Axial mixing and mass transfer in gas-liquid Karr columns

Abstract

The axial mixing and mass-transfer characteristics of a Karr column when used as a cocurrent, gas-liquid contactor were experimentally determined. The liquid-phase backmixlng is extremely small, and the plug flow can be safely assumed in this column over the ranges 0.6 cm/s < VL < 4.34 cm/s, 0.7 cm/s < Vg < 5 cm/s, and 1.8 cm/s < AF < 7.5 cm/s. Over the same ranges, the liquid-side volumetric mass-transfer coefficient kLa was found to increase significantly with an increasing liquid velocity, gas velocity, or speed of plate reciprocation. The effect of the liquid flow rate is particularly strong because of its simultaneous, favorable influence on the liquid-side coefficient kL and the interfacial area a. Both the speed of plate reciprocation and the gas flow rate were found to have a highly adverse effect on kL. Satisfactory correlations of kLa and of kL based on the liquid velocity at the orifices of the plates are presented.

Characteristics of a countercurrent reciprocating plate bubble column. II. Axial mixing and mass transfer

“…Some of these effects, such as axial non-uniformity and turbulence, are well-known; a new effect for which there is some evidence is that of the clustering of the dispersed (air) phase around the reciprocating plates at high agitation. Under the present conditions, axial mixing was found to have a negligible effect upon mass transfer, confirming the earlier observations of Yang et al (1986). 0.20 to 0.5 Unagitated bubble columns, Akita (1965) 7.7-60 cm dia.…”

“…Recent data by Yang et al (1986) for cocurrent conditions show the same upwards trend with agitation as the present data, but there is no increase of E, at zero agitation. Single phase data by Hafez et al (1979) (dotted/dashed line on Figure 2) from a 15 cm diameter KRPC do show the same form as the present data but are generally lower.…”

“…The liquid-phase axial Peclet numbers based on the 94 cm length (T1 to V2) were in the range 10-60 so conditions were close to plug flow. A similar conclusion was reached by Yang et al (1986) from their results under cocurrent conditions in a 5 cm column. However, it should be kept in mind that as bubble columns are scaled up in diameter, the values of E, will increase to the point where axial mixing can become important.…”

“…A slightly adjusted form of Equation (17) in which the preconstant is raised to 0.016 was compared with the present data and gave a standard deviation of 0.0105 s-'; the main reason for disagreement appeared to be that the effect of agitation was underestimated. However, the exponents of the two flow velocities obtained byYang et al (1986) and those given in Equation (16) are quite close. Comparison of measured values of kp with values calculated from Equation…”

“…Yang et al (1986) obtained the following equation from their data for cocurrent flow: in c.g.s. units).…”