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Types of gas fluidization

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Types of gas fluidization

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Abstract

The behaviour of solids fluidized by gases falls into four clearly recognizable groups, characterized by density difference (ϱs–ϱf) and mean particle size. The most easily recognizable features of the groups are: powders in group A exhibit dense phase expansion after minimum fluidization and prior to the commenment of bubbling; those in group B bubble at the minimum fluidization velocity; those in group C are difficult to fluidize at all and those in group D can form stable spouted beds. A numerical criterion which distinguishes between groups A and B has been devised and agrees well with published data. Generalizations concerning powders within a group can be made with reasonable confidence but conclusions drawn from observations made on a powder in one group should not in general be used to predict the behaviour of a powder in another group.

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... Researchers have explored and defined powders [4][5][6] by studying their fluidized behavior. Some of the most common ways to fluidize powder include air or gas fluidization [4,[7][8][9][10], using additives [11,12], and by applying vibrations to the fluidized bed [7,[13][14][15][16][17]. ...
... Researchers have explored and defined powders [4][5][6] by studying their fluidized behavior. Some of the most common ways to fluidize powder include air or gas fluidization [4,[7][8][9][10], using additives [11,12], and by applying vibrations to the fluidized bed [7,[13][14][15][16][17]. Using air-fluidization approach, Geldart et al. [4] classified the powders, based on particle size and the density difference. ...
... Some of the most common ways to fluidize powder include air or gas fluidization [4,[7][8][9][10], using additives [11,12], and by applying vibrations to the fluidized bed [7,[13][14][15][16][17]. Using air-fluidization approach, Geldart et al. [4] classified the powders, based on particle size and the density difference. It includes: the easily fluidized group A (exhibits dense phase expansion), B (bubbling at minimum fluidization velocity), fine and cohesive group C (very difficult to fluidized) and D (coarse grains, which forms stable spouted beds). ...
Preprint
Full-text available
We experimentally investigate the effect of vertical vibrations on the brittle behavior of fine cohesive powders consisting of glass beads of 5 \mu-m in diameter. This is an attempt to understand a sole role of vibrations in fluidizing Geldart's group C powders, which is known for posing difficulty while fluidization. We found that the cohesive powder column can be compacted, fractured, and effectively fluidized by increasing the strengths of external vibrations. This process of vibration-induced fracturing is summarized in a full experimental phase diagram showing four distinct phases of the vibrated powder column: consolidation (CS), static fracture (SF), dynamic fracture (DF), and convective fracture (CF). We found that the boundary separating the consolidated and fracture regimes depends on the dimensionless shaking strength, S. However, in DF regime, the decompaction wave propagation speed normalized to gravitational speed is found to be independent of S. In order to reach our ultimate goal of effective fluidization of group C powders, we explore geometrical parameters like container shapes, sizes, and the base conditions. We find that the circular cylinder with hemispherical base condition is the most effective container in order to achieve effective fluidization of group C powders when vibrated.
... It is noticeable that the fingering instability occurs at experimental conditions of a rough inclined plane with an angle smaller than 34°and mixed materials with particle size larger than 0.075 mm in Pouliquen et al. [50], Pouliquen and Vallance [51], and Woodhouse et al. [62]. At the range of particle size, the mixed material is non-cohesive [21] and tends to segregate when moving on a rough inclined plane, whereas the inclined plate is smooth in this study and the fine particles are cohesive. As a consequence, it is unconvinced that considering the fingers formed in the deposits when m r-= 0.2 and m r = 0.4 are contributed to the particle size segregation. ...
... Particle size is a critical influence that can affect the properties of different granular materials [27,33,37,44,46,49,64]. According to how difficult it was to fluidize the granular materials, Geldart [21] classifies the granular materials into four groups: the aeratable, sand-like, cohesive, and spoutable, based on massive experiments (Fig. 16). The cohesive group is the most difficult one to fluidize, followed by aeratable, sand-like, and spoutable. ...
... This classification was from studies of fluidized bed by injecting gas into granular materials with different particle sizes and densities. This classification of granular materials has been widely used in the field of chemical engineering to study its properties [2,3,21,26,28]. From Fig. 16, the fine particles belonged to the cohesive and aeratable group based on the density (1.5 9 10 3 kgÁm -3 ) and particle size (smaller than 0.075 mm) used in this study. A continuity of the sliding mass was exhibited while moving when m r was smaller, while a multi-stage characteristic was exhibited with a larger m r . ...
Article
Full-text available
Rock avalanches have become a hot spot in the field of geological hazards due to their flow features and long run-out distance. These features are closely related to the mass ratio parameter mr (the proportion of fine particles to the total mass). To explore the influence on the kinetic parameters and deposit morphology of rock avalanches by mr, a tabletop apparatus was developed to conduct sand avalanche experiments. Direct shear tests were performed to provide strength parameters of sand and sand–plate interface systematically. The results show that with the decrease of mean particle size D50, the internal friction angle increases first and then decreases, but the opposite trend has been observed for the friction angle of sand–plate interface. The addition of fine particles smaller than 0.075 mm makes the motion behavior of the sliding mass different. With the increase of mr, the motion of sand avalanches changes from frictional flows to viscous flows. In addition, a critical mass ratio parameter is proposed. The critical mass ratio parameter increases with the increased range of particle sizes. This research supports the study of avalanche events.
... The most well-known classification for the fluidization of powders, based on size and density, was proposed by Geldart in 1973. [30] He performed fluidization experiments with sieve fractions of several powders and looked at minimum fluidization velocity, minimum bubble velocity, bed voidage, and bed height expansion to find the influence of particle properties on fluidization behaviour. The resulting classification is shown in Figure 1. ...
... Whereas the boundaries between type A and B and type B and D were calculated, the shaded line, separating type A and type C powders, is drawn based on empirical data. [30] The Geldart diagram is still widely used, since it gives a reasonable prediction of fluidization behaviour based on few, and easily accessible, properties. ...
... Particles of interest for this paper are all type C and should therefore, according to the diagram, have the same fluidization behaviour. However, the smallest sieve fraction used by Geldart was 10-20 μm, [30] meaning smaller particles could show different behaviour upon fluidization. This would then require an extension of the diagram to make an accurate prediction of the fluidization behaviour of powders within the type C size range possible. ...
Article
Full-text available
The fluidization of cohesive powders has been extensively researched over the years. When looking at literature on the fluidization of cohesive particles, one will often find papers concerned with only micro‐ or only nano‐sized powders. It is however unclear whether they should be treated differently at all. In this paper, we look at differences and similarities between cohesive powders across the size range of several nanometres to tens of micrometres. Classification of fluidization behaviour based on particle size was found to be troublesome since cohesive powders form agglomerates and using the properties of these agglomerates introduces new problems. When looking at inter‐particle forces, it is found that van der Waals forces dominate across the entire size range that is considered. Furthermore, when looking into agglomeration and modelling thereof, it was found that there is a fundamental difference between the size ranges in the way they agglomerate. Where the transition between the types of agglomeration is located is, however, unknown. Finally, how models are made and agglomerate sizes are measured is currently insufficient to accurately predict or measure their sizes consistently.
... Fluidization of the powder bed is one of the most important processes in powder technology. In the past, industrial researchers defined and studied granular powders [1][2][3] and suggested various ways to fluidize the powders: gas fluidization [1,[4][5][6][7], using finer-particles as additives [8,9], and applying vibrations to the gas-fluidized bed [4,10,11]. To characterize flowability, Geldart classified powders into several types, based on the grain size and density [1]: groups A (easily fluidized), B (fluidized readily, causes bubbling, small bed expansion), C (fine, very cohesive particles, lifts as a plug and forms channels), and D (coarse grains, forms stable spouted beds). ...
... Fluidization of the powder bed is one of the most important processes in powder technology. In the past, industrial researchers defined and studied granular powders [1][2][3] and suggested various ways to fluidize the powders: gas fluidization [1,[4][5][6][7], using finer-particles as additives [8,9], and applying vibrations to the gas-fluidized bed [4,10,11]. To characterize flowability, Geldart classified powders into several types, based on the grain size and density [1]: groups A (easily fluidized), B (fluidized readily, causes bubbling, small bed expansion), C (fine, very cohesive particles, lifts as a plug and forms channels), and D (coarse grains, forms stable spouted beds). ...
