Study On Flow Characteristies Of Micro-pressure Inner-loop Bioreactor

Micro-pressure inner-loop bioreactor(MPR)with the property of simple structure and no moving components inside is a new eccentric aeration tank,which is main ly applied in the biological treatment process of municipal sewage and industrial w astewate.The unilateral aeration at the bottom of the reactor makes the activated sl udge mixed liquor form a vertical cyclic flow field in which the velocity is higher at periphery and becomes gradually lower towards the center.Under the interaction of aeration oxygenation and microorganism oxygen consumption,the outermost reg ion manifests as aerabic property;the central region has a certain hypoxia area;and the aerabic,anoxic,anaerobic multifunctional bacterial partitions coexist and synerg ize.Macropore aeration pipes are used as the sole power drive to provide gas sour ces and fluid flow.The gas-liquid-solid three phase interreaction arises at the aerati on terminal.The gases accumulate and excrete together from the effluent terminal t hat is far from the aeration terminal,which exerts pulsating impact on the nearby mixed liquid,but the circulation flow in the center and the central area is rather g entle.The behaviors of fluid mechanics at each region of the flow field in the reac tor present inhomogeneity,and quite complexity.Ideal research results are hard to ob tain by single experimental study because activated sludge and gas bubbles coexist in the experiment of biological treatment of sewage.In recent years,computational fluid mechanics and physical model study have devewloped rapidly,and their resear ch results are widely and deeply applied in fluid mechanics study and structure opti mization study concerning various types of sewage treatment reactors.This paper,through experimental research method and numerical simulation met hod,deeply studies the flow field property of reactors,comes up with optimization schemes of reactor structure,guides the operational control of biological treatment e xperiment of reactors,provides evidences for optimization design of reactor structur e,and so accelerates the popularization and application of the reactors.1)On the basis of flow status analysis of sewage treatment experiment by reg ular Micro-Pressure Inner-Loop Bioreactor,this paper puts forward some improveme nt in experimental study of the distribution of dissolved oxygen in sewage treatmen t,and makes experimental study of velocity distribution of regular and improved re actors on the condition of clear water.In the experiment of concentration distributio n of dissolved oxygen,the measured results showed that the concentration of dissol ved oxygen in the center of the reactor is 11.88% of that at the periphery,and the average concentration at the central region is 34.65% of that at the periphery,and showed a rather clear feature of gradient distribution and distinct oxygen partitions.In the process of this experimental research,it exploited velocity test method via digital image suitable for our reactors,and concentration test method of non-intrutiv e dissolved oxygen.2)This study constructs numerical model and numerical simulation via the flui d mechanics software Fluent 15.0,verifies the correctness of the results of numeric al simulation via the experimental data of velocity distribution;contrasts the gas-liq uid two-phase flow field properties via numerical simulation;and advances the opti mal operation control condition of aeration intensity.The results show that aeration intensity is the main factor affecting the flow field property,as to the reactors of fi xed outline dimention.From the analysis of aeration intensity,the stronger the aerat ion intensity is,the faster the overall velocity is in the reactors.when the aeration intensity gets stronger,the gradient of velocity distribution turns smaller compared with the overall velocity increase in the reactors.And at the same time,the intensit y of dissolved oxygen in the reactors increases and tends to be homogeneous due t o the reinforced mass transfer of convection.And the intensity gradient of dissolve d oxygen becomes correspondingly smaller,the velocity partition and oxygen partiti on in the reactors becomes vague,so its general performance approaches to hybrid aeration tanks.By contrast,if the aeration intensity is too small,the velocity and the intensity of dissolved oxygen in the tanks will decrease generally,and can not develop into good partitions,and the horizontal velocity will also decrease at the b ottom of the reactors to form dead zones at the bottom or at the corners.3)The structure of the reactors get further optimized through the method of n umerical simulation,and the results show that regular reactors with additional cham fers and internal guide plates can decrease the flow reflection from the four corners of the reactors,and can decrease the energy loss in the liquid circulation.Under the same aeration intensity,the velocity of water is raised;the driving force from t he gas turns stronger;the afloat capacity gets increase,and so itis more helpful to the suspension of activated sewage.We eventually choose the optimized reactors w hose peripheral velocity is increased compared with the regualr reactors,and horizo ntal velocity is increased at the bottom of the reactors.And the flow field get mor e stable.The exchange amount of liquid and the volume proportion in each region can be controled via the change of chamfers and internal guide plates.The operatio n control conditions can be changed by adjusting the aeration amount or the numbe r of aeration pipes or the positions of aeration pipes.So our study provides a new idea and method of control and design,and improves the controllablity of reactors.If inlet pipes are adjusted to geometric center from the place which is near the si dewall of exhaust ends,sewage will pour into the anaerobic phase of the central ar ea of the reactors,which can further promote the formation of anaerobic region an d is conductive to the biological treatment process of sewage.Because the velocity at the central area approaches to 0m/s,the resistance of liquid flow around does n ot increase obviously,and does not make greater impact on the flow field of the r eactors.Optimized strucutre and inlet-water from the center are adopted in the follo w-up study of the reactors,which can increase the intensity gradient of dissolved o xygen at each oxygen parttition,and can further improve the biological treatment efficiency;and at the same time,good reactor structure can decrease energy consump tion of mixed levitation.Aeration amount and energy consumption can both be decr eased in the premise of satisfying the biological oxygen consumption demand in the sewage treatment reactors.In conclusion,on the basis of experimental research and the numerical simulati on analysis of the flow field of micro-pressure inner-loop bioreactor,this paper mak es clear the velocity distribution law in reactors and oxygen supplement law of the artificial oxygen aeration.comparative analysis is made for the reactor structure in the process of numerical simulation,and several schemes are further optimized,an d optimization proposals are finally raised in the study.The results of numerical si mulation in this paper are quite consistent with the experimental results,which sho ws that it has feasibility to guide the structure optimization design of sewage treat ment reactors through numerical simulation methods.