A Study On Modeling Of Mass-Transfer In RPB

Rotating packed bed (RPB), a new high-performance equipment, used to intensify mass transfer and transfer related chemical reactions, which appeared in the end of 70s has bright prospect in industries. Researches of mass transfer of liquid-phase controlled systems in RPB had been reported, but along radius direction of rotating packed bed mass-transfer coefficient and concentration distribution measurements have not been reported.Based on the flow status of liquid and gas in RPB, a model describe the gas-liquid mass-transfer in the packing of RPB is presented The phenomenon of surface absorption and super saturated vapor pressure of liquid mist affecting mass-transfer in RPB greatly have been considered. Gas-liquid inter-phase is not in equilibrium state has been discovered. The mass-transfer equations of the liquid-drop and liquid-film in the model are disintegrated by the method of controlled-volume. The numerical methods of solution are also presented.In order to verify the model, water absorbing SO2 in air, operated in counter-current and parallel-flow model, is experimented. Which a system of both gas and liquid phases influence on mass-transfer. The radial concentration distributions of SO, in liquid in the packing are measured by conductance probe in site at different radial position of the rotor. The influence of gas flow rate, liquid flow rate, rotating speed and concentration of SO2 in inlet gas on distributions of the liquid concentration and volume mass-transfer coefficient along the radius direction of the packing layer in RPB are investigated. The results indicate that: 1. Under counter-current, the volume mass-transfer coefficient had a max from 7cm to 8cm. This is liquid-phase end effect zone. Later it increased gradually when radial distance is larger than 9cm. It increased rapidly near the outer edge of rotor. This is gas-phase end effect zone. In co-current, the volumetric mass-transfer coefficient increases rapidly from 7cm to 9cm on rotor. This is because there are liquid-phase end effect zone and a gas-phase end effect zone close to the insider edge of rotor. It decreases gradually when radial distance is larger than 9cm. 2. The volumetric mass-transfer coefficient in packing increases with gas flow rate and rotating speed raises. Liquid flow rate and concentration of SO2 in inlet gas influences less on it.In counter-current and co-current, the gas pressure drop of RPB has been studied. The results show: The gas pressure-drop of dry and irrigating RPB are in direct ratio with the square of gas flow rate. It decreases under co-current mode and increases under counter-current mode when rotating speed raises. 2. With the scope of the experiment, whether counter-current or co-current, the gas pressure drop of irrigating RPB are less than that of dry RPB, and it decreases slightly when liquid flux raises. 3. The simulation agrees with the experiment well. The model explains the experiment phenomena satisfactorily.in counter-current and co-current modes, the gas-liquid mass-transfer model isused to simulate mass transfer in packing layer of RPB. The results show that surface absorption and super saturated vapor pressure of liquid mist affect mass-transfer in RPB greatly, and the gas-liquid inter-phase is nonequilibrium. The simulation agrees with the experiment well.On the basis of the above research, industrial illustration of absorbing sulfur dioxide with RPB from exhaust gas of sulfuric acid factory is carried out in ZiBe. The results indicate that: 1. The degree of equilibrium in RPB (actual absorption efficiency / absorption efficiency at equilibrium 100) is near 100% all, the ammoniated brine in liquid inlet is whether more or less, and the concentration of SO2 in gas outlet is whether higher or lower. The degree of equilibrium in conventional foam tower is about 80% 2. The concentration of SO2 in gas outlet is less 300 ppm, so much as less 50 ppm. 3. Comparing with conventional tower, the investment is about 42% less, the plant area using is about 50% and the energy consumption is about 25% low...