... In the past, industrial researchers defined and studied granular powders [1][2][3] and suggested various ways to fluidize the powders: gas fluidization [1,[4][5][6][7], using finer-particles as additives [8,9], and applying vibrations to the gas-fluidized bed [4,10,11]. To characterize flowability, Geldart classified powders into several types, based on the grain size and density [1]: groups A (easily fluidized), B (fluidized readily, causes bubbling, small bed expansion), C (fine, very cohesive particles, lifts as a plug and forms channels), and D (coarse grains, forms stable spouted beds). In usual granular physics studies, coarse grains categorized into group D have been used as typical granular materials. ...
Preprint
We experimentally study the crack formation and decompaction-wave propagating in a vibrated powder bed consisting of glass beads of 5 {\mu}m in diameter. The vibrated powder bed exhibits three distinct phases depending on the vibration conditions: consolidation (CS), static fracture (SF), and dynamic fracture (DF). Particularly, we found an upward wave propagation in the DF regime when the powder bed is strongly vibrated. As a remarkable feature, we found that in fine cohesive powders, the decompaction-wave propagation speed normalized to gravitational speed is independent of the shaking strength. This result implies that the wave propagation speed is governed by the balance between gravity and cohesion effect rather than vibration strength. We also explore the universality of wave propagation phenomenon in coarser and low-density granular powders.
... According the Geldart diagram, a precursor material in form of powder can be categorized as a function of fluidization behavior in ambient conditions [41]. In the specialized powder technology fields, the Geldart diagram classifies the material into different groups according to the difference between particle density and gas density and the particle size. ...
... 11 Geldart diagram for powder flow classification as a function of the particle size and density. Source: Adapted from Geldart[41]. ...
Chapter
This chapter covers the production of bioactive glass‐ceramic coatings by laser cladding and the additive fabrication of bioactive glass‐ceramics by laser direct glass deposition. The laser cladding technique and the laser direct glass deposition techniques are introduced and their applications in the ceramic biomaterials field are presented. Fundamentals of laser‐material interaction and current technology for coating production and additive manufacturing are reviewed. A deep analysis of the requirements of the bioactive glasses and their properties as precursor materials for laser assisted processing is provided, in addition to the explanation of the reported structural and bioactivity changes. Finally, the impact of processing conditions on the mechanical and bioactive properties of the laser additive manufacturing are described.
... Fluidized beds are often preferred over packed beds due to their superior gas-solid contact, higher mass and heat transfer rates, and efficient gas-solid handling and mixing [1][2][3][4][5][6]. However, the fluidization of ultrafine and fine powders belonging to Geldart group C is difficult due to strong inter-particle forces (IPFs), which lead to severe bed non-homogeneities and poor interphase phase mixing [7][8][9][10][11][12][13][14][15][16]. The fluidization of ultrafine nanoparticles can either display agglomerate particulate fluidization (APF) or agglomerate bubbling fluidization (ABF) owing to the large agglomerate formation as a result of the IPFs. ...
... We used hydrophilic nanosilica in this study owing to its strong agglomeration behavior that results in ABF behavior [3,24]. Apart from widely different voidages, these powders also significantly differ in their physical properties, and therefore belong to different groups of Geldart's classification [15]. Note that commercial grade nanosilica and titania find large-scale applications in several industries such as the paint, catalyst manufacturing, and pharmaceutical industries [37,38]. ...
Article
Full-text available
Bed collapse experiments provide vital information about fluidized bed hydrodynamics. In this study, the region-wise bed collapse dynamics of glass beads, titania (TiO2), and hydrophilic nanosilica (SiO2) particles with widely different voidages (ε) of 0.38, 0.80, and 0.98, respectively, were carefully investigated. These particles belonged to different Geldart groups and exhibited varied hysteresis phenomena and fluidization indices. The local collapse dynamics in the lower, lower-middle, upper-middle, and upper regions were carefully monitored in addition to the distributor pressure drop to obtain greater insight into the deaeration behavior of the bed. While the collapse dynamics of glass beads revealed high bed homogeneity, the upper middle region controlled the collapse process in the case of titania due to the size-based segregation along the bed height. The segregation behavior was very strong for nanosilica, with the slow settling fine agglomerates in the upper bed regions controlling its collapse dynamics. The collapse time of the upper region was 25 times slower than that of the lower region containing mainly large agglomerates. The spectral analysis confirmed the trend that was observed in the pressure transients. The clear presence of high frequency events at 20 and 40 Hz was observed in the nanosilica due to agglomerate movements. The residual air exiting the plenum was strongly affected by the bed voidage, being lowest for the nanosilica and highest for the glass beads.
... Notwithstanding inherent advantages associated with the use of fine and ultrafine powders, their processing remains hugely challenging. This was pointed out long ago by Geldart [1], who examined the effect of the physical properties of the solid particles on their gas-phase fluidization behavior. For particles with a size smaller than 30 µm, the solids, when contacted with an upward gas flow, show cohesive and non-homogeneous fluidization behavior with poor contact and insufficient mixing between the two phases. ...
Article
Full-text available
Assisted fluidization techniques can significantly improve the hydrodynamics of difficult- to-fluidize solids. Among these techniques, the pulsed flow strategy is highly promising owing to its cost-effectiveness and amenability to implementation for largescale processing. Using commercial-grade, highly porous nanosilica that shows strong agglomeration behavior, we implemented the pulsed flow with square-wave pulsation schemes of 0.05, 0.10, and 0.25 Hz frequencies, and compared their effectiveness in each case. Besides the conventional approach of assessing their efficacy using the pressure drop data, we have proposed a new approach in this work that consists of computing the power of the overall pressure drop transient signals. Using the theoretical value, i.e., the effective bed weight per unit area as a reference, the percentage increase in the power was 27 ± 4, 71 ± 5, and 128 ± 4, respectively, for 0.05, 0.10, and 0.25 Hz pulsation frequencies. In fact, the average pressure drop values were substantially higher when the partial bed collapse occurred between successive pulsations when compared with the case of low-frequency pulsations. The pulsation frequency also affected the evolution of local bed dynamics in various bed regions during the expansion and collapse of the bed. Moreover, the local and global pressure transients have shown interesting mutual correlations which were otherwise not evident from their individual transient profiles.
... In the literature, some practical charts were used for predicting flow patterns and behavior of solids which provide valuable information to the design of pneumatic conveyors. Some of these charts were developed by Geldart (1973), Dixon (1996), Mainwaring and Reed (1987), and Pan (1999 ...
Chapter
One of the most common and the most versatile conveying technologies is pneumatic transportation. These conveyors are applied to transport in various industries, one of which is the food industry. In this book chapter, a brief but informative description of the pneumatic transportation systems is provided. First, the advantages and disadvantages of pneumatic systems are presented. System flexibility, higher safety, and easier automation are some of the advantages, while higher energy consumption and the limited conveying speed of fragile material are important disadvantages that should be considered. Some of the applications of pneumatic conveyors in the food industry are also mentioned in this chapter. Cereal, sugar, and coffee processing facilities are some of the users of these conveying systems. There is also useful information about the main components and different types of pneumatic systems in this chapter. Positive and negative modes, and dilute and dense phases are then reviewed. In the last section, a useful narrative about one of the important issues in pneumatic conveying systems, that is, the pressure drop, is provided.
... Note that the particles simulated in the above study belong to Geldart type D with a diameter larger than ∼600 μm. 54 An observable weakness is that the formation of complex clustering structures in real small-particle fluidized bed systems (Geldart type A and B) and its significant impact on fluid-particle transport and reaction behavior are unable to be adequately captured by simulations of large-particle systems (Geldart type D). In fact, the particles widely encountered in industrial reactors such as the fluid catalytic cracking (FCC) riser and the methanol-toolefins turbulent fluidized bed reactor belong to Geldart types A and B particles. ...
