This paper describes experimental test runs utilizing catalytically supported thermal combustion for gas turbine application. Test fuels were No. 2 distillate oil and low Btu synthetic coal gas. The tests were carried out over a range of pressure, temperature, and mass flow conditions. Analysis of these results are presented and the implications for future combustor design are discussed. Catalytically supported thermal combustion demonstrated the potential for very low emission performance.

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.

Liquefied Natural Gas (LNG) from offshore reserves is expected to expand its role in supplementing US natural gas supplies. The quality and hydrocarbon contents of the natural gas imported from these international sources, frequently differs from the compositions of domestic natural gas. With the range of variations in fuel characteristics known to exist with offshore LNG, use of this LNG in gas turbine engines could violate applicable fuel specifications, and lead to operational issues such as, but not limited to, combustion dynamics, flashback, increased emissions, or decreased component life. Another potential issue for gas turbines generating power is that rapid changes in the fuel characteristics that may occur when blending imported and domestic gas, may lead to substantial fluctuations in power output. Fuel flexibility is dominantly tied to the combustion system design. Conventional diffusion flame combustion systems are more tolerant of wide variations in fuel compositions but they are limited by their emission levels. The more advanced premixed flame combustors, the Dry Low NOxs (DLN) and Ultra Low NOx (ULN) combustion systems have significantly better performances in terms of emissions but they are also more sensitive to changes in the fuel composition and characteristics. Siemens has performed test campaigns with commercially operating engines and high pressure combustion test rigs to evaluate their commercially available combustion system configurations for LNG applicability. From these test campaigns, Siemens has defined the set of combustion hardware modifications which is robust to changes in fuel composition within the tested limits. Along with the said combustion hardware upgrade, Siemens has also designed an Integrated Fuel Gas Characterization (IFGC) system (Patent Pending). This IFGC system acts like an early warning system and feeds forward signals into the plant control system. Depending on the changes in the properties of the incoming fuel, the IFGC system is designed to adjust the engine tuning settings to compensate for these dynamic changes in the fuel. Customer implementation of the required hardware as well as associated site-specific engineering will mitigate the operational and emissions risk associated with the fuel changes. Overall, it is Siemens recommendation that LNG type fuels will be acceptable to be used in Siemens Gas Turbines with the preferred combustion hardware in place along with the Integrated Fuel Gas Characterization System. A site specific evaluation would be required to determine the optimal system depending on the expected fuels that the unit would be operating with, along with the emissions permit levels associated with the site.

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Ceramic inlet vanes were tested in a full-size, eight-vane cascade rig to simulate power generation operation at 2200 and 2500 F (1204 and 1371 C). The 2200 F (1204 C) test, using only Si3N2 vanes, successfully completed over 100 start/stop cycles, except for some out-of-tolerance parts that caused edge loading. Initial 2500 F (1371 C) tests resulted in complete failure of the four carbide parts, while the four nitride parts remained funtional. Ramps up and down were somewhat more severe than for normal turbine operation, and all parts received debris impaction from an imploded combustor. Minor cracking occurred in only one nitride airfoil and two different nitride end caps. All LAS CERVIT C-140 insulator material was badly cracked after both test conditions. New insulator materials are being evaluated and cyclic tests are continuing.