Trickle Flow Research Articles

Extrudate Trilobe Catalysts and Loading Effects on Pressure Drop and Dynamic Liquid Holdup in Porous Media of Trickle Bed Reactors

The hydrodynamics of concurrent gas-liquid downflow through a porous media of fixed bed reactor has been studied experimentally in a range of trickling flow rates. A pilot bed is packed with industrial spherical and extrudate trilobe catalysts. The industrial trilobe catalysts are packed in a bed using two different methods: random close or dense packing and random sock packing. The experiments are performed for single phase in the cases of wet and dry packed beds and for two-phase flow conditions. The comparisons of pressure drops as well as liquid holdup are carried out for the above three different porous media, random close, dense packing and random sock packing. It is shown that the pressure drop of the dense loaded bed is higher than that of spherical particles which have approximately the same porosity. The results also revealed that the bed porosity, shape and contact points of the loaded catalyst have significant effects on the dynamic liquid holdup of the TBRs. Finally, a new correlation was developed for dynamic liquid holdup and pressure drop calculation for trilobe dense and sock catalyst beds and beds which are loaded with spherical particles.

Trickle Flow Behaviors of Liquid Iron and Molten Slag in the Lower Part of Blast Furnace

Trickle Flow Behaviors of Liquid Iron and Molten Slag in the Lower Part of Blast Furnace

Eulerian simulation of heat transfer in a trickle bed reactor with constant wall temperature

This paper reports a study of steady-state heat transfer of gas and liquid flowing through a packed bed with spherical particles of 2.06mm and constant wall temperature with Computational Fluid Dynamics (CFDs). The effect of gas and liquid flow rates on heat transfer in packed beds are discussed. The effective radial bed conductivity (λer) is calculated based on the steady-state two dimensional model. The results of the CFD simulations have been validated with experiments and they are in a good agreement. For most of the cases the results of the CFD simulations deviate from the experimental results not more than 10%. The results show that the effective radial bed conductivity increases with increase of the velocity of gas and liquid. In trickle flow regime the effective radial bed conductivity is much bigger than in a dry gas flow regime.

CFD simulation and experimental study of liquid flow mal-distribution through the randomly trickle bed reactors

A numerical model for liquid mal-distribution in randomly trickle bed reactors has been investigated and the results are compared with the experimental data. A CFD model based on the three-phase Eulerian approach is developed and a two-fluid model is utilized to perform the inter-phase momentum exchanges. Furthermore, radial distribution of the bed porosity is considered adjacent to the reactor wall. Two different types of liquid inlet distributors have been used in order to study the accuracy of the CFD model. To validate the CFD model, the simulation results are compared with the experimental data and the results from the porous media concept in which the permeability model has been applied to implement the inter-phase momentum exchange. Experimental results have been obtained on an industrial trilobe catalyst under a trickling flow regime in a pilot scale reactor setup. Co-current liquid and gas streams have entered to the reactor through a mono or multi orifice distributor. Results of the developed CFD model have found more accurate than that of the porous media concept when compared with the experimental data.

Hydrodynamic modeling on the external liquid–solid wetting efficiency in a trickling flow reactor

A three‐region model was proposed, which considers the bed cross section being composed of a stagnant liquid region, a liquid film region, and a rivulet flow region. To estimate the fractions of the three regions, the fraction of film flow was evaluated first, by transforming the complex trickling flow texture into pure liquid film flow. Through the measurements of liquid holdup and pressure drop for the film flow, a relationship between relative permeability and gas saturation was established, and from which the fraction of film flow region was obtained. It shows packing size is most important to the faction of rivulet flow. The external wetting efficiency of the packing was correlated as the sum of two‐third power of the liquid film fraction and the rivulet flow fraction, besides, a correlation based on Reynolds and Galileo numbers of the two phases in the form of was proposed. © 2012 American Institute of Chemical Engineers AIChE J, 59: 283–294, 2013

Trickle flow liquid–solid mass transfer and wetting efficiency in small diameter columns

