Numerical Investigation of Shell-Side Flow Behavior and Vapor Distribution in Waste Heat Boilers

Shell-and-tube waste heat boilers (STWHBs) are essential in the recovery of waste heat from high-temperature industrial processes. Kettle-type STWHBs are known to experience failures due to hold-up of steam, a significant concern in the industry. Multiphase computational fluid dynamics (CFD) simulations are used to study the effect of tube layout on the steam hold-up of an industrial-scale STWHB. Different design specifications are simulated including tube layout, heat flux, and pitch to predict steam hold-up performance and analyze thermo-hydrodynamic phenomena within the tube bundle. Simulation results show that, for similar tube bundle shape and size, 45° rotated square tube bundle layouts perform better, with respect to steam hold-up, than the square and triangle layouts for a range of heat flux duties. It is found that steam hold-up increases linearly with increasing heat flux and decreasing tube pitch, for the conditions simulated. The turbulent kinetic energy of the bubbly flow is greatly influenced by increasing phase fraction. Visualizations of the flow of water and steam within and around the tube bundle show that there is a vertical flow deviation for both staggered tube patterns (rotated square and triangle). These results motivate further multiphase CFD-based study of the thermo-hydrodynamics of STWHBs for improved understanding, retrofit, and new designs.