Methodology for the economic evaluation of gas turbine air cooling systems in combined cycle applications

Abstract

During the last decades, gas turbines (GT) have been widely used to produce electricity power. Despite their numerous applications, one of the most important shortcomings affecting GT behaviour is their power output decrease at higher air ambient temperatures. This problem is frequently solved by installing air cooling systems at GT inlet as a proper alternative in order to stabilise GT power output. Although maximising power output has been usually considered as the main objective of the cooling system, economical profits should also be considered, replacing the usual power increase as the main strategy to select the most suitable temperature. Moreover, especially when electricity markets tend to a deregulated scenario and its prices are settled by a pool system. Hence, an accurate methodology needs to be developed to analyse and compare the different alternatives, including the time-dependent variables involved in the technical and economical system behaviour. These variables include: ambient temperature, relative humidity, hourly electricity prices and natural gas tariff. The proposed methodology takes into account the performance simulation at the combined cycle, the air cooling system, ambient conditions, equipment maintenance and investment, and electricity and natural gas prices, in order to obtain cash flows and another relevant economical variables that maximise the profit of the integrated system. In this paper, this method has been applied as an example to a three-level-pressure combined cycle model with different GT inlet air cooling systems in a certain location and economical framework. The proposed method allows a better results interpretation, showing that some cooling systems, appearing as a proper alternative from a historical point of view, are not necessarily the most profitable option. Consequently, the proposed methodology for the economic evaluation of the cooling systems offers more straightforward information that allows the cooling equipment technology to be sized or selected.