Influence of Variations in the Natural Gas Properties on the Combustion Process in Terms of Emissions and Pulsations for a Heavy-Duty Gas Turbine

The natural gas supply can vary significantly on a day-to-day or even hour-to-hour basis for a power plant equipped with gas turbines. The influence of such variations could potentially have an adverse effect on the combustion process in terms of emissions and acoustic pulsations, even if the fuel properties are within the original equipment manufacturer (OEM) guidelines. Since the operation of a gas turbine typically requires steady emissions within the air permit as well as low pulsations to limit mechanical damage on the unit, fuel variations could significantly affect how the unit can be operated. To investigate this matter, data from an ALSTOM GT11N1 gas turbine was collected and studied during a 6-month period. The data acquired included on-line gas chromatograph readings, frequency-analyzed combustion instabilities, various process data, as well as ambient conditions. The collected data shows the magnitude of the changes in the emissions and combustion noise with changes in the fuel. The conclusion is that normal day-to-day variations in the natural gas properties do not have a significant effect on the emissions and combustion instabilities; however, larger sudden changes, as exemplified in the paper, could lead to considerable changes in the combustion behavior of the unit.