Multiphase Reactors Research Articles

Incorporating hydrodynamics into spatiotemporal metabolic models of bubble column gas fermentation

Gas fermentation has emerged as a technologically and economically attractive option for producing renewable fuels and chemicals from carbon monoxide (CO) rich waste streams. LanzaTech has developed a proprietary strain of the gas fermentating acetogen Clostridium autoethanogenum as a microbial platform for synthesizing ethanol, 2,3-butanediol, and other chemicals. Bubble column reactor technology is being developed for the large-scale production, motivating the investigation of multiphase reactor hydrodynamics. In this study, we combined hydrodynamics with a genome-scale reconstruction of C. autoethanogenum metabolism and multiphase convection-dispersion equations to compare the performance of bubble column reactors with and without liquid recycle. For both reactor configurations, hydrodynamics was predicted to diminish bubble column performance with respect to CO conversion, biomass production, and ethanol production when compared with bubble column models in which the gas phase was modeled as ideal plug flow plus axial dispersion. Liquid recycle was predicted to be advantageous by increasing CO conversion, biomass production, and ethanol and 2,3-butanediol production compared with the non-recycle reactor configuration. Parametric studies performed for the liquid recycle configuration with two-phase hydrodynamics showed that increased CO feed flow rates (more gas supply), smaller CO gas bubbles (more gas-liquid mass transfer), and shorter column heights (more gas per volume of liquid per time) favored ethanol production over acetate production. Our computational results demonstrate the power of combining cellular metabolic models and two-phase hydrodynamics for simulating and optimizing gas fermentation reactors.

Single bubble breakup in the flow field induced by a horizontal jet—The experimental research

AbstractBubble breakup in multiphase reactors has a direct and important impact on the mass transfer and reaction process. This paper experimentally investigated the single bubble behaviors of deformation and breakup under the affecting of a jet submerged in a water‐filled tank. The dispersed phase motion was captured by a high speed camera, while the continuous phase flow field was analyzed by Particle Image Velocimetry. By changing the downstream location of bubble generation, the liquid flow rate and the initial bubble size, the breakup processes were analyzed and discussed. The breakup point, break pattern, and distribution of daughter bubbles were summarized. The position where the bubble gets the maximum acceleration was defined as the shear position, and the forces on the bubble at the shear position had a significant impact on whether breakup will occur. The expected bubble number, which could reflect a combination of the breakup probability and daughter bubbles distribution, was defined and found to be directly proportional to the capillary number of bubbles at the shear position. The research result will contribute to promoting the understanding and control of multiphase flow, and providing a theoretical basis and technical support for the design and optimization of multiphase reactors.

New technique for simultaneous measurement of the local solid and gas holdup by using optical fiber probes in the slurry bubble column

Design and scale-up of the slurry bubble columns, as popular multiphase reactors, is complicated because of the complexity of the hydrodynamics of these types of reactors. In fact, to have a good design, precise information about the local hydrodynamic parameters are required. In this study, a new method is developed for simultaneous measuring of the local solid, gas and liquid holdup in the slurry bubble column. Optical fiber probes were used to measure phase distribution inside the bubble column. Our specific calibration procedure enables probes to measure solid concentration in the slurry phase as well. In order to examine the proposed measurement method, a cylindrical plexiglass column with 270 cm height and 29.2 cm diameter was utilized as the slurry column which contained water, glass beads, and air. The mean diameter of the glass beads is 35 µm and the experiments were done with 1% and 3% solid loading (volume solid/volume slurry). To cover both homogeneous and heterogeneous flow regime in the bubble column, air with a wide range of superficial gas velocity (0–22 cm/s) was injected into the slurry phase. The obtained results showed that the axial distribution of the solid particles is not uniform along the column, and a local minimum concentration observed in the middle of the column. In the homogeneous regime, the local solid concentration increased by raising the superficial gas velocity while solid particle distribution was independent of the gas velocity in the heterogeneous flow regime.

