Gas Phase backmixing in bubble column with internals Mohamed Hamed, Muthanna Al- Dahhan

1. Gas Phase backmixing in bubble column with internals Mohamed Hamed, Muthanna Al-Dahhan • Gas phase backmixing is one of the important hydrodynamic parameters that should be considered in scale up of bubble columns. • The dispersion coefficient is a complex function of the superficial gas velocity, liquid phase properties, and reactor geometry. • The problem is complicated by the need to provide internal reactor structures to improve heat removal. The effect of the configuration and volume percentage of these internals is poorly understood. Problem definition Experimental setup Measuring technique • Column: 18’’ (45.7 cm) • Height:148” (3.75 m) • Pressure: Atmospheric • Distributor: 241 holes (D = 3 mm) in a square pitch of 2.4cm • Variables: • Gas velocity (Ug) = 0.05 m/s up to 0.45m/s • Internals: 5%, 22% occluded area and without internals. • Gas tracer technique • Developed by Lu Han (2007). • The developed gas tracer technique gives the actual RTD of the bubble column reactor and removes the extra dispersion caused by sampling/analytical system and distributor plenum. Previous studies • Wachi et al. (90): Gas phase dispersion in bubble columns. • Shetty et al. (92): Gas phase back-mixing in bubble column reactors. • Kantak et al. (95): Effect of gas and liquid properties on gas phase dispersion in bubble columns. • Mills et al. (96): The Fischer-Tropsch synthesis in slurry bubble column reactors: analysis of reactor performance using the axial dispersion model. • Han (2007): Hydrodynamics, backmixing and mass transfer in a slurry bubble column reactor for Fischer-Tropsch alternative fuels. Future work • Investigate the effect of internals on the gas liquid mass transfer coefficient. • Develop a model for bubble column with internals. Internals design Objectives Acknowledgement • Investigate the effect of the internals on gas phase backmixing. • Study the effect of different internals’ configurations on the degree of gas phase backmixing. 5% occluded area (typical of liquid phase MeOH synthesis) Circular pitch: 2 concentric bundles of 17 and 27 cm diameter. 16 rods 25% occluded area (typical of Fischer-Tropsch synthesis) Triangular pitch = 1.75” 79 rods GTL.F1 SBCR-CAE Chemical Reaction Engineering Laboratory