Gas-solid Fluidized Bed Reactor Research Articles

A comparative assessment of CFD based LSTM and GRU for hydrodynamic predictions of gas-solid fluidized bed

Numerical simulation of large-scale fluidized beds presents significant challenges for both scaling up the simulations and evaluating their performance. However, full-scale computational fluid dynamics (CFD) simulations of these reactors incur substantial computational time and cost. To overcome these challenges, we propose a novel approach that combines CFD simulations with data-driven deep-learning models to predict complex hydrodynamics. In this study, we trained two machine learning (ML) algorithms, namely the Long Short-Term Memory (LSTM) and Gated Recurrent Unit (GRU), using spatiotemporal data obtained from CFD simulations. Impressively, the trained models accurately predicted future events at successive time steps, exhibiting excellent agreement for mean voidage, gas velocity, and particle velocity. Among the models utilized, LSTM outperformed the other. This demonstrated its superior ability to capture spatiotemporal from CFD data while requiring less computational time and power. The trained models provide a reliable means to extrapolate desirable mean particle velocity and voidage values within fluidized beds. These findings hold promising opportunities for enhancing the design and operation of gas-solid fluidized bed reactors, potentially leading to a significant reduction of up to 57–68% in simulation time.

Experimental Investigation on Bubble and Agglomerate Behaviors of Geldart B Particles in a 3D Gas–Solid Fluidized Bed Reactor

Experimental Investigation on Bubble and Agglomerate Behaviors of Geldart B Particles in a 3D Gas–Solid Fluidized Bed Reactor

Dynamic energy-minimization multi-scale heterogeneous continuum evolution model for gas-solid fluidization

Traditional gas–solid continuum model is still computationally inaccurate and physically unreasonable, due to a homogeneous assumption that particles are uniformly dispersed in a computational grid. Therefore, its application to simulate industrial gas–solid fluidization needs further improvement. Here, a novel heterogeneous continuum model, named dynamic energy-minimization multi-scale (EMMS) evolution model, was developed for accurate and fast simulations of gas–solid fluidization systems. In this model, the evolution of gas–solid heterogeneous multiscale structure in each computational grid was directly resolved by EMMS model, which was then coupled with multiphase mixture model to dynamically calculate phase holdup and flow field. Both S-shaped axial voidage profiles and spatial distribution of solid phase with the presence of a core-annulus structure were successfully captured. Compared with two-fluid model, dynamic EMMS evolution model showed great advantages in various aspects, including (a) model accuracy: predicted “S” type distribution of bed voidage was closer to experimental data; (b) stability: a rather larger time step of 0.1 s could be used; and (c) computational cost: dynamic EMMS evolution model was 245 times faster than two-fluid model. Based on dynamic EMMS evolution model, the complex multiscale hydrodynamics can be well simulated and understood, and will help the design and scale-up of large-scale gas–solid fluidized bed reactors.

Flow regimes and transitions in an ultra-high temperature gas-solid fluidized bed

Gas-solid fluidized bed reactors are widely used in industrial operations and thus have led to a significant amount of fundamental research over decades. For better design and operation of fluidized bed systems, it is essential to understand the fluidization regime and the related transition conditions. Dr. John R. Grace, a prominent figure and pioneer in fluidization science and technology, has made significant contributions to understanding fluidized bed systems, including fluidization regimes and their transitions. This study is a tribute to his extraordinary legacy, focusing on investigations of fluidization regimes and transitions in a laboratory-scale gas-fluidized bed operating from ambient to 1600 °C. The results indicate that the fluidization regime transitions follow three distinct pathways across different temperature ranges: below 300 °C, from 300 to 1400 °C, and above 1400 °C. These distinctive transitions arise as a result of the varying significances of hydrodynamic and interparticle forces in the fluidized bed of particles investigated.

