Multiphase Reactors Research Articles

Modeling of an industrial scale hydrodynamic cavitation multiphase reactor for Prileschajew epoxidation

AbstractThe hydrodynamic cavitation multiphase reactor (HCMR) is emerging as a promising alternative for the intensification of liquid–liquid heterogeneous reactions, but research on HCMR modeling is lacking. In this article, an HCMR model was developed using Prileschajew epoxidation as the model system. First, based on experimental measurements of oil/water two‐phase flow downstream of hydrodynamic cavitation devices, semiempirical correlations were proposed to describe the droplet size and droplet size distribution (DSD) as functions of flow conditions and geometry parameters. Then, with boundary conditions calculated by the DSD correlation, a droplet dynamics simulation in a reaction tank was performed by computational fluid dynamics coupled with population balance model to obtain the two‐phase interfacial area. Finally, the acquired reactor model was substituted into an overall kinetic model, to simulate the epoxidation reaction in HCMR. Model predictions were verified by experimental results measured on an industrial scale HCMR.

Adaptive neuro-fuzzy prediction of flow pattern and gas hold-up in bubble column reactors

The prediction of fluid dynamics in multiphase bubble column reactors is a subject of major concern to appropriately design and optimize them. This paper employs the combination of computational fluid dynamics (CFD) (i.e., Euler–Euler approach) and adaptive neuro-fuzzy inference system (ANFIS) to propose new a viewpoint for multiphase modeling, including the accuracy of soft computing technique in prediction of a 3D bubble column reactor. Existing experimental, numerical and correlations results in the literature have been used to validate the implementation of the Euler–Euler approach. The results of Euler–Euler approach for a 3D bubble column reactor has been used for input training data which are liquid velocity, turbulent kinetic energy and gas hold-up. The ANFIS results have been also compared with Eulerian results, using root-mean-square error (RMSE) and coefficient of determination and Pearson coefficient. The results show that, flow pattern and gas hold-up are mainly affected by bubble column height, meaning towards sparger region, gas hold-up has a higher value near the ring sparger. According to the results, a greater improvement in estimation has been achieved through the ANFIS. Overall, the results show that ANFIS is a robust method to predict bubble column hydrodynamics parameters (e.g., liquid flow pattern and gas hold-up) as input. In addition, the exactness of the proposed ANFIS model may be boosted by considering more meteorological parameters as input values.

Aspect ratio of bubbles in different liquid media: A novel correlation

The bubble shape is a required parameter in the modeling and design of multiphase reactors. This communication contributes to the broader discussion and closes the knowledge gap by providing a practical correlation for the bubble shape. The correlation is based on a very large experimental dataset, encompassing a wide range of Morton numbers (Log10(Mo) in the range of −10.8 and 2.3), flow conditions (single bubbles and dense bubbly flows) and considering both gravity-driven flows and flows with an extra-external pressure gradient (counter-current flows). The experimental data were post-processed to derive a simple and physics-based correlation, relating the bubble aspect ratio to the bubble Reynolds and Eötvös numbers. This correlation provides a more accurate description and covers a wider range of applicability compared with literature correlations. As such, it can be helpful in the estimation of the interfacial area and velocity of a dispersed phase rising in a continuous phase.

State estimation for heavy oil hydroprocessing reactors using extended Kalman filters

A state estimator for a class of slurry-phase reactors for heavy oil hydroprocessing is presented. The algorithm is based on the extended Kalman filter formulation for non-linear systems under plant-model mismatch. Although state and parameter estimation have been widely used in the literature for different reacting systems, so far it has not been applied in multiphase slurry reactors for heavy oil hydroprocessing since modeling and simulation of this type of systems is still an emerging area. The reactor and kinetic models used to formulate the filter algorithm were taken from the literature for hydrocracking and hydrotreating reactions of an atmospheric residue (312 °C+) for different slurry-phase reactor configurations. In order to simulate a real plant operation were measurements for heavy oil composition are difficult to obtain online, the present study assumed that the system states were estimated using only temperature measurements and the proposed slurry-phase reactor models. Simulation results have shown that the extended Kalman filter provides acceptable estimations of the systems states and that they can be used for online control and process optimization. However, these results need to be validated once experimental data for this system becomes available.

