Fluidization Research Papers - Academia.edu (original) (raw)

Pressurized water flow through small holes in an embedded pipe in the sediment deposite will lead to increased sediment porosity and subsequently producing drag force that causes sediments to be lifted, agitated and expanded until it... more

Pressurized water flow through small holes in an embedded pipe in the sediment deposite will lead to increased sediment porosity and subsequently producing drag force that causes sediments to be lifted, agitated and expanded until it reaches the phase of incipient flu idization. This mechanism is an important part for the development of fluid izat ion method as a new technique to overcome the water channel sedimentation. Two dimensional experimental works for vert ical jet flu idization in unbounded domain of sediment deposite were performed in the laboratory of Gadjah Mada University, Indonesia. The results show that the hydraulic behaviors in all steps of prefluidization toward incipient flu idization can be explained in detail. Criteria to achieve init ial flu idization given by a certain value of flow rate and hydraulic head in the flu idizer pipe that produces crit ical internal vortex. The critical height of vortex (zc) about 0.5dbwhere db is the thickness of the sediment depo...

An intrusive bioptical probe provides radial profiles of the PDF (Probability Density Function) of the bubble, the cloud and the emulsion phases behaviors in a fluidized bed of GeldartA particles. The fluidizing velocity ranges between... more

An intrusive bioptical probe provides radial profiles of the PDF (Probability Density Function) of the bubble, the cloud and the emulsion phases behaviors in a fluidized bed of GeldartA particles. The fluidizing velocity ranges between 0.20 m/s and 0.80 m/s. The bed porosity, the overall averaged bubble chords and velocities are wellpredicted by correlations of the literature. The cloud thickness is closely related to the bubble chord. The amount of gas traveling through the bubble phase never exceeds 1520 % of the total gas flow rate. The averaged porosity of the bubble, the cloud and the emulsion phases is of 8892 %, 6570 % and 5055 %, respectively. The reduced bubble porosity distribution obeys a constant normal law over the fluidizing velocity range. Each distribution of the reduced bubble chord and velocity, and of the reduced cloud thickness obey a constant log normal law over the fluidizing velocity range. Porosity threshold between the cloud and the bubble phases (m 3 /m 3 ).

Changes in fluidization behaviour of green peas particulates with change in moisture content during drying were investigated using a fluidized bed dryer. All drying experiments were conducted at 50 + 2 0C and 13 + 2 % RH using a heat pump... more

Changes in fluidization behaviour of green peas particulates with change in moisture content during drying were investigated using a fluidized bed dryer. All drying experiments were conducted at 50 + 2 0C and 13 + 2 % RH using a heat pump dehumidifier system. Fluidization experiments were undertaken for the bedheights of 100, 80, 60 and 40 mm and at 10 moisture content levels.

The powder-particle spouted bed process is one of the semi-dry processes that have been developed for flue gas desulfurization. In this study, which is designed for SO 2 removal by a powder-particle spouted bed, the reaction term is... more

The powder-particle spouted bed process is one of the semi-dry processes that have been developed for flue gas desulfurization. In this study, which is designed for SO 2 removal by a powder-particle spouted bed, the reaction term is included in one-dimensional and streamtube models that were presented previously for spouted beds. Hydrated lime is used as the sorbent in this process. The predictions of the models are compared with some published experimental data and it is found that the developed models are valid. The results of two models are compared with each other and their various properties are evaluated. The effects of different operating conditions on SO 2 removal efficiency are also investigated and preferred operating conditions are discussed.

This review reports recent advances on chemical-looping combustion (CLC). CLC is a promising technology for fossil fuel combustion preventing CO 2 dilution with flue gases, mainly nitrogen. In CLC, the solid oxygen carrier supplies the... more

This review reports recent advances on chemical-looping combustion (CLC). CLC is a promising technology for fossil fuel combustion preventing CO 2 dilution with flue gases, mainly nitrogen. In CLC, the solid oxygen carrier supplies the stoichiometric oxygen needed for CO 2 and water formation, and this leads to a free nitrogen mixture. As a result, the requirement of CO 2 separation from flue gases, a major cost for CO 2 capture, is circumvented. Furthermore, formation of NO x is also reduced. A good oxygen carrier for CLC shall readily react with the fuel gas and shall be reoxidized upon being contacted with oxygen. An oxygen carrier is typically formed by a metal oxide and an inert binder, which provide, respectively, oxygen storage, fluidizability and mechanical strength. Over the last 10 years, several research groups have been researching oxygen carriers which are both active and stable under fluidized bed conditions. While Fe, Ni, Cu, Mn and Co oxides are potential oxygen carrier materials, recent studies show that Ni is best suited for CLC. Few studies have been devoted to the solid-state kinetics of both reduction and oxidation with either a nucleation-nuclei growth or unreacted shrinking core models being considered. In order to implement CLC, two interconnected fluidized bed reactors (the fuel and air reactor) with the oxygen carrier circulated between units have been proposed. While reactor design, modeling and hydrodynamics are matters that have been analyzed by several research groups; these topics still require more attention and investigation. Preliminary economic assessments, have suggested that CLC holds great promise for combustion processes, having the potential for achieving very efficient and low cost CO 2 capture. Even with these favorable prospects, commercial scale-up of CLC still depends nowadays on the availability of highly performing and stable oxygen carriers.