Article
Artificial intelligence (AI), machine learning (ML), and data science are leading to a promising transformative paradigm. ML, especially deep learning and physics-informed ML, is a valuable toolkit that complements incomplete domain-specific knowledge in conventional experimental and computational methods. ML can provide flexible techniques to facilitate the conceptual development of new robust predictive models for multiphase flows and reactors by finding hidden pattern/information/mechanism in a data set. Due to such emergence, we thereby comprehensively survey, explore, analyze, and discuss key advancements of recent ML applications to hydrodynamics, heat and mass transfer, and reactions in single-phase and multiphase flow systems from different aspects: (1) development of multiphase closure models of drag force, turbulence stresses and heat/mass transfer to improve the accuracy and efficiency of typical CFD simulations; (2) image reconstruction, regime identification, key parameter predictions, and optimization of multiphase flow and transport fields; (3) reaction kinetics modeling (e.g., predictions of reaction networks, kinetic parameters, and species production) and reaction condition optimization. These sections also discuss and analyze the key advantages and weakness of ML for solving the problems in the domain of multiphase flows and reactors. Finally, we summarize the under-solving challenges and opportunities in order to identify future directions that would be useful for the research community. Future development and study of multiphase flows and reactors are envisaged to be accelerated by ML and data science.
... The fluidisation behaviour varies drastically for different materials depending on the balance of drag, gravity and particle-particle cohesive forces. Four major classes are described in the Geldart classification considering the relative effects of the gas and solid densities, and the particle size in drag and weight [127]. As soon as a bed of Geldart B particles is fluidised, an increase in the gas velocity causes gas bubbles to form and rise through the bed promoting the circulation of solids. ...
Article
Full-text available
Thermochemical energy storage (TCES) has a vital role to play in a future where 100 % of our domestic energy needs are generated by renewables. Heating and cooling represent 51 % of total energy consumption, and as such contribute highly to greenhouse gas emissions. As a society, we have effective solutions for this in the form of renewable energy sources, the primary two being: solar thermal heat and wind power. However, one issue plagues these energy sources, that is their intermittency. Specifically, their seasonal deficit which represents a significant energy surplus in the summer months and significant energy dearth in the winter months. Effective seasonal heat storage is needed to solve this problem. At present, one of the best candidates to solve this issue TCES. Both sorption and reaction present many interesting chemical pairings which optimise various different important parameters, including: Energy density, cycle stability, turning temperature, capital and running costs, power output, charging and discharging speed. However, due to hazardous high temperatures and chemicals associated with reaction based TCES, it can be all but ruled out from domestic application. Sorption TCES presents many different promising subcategories, but salt based composite TCES materials are emerging as the most likely category to succeed in a domestic market. Sorption TCES faces one key issue though, that is its power output. Fluidised bed reactors (FBRs), both bubbling fluidised beds and circulating fluidised beds, have been used extensively in industry to increase the heat and mass transfer of various industrial processes. They have been used in the context of TCES to assist in the charging and discharging of various concentrating solar power plant energy storage systems. And, they have shown to effectively improve the power output of these systems, as well as in other high temperature energy storage systems (sensible energy storage, phase-change energy storage). Overall, it is clear that FBRs have the potential to be applied to domestic sorption TCES to improve its power output, priming it for domestic applications. It is also worth noting that very few studies exist investigating FBRs in the context of domestic TCES, and there is limited knowledge and understanding one how FBRs will affect domestic TCES systems.
... Several studies proposed correlations among material bulk/particle properties and its behavior when submitted to gas flow [1]. One of the pioneering works in this topic and still relevant to date was conducted by D. Geldart in 1973, who proposed to categorize materials into four groups, according to the particle size and density, material cohesiveness, and the corresponding type of fluidization [7]. Subsequent studies used the so-called Geldart groups (from A to D) among other classification methods as a designing tool to predict the phase of conveying in pneumatic systems. ...
Article
Pneumatic conveying of powders is a unit process extensively used in industries for the handling of particulate material of several segments. Academic studies started with empirical dilute-phase pneumatic conveying and, in order to produce better economic results in industrial settings, evolved to include energy efficiency techniques as a significant component. Much work has been done to understand and model pneumatic conveying systems; however, they are highly empirical and the conclusions are, in most cases, limited to a narrow range of experimental conditions. This paper introduces a systematic method to select the air pressure and flow necessary to operate an energy-optimized pneumatic conveying system. This method has been tested and applied to a pressure conveyor fed by a compact blow tank of 100 L in a 133 m long pipeline with a diameter of 3 inches conveying limestone. The tests demonstrated that it is possible to control this pneumatic conveying system with only two input parameters, while operating at the desired pressure and airflow and maintaining the respective conveying rate and power requirements.
... Some examples include dry powder inhalers (Begat et al., 2004;Yang et al., 2013Yang et al., , 2015, dust ingestion in gas turbine engines (Batcho et al., 1987;Bons et al., 2017;Dunn et al., 1996;Sacco et al., 2018), fluidized bed reactors (Mahecha-Botero et al., 2009;Mikami et al., 1998;Pan et al., 2016;van der Hoef et al., 2008), and indoor air quality (Lai, 2002;Lai & Nazaroff, 2000). Many of these applications involve Geldart C-type particles (dust and powders with diameters less than 20 μm) for which cohesive forces such as van der Waals attraction and electrostatics become important (Geldart, 1973). ...
Article
Full-text available
Particle deposition in fully-developed turbulent pipe flow is quantified taking into account uncertainty in electric charge, van der Waals strength, and temperature effects. A framework is presented for obtaining variance-based sensitivity in multiphase flow systems via a multi-fidelity Monte Carlo approach that optimally manages model evaluations for a given computational budget. The approach combines a high-fidelity model based on direct numerical simulation and a lower-order model based on a one-dimensional Eulerian description of the two-phase flow. Significant speedup is obtained compared to classical Monte Carlo estimation. Deposition is found to be most sensitive to electrostatic interactions and exhibits largest uncertainty for mid-sized (i.e., moderate Stokes number) particles.
... Estudos subsequentes usaram os chamados Grupos de Geldart (de A a D) entre outros métodos de classificação como uma ferramenta de projeto para prever a fase de transporte em sistemas pneumáticos. Em 2008,[11] modificaram o diagrama de Geldart original, usando a densidade aparente de sólidos vazada em oposição à densidade de partículas. Eles foram capazes de demonstrar que os materiais pertencentes aos Grupos A e C de Geldart tendem a ser transportados no modo de fase densa fluidizada, enquanto os materiais do grupo D são mais propensos a serem transportados no modo plug e aqueles do grupo B geralmente só podem ser transportados em fase diluída. ...
Conference Paper
Full-text available
O manuseio de materiais particulados por meio de transporte pneumático é um processo amplamente difundido nas indústrias. As aplicações e estudos historicamente tiveram seu objeto de estudo migrado de transportes em fase diluída para transportes em fase densa, devido a sua redução no consumo energético. No entanto, tais estudos se mostram altamente empíricos e suas conclusões são, na maioria dos casos, limitadas a condições experimentais, de forma que para otimizar um sistema levando em consideração tanto a taxa de transporte quanto a eficiência energética, são necessários a realização de testes experimentais. O presente trabalho apresenta um método sistemático para determinar a pressão e o fluxo de ar necessários para operar um sistema de transporte pneumático visando sua otimização energética. O método foi testado e aplicado a um sistema de transporte pneumático industrial, composto por um vaso de pressão compacto de volume de 100 L, que introduz material em uma tubulação de 133 m de comprimento com diâmetro de 3 pol. É demonstrada a possibilidade de controlar o sistema com o mínimo de dois parâmetros de entrada: limitando a pressão e fluxo de ar de transporte, determina-se a respectiva potência consumida e taxa de transporte. A razão entre os dois últimos parâmetros determina a eficiência energética do processo. Palavras-chave: Eficiência energética; Transporte pneumático; Vaso de pressão; Alimentador de sólidos.