Optimization of multiple-chamber fluidized beds using coarse-grained CFD-DEM simulations: Regulation of solids back-mixing

The intense solids back-mixing has been one of the major disadvantages of gas-solid fluidized bed reactors for certain applications. In this study, coarse-grained CFD-DEM simulations are carried out to regulate the solids back-mixing in multiple-chamber fluidized beds by investigating the effect of the orifice size, the orifice location, the gas velocity of each chamber, and then the effect of the pipe length connecting adjacent chambers. The results indicate that optimizing the orifice size, the orifice location, and the gas velocity of each chamber can suppress the solids back-mixing to a certain extent. However, there is still a gap between the optimized design and the ideal situation. Therefore, using a sufficiently long pipe instead of a baffle with orifice is further proposed to completely suppress the solids back-mixing between adjacent chambers, which is validated using coarse-grained CFD-DEM simulations. Present results provide a means to regulate the solids back-mixing in multiple-chamber fluidized beds via proper design of bed geometry.

Bubble dynamics properties of B-particles in a quasi-2D gas-solid fluidized bed: Computational particle fluid dynamics numerical simulation and post-processed by digital image analysis technique

Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds. In this study, the bubble dynamics properties of four B-particles were investigated in a quasi-two-dimensional (quasi-2D) fluidized bed, including bubble equivalent diameter, bubble size distribution, average bubble density, bubble aspect ratio, bubble hold-up, bed expansion ratio, bubble radial position, and bubble velocity. The studies were performed by computational particle fluid dynamics (CPFD) numerical simulation and post-processed with digital image analysis (DIA) technique, at superficial gas velocities ranging from 2umf to 7umf. The simulated results shown that the CPFD simulation combining with DIA technique post-processing could be used as a reliable method for simulating bubble dynamics properties in quasi-2D gas-solid fluidized beds. However, it seemed not desirable for the simulation of bubble motion near the air distributor at higher superficial gas velocity from the simulated average bubble density distribution. The superficial gas velocity significantly affected the bubble equivalent diameter and evolution, while it had little influence on bubble size distribution and bubble aspect ratio distribution for the same particles. Both time-averaged bubble hold-up and bed expansion ratio increased with the increase of superficial gas velocity. Two core-annular flow structures could be found in the fluidized bed for all cases. The average bubble rising velocity increased with the increasing bubble equivalent diameter. For bubble lateral movement, the smaller bubbles might be more susceptible, and superficial gas velocity had a little influence on the absolute lateral velocity of bubbles. The simulated results presented a valuable and novel approach for studying bubble dynamics properties. The comprehensive understanding of bubble dynamics behaviors in quasi-2D gas-solid fluidized beds would provide support in the design, operation, and optimization of gas-solid fluidized bed reactors.

Application of imaging techniques for the characterization of lumps behaviour in gas–solid fluidized-bed reactors

Gas-solid fluidized-bed reactors are often used in waste pyrolysis and gasification processes thanks to their excellent mixing properties, which guarantee temperature uniformity. However, this latter property can fail when large objects, such as lumps, are introduced or form in the system. Understanding the motion characteristics and thermal behaviour of lumps in a high temperature fluidized-bed reactor can help determining how the presence of lumps impact reactors’ performance. This was the object of this study. In particular, this work aims to assess how process variables and physical properties impact the segregation behaviour, dispersion coefficients and heat transfer coefficients of these lumps during operation. The system used in this work is a down-scaled pseudo-2D fluidized bed operated at ambient temperature and at fluidization velocities ranging between 1 Umf and 10 Umf. Rutile sand with four different mean particle sizes (60 μm, 100 μm, 153 μm and 215 μm) was used as bed material. Fabricated lumps were introduced in the fluidized bed to reproduce realistic conditions, as when lumps form in a high-temperature fluid bed. The density ratio between the lump and the bed material particle was varied between 0.32 and 0.55 to account for different lump compositions. X-ray digital radiography and infrared thermography were used respectively to track the fabricated lumps and to obtain their temperature time evolution. The lump density was found not to have a significant effect on the lump dispersion coefficients or on the heat transfer coefficient. Optimal values of fluidization velocities that guarantee proper lump mixing and maximum heat transfer coefficient were obtained. This latter increases by up to 10 times if the optimal fluidization velocity is selected. An increase in the bed material particle size was found to cause an increase in the dispersion coefficients and a decrease in the heat transfer coefficient. The trend of the heat transfer coefficient as a function of the fluidization velocity was found to vary significantly between different bed material particle sizes. A new correlation for the Nusselt number as a function of the object Reynolds number and of the size ratio between lump and bed material was obtained. This correlation applies to cases where particle convection is the dominant mechanism of heat transfer. The results of this work provide important knowledge to minimize the impact of lumps on fluidized-bed reactors and to optimize their operation.

