Research Of Gas-liquid Mass Transfer Mechanism And Strengthening Method In Precise Distillation

With the modern petrochemical industry and fine chemistry industry developing at top speed,.requirements and efficiency at high level were put forward for mixture separation.Generally speaking,mixture to be separated often contains multiple components or components with close boiling points.Because of mature theory,simple equipment and flexible installation,distillation,as one of the most effective and reliable separation means,had been acquired an unprecedented development.Among all distillation equipment,towers were popularly used.In recent years,particulate fillers and regular packing had won the market share even to exceed plate towers of late years due to low pressure drop and high flux.But no matter packing tower or plate tower,high manufacturing costs and complicate structure had became a stumbling block in the industrial promotion,not to mention special design in certain conditions.How to maintain high tray efficiency,and meanwhile to keep the simple structure of sieve tray in trace precise distillation was the main research of this paper.That a mesh was set up on the sieve tray called compound microscale high efficient tray was put forward.A series of theoretical derivation,experimental measurement and numerical simulation were carried out.This paper deduced correlation between bubble diameter and mass transfer coefficient,Murphree efficiency based on:(?)(?).Bubble diameter R was crucial for tray efficiency in precise distillation.So breaking big bubbles,strengthening the surface renewal and enlarging interfacial area could improve separation efficiency.The experimental equipment is designed for investigating the tray pressure drop,gas hold-up and bubble characteristics and compared with the cases of sieve tray.The results revealed that the tray pressure drop of microscale tray was averagely 56%larger than that of sieve tray,up to 0.499kPa.More energy consumption delayed transition of gas-liquid contact state.The gas hold-up of mesh sieve tray was also higher 4.29%than that of sieve tray.Bubble mean diameter of microscale tray was only 2.43mm,which was one sixteenth of value for sieve tray.The average bubble rise velocity of microscale tray was 12.3cm/s,compared to 13.45cm/s for the sieve tray.Both microscale tray and sieve tray followed a similar law related to bubble radial and axial distribution.Coming to a judgment:when theoretical sieve Murphree efficiency Ei,MV<0.25 in precise distillation,microscale tray could be considered to applied.Euler-Euler two phase flow model was used to simulate gas-liquid flowing on trays.Simplified physical model was proved that it could reflect the actual fluid flow.Simulated results showed the effect on gas hold-up and gas velocity imposed by mesh.The gas hold-up presented gradient distribution along axial direction.The microscale tray improved gas uneven distribution and reduce vortex mix area.