Power Engineering - GE adds predictive emissions monitoring systems to its oil and gas offerings

27 September 2004 - To help customers meet increasingly stringent gas turbine emissions regulations, GE Energy's oil and gas division has added Predictive Emissions Monitoring Systems (PEMS) to its "Smart Services" portfolio of high-technology tools, which already includes remote monitoring and diagnostics and remote dry low NOx tuning.

Gas turbine users worldwide are being requested to not only minimize emissions, but also to measure them continuously, either with direct (Continuous Emissions Monitoring Systems, or CEMS), or indirect (PEMS) methods.

GE's new PEMS offering supplies data gathered from operating gas turbines to a computer program that predicts and reports on the emissions of nitrous oxides (NOx), carbon monoxide (CO), and oxygen (O2). Emissions are not actually sampled; rather, turbine operating conditions such as fuel consumption and certain ambient conditions are measured to predict expected levels of emissions.

PEMS offers several advantages over CEMS:
• Lower initial costs for equipment and installation compared to CEMS; for example, a PC requires minimal installation costs

• Minimal operating and maintenance costs
• No exhaust gas sampling or conditioning features are required
• No stack-mounted hardware required
• The system can be easily extended to more than one unit
• No calibration costs
• Ideal for off-shore application, where space and weight are big constraints

Rather than a statistical-based modeling approach, the GE PEMS offering utilizes "first principles"-based modeling techniques. These models employ equations that represent the various mass and energy balances and thermokinetic reactions comprising the combustion process.

The first principles-based model requires fewer sample points than the statistical model. It uses sample data to calibrate or tune the model to the turbine/fuel being measured, while the statistical model is built on the sample data. First principles-based models are generalized models that are tuned to the specific turbine/fuel combination being measured. This tuning process adjusts the model coefficients based on observed emissions paired with observed turbine input parameters.

The GE approach also offers customers the benefits of systems integration that only the gas turbine designer/manufacturer can provide. For example, GE PEMS is compatible with GE's remote monitoring diagnostics system.

PEMS has been accepted by many environmental regulatory organizations including the Regional Environmental Protection Agency (ARPA) in Italy and the Environmental Protection Agency (EPA) in the United States. The technology has already been successfully applied to a number of operating GE gas turbines, including LM 2500, GE10 and PGT 25 models equipped with standard combustors as well as units equipped with DLN/DLE systems.

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