油水界面电荷电动调控及强化船舶油污水分离机理研究

The fine separation units of an oily water separator can be easily blocked by the emulsified oily water. Extending their cleaning and re-new time can be achieved by the improved ability of separating the emulsified oil droplets for the gravity separation method which is very significant for the efficient utilization of the separator on board ship and the development of the green shipping industry...In this proposal, a method of enhancing oil water separation by applying a DC electrical field is put forward. After applying a DC electrical field, two vortices will be generated around the oil droplet which can continually capture emulsified droplets firstly and then carry them floating upwards. That is, the bigger droplet can help float the smaller droplet. In this way, the separation of emulsified oil by gravity is enhanced. Furthermore, the surface charges will be unevenly distributed due to the presence of the applied electrical field, thus decreasing the electrical repulsive forces between two approaching droplets and facilitating the coalesce of droplets. The main contents are as follows: 1) Experimentally evaluating the enhanced oil separation performance of the gravity settling and plate coalescence units by the applied electrical field in macro-scale. This is the fundamentals for the further micro-scale investigation of the enhanced oil demulsification by electrical field. 2) Modeling the ion distribution on droplet surface under the applied electrical field and verifying it with experiments. The model will be used for analyzing the flow field outside the droplet and the coalescence of two droplets. 3) Studying the floating movement of an oil droplet as well as the flow field during the upward movement under the electrical and gravity fields, aiming to clarifying the mechanism of vortex formation and its impact on droplet movement. 4) Studying the droplet deforming and oil bridge forming processes with the purpose of clarifying the mechanism of the enhanced coalescence by the electrical field. In a word, the fundamental researches proposed to be done are to provide reference for the development and application of oil separation enhancement with electrical field on board ship.

船用油水分离器精细元件易被乳化油脏污，切实提高重力法分离乳化油的能力，可延缓部件的清洗和换新，对于油水分离器的高效使用具有重要意义。本项目提出对油污水施加直流电场，一方面可在油滴周围产生电水动力涡，用来持续捕获乳化油滴，获得大油滴“携带”小油滴共同上浮的有益效果，提高了重力式分离乳化油的能力；另一方面，还可使油滴表面电荷非均匀分布，从而降低油滴聚结电斥力，强化了聚结分离。主要研究内容有：1）实验研究电场强化静置和板式聚结油水分离效果，为微尺度电场破乳机制研究奠定基础；2）建立电场下油滴表面电荷分布模型并进行实验验证，为分析油滴外部流场和聚结过程提供依据；3）研究电场和重力场联合作用下，油滴上浮运动及油滴周围流场变化规律，揭示涡的形成机制及对油滴运动的影响；4）研究电场下，油滴形变和油桥形成的过程，揭示电场强化油滴聚合的机理和规律。通过上述研究，可为发展船舶油污水电场强化分离技术奠定基础。

1..项目的背景.目前船用油水分离器聚结滤芯或膜组件极易被油滴堵塞而失效， 切实提高重力法分离乳化油的能力，可延缓部件的清洗和换新。重力场下乳化油滴所受浮力不足以实现有效油水分离，因此，如能通过某种机制，调控油滴双电层之间的静电斥力，则可强化乳化油的聚结。.2..主要研究内容.1）.电场强化船舶乳化油污水分离性能研究.2）.外加电场对油滴表面带电离子分布的影响.3）.电场和重力场联合作用下，单个油滴上浮运动及油滴周围流场分析.4）.电场作用下，油滴聚结过程研究.3..重要结果.1）关于水中油滴局部zeta电势及局部电荷密度分布.（1）电场下，油滴表面的最大zeta电势出现在油滴面向电场强度的方向，最小zeta电势出现面向电场强度的方向，即油滴最初的zeta电势。再分布后的zeta电势随着起初zeta电势的增加而增加。.（2）再分布zeta电势随外加电场强度的增加而增加。.2）电场作用下，油-界面电荷的移动速度与油水界面水的电渗流动速度量级相当，方向相反。.3）电场可以致使油滴变形，这有利于油滴聚合。.4）电场能够破坏乳化液的稳定性，即电场有利于油水分离，并且横向电场比纵向电场更有利于油滴的聚结。.4..关键数据.1）电场作用下，油滴面向电场强度的方向有最多的表面电荷，最小zeta电势出现，背向电场强度的方向有最少的表面电荷。.2）电场作用下再分布后的表面电荷随初始表面电荷的增加而增加。.3）横向电场12V/cm下，500µm油滴聚结所需的时间为35.5s，1600µm油滴聚结所需时间为24.2s。在横向电场4.8V/cm下，1150µm的油滴聚结所需的时间为36.8s；而当电场强度增加至14.4V/cm时，聚结所需时间减少至17.6s。.5..科学意义.理论并实验明晰了电场对弯曲液-液界面电荷分布的影响规律，对于发展基于电场的油滴表面电性调控以及强化油滴聚结技术具有重要的指导作用。