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A model with a high predictive quality to estimate pressure drops and liquid holdups in trickle bed reactors (TBR) is yet necessary to assist in design, up scaling, and the implementation of new processes tasks. The currently available models to estimate pressure drops and liquid holdups on TBRs exhibit important deviations, which lead to uncertainties in their applicability. To overcome the limitations in prediction deviations in the currently available models, a new model is developed based on the volume averaged two‐phase transport equations in a porous media, as developed by Whitaker. In order to develop a model that could simultaneously predict pressure drops and liquid holdup with a high accuracy, the developed model was coupled with a modification of the extended slit model reported in the literature, leading to a new hybrid model with enhanced predictability. Experimentally determined pressure drops and liquid holdup in a column with a 0.14 m internal diameter and a height of 2 m, packed with different extrudate geometries, cylinders, trilobes, and quadlobes, were used to determine the model parameters and to verify the quality of the proposed hybrid model predictions. The developed model, when compared with the experimentally determined data of pressure drops showed mean squared errors (MSE) of 0.89%, 2.31%, and 1.22% for the cylinders, trilobes, and quadlobes particles, respectively, while the liquid holdups were predicted with MSEs of 0.03%, 0.16%, and 0.01% for the cylinders, trilobes, and quadlobes particles, respectively. [ABSTRACT FROM AUTHOR]

A simulation of a trickle bed reactor aided by computational fluid dynamics was implemented. With a Eulerian approach, geometrical characteristics were explicitly considered and two simultaneous heterogeneous reactions were included, hydrodesulphurization (HDS) and hydrodenitrogenation (HDN). This was performed in order to achieve the following: (1) attain further insight into a proper scaling‐up procedure to be able to obtain the same hydrodynamics and kinetics behaviour in two reactors of different length and diameter scales; (2) develop a multiscale analysis regarding the communication of information between scales through the construction of a porous microstructure model from which the geometrical information of the microscale is captured by the effective transport coefficients (which affect the overall reactor behaviour); (3) investigate the effect of operation condition variations on hydrodynamics and kinetics; and (4) assess the deviations and further differences observed from average to punctual conversion values and the assumptions from kinetic literature models through a preliminary multiscale analysis. The CFD results were validated against experimental pressure drop data as well as HDS and HDN conversion theoretical data. An excellent agreement was found. The model produces a significant improvement in hydrodynamic parameter prediction, achieving 5 times better accuracy in predicting pressure drops and 50 % improvement in holdup prediction. The fully coupled model predicts HDS conversion with 96 % accuracy and HDN conversion with 94 % accuracy. Results suggest that the best way to obtain similar kinetic and hydrodynamic behaviour in TBRs with different lengths and diameter length scales is by equaling the liquid holdup (ϵγ) or the mass velocities (L‐G). [ABSTRACT FROM AUTHOR]

Experiments were carried out to investigate the influence of liquid flow modulation of trickle bed reactors (TBR) on biological hydrogen methanation (BHM). The modulation promises to improve the gas‐liquid mass transfer and has already been demonstrated in trickle bed reactors of other fields of application. Therefore, the influence of four different circulation intervals with pauses from two to 1,440 min was investigated in TBR for BHM. The results showed that as pause intervals without sprinkling became longer, the methane content increased from 88.61 ± 1.58 vol‐% at a circulation interval of 2 min to up to 97.19 ± 0.46 vol‐% at a circulation interval of 1,440 min. The analysis of the process liquid indicated a stable biological process at any trial phase. This study demonstrated that the performance of TBR on BHM can be significantly improved by liquid flow modulation, thus significantly reducing operating costs. To increase the performance of biological hydrogen methanation with trickle bed reactors, the influence of four different circulation intervals with pauses from two to 1,440 min was investigated. The results showed that as pause intervals without sprinkling became longer, the methane content increased from 88.61 ± 1.58 vol‐% at a circulation interval of 2 min to up to 97.19 ± 0.46 vol‐% at a circulation interval of 1,440 min. [ABSTRACT FROM AUTHOR]

