1
Figure 2-4.. $team injection in the gas turbine combustor.
Exhaust
Drain
Figure 2-44. Evaporative cooling and steam injection in a gas turbine.
Table 2-1
Evaluation of Various Techniques to Enhance the Operation of the Simple Cycle Gas Turbine
Based on Gas Turbine Operating at .o.er = 110 MW Inlet Temp = .2 0C Efficiency = .2.92 .eat Rate 109.5 KJ/KW-.R
Types of Increase .ercent .ercent .eat Rate Cost US$ Cost/KW Fuel Savings Increase in Total .rocess in .o.er Increase Increase kJ/kW-hr Millions US$/KW per year US. Sales Revenue Earnings (MW) in .o.er in Efficiency per .ear US. US. (%) (%)
Evaporative 3.69 3.32 0.3910，891 0.5 135.67515，264396，755912，019 cooling Refrigeration 12.77 11.51 2.510，672 2.5 195.74605，0751，379，9011，984，977 inlet cooling lce storage 12.77 11.51 2.510，672 1.5 117.44201，692459，967661，659 cooling
lnter-stage 17.41 15.69 14.199，576 2.5 143.563，743，3082，291，3656，034，672 compressor cooling
Heated and 23.44 21.12 21.239，020 3.7 157.845，597，3883，368，3558，965，744 humidified compressed air injection
Steam injection 10.11 9.11 22.13 8954 1.7 168.195，220，1931，466，7926，686，985
Evaporative 13.97 12.59 24.02 8817 2.1 150.345，770，4442，068，6167，839，060 cooling + Steam injection
Theoretical and Actual Cycle Analysis 107
cost outlay of such a system is among the costliest per .W of the cycles evaluated. The Concept here would be to have a single HRSGsupply enough steam to provide cooling for three turbines. The steam would beused to power a steam turbine， which would then operate a refrigeration compressor or use the steam to provide absorption cooling for the three turbines. The concept was to reduce the turbine inlet temperature by about 30-50 oF (17-27 oC). The refrigeration unit could also be supplanted by the use of an ice storage system whose effect would be the same on the perfor-mance of the turbine except for the fact that it would operate for about eighthours in a day， the other 16 hours would be used to produce the ice used for cooling the air. ln thismanner， the refrigeration system could be much smaller than the system required for refrigeration of the inlet air 24 hours a day.
The cooling of the inter-stage compressor air by injecting water is also another very effective way for getting more power from the gas turbine. The problem in most units is that there is no convenient place to inject the water. The gas turbines would require substantial modification to install such a system. Care would have to be taken that any modification would not affect the integrity of the system. This type of a system is very effective in unitswhere there is a low and high-pressure compressor， providing a very con-venient place to inject the water. This type of compressor are mostly avail-able in aeroderivative units.
The concept of injecting humidified and heated compressed air just after the gas turbine compressor is another very interesting way to increase powerand efficiency. ln this system， compressed air is added to the compressed discharge air. The compressed air is about 5% of the main gas turbine air and this air after it has been compressed using an external compressor is then injected into an air saturation device where steam obtained from the HRSG unit is then injected into the device to saturate the air with water and the saturated air then is further heated in the HRSGbefore it is injected into the compressor discharge of the gas turbine.
The injection of steam in the compressor discharge has been utili.ed over the years and has been found to be very effective. The amount of steam to be injected can vary from 5-15%. The injection of steam created from properly treated water does not affect the life of the hot section of the turbines. This is based on a large number of units where steam injection has been used. Steaminjection， with an evaporative cooling inlet system would be best suited for hot humid areas this application based on the efficiency and cost as shown in Figure 2-45.
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