Computational flow analysis of bubble formation dynamics in a liquid column subjected to high centrifugal force

Bubbling of gaseous medium in a liquid column is integral to many multiphase process reactors involving liquid phase and gas phase reactants. In one such reactor called centri-bubble singlet oxygen generator (CBSOG), chlorine gas is injected against a substantively high centrifugal force into a layer of basic hydrogen peroxide (BHP) solution. This process generates small bubbles that facilitate the reaction between chlorine gas and BHP solution at the gas liquid interface, resulting in the production of singlet oxygen. Performance of this device depends primarily on bubble formation time, its shape and size, and its interaction with other bubbles. This paper presents the numerical analysis of bubble formation at high centrifugal force (3800 m/s2) for various gas flow rates at orifice sizes of 0.3mm and 0.5mm. The volume of fluid (VOF) model of the computational flow dynamics (CFD) solver Fluent has been used for the computations to carry out a transient 3-dimensional simulation for generation of bubbles in a laminar incompressible flow.

Multi-objective reactor design under uncertainty: A decomposition approach based on cubature rules

Model-based strategies for chemical reactor design proved to be a reliable tool for the systematic design of resource and energy efficient chemical reactors. The adequacy and accuracy of the underlying model equations (e.g. reaction kinetics and kinetics for heat and mass transport) are crucial for the success of such design approaches. However, the models used in chemical engineering are typically based on experimental data and predictive expressions for the fundamental phenomena and thus the respective model parameters are inevitably subject to uncertainty. Therefore, consideration of parametric uncertainty in the design strategy is necessary to obtain reliable chemical reactor designs. Moreover, the design of chemical reactors involves almost always multiple conflicting objectives which poses an additional challenge.In the present work, we propose an efficient reactor design strategy to tackle the combined challenges of parametric uncertainty and multiple conflicting objectives. The approach combines a scalarization method with a cubature rule to efficiently determine robust compromise solutions. The cubature rule is used to approximate the first two statistical moments of the objectives and of all critical inequality constraints. The approximation of the statistical moments is performed separate from the optimization problem. This leads to an iterative approach with improved computational performance. The proposed approach is illustrated and compared to an existing approach from literature by studying three different reactor design case studies, namely the optimization of a batch, semi-batch and multi-tubular fixed-bed reactor.The results of the newly proposed reactor design approach and the existing method from literature are in very good agreement for all considered case studies. The advantage of the new approach is a significantly lower computational effort compared to the existing method. This is especially visible for the more complex case studies with a higher number of uncertain parameters. The advantage of the approach proposed in the present work is thus particularly relevant and important for the application to complex reactor design tasks such as, e.g., the design of polymerization reactors or multi-phase reactors.

Multiscale modelling of mass transfer in gas jets and bubble plumes

AbstractThe injection of high‐speed gas streams into liquids is common in many industrial applications, such as sparging in multiphase reactors and contacting in mass transfer devices. Modelling the fluid dynamics and associated heat and mass transfer processes in such a system is complex because it involves many governing scales and drastic changes in physical properties. In this study, one formulation of a multiscale computational fluid dynamics model is proposed to simulate the fluid dynamics and mass transfer in such systems. The model uses volume‐of‐fluid interface capturing in regions where high mesh resolution can be attained and the drift‐flux or mixture model approximation in regions where mesh resolution is too low to directly resolve interface dynamics. The model was developed to provide a tunable, automatic transition between the two modelling approaches for both fluid dynamics and mass transfer predictions. The approach was validated through a comparison with results from two published studies. In the first case, the implementation of the drift‐flux model was validated through the simulation of a dispersed gas bubble plume injected into a cylindrical tank. In the second case, the fluid dynamics and mass transfer predictions were compared to results from an experimental study involving the horizontal injection of air into a rectangular tank filled with water for the application of aeration. The results show that the modelling approach can provide a good prediction of the experimental data using only limited fitting of empirical parameters, making it applicable to a broad range of other applications.

Experimental validation of design and performance parameters of radioactive particle tracking (RPT) experimentation

In recent years, radioactive particle tracking (RPT) has emerged as a powerful noninvasive technique for characterization and visualization of flow in opaque multiphase flow reactors. This technique has been applied to a variety of multiphase flow reactors largely based on the theoretical framework for optimal design and performance parameters. No systematic evaluation and validation of the design and performance parameters of the RPT technique has been reported in the literature thus far. Consequently, the theoretical framework for the design of RPT experiments has had limited scalability and application to a wide variety of flow systems. Thus far, design of a “good” RPT experiment continues to be an art, no matter how much the richness of flow of information that the experimental method brings. The present work reports systematic experimental evaluation of design parameters for an optimal RPT experiment and validation of the theoretical results reported in literature. The experiments were performed in a carefully designed setup in which precise positioning of the tracer particle was made possible. The experiments assess the effect of various parameters on the performance of the RPT experiment, such as the choice of radioactive isotope, activity, gamma-ray energy, size of the detector, and relative positioning of detectors. Finally, a set of recommendations based on experimental work are provided to “optimally” perform the RPT experiment in any single or multiphase reactor.