Article
Several aspects of numerically modelling a minimally fluidized gas-solid system have been investigated in this work. The numerical results show that voidage and the resulting pressure drop are not a function of the fluidizing cycle. More interestingly, the pressure drop was not impacted by introducing the lateral axis of gas and solid flow in the 3D models. Under a reduced pressure environment, none of the well-known drag models could capture the effect of the slip flow. A relatively new but not well-known slip flow drag model showed the ability to capture the impact of the slip flow regime. However, improvements in its overall accuracy are desirable. To this extent, the Ergun pressure drop equation was modified to introduce the effect of the slip flow regime. The losses in the slip flow regime were captured by deriving a new correlation using experimental work that predicted a linear relationship between the laminar coefficient and the Knudsen number. The modified Ergun equation showed notable improvement in its pressure drop accuracy. Furthermore, the modified Ergun equation was implemented as a modified Gidaspow drag model. It showed better accuracy in predicting pressure drop and minimum fluidization velocity at reduced pressure for various alumina particle sizes.
Article
We experimentally study the crack formation and decompaction-wave propagating in a vibrated powder bed consisting of glass beads of 5 μm in diameter. The vibrated powder bed exhibits three distinct phases depending on the vibration conditions: consolidation (CS), static fracture (SF), and dynamic fracture (DF). Particularly, we found an upward wave propagation in the DF regime when the powder bed is strongly vibrated. As a remarkable feature, we found that in fine cohesive powders, the decompaction-wave propagation speed normalized to gravitational speed is independent of the shaking strength. This result implies that the wave propagation speed is governed by the balance between gravity and cohesion effect rather than vibration strength. We also explore the universality of wave propagation phenomenon in coarser and low-density granular powders.
Article
The aims of this work are to elucidate the effects that bulk solids properties have on the effective drag experienced by large spheres immersed in an emulsion of group‐B solids under minimum fluidization conditions, and to analyze the ways in which the different suspensions react towards different applied shear rates. To investigate this, Magnetic Particle Tracking was applied to resolve the trajectory of falling‐sphere measurements in which the size, density and sphericity of the bulk solids were varied as well as the size and density of the spherical tracers. The resulting experimental scope included both rising and sinking tracers as well as full segregation and in‐bed stagnation of the tracer. The set‐up provided highly resolved tracer trajectories, from which the drag experienced by the sphere can be calculated. For sinking tracers, the results showed that an increase in bulk solids size, angularity and density reduced the terminal velocity of the sphere. This effect correlated well with the bed expansion and Hausner ratio, indicating that a reduced void space among the bulk solids is the main reason for the increase in motion resistance. At lower shear rates, namely during the de‐acceleration towards the stagnant state, beds of larger, more angular or denser bulk solids yield lower levels of shear stress. The angle of repose of the bulk solids correlated with the rate at which the emulsion thins with increasing shear rate. For rising tracers, shear stress did not show any significant dependency on the properties of the bulk solids. This article is protected by copyright. All rights reserved.
Article
Industrial scale fluidized bed reactors are characterized by limited mixing rates, either local or global, especially when using low-pressure drop gas distributors to reduce operational costs. In this work, partitioning of wide beds using vertical internals is proposed as an effective technique to improve local mixing in large reactors, i.e., mixing in specific zones of the bed. The effect of the vertical internals height on local solids mixing within partitions was experimentally evaluated in a pseudo-2D bed by analyzing the velocity and flow structure of the solids and the circulation time within individual partitions. In the presence of internals, global mixing, i.e., mixing between neighboring partitions and across the entire reactor, may be reduced as vertical internals compartmentalize the bed. Thus, the effect of the internals height on global mixing was also quantified while using bed materials with the same properties, but differing in color, in the different partitions, and analyzing the time evolution of the concentration of solids. Furthermore, the effect of internals on bubbles was also evaluated for different internal heights. It was found that internals with a height between the gulf-stream height and the fixed bed height promote the appearance of vortex pair structures in each partition of the wide bed. These structures substantially improve local mixing within each partition, while global mixing between partitions is practically unaffected by the presence of these short internals.
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The particle fluidization characteristics and transition in a hot gas-solid fluidized bed with liquid injection were investigated on the basis of pressure drop of fluidized bed, the side wall temperature distribution and the weight fraction of agglomerates. It was found that the particle fluidization behavior was controlled by liquid bridge force under low induction heating power, whereas both solid bridge force and liquid bridge force take control of fluidization under higher induction heating power. With increasing liquid injection flowrate, the particle fluidization behavior experienced four types, named fast defluidization, gradual defluidization, agglomerating fluidization and stable fluidization, respectively. Further the transition behaviors between different fluidization types of particles were investigated, and four fluidization regions were distinguished. A dimensionless number ζ was proposed based on the theoretical analysis of interparticle forces and bubble expansion force, thereby establishing the connection between lab-scale experiments and industrial fluidized beds, and providing guidelines for their safe operation.
Article
The Gas-solid Fluidized Bed Coal Beneficiator (GFBCB) is an important technology used in the dry coal beneficiation process, which requires lower bed density and very uniform density distribution. Geldart A⁻ particles, Geldart A magnetite particles “modulated” by a small fraction of Geldart C ultrafine coal particles, is proposed. Fundamental studies are carried out to provide a comprehensive understanding of its hydrodynamics, including the minimum fluidization velocity, bed expansion, and spatial bed density distribution. By adding the ultrafine coal particles, the minimum fluidization velocity (Umf) is lowered, with a modified Umf correlation proposed, the bed expansion drastically increased (by up to 30%), with more gas being retained in the bed for improved flowability, and the corresponding bed density decreased to 1600–2000 kg/m³, with more uniform distribution, all contributing to a more desirable separation environment for coal beneficiation.
Chapter
In the process technology, solid powder is often chosen as the intermedia and final product form, which requires the removal of the solvents, in which the product is produced. Often, the solid-liquid separation takes place in two steps: mechanical solid-liquid separation, e.g., by means of filtration, followed by the thermal separation step—drying. Depending on the source of thermal energy input, the drying process can be roughly divided to three basic categories: convective drying, conductive drying and radiative drying, or a combination of these basic forms. After giving a summary of the physical background of the drying process, this chapter provides an overview of the technical possibilities and discusses the suitability of the technical solutions for individual applications.
Article
Micronized drug powders are generally unsuitable as tableting feed to produce minitablets due to their cohesivity and poor flow. The silicification of fine paracetamol powder (PCMF) with an optimal concentration range of fumed silica (fSi) [0.7 – 0.9 %, w/w] reduced the net negative charge of PCMF and improved powder flow. The optimal fSi concentration range suitable was established through the measurement of charge and flowability of the silicified powders. Silicification of PCMF by physical mix did not satisfactorily overcome the cohesive forces between the PCMF crystals and improve powder flow sufficiently such that it will feed consistently into the smaller die orifices during tableting. Using a specialized fluid bed system with swirling air and side spray, controlled granulation of silicified PCMF packed and agglomerated the interlocking-prone needle shaped PCMF crystals into diminutive granules that are more spherical and free flowing. With optimized fSi concentration (≈ 0.8 %, w/w) and granulation process parameters, high drug load diminutive granules (D50 ≃ 90 μm) were successfully prepared from PCMF as starter seeds (D50 ≃ 30 μm). Minitablets prepared from the diminutive granules had low weight variation, and were mechanically strong with disintegration time of less than 30 s. This study demonstrated the feasibility of producing high drug load minitablets from a cohesive, electrostatic-prone fine drug powder.
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The focus of investigations and research has been shifted in the past decade from conveying bulk materials in dilute phase flow at high velocity to dense phase flow at low conveying air velocity. Dense phase flow offers much less operational problems, such as wear and product attrition, and offers low specific power consumption. It, therefore, enhances the life of pneumatic conveying pipelines and associated components. However, the complete phenomenon of the flow mechanism of fine powder in fluidized dense phase pneumatic conveying has not been exactly explored. It necessitates an understanding of the flow behaviors of a fine powder, factors affecting the flow mechanisms, and approaches to model it. The present work describes the evaluation and assessment of the flow of fine powders in the fluidized dense phase. The performance of the pneumatic conveying system was based on modeling solids friction factor which was used for determining conveying line pressure drop. The predicted results provided by these approaches proved to be inaccurate compared to those of data collected from actual plants. Further, the numerical modeling methods to predict pressure drop for small length pipeline, difficulties, and recent progress in gas-solid prediction investigations are discussed as well. Finally, a bypass dense phase conveying system which has many advantages over the conventional one has been presented.
