Basin Electric Power Cooperative said July 26 that the Dakota Gasification Co. directors have approved a project to install equipment that will reduce mercury emissions at the lignite gasification facility in North Dakota.
The project is in response to Maximum Achievable Control Technology Standards (MACT) standards developed by the U.S. Environmental Protection Agency. The National Emission Standards for Hazardous Air Pollutants for industrial, commercial and institutional boilers and process heaters require Dakota Gas to be compliant by Jan. 31, 2017.
Laura Dronen, Dakota Gas process engineering supervisor, said that most of the time the Synfuels Plant boiler’s exhaust is well within the limits allowed, but excursions over the limit occasionally occur. A multi-disciplinary team continues to investigate the causes, as the trends lack consistency, Basin added. The approved project includes adding a dry sorbent injection system to Riley boilers A, B and S, which would reduce mercury from the flue gas before it exits through the main stack.
“We looked at other methods that were far more costly, some costing nearly $40 million,” Dronen said. “Adding the dry sorbent injection system is much more economical and will reduce our mercury emissions to required limits, especially considering that we are in compliance a majority of the time without any removal equipment.”
The injection system will be designed to operate intermittently when mercury emissions trend above the limits. Engineering and procurement for the $1.91 million project will be complete this summer, with construction set to begin this fall. Tie-ins for the project will be completed during the current maintenance turnaround and the project is expected to be complete by the required compliance date.