AbstractA novel method to simultaneously measure liquid solid mass transfer and external wetting efficiency was employed at column to particle ratios of 10, 6 and 3. Two prewetting procedures representing the upper (Kan) and lower (Levec) hysteresis branches were used. For a multipoint distributor on a Kan prewetted bed wetting efficiency and the specific mass transfer coefficient were almost unaffected by column diameter. The multipoint distributor on a Levec prewetted bed exhibited a decrease in specific mass transfer with decreasing column diameter. Point source experiments resulted in significantly lower wetting and mass transfer measurements with an increasing trend with respect to decreasing column diameter. The results indicate that with proper distribution and prewetting, the effect of column diameter on averaged wetting and liquid–solid mass transfer is almost negligible, a powerful result considering the importance of these parameters on reaction experiments. © 2012 Canadian Society for Chemical Engineering

Computational Modeling of Trickle Bed Reactors

In this study, a three-dimensional Eulerian computational fluid dynamics (CFD) reactive flow model is developed for the trickle flow regime in a packed bed. The experimental study of porosity distribution in a bed of extrudates has been performed and then used to implement the local porosity values in the CFD computational grid. The reactive flow study addressed gas and liquid reactant limited systems. For each case a closed form approach of coupling the bed and particle scale solution within the CFD framework is presented. Model predictions achieved satisfactory agreement with experimental data for liquid holdup, wetting efficiency, and reactant conversion.

Residence time distribution, axial liquid dispersion and dynamic–static liquid mass transfer in trickle flow reactor containing β-SiC open-cell foams

Open-cell foams are a promising new support for gas–liquid contacting and heterogeneous catalysis. Using the Piston-Dispersion-Exchange model, axial dispersion and dynamic–static liquid mass transfer coefficient are estimated from residence time distribution responses measured under co-current down flow configuration.The specific morphological parameters and the high porosity involved within open-cell foams result in low Bodenstein numbers (0.05<Bo<0.2 for 2.5<Re<20) in comparison to conventional packed beds (0.2<Bo<0.7 for 5<Re<23). Furthermore, open-cell foam improves liquid mass transfer coefficient between the dynamic and the static zones under trickle flow conditions.

Trickle/pulse flow regime transition in downflow packed tower involving foaming liquids

The most of past studies in foaming trickle bed reactors aimed at the improvement of efficiency and operational parameters leads to high economic advantages. Conventionally most of the industries rely on frequently used gas continuous flow (GCF) where operational output is satisfactory but not yields efficiently as in pulsing flow (PF) and foaming pulsing flow (FPF). Hydrodynamic characteristics like regime transitions are significantly influenced by foaming nature of liquid as well as gas and liquid flow rates. This study?s aim was to demonstrate experimentally the effects of liquid flow rate, gas flow rates and liquid surface tension on regime transition. These parameters were analyzed for the air-aqueous Sodium Lauryl Sulphate and air-water systems. More than 240 experiments were done to obtain the transition boundary for trickle flow (GCF) to foaming pulsing flow (PF/FPF) by use excessive foaming 15-60 ppm surfactant compositions. The trickle to pulse flow transition appeared at lower gas and liquid flow rates with decrease in liquid surface tension. All experimental data had been collected and drawn in the form of four different transitional plots which are compared and drawn by using flow coordinates proposed by different researchers. A prominent decrease in dynamic liquid saturation was observed especially during regime transitional change. The reactor two phase pressure evident a sharp rise to verify the regime transition shift from GCF to PF/FPF. Present study reveals, the regime transition boundary significantly influenced by any change in hydrodynamic as well as physiochemical properties including surface tension.

