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.

Combined Cycle Power Plants (CCPP) are attractive electricity generation systems due to high cycle efficiency and quick response of the system to load change. Heat recovery steam generator (HRSG) is an important part of a CCPP and it is important to predict the HRSG operating conditions in transient and steady state modes. It should be emphasized that the biggest pressure and thermal stresses are imposed on HRSG superheater and evaporator tubes banks during transient periods (cold start up and load change). Due to these effects a software program was developed for analyzing the HRSG transient and steady state operating conditions. The HRSG software included arbitrary number of pressure levels (usually up to three) and any number of elements (superheater, evaporator, economizer, desuperheater and duct burner). In this paper theories and equations (mass/energy balance and heat transfer coefficients) applied for HRSG thermal analysis are described. Also HRSG program software outputs were compared with real data collected from HRSG cold start-up at Tehran CCPP with specified geometry and arrangement of elements. The closeness of two groups of data in this transient and steady state modes was acceptable. The numerical outputs in steady state condition also were found very close to GT MASTER program software outputs.