Simulation Of Fluidized Bed Reactor Research Articles

Increasing Computational Efficiency of CFD Simulations of Reactive Flows at Catalyst Surfaces through Dynamic Load Balancing.

We propose a numerical strategy based on dynamic load balancing (DLB) aimed at enhancing the computational efficiency of multiscale CFD simulation of reactive flows at catalyst surfaces. Our approach employs DLB combined with a hybrid parallelization technique, integrating both MPI and OpenMP protocols. This results in an optimized distribution of the computational load associated with the chemistry solution across processors, thereby minimizing computational overheads. Through assessments conducted on fixed and fluidized bed reactor simulations, we demonstrated a remarkable improvement of the parallel efficiency from 19 to 87% and from 19 to 91% for the fixed and fluidized bed, respectively. Owing to this improved parallel efficiency, we observe a significant computational speed-up of 1.9 and 2.1 in the fixed and fluidized bed reactor simulations, respectively, compared to simulations without DLB. All in all, the proposed approach is able to improve the computational efficiency of multiscale CFD simulations paving the way for a more efficient exploitation of high-performance computing resources and expanding the current boundaries of feasible simulations.

FBR for Polyolefin Production in Gas Phase: Validation of a Two‐Phase Compartmentalized Model by Comparison with CFD

AbstractTwo different modeling approaches are applied in this work to the simulation of fluidized bed reactors containing solid particles of Geldart A‐B type and operated at typical conditions for polyolefins production. On one side, a fully detailed computational fluid‐dynamics (CFD) model is developed, considering a 2D planar geometry and a multi‐fluid description with kinetic theory of granular flows. On the other, a conventional three‐phase, 1D compartmentalized model (SCM) is also developed, implementing the fluid dynamic description based on popular, semi‐empirical relationships available in the literature. Given the huge difference of computational effort associated with the corresponding numerical solutions, our aim is to confirm the reliability of the simplified model by comparison with the results of the detailed CFD model. The results show that the oversimplified compartmentalized approach is capable to predict the solid mixing features established inside the reactor operated in bubbling fluidization regime with good reliability for non‐reactive polyethylene particles. Average solid volume fractions are particularly close to the values predicted by the CFD model when monodisperse particles are considered inside the examined range of gas velocity values. A generally good agreement is also found when solids with broad size distribution are analyzed.

Coupling Euler-Euler and Microkinetic Modeling for the Simulation of Fluidized Bed Reactors: an Application to the Oxidative Coupling of Methane.

We propose a numerical methodology to combine detailed microkinetic modeling and Eulerian–Eulerian methods for the simulation of industrial fluidized bed reactors. An operator splitting-based approach has been applied to solve the detailed kinetics coupled with the solution of multiphase gas–solid flows. Lab and industrial reactor configurations are simulated to assess the capability and the accuracy of the method by using the oxidative coupling of methane as a showcase. A good agreement with lab-scale experimental data (deviations below 10%) is obtained. Moreover, in this specific case, the proposed framework provides a 4-fold reduction of the computational cost required to reach the steady-state when compared to the approach of linearizing the chemical source term. As a whole, the work paves the way to the incorporation of detailed kinetics in the simulation of industrial fluidized reactors.

Modeling and experimental investigation on the fuel particle heat-up and devolatilization behavior in a fluidized bed

