Study On Liquid Flow Field On Fixed Rotary Valve Tray

Tray efficiency is a key indicator for evaluating tray columns.Tray columns with high efficiencies help to achieve the purpose of energy saving and profit improving in chemical industry.Tray efficiency depends on the in-column mass transfer and contacting among gas and liquid phases,while the on-tray liquid flow conditions impacts greatly on the gas-liquid contacting process.The on-tray liquid residence time distributions are aspects of the liquid flow information.The on-tray liquid phase flow field distributions are closely related to the tray structure.A fixed rotary valve was developed in our laboratory based on the concept of rotating flow field and fixed valve.According to the characterizations of the fixed rotary valve in hydrodynamics and mass transfer performances,it has the advantages of low tray pressure drop and entrainment,wide operating range,high efficiency,and uniform gas holdup,with broad application prospects.The liquid residence time distributions were investigated on the fixed rotary valve tray by using an air-water system,hot water as a tracer,and a temperature array hot water tracer technique in an organic glass column with inner diameter of 1200 mm.The on-tray liquid flow field distributions of 3 types of fixed rotary valve tray with different downcomer and flow-guiding structures were compared,e.g.immersed arch downcomer,suspended arch downcomer and suspended arch downcomer with a guide plate.The temperature array hot water tracer technique used in this thesis is proved to be convenient,tracer saving,effective and accurate method for the study of the on-tray liquid flow field distributions.With the increasing of liquid rate,the on-tray liquid flow rate increase too.The liquid residence time on the immersed arch downcomer fixed rotary valve tray was shortened from 8s to 5.5s,and from 9s to 5s for suspended arch downcomer.The liquid flow field distributions of the immersed arch downcomer fixed rotary valve tray tend to be non-uniform with the increasing of the liquid rate,while that of the suspended arch downcomer is opposite.With the increasing of kinetic energy factor,the on-tray flow speeds up and the bubbling on the tray turns to violent,which enhance the turbulent kinetic energy in the liquid phase and strengthen the flow field rotating effect.The on-tray distributions of the liquid phase of the fixed rotary tray tend to be uniform and the liquid residence time was shortened from 8 s to 7 s and 9 s to 8 s for immersed/suspended arch downcomers,respectively.For large flow rate conditions,the higher liquid flow rate means the higher energy level,which leads to the less impact of gas phase on the liquid phase energy and flow field distributions when they contact.In other words,the kinetic energy factor affects on the on-tray liquid distributions only under low liquid rate conditions.The on-tray liquid flow of the fixed rotary valve tray is complicated,and the rotating flow field is beneficial to the uniform distributions of liquid on the tray.The influence of rotating flow field on the on-tray liquid phase distributions of fixed rotary tray with immersed arch downcomer are more obvious,compared to that of suspended arch downcomer.The liquid phase flow on the fixed rotary valve tray with a suspended arch downcomer has the characteristics of flowing-to-wall,and the residence time on the tray is longer than that of the immersed arch downcomer.The installation of guide plate improves the overall distributions of the liquid on the tray,while the guide plate has a greater effect on the distributions of the liquid in inlet area than in the outlet area.