Study On Vacuum Deaeration Process In Rotating Packed Bed

Water deoxygenation has very important significance in industry. High concentration of dissolved oxygen is harmful to iron equipment, for dissolved oxygen can corrode iron, which would cause equipment failure. Dissolved oxygen can also cause the breeding of Microorganism, which has bad effect on water quality. Water deoxygenation methods that is widely used currently, have obvious shortcomings. Because of the using of chemical deoxidizers, the cost of chemical deoxidizing methods is high, and the chemical deoxidizers using in chemical deoxygenation methods are all venomous, which would also cause secondary pollution of water, so chemical deoxygenation methods cannot be used on domestic water and food industry-used water. The energy consumption of physical deoxygenation methods is high, the equipment is huge, and the fluctuation of operating conditions has a great impact on deoxygenizing effect. Because of its small volume, high efficiency of micromixing and mass transfer, rotating packed bed (RPB) is widely used in industry. Now RPB has already successfully combined with thermal deaeration and desorbed deaeration and used in industry. However, RPB is still not used in vacuum deaeration which is also a kind of physical deoxidizing way. In this study, using tap water as raw materials, the experiment of vacuum deaeration in RPB is conducted. In the experiment, the influence of vacuum degree in RPB, water temperature, rotating speed, water flow rate on deoxygenizing result is investigated. The following results are obtained, the concentration of dissolved oxygen at liquid outlet is raised with the increase of vacuum degree in RPB and water flow rate, and descend with the increase of water temperature and rotating speed. Using a single-stage RPB as vacuum deaerator can make the concentration of dissolved oxygen reduce to100ppb, however, single-stage vacuum tower can only make it reduce to500ppb, which means vacuum deaeration in RPB has obvious advantage. Based on study of liquid flow in RPB and the characteristics of vacuum deaeration, after making some simplifying assumptions, mass transfer model of vacuum deaeration using RPB is established. Numerical simulation of vacuum deaeration using RPB based on the mass transfer model is done, and the following results are obtained. The dissolved oxygen concentration gradient in droplet is raised with the increase of rotating speed and water flow rate, descend with the increase of water temperature. The liquid phase mass transfer coefficient is raised with the increase of water temperature, rotating speed and water flow rate. The concentration of dissolved oxygen at liquid outlet is raised with the increase of water flow rate, descend with the increase of vacuum degree in RPB, water temperature, rotating speed and packing outer diameter. The volumetric mass transfer coefficient is raised with the increase of water temperature, rotating speed and water flow rate, descend with the increase of packing outer diameter.In the experiment, the effect of different operating parameter on volumetric mass transfer coefficient is the same with it in numerical simulation. Compared the deoxygenizing ratio of experiment with it of numerical simulation, the error ratio is under±12%, which means the mass transfer model established can nicely modeling the process of vacuum deaeration in rotating packed bed.