The proper understanding and description of fuel devolatilization behavior in a fluidized bed (FB) is important to the FB reactor design and modeling. Aiming at this issue, two different mathematical models, isothermal (0D) particle model and one-dimensional (1D) particle model, have been developed. The particle heat transfer is solved simultaneously using an iterative approach with the existing nitrogen containing chemical percolation devolatilization (CPD-NLG) model. Experiments in a special designed FB reactor were conducted to help validate both the temperature solver and modifications to the fast nitrogen release chemical kinetic parameters. The results show that when the bed temperature is higher or coal size become smaller, the final volatiles yield increases and the nitrogen remaining in char decreases. Under all conditions given in the present study, the final nitrogen content of char is always lower than that of parent coal. The yields of some volatile species are also affected by the coal size and bed temperature. In addition, simulation analysis reveals that the deviation between the results of these two models cannot be ignored if the particle size exceeds a specific value (transition size), namely, the large particle is improper to be described as isothermal during heat-up, while this transition size decreases with the increase of bed temperature. A selection principle of these two models is proposed for balancing the calculation precision and computational time. The particle model developed in this work makes it possible to carry out further FB reactor simulations with the devolatilization process more consistent with laboratory data.

Development and assessment of speed-up algorithms for the reactive CFD–DEM simulation of fluidized bed reactors

PA and ISAT algorithms are developed to speed-up the CFD–DEM simulations of fluidized reactors. Also, a selection procedure of the most effective algorithm according to the operating conditions is developed, enabling the simulation of lab reactors.

The sensitivity of filtered Two Fluid Model to the underlying resolved simulation setup

The filtered Two Fluid Model (fTFM) is a promising approach for enabling large scale fluidized bed reactor simulations using multiphase flow modelling. A substantial amount of research has been conducted in this field to derive filtered closures for all applicable transport processes including drag, stresses, heat transfer, scalar transport and reactions. This work aims to investigate the effect of TFM closures used in the resolved simulations from which fTFM closures are derived in order to assess the degree of uncertainty stemming from this source. In addition, the filtering approach provides a good platform for building a detailed understanding of the effects of different TFM closures. Simulations showed that the drag model used in the resolved simulations had the most significant effect on the filtered quantities derived. Inclusion of a frictional pressure model also had a large influence in the dense regions of the domain. Selection of a more generic drag model and inclusion of a frictional pressure model is therefore recommended for future studies. Finally, results revealed that the effects of TFM closures on filtered quantities could be grouped into two categories: interphase transport (drag, heat transfer and reactions) and diffusive transport (stresses and scalar transport). This suggests a common methodology in terms of filtered model form for these two groups.

Speeding up CFD simulation of fluidized bed reactor for MTO by coupling CRE model

The methanol to olefins (MTO) process opens an economical and important route to produce light olefins. The design of MTO reactor borrows ideas from the reaction–regeneration configuration of the modern fluid catalytic cracking (FCC) units. However, their hydrodynamic behaviors are quite different in the sense that the fluidized bed for MTO reactions operates in different flow regime from that of FCC, calling for new modeling for scale-up. In addition, the coke deposited on catalysts greatly affects the MTO reaction while its generation is very slow. It normally takes tens of minutes or even hours for catalysts to reach the desired level of coke content. Time-dependent computational fluid dynamics (CFD) simulation of such a long process poses a big challenge to reactive multiphase flow modeling. To speed up it, we try to integrate the classic chemical reaction engineering (CRE) model with CFD. In particular, the continuous stirred tank reactor (CSTR) model is established to estimate the steady state distribution of coke content, which is then set as the initial distribution for CFD simulation to shorten the time to reach the steady state of reactive flows. Comparison with experimental data shows good agreement and also great speed-up ratio compared to traditional CFD simulation.

Grid independence behaviour of fluidized bed reactor simulations using the Two Fluid Model: Detailed parametric study

This short communication builds on previous work on the grid independence behaviour of the Two Fluid Model in reactive bubbling fluidized bed simulations. Regarding hydrodynamic grid independence behaviour (the numerical accuracy with which phase segregation was resolved), the particle relaxation time was confirmed as being directly proportional to the cell size achieving sufficiently grid independent behaviour. This relationship held over different particle sizes, particle densities, gas densities, gas viscosities and drag laws, but the slope of the proportionality changed for particle relaxation times above 0.4. For reactive grid independence behaviour (the numerical accuracy with which reactor performance was resolved), the relationship between the particle relaxation time and the sufficiently grid independent cell size was more complex, depending not only on the resolution of phase segregation, but also on the kinetic rate implemented and on the permeability of the emulsion phase. Simple and practical rules of thumb were proposed for estimating the sufficiently grid independent cell size for hydrodynamic and reactive simulations. For most practical purposes, the simpler and more accurate hydrodynamic grid independent cell size correlation can safely be used to run sufficiently accurate bubbling fluidized bed reactor simulations.

