FLuidization Engineering
Abstract
The book covers fluidization engineering. Topics covered include: Industrial applications of fluidized beds; The dense bed: distributors, gas jets, and pumping power; Bubbling fluidized beds. High-velocity fluidization; Particle-to-gas mass and heat transfer; Conversion of gas in catalytic reactions; Heat transfer between fluidized beds and surfaces; Circulation systems. Design of catalytic reactors. Reviews principles and applications of fluidization engineering; coverage of historical and current research influencing the development of this engineering field; bed-wall heat transfer; drying of solids, fast fluidization, heat exchangers, K-L model for catalytic reactions, mass transfer, and particle movement in beds.
... Dados históricos informam que, desde 1926, a técnica de fluidização já era utilizada para a gaseificação do carvão. As primeiras unidades se localizavam na Alemanha e Japão (Geldart, 1986;Kunii e Levenspiel, 1991 Na década de 1940, a Dorr Oliver aplicou a técnica para queimar minério de sulfeto. ...
... A primeira unidade foi construída em Ontário, Canadá em 1947 (Geldart 1986;Kunii e Levenspiel, 1991 ...
... Segundo Ho (2003), há na literatura duas classes de modelos para descrever o funcionamento de reatores de leito fluidizado; o primeiro é baseado em uma aproximação pseudo-homogênea e o outro na existência de duas fases. O enfoque pseudo-homogêneo propõe a existência de uma fase utilizando modelos convencionais do escoamento multifásico para reatores de leito fluidizado, como por exemplo: modelos de fluxo ideal, modelos de dispersão, modelos de distribuição de tempos de residência (DTR) e modelos de distribuição de tempos de contato (Kunii & Levenspiel, 1991). O enfoque de duas fases considera que os reatores de leito fluidizado consistem em pelo menos duas fases, uma bolha e uma emulsão, ou uma fase gasosa e uma fase sólida (Gidaspow, 1994) e propõem uma equação de conservação para cada fase, a qual descreve a transferência de massa entre as fases. ...
... Fluidized beds can operate in different flow regimes, such as bubbling or fast fluidization. As far as practical feasibility of a dual fluidized bed loop is concerned, assuring quite stationary operating conditions (mainly sorbent conversion and temperature level in the adiabatic reactor) by means of appropriate requirements for solid circulation rate, fresh particle make up and solid regeneration, there are significant examples of coupled fluidized bed processes, most of them developed up to industrial scale applications, well established processes as well as innovative applications (Kunii and Levenspiel, 1991;Koppatz et al., 2009;Adanez et al., 2012). More specifically, the feasibility of two different configurations was examined for the application at relatively large scale of a SE-SMR process, both utilizing fluidized bed reactors (Meyer et al., 2014). ...
... The mass and heat transfer correlation proposed by Gunn is also utilized in Chao et al. (2017) and Chen et al. (2017), both dealing with SE-SMR modelling as well, this time in binary fluidized beds, and in different fluidization studies (Antonini et al., 2015). This correlation provides predictions with order of magnitude in the range between an isolated particle and a fixed bed, corresponding to local heat transfer coefficient for a particle immersed in the fluidized bed, as defined in Kunii and Levenspiel, 1991. Excellent agreement is reported in the literature between experimental data of particle-gas heat transfer and Gunn correlation in bubbling fluidized beds; the conclusion was different for a CFB riser, because the mechanism of heat transfer is different here (Makkawi, 2011). ...
Sorption Enhanced Steam Methane Reforming (SE-SMR) has been proposed as an efficient novel technology to increase hydrogen yield and reduce the environmental footprint in comparison to state of art H2 production processes. Sorbent/catalyst materials characterized by stable behaviour over multiple reforming/calcination cycles may ensure to achieve almost stationary operating conditions utilizing a dual fluidized bed system (the reformer and the sorbent regenerator) with a solid circulation loop. Bifunctional, Combined Sorbent-Catalyst Materials (CSCM) are under development to integrate endothermic catalytic reforming and heterogeneous CO2 sorption in one particle, decrease mass and heat transfer resistances and reduce the solid hold-up in the reactors.
... Particle scouring is one of several unsteady-state shear techniques useful in membrane processes for fouling mitigation and improving the mass-transfer coefficient [123]. In practice, the solid particles are brought into close contact with the membrane surface via fluidization, which is the process whereby the particles are dispersed and suspended by the liquid such that they behave like a fluid [234,235]; thereby, the fouling layer on the membrane surface is mechanically scoured by the particles. A recent review assessed the mechanical cleaning concepts in membrane filtration [27]. ...
... Collectively, these efforts prove the efficacy of particle fluidization in mitigating fouling in submerged HF systems. The benefits conferred by particle fluidization include low energy cost [24,123,242,258,261,264,281], and amenability for scale-up and continuous operation [24,235], all of which make it an attractive means to improve membrane operations. In particular, the AFMBR energy requirement was only 0.028 kWh/m 3 , which is much less than that reported for AMBRs using gas sparging [24]. ...
The submerged membrane filtration concept is well-established for low-pressure microfiltration (MF) and ultrafiltration (UF) applications in the water industry, and has become a mainstream technology for surface-water treatment, pretreatment prior to reverse osmosis (RO), and membrane bioreactors (MBRs). Compared to submerged flat sheet (FS) membranes, submerged hollow fiber (HF) membranes are more common due to their advantages of higher packing density, the ability to induce movement by mechanisms such as bubbling, and the feasibility of backwashing. In view of the importance of submerged HF processes, this review aims to provide a comprehensive landscape of the current state-of-the-art systems, to serve as a guide for further improvements in submerged HF membranes and their applications. The topics covered include recent developments in submerged hollow fiber membrane systems, the challenges and developments in fouling-control methods, and treatment protocols for membrane permeability recovery. The highlighted research opportunities include optimizing the various means to manipulate the hydrodynamics for fouling mitigation, developing online monitoring devices, and extending the submerged HF concept beyond filtration.
... The upper surface of the bed disappears, entrainment becomes appreciable, turbulent motion of solids clusters and voids of gas of various sizes and shapes are observable. With a further increase of gas velocity, solids are carried out from the tube with the gas[2]. Scaling of fl uidized bed dryers as compared to other form dryers are more complex due to intense mixing of phases and the heterogeneous behavior of the bed. ...
... This region penetrated by gas from a rising bubble called as cloud. The three-phase back-mixing (bubbling bed) model was developed by Kunii and Levenspiel[2]. The bubbling bed consists of three distinct phases such as bubble phase, cloud-wake phase and emulsion of dense solid phase. ...
