Axial mixing in modern packings, gas, and liquid phases: II. Two‐phase flow

Abstract

Axial mixing measurements of air and water under two-phase flow conditions were ( ) made in a large-scale packed column 0.43 m diameter using tracer experiments. Part I of this article dealt with single-phase mixing in the same column, with the same internals. Four packings were studied: 25.4-mm ceramic Raschig rings, 25.4-mm metal Pall rings, Sulzer BX structured packing, and Flexipac 2 structured packing. Air and water flowed countercurrently through the column at atmospheric pressure and at gas rates ®arying from 0.25 kgrm 2 ؒ s up to the flooding point, and liquid rates from 3.25 to 8.5 kgrm 2 ؒ s. A diffusion-type model ser®ed to reproduce the experimental response cur®es obtained for both phases. The results confirmed pre®ious obser®ations for first-generation packings: axial mixing in the gas increases with both gas and liquid rates, whereas liquid-phase axial mixing is a decreasing function of liquid rate and is insensiti®e to gas rate up to the flooding point. It was also found that the BX packing produces the least mixing in both phases. The largest mixing effects in the gas phase are found for the Raschig rings, and the largest mixing effects for the liquid phase are found for Flexipac 2. Correlations were de®eloped to reproduce the results, yielding an a®erage " 22% difference between experimental and correlated data.

Advanced absorber heat integration via heat exchange packings

“…Axial dispersion may be ignored provided the dispersive Bodenstein number is large. Macias‐Salinas and Fair 41 reported Bodenstein numbers on the order of 10–100 at gas and liquid flowrates relevant for CO 2 capture. Under these conditions, dispersive fluxes are much smaller than convective fluxes, and may safely be ignored. The total concentration of CO 2 in the liquid was tracked, including CO 2 bound in chemical form. The total equivalent concentration of MEA in the liquid was tracked, including unreacted and reacted MEA in its various ionic forms. As the thermal conductivity of the liquid is much greater than that of the gas, heat released or consumed by vaporization or condensation and liquid‐phase chemical reactions were included as source/sink terms for the liquid phase only 21 …”

Axial Mixing Effects in Packed Gas−Liquid Contactors

“…Bo g ) 0.0878Re g -0.8915 × 10 -0.00075Re l (d p a p ) 8.231 (7) Bo l ) 24.461Re l 0.5544 Ga -1/3 (d p a p ) The above correlations were developed from experimental data for 25.4 mm ceramic Raschig rings and 25.4 mm metal Pall rings (random packings) and Sulzer BX and Flexipac 2 (structured packings). They have been generalized by means of packing diameter (d p , d eq ), specific surface area a p , and corrugation angle θ. Dimensions of the packings may be found in standard handbooks.…”

“…The suitability of this approach, of course, depends on how valid the tracer measurements are under mass-transfer conditions. The model used here, based on the previous experimental work of the authors [6][7][8] as well as that of many others, is valid when relatively small amounts of solute are transferred. When there is significant mass transfer, as in distillation, the dynamic method of Linek et al 10 may be more appropriate.…”

“…The present authors have reported earlier on studies of axial mixing in a 0.43 m column with air and water flowing countercurrently. , A dynamic measurement technique was used to detect mixing effects; pulses of tracers were added to each phase, and dispersion of the pulses was related mathematically to mixing phenomena; the resulting dispersion parameters could be correlated with flow and geometry variables. A representative plot of dispersion in the gas phase is shown in Figure .…”

Liquid residence time distribution in the film flow monolith reactor

“…The residence time distribution (RTD) is a tool frequently used to understand and quantify the actual flow phenomena in chemical reactors. Significant work has been performed around the RTD behavior of trickle beds20–23 and, more recently, for structured packings 24–26…”