Combined Cycles Power Plants
Gas Turbine Cooling
The increasing of the hot gas temperature on the inlet of the gas turbine increases the
efficiency of the gas turbine and thus of the CCPP. The problem of the gas turbine is
the cooling of combustion chamber and particularly in the high temperature of the turbine
blades. In order to bear the usual temperatures of 1000 to 1200°C, apart from the use of
developed materials the turbine components are cooled additionally from the inside, by
compressed and cooled cooling air.
Open Loop Air Cooling
For this open cooling a part of the compressed air is removed from the compressor and used
for the cooling of combustion chamber and turbine blades. In the case of a gas turbine with
sequential firing the compressed air is removed on different pressure levels from the
compressor. The extracted cooling air must be cooled down, before it used as cooling air
in the turbine.
After cooling of turbine components the cooling air is mixed in the turbine with the main
Several concepts are available for matching the cooling requirements to the CCPP.
Open cooling concepts can be used for cooling the compressed cooling air:
- Water injection (quench cooler)
- Steam injection
- Water-Steam cooling in heat exchangers
For avoiding the loss of demineralised make-up water and the loss of evaporating heat
energy in the exhaust gas, the use of water-steam-cycle for the air cooling in CCPP is
the most economical solution (Fig. 060C).
GT-Air Cooler (Air/Water-Steam Heat Exchanger):
The air/water-steam cooler (30) works as a steam generator. The cooling water (32) is
supplied from the feed water of the steam turbine cycle. In the gas turbine cooler the
water is evaporated, superheated and return to the HP superheater (21).
The air/water-steam cooler has limitations of operation range. For a given bundle geometry
the limitations depends on ambient temperature and inlet temperature/pressure of cooling
For more information on Air/Water-Steam GT-Cooler (30) see:
"AIR COOLER FOR POWER STATION PLANT AND USE OF SUCH AN AIR COOLER"
Inventor: YOUSSEF MUSTAFA (CH)
Applicant: ALSTOM TECHNOLOGY LTD (CH)
Patent WO 2004/072544 A1: GT Air Cooler
Closed-loop steam cooling
This steam cooling system permits the higher firing temperatures required for
increased efficiency. Gas turbine cooling steam is supplied from the steam turbine cycle.
The steam cools the gas turbine and return to the steam cycle. The closed loop steam cooling
is in the development.
GE Power Systems developed the closed loop steam cooling (H System). The GE's H System
permits the higher firing temperatures and designed with the capability to achieve
60% thermal efficiency.
The gas turbine cooling system is integrated with the steam cycle. The supply of cooling
steam is from HP steam turbine exhaust. The steam is delivered to the gas turbine stationary
parts through casing connections and to the rotor through a conventional gland connection.
The cooling steam is returned to the steam cycle at the reheat line.
If the gas turbine steam cooling (H System) of GE Power Systems and the gas turbine vacuum
expansion of TPT used in a combined cycle plant, then a net thermal efficiency of over 62%