Liquid distribution and its effect on local mass transfer in a packed column of Pall rings

The spatial variations of liquid distribution and local mass transfer coefficient in a 0.30-m column of 25.4-m Pall rings were investigated. The data of liquid distribution was collected with a 39-cell liquid collector and a wall-flow tube from a doubled-wall section in the column at the packing-support level. The local mass transfer coefficients were measured via the electrochemical technique by individual cathodic nickel-coated Pall rings placed at various spatial positions. Both measurements were conducted at various fluid flow rates with three liquid distributor designs at different bed heights. Liquid distribution and local mass transfer coefficients observed were far from uniform in the column. The wall flow developed along the packed bed until a fully developed flow pattern was reached. With more uniform initial liquid distribution, the less packing height needed to reach the fully developed flow pattern along with higher the mass transfer efficiency in the column. Ladder-type liquid distributor (LLD) showed less angular effect in measurements. Increasing the liquid flow rate slightly improved the uniformity of liquid distribution and enhanced the mass transfer. No influence of gas flow rate on liquid distribution and mass transfer coefficient was found at the range of gas flow rates used. These gas flow rates were much lower than the loading point. Liquid maldistribution factor and mass transfer maldistribution factor decreased with increases in the uniformity of the initial liquid distribution. These values were 0.21(0.48). 0.16(0.26) and 0.14(0.22) for single-point liquid distributor (SPLD), cross-type liquid distributor (CLD) and LLD, respectively. By comparison, a good agreement was observed on the relation of liquid maldistribution factor and mass transfer maldistribution factor.

Liquid distribution and its effect on local mass transfer in a packed column of Pall rings

The spatial variations of liquid distribution and local mass transfer coefficient in a 0.30-m column of 25.4-m Pall rings were investigated. The data of liquid distribution was collected with a 39-cell liquid collector and a wall-flow tube from a doubled-wall section in the column at the packing-support level. The local mass transfer coefficients were measured via the electrochemical technique by individual cathodic nickel-coated Pall rings placed at various spatial positions. Both measurements were conducted at various fluid flow rates with three liquid distributor designs at different bed heights. Liquid distribution and local mass transfer coefficients observed were far from uniform in the column. The wall flow developed along the packed bed until a fully developed flow pattern was reached. With more uniform initial liquid distribution, the less packing height needed to reach the fully developed flow pattern along with higher the mass transfer efficiency in the column. Ladder-type liquid distributor (LLD) showed less angular effect in measurements. Increasing the liquid flow rate slightly improved the uniformity of liquid distribution and enhanced the mass transfer. No influence of gas flow rate on liquid distribution and mass transfer coefficient was found at the range of gas flow rates used. These gas flow rates were much lower than the loading point. Liquid maldistribution factor and mass transfer maldistribution factor decreased with increases in the uniformity of the initial liquid distribution. These values were 0.21(0.48). 0.16(0.26) and 0.14(0.22) for single-point liquid distributor (SPLD), cross-type liquid distributor (CLD) and LLD, respectively. By comparison, a good agreement was observed on the relation of liquid maldistribution factor and mass transfer maldistribution factor.

The flow and mass transfer characteristics of concentric gas-liquid flow in an advanced static mixer

The fluid dynamic and mass transfer characteristics of concentric upward gas-liquid flow were studied in the industrial static mixer with four equally spaced helical inserts (FKSM). The numerical simulations of gas volume fraction in Kenics mixer had a good agreement with the numerical and experimental results provided by Rabha et al. The characteristics of radial gas void fraction and local mass transfer coefficients in the FKSM were evaluated under different operating conditions. The velocity profiles of concentric air phase accelerated by the bubble forces firstly became sharp and narrow until z/l=-3.27 and then slowly decreased and stabilized at z/l=-1.5 before entering the first mixing element. Some extra unimodal profile of radial gas holdup gradually generated near the rectangle cross sections of mixing elements. The ?G gradually enlarged from r/R=0.2 to r/R=0.55 and then weakened from r/R=0.65 to r/R=0.874. The air void fractions in the bulk flow region decreased with the increasing initial uniform bubble diameter. The inlet effect of first leading edge enhanced the air phase dispersion and local mass transfer coefficients sharply increased from 2.04 to 3.69 times of that in the inlet. The local mass transfer coefficients in each mixing group had unimodal profiles.