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Study on Performance Improvement of Bioreactor by Using Waved Baffles

Author: WangLinLin
Tutor: YouXueYi
School: Tianjin University
Course: Environmental Science
Keywords: bioreactor waved baffles flow field performance light-gradient mixing performance evaluation
CLC: X173
Type: Master's thesis
Year: 2012
Downloads: 1
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Abstract


The new-type guide plate together with the good structure parameters is not onlyhelpful to improve bioreactor performance simply and rapidly, but also to optimizethe existing bioreactor structure at a low cost.In this study, the research model based on the flat-phobioreactor with wavedbaffles of Li yuzhe was established by using Euler-Euler two-phase model. After thereliability of the model was validated with the experimental results of Li yuzhe et al.,the simulation analysis of gas distribution, liquid flow and mixing, gas-liquid masstransfer process and the light-gradient mixing in this bioreactor was carried out. Thecontents of the study are as follows:A systematic analysis of the effect of the waved baffles structure on gasdistribution, liquid flow, mass transfer and mixing performance was made. The resultsshowed that the increase of the ratio of waved baffle height to wave length （L/λ） willlead to a little increase of the gas holdup, but the increase of which mainly appearedunder the waved crest. The changes of the ratio of wave amplitude to wave length（A/λ） as well as L/λ can regulate the liquid velocity effectively. When L/λ is12, thegood performance of mass transfer and mixing process were obtained. Thoseparameters which indicate the mass transfer and mixing performance, such as themean liquid volumetric mass transfer coefficient （kLa）, the ratio between cycle time ofthe downcomer and the cycle time of PBR （θ） and averaged turbulence kinetic energy（Em） were large. Besides, the obtained liquid velocity is close to the optimum valuemost favorable to microalgal growth. When L/λ12and A/λ0.8, the mass transferperformance is the best and the value of liquid volumetric mass transfer coefficient(kLa) increased by about10%compared with that of bioreactor with flat baffles. AsL/λ12and A/λ0.4, the mixing performance of the reactor is the best and the valueof averaged turbulent kinetic energy （Em） is increased by14.7%compared with that ofbioreactor with flat baffles. No matter what the condition of L/λ will be, the obtainedvalues of θ are all larger than those of flat baffles, which is helpful to strength themixing performance in the riser and downcomer.The effects of waved baffles structure on light-gradient mixing were investigated.It was shown that the changes of waved baffles could effectively regulate light-gradient mixing process. The optimized waved baffles structure parameters ofL/λ12and A/λ0.2were obtained. Under which, both the average liquid radialvelocity and average turbulent kinetic energy in the downcomer were large. A goodperformance of light-gradient mixing was created. Under this condition, the value ofaverage turbulence kinetic energy in the downcomer increased by35%comparingwith that of traditional flat baffles. The statistic analysis method was applied toanalyze the light-gradient mixing performance. It is shown that the proportion ofnegative velocities during the mixing process was2.5times larger than that of flatbaffles. It is concluded that the performance of waved baffles is better than that of flatbaffles. And waved baffles could greatly improve light-gradient mixing performancecompared with that of traditional flat-baffles.

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