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题名: 计算流体力学及氧传质模型耦合对一体化A2 /O-MBR的模拟与优化
作者: 袁星
学位类别: 硕士
答辩日期: 2015-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 樊耀波
关键词: 一体式 A2/O-MBR,计算流体力学,结构优化,氧传质,溶解氧分布, A 2/O-MBR, computational fluid dynamics (CFD), structure optimization, oxygen mass transfer model, distribution of dissolved oxygen (DO)
其他题名: Simulation and Optimization of A2 /O – MBR Using Computational Fluid Dynamics Coupled with Oxygen Mass Transfer Model
学位专业: 环境工程
中文摘要:     A2/O-MBR工艺,因其具有脱氮除磷效率高、出水水质好、占地面积少等优点,在污水资源化方面越来越受到关注,目前已有数座万吨级A2/O-MBR应用于实际污水的处理中。但其仍然存在着工艺流程长、能耗高等缺点,阻碍着其进一步的推广应用。为了更加节能和结构优化,本课题组构建了一种一体化 A2/O-MBR反应器装置,并对其曝气能耗进行了研究,发现其在低曝气量条件下运行可行。但由于该反应器是在膜池好氧曝气条件下,利用膜池气升动力推动反应器各单元的水力循环,在好氧、缺氧、厌氧各单元中能否建立需求的 DO浓度数值范围,对一体化A2/O-MBR反应器工艺的实现至关重要,因此在探索一体化A2/O-MBR内部流场特性的同时,需要了解其 DO的分布特征,这对考察和控制A2/O-MBR运行条件,确立合理优化的运行参数有重要的实际意义。
    为此,本研究基于计算流体力学方法,将氧传质模型与计算流体力学模型耦合,并将其应用于对一体化A2/O-MBR流场及DO分布的研究,并对一体化A2/O-MBR进行了结构优化。取得主要结果如下:
1)一体化A2/O-MBR反应器的结构优化:
    a)两侧回流孔的直径对中间升流区(膜区和好氧区)速度及膜面剪切力分布没有明显的影响,而对外侧降流区(缺氧及厌氧区)的流场有较大的影响,其中回流孔直径为 10mm情况下,外侧区域流速较低,而中间升流区流场混合程度较高。
    b)导流板高度对膜区的速度及膜面剪切力大小与分布有较大的影响,保持导流板顶部与膜片顶部平齐,发现在导流板底部距反应器底部高度为 110mm时,其相应的膜区速度与膜面剪切力的大小及分布都较好。
    c)曝气管数对膜区流场分布有较大影响,其中在 5根曝气管情况下,其平均膜面剪切力及速度分布较为均匀,且数值也相对较大,对膜区的冲刷效果较好。
d)曝气管布置对反应器内流场和膜面剪切力也有较大影响。从膜面剪切力及膜区速度分布来看,平行布置(曝气管与膜元件平行布置)的均匀性都较好。
2)CFD-DO模型耦合及模拟:
    a)在30、60、90、120 L/min四种曝气强度情况下,反应器中均出现了在中间升流区为好氧区,DO浓度较高,如4mg/L;在外侧降流区较低,且在降流区中上部形成缺氧区(DO<0.5mg/L)和底部形成厌氧区(DO<0.1mg/L)的特征;即在该反应器中可以实现一体化A2/O-MBR的DO浓度分布,利于脱氮除磷功能的实现。
    b)在该种一体化A2/O-MBR反应器中,较低的曝气量强度不仅更易于厌氧-缺氧-好氧及硝化反硝化条件的形成,而且还利于降低MBR的运行能耗,利于高效低耗污水处理和资源化生物反应器的建立。
    c)在一体化A2/O-MBR中污泥粘度对DO浓度分布存在一定影响,随着污泥粘度的增大,DO浓度降低,但污泥粘度对流场影响不明显。
    d)气泡直径对DO分布存在明显影响,气泡直径的增大会导致反应器中DO浓度的明显降低,会导致膜面剪切力的升高。结果表明,存在一个适宜的气泡直径或范围,其可以产生较满意的膜面剪切力也利于反应器厌氧-缺氧-好氧条件的建立。将本研究的 CFD-DO耦合模拟平台应用于实际一体化A2/O-MBR中试装置的模拟,将模拟结果与实验结果校核验证,结果表明:该 CFD-DO耦合模拟平台可行,模拟结果具有较好的可靠性和可信度,可供 MBR特别是一体化 A2/O-MBR研究、设计和工程化应用参考。
英文摘要:     A2/O-MBR is applied in many large-scale sewage treatment  plants, because of its high removal efficiency of denitrification  and phosphorus, higher product  quality and the  smaller footprint.  However,  it  still has  disadvantages,  such as  the  long process flow and  the high energy consumption  which restrict  its further application.  In order to save the energy consumption and  optimize structure, a new kind of A integrated  A2/O-MBR,  was  studied  by  the  research  group.  It  was  found  that  the integrated A2/O-MBR  could be operated  at lower air  flow rate in the  membrane tank with lower  aeration energy consumption.  In the integrated  A2/O-MBR, the  hydraulic A2/O-MBR, the circulation  was driven  by  the  airlift  power  of membrane  tank. A  very  important question  needed  to be  answered  is  whether  the  DO concentrations  in  the  aerobic, anoxic and anaerobic unit can  meet the requirements of A2 /O process  or not under the condition of aeration in the membrane  unit. It is important not only  for inspecting and controlling  the  operation  conditions  of A2 /O-MBR,  but  also   for  establishing  the  reasonable or optimal operation parameters.
    To answer the questions above,  the computational fluid dynamics (CFD) coupled with  oxygen  mass   transfer  model  was   implemented  to  study  the   hydrodynamic characteristics and DO  concentration distribution within the  integrated A2/O-MBR  in this study. The results obtained are summarized as follows:
1) For the structure optimization of the integrated A2/O-MBR:
    a)    The  diameter   of  backflow  holes   had  no  obvious   influence  on   the velocity and wall shear stress  in up flow region. However,  it had a great influence on  down flow  region. The  velocity in down  flow region  was
