Parametric Modeling of Exhaust Gas Emission From Natural Gas Fired Gas Turbines

Increased focus on air pollution from gas turbines in the Norwegian sector of the North Sea has resulted in taxes on CO₂. Statements made by the Norwegian authorities imply regulations and/or taxes on NO_x emissions in the near future. The existing CO₂ tax of NOK 0.82/Sm³ (US Dollars 0.12/Sm³) and possible future tax on NO_x are analyzed mainly with respect to operating and maintenance costs for the gas turbine. Depending on actual tax levels, the machine should be operated on full load/optimum thermal efficiency or part load to reduce specific exhaust emissions. Based on field measurements, exhaust emissions (CO₂, CO, NO_x, N₂0, UHC, etc.) are established with respect to load and gas turbine performance, including performance degradation. Different NO_x emission correlations are analyzed based on test results, and a proposed prediction model presented. The impact of machinery performance degradation on emission levels is particularly analyzed. Good agreement is achieved between measured and predicted NO_x emissions from the proposed correlation. To achieve continuous exhaust emission control, the proposed NO_x model is implemented to the on-line condition monitoring system on the Sleipner A platform, rather than introducing sensitive emission sensors in the exhaust gas stack. The on-line condition monitoring system forms an important tool in detecting machinery condition/degradation and air pollution, and achieving optimum energy conservation.