air pollution control equipment.
“While oxidized mercury compounds were indeed produced by all three additives tested, not all chemical additives resulted in improved mercury removal,” said Strohfus. “And those additives that improved removal also caused operational problems that could limit their prolonged use.”
The mercury control technology tests at Stanton Station were only the fourth full-scale mercury control tests performed in the United States, and the first at a site with a spray dryer. The research of cost-efficient mercury control technologies is precipitated by the EPA’s move toward regulating mercury emissions at power plants by 2007.
“While these results are valuable additions to the body of knowledge on mercury emission and control, they are only individual tests at a single plant,” stated EPRI’s program manager, Dr. Ramsay Chang. “Further work is needed to determine if similar results would be achieved at power plants firing different Western fuels, power plants using different boiler designs, and power plants with different air pollution control systems.”
EPRI, headquartered in Palo Alto, Calif., was established in 1973 as a center for public interest energy and environmental research. EPRI’s collaborative science and technology development program now spans nearly every area of power generation, delivery and use. More than 1,000 energy organizations and public institutions in 40 countries participate in EPRI’s global technical and business program.
Great River Energy, the second largest electric utility in Minnesota, is a generation and transmission cooperative providing electric energy and related services to 29 distribution cooperatives in Minnesota and Wisconsin. Great River Energy is a Touchstone Energy® cooperative.