Alternative Fuel Considerations for Gas Turbine Combustion

Gas turbines have the advantage of being able to operate on a wide range of fuels. Given the escalating cost of conventional fuel sources such as natural gas, there is increasing interest in, and implementation of, systems burning lower cost fuel gases. There are significant combustor performance effects when utilizing different fuels. Flame stability, emissions, durability, and combustion dynamics are critical combustion parameters which must be controlled when varying fuel constituents. Significant emphasis continues to be placed on the use of liquefied natural gas (LNG) as well as syngas derived from coal and petroleum coke. The elimination of carbon from gaseous coal based fuels also offers the possibility of burning hydrogen to reduce or eliminate carbon dioxide emissions. Existing stringent emissions permits must be met by power plants utilizing these different fuels. There is also a requirement for the flexible use of these fuels allowing power plants to switch real time between fuel sources using the same combustion hardware, without affecting commercial generating schedules. This highlights the requirement for fuel preparation and control skids, as well as robust combustion systems, for reliable plant operations. The objective of this work is to review fuel properties which affect combustion and consider the methods and tools used to characterize the subsequent combustion characteristics. The work focuses on gaseous fuel premixed combustion. A full scale high pressure combustion test stand was used to evaluate the effects of various gaseous fuels on given gas turbine combustor configurations. Data collected through the testing of natural gas containing heavy hydrocarbons, as might be expected from liquefied LNG or refinery offgas, and hydrogen based syngas fuel blends with natural gas to simulate various coal gas blends, is presented with conclusions drawn based upon the critical combustion parameters mentioned above. A methodology for fuel characterization and combustor qualification for the acceptable operation of gas turbine combustors on various gaseous fuels is discussed. The practical implementation of multi-fuel systems on commercially operating engines is also discussed, with emphasis on diluent free premixed systems.