【作者】 王晓明；

【导师】 康建雄；

【作者基本信息】 华中科技大学 ， 环境工程， 2021， 硕士

【摘要】 随着当今世界人口逐渐增长,污水的排量越来越来高,环境问题也日益严重,污水的有效处理愈发重要,在高浓度污水处理技术中厌氧生物技术为其中主流之一。同时,工业的迅速发展导致了越来越多含硫废水的排放,有学者发现光合细菌在处理含硫废水中有促进作用,并据此设计了一种结合厌氧生物技术与光合细菌的光照UASB(Up-flow Anaerobic Sludge Blanket,UASB)反应器,但实际运行中启动周期长并且发现反应器存在三相分离效果较差的现象。为了解决现存问题,除了研究光照UASB反应器生化机理之外,还需要结合其内部流场情况进行分析。本文以实验室光照UASB反应器为研究对象,利用计算流体力学软件Fluent对其进行三维数值模拟,针对不同升流速度的反应器以及不同结构参数的三相分离器进行模拟研究并提出优化,主要结果如下:(1)对光照UASB反应器进行单相流稳态模拟,结果表明虽然反应器通过布水管下三个间距相同的布水孔布水,但布水并不均匀:靠近进水口的区域流速更高,距离入口较远的区域流速较低,随着高度的升高这二者差距不断减小,直到基本达到一致;靠近圆环柱体反应器壁面的区域流速较低,越靠近内外壁中间的位置流速越高。(2)对光照UASB反应器进行液-固两相流模拟,分析上升流速u=0～6 m/h时的流场流态,观察到反应器布水的不均匀性;上升流速的升高会使湍流区体积增加以及推流区体积减少,并且会使反应器中部会出现漩涡;较低上升流速下的污泥分布更加均匀,较高的上升流速则会使污泥床高度增加,在实际反应器的启动时可以考虑将先提升上升流速使污泥床层被快速搅动,之后可以适当降低上升流速来使泥水混合更加均匀;综合考虑下u=1.774 m/h时反应器内部流场最优。(3)进行停留时间分布(Residence Time Distribution,RTD)实验,发现污泥床的高度和变化趋势与数值模拟结果基本吻合,误差小于7.14%。数据处理结果显示:随着上升流速u的增加,反应器内的V_d从12.54%逐渐下降至7.71%,并于u=5.321m/h时突增至20.92%;RTD曲线的标准化方差σ_θ~2的值也随着u的增加,由0.23先减小至0.18,后增加到0.24。以串联模型和轴向扩散模型对光照UASB反应器内的流态进行分析,随着u的升高,N由4.39先升高到5.70后下降至4.22,D/μL由0.13降低至0.10后增加到0.14,光照UASB反应器既存在平推流也存在全混流。根据实验结果,综合考虑V_d、σ_θ~2、N、D/μL与污泥床高度等因素,u=1.774 m/h时反应器的处理能力最好。最后将RTD实验结果与模拟结果比较,发现实验结果与模拟结果吻合良好,说明使用模拟代替此反应器实验是可行的。(4)以光照UASB反应器的三相分离器为研究对象,通过对不同下挡板倾角以及回流缝宽度的三相分离器区域进行气-液两相模拟研究,得出最优的尺寸为下挡板倾角为50°,回流缝宽度为3 mm,并进行模拟考察其气体分离效果,结果显示其稳定运行后气体分离效果大于90%,这对以后设计光照UASB反应器具有一定的指导意义。更多还原

【Abstract】 With the gradual growth of the world’s population,the discharge of sewage is getting higher and higher,and environmental problems are becoming more and more serious.The effective treatment of sewage is becoming more and more important.Anaerobic biotechnology is one of the mainstream of the high concentration sewage treatment technologies.At the same time,the rapid development of industry has led to the discharge of more and more sulfur-containing wastewater.Some scholars have found that photosynthetic bacteria have a promoting effect in the treatment of sulfur-containing wastewater,and based on this,they have designed a combination of anaerobic biotechnology and photosynthetic bacteria,light UASB(Up-flow Anaerobic Sludge Blanket,UASB)reactor,but in actual operation the start-up period is long and the reactor is found to have air leakage.In order to solve the existing problems,in addition to studying the biochemical mechanism of the light UASB reactor,It is also necessary to analyze the internal flow field.In this paper,the laboratory UASB reactor was used as the object,and the computational fluid dynamics software Fluent was used to perform three-dimensional numerical simulation on it,and conducts simulation research and proposes optimization for the reactor with different rising speed and the three-phase separator with different structural parameters,the main results were as follows:(1)A steady-state simulation of single-phase flow in the light UASB reactor was carried out.The results showed that although the reactor distributes water through three water distribution holes with the same spacing under the water distribution pipe,the water distribution was not uniform:the area near the water inlet has a higher flow rate,and the flow velocity in the area farther from the inlet was lower,and the gap between the two continues to decrease as the height increases until it was basically the same;The flow velocity in the area close to the wall of the toroidal column reactor was lower,and the closer to the middle of the inner and outer walls,the higher the flow velocity.(2)The liquid-solid two-phase flow simulation of the light UASB reactor was carried out,and the flow field when the rising velocity u=0～6 m/h was analyzed.The change characteristics of the sludge bed when the reactor was started were observed,which also explained the unevenness of the water distribution in the reactor;The increase of rising velocity u can increase the volume of the turbulent flow zone and reduce the volume of the push flow zone,and cause vortexes in the middle of the reactor;The sludge distribution under the lower rising velocity was more uniform and higher The increase of rising velocity also can increase the height of the sludge blanket.When the actual reactor is started,it can be considered to increase the rising velocity first so that the sludge bed can be quickly stirred,and then the rising velocity can be appropriately reduced to make the mud-water mixing more uniform;Under comprehensive consideration,the flow field in the reactor was the best when u=1.774m/h.(3)Carrying out the RTD experiment,it was found that the height and change trend of the sludge blanket are basically consistent with the numerical simulation results,and the relative error was less than 7.14%.The results of data processing show that as the rising velocity u increases,the V_d in the reactor gradually decreases from 12.54%to 7.71%,and suddenly increases to 20.92%when u=5.321 m/h.With the increase of u,the value of the standardized varianceσ_θ~2 of the RTD curve also reduced first from 0.23 to 0.18,and then increased to 0.24.The flow pattern in the light UASB reactor was analyzed by the series model and the axial diffusion model.With the increase of u,N increased first from 4.39 to5.70 and then decreased to 4.22,and D/μL decreased from 0.13 to 0.10 and then increased to 0.14;light UASB reactor has both plug flow and complete mixing flow.According to the experimental results,comprehensively considering factors such as V_d,σ_θ~2,N,D/μL,and the height of the sludge blanket,it was concluded that the reactor has the best processing capacity when u=1.774 m/h.The RTD experimental results are compared with the simulation results,and it was found that the experimental results are in good agreement with the simulation results,indicating that it was feasible to use the simulation instead of the experiment.(4)The three-phase separator of the light UASB reactor was used as the research object.Through the gas-liquid two-phase numerical simulation study of the three-phase separator area with different lower baffle inclination angles and the width of the return crack,the optimal size was that the lower baffle inclination angle was 50°and the width of the return crack was 3 mm.Then the gas separation effect was investigated by numerical simulation.The results show that the gas separation effect was greater than 90%after stable operation,which has a certain guiding significance for the design of the light UASB reactor in the future.更多还原