Study On Ammonia Absorption In A Bubble Column Radiated By Ultrasonics And Numerical Simulation

Bubble column reactor (BCR) isimportant equipment for gas-liquid mass transfer,momentum transfer and energy transfer in chemical industry. A special ultrasonic bubblecolumn and a bubble feature measuring system called double conductivity probes were usedin this research with ammonia-water mixture systems. In this paper, following significantstudies were taken in different ultrasound fields and with/without additivies, which were (1)the distribution of bubble parameters (bubble sauter diameter/bubble rise velocity/bubbleinterfacial concentration/gas hold-up) in radial and axial orientation versus the superficial gasvelocity (SGV);(2) The distribution of ammonia concentration in bubble column byultraviolet spectrophotometry;(3) The law of volumetric mass transfer coefficient ofammonia overall bubble column;(4) A numerical simulation of the cavitions bubble motion,and the influence on the acoustic cavitions of correlative parameters with Matlab Program.The aim of this paper is to study the mechanism of enhancing ammonia absorption byultrasonic field coupling with additivies and to provide theoretical bases for the industrialapplications. The main contents of the studies and achievements are as follows.(1)The flow regime can be identified from the plot of fractional gas hold-up against SGV.The fluid flow pattern is changed from the homogeneous regime to heterogeneous regimewhen the SGV is over0.06m/sin ultrasound field and0.05m/s without ultrasound field.(2) Bubbles parameters areincreasing and then keep stabilization versus the SGVincreasing under different ultrasound field. The value of the bubbles parameters has risenslowly when it is next to the distribution plate, while the value rises fastly when it is far fromthe distribution plate. The distribution of bubble parameters is peak in the center of thecolumn and then decreases away from the center of the column (the distribution of centerpeak). Additivies especially the octanol can reduce the bubble sauter diameter/bubble risevelocity, and enhance the bubble interfacial concentration/gas hold-up.Bubblesparametersareincreasing and then keep stabilization when the octanol concentration is over0.1%(volumeratio) at0.06m/s of the SGV.(3) The ammonia concentration is rising and then keeps gradual when the SGV is over0.06m/s and it is decreaseing as the distance from the measuring hole to the distribution plate increase. Additivies, especially the octanol can elevate the ammonia concentration distinctly.The distribution of sound field is more uniform, which can promote ammonia concentration.(4) The volumetric mass transfer coefficient of ammonia (K_ya) is increasing and thenkeeps stabilization versus the SGV increasing. Ultrasonicwave, especially20-50-100kHzultrasound combining can engender cavitation and perturbation effect, which enhance the thevolumetric mass transfer coefficient of ammonia to165%. With the addition of octanol, thethe volumetric mass transfer coefficient obtained can be further increased to260%(5) From the numerical simulation on the cavitions bubble motion, it is shown thatincreasing the frequency of ultrasound can not always strengthen the cavitation effect. Thebubble motion is much intenser and it can engender more mechanical disturbance in themultiple frequency field, which is more beneficial to mass transfer of gas-liquid.The results of this paper show that ultrasound can make aseriesofeffects, which influencethe distribution of bubble parameters and the volumetric mass transfer coefficient of ammonia.The method of ultrasonic field coupling with additivies can facilitate mass transfer effectively.Meanwhile, through solving the cavitation bubble motion equation by MATLAB, theinfluence on the acoustic cavitions of many correlative parameters was discussed. Theachievement can provide the theoretical basis for the future researches.