Burns & McDonnell provided professional services including detailed engineering, project management and startup assistance for Minnesota Power’s second-largest coal facility, Boswell Unit 3, in Cohasset, Minn.
Boswell Unit 3 is a 350-megawatt (MW) pulverized-coal power facility commissioned for service in 1973. Previously, Minnesota Power controlled particulates and SO2 through a single-stage wet particulate scrubber, while NOx was controlled through burner control techniques.
Minnesota Power developed an environmental improvement plan focused on meeting the requirements of the state’s Mercury Emissions Reduction Act of 2006 and federal emission reduction requirements related to CAIR, CAMR and the Regional Haze Rule. Emission reduction targets for Boswell 3:
NOx: 0.05 lbm/MMBtu
SO2: 98 percent removal
Particulate matter: 0.012 pounds/MMBtu (filterable) and 0.08 pounds/MMBtu (filterable plus condensable)
Mercury removal: 90%
Burns & McDonnell performed design studies to investigate alternative proven technologies that could meet the project emissions criteria.
Low NOx burners with overfire air system in conjunction with an SCR system were selected to control NOx emissions. Forced oxidized wet limestone was the selected FGD technology. A pulse-jet fabric filter (baghouse) was selected to control particulate emissions. ACI upstream of the baghouse was selected for mercury control.
The project was performed under a multiple contract approach with Burns & McDonnell providing the detailed design for foundations, structural steel, buildings and the balance of plant systems, including mechanical, electrical, and instruments and plant control systems. Major equipment procurement contracts included SCR and FGD, fabric filter, induced draft fans and fly ash handling. At a time when labor was scarce due to construction projects nationwide, Minnesota Power relied on its relationship with key area construction contractors for major construction contracts.
Burns & McDonnell provided personnel to assist Minnesota Power with startup of the new systems.
Low NOx burners
Separated overfire air system
Selective catalytic reduction (SCR) system
Fabric filter (baghouse)
Activated carbon injection (ACI)
Wet limestone flue gas desulfurization (FGD) system