Ten years ago, NETL concluded work on its mercury control program – one of its most successful and productive research programs, and one that culminated in highly effective technologies that are now widely used throughout the entire power generation sector, protecting our waters and wildlife.

In just slightly more than 15 years, the Lab brought mercury capture technology from a concept to commercial deployment – a process that generally takes two or more decades. The key to this success was the program’s highly productive public-private partnerships with academia, industry, other research organizations, and the U.S. Environmental Protection Agency (EPA). Today, mercury control technologies developed under the NETL program are installed on more than half of the coal-fired power generation fleet, protecting our health and our environment while contributing to U.S. energy security through domestic energy production.

Title III of the 1990 Clean Air Act Amendment (CAAA) identified 189 pollutants, including mercury, as hazardous or toxic. The CAAA required the EPA to evaluate emissions by source, health effects and environmental implications, including the need to control these emissions.

Thomas Feeley led the Lab’s mercury control technology R&D as Technology Manager for the Innovations for Existing Plants Program. He said NETL identified two critical areas for the Lab’s energy and environmental expertise to support EPA’s efforts to assess air toxic emissions from power plants.

“We recognized several things right away,” he said. “First, there was a strong likelihood that EPA would eventually regulate mercury emissions from the power sector. More importantly from a research standpoint, we realized there was a lot we didn’t know about mercury emitted from coal-fired boilers and that no commercial technologies were available to effectively remove mercury from the diverse population of coal-fired power plants in operation. Our inhouse research together with program and project management capabilities put us in a unique position to be able to work collaboratively with EPA to address these two issues.”

Then, as now, coal-fired stationary sources support the nation’s energy demand with reliable, affordable energy. To keep these essential stations operating efficiently and in compliance with pending regulations, NETL embarked on a comprehensive research program to develop and implement mercury control technologies.

Clean Air at the Forefront

By December 2000, EPA determined the need to regulate the mercury emissions from coal-fired and oil-fired power plants. NETL researchers and their collaborators were already on the case. Starting in 1992, NETL partnered with the Electric Power Research Institute (EPRI) – the research arm of the electric-utility industry – and the University of North Dakota Energy and Environmental Research Center (UNDEERC) to characterize the toxins – with a focus on mercury – emitted from fossil-fuel combustion. This research spanned from emissions testing at a number of commercial power plants burning different ranks of coal and equipped with a variety of emission control equipment, to work conducted on NETL’s own laboratory and pilot-scale combustion units.

“One of the things we discovered early on through our research and our work with EPRI, UNDEERC and our other partners is that the capture of mercury across existing air pollution control devices could vary significantly based on coal properties, flue gas properties, plant configurations, and more. We wanted to understand why,” Feeley said.

Subsequent research revealed that the chlorine and sulfur content of coal greatly affected the form of mercury produced. Researchers discovered that bituminous coals generate a much greater percentage of oxidized mercury, which tends to be easier to capture in conventional pollution control devices. Elemental mercury, on the other hand, passed through the plant’s control equipment and escaped to the atmosphere where it could travel great distances before being washed out in rain. “So, if we could control the form of mercury, we could enhance its removal using the plant’s existing control equipment or by installing mercury specific capture technology. This was a critical finding in our efforts to develop cost-effective mercury capture systems,” Feeley added.

Innovation Leads the Way

From the mid-1990s through 2000, the Lab’s bench- and pilot-scale research focused on developing sorbents such as activated carbon to capture the oxidized mercury using the plant’s existing particulate controls and on methods to oxidize the elemental mercury so it could be removed in a plant’s particulate capture system or sulfur dioxide (SO₂) scrubber.

To ensure that NETL’s program closed the loop on the fate of mercury, research was also conducted on understanding where the mercury goes after it is removed from the power plant’s flue gas stream. The Lab’s research indicated that the mercury was stable once captured in the plant’s fly ash or scrubber liquids and would not re-enter the environment if those materials were beneficially reused or otherwise managed.

Out of the Lab, In to the Field

Starting in 2000, the Lab and its research partners were conducting field testing of the most promising mercury control systems that emerged from the program’s laboratory and bench-scale investigations. The field testing was conducted at operating coal-fired power plants and was crucial in demonstrating the reliability of mercury control technology in real-world situations.

“Our field testing activities really showcased the Lab’s ability to bring together the private- and public-sectors to achieve a common objective and benefit the American public,” Feeley said. “Being a government-owned, government-operated (GOGO) lab enabled us to protect intellectual property, which encouraged the research community to work with us and the electric utilities to provide host sites for our testing. As a GOGO, we were also able to share the results of our work directly with the EPA in their rulemaking process.”

Data collected during the field test program allowed NETL and its partners to validate the cost and performance of the mercury capture technologies. “We set a target early on of developing technologies that could achieve 70 to 90 percent capture at costs per pound of mercury removed below early estimates of $50,000 to $70,000. We exceeded our expectations with capture efficiencies more than 90 percent at costs that dipped in some cases below $10,000 per pound of mercury removed.”

In addition to field tests, technology transfer played an instrumental role in moving mercury capture technology forward. NETL held yearly program reviews to share and discuss progress with state and Federal regulatory agencies, technology developers and vendors, non-government organizations, research institutions, electric utility executives, plant managers, and other interested parties. This, coupled with participation in national and international meetings and the publication of research, ensured that the results of the program were available and effectively communicated to those who needed the information as quickly as possible.

By 2008, NETL and its partners had successfully field tested a variety of control options including activated carbon injection (ACI), sorbent injection, and mercury oxidation systems at more than 30 different coal-fired power plants. ACI had proven to be the best available and maximum achievable control technology for mercury control, and commercial injection systems were being installed across the power generation industry.

Mercury Control Program Results in Success

Today, ACI and other mercury captured systems developed under NETL’s program can be found on more than half of the nation’s coal-fired power plants. “The program was a complete success,” Feeley stated. “In 15 years we brought mercury emissions control from a concept to a commercial reality.”

With the goal met of enabling the existing fleet of coal-fired power plants to reliably and cost-effectively comply with mercury control regulations, NETL ended its mercury control technology R&D to focus resources and expertise on emerging, pressing issues. The Lab continues to uncover new knowledge to inform energy policies that stimulate the economy, ensure security, and protect health, while developing innovations to fuel the nation on home-grown energy with responsible stewardship of the environment.