By Mike Jones, Ph. D
Retired Vice President of Research and Development
Lignite Energy Council
In 2005, the biggest environmental issue facing North Dakota’s lignite industry was finding a cost-effective method to capture mercury from the state’s seven lignite-based power plants. At the time, there were no commercially-available mercury control technologies for power plants that used western coals, such as lignite.
In 2018, the entire fleet of North Dakota’s power plants are now capturing mercury both affordably and effectively. In fact, they have been equipped with mercury technologies for several years and have a proven track record of environmental compliance. So what happened?
Simply put, North Dakota utilities along with the researchers at the Energy Environmental Research Center in Grand Forks, the State of North Dakota through the Industrial Commission and the National Energy Technology Laboratory, a branch of the U.S. Department of Energy collaborated with Texas and Saskatchewan utilities to find a solution.
Saskatchewan, Texas and North Dakota derive a lot of electricity from native lignite resources, so it only made sense that the utilities would want to find a solution to keep their power plants operating cleanly and efficiently.
The challenges in capturing mercury were immense 15 years ago considering that coal contains only trace amounts – measured in one part per billion or even trillion. An analogy popular at the time described the low concentration of mercury in power plant flue gas like this: “Imagine a pipe, one foot in diameter, built from the earth to the moon. If the pipe, which measures 238,000 miles long, was filled with flue gas, and the mercury particles were all brought to one end, it would take up only the first 18 inches of the pipe.” Finding this trace amount of mercury in flue gas was similar to finding a needle in a haystack.
A team approach, led by Harvey Ness, the director of research and development for the Lignite Energy Council, combined the resources in North Dakota with those in Texas where utilities also burn Gulf Coast lignite to generate electricity. North Dakota industry members formed a “mercury team” to champion the efforts to find a solution with regional and national researchers including the Energy & Environmental Research Center in Grand Forks.
In total, about $26 million from various sources was earmarked for mercury research at North Dakota plants with the majority coming from the Department of Energy through NETL funding. The NETL funing was used to leverage additional funding from the North Dakota Lignite Research Program and utilities and lignite mines operating in the state.
Lignite is a low-rank coal and has little natural chlorine. Power plants that burn eastern coal, which contains higher levels of chlorine, have a relatively easier time of controlling mercury if equipped with conventional emissions control technology such as selective catalytic reduction and wet flue gas desulfurization systems.
Activated carbon injection into the flue gas was further enhanced with the introduction of bromine and chlorine, which are both halogens, to oxidize the mercury to make it easier to capture. The technique was termed “Sorbent enhancement additive.”
The technology proved successful and the cost of capturing mercury decreased dramatically for utilities that would need to retrofit their existing plants.
The story of capturing mercury in North Dakota power plants can now be seen as a blue print for how North Dakota utilities are working together to find a cost-effective solution to capturing CO2 from existing power plants.
Project Tundra is considered an already proven technology in a smaller slip-stream project on a Texas power plant. Several North Dakota utilities and mining companies are engaged in a pre-engineering study to determine if the technology would be cost-effective on one of the two units at the Milton R. Young Station near Center, North Dakota.
While it’s impossible to look into the future and determine how successful a technology will become, North Dakota electric consumers should take comfort in knowing that the same type of collaboration that was so successful in capturing mercury from existing power plants is still being employed as the industry looks at finding affordable technologies to capture and use CO2 from the current fleet of power plants.
Development of mercury capture technology is just one example of the many successes of the lignite industry in addressing challenges in order to maintain a low cost, reliable, clean source of electricity for the region.