Fluidized bed dryers are widely used in several fi elds of industry. Suffi ciently accurate thermal models provide an opportunity to
increase the effectiveness of dryers. The required size of a fl uidized bed dryer can be defi ned with the application of mathematical
model. This work is aimed at developing mathematical model to investigate the infl uence of operating parameters in a fl uidized bed
dryer using volumetric heat transfer coeffi cient. After the defi ning the input parameters of the differential equations, the required
entry length of the dryer which effective heat and mass transfer between gas and particles takes place can be estimated. The correct
estimation of the entry length is useful in optimal design of a fl uidized bed dryer. Using the model the impact of the drying parameters
can be determined to the required length.
... and Levenspiel[23] introducedTable 1Fuel properties.To correlate the hydrodynamic parameters with constant a, Kunii and Levenspiel[23] also prepared a graph from the data in the literature which can be predicted as constant a in the following range: ...
... and Levenspiel[23] introducedTable 1Fuel properties.To correlate the hydrodynamic parameters with constant a, Kunii and Levenspiel[23] also prepared a graph from the data in the literature which can be predicted as constant a in the following range: ...
Tar formation and CO2 emission represent the strongest barrier for use of gasification technology for biomass conversion, whereas sufficing for both is only possible with expensive physical methods and further chemical processing. The use of CaO as a CO2 sorbent within an advanced high-temperature gasification system is able to achieve efficient cracking of the tars to the primary syngas with low emissions. The present work aims to propose a semi-kinetic model on the basis of an Aspen Plus model to describe specific catalytic behavior of calcium oxide on the gasification of rice husk. There has also been an attempt to validate the developed model by means of an experimental study and explore the influence of minerals within ash on gasification characteristics, since kinetic data are scarce in the literature. Effects of some critical parameters such as gasification temperature, equivalence ratio (ER), and steam/biomass ratio (S/B) on hydrogen yield and CO2 absorption ratio have been studied. Results showed that CO2 absorption ratio ascends as CaO loading ratio increases, then to continuously decrease due to a significant reduction in endothermic nature of the Boudouard reaction. When ER ascended from 0.15 to 0.25, syngas yield and hydrogen yield did the same thing, increasing from 2.1 to 2.45 Nm³/kg biomass and 37–41 g/kg biomass respectively. In the second stage, ER undertook a rise from 0.25 to 0.3 where gas caloric value and hydrogen yield were decreased.
... (1) and (2) [4,33]. Radicals like • OH and HO • 2 would oxidize and degrade BB3 structure and improve the degradation efficiency [34][35][36]. In each run, the apparent pseudo-first order rate constant (k app ) was established by the mean of slope of -ln Ct C0 against time (t) ( Table 4 and insets of Figures 4, 6-8). ...
... Performance of heterogeneous Fenton process (NM/ H 2 O 2 ) for BB3 degradation with FBR compared with batch reactor (BR) (Figure 13). Higher efficiency of fluidized-bed reactor compared with BR, can be related to enhancement of contact between catalyst particles and the dye, high mass transfer coefficients in FBR, and uniform and suitable blending of fluid inside the reactor [35]. ...
Degradation of basic blue 3 (BB3) was studied in a pilot scale fluidized-bed reactor (FBR) utilizing natural magnetite (NM) nanostructures for heterogeneous Fenton process. The morphology, structure, and specific surface area of NM nanostructure were determined employing scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) methods, respectively. High mass transfer coefficients, continuous operating condition and high reaction rates due to suitable and sufficient contact of phases, can be noted as significant advantages of FBR. Influences of factors, which affect performance of fluidized-bed heterogeneous Fenton process (NM/H2O2), for instances initial concentration of contaminant and H2O2, initial pH of solution and dosage of catalyst were investigated. At the desired operational condition, pH 5, 4 mM of H2O2, and 2.27 g/L of NM after 190 min, the degradation percentage of 84%. Excess amounts of catalyst dosage and hydrogen peroxide tend to scavenge hydroxyl radicals by H2O2 molecules. Whereas low initial concentration of the dye and low initial solution pH, enhanced the BB3 degradation. Reusability of NM through five successive experiments, demonstrated the acceptable proficiency of NM as catalyst for oxidative BB3 degradation. © 2017 American Institute of Chemical Engineers Environ Prog, 2017
... The fluidized bed is simulated in two sections, the BED, and the FREEBOARD, where different hydrodynamic parameters are considered for each one. The hydrodynamics considered takes into account the Kunii & Levenspiel [38] equation to calculate the minimum fluidization speed, as well as experimental correlations [39], [40] to calculate the volumetric fraction occupied by bubbles in the fluidized bed. This correlation considers solid and gas density, particle size, minimum fluidization velocity, and gas superficial velocity, a parameter that is not constant due to the gas production resulting from the homogeneous and heterogeneous reactions that model the process. ...
The development of tools for the synthesis, design, and optimization of biorefineries requires deep knowledge of the thermochemical processes involved in these schemes. For this project, three models from scientific literature were implemented to simulate the processes: fast pyrolysis in a fluidized bed, fixed-bed, and fluidized-bed gasification using the Aspen PlusTM software. These models allow the user to obtain performance, consumption, and cost parameters necessary for the design and optimization of biorefineries schemes. The fast pyrolysis model encompasses a detailed description of biomass decomposition and kinetics of the process (149 reactions). In the fixed-bed gasification process, seven reactions that model the process have been integrated into two equilibrium reactors that minimize the Gibbs free energy. The model used for fluidized bed gasification considers both hydrodynamic and kinetic parameters, as well as a kinetic model that considers the change in the combustion reaction rate of biomass with oxygen leading to a change in temperature. Due to the complexity and detail of all these models, it was necessary to use FORTRAN subroutines and iterative Excel macros linked to Aspen PlusTM. Finally, the results of each simulation were validated with data from the model sources, as well as experimental results from the literature.
... Dados históricos informam que, desde 1926, processos em leito fluidizado já eram utilizados para a gaseificação do carvão. As primeiras unidades se localizavam na Alemanha e Japão (Geldart, 1986;Kunii e Levenspiel, 1991 dá lugar a um sobre craqueamento e a uma redução na seletividade (Kraemer 1990;Chen 2003 ...
... In this study, microalga Chlorella vulgaris having initial moisture content of 90 wt% wb is selected as a sample considering its rapid growth and potential for CO 2 bio-fixation. The fluidization velocity inside the gasifier is calculated with the following Ergun equation [21]. In addition, the total energy efficiency, η tot , is calculated with Eq. (2). ...