Hydrodynamics and Reaction Performances of Multiphase Reactors for Marine Applications – A Review

AbstractHydrodynamics and (catalytic & non-catalytic) reaction [high-pressure hydrodesulfurization; Fischer-Tropsch synthesis; CO2-monoethanolamine (MEA) absorption; simultaneous CO2and H2S absorption in MEA; CO2thermal desorption, enzymatic CO2hydration] performances of trickle-bed and packed-bed column reactors subjected to static inclination, rolling (symmetrical/asymmetrical externally-generated reactor oscillations) and heaving motions were analyzed via detailed dynamic 3-D models which couple the macroscopic volume-averaged momentum, mass, energy and species balance equations in the liquid/gas phases with diffusion/chemical reaction inside the catalyst particles, enzyme washcoat or liquid film near the gas-liquid interface. Axial symmetry breakdown once the packed bed systems become inclined inflicts noticeable reductions of the reactor (or scrubber) performances. Only the performance of Fischer-Tropsch synthesis in the presence of water-gas shift reaction increases slightly with the increase of trickle-bed reactor inclination because of facile uptake of reactants in the key reactions from the gas phase while a fraction of valuable CO can be forwarded in water gas-shift reaction. For most of the reactions examined, the reactor performance is negatively impacted in asymmetric oscillating multiphase reactors with Fischer-Tropsch synthesis as an exception owing to the presence of water-gas shift reaction the performance of which is slightly improved. This performance deterioration/enhancement is maximal for the reactor moving between vertical and an inclined position when the time-dependent performance waves develop around the steady-state solution of the mid-inclination angle. The oscillatory reactor performance moves towards the steady-state solution of the vertical state when the asymmetry between the two inclined positions dwindles. Symmetric oscillating and heaving trickle-bed and packed-bed column reactors generate an oscillatory performance around the steady-state solution of vertical state which is affected by the amplitude and period of the angular and heaving motions of the vessel.

Hydrothermal gasification of sorbitol: H2 optimisation at high carbon gasification efficiencies

Using both experiments and modelling, hydrothermal gasification of sorbitol (SB) aiming at maximal carbon to gas conversion and H2 production was investigated over a wide temperature range (270–350 °C). Kinetics were studied in a continuous tubular reactor using a Pt/γ-Al2O3 catalyst. The addition of N2, resulting in lower H2 concentrations in the liquid phase, was found to have a beneficial effect in terms of higher H2 yield without compromising on the carbon gasification. The highest H2 yield obtained in this work was 4 mol H2/mol SB. Existing reaction schemes for sorbitol gasification were used to derive a path-lumped scheme. A multi-phase reactor model including a path-lumped scheme and gas-liquid-solid mass transfer was developed and parameterized based on datasets with varying temperature, space velocity, inlet gas composition (N2 or H2) and gas-liquid flow ratio. The developed model was used to provide guidelines for the design of an industrial reactor for the gasification of 10 tons/h of 10 wt% aqueous sorbitol. The effect of N2 stripping and industrially attainable kLa values were found to boost the H2 yield from 4 to 12 mol H2/mol SB making it an attractive process for further consideration.

Residence time distribution in rapid multiphase reactors

Residence time distribution (RTD) provides information about average hydraulic residence time and the distribution of material in the reactor. A method for determining RTD for reactors with very short hydraulic residence times is deconvolution based on extraction of real RTD by the analysis of a non-ideal input signal. The mean residence time and dispersion were determined for the spinning fluids reactor (SFR). For the first time the deconvolution method was performed for a system where the tracer pulse signal is wider than actual RTD of the examined device. A prediction model for of the SFR was also developed, and validated.

Evaluation of Fe-Functionalized 4A Zeolite as Ozone Catalyst for an Enhancement of Hydroxyl Radical Pathway in a Multiphase Reactor

ABSTRACTIron doping 4A zeolite (Fe-4A) was prepared and demonstrated as ozone catalyst to enhance hydroxyl radical (HO·) pathway. Fe-4A composites with different iron load were characterized, and the catalytic effects were discussed dealing with para-chlorobenzoic acid (p-CBA), atrazine (ATZ), and oxalic acid (OA) as model compounds. Results showed that Fe-4A/ozone system promoted the production of HO·, which was in-line with the strength of Lewis acidity that might have accelerated ozone-to-HO· transformation. Modeled RCT value validated the enhanced HO· exposure during catalysis that was more evident for 4%-Fe-4A. The Fe-4A exhibited structural stability and allows repeated use after facile regeneration.

