ABSTRACT

The new generation of land-based gas turbine systems to be based on technology developed by the Department of Energy?s Advanced Turbine Systems (ATS) program is intended to represent a significant step forward in overall efficiency, economy of operation, and environmental compatibility. These advances require the hot gas path components to endure increased combustion temperatures for extended times with a minimum of cooling. Improved bottoming cycles including chemical recuperation and humidified air are also being considered. Whereas some of the required improvements in performance will rely on the transfer of component design, materials and processing from aircraft gas turbines, the specific duty cycle of the ATS machines will require increased emphasis on the use of thermal barrier coatings. The high-temperature corrosion issues raised by the severe operating conditions of these turbines and, in particular, those associated with the use of thermal barrier coatings are discussed.

INTRODUCTION

A number of forecasts have been published that indicate that, in the time frame of 2000 to 2014, there will be a need for more than 1,070 GW of new power generation capacity world-wide. Of this new capacity, approximately 600 GW will be coal-fired, and approximately 470 GW will be gas-fired. The U.S. represents only approximately 2070 of the global market for the gas-fired new power generation in this time frame, and only approximately 3% of the coal-fired new generation capacity. Gas turbine systems arc expected to dominate the new gas-fired capacity, and this expectation has triggered increased competition among the major gas turbine manufacturers with the greatest emphasis being placed on the ability to produce the most efficient gas turbine system. The position of U.S. gas turbine manufacturers is being enhanced by the U.S. Department of Energy-sponsored Advanced Turbines Systems program?, which aims to foster the development of advanced cycles which have an overall efficiency of greater than 60 percent (based on the lower heating value of the fuel), which will exceed the increasingly stringent environmental emissions regulations, and which will produce electricity some ten percent cheaper than at present.

The results of this stimulus on the offerings of the major gas turbine manufacturers are indicated in Table 1, which compares some of the features of the state-of-the-art gas turbines currently on offer with those of the recently-announced advanced gas turbines. Using as an example the General Electric Frame-series gas turbines, the 7F-version, which was introduced in 1993, generates (in simple-cycle form) 159MW(e), has a pressure ratio of 14.7 to 1,and has a rotor inlet temperature (RIT) of 1288°C (2350°F). The 7G-version, to be introduced in 1997,has a pressure ratio of 23 to 1,a RIT of 1430°C (2606F), and produces 240 MW(e) in simple cycle mode. The Frame 7H, also to be introduced in 1997,is intended specifically for combined-cycle operation and in this mode will generate more than 400 MW(e) at a claimed efficiently of609h. By comparison, the combined-cycle version of the Frame 7G machine will generate 350 MW(e), and will have an overall efficiency of 5870. The increased efficiency of the H version derives partly from the introduction of steam cooling of the transition nozzles, first-stage vanes, and first-stage blades.

APPROACHES FOR INCREASING OVERALL EFFICIENCY

The major route for achieving increased efficiency of a gas turbine is to increase the rotor inlet temperature. For combined cycle plants, efficiency increases also can be achieved through the adoption of different bottoming cycles, and from changes in the balance of cycle components. In the advanced land-b

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