Combined system for converting algae to hydrogen is developed based on principles of enhanced process integration technology to achieve high total energy efficiency. The system mainly consists of supercritical water gasification, hydrogen separation, hydrogenation, and combined cycle. Enhanced process integration combines both exergy recovery and process integration technologies, therefore, exergy destruction throughout the combined system can be minimized leading to high energy efficiency. Algae are converted initially to hydrogen-rich syngas through supercritical water gasification. Hydrogen separation is performed to produce hydrogen which is hydrogenated to achieve more convenient storage and transport. The remaining gas is combusted for power generation using combined cycle. Process modeling and evaluation regarding the effect of some operating parameters to total energy efficiency are performed. The combined system can achieve high total energy efficiency, higher than 60%.
... Because the feedstock has a certain size distribution, some particles will be transported up to the level of primary gasification agent injection, whilst others remain in the lower bubbling-bed zone or in the moving bed respectively. The calculated particle entrainment velocity, corresponding to Kunii et al. [27], is sufficient consistent with the experimental data of the maximum entrained particle size (see Table 7). ...
Background
Coal gasification is the promising technology for syngas routes to produce chemicals or transportation fuels. Additionally, it enables clean power generation from coal in Integrated Gasification Combined Cycles (IGCC). So far, coal fines with high ash contents could not be feasibly used in such routes.
In this regard, the Internal Circulation gasifier (INCI) is designed to gasify high-ash coal fines efficiently. The staged system is combining a moving bed, a fluidized bed and a jetting fluidized bed in one reaction chamber.
Method
The present paper substantially describes the laboratory-scale prototype development in the COORVED-project (“CO2-reduction by innovative gasifier design”) based on the INCI gasification principle of about 50-125 kW thermal input. Information about the gasifiers compounding, especially the reaction chamber, peripheral components and applied measurement systems are given.
Results
Experimental results are presented, confirming the targeted, typical flow pattern inside the reaction chamber. Furthermore technical and operational limits of the COORVED prefiguration are discussed. Based on these results a major design change of the reaction chamber is required and explained in detail. Additionally, results of the feedstock variation from coke to lignite are shown.
Conclusion
Finally, the operability of the INCI gasification principle is proven by a stationary operating system with controlled ash agglomeration.
... Since the commissioning of fluidization as a field of science, research in this area has been profound and extensive. The basic idea of fluidization conceptualized by Richardson and Zaki [1] now finds applications in many fields owing to some of its notable advantages during operation, like high heat and mass transfer rate, near ideal behaviour and easy handling [2]. Implementation of these concepts to fluidized bed reactors has given rise to the development of circulating fluidized beds which recirculate the solids within the system, essentially improving its efficiency. ...
Circulating fluidized beds (CFB) play a major role in the chemical industry especially as heterogeneous catalytic reactors. Research on hydrodynamic properties of Liquid – Solid CFBs (LSCFB) is significantly under-reported as compared to Gas – Solid CFBs (GSCFB). Steadily, prominent research is being established in fields like food industry (whey protein recovery), waste management (removal of heavy metals from radioactive wastes) and others, which use LSCFBs. In this context, it is important to have significant knowledge about the changes occurring in hydrodynamic properties like solid hold-up, rate of solid circulation etc., on changing certain critical physical properties such as inventory height. An LSCFB of height 2.95 m and riser outer diameter 0.1 m was chosen and the effect of inventory height on the properties was studied by taking the initial inventory heights as 15 cm, 25 cm and 35 cm. The hydrodynamic studies concentrated on axial solid holdup, average solid holdup, solid circulation rate and slip velocity. On increasing the inventory, uniformity of axial solid holdup was confirmed along with studying holdup patterns. Solid flux was seen to follow an inverse relationship to holdup, as expected. The change in slip velocity with varying inventory was also checked, and was found to decrease with inventory. The distribution parameter, C
... The decrepitation indexes have been calculated by using Eqns (1) and (2). [12,25] ...
The decrepitation of two Chinese lump coals was investigated using high-temperature fast pyrolysis in a purpose-designed furnace to simulate the reaction conditions in the coal-based Corex ironmaking process, and evolution of functional group, porosity, crystallite structure as well as CO2 reactivity of resultant coal chars was characterized. The results demonstrate that the decrepitation index varied significantly for different coal samples and their particle sizes, because of the variable thermal stress induced. The decrepitation index increased with increasing temperature and particle size, and severe decrepitation was observed when coal particles were increased to 20 mm. The coal chars derived from Xinglongzhuang lump coal at different temperatures had much more developed macroporous structure than Datong lump coal chars. A significant change of the crystallite height demonstrated a great influence of temperature on carbon structure. The CO2 reactivity of coal chars decreased with increasing annealing time at different temperatures examined, but the effect of carbonization temperatures on their reactivity has the opposite behavior, which is related to the porosity development and carbon structure variation. The interrelations of these phenomena further suggest that the appropriate dome temperature is crucial for ensuring permeability of coal char bed in Corex except for coal type.Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.
... But, in general, both the critical air flow rate and time required to reach a well-mixed regime slightly increased by increasing the biomass weight fraction in the bed for each of the investigated binary mixtures. The classical pressure drop method based on the use of fluidization curve was adopted to determine the value of both the minimum (Umf) fluidization velocity as the point of intersection of the straight lines corresponding to the fixed-bed and fluidized bed portions of the graph (Kunii and Levenspiel, 1991) and the complete fluidization velocity (Ucf) as the minimum value of the superficial gas velocity where a pressure drop equal to the weight of the bed per unit cross-sectional area is detected in the fluidization curve (Brachi et al., 2016). In particular, Umf and Uc were measured upon decreasing the fluidization velocity to avoid dependence on the initial bed configuration. ...
This paper reports on the results of an experimental study aimed at investigating the fluidization and segregation behavior of poly-disperse binary mixtures consisting of small and dense inert particles mixed with less dense and coarse pieces of biomass fuels. In more details, orange peels (OP), conditioned to a moisture
content of about 6% wt. and cut in square pieces (0.5 cm x 0.5 cm), were used as biomass feedstock. Three
different materials (i.e., Ticino sand, quartz sand, alumina powder and alumina spheres) were tested as inert
bed component in order to determine the prevalence of the effect of either size or density on the fluidization
and segregation behavior of the investigated binary systems. Fluidization experiments were performed at
room temperature in order to prevent that the formation of endogenous bubbles from devolatilizing fuel
particles could come into play, which also impacts mixing and segregation phenomena in real fluidized bed
reactors. Tests with different biomass weight fraction in the bed (XB) were performed both to study the effect of the bed composition on the characteristic velocities of the investigated binary systems (i.e., minimum and
complete fluidization velocities) and to determine their maximum batch loading, i.e. the critical value of XB
beyond which the fluidization quality deteriorate (e.g., channelling, irreversible segregation, slugging).
