Effect Of Bubble Models On Simulation Results And Hydrodynamics In A Loop Reactor

The world crude oil is becoming heavier and poorer in quality and the demand of clean fuels is becoming larger.The hydrocracking process is an important process to convert the heavy oil to light fraction,so it plays an important role in oil processing industry in china.The Air-lift Loop Reactor(ALR)is a kind of multiple-phases reactor which is developed based on the conventional bubble column.It is widely used in the gas-liquid or gas-liquid-solid reaction system of bio-engineering,chemical engineering,wastewater treatment and metallurgical industry etc.due to its good gas-liquid mass transfer characteristics,high liquid circulation velocity,and uniform distribution of gas holdup.The bubble diameter and its distribution are important parameters affecting the performance of reactor,which are mainly related to the bubbles’ breakage and coalescence.So far,most studies have been calculated based on a uniform bubble diameter.How to obtain the bubble diameters and its distribution in reactor and study the effect of bubble characteries on the reactor are still a problem.Therefore,it is necessary to build different bubble models to further study the airlift loop reactor.The main work can be summarized as follow:(1)The Euler-Euler two-fluid model was applied in the gas-liquid flow numerical model building to study hydrodynamics in the airlift loop reactors.The model was built to study the gas holdup and liquid circulation velocity with different gas superficial velocities(range from 0.01 to 0.075 m/s)in riser,and the simulation results were tested and verified by comparing with the datas from experiments.Then different outlet boundary conditions(pressure-outlet and degassing outlet)and drag models(Schiller-Naumann,Grace and Tomiyama)were used to study their influence on the hydrodynamics in an air-lift loop reactor.The results of gas holdup and liquid velocity calculated by using the different conditions and models were compared and analyzed.,and the choice of drag models also has important effects on simulation results.Tomiyama drag model coupling with degassing boundary conditions can be better on simulating the flow of gas-liquid two-phase in the reactor,and be in better agreement with the existing results reported in the literature.(2)The large-small bubble model and the population balance bubble model(PBM)were built,and the results calculated by these two bubble models were compared with the single bubble model.The distribution and chang law of the gas holdup of large bubbles,gas holdup of small bubbles,liquid velocity and bubble sizes were studied in the homogeneous and heterogeneous flow regimes,and analyzed the effect of bubble sizes on hydrodynamic behaviors.The better bubble model was selected by comparing the results,and build new reactor models and verify the conclusions about the effect of bubble model.The results indicated that the large-small bubble model and the PBM model also could describe bubbles distribution in reactor better,especially reflected in the differences of simulation results for downcomer.(3)We respectively investigated overall gas holdup,partial gas holdup and liquid velocity in reactor with different static liquid height,draft tube diameter,area of inlet.And then,according to the general principles of reactor amplification,the reactor was proportionally enlarged 1.5 times and 2 times,and analyzed the differences between the enlarged reactors and original reactor.