The United States federal new source performance standards (NSPS) for stationary gas turbines contain NOx limits that are standardized based on the International Standards Organization (ISO) standard for ambient conditions. The measured NOx emissions from stationary gas turbines at test conditions are to be corrected to ISO standard ambient conditions using a recommended equation, which was developed using data from conventional (diffusion flame) combustion systems. It is genearlly expected that this correction equation will require a revision when advanced lean premixed or hybrid combustion system is utilized.

At the site of the first Mars 100S SoLoNOx gas turbine, a continuous emissions and gas turbine performance data gathering system has been installed. From the data gathered, the non-applicability of this NOx ambient correction equation is demonstrated. This points to the need to develop a custom NOx ambient correction equation for gas turbines with an advanced lean premixed system.

Using a proven NOx model, the humidity effect on NOx emissions from an advanced lean premixed system is determined to be much stronger than that for a conventional combustion system. The humidity effect was determined based on an engineering application of the NOx model. Through statistical analyses, this stronger humidity effect is supported by more than one thousand five hundred data points gathered over a eight-month period at the above customer’s site, covering an ambient temperature range over 100°F (56°C). Using this newly determined humidity effect and a least-square curve fit of the data, a custom NOx ambient correction equation has been developed for this prototype Mars SoLoNOx gas turbine.

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