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A CFD-DEM model for aerated vibratory convection was developed to explore the coupled gas-solid interactions governing bulk powder bed dynamics. Each simulation was prepared by carefully characterizing the rough, porous conveyor baseplate and four candidate particle sizes representative of typical powder beds. Trends in the vibratory convection of particles between 20 and 250 μm in diameter could be explained by considering each powder's minimum fluidization velocity and the magnitude of van der Waals cohesive forces. Simulations of fine powders under high cohesive forces exhibited competing effects from drag and cohesion; drag promotes powder-frit liftoff while cohesion suppresses contact separation. Experimental convection velocities were observed to be in good agreement with the simulated mean powder velocity for throw numbers between 0.25 and 0.50.
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All-solid-state lithium-ion batteries (ASSLIBs) are promising candidates for next-generation batteries because of their various attractive properties. The uniform mixing of active materials (AMs) and solid electrolytes (SEs) is important for high-performance ASSLIBs. However, most AMs and SEs have poor flowability owing to their small particle size, which makes it difficult to uniformly mix the AM and SE particles. This study is focused on a high-shear mixer (HSM) as a scalable method to uniformly mix the AM and SE particles. The objective of this study is to determine the optimal operating conditions for HSM and its effectiveness in AM-SE mixing. The higher rotating speed of the chopper caused uniform SE dispersion by deagglomerating the SE particles and improving the adhesion of SE onto the AM particles, affording an electrode with well-balanced electrical/ionic conductivity and lower internal resistance. The ASSLIB with this electrode exhibited lower electrode polarization and excellent rate and cycle performance. Additionally, it has been demonstrated that the HSM could lead to a more uniform SE dispersion than conventional lab-scale mixing methods, resulting in significantly improved battery performance. Moreover, insights into the process-homogeneity-performance relations have been obtained.
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Geldart classified powders into four categories and assigned each category its own unique characteristic. Geldart A particles, being easily aeratable, show a unique feature of ‘Homogenous expansion’ before bubbling. In this work, an additional feature for the Geldart chart is proposed which adds significant utility for the processing of Geldart A particles. CFD was used to characterize the entire Geldart A region of the Geldart chart based on detailed fluidization behavior. For this, Eulerian–Eulerian Two-fluid model (TFM) simulations were conducted for 25 particle systems across the entire span of the Geldart A region. The simulations (Solid volume fraction (SVF) contours) of bed evolution, taken before the appearance of multiple bubbles, were analyzed in detail. The particle systems were then sub-categorized into Red (5% average bed expansion), Orange (12.5% average bed expansion), and Green (30% average bed expansion) sub-types. The sub-types were plotted on Geldart chart, and for the first time a continuum heat map was generated, from which the ‘level of fluidizability’ of all Geldart A powders can be conveniently gaged. The map can be used for a more informed choice of powder for various industrial applications. Also, the A/B boundary proposed by Verloop was found to be a better fit for our proposed continuum when compared to the original Geldart A/B boundary. The 2D Simulation results performed in this work, found adequate validation against experimental findings in literature. Further, fine mesh 2D simulation results compared well with 3D simulations for dense bed, and were thereby deemed adequate for revealing dense bed behavior before onset of multiple bubbles.
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This study was conducted to provide improved relationships on the external solids circulation rate and solids inventory in the riser of the circulating fluidized bed (CFB) through increasing the basic understanding on how the solids flow rate in the riser exit establishes. The relation between the solids inventory in the riser and the solids flow rate in the riser exit was investigated in batch elutriation and CFBs, using air as fluidizing gas at atmospheric pressure and temperature. A batchwise riser (0.1 m-i.d., 2.75 m-height) and the riser of a CFB system (0.1 m-i.d., 2.5 m-height) were used to measure the relation for different gas velocities (1.5–2.4 m/s) and groups of solids (0.064–0.201 mm in diameter, 2045–4080 kg/m³ in apparent density). The batch elutriation indicated that the amount of solids inventory in the riser determined the solids flow rate in the riser exit, increasing with the amount of the solids inventory in the riser. The solids flow rate in the exit of the riser strongly depended on the elutriation rate constant combined with the amount of the solids inventory in the riser. When the riser was same in size, the relationship on the solids flow rate in the riser exit, derived in the batch elutriation, was valid in the CFB. Relationships on the external solids circulation rate and solids inventory in the riser of the CFB were proposed based on the data from this study and the literature. It was found that the external solids circulation rate per cross-sectional area of the riser decreased with increasing the riser diameter, however, the static bed height of solids in the riser (hst,c) increased with the riser diameter. The dependency of hst,c on riser diameter was greater in the fast bed than in the bed of pneumatic conveying.
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A voluminous liquid waste stream is generated as sodium nitrate (NaNO3) solution in Spent Nuclear Fuel Reprocessing Plants. Fluidized bed thermal denitration is a strong contender among various disposal options for this stream. In the present work experimental investigations on thermochemical denitration of NaNO3 have been carried out in an 80 NB laboratory scale fluidized bed reactor. Carbon based reductant was utilized to convert NaNO3 to sodium carbonate (Na2CO3) as well as to reduce denitration temperature. The operating parameters were optimized for maximum conversion of NaNO3 and 99.13% denitrification has been achieved. Pressure fluctuation across bed was also recorded and analysed in the state space domain employing attractor comparison technique. This technique computes a statistical metric ‘S’, as a measure of the fluidization state in the fluidized bed reactor and can be used for early detection of agglomeration in the bed. The sensitivity and early agglomeration detection capability of S-statistics is illustrated with experimental results for a liquid-sprayed gas fluidized bed.
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This study aimed to determine the effect of rice husk fluidization and variation in the equivalence ratio of bubbling fluidized bed gasifiers without sand bed materials. It also aimed to improve the fluidization quality by reducing the diameter of rice husks. Therefore, the bulk density increases, whereas voidage decreases, both of which are the main parameters for improving the quality of fluidization in solid particles. Experiments were carried out at a velocity of 0.82 m/s, by varying the equivalent ratios ranging from 0.20 to 0.35, and analyzing the syngas composition, cold gas and carbon conversion efficiencies, lower heating value, and temperature distribution. An equivalence ratio of 0.30 was obtained for a bubbling fluidized gasifier with syngas compositions of 7.415%, 15.674%, 3.071%, 17.839%, and 56.031% for H2, CO, CH4, CO2, and N2, respectively. Under these conditions, we obtained cold gas and carbon conversion efficiencies and a lower heating value of 31.340%, 37.120%, and 3.881 MJ/Nm3, respectively.
