The output and efficiency of combined-cycle plants can be increased during the design phase by selecting the following features:1
Higher steam pressure and temperature
Multiple steam pressure levels
Reheat cycles
Additional factors are considered if there is a need for peak power production. They include gas turbine power augmentation by water or steam injection or a supplementary-fired heat recovery steam generator (HRSG). If peak power demands occur on hot summer days, gas turbine inlet evaporative cooling or chilling should be considered. Fuel heating is another technique that has been used to increase the efficiency of combined-cycle plants.
The ability of combined-cycle plants to generate additional power beyond their base capacity during peak periods has become an important design consideration. During the last decade, premiums were paid for power generated during the summer peak periods. The cost of electricity during the peak periods can be 70 times more expensive than off-peak periods. Since the cost during the peak periods is much higher, most of the plant s profitability could be driven by the amount of power generated during these peak periods. Thus, plants that can generate large quantities of power during the peak periods can achieve the highest profits.
The addition of most power enhancement techniques to a combined-cycle plant will have a negative impact on the base-load performance. Thus, the net revenue of the plant will be affected adversely during nonpeak periods. In general, the economics of the plant are determined by the efficiency...
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