Petróleo Brasileiro SA (Petrobras) has used computational fluid dynamics (CFD), an analytical simulation tool for studying fluid mechanics, to determine possible causes of and solutions to flow-induced vibrations (FIVs) in a waste heat-recovery steam generator (WHRSG) of the residue fluid catalytic cracking (RFCC) unit at its 53,000-b/d Capuava refinery (Recap) in Mauá, São Paulo, Brazil.
Petrobras used CFD modeling to simulate hot gas flow through the WHRSG's duct and boiler, designing a detailed three-dimensional geometry representing the real system with a roughly 15.5-million node mesh. To reproduce the most important structures of real turbulent flow, Petrobras adopted a Large Eddy Simulation (LES) of the WHRSG at its 100% and 80% rated capacities with a limit for the end of vibrations.
Results of CFD-based simulations and analyses led Petrobras to change duct geometry to smooth inlet flow into the boiler, minimizing pressure oscillations in the boiler's internal flow as a means of reducing FIVs.
This case study examines the benefit of using CFD numerical tools to analyze engineering problems in a refinery unit where obtaining measured data is not always feasible. The findings highlight the need to account for entrance effects in the design of WHRSGs, and heat exchangers in general, to prevent FIVs.