Numerical cost optimization and irreversibility analysis of the triple-pressure reheat steam-air cooled GT commercial combined cycle power plants

Steam-air cooling of the gas turbine (CT) and optimization are important methods for enhancing the efficiency and power of the combined cycle power plants. A steam-air cooled CT uses less air for CT cooling; thus, allows more air to be available for the combustion process and increases output power significantly. In this paper, the commercial triple-pressure reheat steam-air cooled CT combined cycles (The GE Stage 107H and Mitsubishi M501H commercial combined cycles) were presented, optimized relative to its operating parameters, and the irreversibilities of the components were analyzed to identify the magnitude and locations of such irreversibilities and discuss its causes. Constraints were set on many operating parameters such as air pressure ratio, the ratio of the cooling steam flow to the maximum available flow for steam cooling, and stack temperature. The net revenue and cycle efficiency were optimized at 10 different maximum values of turbine inlet temperature (TIT) using two different methods: the direct search and variable metric. The optimized cycles had better performance and lower irreversibilities for the main components than that for the commercial cycles. Optimizing the net revenue could result in an annual saving of about 29.2 million US dollars for a 400 MW power plant. (C) 2012 Published by Elsevier Ltd.