Gas holdup and mixing characteristics of a novel forced circulation loop reactor

Gas holdup and mixing time were characterized in a forced circulation internal loop draft-tube reactor (unaerated aspect ratio ≈ 6, downcomer-to-riser cross-sectional area ratio = 0.493) as functions of the forced liquid superficial velocity in the riser (ULr) and the gas superficial velocity in the riser (UGr). Data were obtained in air–water system. The operation ranges were 0 ≤ ULr ≤ 0.051 m/s and 7.8 × 10−3 ≤ UGr ≤ 3.9 × 10−2 m/s for the liquid and gas velocities, respectively. Under forced flow conditions the reactor always operated in the bubble flow regimen, but operation as an airlift reactor (i.e. no forced flow of liquid) produced a heterogeneous churn-turbulent flow regimen. Forced flow of liquid enhanced gas holdup in comparison with the airlift mode of operation. Mixing time generally declined with increased flow rates of gas and liquid. The ability to maintain a bubble flow regimen through forced flow of liquid allowed the reactor to attain gas holdup values of >0.12 that are difficult to achieve in air–water in conventional bubble columns and airlift reactors.