Comparison of Two Different Approaches for Thermal Performance Evaluation of a Heat Recovery Steam Generator

At one of the ACWA Power CCPP sites, heat recovery steam generator (HRSG) flow diverter baffles were found missing. Detailed engineering drawings were reviewed, and it was observed that the baffles were never installed during the construction phase. HRSG flow diverter baffles were installed between the tube modules as well as at the casing sides. Baffles were also added at the top and bottom of the modules, as flue-gas could bypass heat transfer surfaces by flowing into upper and lower dead spaces. Pre and Post modification performance of the HRSG was evaluated based on two different approaches. In the first approach, HRSG efficiency was compared for pre and post baffles installation. Operating data for similar reference conditions, i.e., similar Gas Turbine load, ambient conditions and operating configuration were compared. It was found that the HRSG efficiency varied with ambient conditions and GT load conditions. A second approach was to evaluate the Steam Turbine power output to Gas turbine power output (ST-GT) ratio shift for similar GT loads and ambient conditions. Improvement in ST to GT ratio was also analyzed for pre and post modification and later translated into heat rate impact. Both approaches for thermal performance evaluation resulted in similar heat rate improvement for baffle installation.