Study On Hydrodynamics And Mass Transfer In An Inner-loop Airlift Reactor

The inner-loop airlift reactor has been used for production of organic acid, fermentation and waste water treatment, etc, due to less energy cost, excellent mixing and liquid circulation. Since the complexity of hydrodynamics and mass transfer in multiphase systems, there are still many remaining problems. It is necessary and important to study the hydrodynamic behavior and mass transfer in such reactors, from the point of application or theoretic research.The relationship between pressure fluctuation signals and flow regime has been investigated. In order to find out the intrinsic relations, origin of pressure fluctuation has been discussed firstly; this thesis has applied wavelet analysis and coherence analysis to obtain two kinds of pressure fluctuation signals: global pressure fluctuation signals and local pressure fluctuation signals. Due to the relationship between flow regime and local pressure fluctuation, it has succeeded in being applied to the varied of energy ratio, chaos characteristic parameter and Hurst exponent to detect flow regime.The effect of phase separator, liquid viscidity, surface tension and solid holdup on average gas holdup has been investigated. It is found that gas holdup in the riser and in the downcomer decreases as phase separator area, liquid viscidity, surface tension or solid holdup is increased. Meanwhile, the effect of phase separator, liquid viscidity, surface tension, solid holdup and axial position on local gas holdup profile has been investigated. It is found that the change of gas holdup along the axial position closed to gas distributor is different from that of other positions; in the zone far from gas distributor, local gas holdup profile becomes steeper as superficial gas velocity, liquid circulation velocity or surface tension is increased; the effect of liquid viscidity on the profile is more complex.A novel theoretical model based on the linear oscillation theory and local isotropic turbulence theory (Kolmogorov-Hinze theory) for bubble breakage has been developed. Meanwhile the modified bubble coalescence model and discretization method of population balance model have been successfully established for estimating bubble size distribution.The effect of phase separator, liquid viscidity, surface tension and solid holdup on liquid circulation velocity has been investigated. Based on multiphase fluid mechanics theory, one dimension of two phase model of liquid circulation velocity has been established, which can be used to estimate the experiment results successfully. It is found that phase separator, liquid viscidity, surface tension and solid holdup have indirect impact on liquid circulation velocity by changing gas holdup in the reactor.The effect of phase separator, liquid viscidity, surface tension and solid holdup on mass transfer has been investigated. The change of phase separator area only change gas-liquid contact area; gas-liquid contact area and gas-liquid mass transfer coefficient both increase as surface tension or liquid viscidity is decreased; the effect of solid holdup is more complex. Based on surface renewal theory and Kolmogoroff's theory of local isotropic turbulence, gas-liquid mass transfer coefficient model has been established and validated by experiment data.