Oxygen transfer in airlift reactors equipped with a high performance sparger

Airlift reactors have been used extensively in industry mainly for the production of several compounds of biological origin (i.e. organic acids, glycols, salts amines, alcohols, antifoams, alkaloids, antibiotics, proteins etc.), treatment of oil contaminated soils, cleaning effluents from fish processing plants, aeration of waste water, production of vinegar, production of bakers yeast etc. Due to their ability to provide excellent mixing and liquid circulation, they have also been used in waste water treatment, ozonation, precipitation of silica, mineral leaching, production of chemicals etc. Unfortunately, the rational design of spargers or bubble generators is restricted by the limited understanding of the factors governing the evolution of bubble size and specific interfacial area particularly in the case of industrial systems where the presence of multi components strongly affects bubble breakage, coalescence and their equilibrium. These crucial issues are believed to control the final values of the bubble size and the specific interfacial area encountered in ALR.; The novel dynamic sparger developed at the multiphase mixing and separation lab was used to disperse the air being introduced to the ALR because of its ability to take advantage of the interfacial characteristics of industrial gas-liquid systems and generate large interfacial area of contact. This was driven by the knowledge that the performance characteristics of airlift reactors are strongly affected by the size of bubbles generated by the sparger and by the interfacial characteristics of the media (particularly the presence of surface active agents). The ability of the sparger to generate small bubbles increases the interfacial area of contact and enhances the hydrodynamic conditions and volumetric oxygen transfer rate whereas the presence of surface active components in the broth retards the coalescence of the fine bubbles thus formed.; The effect of these two parameters on the hydrodynamic conditions and oxygen transfer rate was investigated using a 200 L pilot scale internal loop airlift reactor equipped with a dynamic sparger capable of generating interfacial area as large as 3,500 m2/m3 at superficial velocities of 0.03 m/s. Gas holdup was characterized by using pressure difference method, while the liquid circulation velocity and mixing time were obtained by tracer injection technique. The oxygen transfer rate was determined using the dynamic oxygenation technique. Labview 7.1 software was used to control experiments, data acquisition and to analyze results. The results obtained show that gas holdup values as high as 14%, along with liquid circulation velocity of 1.3 m/s and mixing time of 18 s could be achieved. Oxygen transfer rates obtained using this novel sparger can be more than double those obtained using conventional designs. The amount of oxygen transferred per unit energy dissipated in ALR was observed to be as high as 3.6 kgO2/kWh, whereas alpha factor was obtained upto 2.6.; The advantage of the dynamic sparger becomes more pronounced in the presence of surfactants which are known to adversely affect oxygen transfer in airlift reactors when conventional spargers are used.