- Laramie River Station Overfire Air
Basin Electric Power Cooperative’s Laramie River Station is just east of Wheatland, Wyoming. It consists of three coal-fired units that produce enough electricity to power approximately 1.4 million homes. When Wyoming’s Department of Environmental Quality (WDEQ) notified the station that nitrogen oxide (NOx) emissions from the plant needed to be lowered, Burns & McDonnell was retained to design an overfire air (OFA) system that would minimize those emissions without making major modifications to the boilers. The design optimized boiler OFA coverage and penetration, included flexibility for burner modifications in the future and minimized installation costs. Using a computer model to evaluate many scenarios and design criteria, Burns & McDonnell provided an OFA system tailored to each of Laramie River Station’s three units. It has reduced emissions by up to 30 percent to meet the WDEQ requirements and continue Basin Electric’s commitment to providing clean, affordable power.
Using a computational fluid dynamics (CFD) model to optimize sizing and locations of the OFA system, NOx emissions are reduced by staging the coal combustion process. A portion of the necessary combustion air is diverted from the burners to OFA ports located above the burners. As a result, the burners have less than the total amount of air required for complete combustion. Limiting the combustion air at the burners results in a portion of the fuel converting to carbon monoxide (CO), which readily combines with NOx to produce elemental nitrogen and carbon dioxide (CO2).
The design uses individual OFA port ducts with electronic flow control dampers, specifically automated to match the LRS boiler configuration, which provides maximum flexibility for operating the plant across various loads and fuel conditions.