【作者】 李尔；

【导师】 沈蕴芬； 范跃华；

【作者基本信息】 华中科技大学 ， 市政工程， 2007， 博士

【摘要】 城市污水处理过程的大部分能耗都集中于好氧处理过程中,提高曝气充氧系统的效率成为污水厂运行管理的关键。现行的曝气法有:鼓风曝气、机械曝气和两者结合的鼓风—机械曝气。鼓风曝气系统中的微孔曝气系统因其曝气效率相对较高,适应性较强,应用更为广泛。但其氧的利用率和动力效率的绝对数值实际并不高,其根本原因在于目前微孔曝气的研究和应用存在着以下的问题:(1)经典的气液传质理论认为曝气传质扩散的速度主要受气液界面相际传质的影响,忽略了气泡的搅动扩散对传质效果的贡献和对DO均匀分布的重要作用。(2)经典理论认为在曝气传质过程中应尽可能地增大气液接触比表面积,因此主张在相同条件下气泡尺寸越小越好,但这与大部分的实测结果不符。(3)曝气传质模型多偏重于单一气泡尺寸的研究,而忽视了气泡大小分布对于曝气传质过程的重要影响,(4)经典传质模型偏于理论性而实用性不强、传统的评价指标计算较复杂且不便直接用于曝气系统运行和操作。针对目前研究中存在的这些问题,本研究提出了新的理论模型——微孔曝气最优气泡群理论模型。该理论体系架构主要由最优气泡群理论模型基本观点、最优气泡群数学模型、主要应用指标等组成。其基本观点如下:(1)曝气过程主要包括气液界面相际传质和气泡搅动扩散两个阶段,这两个阶段对水体曝气充氧都有贡献但方式不同,相际传质是将氧从空气泡中传入水体,而搅动扩散是使已传入水体中的溶解氧分布于整个水体中。(2)在相同曝气条件及相同气泡数目的条件下,气泡尺寸并非越大或越小曝气效果越好,而是存在着最优气泡平均直径。(3)在曝气量、曝气池的尺寸和曝气器淹没水深一定时,存在着使曝气效果最佳的最优初始气泡群分布。根据该基本理论,本研究建立了以下相关数学模型,其主要包括:(1)曝气传质有效能耗总利用率最高的最优气泡平均直径数学模型;(2)曝气能谱图与等有效能耗曲面;(3)使曝气过程中有效能耗总利用率最大的最优初始气泡群。基于该理论提出了直观简便的微孔曝气系统性能新指标——最优气水比参数。为验证微孔曝气最优气泡群理论模型体系的合理性,进行了两方面的试验:模型小试验证和复氧中试应用检验。本研究首次将雾化曝气管作为布气扩散装置应用于清水和复氧曝气中。试验结果表明:(1)在相同试验条件下,随着曝气气泡平均直径的增加,相际传质能量利用率逐渐减小而紊动扩散能量利用率逐渐增大,而曝气传质有效能耗总利用率是先上升后下降,其峰值即为最大的有效能耗总利用率;(2)根据试验结果所建立的曝气能谱图和等有效能耗曲面图表明曝气池内存在着有效能耗总利用率最高的高效曝气气泡分布段,不同曝气过程虽其初始气泡的输入能量不同,但其传质的有效能耗却有可能相同,通过控制曝气系统工况,可实现“低气量、高效能”的优化运行;(3)所建立的最优气水比模型与实测值符合得较好,最优气水比作为新的曝气系统性能评价指标,评价结果与常规指标一致,但其更直观,应用更简便;(4)在水槽复氧中试试验中,相同条件下雾化曝气管较其它的曝气设备复气效果更好,曝气后水体的DO下降较小,能在较更长的距离保持DO达标,因此,雾化曝气管作为一个新型的高效曝气扩散装置适用于河流复氧;(5)在水槽复氧中试试验中,雾化曝气管的最优气泡群模型较其它的气泡群复氧效果更好。另外在相同管长和水槽流量条件下,并非初始气泡尺寸越大或越小复氧效果越好,也存在着最优的曝气气泡平均尺寸,这为河流曝气复氧工程设计提供了重要的依据。更多还原