Dynamic Modelling for a Trickle-Bed Reactor Using the Numerical Inverse Laplace Transform Technique

Abstract Experimental evaluation and dynamic modelling were presented for the transient behavior of a trickle bed reactor in which gas and liquid streams flow downwards through a bed of catalyst particles. One-dimensional dynamic mathematical model has been described to study the gas-liquid-solid process in which the gas phase (Ar) with the tracer (SO2) is treated as a continuum. The physical model has been analyzed, including the formulation of initial and boundary conditions and the description of the solution methodology. An experimental procedure to measure the concentrations of the tracer (SO2) has been performed. The concentration measurements for this tracer (SO2) were performed in a fixed be reactor on trickling flow of the gas phase for a range of operating conditions. The gas-liquid mass transfer (kgl) coefficient, liquid-solid mass transfer (kls) coefficient, gas holdup (hg) and partial wetting efficiency (fe) were chosen as the hydrodynamic parameters of the proposed mathematical model. Such parameters have been optimized with the experimental measurents of the tracer (SO2) at the exit of the trickle-bed reactor. The optimized parameters hg, kgl, kls and fe were calculated simultaneously using the equation (51) with minimization of the objective function. Results of the mathematical model was presented and compared to the two experimental cases. Each above parameters were correlated using empirical correlations.

Pressure Drop Hysteresis of Hydrodynamic States in Packed Tower for Foaming Systems

An experimental investigation was carried out to determine the effects of gas and liquid flow velocities and surface tension on the two-phase phase pressure drop a in a downflow trickle bed reactor. Water and non- Newtonian foaming solutions were employed as liquid phase. More than 240 experimental points for the trickle flow (GCF) and foaming pulsing flow (PF/FPF) regime were obtained for present study. Hydrodynamic characteristics involving two-phase pressure drop significantly influenced by gas and liquid flow rates. For 15 and 30 ppm air-aqueous surfactant solutions, two-phase pressure drop increases with higher liquid and gas flow velocities in trickle flow and foaming/pulsing flow regimes. With decrease in surface tension i.e. for 45 and 60 ppm air-aqueous surfactant systems, two-phase pressure drop increases very sharply during change in regime transition at significantly low liquid and gas velocities. © 2011 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Selective Hydrogenation of 1-Heptyne in a Mini Trickle Bed Reactor

The selective hydrogenation of 1-heptyne over a 2 wt % Pd/Al2O3 catalyst was studied in a trickle bed reactor operating in both batch recycle and continuous modes. The reaction was studied in a range of different solvents, including isopropanol, hexane, mixtures of these two solvents, and also isopropanol with small quantities of water and base (NaOH) added. It was found that the rate of reaction was fastest in hexane, owing to the higher hydrogen solubility in this solvent. However, the selectivity toward 1-heptene was higher in isopropanol, with over 95% selectivity being maintained for 120 min of the total 240 min reaction time. The addition of water or base led to an increase in reaction rate, possibly through modification of the adsorption equilibria at the catalyst surface or direct involvement in the reaction. The hydrodynamics of trickle flow upon the reaction were investigated, showing that increasing liquid flow rate led to enhancement of reaction rate, although a plateau was eventually reached ...

Parallel hydrogenation for the quantification of wetting efficiency and liquid–solid mass transfer in a trickle‐bed reactor

AbstractA novel method for the measurement of wetting efficiency in a trickle‐bed reactor under reaction conditions is introduced. The method exploits reaction rate differences of two first‐order liquid‐limited reactions occurring in parallel, to infer wetting efficiencies without any other knowledge of the reaction kinetics or external mass transfer characteristics. Using the hydrogenation of linear‐ and isooctenes, wetting efficiency is measured in a 50‐mm internal diameter, high‐pressure trickle‐bed reactor. Liquid–solid mass transfer coefficients are also estimated from the experimental conversion data. Measurements were performed for upflow operation and two literature‐defined boundaries of hydrodynamic multiplicity in trickle flow. Hydrodynamic multiplicity in trickle flow gave rise to as much as 10% variation in wetting efficiency, and 10–20% variation in the specific liquid–solid mass transfer coefficient. Conversions for upflow operation were significantly higher in trickle‐flow operation, because of complete wetting and better liquid–solid mass transfer characteristics. © 2010 American Institute of Chemical Engineers AIChE J, 2011.

