【作者】 李骏；

【导师】 徐又一；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2011， 硕士

【摘要】 目前,我国水体污染加剧,水资源严重短缺,而我国的环保技术仍然比较落后,传统的充氧技术都不同程度的存在氧气利用低、能耗高、污染空气等问题。采用中空纤维膜无泡充氧(曝气)技术,可以极大提高氧利用率和传质速率,而且过程中无泡沫形成,具有高效节能等显著特点,明显优于传统的曝气技术,是一种很有前景的新工艺。本文首先制备了聚丙烯中空纤维微孔膜,微孔平均孔径为0.15帅,具有孔隙率高、比表面积大、气通量高以及价格便宜等优点。随后采用工业酒精对其进行亲水型改性。使用上述膜材料,设计并制造了一种帘式无泡充氧装置,分别考察了其在横向流和平行流两种形式下,水力因素、气相因素等工艺参数对传质的影响。研究表明,增大液相流速、曝气压强和膜面积,充氧效果都会有明显增加。本文还分别计算了传质过程中的膜阻和液相边界层阻力。研究表明,无论是在横向流还是在平行流体系,膜阻在很大程度上受到曝气压强的影响。针对横向流在结果中产生的偏差,引入修正系数fa加以修正,并得出了相应膜阻关联式。此外,得到的传质关联式也与文献报道符合较好,尤其在Re小的情况下。本文还设计并制造了一种柱式无泡充氧装置,该装置可以对壳程流动的液相加压,在保持气液两相的压差不变条件下进一步提高供气压力。当液相压力为0.2MPa,气液两相压差为O.1MPa,流量在600L/h时,出水的溶解氧浓度可以达到9.9ml/L,已处于过饱和状态。与帘式相比,柱式无泡供氧装置的氧传递速率要大近一倍,充氧效果更好。本文还针对氧气在水中扩散慢的问题,设计并制造了一种旋转式无泡膜式充氧装置。首先在清水中进行实验,研究水力因素、气相因素等工艺参数对传质过程的影响,研究表明随着气相压力和旋转速率的增大,溶解氧浓度也随之上升,并且采用聚丙烯和聚乙烯两种中空纤维膜的充氧效果差别不明显,但采用前者可以获得更高的操作压力。随后进行了模拟废水的生化污泥实验,装置连续运行3个月,污泥池中溶解氧DO浓度大约维持在边缘0.2-0.3mg/L,中央区域0.5-0.6mg/L,COD去除率最高达到了81.2%。本文最后还设计并制造了一种新型的自吸式无泡膜式充氧装置。整个充氧装置直接暴露在空气中,当具有一定流速的液体通过中空纤维膜时,在膜壁微孔处会形成负压,将空气吸入中空纤维膜内与水混合,从而达到无泡充氧的目的。研究表明,当膜管程中水力流动线速度较小时,不足以引起自吸现象,影响充氧效果的主要因素是气液相的接触时间和接触面积。当线速度达到临界线速度时,范围为0.4-1.4 m/s,会产生自吸现象,溶解氧浓度和氧转移速率均出现拐点,此时影响充氧效果的主要因素是水力流动线速度。结果显示,自吸式无泡膜式充氧装置的氧转移速率要比压力式无泡膜式充氧装置的氧转移速率大一个数量级,具有较好的工业应用前景。更多还原

【Abstract】 Water pollution in china is aggravating, and thus leads to a serious shortage of water resources; meanwhile our environmental protection technology is still relatively behindhand. Many problems exist in traditional aeration technologies, such as low oxygen utilization ratio, high energy consumption, air pollution and so on. But all these problems can be solved by using hollow fiber membrane bubbleless aeration technology which greatly improves the utilization of oxygen and mass transfer rate, and no bubbles are formed during the process. Bubbleless aeration, with its feature of high efficiency and energy saving, is a promising technology.In this paper, polypropylene hollow fiber microporous membrane was prepared, with average pore size 0.15μm, whose advantages include high porosity, large membrane area per unit volume, high gas flux, as well as low price. Then The membranes were hydrophilic treated by industrial alcohol.A novel curtain type bubbleless membrane aeration device was designed and manufactured by using the PP membranes. The influences of process parameters, like hydraulic factors and gas-phase factors, on oxygen transfer in cross flow and parallel flow conditions respectively were evaluated. It is indicated that oxygen transfer ability grows significantly with the increase of liquid velocity, air pressure and membrane areas. Besides, the membrane resistances and liquid phase boundary layer resistances were calculated, and the results show that the membrane resistances are significantly influenced by gas pressure. As for the discrepancy of cross flow, additional area correction factor fαwas incorporated. Then the membrane resistances correlation was established. In addition, the mass transfer correlations we achieved are in a good agreement with those in paper, especially when Re is low.Besides, a column type bubbleless membrane aeration device was also designed and manufactured. The advantage of this module is that the gas phase pressures can be further increased by enhancing the liquid phase pressures. The DO value at the outlet can reach up to 9.9ml/L, which is far saturated with oxygen, when the liquid phase pressure is at 0.2MPa, the pressure difference is at 0.1MPa and the flow rate is at 600L/h. The oxygen transfer rate in column type is two times larger than that of curtain type.Furthermore, considering the slow rate of oxygen diffusion in water, a rotary type bubbleless membrane aeration device was also designed and manufactured. The influences of process parameters, like hydraulic factors and gas-phase factors, on oxygen transfer in water were evaluated. The results showed that DO value grows with the increase of gas pressures and rotating rate. There is no significant difference by using PP and PE hollow fiber microporous membranes for bubbleless aeration. Later on, the experiment was conducted in synthesized sewage. The module have run for three months, and the results showed that the DO value at the edge of the tank was 0.2-0.3mg/L, while 0.5-0.6mg/L at the center. The COD removal was up to 81.2%.Finally, another novel self-suction bubbleless membrane aeration device was designed and manufactured in this study, which is exposed to the air directly. When the fluid goes through the hollow fiber tube under a certain flow rate, due to its porosity, negative pressure will be formed in the pores and thus the air will be inhaled into tube and mixed with water. It is showed that when the velocity was low, self-suction phenomenon cannot be caused. Therefore, the major influences on oxygen transfer were liquid-gas contact time and contact area. While the velocity was up to critical velocity, normally at 0.4-1.4 m/s, self-suction phenomenon would occur, and there are significant change both in DO value and oxygen transfer rate. In that situation, the liquid phase velocity was the key factor. It indicated that the oxygen transfer rate in self-suction modules is one order of magnitude higher than in previous modules.更多还原