【Abstract】 Most of energy loss in sewage treatments can owe to aeration, therefore how to improve the efficiency of aeration system is a key point of management and operation of sewage plants. Nowadays common aeration methods can be classified such three types: blow aeration, mechanical aeration, the aeration integrate these two types of aeration. Due to its oxygenation performances and adaptability to varying oxygen requirements, blow aeration, especially fine bubble diffused aeration systems has been widely developed in application. However in fact, the values of its oxygen utilization rate and power efficiency are not high and its energy loss is really high. In addition, the research and application of the aeration systems has such following problems: (1) models integrating mass transfer between liquid-gas phase with turbulent diffusion of dissolved oxygen are not available; (2) classic thoery thinks the better effect of aeration will be gained if the interface aera between water and air bubble increase i.e. the size of air bubble is lessened, but this option doesn’t match the measurement of much research. (3)the conventional aeration transfer models lay particular stress on the size of fine bubble, and ignore the effect of bubble distribution of the aeration. (4) classical mass transfer models focus more on theoretic and less on application, laying particular stress on microcosmic or sub-microcosmic but care little about macroscopic, conventional characteristic criteria of blow aeration are considerable complex and is not convenient for operation and manipulation of the aeration systems.According to the drawbacks of the fine, theory of Optimal Bubble Group for fine bubble aeration was raised. Its construction was composed of such component: basic viewpoints, basic model and main application index. Its basic viewpoints are: (1) mass transfer and turbulent diffusion are both important process in the aeration. Such two process both contributes the aeration, while mass transfer shift the oxygen in the gas bubble enter into the water and turbulent diffusion make the entering DO completely distributes the whole water body ;(2) In the given aeration condition and the number of gas bubbles, there existing optimal average gas bubble diameter; (3) when the gas volume (Qg), the size of the aeration tank and water depth is fix, there existing initial optimal bubble group. Based on these viewpoints, the follow corresponding was developed: (1) in the given aeration condition (the gas volume (Qg), the size of the aeration tank and water depth is fix), the model of optimal average gas bubble diameter; (2) equal effective energy curve space and aeration energy curve (3) the model of average gas bubble diameter (4) To solve the problem of application to engineering, based on the theory of Optimal Gas Bubble Group (OGBG) , the model of optimal gas-water ratio used as a characteristic criterion which is more convenient , easy and applicable for than other conventional index.To validate the model of optimal bubble group, such two part of experiments are done: model experiment and aeration. Fog aeration pipeline used as gas diffused equipment was firstly introduced into aeration of clean water and aeration engineering in this study. The experimental results in this study shows: (1) In the same experimental condition (same air flow rate and same pipeline length), with the average diameter of gas bubble increment, the usage rates of mass transfer between liquid-gas phase gradually decrease in the same time the usage rates of turbulent diffusion gradually increase, but the total usage rate will rise first but then descend, its maximum value is the highest usage rate in aeration (ηT M) . When the air flow rate is same and water height is different,ηT M is not same too, and the maximum is the most optimal value and the corresponding water height is named as optimal water height on that air flow rate. Similarly, optimal air flow rate exist in the same water height.(2) Energy spectral curve surface (ESCS) indicates that although the energy input into the aeration system is different, but the really useful energy may be same. Comprehending ESCS can make total useful energy of different initial energy aeration system move smoothly on ESCS as much as possible, and this will be much helpful to high effective and low energy operation of the aeration system. (3) To verify the validity of air-water ratio, this paper compares the performance of three fine bubble diffused aeration systems evaluated by the ratio with those by SSOTE , N Tand K Lα20, and the process of the calculation of their design and operation based on air-water ratio with those based on the three criteria. The results show that their evaluations are consistent with each other and the process of the calculation based on air-water ratio is more convenient and direct than that based on the other three criteria. (4) According to reaeration experiments on the model flume in Foshan River, compared with other normal bubble group (NBG), the aeration effect of OGBG are much better , and its DO can be sustained for much longer and drop less along the stream distance. These will be propitious to make DO meet the standards in much longer distance. (5) Maximum optimal air flow rate or maximum OGBG in different flow rate have been determined for reaeration for model flume. This proves that the effect of reaeration will not be better when air flow rate is higher or the initial gas bubble size is smaller. This finding will be important reference to reaeration engineering.更多还原