Numerical simulation of reactive pulsing flow for the catalytic wet oxidation in TBR using a VOF technique

Guided by the intrinsic advantages of the dynamic nature of mass/heat transfer fluctuations in pulsing flow, here we performed volume-of-fluid (VOF) numerical simulations to evaluate how liquid flow modulations can improve the detoxification of liquid effluents by catalytic wet oxidation. First, prominent numerical parameters were optimized in terms of mesh aperture and time step. Second, the effect of oxidation temperature and the influence of gas and liquid flow rates have been investigated comparatively under different flow regimes. The VOF computations have correctly handled the experimental observations both in terms of the axial conversion and temperature. The increase of oxidation temperature was found to move the trickling and pulsing intersection point on the conversion toward the top of the trickle bed. Finally, in comparison with trickling flow regimes, these computed and experimental findings revealed a considerable improvement on the detoxification of organic matter highlighting the benefits of process intensification covered by the periodic liquid flow modulations. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Enantioselective hydrogenation of dimethyl itaconate with immobilised rhodium-duphos complex in a recirculating fixed-bed reactor

The catalytic hydrogenation of dimethyl itaconate was studied in lab-scale shake flask and transferred to continuous flow with recirculation in a trickle bed reactor. All experiments were performed under ambient conditions (20 °C and atmospheric pressure). The catalyst complex [Rh((R,R)-Me-DuPhos)(COD)]BF 4 was anchored to powder and trilobe alumina supports using phosphotungstic acid (PTA) as an anchoring agent. For the powder alumina, tests were conducted in the shake flask to ensure that the reaction was not influenced by mass transfer limitations by varying the stirrer speed and catalyst mass, thus ensuring the reported data are in the kinetic regime. In the shake-flask [substrate to catalyst molar ratio of 60, atmospheric pressure (101,317 Pa), room temperature (293.15 K), H 2 flow rate of 100 ml min −1 (1.7 × 10 −6 m 3 s −1) and agitation speed of 200 rpm], a turnover frequency (TOF) of 50 h −1 (1.4 × 10 −2 s −1) was achieved with powder alumina support in comparison to a TOF of 20 h −1 (5.6 × 10 −3 s −1) obtained with the trilobes. Under these conditions, the enantioselectivities obtained from immobilising the catalyst complex onto the powder and trilobe supports were 96% and 97%, respectively. Fitting Osborn–Wilkinson kinetics to the concentration profiles indicated that complexation with the olefin before reaction with hydrogen was the preferred path. The trickle bed reactor (TBR) was operated in the trickle flow regime using the trilobe support. Optimal gas and liquid flow rates were selected which were found to have a noticeable effect on initial reaction rate and enantioselectivity. Under optimized conditions in the TBR [substrate to catalyst molar ratio of 223, atmospheric pressure (101,317 Pa), room temperature (293.15 K), gas flow rate of 100 ml min −1 (1.7 × 10 −6 m 3 s −1) and liquid flow rate of 20 ml min −1 (3.3 × 10 −7 m 3 s −1)], 99% conversion and enantioselectivity of up to 99.9% were achieved.

CFD and experimental studies of reactive pulsing flow in environmentally-based trickle-bed reactors

Pulsing flow in trickle-bed reactors (TBRs) has been claimed to promote the averaged heat and mass transfer rates, thereby enhancing the overall conversion and productivity. In this work, we focused on the mineralization of organic matter by catalytic wet oxidation at different liquid flow modulations. The convective nature of the disturbances that lead to pulsing was simulated by an Eulerian Computational Fluid Dynamics (CFD) model and validated with experimental data. In order to evaluate the predicted effects of pulsing on reaction outcome, first the multiphase flow governing equations were detailed with the computational methodology used in the simulation procedure. Prominent numerical parameters were optimized in terms of mesh aperture and time step. Second, to enable objective assessments of the merits of the different cyclic strategies, several computational runs were performed addressing the effect of nominal gas and liquid flow rates as well as the oxidation temperature. Here, we found that the concentration profile computed by the CFD model for pulsing flow conditions demonstrated superior oxidation performance over the trickling flow regime, which has been further corroborated by experimental evidences. Afterwards, the normalized concentration series close to the top of the TBR exhibited sharp fronts and gradually become less intense as they travel downward that reflected the nonisolated nature of the traveling liquid pulsations. Finally, these computational and experimental findings enabled us to intensify the detoxification of high-strength wastewaters and can be further exploited due to advantageous dispersive and convective heat/mass transfer phenomena under pulsing flow conditions.