Computational Modeling of Biomass Thermochemical Conversion in Fluidized Beds: Particle Density Variation and Size Distribution

The design and scale-up of fluidized-bed reactors is an important step to commercialize viable conversion pathways (such as fast pyrolysis) for biomass into hydrocarbon intermediates and fuels that lead to “drop-in” replacements for jet fuel, diesel, gasoline, and other petroleum-based products. Detailed information about the particle size distribution (PSD) and particle density evolution throughout the fluidized-bed reactor can play a critical role in determining in situ catalyst selectivity, intermediate components, and reactor performance. This work presents an Euler–Euler computational fluid dynamics (CFD) model applied to biomass thermochemical conversion for use in fluidized-bed reactor simulations. The complex chemical and physical processes of particle devolatilization and their interaction with the reacting gas environment are described within a multifluid framework based on the kinetic theory of granular flows. The direct quadrature method of moments is used to describe the biomass PSD. Continuo...

Grid independence behaviour of fluidized bed reactor simulations using the Two Fluid Model: Effect of particle size

It is well known that particle size has a significant influence on the grid independence behaviour of fluidized bed reactor simulations carried out using the Two Fluid Model (TFM) approach. The general rule of thumb states that the cell size should scale linearly with the particle size so that the cell size is always at most a factor of 10 larger than the particle size. In this study, however, the effect of particle size on grid independence behaviour was shown to be unexpectedly large. In particular, a five-fold increase in particle size permitted the use of a 63 times larger cell size, implying a 633≈250,000 times speedup for resolved simulations in the planar 2D domain considered in this study. Thus, the general rule of thumb was found to be overly cautious, especially for larger particles. Closer investigation revealed the particle relaxation time to be a very good predictor of the grid independent cell size. Although this finding needs to be confirmed for parameters other than only the particle size, this relation can theoretically be used to greatly shorten the time-consuming grid independence studies that are required before any fluidized bed simulation campaign. In general, the rapid increase in cell size allowed by larger particle sizes showed that reasonably accurate industrial scale simulations (5m inner diameter reactor) are already possible in 2D for large particles (~600μm). If the 2D grid independence behaviour assessed in this study is extendible to 3D, larger particle sizes in the range of 500–1000μm can already be simulated in full 3D for reactor sizes ranging from 1–4m. Simulation of smaller particle sizes (<200μm) will remain out of reach for many decades to come, however, and a filtered coarse grid approach will definitely be required to make such simulations possible.

Simulation for Supporting Scale-Up of a Fluidized Bed Reactor for Advanced Water Oxidation

Simulation of fluidized bed reactor (FBR) was accomplished for treating wastewater using Fenton reaction, which is an advanced oxidation process (AOP). The simulation was performed to determine characteristics of FBR performance, concentration profile of the contaminants, and various prominent hydrodynamic properties (e.g., Reynolds number, velocity, and pressure) in the reactor. Simulation was implemented for 2.8 L working volume using hydrodynamic correlations, continuous equation, and simplified kinetic information for phenols degradation as a model. The simulation shows that, by using Fe3+ and Fe2+ mixtures as catalyst, TOC degradation up to 45% was achieved for contaminant range of 40–90 mg/L within 60 min. The concentration profiles and hydrodynamic characteristics were also generated. A subsequent scale-up study was also conducted using similitude method. The analysis shows that up to 10 L working volume, the models developed are applicable. The study proves that, using appropriate modeling and simulation, data can be predicted for designing and operating FBR for wastewater treatment.

