Monitoring of all components of large size combined cycle power plants (gas turbine, HRSG, steam turbine, auxiliaries) plays a determinant role in improving plant availability, profitability and scheduling of maintenance. This paper presents a research project carried out by TPG (Thermochemical Power Group) of University of Genoa in collaboration with Ansaldo Energia S.p.A. to improve existing monitoring and diagnostics procedures and to develop innovative software tools for software-aided maintenance and customer support: the first part of activities is concerned with the monitoring of a three pressure level HRSG (Heat Recovery Steam Generator), which is presented in this paper.A procedure for estimating HRSG performance in large size combined cycle power plant is presented. The work consists in the development of an original Matlab code which calculates heat exchangers performance, at different power plant operating conditions. The Matlab code uses some parameters (areas of heat exchangers, heat transfer coefficient, heat loss, pressure drop) coming from a detailed on-design model necessary only for setting some parameters for the calculation. The original Matlab code was developed with a twofold objective: to calculate the actual gas path inside the HRSG starting from the available measurements, thus obtaining the current effectiveness of all the heat exchangers in the HRSG; to estimate the expected performance of each heat exchanger to be compared with the actual ones. Once the actual efficiency and the expected efficiency of the heat exchanger are defined, non-dimensional performance parameters suitable for degradation assessment can be defined. Such parameters will be used to monitor plant degradation, to support plant maintenance, and to assist on-line troubleshooting. As a result of the sensitivity analysis, each performance parameter is coupled with an accuracy factor. The accuracy of each performance parameter is estimated through the sensitivity analysis, which allows to determine the best parameters to be monitored and to define the related tolerance due to measurement errors. The methodology developed has been successfully applied to historical logged data (2 years) of a large size (400 MW) combined cycle in Italy, showing the good capabilities in estimating the degradation of the HRSG along plant life.