Feasibility of Using Radioactive Particle Tracking as an Alternative Technique for Experimental Investigation in Bubble Column Reactor

Radioactive particle tracking (RPT) is one of the non-invasive techniques for monitoring and investigating multiphase flow system. This technique have been widely utilized in the field of chemical process engineering for better understanding and optimizing process hydrodynamics especially in the multiphase reactor such as bubble column reactor. Due to opaque nature of industrial process systems, especially in the case of multiphase flows, noninvasive methods based on ionizing radiation have been considered for evaluating the hydrodynamic parameters. The feasibility study of radioactive particle tracking techniques in quadrilateral bubble column reactor has been successfully achieved. The radioactive particle tracking facility and data acquisition system has been developed and experimental calibration using single particle radioactive particle 46Sc to investigate dynamics behaviour of quadrilateral bubble column reactor is completed. The results indicated that there is back mixing behaviour in the bubble column process. The results also reported that the radioactive particle 46Sc is still in good condition and there is no radiation contamination problem arises while performing radioactive particle tracking techniques. The RPT technique was performed to reveal the instantaneous velocity and time-averaged liquid velocity in the current bubble column reactor.

Industrial Manufacturing of Aqueous Solutions of Sodium Sulfhydrate (NaHS 43%) in a Multi-Phase Reactor

Background:This research deals with the manufacture of sodium sulphides and sodium sulfhydrate in an isothermal multiphase chemical reactor to produce concentrated aqueous solutions of sodium sulfhydrate (greater than 43%) through Gas-Liquid-Solid reactions from hydrogen sulfide and hydroxide of sodium at 50%.Methods:A method is proposed that integrates the recovery of hydrogen sulfide from an industrial chemical process where the H2S gas is generated as a sub product, the strategy of the developed process was integrated into a manufacturing plant of dithiophosphoric acids (ADTF) where it was possible to recover the hydrogen sulfide in the form of an aqueous solution of NaHS with a concentration higher than 43%.Results:The experimental tests showed that the biphasic reaction mixture formed by Na2S, NaHS and H2O with global compositions of 13.3%; 26.9% and 59.7% respectively, is appropriate to obtain 43% sodium sulfhydrate in a stirred tank reactor, operated at temperatures ranging from 50°C to 55°C, where gaseous hydrogen sulfide is continually bubbled.Conclusion:Sodium sulfide (specifically Na2S.5H2O crystals) of the biphasic mixture is produced from a solution of sodium sulfhydrate (43% NaHS) and aqueous sodium hydroxide (50% NaOH). The environmental problem generated by the H2S was solved with a 90% recovery in the multiphase reactor and 5% in the safety absorber.

Image analysis assessment of the effect on mixing on aqueous dissolution of CO2 and air bubble swarms in a bubble column

Many processes for capture and use of carbon dioxide, CO2, involve aqueous solutions containing salts, the dissolution of CO2 being rate-determining. For bubble column reactors, mixing the solution may increase the dissolution rate, reducing the necessary height. For this paper, extending an experimental cylindrical bubble tower set-up by the inclusion of mixers enables to observe the performance of multiphase bubble reactors. These experiments were done to gain deeper understanding on the dissolution and later chemical conversion of CO2 bubble swarms in agitated vessels. Bubble swarms of ∼100 bubbles were tracked using a high-speed camera. Comparison of the dissolution rate of bubble size distributions at different heights in a 2 m column revealed significant rates of CO2 mass transfer in contrast with hardly any change in the bubble size distribution for air. Results are consistent with the dissolution of single rising bubbles, and previous one-way coupling simulation shows a fair agreement with the experimental results. CO2 bubbles showed a smaller average size while increasing their bubble sphericity as function of height in the column. Initially, bigger CO2 bubbles present a wobbly behavior and trajectories, becoming more spherical while dissolving. The effect of the stirred environment increases as bubbles dissolve, affecting trajectories and velocities, as smaller spherical bubbles don’t show a linear rising trajectory. Comparing results without and with mixing showed that increased mixing rates bring down the height needed for dissolution, especially in the middle section of the column, where bubbles are no longer wobbly yet are not yet very small.

