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Applied Thermal Engineering 18 (1998) 837±846

Advanced gas turbine cycles for power generation: a critical review
T. Heppenstall
The Pipe Dream Company, PO Box 76, North Shields, Tyne and Wear, NE29 6YX, UK Received 27 November 1997

Abstract The use of gas turbines for power generation has increased in recent years and is likely to continue to increase in the medium term. Thispaper describes and compares several power generation cycles which have been developed to take advantage of the gas turbine's thermodynamic characteristics. Emphasis has been given to systems involving heat recovery from the gas turbine's exhaust and these include the combined, Kalina, gas/gas recuperation, steam injection, evaporation and chemical recuperation cycles. Thermodynamic and economiccharacteristics of the various cycles are considered in order to establish their relative importance to future power generation markets. The present dominance of the combined cycle as the preferred option for a new plant is thought likely to continue. # 1998 Elsevier Science Ltd. All rights reserved.
Keywords: Power generation; Gas turbine; Combined cycle; Kalina cycle; Steam injection;Evaporation cycle; Chemical recuperation; Recuperator

1. Introduction This paper is mainly concerned with heat recovery from the exhaust streams of open cycle gas turbines used for large scale power generation. In this form of the gas turbine cycle, more than 60% of the total energy output is normally in the form of heat in the exhaust stream. Moreover, the exhaust temperature is typically around 5008Cand, consequently, there is considerable scope for heat recovery applications. Gas turbine cycles with heat recovery are examples of what are generally known as advanced cycles. Heat recovery schemes are one of the most important ways of increasing the eciency of the power generation process, usually with the aim of improving commercial performance. Improved eciency also results in lower levelsof pollution for a given output of electricity and this is a further, important consideration.
1359-4311/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 9 ± 4 3 1 ( 1 9 ) 7 0 0 1 1 - 6 6

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T. Heppenstall / Applied Thermal Engineering 18 (1998) 837±846

The combination of environmental and economic pressures on power generation and the wide availability ofnatural gas has resulted in the development of several types of gas turbine cycle. This paper provides a critical review of some of the more important concepts. 2. Advanced cycles Most of the following discussion is concerned with cycles in which heat recovery plays an obvious and direct role. However, there are many other examples of cycles which would also be referred to as advanced including, forexample, inter-cooled and/or re-heated cycles and a range of gas turbine systems for use with coal. Cycles which are essentially based on heat recovery need to be judged against this wider range of potential provision and, consequently, other schemes are discussed brie¯y in a later section. 3. Bottoming cycles and recuperation Two basic exhaust heat recovery arrangements can be used to improve cycleeciency: 1. recuperation, in which the recovered heat is used in the same gas turbine cycle; 2. bottoming cycles, in which the exhaust is used as a heat source for an essentially independent power cycle.

4. Recuperative cycles 4.1. Gas to gas recuperation Exhaust recuperation has been used in conjunction with industrial gas turbines for more than 50 years but there have always been underlyingmetallurgical problems due to the heat exchanger temperature. Increasing the pressure ratio increases the compressor exit temperature but reduces the exhaust temperature and, in modern gas turbine designs, the limiting conditions for the transfer of heat from the exhaust stream are easily achieved. Inter-cooling reduces the heat transfer problem and allows recuperation with high eciency...