Simulation Study On Flow Pattern Of Upflow Anaerobic Sludge Blanket Reactor

Nowadays, water pollution is very serious problem. Anaerobic biological process of wastewater is a low-cost technology that combined wastewater treatment and energy recovery. Anaerobic reactor is the core carrier of anaerobic biological process. There is over one hundred years of anaerobic reactor being applied. Anaerobic reactor has been developed three generations. All of the upgrade of anaerobic reactor every time is improving sludge concentration, enhancing the contact of wastewater and sludge, optimizing microbial environment, whose essence is improving reactor flow pattern. UASB reactor is a typical symbol of the second generation anaerobic reactors, based on which many third generation anaerobic reactors has been developed. Therefore, it has important theoretical significance and practical value of studying UASB reactor flow pattern.In this thesis, the author simulated the whole UASB reactor, using RNG k-ε model, in the case of liquid single-phase flow, based on which the influence of water distribution methods and hydraulic retention time on UASB reactor flow pattern has been analyzed. As well as, the author simulated the UASB reactor reaction zone, using Euler-Eulerian multiphase flow model, In gas-liquid-solid three-phase flow conditions. By analyzing the velocity field distribution of gas and solid phase volume fraction, the author studied the reaction zone flow pattern at the situation of the three-phase flow. Both of the simulation are used Computational Fluid Dynamics (CFD) commercial software Fluent. Through numerical simulation, this study obtained some useful conclusions:①With water the distribution points growing in number, turbulence intensity and hydraulic dead zone are reduced, the liquid flow tends to plug flow. The influence of hydraulic retention time on UASB reactor flow pattern is very slight, when water distribution is uniform, in the case of liquid single-phase flow.②When the liquid flow upward with a moderate velocity to obtain an appropriate HRT, axial pulsation and disturbances between granules of sludge are small, but compared with the velocity of lower fluid levels, the turbulent motion and velocity distribution are greater.③The simulation indicated that the gas-liquid-solid system exhibits a more heterogeneous structure, with particle clusters forming and dissolving dynamically. The sludge cluster formation, which may involve gas-sludge, sludge-sludge, and sludge-wall interactions, is currently too complex to be well understood. Bubble movement, bursting, and size change are key factors affecting particle circulation and cluster formation in the reactor.Last but not least, the application and limitation of the models mentioned above have been discussed, and suggestions have been stated for further study.