Development of a 3D Hybrid Intelligent‐Mechanistic Model for Simulation of Multiphase Chemical Reactors

AbstractA novel intelligent‐mechanistic model was developed to understand the behavior of multiphase chemical reactors. Computational fluid dynamics (CFD) and an intelligent algorithm were combined to predict different levels of 3D cylindrical bubble‐column reactors. An adaptive neuro‐fuzzy inference system (ANFIS) was used as the intelligence algorithm, and different ANFIS parameters were evaluated. With about one third of the training data the method can predict the overall behavior of the gas fraction in the reactor. A number of rules significantly influence the accuracy of the ANFIS method. After finding appropriate parameters, the method is applied for prediction of points which are not simulated with CFD, representing ANFIS mesh refinement. Also, bubble‐column reactors without training of exact values of measured data or numerical results can be predicted. Main advantages are time savings and reduction of computational expenses.

Advanced trust region optimization strategies for glass box/black box models

We present an improved trust region filter (TRF) method for optimization of combined glass box/black box systems. Glass box systems refer to models that are easily expressed in an algebraic modeling language, providing cheap and accurate derivative information. By contrast, black box systems may be computationally expensive and derivatives are unavailable. The TRF method, as first introduced in our previous work (Eason and Biegler, AIChE J. 2016; 62:3124–3136), is able to handle hybrid systems containing both glass and black box components, which can frequently arise in chemical engineering, for example, when a multiphase reactor model is included in a flow sheet optimization problem. We discuss several recent modifications in the algorithm such as the sampling region, which maintains the algorithm's global convergence properties without requiring the trust region to shrink to zero in the limit. To benchmark the development of this optimization method, a test set of problems is generated based on modified problems from the CUTEr and COPS sets. The modified algorithm demonstrates improved performance using the test problem set. Finally, the algorithm is implemented within the Pyomo environment and demonstrated on a rigorous process optimization case study for carbon capture. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3934–3943, 2018

A New Concept of Stirred Multiphase Reactor Using a Stationary Catalytic Foam

Developing new stirred gas–liquid–solid reactors with high mass transfer capabilities is still a challenge. In this publication, we present a new concept of multiphase reactor using a stationary catalytic foam and a gas-inducing impeller. The gas–liquid (GL) and liquid–solid (LS) mass transfer rates in this reactor were compared to a stirred reactor with basket filled with beads. Batch absorption of hydrogen and measurement of α-methylstyrene hydrogenation rate on Pd/Al2O3 catalyst were used to evaluate kGLaGL coefficients and kLS coefficients, respectively. With similar LS transfer rates to the basket-reactor and much higher GL transfer rates, the new reactor reveals a very promising tool for intrinsic kinetics investigations.

Investigation of phases interactions and modification of drag models for liquid-solid fluidized bed tapered bioreactors

Fluidized bed bioreactors have been increasingly applied to wastewater treatment, since they offer advantages when compared to other reactors, such as high mass transfer and low excess of sludge per unit of reactor volume. Numerical techniques such as Computational Fluid Dynamics (CFD) can be applied to study these multiphase reactors in detail. However, in most of the available literature it is possible to find only models developed to predict gas-liquid or gas-solid interactions, even though the dynamics in anaerobic bioreactors is dominated by interactions between the liquid and solid phases. The aim of the present study is to evaluate the effect of the drag force together with the influence of the lift force and particles collisions on the prediction of bioparticles fluidization. Moreover, a modification to the drag model will be presented in order to achieve better agreement with experimental data. Simulations were performed with a two-phase, transient and turbulent approach, applied to a symmetrical three-dimensional geometry. Results show a redistribution of the bioparticles along the radial direction due to the lift force. Moreover, the use of different restitution coefficient values did not significantly affect the height of the fluidized bed. It was also observed that the usual drag models are unsuitable for predicting the height of the liquid-solid fluidized bed in the case considered, i.e. with bioparticles. A modification of the drag force with a dimensionless number provided good agreement with the experimental data under different operational conditions.