Article
Fluidized bed strippers play a significant role in fluid catalytic cracking (FCC) and fluid coking hydrocarbon processing operations. In the FCC process, the catalyst particles retained by the reactor cyclones contain substantial product hydrocarbon vapors. Failure to remove these vapors from the catalyst results in the loss of valuable products and undesirably high temperatures in the regenerator. In FCC applications, entrained and adsorbed hydrocarbon vapors are typically removed from the catalyst in a fluidized bed stripper using steam. In a fluid coker stripper, steam is propelled upwards to remove entrained and adsorbed hydrocarbons from the coke particles downflowing from the fluid coker reactor, thereby minimizing the carry-under of valuable hydrocarbon product. For both applications, several different proprietary and standard baffles have been used in these fluidized bed strippers. The most prevalent types of baffles are disk and donut trays, grating trays, horizontal sheds, and structured packings. This review summarizes studies available in the open literature on fluidized bed strippers as applied to the FCC and fluid coker unit operations. Overall, fluid catalytic cracking strippers, in particular disk and donut strippers, have received the most attention due to their much wider industrial usage. In past studies, experimental efforts have been dedicated to stripping efficiencies of various internals as a function of solids mass flux and stripping gas velocity, as well as stripper flooding and other flow dynamics issues. Typical commercial stripper operating problems have been pointed out, and methods to diagnose the problems have been identified. Fundamental theories on mass transfer in strippers are lacking. ______________________________________________________
Article
BACKGROUND: The strawberry is a fruit with great acceptance by the consumer due to its pleasant flavor and functionality; It is rich in vitamin C, tannins, flavonoids, anthocyanins, catechin, quercetin and kaempferol, organic acids and minerals. OBJETIVE: The objective of the research was to evaluate the effect of the feed formulation and the spray-drying process on the quality of strawberry extract microcapsules (EMs). METHODS: The response surface methodology was used with a central composite design centered on the face (α= 1), considering the factors: maltodextrin (MD), inlet air temperature (IAT), outlet air temperature (OAT) and atomizing disk speed (ADS), and the response variables: humidity (Xw), water activity (aw), solubility (S), wettability ( We ), hygroscopicity (Hy), bulk density (ρ b), compacted density (ρ c), total phenols (TP), antioxidant capacity, angle of repose (AR), strawberry powder particle size (D [3 ;2] ), color (CIE-Lab), and process yield (Y). RESULTS: The aw and Xw values guarantee microbiological stability and control over degradation reactions in EMs. For the levels evaluated, the S was affected by OAT and ADS, and interaction IAT*MD, ADS*MD, IAT2, and MD2. The We depended on the factors IAT, OAT, and the interactions IAT*OAT and IAT*MD. ABTS activity was affected by the factors ADS, ADS*MD and IAT2. The Y was affected by OAT, MD, IAT*OAT, IOT*ADS, IOT*MD, OAT*ADS, ADS*MD, IOT2, and OAT2. The increase in MD caused a decrease in Hy. The value of L* was affected by ADS and MD, effects due to temperature did not affect the levels evaluated, and chromaticity a* was positively affected by the increase in ADS. IAT and MD presented a statistical effect on AR. CONCLUSIONS: The experimental optimization reached a desirability of 73.7%, being the optimal conditions: IAT (154°C), OAT (89°C), ADS (16,805 rpm), and MD (11.5%).
Article
Wet particle drying process is complex due to the change of particle moisture, which has big effect on the gas-solid properties, flow dynamics and mass and heat transfer behavior. In this research, a two-fluid model (TFM) coupled with the mass and heat transfer was used to simulate the particle drying process in a fluidized bed dryer. Meanwhile, online electrical capacitance tomography (ECT) was used to measure the solids concentration and off-line moisture meter was employed to measure the particle moisture. Two periods, i.e., constant-rate period and falling-rate period, were captured in the experimental drying curve. The continuous drying curve was obtained by the 2D CFD simulation. The drying rate increases sharply in the pre-warming period, reaches high in the constant-rate period, and decreases markedly in the falling-rate period at the beginning and then decreases slowly. The particle temperature increases gradually until it reaches the air temperature and keeps constant. In order to capture detailed flow dynamics in the drying process, 3D CFD simulations at certain moisture contents were performed. It is found that the simulated cross-sectional particle volume fraction shows core-annular structure and is verified by the on-line ECT measurement. An internal circulation is formed along the reactor height. The mass and heat transfer mainly happens at the lower part of the dryer and at the contact region between the bubbles and the solids phase. The minimum fluidization velocity decreases, and the bubble rising velocity increases when the particle moisture level decreases.
Article
Based on a reliable dataset of particle dynamics from DNS, a R–CNN model combining the functional structures of RNN and CNN was proposed to systematically learn both the temporal and spatial inhomogeneities of particulate flow and predict the particle dynamic. The particle pattern matrix sequence with length of 10 (ms) and β after a specific period of 1 ms were selected as the input and output. The matrix size was set as 25×25 according to the particle size of 0.5 mm and the proportion of particle size to the sampling domain of 1:25. Through validation and final testing, the R–CNN model maintained good predictive accuracy and robustness (validation: δ¯=0.13, R² = 0.63; testing: δ¯=0.12, R² = 0.64). The model was proven to be effective with an appropriate input sequence length of 3 (ms) and in an appropriate time span of 4 ms. The model performance is affected by the comprehensiveness of local particle pattern. The particle resolution corresponding to the best performance of the model was 0.8–1. Additionally, adding the feature (ur¯) that do not have a high correlation with the target is not necessarily effective in improving the model's performance. Overall, the feasibility of a physical–meaning–oriented R–CNN model with an optimizable combination of functional architecture and parameters was confirmed.
Article
Fluidization and reduction behaviors of ultrafine CuO powders with the assistance of iron microspheres are investigated. The ultrafine CuO powders that belong to Group C particles are difficult to fluidize due to the strong interactions between particles. However, robust fluidization is achieved with the addition of iron microspheres and the Cu products after the reduction reaction can be completely separated by using a magnetic field. Furthermore, the difference of improvement on fluidization with the assistance of iron microspheres between cold state and reaction state at high temperatures is revealed in the view of interactions between particles. This approach to enhance fluidization during reaction and simplify separation after reaction could be applied to the reaction of other Group C powders.
Article
BACKGROUND: The microencapsulation process using spray drying (SD) represents an effective alternative in protecting the active components present in strawberries. However, microcapsules of strawberry powder mixtures present problems of instantanisation and flowability; an aspect that can be solved by agglomeration of the particles. OBJECTIVE: The aim of this study was to evaluate the influence of the fluidised bed agglomeration process on the flow, instantaneity and antioxidant properties of strawberry powder obtained by SD. METHODS: The response surface methodology (RSM) was used with a centred composite central design (α=1), considering the factors: fluidisation air temperature (50-70°C), time (30-50 min) and atomisation air pressure of the binder agent (1-2 bar). RESULTS: An increase in particle size was observed in the agglomeration process; the agglomerated particles showed a decrease in wetting time, the agglomerates of strawberry powder mixtures presented excellent instantanisation and fluidity, solving the problems identified in the microcapsules obtained by SD. CONCLUSIONS: Although the moisture and aw levels were increased in the agglomeration process, the values are within the microbiological and physicochemical food safety range; moreover, there was no effect on the phenol content and antioxidant capacity. The experimental optimisation achieved desirability of 68.4%, the optimum conditions being 70°C, 30 min and 1 bar.
Article
Injection of gas–liquid sprays into gas–solid fluidized beds finds application in many industries. Effective mixing and distribution of liquid feed and solid bed material is paramount to ensure an efficient and profitable process. Despite its long-term use, the mechanism of liquid injection into gas–solid fluidized beds continues to raise questions and is only partially understood. This paper provides a thorough and up-to-date review of experimental and numerical investigations of gas–liquid sprays into gas–solid fluidized beds conducted over the past decades. Based on the surveyed literature, a phenomenological description of the prevalent mechanisms of gas–liquid injection under different operating conditions is presented. This review identifies suitable computational fluid dynamic models for simulating the mechanisms involved in gas–liquid–solid interactions along with recommendations for future numerical and experimental work.
Chapter
Deposition process: beam solid deposition (laser, electron beam based); arc welding based deposition using gas Tungsten arc, gas metal arc, and plasma arc; cold spray based deposition; friction based deposition such as additive friction stir deposition and friction surfacing based AM; extrusion based deposition using filaments, pellets; air and ion depositions; water deposition, slurry deposition; and layerless deposition are described. Powder depositions such as coaxial continuous, coaxial discrete, and off-axial are given while laser–powder interactions are briefly explained. The difference between feedstocks: wire and powder is given.KeywordsDeposition mechanismRobocastingFused deposition modelingDirect writingElectrochemicalClassification
Article
Fluidized bed is the main reactor for the heating and gasification of coal, biomass, and other solid fuels. The diameter, density, and shape of the particles significantly affects the gas–solid two-phase flow process. Based on the numerical method combining computational fluid dynamics and discrete element method (CFD–DEM), this paper mainly performs numerical simulation on the gas–solid two-phase flow process of coarse particles under different inlet mass flow rates with diameters of 2.5 mm, 3.0 mm, and 3.5 mm, respectively. The high-speed photographic experiments were carried out to validate the numerical results successfully. The effects of particle diameter on bubble morphology have been compared, such as bed height and initial bed mass change rate. The maximum value of the bed height reached gradually decreases as the particle diameter increases. Two typical C-shaped bubbles were found above the large bubbles during the fluidization processes, which further improve the uniformity of mixing. Slugging appears as the width of the bubbles in the fluidized bed is close to the width of the fluidized bed, which has great effects on the mass and heat transfer. This study could serve as reference for further optimal design of fluidized bed, especially for biomass or chemical looping combustion application with coarse particles.
