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Faïçal Larachi - One of the best experts on this subject based on the ideXlab platform.
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prospect of open cell solid foams for floating platform Multiphase Reactor applications maldistribution susceptibility and hydrodynamic behavior
Chemical Engineering Journal, 2018Co-Authors: Amir Motamed Dashliborun, Alexander Fussel, Faïçal LarachiAbstract:Abstract Open-cell solid foams are tested for the first time as prospective structured packings in floating columns to evaluate their potential for offshore Multiphase Reactor applications. Using a hexapod ship motion simulator and low-intrusive wire-mesh sensors, the effect of floating vessel motions on the hydrodynamic behavior of SiSiC foam packed beds operated with concurrent descending gas-liquid flow was comprehensively investigated. The response of gas-liquid distribution, overall bed pressure drop, and liquid axial dispersion to column tilts as well as translational and rotational motions was acquired and compared to their corresponding stationary (onshore) analog configuration. Maldistribution sensitivity and susceptibility of solid-foam packed beds subject to ship tilts and accelerations were interpreted in terms of fluid uniformity factor. Moreover, a stimulus-response tracer pulse technique and a macro-mixing model were used to estimate the liquid mean residence time and Peclet number. Similar to random packings, fluid maldistribution was found to prevail in solid-foam beds with deviations from uniformity greater for rotational than for translational perturbations. Vessel tilts and oscillations adversely affect open-cell foam bed hydrodynamic performance yielding transient gas-liquid segregated flow regimes, oscillations of pressure drop and uniformity factor, as well as notable deviation from liquid plug flow.
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concept of bifunctional redox iron chelate process for h2s removal in pulp and paper atmospheric emissions
Chemical Engineering Science, 2003Co-Authors: Ion Iliuta, Faïçal LarachiAbstract:Utilization of ferric chelates for the oxidation of hydrogen sulfide is beneficial from the standpoint of iron-sequestration and protection against precipitation in the alkaline environments characteristic of the Kraft mill effluents. Availability of oxygen along with hydrogen sulfide in the atmospheric emissions of pulp and paper industries is beneficial for the simultaneous Redox regeneration from ferrous to ferric chelates. By putting together these two premises, the concept of a multifunctional Redox process for the scrubbing of hydrogen-sulfide-contaminated atmospheric effluents emanating from the Kraft mills is formulated, modeled and simulated. This paper discusses from a Multiphase Reactor engineering perspective, the design of a countercurrent packed-bed bifunctional scrubber by setting an exhaustive modeling framework in which are solved both the oxidation of hydrogen sulfide in reactive ferric chelate solutions of ethylenediaminetetraacetic acid (EDTA chelate) and the simultaneous oxidative regeneration of ferrous chelates resulting from oxidation of hydrogen sulfide. A one-dimensional model based on the transient species balance equations in the gas and liquid phases coupled with the transient film model according to the film-penetration theory was developed for the description of the time and space evolution of the species concentrations along the scrubber. The oxidative regeneration of the ferrous chelate showed a synergistic effect resulting in increased enhancement factor for the hydrogen sulfide oxidation. Availability of plenty of oxygen in the atmospheric effluent precluded starvation of the ferric form and maintained high reaction rates of hydrogen sulphide removal along the whole Reactor length.
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Multiphase catalytic Reactors a perspective on current knowledge and future trends
Catalysis Reviews-science and Engineering, 2002Co-Authors: M P Dudukovic, Faïçal Larachi, P L MillsAbstract: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...
J Jaap C Schouten - One of the best experts on this subject based on the ideXlab platform.
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gas liquid mass transfer in a rotor stator spinning disc Reactor
Chemical Engineering Science, 2010Co-Authors: Van Der John J Schaaf, Marco M Meeuwse, Bfm Ben Kuster, J Jaap C SchoutenAbstract:Abstract This paper describes a new Multiphase Reactor, the rotor–stator spinning disc Reactor, which shows high rates of gas–liquid mass transfer in comparison to conventional Multiphase Reactors. The volumetric gas–liquid mass transfer coefficient k GL a GL in the rotor–stator spinning disc Reactor increases with increasing rotational disc speed, due to the higher surface renewal rate caused by the increasing turbulence, and with increasing gas flow rate. Measured k GL a GL values are as high as 0.43 m L 3 m R - 3 s - 1 at 7.3 × 10 - 6 m 3 s - 1 gas flow and a rotational disc speed of 179 rad s - 1 , and are expected to increase even further at increasing rotational disc speed. This is twice as high as for conventional Reactors as bubble columns, in spite of the low gas holdup of 0.021 m G 3 m R - 3 with only one gas inlet. The volumetric mass transfer per unit volume of gas, k GL a GL / ɛ G , of 20.5 m L 3 m G - 3 s - 1 is 40 times higher than 0.5 m L 3 m G - 3 s - 1 for a bubble column.