Thermite mixtures with improved contact between the fuel and oxidizer can provide increased reaction rates compared with traditional thermite mixtures. One technique to create thermite mixtures with improved contact is to deposit the... more

Thermite mixtures with improved contact between the fuel and oxidizer can provide increased reaction rates compared with traditional thermite mixtures. One technique to create thermite mixtures with improved contact is to deposit the oxidizer directly onto nanometer-sized fuel particles. This study investigates the atomic layer deposition (ALD) of SnO 2 onto nanoparticles using SnCl 4 and H 2 O 2 reactants. The nanoparticle ALD was performed in a small, hot wall, vertical fluidized bed reactor. The SnO 2 ALD was first demonstrated on ZrO 2 nanoparticles. Auger electron spectroscopy, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), transmission electron microscopy (TEM) and particle size distribution analysis were used to characterize the SnO 2 -coated ZrO 2 nanoparticles. Subsequently, SnO 2 ALD was performed on Al nanoparticles. The SnO 2 -coated Al nanoparticles were analyzed using ICP-AES and TEM. The SnO 2 -coated Al and the uncoated Al particles were also ignited and filmed with a digital video recorder. Although the SnO 2 -coated Al particles were far from stoichiometric thermite composites, the SnO 2 -coated Al particles reacted much more quickly and violently than the uncoated Al particles. The lower than expected Sn percent by mass observed on the SnO 2 -coated Al nanoparticles highlighted a major difficulty with coating nanoparticles. The nanoparticles have an extremely high surface area and the required reactant exposures are large even when assuming 100% reactant efficiency. These results illustrate the utility of ALD techniques to coat oxidizers on fuel nanoparticles to create enhanced thermite materials. D

After a brief review of achievements of fluidization engineering over decades, a discussion is made on one of the latest issues for applications in material industries as well as for the improvements in reliability of many fluidization... more

After a brief review of achievements of fluidization engineering over decades, a discussion is made on one of the latest issues for applications in material industries as well as for the improvements in reliability of many fluidization processes, i.e., granulation and defluidization issues.

A pilot-scale dual fluidized bed combustion system was used for CO 2 capture using limestone sorbent with CaO-CaCO 3 looping. The sorbent was regenerated at high temperature using an air-or oxygen-fired fluidized bed calciner with flue... more

A pilot-scale dual fluidized bed combustion system was used for CO 2 capture using limestone sorbent with CaO-CaCO 3 looping. The sorbent was regenerated at high temperature using an air-or oxygen-fired fluidized bed calciner with flue gas recycle firing hardwood pellets. Two limestones were evaluated for CaO-CaCO 3 looping. Changes in the sorbent morphology during the tests were identified by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). Changes in pore size distribution and sorbent surface area that occurred during reaction were determined by N 2 BET porosimetry. Thermogravimetric analysis (TGA) was used to determine the activity of the sorbent after processing in the dual fluidized bed combustion system. It was found that oxygenfired calcination with high CO 2 partial pressure reduced the effectiveness of the two limestone sorbents for CO 2 capture when compared to material calcined under oxygen-enhanced air combustion. A shell 1-2 lm thick, with reduced porosity, was formed around the sorbent particle and is believed to be responsible for reduced conversion of CaO to CaCO 3 . It is believed that ash deposition contributes to the formation of the shell.

This work reports experimental results on the heat transfer between a fluidised bed of fine particles and a submerged surface. Experiments have been carried out using different bed materials (polymers, ballotini, corundum, carborundum and... more

This work reports experimental results on the heat transfer between a fluidised bed of fine particles and a submerged surface. Experiments have been carried out using different bed materials (polymers, ballotini, corundum, carborundum and quartz sand) with Archimedes number between 2 and 50. Dry air at ambient pressure and temperature has been used as fluidising gas. Three different exchange surfaces, namely a sphere and two cylinders with different base diameter and same height, have been used. Experimental results show that the heat transfer coefficient increases with particle Archimedes number and is almost independent from particle thermal conductivity for K p /K g N 30. Finally, the comparison of heat transfer coefficient for the different surfaces shows that the effect of the surface geometry may account for a 30% variation in the heat transfer coefficient, with higher differences occurring for coarser particles.

