Dynamic Liquid Holdup Research Articles

Development of Gradient Boosting Machines for Estimation of Total and Dynamic Liquid Holdup in Trickle Bed Reactor

Development of Gradient Boosting Machines for Estimation of Total and Dynamic Liquid Holdup in Trickle Bed Reactor

Modeling and experimentation for novel aerofoil embedded mesh disk-based partially submerged rotating reactor

A novel aerofoil embedded fiber mesh disk-based rotor has been proposed as an alternative to currently available rotating biological contactors. Specially designed aerofoil structures were incorporated into the rotor to increase its mass transfer performance and liquid hold capacity. The volumetric mass transfer coefficient and liquid hold-up for the novel rotor were determined at the rotational speeds of around 10, 15, 20, 25, 30, and 35 rpm under various submergence levels of 17.4, 21.7, 26.1, 27.8, 30.4, 34.8, 39.1, 43.5, and 50%. A dimensionless correlation for the dynamic liquid hold-up was proposed in terms of the Reynolds number, Froude number, and the submergence ratio. Another dimensionless term Oxygen transfer number (OT number) was proposed to characterize the mass transfer behavior of the reactor. The dependency of OT number was expressed in terms of Peclet number, Froude number, and dimensionless geometrical factor. The volumetric mass transfer coefficient and liquid hold-up were found to be strongly dependent on the rotation speed and submergence level.

A performance analysis of the spray-type packed bed thermal energy storage for concentrating solar power generation

The concept of spray-type packed bed thermal energy storage (medium and high temperature thermal energy storage, from 200 °C to 350 °C, Alumina pellets+T66 fluid) has been proposed in our previous investigation. Its low-cost and high-efficiency shows its promising application prospect. Further investigation of the new concept is carried out both numerically and experimentally in this paper. First, the “charging-standby-discharging” cycle of a pilot spray-type packed bed is investigated experimentally. Second, the dynamic liquid holdup of the spray-type packed bed is correlated with the experiment data and is applied to build the mass balance equations. Based on the energy balance equations and mass balance equations, a three-phase one-dimensional transient model for the spray-type packed bed is established. Results from the experiment confirms the correctness of the numerical model. Based on the model, the liquid holdup of the packed bed during the “charging-standby-discharging” cycle is studied. At last, sensitivity analysis was carried out to study the influence of the parameters of the “charging-standby-discharging” process on the thermal performance of the spray-type packed bed. Values of these parameters can be found to achieve the best thermal performance of a spray-type packed bed.

Bed structure and its impact on liquid distribution in a trickle bed reactor

AbstractTrickle bed reactors, which has been a workhorse for the process and refining industry for many decades, are progressively being challenged to provide solutions to deep processing of feedstocks. It is known that the structure of the packed bed which is formed with a certain arrangement of catalyst particles in the three‐dimensional space within the reactor modulates in an unknown fashion the flow of fluids in the trickle bed, and in turn affects the conversion and selectivity in the trickle bed. Under deep processing conditions, the impact of the bed structure in modulating the overall reactor performance in a trickle bed is not as yet established. The question begets three sequential studies: estimating and quantifying the bed structure, measuring the liquid distribution, and estimating transport parameters (that are dependent on the bed structure and liquid distribution) so that the overall performance metrics as a reactor may be quantified. This contribution relates to the second of these questions, the first being already addressed to some extent by our earlier work. The current investigation aims at quantifying the effect of structure of the packed bed on hydrodynamics of the reactor. The impact of various packing techniques is discussed along with the development of correlations for two‐phase pressure drop and dynamic liquid holdup. Liquid distribution is studied in depth for various operating parameters such as gas and liquid superficial velocities and column aspect ratio for uniform and non‐uniform packing methods. The packing devices consist of various inserts attached to a hopper which can generate packing structures having void fraction in the range of 37.2%–46.4%. The maldistribution factor and flow maps for various aspect ratio of column suggest that maldistribution rises along with the increased channeling effect along the height of the column. Uniformly packed bed were measurably less prone to maldistribution along the length than the non‐uniformly packed beds.

External Wetting Efficiency in a Three-Phase Fixed Bed Loaded with Porous and Non-Porous Packings

Films and rivulets are the two basic forms of dynamic liquid in a three-phase fixed bed (trickle bed), which determines the wetting efficiency of the catalyst. This paper is devoted to the conflicting wetting performance observed between non-porous glass beads and less wettable porous alumina, and a parallel zone model is applied to resolve the complex liquid flow texture. It shows in both cases of glass beads and aluminium pellets, the pressure drop, film flow and rivulet flow fractions all display pronounced multiplicities along with the liquid flow rates in increasing and decreasing branches, although the rivulet flow fraction is reduced to 0 in the liquid decreasing branch started from pulsing flow in both cases. Different from the glass beads, there is almost no wetting efficiency difference for the alumina pellets with respect to liquid flow rate increasing or decreasing, which is in agreement with the dynamic liquid holdup measurements. The liquid is significantly more uniformly distributed over the crosssection in the Al2O3 bed since rivulet flow is much reduced than in the case of glass beads.

