Study On Residence Time Distribution And Numerical Simulation Of Gas-liquid Two-phase Flow In Continuous-flow Integrated Biological Reactor

Continued-flow Integrated Biological Reactor (CIBR) is a new efficient andintegrated reactor for the removal of nitrogen and phosphorus, especially for low C/N ratiowastewater. But in the actual operation, there is some dead-zone in the reaction zone andthe separation efficiency of gas-liquid-solid in the three-phase separator is low, these allaffect the reaction efficiency of the reactor. In this paper, the flow patterns of CIBR werestudied by computational fluid dynamics, which can provide guides of the reactor design,optimizing the reactor operation and improving reaction efficiency.Firstly, the flow patterns of the CIBR reactor in aeration and agitation status werestudied by tracer experiments. The Pe values of aeration and agitation zone in the reactorwas2.21and2.35, both of them are between0to∞, which indicates that flow patterns ofaeration and agitation zone are both between the status of completely mixing and plugflow. When in the aeration status, the retention time of the effluent in precipitation zone is85min. While in the agitation status, the tracer can be detected in the precipitation zonewhen the time is zero. What’s more, the concentrations of tracer are equal in the entranceand export of precipitation zone. All of these verify that in the aeration status the flowpattern of precipitation zone is plug flow and in the agitation status the flow pattern ofprecipitation zone is completely mixing.Then, the gas-liquid two-phase flow model in the aeration status was established withEuler multiphase flow model and the dispersed turbulence model of standard k-modelby CFD commercial software. The simulation results indicate that the changing rules ofvelocity field, gas distribution, pressure field and turbulence intensity in the reactor. Andthe tracing simulation of the reactor in aeration status was studied by discrete phase modelbased on gas-liquid two-phase flow pattern simulation. The maximum deviation betweensimulation results and tracer experiment results is22%, which verify the reliability ofnumerical simulation.Finally, the influences of three-phase separation structure to the flow patterns werestudied by tracer experiments and numerical simulation. when the diameter of lowdeflector hole increase from2cm to8cm, the area utilization in the reaction zone increases from81.8%to84.7%in aeration status, it increases from77.5%to82.7%in agitationstatus. At the same time, the turbulent kinetic energy of three-phase separation zone backflow is remarkably increased. Thus, the larger the diameter of low deflector hole, thebetter the performance of the three-phase separation, which will promote the treatmenteffect of the reactor. What’s more, when the folding angle is35°, the liquid velocity,volatility and gas holdup in the three-phase separation and precipitation zone are all higherthan folding angle is45°or50°, which will do harm to the gas-liquid separation in thethree-phase separation zone and the precipitation of particles in the precipitation zone. Asa result, the best folding angle of three-phase separator is45°to50°.