Experimental investigation on the effect of superficial gas velocity on bubble dynamics properties of B particles in gas–solid fluidized bed reactor using digital image analysis technique

The bubble dynamics properties in gas–solid particle system play a crucial role in the design and optimization of gas–solid fluidized beds, and are significantly influenced by superficial gas velocity. In present study, the effect of superficial gas velocity on bubble dynamics properties in a classical B particle system were investigated at gas velocity ranging from (0.41 to 0.59) m·s−1 with umf = 0.067 m·s−1 in a quasi-two dimensional (quasi-2D) fluidized bed domain, including bubble equivalent diameter, bubble size distribution, bubble density, aspect ratio, bubble hold-up, bed expansion ratio, bubble rising and lateral velocity. Those were derived from the taken image by digital image analysis (DIA) technique. The results show that superficial gas velocity has a significant effect on the bubble equivalent diameter, while it has little effect on bubble size distribution (BSD), average bubble density distribution and bubble aspect ratio distribution for the same particle system. Both time-averaged bed expansion ratio and bubble hold-up increase with the increase of superficial gas velocity under the range of gas velocity in this work. Two uniform core-annular flows form in the bed for all cases. The bubble rising velocity coefficients of developed correlation range from 0.69 to 1.00. For bubble lateral movement, smaller bubbles may be more susceptible, and superficial gas velocity has a little influence on the absolute lateral velocity of bubbles. Overall understanding the effect of gas velocity on bubbles dynamics properties is good for the design and optimization of fluidized bed reactors, leading to the better process outcomes and performance.

Experimental investigation on the impact of tube bundle designs on heat transfer coefficient in gas-solid fluidized bed reactor for Fischer-Tropsch synthesis

The impact of vertical heat exchanging tube bundle on heat transfer coefficient (HTC) has been investigated locally and instantaneously using a sophisticate heat transfer technique using glass beads solid particles of 210 μm average size and 2500 kg/m3 solid density (Geldart B particles), with a static bed height of 0.35 m as bed material. A mimicked Fischer-Tropsch fluidized bed with vertical heat exchanging tubes is designed and built in this study. Heat transfer performance is also investigated by using two different tubes arrangement (square-pitch and triangular-pitch tubes arrangement). To represent the heat exchanging tubes used in the Fischer–Tropsch process, stainless-steel heat exchanging tubes inserted vertically, each with a diameter of 0.012 m, were used in each tubes arrangement occupying 25% of the column cross-section area. The experiments were performed in a 0.13 m inner diameter Plexiglas fluidized bed reactor with varied gas flowrates (0.2–0.48) m/s at numerous radial positions along the diameter of the column (±0.58, ±0.33, and ± 0.03) and two axial locations (H/D = 1.153 and 1.923). It was found that HTCs significantly enhance with increasing the gas flowrates for all radial positions for square-pitch tubes arrangement. While different behavior can be noticed in the radial positions with triangular-pitch tube arrangement, especially near the wall region (±0.33). Also, the local heat transfer coefficient (LHTC) improved with increasing the axial positions by 12.06% at highest gas flowrates (0.48 m/s). Moreover, the square-pitch tubes arrangement showed a significant increase and uniformity in HTC when measured instantaneously comparing with other tubes arrangement. Furthermore, the findings of this study will improve awareness of vertical tubes' effect on heat transfer in a fluidized bed reactor. Moreover, the data acquired from this investigation can be employed to validate reactor models, CFD codes, and simulations in order to support the design and scale-up processes of such reactors.