Hydrogen and methane bio-production and microbial community dynamics in a multi-phase anaerobic reactor treating saline industrial wastewater

This study investigated the biogas (hydrogen and methane) production and microbial community dynamics in the anaerobic treatment of saline industrial effluents containing mono-ethylene glycol (MEG) as a major pollutant. An immobilized sludge anaerobic baffled reactor (ISABR) inoculated with salt-adapted mixed culture was developed as a lab-scale experiment, and effects of operational conditions (e.g., salinity, organic loading rates (OLRs), and temperature) on the system performance were examined. First, different OLRs of 0.64–2.34 gCOD/L/d, by increasing the initial MEG concentrations at a fixed hydraulic retention time (HRT) of 4.5 d, were examined from day 1 to 100 at lower salinity of 10 gNaCl/L and ambient temperature (25 ± 6 °C). Under such operational conditions, maximum methane yield (MY) of 165 mL CH4/gCODadd and hydrogen yield (HY) of 102 mL H2/gCODadd were achieved at the lowest OLR of 0.64 gCOD/L/d. Afterwards, impacts of higher salinities of 15–25 gNaCl/L were investigated from day 101 to 208 at a controlled mesophilic temperature of 35 °C and fixed OLR (0.64 gCOD/L/d). As a result, enhanced HY and MY (∼2-fold) at elevated salinities up to 25 gNaCl/L were obtained. Moreover, the compartment-wise water and gas analyses, for both experiments, revealed that hydrogen and methane peaked in former and latter compartments, respectively, and the peak location shifted depending on overall imposed OLR. The relative abundance of dominant salt-tolerant bacterial genus Desulfovibrio increased when OLR and operational temperature were increased, while dominant archaeal genera responded substantially when temperature was increased. Economic feasibility of ISABR for bioenergy recovery and treatment of MEG was evaluated by a cost-benefit analysis, suggesting that salinity level along with suitable operational temperature substantially affects the maximum net profit.

110th Anniversary: Marinization of Multiphase Reactors through the Prism of Chemical Engineers

Offshore oil/gas industries have been employing multiphase scrubbers and reactors to treat hydrocarbons extracted from undersea reservoirs. Operation of floating scrubbers and reactors on nonstationary platforms undergoes remarkable technical and operational challenges stemming from the complex sea states. Indeed, ship tilts and motions affect the reactor hydrodynamics and consequently its chemical performance. Therefore, imperatives for predicting and controlling the performance of offshore reactors by accounting for the contribution of marine swells have opened up considerable opportunities for research. This contribution presents an extensive chemical engineering overview on experimental and theoretical studies related to the effect of floating vessel motions on the performance of multiphase reactors and scrubbers. Cocurrent downflow, cocurrent upflow, and countercurrent gas–liquid packed beds, spinning gas–liquid packed beds, gas–solid fluidized bed, and bubble columns are reviewed with an emphasis on...

Micromixing efficiency in a multiphase reactor with a foam block stirrer

ABSTRACTA rotating foam reactor (RFR), which comprises a solid foam block stirrer as opposed to the agitator blade in stirred tanks, has recently received a significant amount of research interest due to its high mass transfer rates. For a deeper insight into the RFR the work herein investigated the micromixing efficiency of the RFR in terms of segregation index (Xs) using the iodide‐iodate reaction system. The effects of various operating parameters including injection time, rotational speed, acid concentration, volume of liquid, volumetric ratio, and gas flow rate on segregation index were systematically examined. Results showed that the segregation index remained constant when injection time exceeded 100 s. Moreover, the Xs increased with an increase in acid concentration but decreased with an increase in rotational speed, volume of liquid, volumetric ratio, and gas flow rate. Micromixing time was also calculated based on the incorporation model and was established to range from 1.1 × 10−3–4.5 × 10−2 s, which is much shorter than that of conventional reactors. The results herein demonstrate that an RFR exhibits excellent micromixing efficiency and has a significant potential for use in chemical industries.

Hydrodynamics and scale-up of bubble columns in the heterogeneous regime: Comparison of bubble size, gas holdup and liquid velocity measured in 4 bubble columns from 0.15 m to 3 m in diameter

The development of CFD models coupled with Population Balance is a very promising topic concerning multiphase reactors. In the case of bubbly flows and bubble columns, a serious lack of local hydrodynamic characterizations still harms development and validation of relevant models. To fill partially this gap, a new bubble size measurement technique, previously introduced by Maximiano Raimundo et al. (2016), has been applied on a very wide range of bubble column diameters (from 0.15 m to 3 m) and superficial gas velocities (from 0.06 m/s to 0.35 m/s). Size measurements have been coupled with others concerning gas holdup and axial liquid velocity, in order to provide an experimental database allowing to clarify the scale-up rules and to assist future modelling works. Average bubble sizes have been measured as globally similar at every scale. Measured holdup and average liquid velocity confirm already reported behaviours at lower column diameters. Liquid velocity fluctuations also follow self-similar radial profiles and are proportional to the average liquid velocity at the centre of the column leading to a strong turbulence intensity. The fact that the quantity (gD)1/2 appears as a natural velocity scale and the presence of strong gas-holdup gradients underline the similarity between bubble columns operated heterogeneous regime and free thermal convection in pipes.

