Residence time distribution in an internal loop airlift reactor: CFD simulation versus digital image processing measurement

Residence time distribution (RTD) curve as the global flow characteristic in a rectangular internal loop airlift reactor (ALR) was obtained using Computational Fluid Dynamics (CFD) technique. CFD analysis of the laboratory ALR with a working volume of 2400 cm3 has been conducted under unsteady state conditions at low superficial gas velocities. Simulations were performed with water and air as the liquid and gas phase, respectively. To determine RTD, a pulse injection of a colored tracer was considered at top of downcomer and its concentration was obtained theoretically at different cross-sections of the reactor. The numerical Eulerian-Eulerian laminar two-fluid model was applied in transient 3D modeling of the fluids. RTD predictions using CFD simulation were compared with the experimental results obtained using Digital Image Processing (DIP) technique. For superficial gas velocities ranging from 0.01 to 0.03 m/s, there was a good agreement between the predictions and the experimental values. Results of this study indicate the potential of CFD simulation in describing the fluid hydrodynamics of rectangular ALRs with internal circulation loop.