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Dave Gates Generating Station

Dave Gates Generating Station

NorthWestern Energy operates the Dave Gates Generating Station (DGGS) in Anaconda, Mont. The 150-megawatt (MW) natural gas facility serves as a regulating resource to stabilize the transmission grid due to supply and load variations and the integration of unpredictable fluctuations from intermittent renewable resources, such as wind and solar power.

DGGS consists of three 50-MW generating units with each generating unit consisting of two aero-derivative combustion turbines and one electric generator. We control carbon monoxide (CO) and volatile organic compounds (VOCs) by catalytic oxidation. Nitrogen oxide (NOx) emissions are controlled using water injection and selective catalytic reduction (SCR).

We inject demineralized water into the turbines by cooling the combustion temperature, thereby reducing the formation of thermal NOx. We reduce NOx even further when the SCR injects aqueous ammonia across the face of the NOx catalyst, converting nitrogen oxides to nitrogen and water vapor. We monitor emissions with continuous emissions monitoring systems (CEMS). The CEMS measures the stack emissions and provides feedback to the SCR to optimize ammonia injection rates for better NOx reduction and preventing over injection of ammonia.

Aberdeen Generating Station

Aberdeen Peaker PlantThe Aberdeen Generating Station, located in Aberdeen, S.D., is a peaking facility. The site has two units. Historically, we used the facility during extreme heat or cold, or as a backup supply for renewable generators in the area. In 2016, the facility joined a new power pool and marketing group, and since then we have dispatched the units to run more frequently.

Unit 1 is an existing 1976 GE Frame 5 simple cycle, fuel oil-fired combustion turbine capable of generating 27 MW. The unit does not have any emissions controls and typically operates less than 200 hours per year.

Unit 2 is a Pratt & Whitney Power SystemsF T8-3 Swiftpac simple-cycle combustion unit with a maximum output of 60 MW. The Swiftpac contains two aero-derivative combustion turbines – Units 2A and 2B. These units can operate on pipeline natural gas or ultralow sulfur No. 2 fuel oil. Pipeline natural gas is the fuel of choice for normal operations and startup. Individual gas and liquid fuel flowmeters at each turbine measure fuel flow for calculation of heat input to determine compliance with 40 CFR Part 60 and AQCP emission limits. Units 2A and 2B use water injection for the control of NOx emissions. The Continuous Emissions Monitoring Systems (CEMS) provide real-time data.
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