Study On Aeration Performances And Local Gas Hold-up Distribution Of Rotary Bubble Diffuser

In the actual sewage treatment process,the characteristics and installation of the fine bubble diffuser often lead to uneven oxygenation distribution,e.g.the gas hold-up distribution decreased significantly in the areas deviated the central part above the diffuser,which reducing the oxygenating ability of aeration tank.In the research of gas-liquid two-phase flow and mass transfer,a novel active rotary valve was developed,and a tray installed with such valves owns better gas hold-up distribution when compared with a rotary valve tray,due to the active rotary valve promoting the more uniform contact of the gas-liquid and strengthening the mass transfer.In order to improve the oxygenation uniformity,a novel rotary bubble diffuser was presented in this thesis which was an improved fine bubble diffuser.The aeration performances and local gas hold-up distribution of rotary bubble diffusers were experimentally observed in a Plexiglas aeration tank with an inner size of 600 mm×800 mm×910 mm,by using an air-water system.The oxygenation uniformity index,oxygen transfer coefficient,oxygen transfer rate,oxygen transfer efficiency and aeration efficiency,and radial distribution and axial distribution of gas hold-up of the rotary bubble diffusers were measured and compared with those of a fine bubble diffuser.The results showed that the oxygenation uniformity index of the rotary bubble diffuser range from 0.0404 to 0.0494,while that of the fine bubble diffuser range from 0.0547 to 0.1275,which indicates that the oxygenation uniformity of the rotary bubble diffuser is much higher than that of the fine bubble diffuser.The oxygen transfer coefficient,oxygen transfer rate,oxygen transfer efficiency and aeration efficiency of rotary bubble diffuser are very close to those of the fine bubble diffuser.The rotary flow field across the tank with the rotary bubble diffuser can enhance the surface regeneration of the gas and liquid,and narrow the mass transfer dead zone in the aeration tank.The rotation of the rotary bubble diffuser leads to its higher uniformity in gas hold-up distribution than that of a fine bubble diffuser,and the difference increases with the increasing of the distance from the center of the aeration tank.The average gas hold-up distribution of the rotary bubble diffuser increases from 0.0971 to 0.1227 with the increasing of measured height,while that of the fine bubble diffuser increases from 0.0566 to 0.0885,which indicated that the uniformity of aeration of rotary bubble diffuser is higher than that of fine bubble diffuser.The radial gas hold-up distribution increases gradually with the increasing of the air flow,while increases significantly when the air flow is close to 3.0 m3?h-1.The average gas hold-up distribution decreases with the increasing of the measured height,especially,changes rapidly when the measured height is from 625 to 725 mm or the air flow increases from 2.5 to 3.0 m3?h-1.The results of this paper provide the basis for the actual operation and engineering design of the rotary bubble diffuser,which lays the foundation for further research and improvement.