Study On The Hydrodynamic, Mixing And Mass Transfer Characteristics Of Airlift Loop Reactors

The airlift loop reactor possesses a lot of advantages in terms of simple structure, low power consumption, low shear rates, effective mixing, high mass transfer rate as well as good hydrodynamic characteristics. Therefore, this kind of reactors has been widely employed in the biological treatment processes of the environmental engineering.In order to provide the sound quantitative basis and theoretical tools for the best design and scale up of the biological airlift reactors, combining with the specific condition in the biological treatment processes, this work conducts experimental study and theoretical analysis on the hydrodynamic, mixing and mass transfer characteristics of the air-CMC non-Newtonian fluid two-phase system and air-water-activated carbon particles three-phase system in a 0.026m3 internal-loop airlift reactor.The gas holdups in the riser and downcomer, liquid circulation velocity, circulation time, mixing time and volumetric mass transfer coefficient are measured through the online gathering and recording system by using classical manometric method, conductance tracer response technique and dynamic gassing-in method, respectively. The effect of parameters such as the liquid-phase properties, solids loading and the superficial gas velocity is studied. It is shown that for the air-CMC solution two-phase system, the gas holdups in the riser and downcomer, liquid circulation velocity and volumetric mass transfer coefficient generally decrease with the increasing of CMC solution apparent viscosity. On the contrary, the circulation and mixing time increase with the increasing of CMC solution apparent viscosity; For the air-water-activated carbon particles three-phase system, the increase of solids loading leads to the decrease of the gas holdups in the riser and downcomer, liquid circulation velocity and volumetric mass transfer coefficient, but the increase of circulation time. Because the progressive introduction of solids exerts a complicated influence on the radial gas holdup and liquid velocity profile, the mixing time changes randomly with the increase of solids loading; For the two systems, the gas holdups in the riser and downcomer, liquid circulation velocity and volumetric mass transfer coefficient increase, but the circulation time and mixing time decrease with the increasing of the gas superficial velocity.Based on the experimental results, the quantitative correlations for these parameters with operation condition, liquid-phase property and solids loading are presented by using Fr number, Ga number and dimensionless solid concentration Cs, respectively.In addition, based on the analysis for the experiment result, combining with the energy balance and drift flow model, the relative mathematical models are developed separately to estimate liquid circulation velocity in the riser for air-CMC solution two-phase system and air-water-activate particle three-phase system. The values predicted by the mathematical models agree with that of experiment well.