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Kinetic theory is a common choice for closing the solid phase stress in the continuum theory for dilute and moderate dense gas-solid flows. In this article, methods are proposed for postprocessing the data obtained from discrete particle simulations, the results are then used to critically assess the fundamental assumptions of kinetic theory. It is shown that (i) the fundamental assumptions and predictions of kinetic theory are respectively valid and accurate in homogeneous granular flows, as expected. Those results prove that the methods for data postprocessing are effective; (ii) in case of nonequilibrium and heterogeneous gas-solid flows, nearly all fundamental assumptions get challenged and the predictions of kinetic theory, in terms of collision frequency and particle pressure, deviate significantly from the statistical results of discrete particle simulation. Therefore, standard kinetic theory is insufficient to provide the constitutive laws for continuum modeling of heterogeneous gas-solid flows.
Article
The minimum fluidization velocity of a fluid–solid particle fluidized bed is the primary focus of this paper. The computationally economic Eulerian Granular model has been used to analyze fluidization for both gas–solid particle and liquid-solid particle fluidized beds. The conventional approach of finding minimum fluidization velocity (umf) is either with a pressure drop across the particle bed or the change in bed height. However, these parameters are often unstable and cannot be used to generalize the degree of fluidization accurately. In this paper, the dominant factor of unstable pressure drop estimation in the 2D Two-Fluid Model (TFM) and a key non-dimensional Euler number has been investigated in determining minimum fluidization velocity for different quasi-2D fluidized beds for different bed sizes, particle sizes, and particle numbers. Averaging assumptions and limitations of these numerical models are discussed in detail for four different fluidized bed cases. A comparative study of the drag model shows little to no influence in unstable pressure drop estimation near fluidization velocity, and all drag models perform similarly. It is observed that particle-particle collision is not the dominant reason for unstable pressure drop near minimum fluidization. Instead, wall effects on the particle bed including frictional losses and wall-particle collision play a key role in unstable pressure drop calculation for the quasi-2D fluidized beds. Pressure drop characteristics alone do not suffice to obtain minimum fluidization velocity with 2D TFM using existing models. Thus, a different approach has been proposed to investigate minimum fluidization involving the Euler number, which has shown promising performance in determining minimum fluidization velocity and characterizing fluidization with 2D TFM. Results show consistency in Euler number characteristics for all different fluidized bed cases considered in this paper. This can revitalize computationally economic 2D Eulerian simulations, increase the range of possible applications, and provide guidance to the future development of computationally efficient and more accurate numerical models, and empirical correlations for minimum fluidization velocity.
Article
Although calcium-based materials are the most promising adsorbents used in calcium looping process for carbon dioxide removing, their CO2 capture capacity decaying besides poor fluidization, still are the important challenges. In the present investigation, eggshell as a cheap, easily available and unpolluted source of calcium carbonate was used for CO2 capturing in calcium looping process. Eggshell particles were treated with various volume concentrations of acetic acid to improve its sorption capacity. According to the TGA results after 20 carbonation/calcination cycles, the effective carbonation conversion of modified eggshell with 5%, 20%, 30% and 40%. v/v acetic acid was 21.33%, 24.26%, 25.97% and 28.97%, respectively, which is considerable compared to 20.54% for untreated eggshell. The effect of initial eggshell particle size on the adsorption behavior of final adsorbent was also investigated by using two different sizes including dp< 45 µm and dp> 320 µm. The results showed that the effective conversion of the adsorbent containing 40%. v/v acetic acid derived from small particle size eggshells was 9.32% higher than that from larger particle size eggshells. In terms of fluidization behavior, surprisingly the addition of acetic acid to the eggshell particles also increased the bed expansion ratio as 8% and 36.2% at gas velocities of 0.27 and 6.67 cm/s, respectively. Further improvement in the fluidity of eggshell modified with 40% acid was performed by manually mixing of SiO2 nanoparticles at different weight percentages. According to the results, adding 7.5 wt% SiO2 leaded to the homogeneous and agglomerate particulate fluidization.
Article
The present work shows the experimental results obtained with sand particles, which where coated to increase the thermal absorptivity for CSP applications. The particles were tested in a lab-scale fluidized bed with concentrated irradiation on the top. The experimental results indicates that two of the three coatings tested, based on graphite and carbon black, worked properly and absorbed between 30 and 40% more energy than raw sand due to the higher thermal absorptivity. Both coatings were also experimentally tested during 10 cycles of charging/discharging without apparent deterioration of their thermal properties. Sand coated with graphite exhibited color change, from an initial dark black to a greyish tone that did not have an impact on the particles thermal response. The extrapolation of the results observed at lab-scale, to the maximum expected temperatures in new generation of CSP plants with solid particles, up to 1250 K, shows that coated particles may enhance the energy effectively stored in the bed by 60–80% compared to raw sand.
Chapter
There are two main criteria for classifying solar receivers, namely, geometric design and adapted heat transfer fluid. Based on geometric factors, receivers fall into five classes: tubular, volumetric, microchannel, linear and point focus, and external and cavity receivers. Tubular and volumetric receivers are in the most advanced developmental stage. Point focus receivers can attain higher outlet temperature (>1000 K) of the heat transfer fluid than the linear focus variety, and they are exploited in solar tower and parabolic dish power plants. Based on the adapted heat transfer fluid, receivers are classified into three major categories: gas, liquid, and particle. Gas receivers can further be classified into pressurized and supercritical categories. Most of the operating concentrating solar power use molten salt as a heat transfer fluid to indirectly generate steam. Particle receivers are an emerging concept. In this chapter, different classes of receivers are presented and discussed in detail.
Article
Understanding the mixing behaviors of different particles is significant for improving the mass and heat transfer performance of a pressurized fluidized bed. A numerical simulation study on the mixing behavior of binary Geldart-D particles in a pressurized bubbling fluidized bed is performed based on the CFD-DEM method. The mixing characteristics and bubble behavior of binary Geldart-D particles with different physical properties under elevated pressure are investigated in the current study. Increasing the fluidization gas velocity ug and operating pressure P could promote the mixing of the particles. Raising the operating pressure P would cause a smaller bubble size and large bubble quantity at the same fluidization number ug/umg. Higher operating pressure P and fluidization number ug/umg could create a stable and uniform distribution of jetsam in the fluidized bed.
Article
Catalytic methanation processes allow the production of natural gas substitutes on a sustainable and renewable basis. This study investigates the catalytic methanation of syngas from dual fluidized bed steam gasification of biomass in an innovative bubbling fluidized bed methanation reactor with an optimized catalyst. Syngas from conventional gasification and a novel combination with syngas from sorption enhanced reforming were investigated. The applied fluidized bed reactor allowed an almost isothermal operation with optimal reaction temperatures between 320 °C–360 °C. Simultaneously, no chemical deactivation or mechanical attrition during 200 h of operation indicates a high long-term stability of the catalyst. The methane concentration downstream the methanation reactor increased from 43 to 74 vol.-%db through the methanation of a hydrogen-rich syngas produced via sorption enhanced reforming. Simultaneously, the methane yield is doubled to 95% and the hydrogen, carbon monoxide and carbon dioxide conversions are improved. Furthermore, it could be shown that a CO2 content below 1 vol.-%db is feasible in the (raw) synthetic natural gas, allowing grid injection without CO2 separation. The results indicate that sorption enhanced reforming in combination with an optimized fluidized bed methanation can lead to technical and economic improvements in sustainable synthetic natural gas production.
