Gas-liquid downflow

Cocurrent gas-liquid downflow fixed-bed reactors trickle-bed reactors (TBR)... 

Consider a catalyst column consisting of randomly packed, spherical particles of a uniform size, dg, with cocurrent gas-liquid downflow. Under trickling flow conditions, a liquid film flows on the surface of the particles. The void space inside the bed is made up of small constrictions and relatively larger pore chambers. For such a constriction connected with a pore chamber above it, the interstitial gas velocity at the constriction, Ug, is greater than that at the pore chamber, ug1. Based on continuity considerations,... 

As mentioned earlier, the cocurrent gas-liquid downflow and, in particular, the trickle-flow operation is one of the most widely used three-phase operations in the hydroprocessing industry. The liquid holdup in such a reactor takes on added importance because it is usually low compared to the one for cocurrent upflow under similar flow conditions. Earlier we showed that the pressure drop in a trickle-bed reactor can be related to the liquid holdup. The effective catalyst wetting, as well as the thickness of the liquid film surrounding the catalyst particles, also depends strongly on the liquid holdup. 

Tabic 6-8 Experimental data av ailable in the literature Tor cocurrent gas-liquid downflow in packed beds12... 

Rao, V.G. Drinkenburg, A.A.H. A model for pressure drop in two-phase gas-liquid downflow... 

Gas-liquid downflow over fixed catalyst see trickle reactors. Section 16.11.6.15. 

Figure 4.2 Flow regimes in fixed-bed reactors under gas/liquid downflow conditions.

Bnrghardt, A., Bartehnns, G., Jaroszynski, M., and Kolodziej, A. (1995), Hydrodynamics and mass transfer in a three-phase fixed-bed reactor with cocnrrent gas-liquid downflow, The Chemical Engineering Journal and the Biochemical Engineering Journal, 58(2) 83-99. 

Gas-liquid downflow through fixed beds of catalyst particles is frequently selected in chemical reactor design. These trickle-bed reactors are often applied to perform strong exothermic reactions as the hydrogenation of unsaturated hydrocaabons [1]. At the present, steady state operation in the trickle flow regime is most common in industrial applications. 

Blok JR. Varkevisser J, Drinkenburg AAH. Transition to pulsing flow, holdup and pressure drop in packed columns with cocurrent gas-liquid downflow. Chem. Eng. Sci. 1983 38 687. 

Rao VG, Drinkenburg AAH. Solid-liquid mass transfer in packed beds with cocurrent gas-liquid downflow. AIChE J. 1985 31 1059. 

Rode SN, Midoux N, Latifi MA, Storck A. Hydrodynamics and liquid-solid mass transfer mechanisms in packed beds operating in cocurrent gas-liquid downflow an experimental study using electrochemical shear rate sensors. Chem. Eng. Sci. 1994 49 1383. 

J. Flow Patterns and Pulsation Properties of Cocurrent Gas-Liquid Downflow in Packed Beds. Chem. Eng. Japan 6 (1973) 315-319. 

Hirose, T.M., Y. Mori and Y. Sato, "Liquid-to-Particle Mass Transfer in Fixed Bed Reactor with Cocurrent Gas-Liquid Downflow", J, of Chem, Eng. Japan (1976) 220-224. 

Midoux, N, N, Favier and J.C, Charpentier, "Flow Pattern, Pressure Loss and Liquid Holdup Data in Gas-Liquid Downflow Packed Beds with Foaming and Non-foaming Hydrocarbons", Jo Chem. Eng, Japan, (1976) 350-355. 

It Is known that In some trickle flow systems. Incomplete catalyst contacting, axial dispersion, and external mass transfer limitations do occur. Studies using this same approach could be used to examine a wider variety of systems. Including In particular, reactions In which extremely high conversion, > 99% Is desired. This approach may also be useful In establishing the conditions, if any, under which a reactor might better be designed as a packed bed in gas/llquld upflow rather than in trickle flow (gas/liquid downflow). 

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