... The natural pyrite ore was crushed by milling method (Kian Madan Pars Co., Tehran, Iran) to gain micro-grained particles and next classified by screening in order to obtain various mean particle sizes (Kunii 2013). The obtained catalyst was washed by the distilled water and dried at 70°C for a day. ...
The ability of fluidized-bed Fenton oxidation of Acid Yellow 36 (AY36) as a model azo dye was investigated using natural pyrite (NP) particles in a recirculating pilot system. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out for characterization of the pyrite. The degradation efficiency (DE%) of AY36 in NP/H2O2 process was noticeably affected by operational parameters. The DE% of 92% was obtained for the AY36 treatment (15 mg/L) at the desired conditions as suspension pH 4, 2 mM H2O2, and 0.6 g/L NP after 120 min of the reaction time. The degradation rate in all of the experiments obeyed the pseudo-first order kinetic with high correlation coefficients (R2 ≥ 0.98). The low leached iron concentration, successive reusability at the milder pH and the recirculation mode with proper mixing are the significant advantages of the NP/H2O2 utilization.
... In this manner, the mathematical description of the gas flows from one compartment another consists of two parts: the first is linearly dependent from input and output flow, while the other depends on temperature dynamics, which is relatively slow (De Lange, 1996 andKunii, 1991). ...
By signature of the Kyoto protocol, the industrialised countries undertook to reduce the emissions of Greenhouse gases into the atmosphere. As a consequence, the use of fossil fuels must be reduced and substituted by renewable energy. One of the near-future options to produce power from renewable energy sources is to use biomass as a fuel in an Integrated Gasification Combined-Cycle (IGCC) plant. A plant of this type is currently under construction near Pisa and represents a pioneer project in this field. IGCC plants offer a high conversion-efficiency, but are rather complex. The understanding of the main process phenomena and the design of the plant's control system may benefit from a simplified dynamic model described in the paper.
... The dynamic simulator is implemented by a modular structured Fortran 90 code and has the following features: 1) can predict the state variables in the reactor, regenerator, main-fractionator, and auxiliary units of an FCC process; 2) can simulate both full and partial combustion modes of the regenerator; 3) can predict the yields of 10 lumps and light gas components based on the 1O-lump model and on the light gas yield model; 4) employs the momentum balance to predict the molar expansion and catalyst slip in the riser; 5) and adopts the tworegion, two-phase theory (Kunii and Levenspiel, 1991) for the regenerator model. ...
The purpose of this study is to investigate the performance of a dynamic matrix control (DMC) algorithm when applied to a fluidized catalytic cracking (FCC) process operated under full and partial combustion modes. A hierarchical control system comprised of a DMC and a basic regulatory controller was constructed. The DMC consisting of 10 controlled, 6 manipulated, and 2 feed forward variables was designed for the full and partial combustion modes, and then two different dynamic matrices were obtained by applying step tests to each combustion mode of the FCC process. From the control simulations, it was shown that the DMC as a supervisory control outperfonns conventional PID controller in both the full and partial combustion modes under process constraints.
... This study utilizes the dynamic simulator developed byHan et al. (2000). As the major features, the simulator (1) simulates the reactor, regenerator, and some auxiliary units of an FCC process, (2) can simulate both full and partial combustion modes of the regenerator, (3) adopts the well-known IO-Iump model (Jacob et aI., 1976) and can predict the light gas yields (hydrogen, methane, ethane, propylene, npropane, I-butene, iso-butane, and n-butane), (4) can predict the molar expansion and catalyst slip in the riser by introducing the momentum balance, (5) adopts the two-region, two-phase theory (Kunii and Levenspiel, 1991) for the regenerator model, and (6) is implemented by modular structured Fortran 90 code. The dynamic simulator was revised to support optimization studies. ...
A systematic optimization procedure for a fluidized catalytic cracking (FCC) process is presented. First, steady-state process mode ling is carried out for the reactor, regenerator, main-fractionator, and most of auxiliary units including the feed pre-heater, catalyst cooler, air blower, wet gas compressor, stack gas expander, boilers, and valves. Then, the resulting steady-state model is utilized to develop the model parameter estimator and the process optimizer both of which adopt a successive quadratic programming algorithm to efficiently locate the optimum solutions. The developed optimization system is applied to several optimization cases to maximize the economic profit of the FCC and then successfully finds the model parameters and the optimal values of the decision variables.
... The dynamic simulator is implemented by a modular structured Fortran 90 code and has the following features: 1) can predict the state variables in the reactor, regenerator, main-fractionator, and auxiliary units of an FCC process; 2) can simulate both full and partial combustion modes of the regenerator; 3) can predict the yields of 10 lumps and light gas components based on the 10-lump model and on the light gas yield model; 4) employs the momentum balance to predict the molar expansion and catalyst slip in the riser; 5) and adopts the tworegion, two-phase theory (Kunii and Levenspiel, 1991) for the regenerator model. ...
The purpose of this study is to investigate the performance of a dynamic matrix control (DMC) algorithm when applied to a fluidized catalytic cracking (FCC) process operated under full and partial combustion modes. A hierarchical control system comprised of a DMC and a basic regulatory controller was constructed. The DMC consisting of 10 controlled, 6 manipulated, and 2 feed forward variables was designed for the full and partial combustion modes, and then two different dynamic matrices were obtained by applying step tests to each combustion mode of the FCC process. From the control simulations, it was shown that the DMC as a supervisory control outperforms conventional PID controller in both the full and partial combustion modes under process constraints.
... There are several ways to increase productivity. To increase a gasifier throughput one must increase the oxidant flow rate, but this method has a limitation related to the failure of the dense bed at a high oxidant flow rate (fluidization of the bed) [20]. Another way is to increase the reactive surface of the fuel by reducing the size of its particles. ...
A new method for the gasification of fine solid fuel was proposed and worked out, by partial oxidation in a flow of gaseous oxidant with filtration of the suspended fuel through an inert porous matrix. In this case, the solid fuel gasification was carrying out similar to the filtration combustion of gases. The gasification of fine solid coal allows one to produce a combustible gas rich in H2 and CO was studied. A possibility of pulverized coal gasification in a fixed bed reactor with production of gaseous products containing up to 13% by volume of hydrogen and carbon monoxide was shown experimentally.