lower  and   the   hydrodynamic  characteristics   were  better   when  the diameter of backflow holes was set at 10mm.
    b)    The distance between baffles and underside  had a great influence on the velocity and  wall shear stress  within the reactor.  The velocity and  wall shear stress  became higher when  the distance was  110mm. Meanwhile,the distribution of velocity and wall shear stress was more uniform.
    c)    The  number  of  diffusers  had  a  great  influence  on  the  flow  field  in membrane region. When the number of diffusers  was 5, the velocity and wall  shear   stress  in   membrane  region   were  higher.   Moreover,  the distribution of  velocities and  wall shear stresses  was more  uniform, so that it was better for the scouring of the membrane.
    d)    The layouts of  diffusers had an  obvious effect on  the velocity and  wall shear  stress within  the  reactor. The  distribution of  velocities  and wall shear  stresses  was  more   uniform  when  the  layout  of  diffusers   was parallel.
2)    For the simulation of DO distribution by CFD-DO:
    a)    At  four  different aeration  intensities,  30,  60,  90,  120 L/min,  the  DO concentration  in  up  flow region  was  4  mg/L,  which  was  also called aerobic  zone. The  DO  concentration was  lower  in down  flow  region,where the upper  zone was called  anoxic zone (DO <  0.5 mg/L) and  the lower  zone   was  called  anaerobic   zone  (DO<   0.1  mg/L).   The  DO concentration distribution  in the  reactor could  meet the  requirement of the  integrated  A2 /O-MBR  to  remove  the  eutrophication   materials  of denitrification and phosphorus.
    b)    Lower  aeration   rate  in   the  integrated   A2 /O-MBR  was   not  only   a requirement to  establish the necessary  reaction conditions in  anaerobic, anoxic or aerobic region, but  also an expected situation to reduce energy consumption in sewage treatment and reuse.
    c)    Sludge  viscosity   had  a  certain   influence  on   the  DO  concentration distribution  in the  integrated  A2 /O-MBR.  With the  increase  of sludge viscosity, the DO  concentration became lower,  but it had little  effect on the flow field.
    d)    Diameter of  bubbles had  an obvious  influence  on the  DO distribution and with  the increase of  the diameter of bubbles,  the DO  concentration in  the  reactor  reduced significantly,  but  the  wall  shear  stresses  were increased  at the  membrane surfaces.  However, the  variation of  bubble sizes  had no  evident  effect  on  the value  and  distribution of  velocties within the  reactor. The  results showed that  there was  a suitable bubble size   that  could   not   only  produce   satisfactory   shear  stress   at   the membrane,   but   also    establish   the   desire   DO   conditions    in   the anaerobic-anoxic-aerobic region. The  CFD-DO   model  and  the  modeling   results  in  this   study  were successfully   validated   against   the   experimental   results    from   a   pilot integrated A2 /O-MBR.  The results showed that  the coupled CFD-DO model and  the  simulation platform  established  were  feasible  and  the  simulation results showed  the effectiveness  and credibility of  the CFD-DO  model and the  simulation  platform.   It  could   be  used  as  technical   support  for  the research and development of the new integrated A 2/O-MBR.

   
 
 
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/34459
Appears in Collections:水污染控制技术研究室_学位论文

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Recommended Citation:
袁星. 计算流体力学及氧传质模型耦合对一体化A2 /O-MBR的模拟与优化[D]. 北京. 中国科学院研究生院. 2015.
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