CFD-DEM study on fluidization characteristics of gas-solid fluidized bed reactor containing ternary mixture

Coupled computational fluid dynamics - discrete element method (CFD-DEM) simulations are carried out to investigate the fluidization characteristics of gas-solid fluidized bed reactor (FBR) containing ternary particles (spheres, ideal and elongated cylinders, the latter two are rod-like particles). The mixing efficiency, velocity distribution, orientation distribution and height change of different particles during the mixing process are fully investigated and discussed. Numerical results show that when the superficial gas velocity is low, the mixing efficiency would decrease with the increase of the volume fraction of elongated cylinders due to the inter-locking. However, the discrepancy of mixing degree induced by particle shape can be weakened by increasing the superficial gas velocity. Elongated cylinders become quite active when the inter-locking is broken with more uncertainty in their motion. Ideal cylinders prefer to be horizontal at all the superficial gas velocities considered but elongated ones only show similar behavior at low superficial gas velocities. When the superficial gas velocity is high, the time-averaged orientation of elongated cylinders becomes quite uniform. The inclined angle of both ideal and elongated cylinders decreases with the increase of height and large inclined angles are found at the two lower corners of the reactor. The ideal cylinders turn to be more vertical when the position moves to the central line of the FBR. In the lower half of the bed material, the elongated cylinders prefer to be horizontal in the near-wall region but more vertical in the center of the upper half. Within the range of currently considered superficial gas velocities, the overall mixing degree of the ternary mixture can be enhanced by increasing the superficial gas velocity both in efficiency and stable mixing degree. The findings can be very useful to guide the improvement of existing reactors and the design of novel ones.Numerical simulation; Fluidization; Ternary granular mixture; Mixing behavior; Rod-like particles.

Development of a novel silica-based microwave receptor for high temperature processes

A novel silica-based microwave receptor was developed via a fluidized bed chemical vapor deposition (FBCVD) technique. In this study, the silica sand particles were successfully coated in an induction heating-assisted reactor, with carbon produced from thermal degradation of methane (TDM) at various reaction temperatures and times. The effect of FBCVD reaction parameters, temperature and reaction time, on the amount of carbon deposition, and the composition, coherence and thickness of the carbon coating layer were investigated using thermogravimetric and morphological analysis, respectively. The microwave heating performance of such developed receptors was further investigated in an innovative single-mode microwave apparatus and was subsequently compared with the relevant performance of sand and graphite particle mixtures. The developed microwave receptor stipulates low level of carbon content and high layer uniformity, extreme microwave heating rate, high durability, and excellent potential for application in gas-solid fluidized bed reactors as heat generator and catalyst support/promoter simultaneously.

CFD-DEM investigation into flow characteristics in mixed pulsed fluidized bed under electrostatic effects

Static electricity has an important effect on gas–solid fluidized bed reactor fluidization performance. In the process of fluidization, electrostatic interaction between particles will obviously accelerate particle agglomerate formation, which consequently reduces the fluidization performance. Pulsed gas flow injection is an efficient method to enhance particle mixing, thereby weakening the occurrence of particle agglomerate. In this study, the two-dimensional hybrid pulsed fluidized bed is established. The flow characteristics are studied by using the coupled CFD-DEM numerical simulation model considering electrostatic effects. Influences of different pulsed frequencies and gas flow ratios on fluidized bed fluidization performance are investigated to obtain the optimal pulsed gas flow condition. Results show that in the presence of static electricity, the bubble generation position is lower, which is conducive to the particle flow. Pulsed gas flow can increase the particle velocity and improve the diffusion ability. The bubble generation time is different at different frequencies, and the frequency of 2.5 Hz has the most obvious effect on the flow characteristics. Different gas flow ratios have significant impacts on the particle movement amplitude. When the pulse gas flow accounts for a large ratio, the particle agglomerate tends to be larger. Therefore, in order to improve the fluidization effect, the ratio of pulsed gas flow to stable gas flow should be appropriately reduced to 0.5 or less.