... Ciesielczyk et al. [7] applied a mathematical model of bubbling fluidized bed drying kinetics. Bubbling fluidized bed model was used to characterise the fluidized bed system in number of publications [8]. Using bubbling fluidized bed model the variation of the temperature and absolute humidity of gas, and the variation of the temperature and moisture content of material can be determined in the function of time in the constant and falling drying rate periods [7]. ...
Fluidized bed dryers are often used in several industrial processes to dry wet granular solids with high moisture contents. During the drying process, simultaneous heat- and mass transfer occurs between the material and drying gas. Drying is an extremely energy intensive process, therefore the invested energy should be mitigated during planning the operation, granting optimal geometric and operational parameters of the device. During the planning, sufficiently accurate thermal models provide an opportunity to increase the effectiveness of dryers. The purpose of our work is to develop mathematical model to investigate the influence of operating parameters describing the simultaneous heat- and mass transfer in a fluidized bed dryer. The input parameters of the model are the volumetric transfer coefficients between the drying gas and the granules, due the uncertain heat- and mass transfer surface. A pilot plant fluidized bed dryer device is developed to determine the volumetric transfer coefficients and to study the heat- and mass transfer phenomena during the drying processes. The goal of our work is to model the fluidized bed drying process more accurately using volumetric transfer coefficients.
... Fluidized bed systems are extensively employed in several industries such as: agroindustry, chemical and pharmaceutical (Kunii and Levenspiel, 1991). Generally, fluidized systems allow significant improvements in heat and mass exchanges, with associated space and monetary revenues. ...
... ð7:10Þ Equations (7.7), (7.9), and (7.10) are based on analytic expressions of the drag coefficient from the work of Kunii and Levenspiel (1969). An alternative method for determining the settling velocity is to curve-fit experimental data. ...
A volcanic eruption is an amazing event. The associated earthquakes, lava flows, and ash clouds are both intriguing yet potentially dangerous features that can cause enormous changes to the landscape, damage to infrastructure, and even loss of life. Obviously, the ability to predict the occurrence and dynamics of an eruption is both desirable and necessary for public safety. Despite many advances in the understanding of what leads to volcanic eruptions, predicting the commencement of an eruption remains difficult. Once an eruption has begun, predicting its behavior is equally if not more important in order to minimize the potential financial and human costs.
This paper reviews the recent advances in multi-scale computational fluid dynamics (CFD) simulations of biomass pyrolysis in fluidized bed reactors. The interconnection among molecular-scale, particle-scale, CFD cell-scale, and reactor-scale are first introduced, together with the Eulerian-Lagrangian (E-L) and Eulerian multi-fluid model (MFM) frameworks. Then an overview of the theoretical basis and practical applications of four main particle-scale models, i.e, uniform conversion model, progressive conversion model, interface-based model, and corrected uniform conversion model, are highlighted. The coupling of particle-scale models with CFD cell-scale models is discussed, as well as with molecular-scale models. Finally, the perspective of future work to develop reliable and efficient CFD models for simulating biomass pyrolysis in fluidized bed reactors is outlined.
Popping/puffing have been traditionally practised for enhancing storage life, improving organoleptic properties and ease of incorporation in ready-to-eat-foods. Currently, batch type sand and electric popping/puffing machines involving conduction mode of heat transfer are employed. The major drawbacks of these methods are high-energy consumption, scorching of grains, non-uniform product quality, contamination (by sand/ash) and problems in scale-up. Since fluidization is known to increase heat and mass transfer, a continuous fluidized popping/puffing machine (capacity 10-20 kg/h) involving convective mode of heat transfer is designed/developed. Hot-flue gas generating from burning of LPG was used as the eco-friendly fuel. Process parameters such as expansion ratio, fluidization velocity, terminal velocity, carry over velocity, bulk density and voidage were estimated for un-popped and popped/puffed rice, maize, jowar (sorghum) and paddy. Fluidization and carry over velocities for these grains were in the range of 4.18-5.78 m/s and 2.15-6.18 m/s, respectively. Based on the terminal velocity of the grains and volumetric air flow rate of the blower, fluidization chamber diameter was arrived. Chamber diameter of 0.15 m was found to be sufficient to generate required air velocity of 6.89 m/s which met the fluidization and carry over velocities of popped/puffed grains. The designed fluidization chamber was analyzed for heat and mass transfer during popping/puffing. Convective heat and mass transfer coefficients were estimated to be in the range of 103-187 W/m2 oC and 0.124-0.162 m/s, respectively. Theoretical values for total heat and mass transfer were similar to the experimental values.
The relative distribution of gas flow between the bubble phase and the dense phase is a very important factor that determines the performance of a gas-solid fluidized bed reactor, because the dense phase provides a better gas-solid contact than the bubble phase. The gas flow through the dense phase was initially considered to be at minimum fluidization (the so-called two-phase theory) but was found to be higher with fine Group A particles. Using even smaller particles in this study, the fluidization of Group C+ particles, Geldart Group C particles with nano-additives, exhibited lower bubble rise velocity, lower bubble holdup, and higher gas holdup in the dense phase, etc., signifying more gas flow through the dense phase and subsequently contributing to better gas-solid contact than other particles that have ever been tested, being Groups A or B. The correction factor Y that accounts for increased dense phase gas flow in the modified two-phase theory was also found to be not a constant but a function of the superficial gas velocity, and a correlation was then proposed to characterize the division of gas flow between the two phases for these fine Group C+ particles, based on the experimental results. The higher dense phase gas velocity and the lower bubble phase gas velocity could improve the gas-solid contact and the reactor performance for Group C+ particles.
The aim of this work was to study the production of diethyldichlorosilane [(C 2 H 5) 2 SiCl 2 ]. The catalytic reaction of silicon (Si) of purity 99.9% with ethylchlo-ride (C 2 H 5 Cl) was investigated in a fluidized bed reactor. Cuprous chloride (CuCl) of purity 99.9% was used as a catalyst of the reaction. Gas chromatography was used on-line for analysis of the reaction products. The experimental work was carried out using a stainless steel column of 5cm internal diameter and 50cm height as the fluidized bed reactor. The experiments start with different bed temperatures between 200 and 300 C to identify the optimum reaction temperature. This temperature was found to be at 250 C, which resulted in the maximum of ethylchloride (EtCl) conversion and diethyldichlorosilane yield. In fifteen runs, the variables considered were sieve-analysis average particle size dp (50,100, and 150 µm), contact mass weight wt (100-200 gm) and reacted gas velocity Ug (1.41-2.83 cm/s). It was found that the conversion of EtCl increases with decreasing reacted gas velocity, increasing bed contact mass and particle diameter. The yield of Et 2 SiCl 2 was not affected by these variables, but bed temperature was found to have a significant affect. Two mathematical models, the Orcut model and the continuous CSTR model were used to predict theoretical data for the conversion of EtCl. The comparison between the experimental and the theoretical data showed good agreement with an absolute error of less than 9%.
