Interpretation of federal emissions regulations by a local regulatory agency resulted in the requirement to develop a special water control system for stationary gas turbines to meet stringent NOx and CO emissions limits. Extensive field testing of two 7-MW industrial gas turbines burning natural gas was performed to establish the effects of ambient air temperature, humidity and water injection on NOx and CO emissions. The predictions from a proven NOx model were shown to be within the uncertainty of the field measurements and were used to determine the water flow rates required when burning No. 2 distillate oil. Over the ambient temperature range considered, the analytical model predicted a linear increase in NOx emissions as ambient temperature increases. This was supported by the data gathered and the thermal NOx rate equation. Subsequently, a water injection system was successfully developed to control NOx and CO emissions from the 7-MW dual fuel gas turbine as a function of ambient temperature and turbine load.

A diffusion limited model has been described previously to simulate accurately the thermal NOx emission processes in various gas turbine combustors for fuels containing negligible amounts of fuel bound nitrogen. The application of this model to simulate accurately the water injection process has also been demonstrated. It is currently proposed that any bound nitrogen in fuel is completely reacted to form nitric oxide during the hydrocarbon combustion process; the ultimate net conversion is determined subsequently based on the Zeldovich mechanisms. With this additional assumption, this model has been generalized to include the use of fuels containing significant amounts of bound nitrogen, such as crude or residual oils. The predicted NOx emissions from these nitrogen containing fuels are in excellent agreement with laboratory and field data including the effect of water injection. Comprehensive understanding of the NOx formation processes has been gained from the current analytical study.

This paper describes the successful development and application of industrial gas turbines using medium-Btu gaseous fuels, including those derived from biodegradation of organic matters found in sanitary landfills and liquid sewage. The effects on the gas turbine and its combustion system of burning these alternate fuels compared to burning high-Btu fuels, along with the gas turbine development required to use alternate fuels from the point of view of combustion process, control system, gas turbine durability, maintainability and safety, are discussed.

An analytical model has been developed to simulate the thermal NOx emission processes in various gas turbine combustors for a variety of fuels. The NOx emissions predicted by the model are in excellent agreement with available laboratory and field data. Its capability to simulate the water injection process accurately has been demonstrated previously. Comprehensive understanding of the NOx emission processes in gas turbine combustors has been gained through the current analytical studies. NOx emissions as influenced by ambient humidity, changes in combustor geometry, type of fuel used and changes in operating parameters can now be evaluated quantitatively through a priori prediction and have been verified by available laboratory and field data. The analytical model has also been demonstrated to be a powerful guidance tool in directing the experimental testing program in an effort to reduce NOx emissions from gas turbine combustors.

An experimentally verified NOx emission model has been described previously to predict accurately the NOx emission characteristics of conventional gas turbine combustors as well as laboratory scaled premixed combustor. Experimental data and analyses indicated that a hybrid combustor, which utilizes features of both the conventional and the premixed combustors, has the potential to be a viable low NOx emission combustor. Initial calculations indicated low NOx emission levels for the hybrid combustor. This hybrid combustion concept was tested in the laboratory. The measured NOx emissions from this laboratory-scaled hybrid combustor were in excellent agreement with the analytical predictions. The emissions of carbon monoxide and unburned hydrocarbons were also measured. It has been concluded from an analysis of the measured data that a gas turbine combustor, designed with the hybrid combustion concept, has the best potential to be a near-term viable combustor in meeting the EPA proposed gas turbine emission regulations. The experimental effort thus far has focused on the emission characteristics. Other areas of the design, such as the vaporization of liquid fuels, require additional development work prior to the incorporation of this concept into a viable system for an engine application.