Trickle Flow Regime Research Articles

Guard of hydrotreating catalysts of oil fractions from solid particulates: experimental studies and calculation

A study was made of the efficiency of trapping solid microparticulates contained in diesel fuel for catalyst loading – an analogue of an industrial package of guard beds of hydroprocesses. The package of catalysts consisted of catalyst granules ranked by shape and size: segmented rings, hollow cylinders of two standard sizes and trilobe shape. The experiments were carried out in the trickle flow regime with a constant ensemble of microparticulates – iron scale with a size of 5 to 150 μm at the inlet of the catalysts loading. It was found that the penetration coefficient of the catalysts loading of the guard beds did not change significantly (K ≈ 0.985) during the experiment. At the same time, a linear increase in the pressure drop on the catalysts loading of the guard beds with a height of 17 cm from 220 to 408 Pa was observed which occurred as a result of the trapping of solid microparticulates by the catalyst granules. The theoretical estimate of the initial pressure drop (228 Pa) coincides with the experimental data (220 Pa) with good accuracy.

Optimization of grading guard systems for trapping of particulates to prevent pressure drop buildup in gas oil hydrotreater

A new approach to optimize grading guard systems for gas oil hydrotreating reactor based on the phenomenon of clogging of catalyst beds with microparticulates and coke deposits was developed. Pellets with different shapes have been tested to obtain dynamic dependencies of filter coefficient and pressure drop buildup. The experiments were performed in the trickle-flow regime with different ensembles of microparticulates having sizes from 15 to 165 μm. The observed effect of a filter cake formation was characterized in terms of average porosity of the interface beds and it was introduced in simulations plugging of catalyst bed. Estimation of the growth of coke deposits was made using modified Voorhies’s equation and experimental samples obtained in the microreactor under hydrotreating process conditions using foulants of industrial gas oil hydrotreater. The analysis of coked samples was carried out using TGA. Based on the discrete model and experimental data, optimization procedure of grading guard systems was carried out using brute force search. All combinations of schemes of guard-beds were compared using integrated hydrodynamic resistance as a criterion. It was shown that an optimized scheme of guard-beds can reduce hydrodynamic resistance as compared to the schemes without guard-beds or with non-optimized guard-beds.

Heterogeneous Catalytic Ozonation of Phenol over Iron-based Catalysts in a Trickle Bed Reactor

The use of continuous reactors for heterogeneous catalytic ozonation is yet to be investigated in order to develop a viable technology for industrial applications. This paper presents hydrodynamic and degradation studies on the use of a co-current down flow trickle bed reactor for heterogeneous catalytic ozonation of phenol (as model pollutant) over Fe-Diatomite pellets and Fe-coated glass beads. It was found that the reactor can operate under trickle or pulsing flow regimes, promoting mass transfer augmentation. Residence time distribution data, fitted with n-CSTR and axial dispersion (ADM) models, showed low axial dispersion and high flow distribution. Just the Fe-diatomite pellets showed important phenol adsorption (16 %). Degradation experiments demonstrated that phenol conversion was substantial when using both catalysts, up to 19,7 % pollutant conversion with liquid-phase space times of just 6 s. Compared to direct ozonation, the use of the Fe-diatomite pellets and Fe-coated glass beads enhanced the reactor performance by 48 % and 23 %, respectively. It was confirmed that mass transfer is an important factor that restricts this reaction system performance; consequently, further improvement in mass transport rate is necessary for system optimization.

Dynamic Liquid–Solid Mass Transfer in Solid Foam Packed Reactors at Trickle and Pulse Flow

The effective liquid–solid mass transfer (LSMT) has been investigated in solid foam packed reactors under cocurrent gas–liquid downflow. Based on a comprehensive literature analysis, the limiting current technique was adapted successfully to solid foam packings enabling measurements of dynamic mass transfer coefficients at different axial packing positions. The flexible reactor setup was used to analyze the appropriateness of various setup configurations. The LSMT coefficients are presented for two different solid foam pore densities for a wide range of gas and liquid velocities covering trickling and pulsing flow regime. To illustrate the difference in the LSMT dynamics in terms of electric current compared to the liquid holdup at pulse flow, a compartment model is developed. Excellent agreement is achieved between simulations and measurement data. Eventually, the effective mass transfer data are compared with conventional random and structured packings.