Processing of particles in a moving bed, such as a fluidized bed or a spouting bed, is commonly used in the operations of drying, coating, and granulation of particulate systems. This process has applications in the chemical, pharmaceutical and, presently, agronomical industries, especially for seed treatment/coating. This research aimed to analyze the fluid-dynamic behavior of fluidized and spouting beds with different air temperatures and loads of flaxseeds (Linum usitatissimum L.), with estimates of the fluid-dynamic parameters correlated to each process. The parameters were compared with the values obtained from classical correlations in the literature, with indications of associated percentages of deviation. Influence of fluid dynamics on the physiological quality of seeds was assessed by germination tests and the germination speed index. An analysis of the results indicated that seed processing was adequate for processing in dynamically active beds; however, temperatures above 50ºC in both beds caused significant reductions in the physiological quality of the seeds. Processing in a fluidized bed presented a smaller reduction of the physiological properties of the flaxseed.
Introduction Fluidized Bed Reactors Fixed Bed Reactors Pressure Drop Calculations Catalytic Reactor Design Considerations
Introduction Fixed Beds Permeability Minimum Fluidization Velocity Bed Height, Pressure Drop and Porosity Fluidization Modes Fluidization Experiment Data and Calculations
Summary Introduction FCC Process Description Atmospheric Contaminants from the Regenerator—Origin and Treatment Summary
The upwards flow of particles in an Upflow Bubbling Fluidized Bed (UBFB) is studied experimentally and modelled from pressure drop considerations and energy loss equations. For Geldart group A powders tested, the upward solid flux, Gs, in the tube can be expressed in terms of the applied superficial gas velocity, the free fall (terminal) velocity of the particles during their hindered settling, KUt, the pressure exerted at the base of the conveyor tube, and the tube length. The model expression Gs=ΔP(Ug−KUt)+K2gL(Ug−KUt) can be used for design purposes, with K, the correction factor for hindered settling of the particles, approximately equal to 0.1 at high Gs-values, but a function of the solids fraction in the upward conveying. The energy efficiency of the system increases with increasing U and Gs. The model equation was tentatively applied to predict the effects of particle size, tube length and operation in Circulating Fluidized Bed mode. It is demonstrated that the UBFB is an efficient and flexible way of transporting particles upwards, with limited particle attrition or tube erosion due to the low gas velocity applied.
Gas-solid flow occurs in many industrial furnace processes. The majority of chemical engineering unit operations, such as drying, separation, adsorption, pneumatic conveying, fluidization and filtration involve gas-solid flow.
de Bei Verpackungsprozessen von Nahrungsmittel‐ und Medikamentepulvern ist die sichere und reine Verpackung des Endprodukts während der Herstellung von großer Wichtigkeit. Um längere Haltbarkeit der Produkte zu garantieren finden viele dieser Prozesse unter Zuhilfenahme von Inertgasen statt. Zur Untersuchung der Schleppwirkung von freifallendem Schüttgut auf verschiedene Gasspezies wurde ein Versuchsaufbau entwickelt, mit dem unterschiedliche Partikelgrößenverteilungen und Fallhöhen untersucht werden können. Die erreichten Ergebnisse werden zur Validierung numerischer Simulationen unterschiedlicher Ansätze genutzt.
Abstract
en For packaging processes of food and drug powders safety and cleanliness of the final product is one main aspect of the manufacturing process. To reach longer life periods of the products many of these processes are using inert gases during dosing procedure. To examine the entrainment of different kinds of gas species by free‐falling bulk material during the dosing process an experimental setup was built. Therefore different particle‐size distributions as well as different falling heights were analysed. The achieved results are used for the validation of numerical simulations based on different numerical methods.
de Verpackungsprozesse von Pulvern aus dem Bereich der Nahrungsmittel und Medikamente finden häufig unter Schutzatmosphäre statt, um bereits während des Dosierprozesses die Sauerstoffkonzentration der umgebenden Gasphase zu reduzieren und damit eine längere Haltbarkeit der Produkte zu garantieren. Eine neue numerische Simulationsmethodik basierend auf einem Lagrange'schen Modell unter Verwendung von OpenFOAM® wurde entwickelt, um neue Dosiersysteme im Vorfeld auf ihre Sicherheit bzgl. der Restsauerstoffwerte im Produkt beurteilen zu können. Zur Validierung dienen experimentell ermittelte Grenzwerte.
Abstract
en Packaging processes of food powders and drugs often take place under a protective atmosphere in order to reduce the oxygen concentration of the surrounding gas phase during the dosing procedure, thus guaranteeing a longer shelf life of the products. A novel numerical simulation method based on a Lagrange model using OpenFOAM® was developed to evaluate new dosing systems in advance for their safety regarding the residual oxygen level in the product. The results of experimental setups are used for validation.
This paper presents an experimental study on the effects of elevated pressure and particle size distribution (PSD) on the minimum fluidization velocity (Umf) and the bed expansion. It was developed with Geldart B and D-type polystyrene particles. Four wide PSDs and five narrow PSDs were investigated. The four wide PSDs studied included a Gaussian distribution, a flat distribution, a ternary mixture, and a binary mixture, all with the same mean diameters. Operation pressure ranged from 0.1 MPa (absolute pressure) to 2.7 MPa. The results revealed that the Umfs of the wide PSDs were lower than that of the reference narrow PSD with the same diameter at pressures exceeding 0.3 MPa. The segregation tendency of wide PSDs decreases with the increase in the operating pressure. The four wide PSDs had obviously different Umfs at pressures below 0.9 MPa; however, this difference in the Umfs was gradually reducing with a further increase in the pressure (> 0.9 MPa). The bed expansion increased with increasing the pressure at same excess fluidized gas velocity. Correlations basing on experimental data were proposed in order to predict the Umf and bed expansion for the narrow PSD at elevated pressures, and three correlations were investigated for predicting the Umf of wide PSD.