Selecting carrier material for efficient biomethanation of industrial biogas-CO2 in a trickle-bed reactor

Biogas upgrading via biomethanation of renewable H2 and the CO2 in biogas poses a potential key technology in the decarbonized energy system. This study uses a methanogenic trickle-bed reactor for upgrading raw biogas from an industrial anaerobic digester to natural gas-grade biomethane through ex situ biomethanation. The carrier material comprises a critical design parameter for trickle-bed reactors by supporting the catalytic methanogenic biofilm and thereby the interfacial area for H2 mass transfer. The present study applied an abiotic mass transfer-based screening of six different carrier types to identify a candidate material that can facilitate efficient H2 mass transfer in a biomethanation trickle-bed reactor. The screening included gas-liquid mass transfer experiments in an air-water system in addition to characterizations of the carriers’ surface area, dynamic liquid hold-up volumes, and external porosities. The abiotic experiments showed that the gas-liquid mass transfer coefficient is highly influenced by material type and cannot be predicted solely from differences in the carriers’ surface area. The abiotic characterizations led to the selection of crushed clay particles, whose application in biomethanation-based upgrading of raw biogas from an industrial anaerobic digester was examined. The clay particles facilitated an apparent volumetric mass transfer coefficient for H2 of 10 min−1, enabling CH4 production rates up to 6.1 L · L−1 · d−1 and more than 99 % H2 conversion over 30 days of continuous operation, where after accumulation of metabolic water in the packed bed impaired H2 mass transfer. Apart from the adverse effect of water accumulation, there was no indication that the maximum H2 mass transfer rate was reached, demonstrating the selected carrier material’s industrial potential for biomethanation-based biogas upgrading.

Flow regime transition and liquid distribution in a 3D concurrent downflow three-phase moving bed

Based on a cold-flow experimental setup, the transition between trickle flow and pulse flow in a 3D concurrent downflow three-phase moving bed is investigated by the standard deviation of pressure drop and visual observations. Results show that at a constant gas flow rate, the trickle-to-pulse transition shifts to a higher liquid flow rate with the increasing solid flow rate because the particle moving inhibits the formation of local liquid blockage. Furthermore, an empirical model is proposed to fit the trickle-to-pulse transition boundary by correlating the dynamic liquid holdup at the boundary with the gas Reynolds number, the particle velocity, and the relative viscosity. Finally, the effects of the particle moving on the liquid distribution are investigated, which shows that the particle moving makes the liquid distribution more uniform when the solid flow rate is smaller than a certain value. But further increasing the solid flow rate, the liquid distribution becomes uneven.

Maldistribution and dynamic liquid holdup quantification of quadrilobe catalyst in a trickle bed reactor using gamma-ray computed tomography: Pseudo-3D modelling and empirical modelling using deep neural network

The dynamic liquid distribution and holdup in a TBR packed with porous quadrilobe catalyst were studied using advanced Gamma-ray Computed Tomography. A multi-compartment module is used to quantify the maldistribution factor which shows that there is a transition region from high maldistribution to relatively uniform distribution depending on the flowrates. The 3D maldistribution maps show that there is more dynamic liquid close to the column center at high bed height and there is no high correlation between the average dynamic liquid holdup and the bed height. If the gas flowrate increases while keeping the liquid flowrate fixed, the average dynamic liquid holdup decreases; however, if the gas flowrate is fixed, there is no dominant increasing or decreasing trend showing up. A Deep Neural Network model and a pseudo-3D model are developed showing high accuracy for predicting the local dynamic liquid holdup at different bed heights, radius, and flowrates.