Hydrodynamic data obtained from laboratory‐scale trickle‐beds often fail to accurately represent industrial‐scale systems with high packing aspect ratios and column‐to‐particle diameter ratios. In this study, pressure drop, liquid holdup, and flow regime transition were investigated in a pilot‐scale trickle‐bed column of 33 cm ID and 2.45 m bed height packed with 1.6 mm × 8.4 ± 1.4 mm cylindrical extrudates for air‐water mass superficial velocities of 0.0023 – 0.094 kg/m2s and 4.5 – 45 kg/m2s, respectively, at atmospheric pressure. Significant deviation was observed from pressure drop and liquid holdup correlations at low liquid flows rates, corresponding to gravity‐driven flow limit. Likewise, liquid saturation is overestimated by correlations at high liquid flow rates, owing to significantly reduced wall effects. Lastly, trickle‐to‐dispersed bubble flow and trickle‐to‐pulsing flow regime transitions are reported using a combination of visual observations and analysis of the magnitude of local pressure fluctuations within the column. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2560–2569, 2018 [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Hydrogenolysis of glycerol to glycols in continuous flow three phase reactors is of practical importance due to the need to give value to huge amounts of surplus glycerol. Thermodynamic and kinetic aspects must be revised for a proper design. The system was studied in a trickle‐bed reactor using copper chromite and Cu/Al2O3 as catalysts. RESULTS: Phase equilibrium and flow pattern were verified. Solid, liquid and gas phases were present, with the liquid phase in ‘trickling’ flow. Catalysts were characterized by inductively coupled plasma (ICP), nitrogen sortometry, X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), temperature programmed reduction (TPR) and pyridine thermal programmed desorption (TPD). The average reaction rate was found to be practically constant under different process conditions. A theoretical analysis indicated that the resistance to the transfer of hydrogen from the gas to the liquid phase dominated the overall kinetics. Selectivity to 1,2‐propanediol varied with temperature, with a maximum at 230 °C (97%). Selectivity was a function of the catalyst acidity. When the pressure was increased the selectivity to 1,2‐propanediol was increased, up to 97% at 14 bar. Higher pressures did not modify this value. CONCLUSIONS: Optimum reaction conditions for maximum selectivity to 1,2‐propanediol with Cu‐based catalysts are 230 °C and 14 bar. System kinetics are, however, dominated by the gas–liquid mass transfer resistance. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

We performed a numerical analysis for simulating granular media structures containing non-spherical elements and the liquid trickle flow characteristics of such structures. Fully-Lagrangian numerical simulation methods can track all motion information for solid or liquid elements at each point in time. We introduced suitable compressibility to moving particle semi-implicit (MPS) and performed individual packing behavior calculations for non-spherical elements, based on discrete element method (DEM) with expanded functions. Rigid bodies-DEM is a method using a DEM contact force model that is expanded to handle the motion of freely shaped solids. It expresses complex shapes to enable low calculation costs and intuitive mounting. We used the boundary for the granular media configured with non-spherical elements to implement a trickle flow simulation based on weakly compressible-MPS. Even for elements of equal volume, different shapes changed the liquid passage velocity and hold-up amount. The mean downflow velocity of the liquid phase was not always dependent on the void fraction. For the plane of projection, we obtained a good correlation with the mean downflow velocity in each packed structure, and successfully performed arrangements according to the new liquid-passage shape coefficient. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2257-2271, 2017 [ABSTRACT FROM AUTHOR]

A Trickle Bed Reactor equipped with a non-ideal distribution tray is investigated. First, a non-ideal co-current trickling flow of nitrogen and heptane, induced by a partially plugged tray, is characterized experimentally using the γ-tomography technique. Resulting liquid saturation data are used to validate the Euler-Euler CFD model developed in previous work of Solomenko et al.[16] on a 3D realistic flow. The resulting 3D CFD model is then coupled with simple isothermal kinetics of heteroatom removal of heavy petroleum cuts, and the effect of maldistribution on reactor performance is discussed. The problem of CFD model reduction to a 1D reactor model is finally addressed based on transport of internal ages distribution theory. Different 1D models are compared based on reactor effluent throughput. It is shown that a 1D-Multi Exit reactor model that respects both the age variance at the system outlet as well as the degree of mixing inside the reactor gives the best prediction of the reactor performance. [ABSTRACT FROM AUTHOR]

A stochastic model was developed to describe the liquid radial dispersion in a trickle-bed reactor, which has conventionally been modeled by the effective diffusion model. To establish the stochastic model, the column was divided into some layers of particles in the axial direction and several annulus rings in each layer in the radial direction. The liquid spreading was regarded as a fluid transport process and the matrix of transfer probability was derived based on the coordinates of the particle network in the cross-section of the column. With this transfer probability matrix and the initial liquid distribution, the liquid distribution in the downstream was predicted. In order to evaluate the model parameters, experimental data of the liquid dispersion were obtained from electrical capacitance tomography images and tracer injection. Good agreement was obtained between the stochastic model and the experimental liquid distribution data. [ABSTRACT FROM AUTHOR]