Prediction of multi-inputs bubble column reactor using a novel hybrid model of computational fluid dynamics and machine learning

ABSTRACTThe combination of machine learning and numerical methods has recently become popular in the prediction of macroscopic and microscopic hydrodynamics parameters of bubble column reactors. Such numerical combination can develop a smart multiphase bubble column reactor with the ability of low-cost computational time when considering the big data. However, the accuracy of such models should be improved by optimizing the data parameters. This paper uses an adaptive-network-based fuzzy inference system (ANFIS) to train four big data inputs with a novel integration of computational fluid dynamics (CFD) model of gas. The results show that the increasing number of input variables improves the intelligence of the ANFIS method up to , and the number of rules during the learning process has a significant effect on the accuracy of this type of modeling. Furthermore, the proper selection of model’s parameters results in higher accuracy in the prediction of the flow characteristics in the column structure.

Liquid‐phase chemical reactors: Development of 3D hybrid model based on CFD‐adaptive network‐based fuzzy inference system

AbstractThe Euler‐Euler method plus an intelligent algorithm was used to predict bubbly flow in a reactor as a function of column height. The combination of computational fluid dynamics (CFD) and the adaptive network‐based fuzzy inference system (ANFIS) method was used for a chemical bubble column reactor to understand the complex behaviour of fluids in a multiphase reactor. Air fraction as one of the main factors in the scale‐up of reactors was selected as an output parameter for the prediction tool (ANFIS method) at different positions in the reactor. To train and test the prediction ability of this method, a 3D position of one CFD element was selected and, based on that position, a training algorithm was started. After an appropriate learning step, the method was used to simulate gas at different locations of the reactor. The different structures of the ANFIS algorithm were designed to obtain a correct predictive tool for fluid behaviour inside the bubble column. The ANFIS approach shows that it can simulate the liquid behaviour and the CFD results and ANFIS output correlate with one another.

Axial dispersion and mixing of coolant gas within a separate-effect prismatic modular reactor

Multiphase Reactors Engineering and Applications Laboratory performed gas phase dispersion experiments in a separate-effect cold-flow experimental setup for coolant flow within heated channels of the prismatic modular reactor under accident scenario using gaseous tracer technique. The separate-effect experimental setup was designed on light of local velocity measurements obtained by using hot wire anemometry. The measurements consist of pulse-response of gas tracer that is flowing through the mimicked riser channel using air as a carrier. The dispersion of the gas phase within the separate-effect riser channel was described using one-dimensional axial dispersion model. The axial dispersion coefficient and Peclet number of the coolant gas phase and their residence time distribution within were measured. Effect of heating intensities in terms of heat fluxes on the coolant gas dispersion along riser channels were mimicked in the current study by a certain range of volumetric air flow rate ranging from 0.0015 to 0.0034 m3/s which corresponding to heating intensity range from 200 to 1400 W/m2. Results confirm a reduction in the response curve spreads is achieved by increasing the volumetric air velocity (representing heating intensity). Also, the results reveal a reduction in values of axial dispersion coefficient with increasing the air volumetric flow rate.

Potential Impact of Computational Techniques to Express the Solid Dynamics in (Gas-Liquid-Solid) Multiphase Reactors

The computational fluid dynamics codes play a paramount role by demonstrating the system dynamics. The solid dynamics in a multiphase reactor can be analysed from (Chaos, Fractures, Clustering Discrete Element and Eulerian-Langrangian) simulation methods. The Chaos analysis is studied from pressure variation and time series. It includes the characterization of the flow region and their transition. The correlation dimension from the gas phase will describe the scale behaviour in the Chaos analysis. An effective flow model with definite investigation is obtained from this analysis. The flow regimes will be characterized by the structures variation. The volume of fluid and continuum surface force models elaborate on the fluidized bed bubble dynamics in the reactor. The bubbles formation and gasification process of (Fuel gas) are studied from parameters by including (Minimum fluidization velocity, Gas surface tension, Gas viscosity and Density). The results demonstrate the parameters which are influenced by (Particle density and Size). The investigation in time series signals for the biomass gasification process will be demonstrated from the fluidized bed hydrodynamics and system basics. The solid dynamics has been investigated by indicating a novel bubbling in biomass (Wood) in the gasification process time signals. The indication of complex signals in solid dynamics can be obtained from it simultaneously.

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.