Periodic open cellular structures (POCS) for intensification of multiphase reactors: Liquid holdup and two-phase pressure drop

Structuring concepts for catalytic reactors provide promising options for process intensification on the process unit level [1,2] as they offer a better control on the occurring transport processes, e.g. on the fluid flow, species distribution, pressure drop and heat transfer. Process intensification aims at the realization of processes that are only limited by reaction kinetics, but not anymore on hydrodynamics [3]. For this reason, in multiphase reactors it is desirable to achieve good liquid distribution, advanced heat transport and low pressure drop, just to mention a few transport characteristics. In this regards, the use of periodic open cellular structures (POCS) is a recent and very promising structuring concept, as packings of these structures offer superior and adjustable properties (e.g. low pressure drop, high surface area, good liquid distribution, advanced heat transfer) [4–8].In this contribution, static and dynamic liquid holdup as well as single- and two-phase pressure drop was measured in POCS. These kinds of structures can be used as catalyst support in packed bed reactors, and also as liquid distributor for trickle-bed applications. The POCS investigated in this study were fabricated with different additive manufacturing methods (fused deposition modeling, stereolithography and selective electron beam melting) to study the influence of different materials (ABS, resin, Ti6Al/4V). For the description of the static liquid holdup, a modified Eötvös correlation, which takes the contact angle of the different materials into account, is proposed. Dynamic liquid holdup and two-phase pressure drop was modelled using an extension of the concept of hydrodynamic tortuosity proposed by Inayat et al. [8], and a modification of the relative permeability model introduced by Saez et al. [9]. Furthermore, equations for the geometric characterization of POCS consisting of different unit cell types, namely Diamond, Kelvin and the recently presented DiaKel hybrid cell [5] were derived. The window diameter of the used unit cells as well as the porosity has a strong influence on the liquid holdup and the pressure drop. By taking the contact angle into account the static liquid holdup can be calculated with good precision (errors smaller than 20%). The concept of geometric tortuosity and the relative permeability model also is applicable to predict the (two-) phase pressure drop and the dynamic liquid holdup in stacked packings of POCS segments of different unit cells and materials. Both, pressure drop and liquid holdup can be predicted a priori (i.e., without further fitting) with good precision using the correlations established in this work solely based on geometric properties of the packing.

Optimal operation and stabilising control of the concentric heat-integrated distillation column (HIDiC)

Abstract This paper presents the application of a systematic control configuration design procedure on the HIDiC with a reboiler. The application is illustrated through two case studies of industrial relevance, namely the separation of benzene/toluene and a multicomponent mixture of aromatic compounds. Results of static optimisations and dynamic simulations are presented based on a realistic column model, which accounts for dynamic pressure drops and liquid holdups, dynamic energy balances and more. Using a decentralised control scheme, good stabilising and economic performance are achieved by controlling both column section pressures and the temperature profile in one of the sections, while the economic variables are controlled by cascade control loops. Guidelines for the design of both the regulatory control layer and the supervisory control layer are provided.

Experimental Investigation of Liquid Axial and Radial Dispersion in Winpak Modular Catalytic Structured Packing

The response technique was employed to investigate the axial and radial dispersion characteristics of the liquid phase in modular catalytic structured packing (MCSP) reaction elements. Residence time distribution (RTD) experiments were performed at ambient temperature and atmospheric pressure. A two-dimensional dispersion model was solved analytically to determine the axial and radial dispersion coefficients and the dynamic liquid holdup from the RTD curves. Three different reaction elements containing Winpak packing sheets, Mellapak packing sheets, or only catalytic particles were employed. The radial dispersion coefficient in these structures is approximately 1–2 orders of magnitude higher than the axial dispersion coefficient. The axial and radial dispersion coefficients in the Winpak elements are greater than those in the other structures. Thus, it can be concluded that the liquid dispersion characteristics in the Winpak elements are satisfactory. These measured dispersion coefficients enable the reli...

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.

Hydrodynamic Behavior and Residence Time Distribution of Industrial‐Scale Bale Packings

AbstractThe hydrodynamic behavior of bale packing was tested in a catalytic distillation column. Models and empirical equations for predicting pressure drop and dynamic liquid holdup were proposed and compared with experimental results. The examination of residence time distribution (RTD) relied on the pulse method and a conductivity meter which deduced the axial Péclet number, axial dispersion coefficient, and dynamic liquid holdup. The relations of dynamic liquid holdup obtained from gravimetric draining experiments and RTD studies were discussed with static and total liquid holdup. Potential impacts of the liquid distributor and conductivity cell were also assessed. The results prove that models and empirical equations fit well and are reliable in design and scale‐up.

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.

Investigation of dynamic liquid distribution and hold-up in structured packings using ultrafast electron beam X-ray tomography

Dynamic cross-sectional liquid distribution and hold-up in a DN80 separation column filled with structured packings was studied using an ultrafast electron-beam X-ray tomograph with high temporal resolution of 2000 images per second. The modality allows visualisation and characterisation of the counter-current flow before and at the flooding point representing the upper operation limit. Two packings of the same type (Montz B1-MN) with different specific surface area were used to investigate the influence of the packing geometry on the spatial liquid distribution. The system studied was water/air at different gas and liquid loads. The results of the tomographic imaging and corresponding post-processing routines were validated by comparison with conventional draining measurements.