A simplified model is used to explore the mechanisms for droplet vaporisation in fluidised bed reactors used for the production of polyethylene in the gas phase. Both homogeneous and heterogeneous vaporisation models are considered. It is shown that for a reasonable range of droplet sizes (less than 1 mm in diameter), droplet vaporisation will be essentially complete at bed heights on the order of 1 m. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) simulations are becoming increasingly widespread with the advent of more powerful computers and more sophisticated software. The aim of these developments is to facilitate more accurate reactor design and optimization methods compared to traditional lumped-parameter models. However, in order for CFD to be a trusted method, it must be validated using experimental data acquired at sufficiently high spatial resolution. This article validates an in-house CFD code by comparison with flow-field data obtained using magnetic resonance imaging (MRI) for a packed bed with a particle-to-column diameter ratio of 2. Flows characterized by inlet Reynolds numbers, based on particle diameter, of 27, 55, 111, and 216 are considered. The code used employs preconditioning to directly solve for pressure in low-velocity flow regimes. Excellent agreement was found between the MRI and CFD data with relative error between the experimentally determined and numerically predicted flow-fields being in the range of 3-9%. © 2012 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

We extend the macroscopic nonequilibrium thermomechanical multiphase flow theory proposed by Hassanizadeh and Gray for porous media to analyze a set of drainage and imbibition experiments in trickle beds. The nonequilibrium model rests on inclusion of mass and momentum conservations for the gas-liquid interface, nonequilibrium capillary pressure, Helmholtz free energy gradients in the body supply of momentum for fluid bulk phases and gas-liquid interface, and mass exchange rates between interface and fluid bulks accounting for production and destruction of gas-liquid interfacial area. To solve the nonequilibrium model, entropy-consistent constitutive relationships are derived and calibrated using liquid holdup and bed pressure drop measurements in drainage and imbibition. The model captures very well the decay (drainage), and breakthrough (imbibition) curvatures of liquid holdup and pressure drop kinetics, while model closer inspection allows assessing the role of nonequilibrium capillary pressure and of dynamic interfacial mass exchanges for the production/destruction of interfacial area. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3123-3134, 2012 [ABSTRACT FROM AUTHOR]

Modulation of electrical conductivity in kaolin/kerosene suspensions was examined as a means for the attenuation of fines retention in trickle-bed reactors. The suspension stability was remarkably enhanced through ON-OFF concentration modulation of an electrolyte-based kerosene conductivity improver and resulted in an efficient bed-cleaning strategy under operating conditions. Periodic additions of the conductivity improver enabled fines and deposits to gain momentarily large and similar electrical charges undoing, or impeding, multilayer deposition. The time evolution of the two-phase pressure drop and specific deposit with/without conductivity improver was monitored, as well as the corresponding local deposition structure via electrical capacitance tomography (ECT). Electrical conductivity modulation was found to reduce the bed-specific deposit by an order of magnitude and the bed pressure drop increment by a factor 14. ECT imaging evaluated the efficacy of this modulation strategy in mitigating deposition and in preventing filtration-induced flow maldistribution. © 2010 American Institute of Chemical Engineers AIChE J, 2011 [ABSTRACT FROM AUTHOR]

The article reports on the design and flow characterization of a silicone-based trickle-bed system for singlet-oxygen production. The integration of several microsystem components into a single device in order to produce miniaturized singlet oxygen is mentioned. The miniature trickle-bed reactor provided experimental verification of macroscale design equations for the loss of pressure and rates of heat transference. Data from the study is compared to conventional multiphase flow maps, noting that the maps do not satisfactorily predict flow regime trends within the miniaturized system. Operation of the silicon-based reactor reached singlet-oxygen yields in line with expectations based on modeling predictions.

The article discusses a study which investigated the effect of hydrodynamic multiplicity on trickle bed reactor performance. It presents the reaction data for α-methyl styrene hydrogenation in a trickle bed reactor over a range of conditions that include gas and liquid limitations. The authors hypothesize that liquid flow rate variation induced hysteresis has a large impact on the conversion. They propose that the gas-liquid mass transfer rate is the limiting step in gas-limited reactions, while the liquid-solid mass transfer rate is the limiting step in liquid-limited reactions.