Research contributions of Leo A. Behie to chemical and biomedical engineering

AbstractLeo Augustus Behie was known as a dedicated teacher and mentor, a team builder, and an outstanding researcher and innovator. He had a most productive and illustrious career, spanning five decades, that covered both industrial and academic sectors. His academic research career started with tackling classical chemical engineering challenges and, with time, shifted to biotechnology and biomedical engineering. He was the founding director of a unique research laboratory for undertaking innovative biotechnology and biomedical engineering research at the University of Calgary, called the Pharmaceutical Production Research Facility (PPRF). This paper presents an overview of his academic and research accomplishments, which also included the training of 17 doctoral students, 21 master's degree students, and many postdoctoral scholars. His main research areas under the classical chemical engineering theme included the investigation of the grid region in gas–solid fluidized bed reactors; gas–liquid and liquid–solid multiphase systems; fluidized bed reactors for metals recovery from coal ash; spouted fluid‐bed reactors; kinetics of pyrolysis chemical reactions; transport phenomena in rotary drums; and reactions, thermodynamics, and reactor modelling of sulphur systems. His main research areas under the biotechnology and biomedical engineering theme included advances in biotechnology and bioreactor design; production of antibiotic and monoclonal antibody; protein production in insect cells; process development for the production of neural stem cells, cancer stem cells, and islet cells; mesenchymal stem cells; and cellular secretome studies aimed at developing a cure for Parkinson's disease.

Different bubble behaviors in gas-solid fluidized bed of Geldart group A and group C+ particles

A gas-solid fluidized bed reactor composed of Geldart Group C fine powers with the addition of nano-additives (Group C+) has recently been shown to have higher reaction conversion and better contact efficiency than the same reactor composed of Geldart Group A particles due to the increased gas holdup in the dense phase and the increased gas-solid interfacial area. Based on our earlier findings that significantly smaller bubbles were observed in such a Group C+ particle fluidized bed, the bubbling behavior is fully characterized in this work using the bubble position, diameter, rise velocity and residence time. The results indicated that bubbles were smaller in diameter, lower in rise velocity, and had a longer residence time in the Group C+ fluidized bed when compared with the same bed using Geldart Group A particles. All these factors contributed to better fluidization quality and enhanced gas-solid contact, thus improving reaction performance.

Comparative CFD modeling of a bubbling bed using a Eulerian–Eulerian two-fluid model (TFM) and a Eulerian-Lagrangian dense discrete phase model (DDPM)

Eulerian–Eulerian and Eulerian-Lagrangian numerical approaches are both widely used to investigate hydrodynamic behavior in dense gas-solid fluidized bed reactors, yet there has been a lack of comparative investigations involving the two. Therefore, the present work compares the numerical performance of a two-fluid model (TFM) and a dense discrete phase model (DDPM) in describing the hydrodynamic behavior of a pilot-scale bubbling bed reactor. The effects of several different parameters – drag force, grid size, fluid time-step, time-averaging interval, particle-wall specularity coefficient, particle-particle restitution coefficient, particle-wall reflection coefficient, and numbers of parcels (the latter two parameters only for the DDPM) – are investigated and compared for the two approaches using two-dimensional (2D) simulations. The numerical results for both models indicate that sub-grid drag correction based on the energy minimization and multiscale (EMMS) theory is the most essential modeling parameter to account for the multiscale structures (i.e., bubbles and void spaces) and to resolve the axial and radial solid distributions. Both the TFM and DDPM, coupled with the EMMS/bubbling drag, predict similar hydrodynamics behavior; however, the better accuracy in terms of axial and radial solids concentration profiles is achieved from the TFM approach. Further, our grid size analysis results indicate that the DDPM generates a better grid-independent solution than the TFM. This important advantage of the DDPM over TFM makes it a suitable candidate for large-scale industrial applications by employing it on much coarser grids. Meanwhile, the results from the time-step, time-averaging interval, specularity coefficient, restitution coefficient, reflection coefficient, and numbers of parcels represent a minor effect on the overall hydrodynamics behavior of the pilot-scale bubbling bed reactor.

Numerical investigation on the scale-up rules of a supercritical water fluidized bed reactor using the two-fluid model

The supercritical water fluidized bed reactor (SCWFBR) is a novel hydrogen production technique, so the understanding on its scale-up is limited. In this regard, the trial-and-error procedure is not an option for traditional experimental research because it is costly and high risk. To overcome these problems, numerical simulations were carried out in this study based on the two-fluid model (TFM) to examine the capability of different scale-up rules for the SCWFBR. The numerical model was first validated based on experimental results. Then, four different-sized SCWFBRs were designed, in which numerical simulations for both air–solid and supercritical water (SCW)–solid systems were conducted following different scale-up rules. The distributions of solid volume fraction, solid velocity and pressure in these reactors were fully investigated. Comparisons among the numerical results showed that keeping the Reynolds number, Froude number and dimensional inlet velocity constant is critical for the scale-up of both SCWFBRs and traditional gas–solid fluidized bed reactors (FBRs). Moreover, keeping the particle diameter constant is helpful in obtaining the similarity of the multiphase flow behavior. For the SCWFBR, but not for the traditional gas–solid FBR, a constant density ratio between solid and fluid should be kept during the scale-up. Finally, for the SCW–solid system with more active particle motions, the effect of the interparticle collisions should be considered in the scaling parameters at high Reynolds numbers.

