Studies Of Liquid Flow Visulasiton And Mass Transfer Model In Rotating Packed Beds

Chemical industry plays a significant role in national economy,which provides a large amount of chemicals and basic material for social development and national defense construction. Chemical industry also produces a lot of harmful substances such as wastewater, waste gas in the production processes, which seriously restricts the sustainable development of chemcal industry in China. The pursuit of clean and energy saving in chemical production process is the goal of scientists and engineers. A rotating packed bed （RPB） is one of the process intensifaction equipment and expected to achieve this goal.The liquid is sheared into the tiny droplets and films by the porous packing in the RPB and the gas-liquid contacting area is sharply increased which enhances micro-mixing and mass transfer. The end effect zone is a zone of better mass transfer and mixing, which occurs in several millmeters on the inner part of the packing of the RPB. Based on the phenomenon of end effect, the mass transfer region of RPB can be divided into end zone, bulk zone, and cavity zone （so-called three zones）.However, the liquid moves fast inside the packing in the RPB and it is difficlut to observe. Studies about liquid flow pattern and size is not systematic and enough in the thress mass transfer zones of a RPB.Meanwhile, the study about mass transfer of the cavity zone and end zone are not clear. The lack of basic research such as liquid flow and mass transfer hinder the further structure optimizaiton and industrial application of the RPB.In this work, firstly, the liquid flow of cavity zone is observed by a high-speed camera and the mass transfer model of cavity zone is developed. Then, the end zone and bulk zone can be distinguished by the way of probability calculation. The liquid mass transfer coefficient model was established and comprised the end zone, bulk zone, and cavity zone（called liquid mass transfer model of three zones）. Combined with the gas mass transfer and chemical reaction, mass transfer model of three zones was developed to predict the monoethanolamine（MEA） absorption process of CO₂, and to provide theoretical support for the design and application of the RPB. Main conclusions are as following:1.The liquid flow in the cavity zone of a RPB was studied by a high-speed camera. The work investigated effects of rotational speed,liquid volumetric rate, outer packing radius, liquid vicosity and surface tension on liquid flow pattern, average droplet diameter, droplet size distribution, and average droplet velocity in the cavity zone.Experimental results showed that two typical liquid flow patterns（ligament flow and droplet flow） and two typical liquid disintegrating modes （film-droplet disintegration and film-ligament-droplet disintegration） were observed. The liquid flow transition curve under different operating conditions was also observed. The average droplet diameter decreased with an increasing rotational speed, outer packing radius, and liquid viscosity and increased with an liquid surface tension.The average droplet diameter was unchanged with an liquid initial velocity. The droplet diameter distribution conformed to the R-R distribution. The value of distribution width ranged from 4.47 to 9.43.The average droplet resultant and radial velocity increased with an rotational speed and outer packing radius and was unchanged with liquid initial velocity, liquid viscosity, and liquid surface tension. In addition,the correlation of the average droplet diameter and velocity was obtained by dimensional analysis and the relative errors between experimental and predicted results from the correlation are within ±20% and ±10%,respectively.2. Based on the results of visual observation in the cavity zone, it could be found that the mass transfer of cavity zone comprised mother droplet, liquid film, and daughter droplets. The total mass transfer area model was developled on the basis of the above three mass transfer parts.It can be seen from the results of the mass transfer model that the liquid film and daughter droplet contributes the most of the total mass transfer surface area in comparision with the mother droplet. Then, the model was validated by the chemical absorption experiment of NaOH-CO₂ and the experimental investigated the effects of rotational speed, liquid initial velocity, and outer packing radius on the mass transfer surface area of cavity zone. The experimental results showed that the predicted mass transfer surface area agreed well with the experimental data with deviation within ±20%. The model was also considered to capable of providing a reasonable prediction of total mass transfer surface area of the cavity zone.3. The thickness of end zone was calculated by using the probability calculation method. Combined with the thickness of the end zone and the results of present and previous studies of the liquid flow and mass transfer of the RPB, the liquid volumetric mass transfer coefficient model of three zones was established based on the end zone, bulk zone, and cavity zone. It can be found that the model was within ±15% of the experimental data by validating of chemical absorption experiment NaOH-CO₂, indicating the feasibility of employing the model to predict the mass transfer process and provide theoretical support for the design of RPBs.4. Based on the liquid mass transfer model of three zones, the mass transfer model of three zones was predicted to MEA-CO₂ absorption process by considering the influence of gas-phase mass transfer and chemical reaction of the three mass transfer zones. The results of absorption experiment of MEA-CO₂ showed that the experimentally obtained values of absorption efficiency were in agreement with model predictions within ±20%. The absorption efficiency fisrtly increased and then decreased with an increasing rotational speed. Also, the absorption efficiency increased with an increasing liquid volumetric rate and MEA concentration. Additionally, the absorption efficiency decreased with a decreasing gas volumetric rate.