The turbine inlet gas temperature ( Toso ) is an important parameter in design and performance analysis of gas turbine cycles. By increasing Toso, air bleeding for blade cooling increases and it can be about 25 percent of compressor inlet air mass flow rate for Toso equal to 1600 K. Therefore air bleeding has an important impact on thermal efficiency, specific power output and the optimum compressor pressure ratio at which maximum efficiency occurs. For the gas turbine part of a combined cycle, these performance curves are obtained and shown using a developed simulation program (GTE). Also for heat recovery steam generator (HRSG) part of a combined cycle plant, HRSG simulates the transient and steady state temperature distribution of hot gases, steam and tube metal at different parts of HRSG. Any number of pressure levels (high, intermediate and low) and heating elements (superheater, evaporator and economizer) including desuperheater and deaerator can be included. GTE outputs show less than two percent difference from reported measured values. This difference was less than six percent for HRSG model.

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Heat Recovery Steam Generators (HRSGs) are major Componets in Combined Cycle Power Plants (CCPPs) which are particulary subject to severe thermal and flow stresses specially during cold start-up period. Hence it is important to predict the operational parameters of HRSGs such as temperature of steam, water steam, water, tube metal and flue gas at various parts sections during the transient operation as well as steady sate conditions. In this paper, the transient model proposed by Pasha and Jolly et al. [2,3] has been selected and developed as a program (HRSG) to predict the operational conditions of the whole HRSG elements during transient and steady state operations. The program is able to analyze arbitrary number of pressure levels and any number of elements such as superheater, evaporator, economizer, deaerator and desuperheater. To assess the correct performance of the developed model and program, and to predict the capability of the method in predicting variations of temperature with time at various elements, three groups of data verifications were performed. First, the numerical outputs were checked against the same outputs reported by Jolly et al. [3]. Second, the theoretical results were checked with experimental data obtained for HRSG at Tehran CCPP during cold start run. The variations with time of gas, metal, water and steam temperatures at various sections of HRSG were among the studied parameters. Third, the model outputs were checked against the data reported for the HRSG performance test at Neyshaboor CCPP, at base and part loads. In all above cases the theoretical and measured or reported values were compared and satisfactory closeness was found.