Simulation of fluidized bed reactor for producing synthesis gas by catalytic CH4–CO2 reforming

Catalytic CH4–CO2 reforming combines methane and CO2 to produce synthesis gas. In the present paper, dry reforming of methane has been simulated in a fluidized bed reactor using a modified comprehensive reactor model. The model has been employed to study the effect of various operating parameters like CO2/CH4 feed ratio, gas hourly space velocity (GHSV), pressure (P) and catalyst loading (w) on CH4 conversion (XCH4), CO+H2 productivity and CO/H2 molar ratio in product. Simulation results were compared with experimental data reported in the literature (Chem. Eng. Sci. 2000, 55, 3955–3966). At the optimum condition (CO2/CH4 molar ratio=1.5, temperature=1073K, GHSV=1100h−1, pressure=0.1MPa and catalyst loading (w)=120g), values of XCH4, CO+H2 productivity and CO/H2 molar ratio in product were found to be 97.64%, 2.41 and 1.26, respectively.

Modular Simulation of Fluidized Bed Reactors

AbstractSimulation of chemical processes involving nonideal reactors is essential for process design, optimization, control and scale‐up. Various industrial process simulation programs are available for chemical process simulation. Most of these programs are being developed based on the sequential modular approach. They contain only standard ideal reactors but provide no module for nonideal reactors, e.g., fluidized bed reactors. In this study, a new model is developed for the simulation of fluidized bed reactors by sequential modular approach. In the proposed model the bed is divided into several serial sections and the flow of the gas is considered as plug flow through the bubbles and perfectly mixed through the emulsion phase. In order to simulate the performance of these reactors, the hydrodynamic and reaction submodels should be integrated together in the medium and facilities provided by industrial simulators to obtain a simulation model. The performance of the proposed simulation model is tested against the experimental data reported in the literature for various gas‐solid systems and a wide range of superficial gas velocities. It is shown that this model provides acceptable results in predicting the performance of the fluidized bed reactors. The results of this study can easily be used by industrial simulators to enhance their abilities to simulate the fluidized bed reactor properly.

Mathematical modelling for supporting scale-up of an anaerobic wastewater treatment in a fluidized bed reactor

The paper deals with a mathematical model for anaerobic treatment of waste water from sugar industry which has been developed for supporting the scale-up of a fluidized bed reactor. The dynamic model is based on material balance equations for substrates and products in gas and liquid phase. The effects taken into account are the biological degradation steps including chemical equilibria and mass transport between gas and liquid phase as well as convection and dispersion. Axial gradients of pH-values are calculated from a charge balance. Simulation results show reasonable agreement with measured gradients of substrates and pH in a 10 m3 fluidized bed reactor. For a new 500 m3 fluidized bed reactor simulations are performed to study the effects of increased hydrostatic pressure and increased ratio of feed to recirculation rate on the pH-values at the bottom of the reactor. The results indicate that for high COD-loading rates stationary pH-gradients may have significant influence upon the outcome of the process.

Mathematical modelling for supporting scale-up of an anaerobic wastewater treatment in a fluidized bed reactor

The paper deals with a mathematical model for anaerobic treatment of waste water from sugar industry which has been developed for supporting the scale-up of a fluidized bed reactor. The dynamic model is based on material balance equations for substrates and products in gas and liquid phase. The effects taken into account are the biological degradation steps including chemical equilibria and mass transport between gas and liquid phase as well as convection and dispersion. Axial gradients of pH-values are calculated from a charge balance. Simulation results show reasonable agreement with measured gradients of substrates and pH in a 10 m3 fluidized bed reactor. For a new 500 m3 fluidized bed reactor simulations are performed to study the effects of increased hydrostatic pressure and increased ratio of feed to recirculation rate on the pH-values at the bottom of the reactor. The results indicate that for high COD-loading rates stationary pH-gradients may have significant influence upon the outcome of the process.