Development of a lumped paramter model for the CFD simulation of the superheating section of a HRSG

In the last few years, the European electricity market has witnessed a fast spread of renewable energy sources. For this reason, thermoelectric units need to switch from base-load to cycling operation: a mode characterized by fast load ramps, short start-up and shutdown time that permits to enhance the power plant's competitiveness. This new kind of operation strategy guarantees high pro ts in the short term, but determines a signi cant lifetime reduction of the most critical power plant devices, which are those subjected to thermo-mechanical fatigue. The objective of this thesis is to develop, in partnership with Nooter Eriksen, a HRSG (heat recovery steam generator) designer, a methodology to aid the pre- liminary design of the boiler. In particular, the focus was set on the study of the thermal conditions of super- heating collectors, which is of paramount importance to determine the residual life of the power plant. In order to perform a CFD analysis of the boiler capable of estimating the ther- mal conditions within the shell containing the collectors, porous media approach was applied to model separately the heat transfer and momentum loss terms occurring in the tube banks of the HRSG in a computationally reasonable way. For this purpose, a Python code was developed to implement the solution of the convection-conduction problem for an in nite cylinder, representing the average conditions of the tube bank. The code was extended for the evaluation of the internal convection coe cient too. In order to evaluate external convection coe cient and heat ow rates, an it- erative process was set and Excel spreadsheets were exploited to exchange the information with Python and consequently store the results. At the end, for validation purposes, a CFD analysis simulating the full load of the gas turbine was performed. The outcomes were consistent with the temperature and pressure data supplied by Nooter Eriksen.