Continuous Ethanol Production from Synthesis Gas by Clostridium ragsdalei in a Trickle-Bed Reactor

A trickle-bed reactor (TBR) when operated in a trickle flow regime reduces liquid resistance to mass transfer because a very thin liquid film is in contact with the gas phase and results in improved gas–liquid mass transfer compared to continuous stirred tank reactors (CSTRs). In the present study, continuous syngas fermentation was performed in a 1-L TBR for ethanol production by Clostridium ragsdalei. The effects of dilution and gas flow rates on product formation, productivity, gas uptakes and conversion efficiencies were examined. Results showed that CO and H2 conversion efficiencies reached over 90% when the gas flow rate was maintained between 1.5 and 2.8 standard cubic centimeters per minute (sccm) at a dilution rate of 0.009 h−1. A 4:1 molar ratio of ethanol to acetic acid was achieved in co-current continuous mode with both gas and liquid entered the TBR at the top and exited from the bottom at dilution rates of 0.009 and 0.012 h−1, and gas flow rates from 10.1 to 12.2 sccm and 15.9 to 18.9 sccm, respectively.

Catalytic Denitrification in a Trickle Bed Reactor: Ion Exchange Waste Brine Treatment

Catalytic reduction of nitrate in ion exchange (IX) waste brine for reuse is a promising option for reducing IX costs and environmental impacts. A recycling trickle bed reactor (TBR) was designed and optimized using 0.5 percent by weight (wt%) palladium–0.05 wt% indium catalysts supported on US mesh size 12 × 14 or 12 × 30 activated carbon particles. Various liquid superficial velocities (Ur) and hydrogen gas superficial velocities (Ug‐H2) were evaluated to assess performance in different flow regimes; catalyst activity increased with Ug‐H2 at all Ur for both catalysts and was greatest for the 12 × 30 catalyst at the lowest Ur (8.9 m/h). The 12 × 30 catalyst demonstrated up to 100% higher catalytic activity and 280% higher mass transfer rate compared with the 12 × 14 catalyst. Optimal TBR performance was achieved with both catalysts in the trickle flow regime. The results indicate that the TBR is a promising step forward, and continued improvements are possible to overcome remaining mass transfer limitations.

Analysis of Hydrodynamic Parameters Effect on the Hydropurification Reactor Operation through Numerical Simulation

In the class of three-phase catalytic reactors, trickle-bed reactors (TBRs) are the most extensively used in industry. They are utilized in petrochemicals, petroleum, chemicals, waste treatment, electrochemical and biochemical processing, and many other applications. One of the most significant applications of TBRs is their utilization in the process of purification. Since the purified product has to meet the required specifications of a high quality chemical, the TBRs operation control is very critical. Considerable fluctuation of the operating parameters values adversely affects the reactor efficient performance. In this paper, the effect of hydrodynamic parameters on the hydropurification TBR operation is investigated considering the product quality. A first principle heterogeneous model incorporating the hydrodynamic parameters and catalyst deactivation has been developed to analyze the reactor performance under the fluctuation of the hydrodynamic parameters. The devised model along with its mathematical solution has been coded into MATLAB R2016a environment. The results reveal that the deviation of hydrodynamic parameters of liquid holdup and gas holdup considerably influence the efficiency of the purified terephthalic acid reactor operation in term of product quality. Moreover, the impact of liquid holdup on the reactor operation is more than gas holdup in term of product quality. These research findings might be applied into an actual operating system mentioning that the deviation from trickling flow regime is to be avoided in the reactor.

An interfacial heat transfer in a countercurrent gas–liquid flow in a trickle bed reactor

The paper is devoted to interfacial heat exchange between gas and liquid flowing countercurrently through a packed bed in a trickling flow regime. The lack of correlations describing the interfacial gas-liquid heat transfer coefficient makes problems when numerical models of non-isothermal flows in porous media are being developed. Thus the experimental investigation was undertaken with the use of a column of 0.1m inner diameter, equipped with 6mm glass Raschig rings. Air and water were used as working fluids. The loads of media ranged between 0.0177–0.1415m3·(m2s)−1 and 0.0007–0.0053m3·(m2s)−1 for gas and liquid phases, respectively. The inlet water temperature was changed within the range between 30°C and 70°C whereas the inlet air temperature was kept constant at the level of (21±1)°C. It was found that interfacial heat transfer coefficient is strongly dependent on the gas load, noticeably dependent on the temperature difference between phases and slightly dependent on the liquid load. The results of the experiment were used to develop a new correlation describing the interfacial heat transfer in the packed bed expressed by the Nusselt number. Various group numbers were considered in order to account for the impact of gravity, surface tension, thermal diffusion and free convection on the interfacial heat transfer. After detailed regression analysis the correlation of the form Nu=ReG1.169·GaG-0.8399·Eo¨0.7176 was finally proposed as the most fitting the experimental data.