Fluid dynamics of horizontal air–water slug flows through a dividing T-junction

Experimental data from horizontal air–water slug flows were obtained in a test facility which was a 34mm internal diameter, 10m long Plexiglas pipe connected to the 90° branch arms from a T-junction. The test points were located on the flow pattern map in the proximity of the transition lines which separates different flow patterns. Capacitive probes with helical and concave plate sensors were used to quantify the dynamic liquid holdup in each branch. They were combined with Venturi nozzles+differential pressure transmitters in each outlet branch for measuring the two-phase mass flow rates. The dynamic characteristics of the slug flow splitting in a T-junction were studied from the acquired signals. Diaphragm straight-through type valves were used in the run and in the lateral branch arms to imitate equipments consuming the two-phase flow after the T-junction. This assembly can also be used as a gas–liquid separation system. The results showed different mechanisms acting on the slug flow division phenomenon. Liquid accumulation into the run branch, between the TJ and the control valve, caused more gas to come to the lateral branch.

Pressure Drop and Residence Time Distribution in Carbon-Nanofiber/Graphite-Felt Composite for Single Liquid-Phase Flow

Fibrous carbon nanofiber composite is prepared by growing carbon nanofibers on graphite felt. Pressure drop experiments are carried out with ethanol solution to study the influence of the liquid surface tension on the permeability of the composite, and residence time distribution experiments with cyclohexane and water respectively are performed to study the effect of the fluid wettability on the flow behavior in the composite. Piston dispersion exchange (PDE) model is employed to determine the dynamic liquid holdup, the axial dispersion, and the mass transfer between the dynamic and static liquids. When the fluid is less oleophilic, less space in the CNF layer will be open for the flow, and the fluid will be more likely to slip over the carbon surface. Compared with the flow in spherical particle packing and in monolith, the mass transfer in the composite is high owing to its fibrous structure that splits the fluid into streamlets. The rate of mass transfer in water is lower than that in cyclohexane becau...

Hydrodynamics and flow regime transition study of trickle bed reactor at elevated temperature and pressure

The hydrodynamics in a trickle bed reactor (TBR) in non-ambient conditions are studied for air–water and air–acetone (pure organic liquid of low surface tension) systems. A flow map experiments for air–water and air–acetone systems are performed in a pilot plant reactor of 0.05 m i.d. and 1.25 m height. It has been demonstrated from the experimental results that the pressure drop tends to increase with increasing superficial gas and liquid velocity and reactor pressure, while it tends to decrease with increasing bed temperature. The results also show that the dynamic liquid holdup increases with increasing liquid velocity and decreases with increasing superficial gas velocity, reactor pressure and bed temperature. The dynamic liquid holdup and pressure drop values are obviously higher than those measured for air–water system at the same fluid fluxes, reactor pressure and bed temperature due to the surface tension effects. For higher reactor pressure and temperature, the trickle to pulse transition boundary shifts towered higher superficial velocities of both gas and liquid.

CFD simulation and experimental study for two-phase flow through the trickle bed reactors, sock and dense loaded by trilobe catalysts

In this study single and two phase flow through the trickle bed reactor loaded with a two different loading manner, sock and dense, have been investigated numerically and experimentally. The CT-scan imaging and an image processing code have been used for investigation of radial porosity distribution of trilobe catalyst in sock and dense loading procedure in trickle bed reactors and two different correlations have been proposed. These correlations were used in a single and two phase CFD code for prediction of pressure drop of gas flow in dry and prewet trilobe catalyst packed bed and also pressure drop and dynamic liquid holdup for two phase flow. In addition, these variables were studied experimentally with a laboratory scale trickle bed reactor. The results of CFD simulations show a very good agreement with experimental data.

Gas–liquid mass transfer in periodically operated trickle-bed reactors: Influence of the liquid-phase physical properties and flow modulation

The influence of periodic operation on trickle-bed reactor (TBR) hydrodynamics and gas–liquid mass transfer was investigated. Two-phase pressure drop, dynamic liquid hold-up and gas–liquid mass transfer coefficient ( k L a) were determined at various liquid flow rates and for different modes of liquid flow variation (increasing and decreasing liquid flow rate). The results reveal the considerable influence of type of liquid flow rate modulation on k L a values (deviations of up to 80% in k L a). Simulation studies on gas-limited reaction in a periodically operated TBR indicate that an enhancement in conversion of about 14% can be expected from an appropriate selection of the operating mode, thus clearly demonstrating the quantitative process intensification feasible through increased gas–liquid mass transfer.