Abstract
Hydrodynamics of two external loop circulating bubble columns with open channel gas separators were investigated experimentally. The hydrodynamics were studied under the effects of three operating parameters and one design parameter. The operating parameters were superficial gas velocity in the riser, UGR, gas-liquid dispersion property, σ, and efficiency of gas separation, TVR. The design parameter was the scale-up factor of the riser to downcomer cross-sectional area AD/AR. The gas-liquid dispersion property was varied by using various concentrations of additives like antifoam, alcohol and wettable suspended solids. All experiments were conducted using compressed air and tap water from the university main supply system. Time-dependent hydrodynamics variation related to air-water quality was minimized by using consistent air-water samples in order to satisfy experimental reproducibility. The results show that for any gas-liquid-additive system, there is an optimum volume of the liquid in the gas separator, TVRO, that gives the minimum gas recirculation in the downcomer, εGD. At any AD/AR and TVR, the effects of antifoam and suspended solids were found to reduce the gas holdup, while the alcohols were found to increase gas holdup. At TVRO, the efficiency of the gas separator was improved significantly by increasing the scale-up factor, AD/AR. Liquid circulation was increased in the antifoam system, but reduced in the presence of wettable suspended solids. The results of this study indicate that the design and operating conditions were better at scale-up factor AD/AR=0.55 and volume ratio TVR>20%, than that at AD/AR=0.25 for all the additives investigated.