Experimental Visualization and Investigation of Multiphase Flow Regime Transitions in Two-Dimensional Trickle Bed Reactors

Different flow regimes are known to occur in the interaction of multiphase gas–liquid flows over packed beds of solid particles, such as those observed in trickle bed reactors (TBRs). There are four major flow regimes that are known to occur in downward cocurrent flow in TBRs, namely: trickle, pulse, bubble, and mist flow regimes. In this work, the focus is on macro-scale experimental visualizations and investigations of the flow regimes in a two-dimensional TBR.Experimental observations are made to investigate the development and transition of these flow regimes over a wide range of liquid and gas velocities. Cylindrical particles are placed between two glass plates that are sealed on the sides, and water and air are injected over them using an injection manifold to simulate multiphase flow in a TBR. A diffused light emitting device (LED) light table is used to illuminate the experimental window, while real time images are obtained using a high-speed camera. Flow maps are reported depicting all four regimes and the transition regions between them. Transition regions occur where the characteristics of more than one flow regime coexist.The 2D experimental results are then compared with the existing literature data of three dimensional results and found to be in good agreement. Emphasis is placed on the transition between the trickle and pulse regimes, since that is the most important mode of operation in industrial TBRs. It is observed that the change in diameters of the cylindrical particles in a two-dimensional TBR has little effect on the transition between the flow regimes when the porosity of the bed is kept constant.

Experimental investigation of gas-liquid distribution in periodic open cellular structures as potential catalyst supports

Radial and axial liquid distribution was measured in a packed column of 500 mm length and 100 mm inner diameter under various gas- and liquid superficial velocities to achieve trickle flow regime. Liquid maldistribution was determined using a liquid collector at the outlet consisting of 21 collection zones of equal area. In this work, as packings inside the column, periodic open cellular structures (POCS) were manufactured and applied. Such POCS can be used as structured catalyst support and/or liquid distributor.The hydrodynamic behavior of packings with Kelvin cell, Diamond cell and a hybrid combination of both unit cells was studied to identify unit cells with high potential for achieving homogeneous liquid distribution over the entire reactor cross-section. The liquid superficial velocity had a strong influence on the liquid distribution, while an increasing gas flow rate did not change the flow patterns. Kelvin cell packings tend to distribute the liquid towards the center whereas Diamond cell packings predominantly spread the fluid towards the rim. As a consequence of these observations, in this work a novel POCS structure is proposed: The combination of Kelvin and Diamond unit cells, called hybrid DiaKel unit cell. With POCS consisting of this unit cell type, a significantly improved liquid distribution can be achieved. Thus, this structure features high potential as liquid distributor and/or catalyst support in gas-liquid reaction systems.

Liquid hold-up and gas–liquid mass transfer in an alumina open-cell foam

Open-cell foams are solid structures formed by an intricate network of macroporous interconnected channels. The high porosity and tortuosity of the channels results in high external surface area, so open-cell foams are very efficient for promoting phase contact, e.g. in gas–liquid packed-bed reactors. In addition, the tortuous path of the channels breaks up the flow and enhances mass transfer with respect to other structured beds, such as honeycomb monoliths, and pressure drop is comparatively low.The liquid hold-up (system water–air), and the mass transfer coefficient (oxygen from water to nitrogen), have been measured for a ceramic foam, specifically a 20ppi alumina foam bed of 50mm diameter and 100mm length (average pore diameter 1.25mm and strut diameter 0.42mm), for co-current down flow. Gas and liquid flow rates have been varied in the range corresponding to 0–8.5·10−2 and 0–3.2·10−3m/s superficial velocities, respectively. At these conditions, the bed operates at trickle flow regime. The dynamic liquid hold-up and the mass transfer coefficient have been correlated as a function of relevant dimensionless numbers.