Schouten J.c. - One of the best experts on this subject based on the ideXlab platform.
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A numerical study on gas–liquid mass transfer in the rotor–stator spinning disc Reactor
2015Co-Authors: Eeten, K.m.p. Van, Schaaf, John J Van Der, Verzicco R., Heijst, G.j.f. Van, Schouten J.c.Abstract:The gas–liquid mass transfer coefficient was investigated in a novel Multiphase Reactor: the rotor–stator spinning disc Reactor. Direct Numerical Simulations of the flow field around a single bubble in the Reactor showed that vortex stretching invoked the presence of turbulence inside the thin liquid film surrounding the bubble. The Direct Numerical Simulations further provided a measure for the eddy diffusivity in the thin liquid film caused by this increase in vorticity. An expression was subsequently derived from a mass balance using these eddy diffusivities in order to estimate the order of magnitude of gas–liquid mass transfer coefficients. These estimates were found to lie more in line with experimental results in literature than previously used mass transfer models based on Higbie׳s penetration theory
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Hydrodynamics and gas-liquid mass transfer in a horizontal rotating foam stirrer Reactor
2013Co-Authors: Leon Matheus, Schaaf Van Der, J., Bieberle A., Hampel U., Maas R.j., Schubert M., Nijhuis T.a., Schouten J.c.Abstract:This paper describes a new Multiphase Reactor, the horizontal rotating foam stirrer Reactor, which uses a donut-shaped foam block mounted on a horizontal shaft functioning as a stirrer and as a catalyst support. The effect of different operational conditions such as stirring speed, Reactor length, foam porosity, foam thickness and the presence of baffles on the gas–liquid mass transfer and the gas–liquid flow distribution is discussed for the systems water/air and glycerol/air. The rate of gas–liquid mass transfer is measured spectrometrically while the hydrodynamics of the Reactor is studied by ¿-ray tomography. For a partially filled Reactor, three flow states could be distinguished: the trickle state, the slosh state and the ring state. In the trickle state the liquid flows in a thin stream over the foam while in the slosh state the liquid is pushed upward by the stirrer and sprayed, leading to the formation of fine liquid droplets and fine gas bubbles. The transition between the trickle state and the slosh state occurs at 200 rpm. This is drastically affected by the liquid viscosity and in some extent by the Reactor length and the foam thickness. When the stirring speed is constant, the ring state, which results in a cylindrical liquid layer on the inside wall, appears with increasing the liquid content in the Reactor (above 70%). Due to a large gas–liquid interface in the slosh state, a high gas–liquid mass transfer is achieved. kGLaGL values up to 0.32 s-1 are found. This is comparable to gas–liquid mass transfer rates in slurry Reactors. However, in case of the foam stirrer a higher power input per liquid volume is needed in order to achieve the minimum stirrer speed required for complete dispersion of the gas. It is shown that mass transfer coefficients decreased with increasing viscosity, while the centrifugal force revealed to be effective in enhancing mass transfer in a viscous media. Conclusions on the optimal Reactor configuration are drawn for the application in the fine chemical industry
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Liquid-liquid mass transfer in a rotor-stator spinning disc Reactor
2012Co-Authors: Visscher F., Schaaf Van Der, J., Croon, De M.h.j.m., Schouten J.c.Abstract:The liquid–liquid flow behaviour and mass transfer rates for a rotor–stator spinning disc Reactor are reported. The measured mass transfer rate is at least 25 times higher compared to packed column. This makes that the rotor–stator spinning disc Reactor is a promising Multiphase Reactor
Rosa M Quintaferreira - One of the best experts on this subject based on the ideXlab platform.
