**1. Introduction**

44 Will-be-set-by-IN-TECH

164 Efficiency, Performance and Robustness of Gas Turbines

Uematsu, K., Mori, H. & Sugishita, H. (1998). Topping recuperation cycle for hydrogen

http://www.enaa.or.jp/WE-NET/ronbun/1998/16/1698.htm.

combustion turbine in WE-NET,

Gas turbines have established an important role in the industrial production of mechanical energy owing to the very high power-to-weight ratio achievable with simple-cycle configurations and to the high conversion efficiency that can be obtained in systems that envisage waste heat recovery from the exhaust gases.

Exhaust heat from gas turbines can be recovered externally or internally to the cycle itself [1- 4]. Of the various technology options for external heat recovery, the combined gas–steam power plant is by far the most effective and commonly used worldwide. For internal heat recovery, conventional designs are based on thermodynamic regeneration and steam injection, while innovative solutions rely on humid air regeneration and steam reforming of fuel.

In this chapter different techniques for recovering the exhaust heat from gas turbines are discussed, evaluating the influence of the main operating parameters on plant performance.

A unified approach for the analysis of different exhaust heat recovery techniques is proposed. This methodology is based on relationships of general validity, in the context of interest, and on a characteristic plane for exhaust heat recovery, that indicates directly the performance obtainable with different recovery techniques, compared to a baseline nonrecovery plant.

Then an innovative scheme for external heat recovery is presented: this envisages repowering existing combined cycle power plants through injection of steam produced by an additional unit consisting of a gas turbine and a heat recovery steam generator.