Rapid digestion of shredded MSW by sequentially flooding and draining small landfill cells

This paper compares the digestion of a packed bed of shredded municipal waste using a flood and drain regime against a control digestion of similarly prepared material using a trickle flow regime. All trials were performed on shallow (2m) beds of the sub-8cm fraction of shredded mixed MSW, encapsulated in a polyethylene bladder. The control cell (Cell 1) was loaded with 1974 tonnes shredded municipal waste and produced 76±9m3 CH4dryt−1 (45±2m3 CH4 ‘as received’t−1) over 200days in response to a daily recirculation of the leachate inventory which was maintained at 60m3. The flood and drain operation was performed on two co-located cells (Cell 2 and Cell 3) that were loaded simultaneously with 1026 and 915 tonnes of the sub-8cm fraction of shredded mixed MSW, with a third empty cell used as a reservoir for 275m3 of mature landfill leachate. Cell 2 was first digested in isolation by flooding and draining once per week to avoid excessive souring. Gas production from Cell 2 peaked and declined to a steady residual level in 150days. Cell 3 was flooded and drained for the first time 186days after the commencement of Cell 2, using the same inventory of leachate which was now exchanged between the cells, such that each cell was flooded and drained twice per week. Biogas production from Cell 3 commenced immediately with flooding, peaking and reducing to a residual level within 100days. The average CH4 yield from Cells 2 and 3 was 123±15m3dryt−1 (92±2m3 ‘as received’t−1, equal to 95% of the long term (2month) BMP yield.

English

An experimental investigation of the hydrodynamic parameters in a trickle bed reactor is presented. The operating conditions are selected for the operating system to be at trickle flow regime. The effects of the two-phase flow rates, reactor pressure and temperature on the pressure drop, external liquid holdup and liquid axial dispersion are discussed. Pressure drop was measured using differential pressure transducer, while liquid holdup and axial dispersion were estimated using RTD technique with a reactive dye as a tracer. The results confirmed that pressure drop is proportional to flow rate of fluids and operating pressure while it is inversely proportional to temperature. Liquid flow rate has a proportional effect on liquid holdup and axial dispersion while gas flow rate and temperature presented a different image. A comparison between the results of present work and that of literature is presented and discussed. Empirical correlations for pressure drop, liquid holdup and axial dispersion with operating conditions are developed with correlation coefficient of 98.4 to 99.7 %.

Numerical evaluation of the gas–liquid interfacial heat transfer in the trickle flow regime of packed beds at the micro and meso-scale

In the present work, two different models (micro-scale and meso-scale) were developed to investigate the heat transfer between the gas and liquid phases in the trickle flow regime of a packed bed reactor. In the micro-scale model, a simplified description of bed geometry, known as the double-slit model, was implemented to study the effects of different operating parameters, in terms of gas and liquid Reynolds, Prandtl and Eötvös numbers, on the interfacial Nusselt number. In the meso-scale model, the Volume-of-Fluid (VOF) approach was used to simulate trilobe, cylindrical and spherical catalyst shapes and accurately predict the effects of interface morphology and bed geometry on interfacial heat transfer. To validate the implemented methods, a simple packed bed reactor with spherical catalysts was developed to experimentally investigate the interfacial heat transfer of co-current, downward gas–liquid film flows. The results obtained from CFD simulations and experimental data were in agreement and accurately predicted bed reactor temperature profiles with a mean relative error of 2.15%. In both the micro- and meso-scale models, an increase in the Reynolds and Prandtl numbers increased the interfacial Nusselt number; whereas, an increase in dimensionless groups of the liquid phase or the Eötvös number caused the opposite effect. Finally, a new correlation was proposed that evaluated the gas–liquid Nusselt number in the trickle flow regime with a standard deviation of 7.19% compared to results acquired using the micro-scale model.

Pressure drop and its reduction of gas–non-Newtonian liquid flow in downflow trickle bed reactor (DTBR)

The influences of concurrent flow of air–Newtonian and non-Newtonian liquid systems on pressure drop and on its reduction in downflow trickle bed reactor are presented in the present work. The pressure drop at different flow regimes in the trickle bed is enunciated by the dynamic interaction model based on the framework of the momentum balance. From the analysis, it is observed that the non-ideality factor of bubble flow regime is higher than that of pulse and trickle flow regimes which may influence efficiency of the reactor. The present work also concludes that the percentage of pressure reduction increases with increasing the surfactant concentration. However there is a limitation of change of concentration, above which no more reduction can be obtained. The present study may be useful for further understanding and modelling of multiphase reactor with non-Newtonian liquid, which has great industrial applications.

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.

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.

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)

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.