CFD Simulation Of Multiphase Fluid Flow In Internal Circulation Anaerobic Reactor

As one of the most efficient anaerobic reactors, the Internal CirculationAnaerobic Reactor (IC reactor) was attractive to the treatment of wastewater fromvarious proceses, including sewage, alcohol production, etc. The researches on ICreactor mainly focused on the performance of reactor startup, operating characteristics,the removal of organic matter as well as processing efficiency. However, the fluiddynamics on such kind of reactors is rarely reported.In the present work, the Computational Fluid Dynamics (CFD) method was usedto simulate the dynamic flow of gas-liquid two-phase and gas-liquid-solid three-phasein the IC reactor.The formation of the internal circulation is the key point of the operarion of ICreactor, and the superficial gas velocity plays an important role in the formation ofinternal circulation. The calculated results showed that the internal circulationcouldn’t be formed when uGwas lower than0.003m/s and the reactor couldn’toperate normally when uGwas higher than0.02m/s; when uGwas0.007m/s, theinternal circulation formed fastest and the reator performed best.The ratio of height anddiameter (H/D) is important in the design andoptimazation of IC reactor. A series of three-dimensional models with H/D as4,6and8were studied under the condition of the same reactor volum and the same flowrate.The obtained results showed that the reactors of H/D=6showed betterperpormance: the time needed for liquid circulation and steady state was less; thevalue of rising liquid matched with the value of circulated liquid.Solid granular sludge is a key factor of IC reactor. In this paper, the influence ofthe solid was investigated. The simulation results demonstrated that the three-phaseseparator used in the two-phase model could be used in the three-phase process, theliquid and solid circulated successfully in the backflow pipe; the introduce of solidmade the volume fraction decreased by18%and8%respectively in the1stand2ndraising pipes, which weakened the raising capacity of the raising pipe. With theaddition of the solid, the axial velocity in the backflow pipe and the1stand2ndraisingpipes decreased by35%,13%and60%which reduced the circulation.In the present work, the CFD was used to investigate the unsteady liquid-gas two phase and gas-liquid-solid three phase flow in the IC Reactor, which aims at offeringsome theoretical guidance for the further study.