Abstract
The effects of draft tube structure on the performance of pilot-scale Internal Loop Airlift Reactors (IL-ALRs) were investigated by Computational Fluid Dynamic (CFD) simulations and experiments. The Euler-Euler two fluid model and the κ-e turbulence model were adopted in the CFD model to predict the influence of draft-tube structure on the key flow parameters including gas holdup, gas distribution and liquid circulation velocity. A good agreement was obtained between the CFD predictions and experimental measurements. In present study, perforation was applied to the expanding section of the draft tube, and numerical results show the optimized structure can enhance the gas-liquid separation, promote the oriented liquid circulation, increase the superficial gas velocity and maximize the productivity. Further optimization was conducted on the perforated design based on the CFD simulation.
Highlights
Airlift Reactor (ALR) has been widely applied in the chemical and petrochemical industries, biochemical fermentation, as well as wastewater treatment
The airlift reactors are classified into two categories: External Loop Airlift Reactors (EL-ALRs) and Internal Loop Airlift Reactors (IL-ALRs)
A typical internal loop airlift reactor mainly consists of four sections named as riser, draft tube, top and bottom section
Summary
Airlift Reactor (ALR) has been widely applied in the chemical and petrochemical industries (such as FT process, methanol synthesis), biochemical fermentation (microalgae cultivate), as well as wastewater treatment It has a relative simple mechanical structure without internal or moving parts, which is easy to scale up, low shear stress, excellent heat and mass transfer efficiency, and good mixing characteristics with low energy consumption. Liquid circulation velocity, bubble size, bubble distribution and mass/heat transfer coefficient are the key hydrodynamic parameters for ALRs, a good understanding of the influence of operating conditions (superficial gas velocity, pressure etc.), reactor geometry, structures of gas sparger and internals on these parameters is essential for the design and scale-up of ALRs. Extensive studies on the hydrodynamics in the airlift reactors have been reported in the last decades [6,7,8,9] and most of the work has been focused on the design of reactor structure and gas sparger [10,11,12,13]. A cold model facility was built up to exam the performance of various draft tubes, in the meantime, CFD simulations were performed to validate the experimental observations, as well as the design of the sectional perforated draft tube was further optimized
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