Production of ultra low sulfur diesel through biodesulfurization process has been studied in a trickle bed reactor having a diameter of 0.066 m and a height of 0.6 m. Rhodococcus sp.(no. 2891 NCIM, Pune) in immobilized form has been used to desulfurize hydrotreated diesel having sulfur concentration in the range of 200-540 ppm. The initial substrate concentration, recycle ratio and volumetric flow rate have been chosen as process parameters. Excess biomass accumulation, which is reflected by the increment of pressure drop within the reactor, has been avoided by backwashing technique. Backwashing time has been correlated to volumetric flow rate. A deterministic mathematical model based on the growth kinetic parameters, namely, maximum specific growth rate µmax, saturation constant Ks and yield coefficient YA/B, determined using systematic batch studies has been developed. Simulated data have been compared with the experimental results, which signify that the model predictions can explain the reality satisfactorily. [ABSTRACT FROM AUTHOR]

Local and average partial wetting efficiencies in trickle-beds have been directly measured by image processing and PIV analysis. Two different setups have been implemented: a vertical monolayer of pellets where the wetting structure and stability and also local velocity gradient are characterized by PIV, and a fixed bed to analyze (by photography) the axial evolution of wetting over bed cross section after a transient injection of dye. Porous alumina spheres and different liquids have been used to examine the effect of liquid-solid affinity; two liquid distributors, and bed prewetting were investigated at low liquid superficial velocities (0.5 x 10-3-10-2 m/s). Contrary to usual techniques (excepting MRI), not only average wetting efficiencies are derived from the colorimetric tracing, but also local features: axial evolution of wetting, size, and locations of dry zones, distributions of wetting efficiency at a particle scale. All those local data are important to improve reactor models assuming uniform pellet wetting. The effect of liquid-solid affinity is predominant in the case of the monolayer of beads, and, contrary to usual assumption, is still significant for the real trickle bed in the low range of wetting efficiency, corresponding to liquid superficial velocity lower than 2 x 10-3 m/s. [ABSTRACT FROM AUTHOR]

The article focuses on a study on liquid wetting fraction of a catalyst on the molecular level from adsorption and desorption isotherm experiments. Characterization of catalyst wetting condition is important to modeling and control of trickle-bed reactors. An adsorption method will be used since it can provide the essential point of capillary condensation from the interaction of the hysteresis loop formed by the adsorption and desorption isotherms.

Periodic operation, as a process intensification measure for trickle beds, is still tepidly greeted by industry despite numerous benefits underlined in the literature. This state of aloofness is partly ascribed to the paucity of experimental data acquired under elevated temperature and pressure, which, in practice, most catalytic reactions are subjected to. Currently, the hydrodynamics of trickle bed periodic operation at elevated temperature and pressure remains by and large an uncharted territory. This study specifically approaches from a hydrodynamic perspective the pros and cons of slow-mode induced pulsing for Newtonian and non-Newtonian power-law liquids at elevated temperature and moderate pressure. Four morphological features of the liquid holdup periodic pattern were analyzed: shock wave breakthrough, shock wave decay times, shock wave plateau, and shock wave breakthrough amplitude. The shock wave decay and breakthrough times were found to shorten, while correspondingly the shock wave plateau to lengthen, with increasing pressure and temperature. Conversely, the breakthrough amplitude of the shock wave underwent palpable collapse the higher the temperature (and/or pressure). The collapse of the bursting pulses with increasing temperatures and pressures was the result of the reduction of base and pulse liquid holdup levels, delivery of liquid cargo from pulse to baseline flow, and occurrence of dispersive hydrodynamic effects with a tendency to flatten the pulses. Qualitatively, similar effects of temperature and pressure were equally observed whether Newtonian or non-Newtonian liquids were used. The less sensational contrasts prevailing between base and pulse holdups might question the opportunity for implementing induced pulsing strategies in high-temperature, high-pressure tall trickle beds. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Chemical Engineering is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A novel technique is used to obtain the distribution of particle wetting in trickle-bed reactors for different flow and prewetting conditions. Two prewetting methods were investigated: (1) Levec prewetting, in which the packed catalyst bed is completely flooded and then left to drain before steady state trickle-flow is commenced; (2) Kan prewetting, in which the bed is prewetted by pulsing with the liquid before flow, after which the liquid flow is gradually set back to the required rate. It is shown that the method of prewetting has a major influence on average wetting efficiency and wetting distributions: Average wetting efficiencies differ with as much as 20% between the prewetting modes, and Levec prewetting leads to a considerable fraction of the bed that is not used (up to 7% at the investigated flow conditions), whereas the entire catalyst is used in Kan prewetted beds. It is shown that the particle wetting distributions can influence the modeling of Levec prewetted beds for liquid- and gas-limited conditions. [ABSTRACT FROM AUTHOR]