Flow properties of solids in an inclined standpipe were investigated while the solid particle was fed to the bottom of a bubbling fluidized bed (diameter 0.1m, 1.34m tall) via the standpipe and discharged out of the bed through the overflow exit. A group of K-based CO2 adsorbent particles was used as solids. The pressure drop of the fluidized bed, the height of solids bed in the standpipe, and flow rate of gas bypassing the fluidized bed through the standpipe were measured at room temperature and pressure as varying the fluidizing gas velocity, solids flow rate, and height of the overflow exit of fluidized solids. The pressure drop of the fluidized bed, the height of the solids bed in the standpipe, and the ratio of gas bypassing through the standpipe to the total gas in flow rate decreased with increasing the fluidizing gas velocity. Both the pressure drop of the fluidized bed and the height of the solids bed in the standpipe increased a little with the solids feed rate. The effect of the solids feed rate on the flow rate of gas bypassing through the standpipe could be ignored. The pressure drop of the fluidized bed and the height of the solids bed in the standpipe increased as the height of the overflow exit for solids increased in the fluidized bed. However, the effect of the height of the overflow exit on the flow rate of gas bypassing through the standpipe was negligible. Correlations on the pressure drop of the fluidized bed, the height of the solids bed in the standpipe, and the flow rate of gas bypassing through the standpipe were proposed successfully.
Under certain conditions, gas-solid fluidized beds are known to develop a structured flow of bubbles when exposed to periodically pulsating air flows. In quasi-two-dimensional beds, periodically rising bubbles form a triangular tessellation in the vertical plane. Bubble nucleation sites at the distributor plate alternate during each cycle. This pattern sets an excellent benchmark for fundamental studies of fluidization. Notably, most common Eulerian descriptions of granular flow do not yet capture this interplay between solid mechanics and fluid-solid momentum exchange, which we show to be instrumental to the dynamic rearrangement of bubbles in a pulsed bed. We report the first successful CFD simulations of structured bubble flows in a deep, quasi-2D geometry using a Eulerian-Lagrangian CFD-DEM framework. Numerical results are in quantitative agreement with experiments. The simulated dynamics reveal that the patterns emerge from the transition of the granular collective behavior between solid-like and fluid-like, which is an outcome of dynamical coupling between gas and particles. The simulated results point out the essential role of solid frictional stresses on inducing and maintaining the formation of bubble patterns. This underscores the value of investigating pulsation-induced patterns as a prime manifestation of the mesoscopic physics underpinning fluidization, and highlights the direction for improving current practices.
Solids mixing affects thermal and concentration gradients in fluidized bed reactors and is, therefore, critical to their performance. Despite substantial effort over the past decades, understanding of solids mixing continues to be lacking because of technical limitations of diagnostics in large pilot and commercial-scale reactors. This study is focused on investigating mixing dynamics and their dependence on operating conditions using CFD simulations. Towards this end, fine-grid 3D simulations are conducted for the bubbling fluidization of three distinct Geldart B particles (1.15 mm LLDPE, 0.50 mm glass and 0.29 mm alumina) at superficial gas velocities U/Umf$=2-4 in a pilot-scale 50 cm diameter bed. The Two-Fluid Model (TFM) is employed to describe the solids motion efficiently while bubbles are detected and tracked using MS3DATA. Detailed statistics of the flow-field in and around bubbles are computed and used to describe bubble-induced solids micromixing: solids upflow driven in the nose and wake regions while downflow along the bubble walls. Further, within these regions, the hydrodynamics are dependent only on particle and bubble characteristics, and relatively independent of the global operating conditions. Based on this finding, a predictive mechanistic, analytical model is developed which integrates bubble-induced micromixing contributions over their size and spatial distributions to describe the gross solids circulation within the fluidized bed. Finally, it is shown that solids mixing is affected adversely in the presence of gas bypass, or throughflow, particularly in the fluidization of heavier particles. This is because of inefficient gas solids contacting as 30-50% of the superficial gas flow escapes with 2-3x shorter residence time through the bed. This is one of the first large-scale studies where both the gas (bubble) and solids motion, and their interaction, are investigated in detail and the developed framework is useful for predicting solids mixing in large-scale reactors as well as for analyzing mixing dynamics in complex reactive particulate systems.
This paper presents the experimental work and performance evaluation of continuous vibrated fluidized bed dryer on green tea production. In order to maintain high catechin content, drying is a significant process in green tea production. Tea leaves after steaming process which has 75–80% moisture content was dried in different temperature (50 , 60 and 70) and air inlet velocity (0.71 m/s, 0.94 m/s, 1.09 m/s). The result shows that the temperature distribution along the bed is uniform. Temperature and air velocity have a significant effect on drying temperature. Shortest drying time was achieved at the temperature of 70 C with an air velocity of 1,09 m/s.
An analytical procedure was developed for reduction in fluidized beds with batch-wise iron ore feed based on the bubble assemblage model and the three-interface reaction model with solid-state diffusion. The experimental results of hydrogen reduction in the high pressure fluidized bed were analyzed according to the proposed procedure. The simulated results were able to describe the experimental data up to the final stage in which the reduction rate became extremely low. Effects of pressure, temperature, gas velocity, bed height, and fractional reduction on the reduction rate and the utilization factor for hydrogen were elucidated quantitatively by the proposed analytical procedure.
A steady-state one-dimensional heat transfer method was used to measure the effective thermal conductivity of Sultani and El-Lajjun oil shale particles. The particles were packed in a cylindrical bed and heated uniformly over a temperature range of 25 to 250°C. The effect of particle sizes of < 250, 500-710, and 1000-1400 w m on thermal conductivity was also investigated. The effective thermal conductivity of the samples was observed to decrease with increasing temperature. Moreover, the values of thermal conductivity were found to increase with increasing oil content of the shale samples. Over the tested range, particle size showed little effect on thermal conductivity.
This chapter presents the energy and exergy analysis of drying processes and systems. First, the balance equations and other equations relevant to modeling and analysis of drying processes through energy and exergy methods are introduced. Next, the efficiency definitions which are specific to drying systems and other assessment parameters are given. Then, the chapter presents an analysis, based on energy and exergy methods, of continuous-flow direct combustion dryers. With a heat pump dryer, an excellent match of temperature levels between supply side and demand side can be obtained. Minimization of the temperature differences leads to reduced exergy destructions. Fluidized bed dryers are very important in the industry when granulate materials or powders must be dried. The chapter presents the energy and exergy analyses for fluidized bed dryers.
As already noted in Sect. 1. 1 (Fig. 1. 2) and Chap. 2, the balance equations for mass, momentum, energy, substances, and phases and the constitutive equations or models for heat and mass transfer, substance transformation and phase transition, turbulence, and physical characteristics form a coupled system of non-linear partial differential equations (PDE). The complexity (number of equations) depends on the problem to be modeled and the expected detailing of the results.
