Experimental And Numerical Studies On Hydrodynamics Of The Jet Loop Reactor

Internal loop reactor is widely utilized on biologic fermentation,wastewater treatment and hydrogenation of heavy oil,etc.Internal loop reactor with uniform gas distributor is commonly used industrially,which only provides a limited liquid circulation velocity due to homogeneous bubble distribution.Gas jetting is an efficient method to generate distinct bubble size distribution and enhance the turbulence and mass transfer.Combining internal loop reactor and jetting would be an ideal reactor configuration,called jet loop reactor,which could improve liquid circulation significantly.Extensive research on the integral loop reactor with uniform gas distributor has been reported.However,the study on the experimental and numerical simulation of the jet loop reactor is very rare.With high speed jetting,wide bubble size distribution and macroscopic liquid circulation,hydrodynamics of jet loop reactor is complicated and dimness.In this paper,experimental research was carried out in a column of(?)200 × 2500mm which contains a draft tube of 0100 X 1400mm,jet nozzle and a conic bottom.Fluid dynamics of jet loop reactor is systematic studied by measuring distribution of gas holdup and liquid velocity.And relative CFD models were proposed.The experimental data indicated that large bubbles were generated by gas jetting,and then broken into small bubbles during its rising,which leaded to an ascending profile of gas holdup along axial position in riser.It proved that sparger zone of jetting was remarkable extended and the fully development zone was never existed throughout the whole reactor.As to the downcomer,the same tendency was emerged due to the different following characteristics between small bubbles and large bubbles.And liquid circulation was significantly enhanced by jetting,which was very positive for liquid mixing and solid suspension.According to the experiment,a modified drag model was determined and large eddy simulation was proved to be superior to realizable k-ε model.This CFD model result in a good agreement on predicting macroscopic variable.However,due to the defection of constant bubble diameter model an unsatisfied numerical result on local hydrodynamics was obtained,expect for gas holdup and liquid velocity profiles in downcomer.The simulant accuracy for riser was so poor that the model failed to exhibit the extension of spared zone caused by jetting.More kinetic energy and turbulence was input by liquid feeding,which generated more small bubbles and increased the gas holdup.In order to adapt the inhomogeneous distribution of bubbles in the jet loop reactor,a CFD-PBM coupled model was utilized.In riser,the model succeeded in simulating the ascending distribution of gas holdup and the breakup process of large bubble during its rising,which indicated that the hydrodynamic characteristic of extension of the sparger zone was depicted accurately.The agreement of gas holdup profile in downcomer was also acceptable.Meanwhile,the numerical model demonstrated that jetting could accelerate liquid circulation flow much more than uniform gas distributor could.By comparing the vector of liquid phase and contours of bubble size distributions,the bubble breakup frequency was higher in the area where the direction of liquid velocity changed violently.Experimental and CFD study proved that jet loop reactor was an ideal reactor configuration providing a good performance on solid suspension,liquid mixing and mass transfer.