Numerical Simulation And Improvement Research Of Upflow Anaerobic Sludge Blanket Reactor

Fluid movement in the UASB (Up-flow Anaerobic Sludge Bed) reactor is a verycomplicated process which is with biochemical reactions.It is difficult to have a clearunderstanding of the internal fluid movements of UASB reactor. This topic is based on theresearches about UASB reactor which is a typical second generation anaerobic reactor, andanalyses the internal flow fields of theconventional UASB reactor and the improved UASBreactor through numerical simulation.This topic has two models. One is the conventionalUASB reactor without mixing propeller, the other is the improved UASB reactor with mixingpropeller. This topic is to solve the problem of the internal uneven mixing wastewater andsludge of UASB reactor by numerical simulation calculation. At the same time, analyzing theadvantages of improved UASB reactor which is with mixing propeller.This topic applies a kind of software called FLUENT of computational fluid dynamics(CFD) to simulate the internal flow field in UASB reactor through three changes of processparameter like the hydraulic retention time, add the impeller as well as the stirring rotationspeed. This research wants to seek the optimal combination ofimpeller rotational speed andhydraulic retention time,thenreduce internal dead zone in the UASB reactor, make the wastewater mixed with sludge fully and reduce the cost of sludge and so on.Numerical simulation results show that: we found that the bottom of the UASB reactorappears the phenomenon of dead zone and the dead zone phenomenon more obvious when theinlet velocity is0.5m/h,0.3m/h and0.2m/h through the results of steady-state numericalsimulation of internal flow field in the conventional UASB reactor under the condition ofdifferent hydraulic retention time (0.5to1.5h, h,1h,2h,3h,4h).And the last one is themost obvious.The dead zone was less When the inlet water speed were0.8m/h. And when thewater velocity was1.6m/h, some sludge particles got lost. Only ensure appropriate hydraulicrising velocity can make the water distribution even within the reactor and can make thereaction zone of sludge particles in the sludge bed evenly distributed at the same time. Theformation of dead zone is more obvious when the hydraulic rising velocity is insufficient andthe sludge particles are not likely to be evenly distributed and completely mixed with wastewater.Then treatment effect of UASB reactor would be reduced. Adding a mixing propeller modified the traditional UASB reactor. This researchanalyzed internal flow field in the reactor through three-dimensional steady-state numericalsimulation of UASB reactor under the nine different mixing speed like50r/min,70r/min,90r/min,110r/min,130r/min,150r/min,170r/min,190r/min and210r/min. The modifiedUASB reactor system is analyzed from the velocity vector diagrams of different positions andthe solid phase volume fraction distribution diagrams.We found that the sludge particledistributeevenly and there was no dead zone in the reactor when the mixing speed is150r/min and the constant hydraulic rising velocity is0.2m/h from the analysis of the results. Atthe same time, the wastewater can be evenly distributed in the reactor and the sludge particlescould contact with waste water well under the same condition.We could also improve theprocessing capacity and volume load of the reactor under this condition.We have a relatively clear understanding of internal flow field in the UASB reactorthrough the numerical simulation and can also have more in-depth analyses of internal flowfield of the reactor.The bad design situation has improved in this way. We can also achieve thegoals of efficiency optimization, new appearance of UASB reactor and the engineeringpractice of the UASB reactor trough this kind of simulation.