Load-dependent contact mechanics of particulate assemblies: Multi-variant particle size, shape and surface roughness in advanced materials and process applications

Many of the industrial manufacturing processes of particulate materials are presently modeled using Discrete Element Models (DEM), and in some instances hybrid multi-phase models combining DEM with CFD and other hydrodynamic variants, see Chareyre (2018) and Mehta (2007). The early tribology work in 80s and 90s on load-dependent particle contact mechanics for use in computational algorithms relied on considerations of single-point contacts between smooth elastic and rigid-plastic spheres and curvilinear surface contacts between cylindrical shapes; see Johnson (1985). Later developments included multiple-asperity surface contacts and elastic/plastic surface interactions as well as contact angle variations; see Tuzun and Walton (1992), Tuzun et al. (2004) and Smith and Tuzun (2002a) that include many other references. In this paper, the established theoretical framework is reviewed first for calculating bulk assembly stresses and bulk shear patterns from single-particle contact mechanics highlighting the importance of the particle shape, size and surface roughness. Subsequently, illustrations are provided of the effects of relaxing the assumptions of mono-disperse particle size and shape on the bulk shear patterns observed during slow-shearing, packed assembly flows as seen in chutes and hoppers and in particle heaps respectively. Finally, an analogy is provided between the studies of the deformation response of material composites comprising of particles embedded within a matrix structure to sustained stress-loading and unloading cycles; see Hull and Clyne (2017) and those observed in flowing particle assemblies under compression and shear. Such an analogy can be particularly useful in predicting the flow behaviour of particles “tailor-made” for advanced functionality commonly encountered in applications as widely ranging as multi-phase catalytic reactors and separators, drug manufacture, renewable energy production and storage and in chemical and physical abatement of harmful environmental emissions.

Plenum-to-plenum natural convection heat transfer within a scaled-down prismatic modular reactor facility

Multiphase Reactors Engineering and Applications Laboratory (mReal) at Missouri University of Science and Technology (S&T) has developed a natural convection heat transfer test facility with one riser and one downcomer between two plena to investigate loss of flow accident scenario (LOFA) for a prismatic very high temperature reactor (VHTR). Using advanced heat transfer coefficient probe and T-thermocouples (1.6 mm), this paper reports the effect of the outer surface temperatures of the upper plenum and downcomer channel (278.15, 288.15, 298.15, and 308.15 K) on the intensity of natural circulation during LOFA with helium at 413.685 kPa. The results showed that there is a reduction in the centerline temperature of ∼10.14% and inner wall surface temperatures of ∼7.4% along the riser channel with decreasing upper plenum and downcomer temperatures from 308.15 K to 278.15 K. A reversal in the direction of heat transfer is observed close to the exit of the riser channel (Z/L = 0.773) for outer surface temperature 288.15, 298.15, and 308.15 K due to the end effect. It is worth mention that, the negative signals of heat fluxes are observed along the downcomer channel for all operating conditions, which confirms heat removal from helium and a downward flow along the downcomer channel, hence establishment of natural circulation. The results also showed a gain in the values of heat transfer coefficients along the riser channel with decreasing the outer surface temperature which is consistent with the literature. In comparison to the literature with air as coolant, the current results showed the role of helium on the thermal performance of natural circulation loop in terms of co-circulation of plumes and end effects.

Particle Scattering Photography Approach for Poorly Illuminated Multiphase Reactors. II: Experimental Validation and Optimization

Based on the particle scattering photography approach proposed in Part I, a series of experiments are conducted in this work to validate the theoretical analysis, demonstrate the application features qualitatively and quantitatively, and evaluate the measurement errors. As expected, aided respectively by scattering light of four representative oxide powders (TiO2, Al2O3, CuO, and SiO2), the grayness differences between the bubbles and continuous phases in all images are improved with different extents, and especially the TiO2 particles perform the best. Grayness differences present a unimodal distribution with TiO2 concentration variation, and the optimum concentration is 7.3 mg/L. This particle scattering approach is proven to be more accurate, with an average error of 20%).

Particle Scattering Photography Approach for Poorly Illuminated Multiphase Reactors. I: Theoretical Model and Simulation

The great challenge is encountered in photographic measurement, with regard to distinctly distinguishing the particle profiles from the background (continuous phase) in poorly illuminated multiphase reactors. In this work, a novel approach utilizing particle scattering is proposed to enhance the brightness contrast. The theoretical basis of this approach is described in detail. A single particle scattering model based on noncoherent scattering hypothesis is built up to evaluate the scattering property. The quantitative relationships between scattering flux and scattering coefficient/absorption coefficient are established. Furthermore, the partial light fluxes projected onto the focal plane by single particles of different sizes are also calculated. Combined with the particle scattering and dispersion, an optimal particle size of ∼0.5–1.5 μm is designated. On this basis, four representative oxide powders are tested as scattering particles, i.e., TiO2, Al2O3, CuO, and SiO2; in addition, the TiO2 particles a...

