Page 128 - Advanced Gas Turbine Cycles

Advanced gas turbine cycles

HRSG

EXHAUST

Fig. 6.13. Advanced steam topping (FAST) plant.

6.4.2.1. The RWI cycle
Frutschi and Plancherel [ 11 not only described the basic EGT cycle, but also a modified
version with an intercooler added. Macchi et al. [9] called this intercooled EGT the RWI
plant and the simplest version is shown in the top part of Fig. 6.14. Macchi et al. also
considered more complex versions (some with evaporative intercooling and aftercooling),
the performance of which are discussed in Section 6.6.

6.4.2.2. The HAT cycle
A further major innovation is the humidified air turbine (HAT) cycle, which involves
introduction of a humidifier before the combustion chamber, rather than the mixer origin-
ally proposed by Frutschi and Plancherel. The resulting HAT cycle is shown diagramma-
tically, as a modification of the simply intercooled RWT cycle, in the lower part of Fig. 6.14.
There is now a smaller exergy loss in the evaporation process, both from increasing the
water temperature at entry to the humidifier (by using cooling water passing through the
intercoolers between LP and HP compressors and an aftercooler), and from reduction of
the temperature difference between the water and air within the humidifier itself.

6.4.2.3. The REVAP cycle
De Ruyck et al. [IO] proposed another variation of the EGT cycle, in an attempt to
reduce the exergy losses involved in water injection (the REVAP cycle). Rather than
introducing the complication of a saturator, De Ruyck proposed several stages of water
heating (in an economiser, an intercooler and an aftercooler). The efficiency claimed for
this cycle is only a little less than the HAT cycle.