Mass-transfer correlations developed during the last several decades for packed column used for industrial fractionation, adsorption, etc. are reviewed. Theoretical basis and applicability of the reviewed correlations are discussed and compared concisely. Some dominant correlations and their parameters, as well as some considerations for further improvement, are also summarized and discussed.

Review of Mass-Transfer Correlations for Packed Columns*

Rate-based calculations for trayed and packed columns offer process engineers a more rigorous and reliable basis for assessing column performance than the traditional equilibrium-stage approach, especially for multicomponent separations. Although the mathematics, thermodynamics, and transport-related physics upon which nonequilibrium separations theory is founded are generally true, it is also true that rate-based simulations today suffer from a serious weakness—they are ultimately tied to underlying equipment performance correlations with questionable predictive capability. In the case of packed columns operated countercurrently, correlations are required for the mass-transfer coefficients, kx and ky, for the specific area participating in mass transfer, am, for the two-phase pressure drop, (Δp/Z)2ϕ, and for the flood capacity of the column. In particular, it is generally well known that packing mass-transfer correlations available in the public domain are unreliable when they are applied to chemical systems and column operating conditions outside of those used to develop the correlations in the first place. For that reason, we undertake the development of dependable, dimensionally consistent, correlating expressions for the mass-transfer-related quantities kx, ky, and am for metal Pall rings, metal IMTP, sheet metal structured packings of the MELLAPAK type, and metal gauze structured packings in the X configuration, using a new data fitting procedure. We demonstrate the superior performance of these correlations for a wide range of chemical systems and column operating conditions, including distillations as well as acid gas capture with amines. Further, we show that these new correlations lead to predictions for the relative interfacial area participating in mass transfer that can be greatly in excess of the geometrical surface area of the packing itself. © 2011 American Institute of Chemical Engineers AIChE J, 2012

New mass-transfer correlations for packed towers

A comprehensive total reflux distillation study of sheet metal structured packings was carried out with the cyclohexane/n-heptane test mixture. The experiments covered a wide range of pressures, two corrugation angles, two surface areas, and two surface designs. Experimental results include pressure drop, capacity, and mass-transfer efficiency. The database generated has been used to evaluate generalized performance models developed independently at The University of Texas Separations Research Program (SRP model)) and at Delft University of Technology (Delft model). This paper reports the experimental results and compares them with predictions from the two models. Deviations of predictions from measurements are discussed in terms of likely contacting mechanisms in the packed bed.

Structured packing performance-experimental evaluation of two predictive models

https://hal.archives-ouvertes.fr/hal-00920822/document

Mass transfer and liquid hold-up determination in structured packing by CFD

Although the structured packing is a well established gas–liquid contacting device, the understanding of its function is insufficient and often leads to poor exploitation of the available phase separating potential. This is a consequence of a rather superficial approach to modelling the packing performance through the years resulting in a lack of information on the nature and extent of interaction between counter-currently flowing gas and liquid phases and the micro and macro geometry of a rather ordered structure with a pronounced flow discontinuity at the transition among packing elements. This paper addresses the relation between the fluid-dynamics imposed by packing geometry and the mass transfer efficiency, and introduces a performance prediction method which does not require packing specific constants to describe mass transfer coefficients of phases.

A corrugation geometry based model for efficiency of structured distillation packing

The foundations have been laid out for estimating design parameters in ordered packing materials based on fluid mechanics and mass transfer without any adjustable parameters. Design parameters for heat- and mass-transfer processes over ordered packing materials can be estimated using the knowledge developed on the study of flow patterns and velocity parameters for thin viscous films over complex surfaces. Velocity profiles can be integrated to calculate liquid holdup and interfacial areas. The effect of the size of the structured packing as well as liquid properties on these parameters was explored. Flow visualization experiments were performed to determine the path followed by tracer particles in the liquid film flowing over the inclined corrugations of a packing element. Contact times for tracer particles to travel one wave of the packing element can be evaluated using the packing geometry and the path followed by the particles. Mass-transfer coefficients for the liquid phase were estimated using a pene...

Fundamental Liquid Flow Correlations for the Computation of Design Parameters for Ordered Packings

The flow of thin viscous films over complex surfaces is relevant to the description of heat- and mass-transfer processes over ordered packings. This work focuses on the gravity-induced bulk spreading of a liquid point source over periodic surfaces. This simulates the flow from a drip point over ordered packings in packed beds. Experimental observations indicate that in the absence of contact lines, for corrugations normal to the vertical, the liquid film adopts a shape similar to a Gaussian distribution as it spreads down the solid surface. For this type of flow, a viscous long-wave-type approximation was used to derive a film evolution equation. The film evolution equation retains all three possible driving forces, i.e., components of gravity normal and tangent to the solid surface and capillarity. Agreement between experimental and predicted film thicknesses is seen to be quite good. Experimental data are given also on flow over complex surfaces with corrugations inclined with respect to the vertical.

Spreading of a Liquid Point Source over a Complex Surface

The spreading of a wetting liquid introduced as a distributed source over solid surfaces has many interesting practical applications in heat and mass transfer contacting devices. The work analyzes the spreading of liquid over inclined flat surfaces. The study is the first of a program designed to understand the development of film flows from drip points over ordered packing in packed beds used in heat and mass transfer applications. The free surface of the liquid stream introduced as a point source retains a shape similar to a Gaussian or exponential distribution as it spreads down the solid surface, increasing the surface area as well as distribution of flow over the surface. The three-dimensional flow field, described using a 3D vector potential function, satisfies continuity and the first-order terms of the Navier-Stokes equations in the main direction of flow and in the direction normal to the main direction of flow. A viscous long-wave approximation was used to derive a film evolution equation and the kinematic boundary condition at the free surface. Experiments were carried out with fluids of two different viscosities and at varying inclination angles of the solid surface

Sanat Shetty

Papers

Fundamental Liquid Flow Correlations for the Computation of Design Parameters for Ordered Packings

Spreading of a Liquid Point Source over a Complex Surface

Spreading of liquid point sources over inclined solid surfaces