Chapter
Biomass gasification is a thermochemical conversion process that transforms feedstock into gas fuels, also known as syngas. Gasification involves partial combustion of the biomass under limited oxygen supply, generating producer gas composed of the combustible gases H 2 , CO, and CH 4 , CO 2 , N 2 , tar, and ash by‐products. Syngas can be used as a fuel for internal combustion engines to generate electricity. This chapter explains the gasifier configuration, the size, and the feedstock, how the gasification occurs, and the operational parameters’ influence on the gasification system's performance. This chapter also describes the importance of the design and operating parameters on a gasification plant system efficiency. The feedstock classification was founded on biomass physical‐chemical, and energetic characterization techniques, using agricultural and solid urban waste samples. Studies were carried out in a lab‐scale gasifier to evaluate several raw materials’ potential for electricity production. The syngas production was properly analyzed using wood as renewable feedstock in a downdraft fixed bed gasifier and its practical use in generating renewable electricity for rural homes. The construction of the bubbling fluidized‐bed gasifier for biomass conversion and its hydrodynamic characterization are also described.
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Thesis (Ph. D.)--University of Washington
Article
As the result of an experimental study of the fluidization of light solids by gases under various pressures and the fluidization of heavy solids by water, a general family of curves has been produced relating a generalized fluid velocity to a bed porosity function for a series of values of a parameter P involving the fluid and solid properties only. This correlation satisfies both liquid- and gas-fluidised beds and indicates that there is no fundamental difference in mechanism between a liquid-fluidized bed and a gas-fluidized bed. It also enables direct comparison to be made between flow through a fluidized bed and flow through a fixed bed of similar porosity. By treating an aggregatively-fluidized bed as a two-phase system and making reasonable assumptions about the rise of bubbles the general bed expansion correlation is used to produce general correlations of mean bubble velocities, frequencies, concentrations and volumes in terms of the mean bed porosity and the parameter P. These correlations predict that a gas system normally has a comparatively small number of large bubbles and appears to fluidize aggregatively. A liquid system may have a large number of small bubbles and appear to fluidize particulately although certain liquid-solid systems will fluidize aggregatively. The values of the bubble characteristics for both liquid and gas systems are in approximate agreement with those observed. These correlations can also be used to predict the fraction of fluid passing through the bed in bubble form and hence gives assistance to the estimation of the efficiency of the fluidized bed as a chemical reactor. The effect of gas pressure on this efficiency is also discussed.
Article
Gas flow through a fluidized bed is normally streamline and the pattern of flow depends on the bubbles within the bed and their velocities relative to gas. When the gas velocity for fluidization is low compared with the bubble velocity (as in beds of fine particles) a region of gas circulation or a “cloud” as it is called, is formed around the bubble.This paper describes experimental observations of the shape and size of gas clouds as they form around bubbles in two-dimensional fluidized beds of spherical and irregular particles. Exchange of gas between the cloud and interstitial phases is shown to occur by a process of “cloud shedding,” and the behaviour of clouds as their parent bubbles split and coalesce is described. The observations of cloud shape are compared with the theoretical predictions of Davidson, Jackson and Murray and from this an estimate of the cloud shape in real three-dimensional beds is made.RésuméL'écoulement du gaz à travers un lit fluidisé se produit ordinairement en ligne droite et sa disposition dépend des bulles au sein du lit et de leur vitesse relative par rapport au gaz. Quand la vitesse du gaz de fluidisation est basse comparée à celle de la bulle (comme dans les lits de fines particules) il se forme autour de la bulle une région de circulation gazeuse que l′on appelle “nuage”.Cet article décrit des observations expérimentales sur la forme et la dimension de nuages gazeux qui se forment autour les bulles dans des lits fluidisés, à deux dimensions, de particules sphériques ou irrégulières. L'auteur montre que l'échange de gaz entre le nuage et la phase intersticielle se produit par un procédé de “cloud shedding” et décrit le comportement des nuages quand leurs bulles associées se divisent et coalescent. Il compare les observations sur la forme des nuages avec les prédictions théoriques de Davidson, Jackson et Murray et en déduit une prévision de la forme des nuages dans les lits réels à trois dimensions.
Article
The fluidisation characteristics of particles which are of such a size and density that the velocity of gas in the dense phase exceeds the rising velocity of the bubbles have been studied.Spherical particles in the range 1–2 mm were fluidised in two- and three-dimensional equipment. Minimum fluidisation velocities measured in the 3D equipment at 200° C and 350°C were found to agree reasonably well with those predicted using an equation based on Ergun's equation for packed beds.Measurements were made in the 2D bed of bubble shapes, sizes, velocities and concentrations, as well as of bed expansion and solid mixing rates. The distribution of gas between the dense and bubble phases was found to be significantly different from predictions based on the two-phase theory of fluidisation.
Article
Measurements of bubble velocities in freely bubbling beds have shown that the velocities of individual bubbles are influenced more markedly by the disposition of surrounding bubbles than by the size of the individual bubble itself. Bubbles present in high concentration rise at much greater velocities than isolated bubbles of the same volume.The apparent anomalies reported by Pyle and Harrison for the expansion of bubbling beds have been explained in terms of bubble velocities in excess of slug velocities.RésuméLes calculs des vélocités des bulles dans une couche à bouillonnement libre ont montré que les vélocités des bulles individuelles sont davantage influencées par la disposition des bulles environnantes que par le grosseur de la bulle elle-même volume. Les bulles présentes dans des concentrations élevées s élévent plus rapidement que des bulles isolées de même volume. Les anomalies apparentes rapportées par Pyle et Harrison pour l'expansion de couches bouillonnantes ont été expliquées en terme de veólocités des bulles en excès des veĺocités en bloc.ZusammenfassungMessungen der Blasengeschwindigkeiten in frei durchperlten Betten haben erwiesen, dass die Geschwindigkeit der Einzelblasen stärker durch die Verteilung der umgebenden Blasen als durch die Grösse der Einzelblasen selbst beeinflusst wird. In hohen Konzentrationen anwesende Blasen perlen wesentlich schneller als isolierte Blasen des gleichen Volumens.
Article
A method is described to determine quantitatively the change of the heat conductivity in an electric field parallel to the temperature gradient. Measurements were performed on NF3, CHCl3, C2H5Cl, CH3CN and C2H5CN. While the heat conductivity of NF3, CHCl3 and C2H5Cl decreases in an electric field, an increase of the conductivity has been found for CH3CN and C2H5CN.
Article
A critical examination of the results of previous workers together with new experimental work carried out in a 30.8-cm-diam. bed by the author has shown the fluidisation behaviour of many powders to be independent both of mean particle size and—more significantly—of particle size distribution. In particular, mean bubble size is found to depend only upon the gas distributor, the distance above the distributor and the excess gas velocity U-U0. An equation relating these variables gives good agreement with published data on bubble sizes observed in larger beds fitted with commercial type distributors.
Article
The apparent viscosity of air-fluidized beds of spherical particles has been measured with a torsion pendulum viscometer especially designed to minimize disturbance of the bed. Beds were made of closely sized uniform spheres or of binary mixtures of these. Sphere diameters ranged from 125 to 305 microns. Superficial air velocities ranged up to 10 cm. per second. A general viscosity correlation for uniform beds of this particle density has been obtained. The measurements tend to indicate Newtonian behavior, in which case the observations would be of a true kinematic viscosity. Evidence that fluidized beds can assume certain crystal-like structures has been found.
Article
By examining the equations for unsteady motions of solid particles and fluid through a bed of uniform solids concentration it is found that, owing to the inertia of the solid and fluid, a small disturbance in the mixture density will grow exponentially as it moves upward through the bed. A uniform density distribution is therefore unstable and a fluidized bed cannot be expected to be free of small irregularities, which may grow into "bubbles." The rate of growth of the waves of solids concentration depends on the wavelength of the disturbance, on the void fraction, and on the mean fluidizing velocity. The growth rate is generally greater the shorter the wavelength, but growth of the shortest waves is inhibited by the bed's resistance to shear. As a result, there is a wave that grows faster than any other; its wavelength is presumably related to the initial size of the "bubbles" that form spontaneously at all points in the bed.
Article
The transition from homogeneous to heterogeneous fluidization is described by the occurrence of shock waves. Shock waves will arise in a fluidized bed when the rising velocity of a porosity fluctuation exceeds the longitudinal propagation velocity of an equilibrium disturbance. An expression for the latter velocity has been derived via the elastic properties of a fluidized system. The elasticity modulus of this system has been calculated from a drag force-interparticle distance relation. It is shown that along these lines a satisfactory criterion for the transition between homogeneous and heterogeneous fluidization has been obtained.
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