Simulation Studies On Water Deoxygenation Process In A Rotating Packed Bed

The presence of dissolved oxygen in water can lead to oxygen gas transport pipeline and equipment corrosion, but traditional water deoxygenation device exists the disadvantages of bulky and high operating costs. As one new and efficient mass transfer equipment, rotating packed bed greatly strengthens the micro-mixing and mass transfer and has been increasingly used in water deoxygenation process. However, in previous studies, the gas-liquid two-phase flow and mass transfer of water deoxygenation process were not discussed in depth, and some literatures regarded the liquid phase as a continuous medium when calculating the liquid volumetric mass transfer coefficient. But that was inconsistent with the actual liquid state, which existed in the presence of discrete phase in a rotating packed bed at higher speed (>600rpm) and constantly coagulated and dispersed during motion.In this paper, generally theoretical model, coupling with porous media model and particle trajectory model for water deoxygenation process, is established by the use of computational fluid dynamics (CFD) methods in a counter-current rotating packed bed where blowing dissolved oxygen in water with nitrogen. In the meantime, the accuracy of that model is verified by comparing simulation data with literature data in terms of grid independence and accuracy of gas-liquid motion model and oxygen content at the outlet.After analyzing of two-phase flow field in the water deoxygenation process based on mathematical model, it can be seen that nitrogen velocity has strong unevenness in the packing section and rises to the maximum speed in the interface of packing and cavity region. Gas pressure drop in the packing area increases with rotor speed and gas flow rate, but little changes in the cavity region. After sprayed into the RPB in the form of discrete droplets, the radial velocity of water increases to the maximum value then sharp declines after entering the cavity area. Droplet trajectory seems to radiation spiral and disperses small in the circumferential direction. Droplets collide with high-speed rotary filler screen after entering into the packing area. Then droplets constantly coagulate and disperse and droplet diameter changes increasing or decreasing, whose path trend is close.Preheating operation unit is added to the water deoxygenation process. Effects of difference of preheating temperature, rotor speed, liquid feed rate and gas-liquid volume ratio on oxygen content at the outlet, removal of oxygen and liquid volumetric mass transfer coefficient were investigated in orthogonal experiment method. The results show that the order of the impact on oxygen content is rotor speed>preheat temperature>fluid feed rate>gas-liquid volume ratio at the outlet from various operation factors. The oxygen content at the outlet decreases with increasing of preheating temperature and gas-liquid volume ratio, but increases with the liquid feed rate. In other cases, it decreases first and then increases with increasing of rotating speed. The effects on removal of oxygen are completely opposed to that. Liquid volumetric mass transfer coefficient increases with the preheating temperature, gas-liquid volume ratio and liquid feed rate, and slowly declines with increasing speed after the first increasing. Under the optimized experimental conditions, water at the outlet is operated by twice nitrogen strip to get oxygen content of0.048mg/L and removal of oxygen of99.7%, fulfilling a request for industry producing.