Mass Transfer Modeling And System Optimization Of CO₂ Removal From Bubble Plume

The bubble column reactor is widely used in the water treatment process.The gas bubbles are used to drive the surrounding fluid to form a bubble plume,and the gas-liquid two phases are fully contacted.The target gas in the liquid phase can be blown off and transferred into the gas phase.For a given reactor size,we need to determine the best conditions for water treatment to achieve the best results with the lowest energy consumption.Due to the limitations of the experiment,we use numerical simulation as the main method and experimental method as the auxiliary means to study the mass transfer process of CO₂ in bubble plume,and provide a computational model which can predict the quantitative relationship of unsteady dynamics and various designs for practical problems.This paper begins with the study of the dynamic mass transfer of single bubbles,and then uses computational fluid dynamics and experimental measurement techniques to study the physical model of the aeration tank and the bubble plume in the prototype.Based on the characteristics of gas-liquid two-phase flow field,the dynamic characteristics of bubble plume are studied,and the relationship between single bubble and bubble group mass transfer is established,and the dynamic mass transfer of bubble plume is further studied.Based on the discrete phase model,the following researches are carried out:Firstly,the motion of single bubble in water and the mass transfer are analyzed theoretically,and the coupled model of floating bubble mass transfer in water is established.The coupled ordinary differential equations are solved by Matlab.Compared with previous research conclusions,the feasibility of simulating the mass transfer process of the single floating bubble mass transfer model is verified.The results show that the model can successfully simulate the dissolution of single bubble in water,that is,its mass transfer into the liquid phase.Although the mass transfer of bubbles into water is opposite to the mass transfer direction of“blow off”to be done in this paper,the situation of a single bubble is the same as that of the mass transfer mechanism between the two phases.Finally,by establishing the relationship between single-bubble mass transfer and bubble plume mass transfer,the mass transfer of is extended to the mass situation of bubble plume.Secondly,the bubble column reactor is designed and processed and the gas-liquid two-phase flow field in the column is taken by high-speed camera.The video of the experiment is analyzed by PIV?Particle Image Velocimetry?,and the gas-liquid two-phase flow parameters such as flow field velocity and streamline is obtained and it provides a better analysis method for practical problems.After that,the discrete phase model is used to simulate the flow state of the bubble plume in the bubble column reactor,that is,the influence of the intake air amount on the gas-liquid two-phase flow field.In the existing numerical simulation studies,the Euler-Eulerian method is used to study the bubble plume.Although the Euler-Eulerian method can obtain the low-frequency oscillation of the bubble plume and its time-average flow characteristics to some extent,the motion trajectory of a single bubble in the bubble plume and its force motion characteristics cannot be presented.In this paper,the Euler-Lagrangian method is used to study the dynamics of the bubble plume formed by the force and motion of each discrete phase bubble.The flow of the bubble plume,the concentration distribution of the discrete phase,the change of the velocity field under different intake air amounts,and the influence of different intake air amount on the bubble residence time are considered respectively.The result shows that the intake air amount is larger,the higher the concentration of the discrete phase and the greater the velocity of the flow field are.The intake air volume and bubble residence time are not a simple linear relationship,that is,with the increasing of intake air to a certain extent,the bubble residence time will decrease because the bubble moves in the flow field,and there is pulsation and oscillation itself,and a vortex of the bubble plume formed by the aeration.There is also a vortex.The discrete phase model reproduces the bubble plume behavior well.Finally,the efficiency of CO₂ removal from bubble plume is calculated by combining the mass transfer mechanism of single bubble with the parameters from simulation and experiment.The removal efficiency of CO₂ under different intake air is calculated and the conversion trend of aeration time efficiency for practical engineering reference.