Mercury control technology earns patent

Coal Creek Station power plant

Great River Energy employees discovered an effective and cost-efficient way to reduce mercury emissions to comply with the Mercury and Air Toxic Standards.

Great River Energy employees discovered an effective and cost-efficient way to reduce mercury emissions to comply with the Mercury and Air Toxic Standards.

When facing tighter regulations for mercury emissions at the Coal Creek Station power plant, Great River Energy employees met the challenge head on and created a new, better and more cost-efficient way of reducing emissions. The process resulted in the cooperative receiving a patent in late October.

The process started over a decade ago when the Mercury and Air Toxic Standards, or MATS, were starting to emerge. The standard required power plants to lower the amount of mercury emitted.

“Coal contains variable concentrations of mercury and sulfur. That sulfur and mercury is entrained in the flue gas in gaseous or vapor form when coal is burned,” said Derek Laning, leader, engineering and projects at Coal Creek Station.

However, removing mercury can be challenging. “Mercury typically resists bonding to other compounds, making it difficult to capture,” added Laning.

Early testing of several technologies revealed methods to reduce mercury, but the costs were high.

“Most coal-based power plants reduce mercury emissions by injecting activated carbon into the flue gas. Unfortunately, this process has higher capital and operating costs,” said Laning. “Our goal was to find a technology that would help our power plant remain competitive in the energy market. Therefore, employees at Coal Creek Station kept working to find a solution.”

The better solution, which was eventually patented, was found during additive testing in 2013 and 2014. The solution was to add calcium bromide to the coal before it enters the boiler and add a liquid additive called KleeNscrub to the scrubber. Through this process, mercury is oxidized in the boiler, removed in the scrubber and collected in the scrubber sludge stored in impoundments near the power plant.

“We would not be able to do this without the hardworking employees who have helped out over all the years with testing and determining what would work best for our plant,” said Laning.