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assessment of cfd euler euler method for trickle bed Reactor modelling in the catalytic wet oxidation of phenolic wastewaters
Chemical Engineering Journal, 2010Co-Authors: Rodrigo J G Lopes, Rosa M QuintaferreiraAbstract:A Multiphase volume of fluid (VOF) model was developed to provide a more detailed understanding of the transient behavior of a laboratory-scale trickle-bed Reactor. The gas−liquid flow through a catalytic bed of spherical particles was used to compute velocity field and liquid volume fraction distributions considering interfacial phenomena as well as surface tension effects. The computational model was used to simulate the catalytic wet air oxidation of a phenolic model solution in the Multiphase Reactor. Several runs were carried out under unsteady-state operation to evaluate the dynamic performance addressing the total organic carbon concentration and temperature profiles. In all runs, some level of backmixing was predicted, being lower at high operating temperatures. These axial concentration profiles were then correlated with the radial ones revealing a poor radial mixing for the simulated flow regime, namely, at the hot spots. The influence of the operating temperature on the thermal profiles illustr...
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turbulence modelling of Multiphase flow in high pressure trickle bed Reactors
Chemical Engineering Science, 2009Co-Authors: Rodrigo J G Lopes, Rosa M QuintaferreiraAbstract:Abstract Computational fluid dynamics (CFD) has been used as a successful tool for single-phase Reactors. However, fixed-bed Reactors design depends overly in empirical correlations for the prediction of heat and mass transfer phenomena. Therefore, the aim of this work is to present the application of CFD to the simulation of three-dimensional interstitial flow in a Multiphase Reactor. A case study comprising a high-pressure trickle-bed Reactor (30 bar) was modelled by means of an Euler–Euler CFD model. The numerical simulations were evaluated quantitatively by experimental data from the literature. During grid optimization and validation, the effects of mesh size, time step and convergence criteria were evaluated plotting the hydrodynamic predictions as a function of liquid flow rate. Among the discretization methods for the momentum equation, a monotonic upwind scheme for conservation laws was found to give better computed results for either liquid holdup or two-phase pressure drop since it reduces effectively the numerical dispersion in convective terms of transport equation. After the parametric optimization of numerical solution parameters, four RANS Multiphase turbulence models were investigated in the whole range of simulated gas and liquid flow rates. During RANS turbulence modelling, standard k – e dispersed turbulence model gave the better compromise between computer expense and numerical accuracy in comparison with both realizable, renormalization group and Reynolds stress based models. Finally, several computational runs were performed at different temperatures for the evaluation of either axial averaged velocity and turbulent kinetic energy profiles for gas and liquid phases. Flow disequilibrium and strong heterogeneities detected along the packed bed demonstrated liquid distribution issues with slighter impact at high temperatures.
Van Der John J Schaaf - One of the best experts on this subject based on the ideXlab platform.
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gas liquid mass transfer in a rotor stator spinning disc Reactor
Chemical Engineering Science, 2010Co-Authors: Van Der John J Schaaf, Marco M Meeuwse, Bfm Ben Kuster, J Jaap C SchoutenAbstract:Abstract This paper describes a new Multiphase Reactor, the rotor–stator spinning disc Reactor, which shows high rates of gas–liquid mass transfer in comparison to conventional Multiphase Reactors. The volumetric gas–liquid mass transfer coefficient k GL a GL in the rotor–stator spinning disc Reactor increases with increasing rotational disc speed, due to the higher surface renewal rate caused by the increasing turbulence, and with increasing gas flow rate. Measured k GL a GL values are as high as 0.43 m L 3 m R - 3 s - 1 at 7.3 × 10 - 6 m 3 s - 1 gas flow and a rotational disc speed of 179 rad s - 1 , and are expected to increase even further at increasing rotational disc speed. This is twice as high as for conventional Reactors as bubble columns, in spite of the low gas holdup of 0.021 m G 3 m R - 3 with only one gas inlet. The volumetric mass transfer per unit volume of gas, k GL a GL / ɛ G , of 20.5 m L 3 m G - 3 s - 1 is 40 times higher than 0.5 m L 3 m G - 3 s - 1 for a bubble column.