Study On Reducing Pressure Loss And Increasing Separation Efficiency Of PV Cyclone

PV cyclone is a type of high-efficiency separator led by China University of Petroleum(Beijing)and has been widely used in high temperature industrial process of petroleum catalytic cracking and has achieved good economic and social benefits.With continuous advancement of national energy conservation and emission reduction action,cyclone separators with higher efficiency and lower pressure drop are required.In this thesis,effects of the inlet and vortex finder on the collection efficiencies and pressure drops of the PV cyclone separator are investigated by using the numerical simulation with the experiments which may provide technical support for the design of PV cyclones with low pressure drop and high efficiency.The contents and conclusions of the thesis are as follows:The rectangular inlet of conventional PV cyclone may lead to velocity inhomogeneity at inlet tube,resulting in top dust ring and short-cut flow,which reduces separation efficiency.Based on the above phenomenon,this thesis investigated the effects of inlet guide vanes and inlet shapes.In the fourth and fifth chapter,in view of large turbulent flow loss in vortex-finder,the column-insert in vortex-finder is investigated to occupy the strong turbulent flow area to reduce pressure drop.The inlet guide vane could increase tangential velocities of outer flow in cyclones,increasing the centrifugal force exerted on particles,which results in efficiency improvement.Also,radial velocities are increased to decrease the short-cut flow.However,pressure drop is greatly increased.According to the simulation results,the guide vane with gap of 5 mm width and radius of 153 mm could help ease the impact between the swirling gas and the cyclone wall,which could decrease the pressure drop.Also,the height of guide vane decreases along the inlet pass way,which could help a part of gas enter the annular space directly,decreasing the secondary flow under the roof of cyclone.In this way,the separation efficiency could be increased.The semi-trapezoid inlet could improve the inlet velocity and flux distribution homogeneity;also,it helps increase the tangential velocity of outer flow in cyclones,hence increasing the centrifugal force exerted on particles.At the same time,the natural vortex length is shortened which avoids particle re-entrainment at expansion chamber and dipleg and improve the separation efficiency.The column-insert could decrease the pressure drop and efficiency.With the insert depth growing,tangential velocities are decreased firstly and then increased.Therefore,it doesn't work well when the depth is too short.With the insert depth growing,the efficiency and pressure drop are decreased firstly and then increased.This is because it can strengthen the stability of flow filed in separation space when its column-insert is long,hence increasing the maximum tangential velocity and separation efficiency.However,the maximum tangential velocity in the vortex finder is also increased,which does not help improve the turbulent energy loss.That is why the pressure drop isn't greatly decreased.