The formation of local instabilities, identified as isolated pulsing events, in the gas-liquid distribution within a trickle-bed reactor is shown to be central to the mechanism of the hydrodynamic transition from trickle-to-pulsing flow. The evolution of these instabilities as the bed moves through the transition is imaged in 3-D using ultrafast magnetic resonance imaging (MRI). The reactor was of internal dia. 43 mm and packed with cylindrical packing elements of length and diameter 3 mm, operating under conditions of air-water, cocurrent downflow. Superficial gas and liquid velocities in the range 25-300 and 0.9-13.0 mm s-1, respectively, were used. For a given gas velocity, the transition point is defined to be the liquid velocity at which the maximum number of isolated pulses occurs. The transition point determined using this approach is critically compared with the predictions of existing correlations and theoretical models. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Chemical Engineering is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Monolith reactors are being studied as a replacement for conventional multiphase reactors such as trickle-bed reactors, slurry reactors, and slurry bubble column reactors for gas-liquid-solid reactions. Reactors with monolith catalyst packing have been found to be hydrodynamically superior to existing industrial reactors. This review covers multiphase reactions carried out in monolith reactors by various researchers. It first defines the monolith reactor and looks into the geometrical aspects of monolith. The section dealing with hydrodynamics reviews pressure drop, phase holdup, flow distribution, and dispersion characteristics. This study also considers the tools used to characterize the hydrodynamic parameters and their typical values. Although the available literature is scarce, monoliths are considered to have superior mass transfer characteristics. This review lists the mass transfer correlations for each category (gas-liquid, gas-solid, liquid-solid). The last section discusses the reaction aspects of monolith reactors. The ultimate goal is to implement such reactors for multiphase reactions. This section also compares the performance of monolith reactors with conventional multiphase reactors and lists the various reactor models reported to predict the overall performance of monolith reactors. [ABSTRACT FROM AUTHOR]

Excessive biomass formation in two-phase flow trickle-bed bioreactors induces clogging and leads to the progressive obstruction of the bed that is accompanied with a buildup in pressure drop and flow channeling. Currently, physical models linking the two-phase flow to the space-time evolution of biological clogging are virtually nonexistent. An attempt has been made with this contribution to fill in this gap by developing a unidirectional dynamic multiphase flow model based on the volume-average mass, momentum, and species balance equations. Phenol biodegradation by Pseudomonas putida as the predominant species immobilized on activated carbon was chosen as a case study to illustrate the consequences of formation of excessive amounts of biomass. Furthermore, in developing the transient model, the following basic processes were assumed to occur and have been accounted for in the mathematical model: oxygen transport from gas into liquid bulks, phenol, and oxygen transport from the liquid phase to the biofilm surface, simultaneous diffusion and reaction of phenol and oxygen within biofilm, as well as their simultaneous diffusion and adsorption within the porous supporting particles. [ABSTRACT FROM AUTHOR]

Intensified trickle bed reactors were developed for catalytic wet air oxidation (CWAO) of phenol, by generating microbubbles before gas/liquid fluid flows along catalyst packed‐beds. By coupling gas‐liquid microdispersion module, phenol disappearance rate significantly increases under the same operating conditions and phenol conversion reaches 92% in 22 seconds at 160°C and 1000 kPa. Effects of operating conditions were studied systematically and results demonstrated characteristics of high‐interaction regime at low Reynolds number. Comparison of effects among mass transfer and reaction steps shows CWAO reaction is controlled by resistance to liquid‐solid mass transfer of phenol in most cases, while gas‐liquid mass‐transfer‐resistance is ignorable. A dimensionless correlation, Sh = 2.29φ−0.91(ReL + ReG)0.04, was established, by considering influences of liquid film thickness and fluid flow situations on liquid‐solid mass transfer coefficient in microbubble‐in‐liquid/catalyst‐particle system. The study would provide an effective method for intensifying CWAO and other liquid‐solid‐mass‐transfer‐resistance‐controlled gas/liquid/solid catalytic reactions and help understand mass transfer mechanism in new gas/liquid/solid system. [ABSTRACT FROM AUTHOR]