Wednesday, August 29, 2012

Continuous Emissions Monitoring System (CEMS)

Electric utility companies must meet stringent regulatory standards for environmental quality with a continuous emissions monitoring system (CEMS) that provides reliable and accurate data.


Figure 1: Oswald Generating Station
The Oswald Generating Station is a 510-megawatt (MW), combined-cycle, natural gas combustion turbine plant located in Pulaski County, 0.5 miles south of Wrightsville, Arkansas. The plant (Figure 1) consists of six GE LM6000 aeroderivative combustion turbines, one GE Electric Frame 7EA combustion turbine, seven duct burners and two steam turbines. The plant configuration is commonly known as a 'Seven on Two.' "
This means the seven combustion turbines (CTs), or fewer, provide steam to one or both steam turbines, depending on the current power demand. The plant is not configured for the CTs to operate in simple cycle mode.

The plant is designed to supply approximately 75 MW to 510 MW of power during high electrical demand hours of each day, usually between the hours of 7:00 a.m. and 11:00 p.m., and ramp down to approximately 75 MW during off-peak hours. This daily load cycling results in reduced power production each day during hours when there is less demand for the power.

The six LM combustion turbines are equipped with steam injection for emission control of oxides of nitrogen (NOx). The Title V Air Permit limits the six LMs to a three- hour rolling average of 25 ppm and a yearly average of 22 ppm NOx corrected to 15% oxygen (O2). The 7EA combustion turbine utilizes dry low NOX (DLN) burners for NOx control. The 7EA is limited to a three-hour rolling average of 9 ppm NOx corrected to 15% O2.
The facility currently operates and maintains seven Continuous Emissions Monitoring System (CEMS) that are subject to the Acid Rain Program under 40 CFR Part 75 and the Clean Air Interstate Rule (CAIR) for the NOx ozone season trading program. Each system is comprised of an O2 monitor and a NOx monitor. The emissions are monitored every minute, and the data is passed to the existing, common data acquisition handling system (DAHS), which calculates the hourly emissions for each CT. Each calendar quarter the NOx (lbs/mmBtu) and other plant data are electronically reported to the U.S. Environmental Protection Agency (EPA). The CEMS undergo a calibration check each operating day, linearity checks each quality-assured (QA) quarter and an annual relative accuracy test audit (RATA).

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