Study On Mass Transfer Performances Of Fixed Rotary Valve Tray And Local Gas Hold-up Fraction

Some shortcomings exist for the float valve tray in real applications,e.g.waste of materials for manufacturing,high manufacturing costs,tendency of wear and falloff and so on,while the fixed valve tray has the merits of simplicity and low costs for manufacturing and is gradually concerned by researchers.A new type of fixed valve tray,which changes the direction of gas blowing from the side and reduces the amount of entrainments and weeping,and consequently improves the handling capacity and mass transfer efficiency,has been developed previously.However,the entrainments of the fixed valve tray are quite high under the conditions of high gas loads.Therefore,the possibilities of improving in the upper limit of operation and mass transfer efficiency are obvious.A novel type of fixed rotary valve tray was introduced in our lab based on the above mentioned fixed valve tray considering the tray structure optimization,flow field strengthening and efficiency improving,and concept of rotating flow field,of which the hydraulics have been investigated.In this thesis,the mass transfer performances of the fixed rotary valve tray were experimentally investigated with an air-water-oxygen system in a stainless steel column with an inner diameter of 600 mm,and the gas hold-up fraction distributions were characterized with a conductivity probe in a rectangular organic glass column with an inner size of 300 mm×400 mm.Additionally,the characterizations of the fixed rotary valve tray were compared with those of an F1 valve tray with a similar porosity.The results of efficiency experiments show that the efficiency of the fixed rotary valve tray increases with the increasing of kinetic energy factor(F-factor)for lower F-factor and decreases for higher F-factor for certain constant liquid-phase spray densities.The efficiency of fixed rotary valve tray is obviously higher than that of the F1 valve,and the differences are more obvious for higher F-factors.The fixed rotary valve tray owns the better operating performances and higher handling capacity when compared with F1 valve tray.The results of gas hold-up fraction distributions show that the average gas hold-up fraction αG of both the fixed rotary valve tray and the F1 valve tray increases gradually with the increasing of F-factor,and the values for the former are about 10.48% higher than the later.The gas hold-up fraction uneven index Ergas of the two kinds of tray increases gradually with the increasing of the F-factor and the Ergas of the former is lower than that of the later,and the differences strengthened with the increasing of F-factor.The αG of both trays increases with the increasing of the height of the position on tray for certain constant height of liquid layer and gas load.The αG of the fixed rotary valve tray is about 12.2% higher than that of the F1 valve tray for occasions with the height of the location on tray higher than 35 mm.Meanwhile,the Ergas of both trays is gradually decreased with the increasing of the height of the location on tray,and tended to be stable.Wings of the fixed rotary valve performed a strong guiding effect,which formed the rotary flow field among valves and avoided the direct hedge of the gas flows from neighbor valves,and consequently increased the gas residence time in the liquid layer and strengthened the degree of turbulence of the gas-liquid field,and finally improved the average gas hold-up fraction and distribution uniformity in the liquid layer.Generally,the mass transfer performance and local gas hold-up fraction distributions of the fixed rotary valve tray are investigated and conclusions are arrived.The efficiency of fixed rotary valve tray is higher than that of F1 valve,and the differences are more obvious for higher F-factor.The fixed rotary valve tray owns better operating performances and higher handling capacities when compared with F1 valve tray.The interactions of the wings and valve cover,which formed a rotary flow field among valves,improved the average gas hold-up fraction and distribution uniformity in the liquid layer on tray.