Hydrodynamics of molten-metal bubble columns in the near-bubbling field using volume of fluid computational fluid dynamics

[Display omitted] •CH4 pyrolysis using molten-metal bubble columns (MMBCs) for low-carbon H2 production.•A VOF-CFD model with LES and bubble detection algorithm was developed and validated.•The gas holdup and bubble size were estimated for a CH4-Sn MMBC in near-bubbling field.•The VOF-CFD can provide the initial bubble size distribution near gas distributors. Using molten-metal bubble columns (MMBCs), non-oxidative CH4 pyrolysis producing H2 and solid carbon has emerged as an efficient low-carbon H2 production compared to steam-methane reforming (SMR). Because hydrodynamic parameters such as gas holdup and bubble size have significant impacts on heat and mass transfer, understanding the hydrodynamics of MMBCs is crucial for determining the optimal operating conditions and reactor design. A volume of fluid computational fluid dynamics (VOF-CFD) model coupled with a large eddy simulation (LES) turbulence equation was developed and validated for MMBCs. A novel bubble detection algorithm was also proposed for the CFD simulation. Using the validated CFD model, the hydrodynamics of a CH4-Sn system were investigated in a near-bubbling field at 900 °C and ambient pressure. The gas holdup increased from 1.1 to 1.9 % as the superficial gas velocity rose from 2.6 to 5.2 mm/s. The mean bubble size also increased from 4.7 to 5.4 mm for the gas velocities under the bubbling flow regime. The interfacial surface area between the gas and liquid phases was approximately 8.6 to 15.1 m2/m3 in the bubbling flow regime. The VOF-CFD simulations near the nozzle may thus provide the bubble size generated from the gas distributor according to operational and geometrical modifications.