Kapitel 8 widmet sich den mehrphasigen Reaktionssystemen, nämlich den heterogen katalysierten, den Fluid-Fest- sowie den Fluid-Fluid-Reaktionen. Zunächst wird in die Bilanzierung mehrphasiger Reaktionssysteme eingeführt und gezeigt, wie Stoff- und Wärmeübergang kinetisch zu berücksichtigen sind (Makrokinetik) und wie mit Hilfe des Wirkungsgradkonzeptes Vereinfachungen der Bilanzgleichungen vorgenommen werden können. Heterogen katalysierte Reaktionen werden umfassend hinsichtlich der kinetischen Relevanz auftretender Stoff- und Wärmetransportlimitierungen diskutiert und anschließend wird ausführlich auf die Auslegung isothermer, adiabater und polytroper Festbettreaktoren eingegangen. Die Auslegung von Wirbelschichtreaktoren wird ebenfalls behandelt und verschiedene Reaktormodelle vorgestellt. Bei den Fluid-Fest- und Fluid-Fluid-Reaktionen wird insbesondere die Auswirkung von Stofftransportlimitierungen auf die Kinetik diskutiert und jeweils die Reaktorauslegung erläutert.
Concepts, Processes and ExamplesCharacteristics of the Moist Product, Movement of MoistureProperties of Wet Gases, h-X DiagramMass and Heat Transfer in Convection DryingDrying Kinetics, Course of Drying, Drying TimeConvection DryingContact DryingRadiation DryingDielectric DryingFreeze Drying (Sublimation Drying)Design of Dryers
Cost effective CO2 capture processes are of paramount importance for significantly reducing greenhouse gas emissions. In order to accelerate the development and scale up of such technologies, the U.S. Department of Energy's Carbon Capture Simulation Initiative created an innovative suite of computational tools and models. The resulting computational framework supports (1) rapid synthesis of complete, optimized processes, (2) identification of promising device configurations, (3) assessment of sources and effects of model and parameter uncertainty, to guide experimental and pilot scale testing towards acquiring the most important types of data, and (4) assessment of dynamic process behavior and deployment of advanced process control techniques, to minimize the impact on the power plant and ensure that the integrated power/capture/compression system is able to respond to changing plant conditions and disturbances. A case study on a solid sorbent CO2 capture system describes the advanced process models and demonstrates the capabilities of the framework.
Particles entrained from a pilot scale fluidized bed of sand having a mean size of 102 μm have been captured and analysed at superficial air velocities up to 1.3 m/s. Variation of bed temperature over the range 300 to 445 K and insertion of a tube bundle in the splash zone had little effect on the measured entrainment fluxes. Existing correlations for predicting entrainment from fluidized beds gave widely divergent results, and generally differed markedly from the experimental data. Of the correlations tested, the graphical saturation carrying-capacity correlation of Zenz and Weil gave the best agreement with the experimental data. The size distribution of particles carried over differed widely from the size distribution in the bed at low gas velocities but approached the in-bed distribution at higher velocities.
On a collecté et analysé les particules entrai'nées hors d'un lit à l'échelle pilote, flidisé de sable, la grosseur moyenne étant de 102 μm aux vitesses superficielles d'air allant jusqu'à 1.3 m/s. La variation de la température du lit, sur une gamme de 300 à 445 K, et l'introduction de tubes dans la zone de projection n'ont eu que peu d'effet sur les flux d'entrai'nement mesurés. Les corrélations qui existent actuellement pour prévoir l'entrai'nement de particules à partir de lits fluidisés, ont fourni des résultats très divergents et leurs données diffèrent, en général, d'une manière marquée des résultats expérimentaux. Parmi les corrélations que nous avons examinées, la corrélation graphique de Zenz et Weil, relative à la capacité de transport à saturation, a le mieux concordé avec les résultats expérimentaux. La granulométrie des particules entrai'nées diffère beaucoup de celles des particules dans le lit, lorsque la vitesse du gaz est faible, mais elle s'en approche lorsque les vitesses du gaz sont plus élevées.
Entrainment from a gas fluidized bed of cracking catalyst in a 2-ft diameter column equipped with continuous solids recycle has been studied. Radial profiles of entrainment rate and mean particle size were relatively flat. The entrainment rate decreased rapidly with increasing height above the bed and with decreasing fluidizing velocity. The existence of a transport disengaging height above which the entrainment rate and mean particle size become essentially constant was confirmed experimentally. This may be taken as the height above the bed surface at which the inverse Froude number becomes equal to 1000.
On a étudié l̂entraînement provenant d̂un lit de catalyseur de craquage fluidisé an gaz, dans une colonne de 2 pieds de diamètre et pourvne d̂un dispositif pour recycler dcs solides d̂une manière continue. Les profils radiaux du taux d̂entraînement et des dimensions moyennes des particules se sont avérés relativement plats. Le taux d̂entraînement a diminué rapidement en raison inverse de la hauteur et directement avec la vélocité décroissante de fluidisation. On a confirmé expérimentalement l̂existence d̂une hauteur de dégagement au-dessus. de laquelle le taux d̂entraînement et les dimensions moyennes des particules devenaient essentiellement constants; on peut la considérer comme la hauteur au-dessus de la surface dn lit à laquelle le nombre inverse de Froude devient égal à 1000.
The elutriation of fines from fluidized beds of two- and multiparticle systems is investigated. Materials used are glass beads and coal powder with air and helium as the elutriating gases.
A specific elutriation rate constant which takes into consideration the particle stratification and thus is nearly independent of the bed dimensions is employed in the correlation of the elutriation of fines.
The proposed generalized correlation applicable to a system of two particle sizes and to more complex ones is presented. Recorrelation of pertinent literature data by the dimensionless equation indicates good agreement in spite of a diversity of bed geometries. The effect of fluidized-bed parameters on the rate of elutriation is examined, and applications and limitations of the correlation are shown.
A means of calculating the rate of entrainment of solids from commercial-size continuously operating fluidized beds was developed from the combined results of a theoretical and an empirical approach which through different channels arrived at the same fundamental mechanism. The calculation method shows agreement with data obtained from an apparatus simulating flow characteristics in large-scale equipment and compares favorably with smaller scale tests reported in the literature at pressures up to 200 1b./sq. in. gauge.
A model describing the entrainment of solid particles in the freeboard region of a fluidized bed is proposed. Published experimental data have been used to correlate the entrainment rate near the bed surface and the elutriation rate above the bed. It has been shown that the column diameter can have an important influence on the amount of fines elutriated.