Fluidization characteristics of wide-size-distribution particles in a gas-solid fluidized bed reactor

AbstractFluidization characteristics of wide-size-distribution particles in the gas-solid fluidized bed reactor are investigated by applying experiment and computational fluid dynamics (CFD) methods. In this study, three types of narrow-cut particles and two sets of wide-size-distribution particles are used. A model considering particle size distribution is developed in the Eulerian frame, and good agreement between numerical results and experimental data is observed. The particle size distribution has an important effect on the average bed voidage. The axial particle diameter profiles along bed height have a “S” type feature. Minimum fluidization velocity is determined from the standard deviation of pressure fluctuations and bubble dynamics are analyzed based on power spectra. Results indicate that fine particle composition can reduce the minimum fluidization velocity of wide-size-distribution particle system and the bubble diameter in the fluidized bed.

Verification and validation of the DDPM-EMMS model for numerical simulations of bubbling, turbulent and circulating fluidized beds

Compared with the traditional Eulerian-Eulerian two-fluid modeling (TFM) approach, dense discrete phase model (DDPM) is potentially promising for industrial-scale applications of fluidized bed reactors, due to its capability of tracking the trajectories of particle parcels and resolving the particle size distributions (PSD). However, DDPM is yet at its early stage of mature implementation. Hence, verification and validation of the DDPM approach is still required for future applications of different gas-solid fluidization regimes.In the present work, verification and validation of the DDPM is systematically investigated for the first time, with regards to bubbling, turbulent and circulating fluidized beds. The sensitivity of the drag force, a key modeling parameter in gas-solid fluidized bed reactors is investigated with two different drag models i.e., Gidaspow and EMMS/bubbling. Numerical results of bubbling, turbulent and circulating fluidization regimes are presented in terms of discrete particle distributions, axial and radial solid concentrations and radial solid velocity profiles distributions. The results indicate that the sub-grid correction based on the EMMS approach is essential for the DDPM to correctly account for the effects of dissipative structures in all three fluidization regimes. While, the DDPM with the conventional Gidaspow drag failed to do so. Further, validations of the numerical results with the experimental data also prove that the DDPM approach with EMMS/bubbling drag model can resolve the time-averaged axial and radial solid concentrations and radial solid velocity profiles better than the conventional Gidaspow drag model.

On the Two-Phase Theory of Group C+ and Geldart Group A Particles

The relative distribution of gas flow between the bubble phase and dense phase is a very important factor that determines the performance of a gas–solid fluidized bed reactor because the dense phas...

Effects of liquid content and surface tension on fluidization characteristics in a liquid-containing gas–solid fluidized bed: A CFD–DEM study

The fluidization process within gas–solid fluidized bed reactor can be intensified by adding liquid, as it can enhance mass and heat transfer between gas phase and solid phase. With the help of computational fluid dynamics(CFD) and discrete element methods(DEM), fluidization characteristics are investigated at different liquid contents(V^) and surface tension(Bog). To be specific, the bed expansion ratio, particle concentration and particle velocity profiles are compared and analyzed. Numerical simulations show that Bog should be less than 5 at V^ = 0.013. At this recommended range, liquid addition makes interparticle force increase and has little effect on fluidization performance. From transient particle agglomeration behavior, the Bog increase is more likely to enhance interparticle force, resulting in obvious particle agglomerations during fluidization process. The variation of stagnation zone height can be reflected from the abrupt increase of particle velocity in annulus region. It can be found that V^ increase reduces particle velocity at critical height but Bog increase is more likely to cause larger stagnation region. By analyzing the distribution of spout, annulus and fountain regions at different V^ and Bog, the annulus region expands with V^ increase below the initial bed height while the spout region expands with Bog increase.