Numerical assessment of diffusion–convection–reaction model for the catalytic abatement of phenolic wastewaters in packed-bed reactors under trickling flow conditions

Computational fluid dynamics (CFD) modeling of trickle-bed reactors with detailed interstitial flow solvers has remained elusive mostly due to the extreme CPU and memory intensive constraints. Here, we developed a comprehensible and scalable CFD model based on the conservative unstructured finite volume methodology to bring new insights from the perspective of catalytic reactor engineering to gas–liquid–solid catalytic wet oxidation. First, the heterogeneous flow constitutive equations of the trickle bed system have been derived by means of diffusion–convection–reaction model coupled within a Volume-of-Fluid framework. The multiphase model was investigated to gain further evidence on how the effect of process variables such as liquid velocity, surface tension and wetting phenomena affect the overall performance of high-pressure trickle-bed reactor. Second, as long as the application of under-relaxation parameters, mesh density, and time stepping strategy play a major role on the final corroboration, several computational runs on the detoxification of liquid pollutants were validated accordingly and evaluated in terms of convergence and stability criteria. Finally, the analysis of spatial mappings for the reaction properties enables us to identify the existence of relevant dry zones and unveil the channeling phenomena within in the trickle-bed reactor.

Hydrodynamics of cocurrent two‐phase flows in slanted porous media—Modulation of pulse flow via bed obliquity

AbstractA packed bed operated with descending gas–liquid cocurrent flows in slanted configuration to force trickle flow pattern to segregate due to gravity was studied, in addition to dependences to inclination angle of liquid saturation and pressure drop. Inception of pulse flow regime could take place regardless of inclination angle and the transition from segregated/trickle regime to pulse flow regime was experimentally determined. The Grosser et al. flow regime transition model was modified by considering only axial components of the gas and liquid superficial velocities to predict the slant‐dependent shifts in transition from segregated/trickle to pulse flow and was found to agree with experimental data. Pulse flow regime at different inclinations was characterized with respect to frequency, velocity, and shape of pulses. Bed obliquity was unveiled as a new artifice to pulse flow modulation with possible prospects for catalytic reactions requiring antagonistically high‐interaction regime mass transfer coefficients and partial catalyst wetting. © 2010 American Institute of Chemical Engineers AIChE J, 2010

High-Pressure Modeling of Unsteady-State Hydrodynamics in Cocurrent Gas−Liquid Trickle-Bed Reactor

In the present study, a computational modeling approach capable of simultaneously tracking the multiphase attributes of trickle flow is accomplished at high-pressure by means of computational fluid...

Cyclic Operation Strategies in Trickle Beds and Electrical Capacitance Tomography Imaging of Filtration Dynamics

The dynamics of propagating liquid pulsations generated via various cyclic operation strategies in trickle beds was monitored through electrical capacitance tomography (ECT) for gas and liquid superficial velocities in the range of trickle flow regime. The characteristics of ON−OFF liquid, ON−OFF gas, and gas/liquid alternating cyclic operations were compared in terms of mean liquid holdup, pressure drop, pulsation intensity, pulsation propagation velocity, and spatial maldistribution maps of liquid holdup and liquid pulsation propagation velocity. The morphological features of liquid holdup pulsations as a function of cycle frequency were characterized in terms of breakthrough, plateau, and decay times. Gas/liquid alternating cyclic strategy was shown to produce long-lived liquid pulsations under the applied operating conditions and thus could be viewed as a new process intensification means to achieve uniform phase holdup and velocity distributions. In ON−OFF liquid cyclic operation, pulsation velocity ...