A Novel Continuous Multiphase Reactor for Chemically Processing Polymer Fibers

Chemical reactions on the surface or throughout a thermoplastic fiber present an interesting and challenging reaction engineering problem. This paper presents the design and implementation of a mod...

Mathematical modelling of expanded bed adsorption-a perspective on in silico process design.

Expanded bed adsorption (EBA) emerged in the early 1990s in an attempt to integrate the clarification, capture and initial product concentration/purification process. Several mathematical models have been put forward to describe its operation. However, none of the models developed specifically for EBA allows simultaneous prediction of bed hydrodynamics, mass transfer/adsorption and (unwanted) interactions and fouling. This currently limits the development and early optimization of EBA‐based separation processes. In multiphase reactor engineering, the use of multiphase computational fluid dynamics has been shown to improve fundamental understanding of fluidized beds. To advance EBA technology, a combination of particle, equipment and process scale models should be used. By employing a cascade of multiscale simulations, the various challenges EBA currently faces can be addressed. This allows for optimal design and selection of equipment, materials and process conditions, and reduces risks and development times of downstream processes involving EBA. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Computational fluid-dynamic modeling of the mono-dispersed homogeneous flow regime in bubble columns

Two-phase bubble columns are equipment used to bring one or several gases into contact with a liquid phase. Despite the simple system design, bubble columns are characterized by complex fluid dynamic phenomena at different scales; for this reason, their correct design, operation and scale-up rely on the precise estimation of global and local fluid dynamics properties. In this respect, multi-phase Computational Fluid Dynamics (CFD), in the Eulerian multi-fluid framework, is particularly useful to study the fluid dynamics in multi-phase reactors. Within this approach, the accurate prediction of the fluid dynamics depends on the correct modeling of (a) the momentum exchange between the phases, (b) the effects of the dispersed phase on the turbulence of the continuous phase, and (c) the bubble coalescence and break-up phenomena. Furthermore, the global and the local fluid dynamic properties are related to the prevailing flow regime, i.e., the homogeneous flow regime and the heterogeneous flow regime. This paper mainly focuses on the homogeneous flow regime, which can be classified as “pseudo-homogeneous” or “mono-dispersed homogeneous”, depending on the prevailing bubble size distribution. The numerical modeling of the “pseudo-homogeneous” flow regime has been discussed in our previous papers (i.e., modeling closures and suitable boundary conditions); conversely, this paper contributes to the existing discussion on the modeling closures by investigating the “mono-dispersed homogeneous” flow regime in “small-scale” and “large-scale” bubble columns. To this end, two test cases have been considered: (a) a “small-scale” bubble column (a test case taken from the previous literature); (b) a large-scale bubble column (a test case experimentally studied within this paper by image analysis, optical probe and gas holdup techniques). In particular, this paper studies the effects of the interfacial forces and bubble induced turbulence modeling within the Eulerian two-fluid approach. Three-dimensional transient simulations have been performed and the numerical results were compared with experimental data (both local and global fluid dynamics parameters). The results have been critically analyzed and the reasons for the discrepancies between the numerical results and the experimental data have been identified and may serve as a basis for future studies. Likewise, recommendations on suitable closures as well as guidelines for future studies have been provided. In conclusion, this paper extends the validation of a previously proposed set of closure relations (validated for the “pseudo-homogeneous” flow regime in a “large-scale” annular gap bubble column) to the “mono-dispersed homogeneous” flow regime in “small-scale” and large-scale bubble columns.

Dual emission LIF technique for pH and concentration field measurement around a rising bubble

Mass transfer plays an important role in chemical engineering applications involving multiphase systems. Several techniques have been developed in the field to measure the global mass concentration in multiphase chemical reactors. However, because of the complexity of multiphase processes, only few techniques are able to provide local and quantitative information. In this study a dual-emission Laser Induced Fluorescent technique (LIF) has been developed to locally measure the mass transfer of a rising CO2 bubble in a quiescent fluid. Details of the pH field with an overall precision of ±0.04 pH units, dissolved CO2 concentration, and the mass transfer evolution in the bubble wake can now be measured quantitatively. It is capable to provide quantitative comparison with simulation results and as such experimental validation of multiphase CFD models.