Study On Gas Absorption And Liquid Flow In The High-speed Disperser

High-speed disperser(HSD)reactor is a process intensification device which is consisted of single or multi-stage rotors.In the present work,the liquid flow pattern and mass transfer characteristics in a HSD reactor were investigated,providing a deep understanding of the fluid mechanics and transfer mechanism in such reactor.Liquid flow characteristics in HSD reactor with four rotors and various packing combination is investigated by experiments and numerical simulation.The mean droplet diameter in HSD reactor with four rotors decreases with the increasing rotational speed and the decreasing liquid flow rate.Under the various packing combinations,the mean droplet diameter decreases with the the increase of packing ring radius,packing ring numbers and packing radius.Moreover,the probability distribution of droplet diameter in HSD reactor with four rotors and packing combination both conform to the normal distribution.The distribution with four rotors becomes concentrated with the increasing rotational speed and the decreasing liquid flow rate.And this distribution with packing becomes concentrated with the increasing packing ring number and the packing radius,while the effect of packing ring radius is insignificant.In addition,a two-dimensional simulation on the liquid flow is conducted to analyze the droplet diameter,it shows that the simulation results agree well with experimental results under different rotational speeds.In HSD reactor with four rotors,a liquid flow model is established to describe the droplet flow in the cavity zones and the liquid films flow on the rotors.When passing through single rotor,liquid transforms from droplet,liquid film,rivulet to ligament,resulting in smaller droplets in the next cavity zone.Moreover,a modified inclined impact model based on the energy conservation is established to describe the impact and spread process,during which droplet transforms to liquid film and reaches the maximum spread diameter on the rotating rotors.The maximum spread diameter increases with the increase of rotational speed,and it increases with the increase of liquid flow rate under low rotational speed,while decreases under high rotational speed.A mass transfer area model based on the liquid flow model is proposed to calculate the total effective mass transfer area,which includes the area of liquid film on the inner surface of rotors and reactor wall,as well as the area of droplets in four cavity zones.The model results agree well with chemical experimental values.The total effective mass transfer area increases with the increasing rotational speed and liquid flow rate,but the effect of gas flow rate is marginal.The effect of rotational speed on droplet area and the effect of liquid flow rate on liquid film area were significant.Also,the contribution of mass transfer area mainly comes from the liquid films on the reactor wall as well as the droplets in the fourth cavity zone.An experiment is conducted to study the mass transfer characterisitcs of HSD reactor with four rotors and various packing combination.Results show that absorption efficiency increases with the increase of rotational speed,rotor number and liquid flow rate,and it decreases with the increase of gas flow rate.The absorbent capacity increases with the increase of rotational speed and gas flow rate,and it decreases with the increase of liquid flow rate.The total effective mass transfer area increases with the increasing rotational speed,rotor number and liquid flow rate,but the effect of gas flow rate is insignificant.Moreover,the mass transfer area increases with the increasing packing ring radius,packing ring number and packing radius.Considering the droplet diameter and mass transfer area,the split packing is regarded as an optimum packing combination,as it can increase the number of end effect zones.In HSD reactor with full packing,a mass transfer area model is established.The contribution of packing zone to the total mass transfer area ranges from 61%to 82%,and the mass transfer area difference between the packing zone and the cavity zone increases with the increasing rotational speed.An enhancement factor based on the mass transfer area of first layer packing ring is proposed.The enhancement factor increases with increasing packing ring radius and numbers,and it increases with increasing packing radius at low rotational speed,but the trend is inhibited at high rotational speed.In order to verify the liquid flow model,the collision between droplet and various solid surfaces is investigated.Results show that the maximum spread diameter on the static impermeable wall increases with increasing droplet velocity and decreasing liquid viscosity and surface tension.When colliding with moving impermeable wall,the droplet will spread asymmetrically.The maximum spread diameter increases with the increasing droplet velocity and surface velocity.When colliding with static permeable surface,the stretch and bend of ligament increases with the increasing droplet velocity and decreasing droplet viscosity.When colliding with moving permeable surface,the stretch and bend increases with increasing droplet velocity and surface velocity,resulting in a larger probability of ligament breakup.