Effective interfacial area in gas-liquid cocurrent downflow through packed beds

Multiphase catalytic reactors: a perspective on current knowledge and future trends

Abstract: Conventional and emerging processes that require the application of multiphase reactors are reviewed with an emphasis on catalytic processes. In the past, catalyst discovery and development preceded and drove the selection and development of an appropriate multiphase reactor type. This sequential approach is increasingly being replaced by a parallel approach to catalyst and reactor selection. Either approach requires quantitative models for the flow patterns, phase contacting, and transport in various multiphase reactor types. This review focuses on these physical parameters for various multiphase reactors. First, fixed-bed reactors are reviewed for gas-phase catalyzed processes with an emphasis on unsteady state operation. Fixed-bed reactors with two-phase flow are treated next. The similarities and differences are outlined between trickle beds with cocurrent gas–liquid downflow, trickle-beds with countercurrent gas–liquid flow, and packed-bubble columns where gas and liquid are contacted in coc...

Gas}liquid interfacial mass transfer in trickle-bed reactors: state-of-the-art correlations

Abstract: The state-of-the-art of the gas-liquid mass transfer characteristics in trickle-bed reactors was summarized and its quantification methods were reevaluated based on a wide-ranging data base of some 3200 measurements. A set of three unified whole-flow-regime dimensionless correlations for volumetric liquid- and gas-side mass transfer coefficients, and gas–liquid interfacial area, each of which spanned four-order-of-magnitude intervals, were derived. The correlations involved combination of artificial neural networks and dimensional analysis. The dimensionless interfacial area, ShL and ShG were expressed as a function of the most pertinent dimensionless groups: ReL, ReG, WeL, WeG, ScL, ScG, StL, XG, MoL, FrL, Eom, Sb.

Heat and Mass Transfer in Cocurrent Gas−Liquid Packed Beds. Analysis, Recommendations, and New Correlations

Abstract: Meticulous inspection of the literature has unveiled the weakness of several empirical methods for predicting the macroscopic mass- and heat-transfer characteristics relevant to gas−liquid cocurrent downflow and upflow packed-bed reactors. In response, using a wide experimental database consisting of 5279 measurements for trickle beds (downflow) and 1974 measurements for packed bubble columns (upflow), a set of reliable correlations has been recommended for the prediction of the gas−liquid interfacial area (agl), the volumetric liquid- (kla) and gas-side (kga) mass-transfer coefficients, the wall (ηeklw) and bed (ηekls) liquid−solid mass-transfer coefficients, the wall heat-transfer coefficient (hw), the bed effective radial thermal conductivity (λe), and the particle-to-fluid heat-transfer coefficient (hp). Some of these correlations are from the literature, and others have been developed by combining artificial neural networks and dimensional analysis. The accuracy of the proposed correlations surpasses...

Gas-liquid interfacial mass transfer in trickle-bed reactors at elevated pressures

Abstract: A phenomenological description and a semiempirical two-zone model are proposed for the gas−liquid interfacial areas and the volumetric liquid-side mass-transfer coefficients in cocurrent downflow t...

A comparative study of mass transfer coefficients of reduced volatile sulfur compounds for biotrickling filter packing materials

Abstract: Biofiltration is a cost-effective technology for reduction of odor emissions from intensive pig production, but removal of volatile sulfur compounds may be limited by low mass transfer. Among these volatile sulfur compounds, hydrogen sulfide and methanethiol are essential odorants emitted from animal houses according to the low odor threshold values. In order to get a better understanding of the limitations for optimization and further development of biofiltration for odor control, a study of overall mass transfer coefficients of volatile sulfur compounds for packing materials potentially used for biotrickling filters is presented. Mass transfer coefficients were obtained by taking advantage of online PTR-MS experiments of breakthrough curves, combined with a developed mass transfer model. The experiments were performed at different air and liquid velocities for selected packing materials. The results demonstrate that the overall mass transfer coefficients of volatile sulfur compounds depend on the velocity of both air and liquid. When the mass transfer coefficients are normalized to (divided by) the corresponding pressure drop, the results indicate that the filter packed with ceramic saddles or cellulose pads have higher normalized mass transfer coefficients, compared to the other materials investigated in this study. Correlating the mass transfer coefficients to characteristics of different packing materials did not succeed and as an alternative empirical relationship between mass transfer coefficients and the gas and liquid velocities were established.

Hydrodynamics of two-phase cocurrent downflow through packed beds. Part I. Macroscopic model

Abstract: Pressure drop and liquid saturation are two important design parameters in cocurrent gas-liquid downflow through packed beds. A macroscopic model based on momentum balance is formulated for the condition of no radial pressure gradients. The model includes the effect of bubble formation on the pressure drop and holdup and is compared with the experimental data of the earlier investigators and of the present study. The model provides a functional form for correlating pressure drop and liquid saturation but some parameters have to be determined by fitting the experimental data.

Interfacial area and boundary of hydrodynamic flow region in packed column with cocurrent downward flow.

Abstract: Liquid holdup and interfacial areas were measured in packed columns with cocurrent downward flow. An empirical equation of liquid holdup Φt is presented in terms of Reynolds numbers of gas Reg(=dsGg/μg) and liquid Rel, surface shape factor of packing φ, void fraction e and ratio of packing to column diameter dp/T, where the ratio is smaller than 0.13. This equation is different for the dispersed bubble flow and other flow regions. The empirical equation of interfacial area ap in the respective flow regions varies as follows: apdp/(1-Φl/e)=ωΦ-mRenlReqg(dp/T)-twhere ω=7.5×10-5, m=Q.2, n=Q.15, q=2/3, t=2.5 for spray flow; ω=2.2×10-4, m=0.3, n=2/3, q=0.2, t=2.5 for pulse flow; ω=3.9×10-3, m=0.1, n=0.4, q=p. t=2 for trickle flow; ω=2.8×10-7, m=0.9, n=1.8, q=0, t=3.3 for dispersed bubble flow. The equation of the boundary in the respective flow regions was found by equating the two of them. The predicted boundaries are in excellent agreement with the literature data given from the analysis of liquid pulse frequencies. The predictions for interfacial areas also agree well with the literature data.

Flow pattern of the phases and liquid saturation in gas‐liquid concurrent downflow through packed beds

Abstract: Flow pattern was visually observed for non-foaming and foaming Newtonian and non-Newtonian liquids under concurrent downflow with air in packed beds using different configurations of column geometry and packins. Flow maps delineating the different flow regions were presented based on the present study as well as that of earlier investigations. The total and dynamic liquid saturation were experimentally measured and correlations were presented in terms of (i) the Lockhart-Martinelli parameter, χ, and (ii) the flow variables. On a observe de maniere visuelle les profils d'ecoulement pour des liquides newtoniens ou non newtoniens, moussants et non moussants, dans le cas d'un acoulement descendant de liquides et d'air dans un lit a garnissage. On a fait varier la gaomatrie de la colonne et le garnissage. Les diagrammes d'ecoulement delimitant les differentes regions d'ecoulement, presentes dans cette etude, s'appuient sur le travail actuel ainsi que sur des recherches anterieures. On a mesure de maniere experimentale la saturation du liquide dynamique et to tale, et les correlations sont presentes en fonction (i) du parametre Lockhart-Martinelli, χ, et (ii) des variables d'ecoulement.