No abstract

The Department of Energy's Advanced Turbine Systems (ATS) program is aimed at fostering the development of a new generation of land-based gas turbine systems with overall efficiencies significantly beyond those of current state-of-the-art machines, as well as greatly increased times between inspection and refurbishment, improved environmental impact, and decreased cost. The proposed duty cycle of ATS machines will emphasize different criteria in the selection of materials for the critical components. In particular, thermal barrier coatings (TBCs) will be an essential feature of the hot gas path components in these machines. In fact, the goals of the ATS will require significant improvements in TBC technology, since these turbines will be totally reliant on TBCs, which will be required to function on critical components such as the first stage vanes and blades for times considerably in excess of those experienced in current applications, Issues that assume increased importance are the mechanical and chemical stability of the ceramic layer and of the metallic bond coat; the thermal expansion characteristics and compliance of the ceramic layer; and the thermal conductivity across the thickness of the ceramic layer. Obviously, the ATS program provides a very challenging opportunity for TBCs, and involves some significant opportunities to extend this technology. A significant TBC development effort is planned in the ATS program which will address these key issues.

A development thrust for the adoption of ceramic components in industrial gas turbines, now being sponsored by the U.S. Department of Energy, may have a considerable impact on the growth rate and ultimate capacity of the cogeneration sector. The economic justification for cogeneration rests on the ability to undercut the cost of purchased power after taking credit for the useful heat recovery, and it is frequently marginal after consideration of fuel, maintenance, and pollution control devices. After reviewing briefly the factors contributing to the economic viability of cogeneration systems, this paper presents arguments to show how the use of ceramics in industrial gas turbine can be instrumental in reducing installation and operating costs. Improved gas turbines based on ceramic materials technology also will provides means for meeting environmental protection requirements without the use of back end flue gas treatment, and will be able to utilize byproduct industrial gaseous and liquid fuels more effectively. These improvements can increase substantially the economic return from cogeneration systems, and are expected to result in increased cogeneration capacity and a sustained market for industrial gas turbines. Predictions are made of the size of the U.S. industrial gas turbine cogeneration market. The annual fuel savings resulting from displacement of utility generation capacity could amount to 2 × 1017 joules (2 × 1014 Btu’s) by the year 2010.

A Babcock and Wilcox - Solar Turbines Team has completed a program to assess the potential for structural ceramic composites in turbines for direct coal-fired or coal gasification environments. A review is made of the existing processes in direct coal firing, pressurized fluid bed combustors, and coal gasification combined cycle systems. Material requirements in these areas were also discussed. The program examined the state-of-the-art in ceramic composite materials. Utilization of ceramic composites in the turbine rotor blades and nozzle vanes would provide the most benefit. A research program designed to introduce ceramic composite components to these turbines was recommended.

This brief review provides a general account of work directed at the use of catalytic combustion in gas turbine engines. A major potential advantage of using catalytic combustion is that the fuel can be burnt efficiently at temperatures low enough ( < 15OOOC) to avoid significant oxidation of atmospheric nitrogen. This advantage was less important when catalytic combustion was demonstrated in the 1970's than it is today and received relatively little attention until the following decade.After discussion of the principles involved in the design of a combustor that must meet the mixing, size, performance and durability goals of a based gas turbine application, the review turns to accounts of experiments conducted on a laboratory scale with simple configurations. These established basic operating parameters for satisfactory combustion performance and led to larger scale work and to prototype design concepts for industrial gas turbines in the late 70's and early 80's. Test results were encouraging but were not pursued definitively in the U.S.A. Activity continued at several centres in Japan, with exploration of a number of different catalyst arrangements, geometries, and control systems, again with encouraging results. At the same time, there has been renewed interests in the U.S.A. and in Europe, spurred largely by the emphasis on reducing emissions of nitrogen oxides (NOx).The paper concludes with suggestions for further development of catalytically stabilized combustion systems for gas turbines. These systems must ensure adequate pre-catalyst temperature, with evenly premixed fuel and air, and sufficient temperature rise across the catalyst to ensure effective completion of reaction in a homogeneous reaction mode. The outstanding problems are largely concerned with questions of catalyst integrity and longevity in practical configurations and realistic engine operating conditions.