Monitoring of all the components of large size combined cycle power plants (gas turbine, HRSG, steam turbine, auxiliaries) plays a determinant role in improving plant availability, profitability and maintenance scheduling. 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. This work is concerned with the preliminary outcomes regarding the thermo-economic monitoring of the bottoming cycle (BC) of a combined cycle power plant, using real historical logged data. The software, developed in a Matlab environment, is able to calculate functional exergy flows (y) and their related costs (c), calculated on the basis of the whole plant functional diagram. Once the exergy flows costs has been defined, it is possible to determine non-dimensional parameters also for the characteristic exergonomic indexes (?c, ?c*, ?k*). Through a plant optimization (not described in the paper) the reference conditions of the plant at each operating condition can be determined. Then, Non Dimensional Indexes (NDI) related to each thermoeconomic parameter are defined, in order to depict a “cost degradation”, and thus a significant rise in the production cost of the main products of the Bottoming Cycle (i.e.: steam and power). The methodology developed has been successfully applied to historical logged data (2 years) of an existing large-sized (400 MW) combined cycle power plant, showing the capabilities in estimating the “cost degradation” of the elements of the BC over the life of the plant, and the trends in the thermoeconomic indexes.
