On some perspectives for increasing the efficiency of combined cycle power plants

The paper proposes an analysis of some possibilities to increase the combined cycle plant efficiency to values higher than the 60% without resorting to a new gas turbine technology. Optimization of heat recovery steam generator (HRSG) with the use of parallel sections and of limit subcritical conditions (up to 220 bar) is the key elements to obtain this result. The HRSG optimization is sufficient to obtain combined cycle plant efficiencies of the order of 60% while, joining HRSG optimization with the use of gas turbine reheat (postcombustion) and gas to gas recuperation can lead the efficiency of the whole plant to the limit value of 65%. Results are proposed with reference to a turbine inlet temperature of 1500 K, corresponding to those of usual commercial D–F series gas turbine.