Softening at drinking water treatment plants is often realised by fluidised bed pellet reactors. Generally, sand is used as seeding material and pellets are produced as a by-product. To improve to sustainability, research has been carried... more

Softening at drinking water treatment plants is often realised by fluidised bed pellet reactors. Generally, sand is used as seeding material and pellets are produced as a by-product. To improve to sustainability, research has been carried out to replace the seeding material by re-using grained and sieved calcite pellets as seeding material. An explicit fluidisation model is developed to predict the fluid bed state in fluid bed pellet softening reactors with calcite as seeding material. The fluidisation theory is extended in a model whereby soft sensors are derived and experimentally tested for a wide range of seeding material and pellets. With the soft sensors porosity, particle size and pressure drop can explicitly be calculated. Pilot research has been carried out to calibrate and full-scale experiments to validate the fluidisation models. Four different fluidisation models were reviewed from which the original Richardson-Zaki fluid bed model has been selected as the best explicit fluidisation model to predict the porosity, particle size and pressure drop. Applying a discretisation model for the fluid bed pellet reactor, the current operation of the treatment softening can be improved by estimating the fluidisation, pressure drop behaviour and particle profile. Waternet can apply the Richardson-Zaki fluid bed model in practice for building a soft sensor to achieve optimal bed fluid conditions for the softening process.

Granular media filtration is one of the most important and commonly used operations in water treatment and is also widely used for advanced wastewater treatment. Successful filter design requires a correct specification of backwash rates... more

Granular media filtration is one of the most important and commonly used operations in water treatment and is also widely used for advanced wastewater treatment. Successful filter design requires a correct specification of backwash rates for filter cleaning. Significant progress has been made in recent years towards a capability of accurate predictions of backwash expansion of uniform (sieved) fractions of nonporous and porous nonspherical media. Graded filter media, however, have not been studied in a systematic and satisfactory way so far. Current design calculations consider a bed with a size gradation to consist of several layers of approximately uniform size according to the sieve analysis data, and the expansion of each layer is separately calculated. The total expansion is calculated by adding the expansions of all the layers. The present work evaluates the accuracy of this approach and a number of alternative calculation methods by carrying out fluidization experiments with actual filter media including silica sand, garnet sand, perlite, crushed recycled glass, activated carbon, anthracite coal, and zeolite.

The powder-particle spouted bed process is one of the semi-dry processes that have been developed for flue gas desulfurization. In this study, which is designed for SO 2 removal by a powder-particle spouted bed, the reaction term is... more

The powder-particle spouted bed process is one of the semi-dry processes that have been developed for flue gas desulfurization. In this study, which is designed for SO 2 removal by a powder-particle spouted bed, the reaction term is included in one-dimensional and streamtube models that were presented previously for spouted beds. Hydrated lime is used as the sorbent in this process. The predictions of the models are compared with some published experimental data and it is found that the developed models are valid. The results of two models are compared with each other and their various properties are evaluated. The effects of different operating conditions on SO 2 removal efficiency are also investigated and preferred operating conditions are discussed.

A new approach to model media expansion during filter backwash is presented. The proposed approach is based on the assumption that the Ergun equation remains valid after fluidization. Mathematical formulas are derived for predicting... more

A new approach to model media expansion during filter backwash is presented. The proposed approach is based on the assumption that the Ergun equation remains valid after fluidization. Mathematical formulas are derived for predicting expanded porosity for a given backwash velocity or backwash velocity for a given expanded porosity. These formulas can be easily used by the engineer. Values predicted using the proposed approach are in good agreement with experimental measurements.

Inverse fluidization is a technique in which solid particles having lower density than that of the liquid are kept in suspension by the downward flow of continuous liquid phase. Inverse fluidization has several advantages such as high... more

Inverse fluidization is a technique in which solid particles having lower density
than that of the liquid are kept in suspension by the downward flow of continuous liquid
phase. Inverse fluidization has several advantages such as high mass transfer rates due to
reduced film thickness resulting from rotation due to low inertia, minimum carry over of
coated microorganisms due to less solids attrition, efficient control of bio-film thickness
and ease of re-fluidization in case of power failure. These significant advantages found
many applications of inverse fluidized beds in biochemical processes like ferrous iron
oxidation and aerobic and anaerobic biological wastewater treatment like treatment of
wine distillery wastewater. Even though, the applications of the inverse fluidized bed
technique to industrial processes are fast growing, much information on hydrodynamics,
mass transfer and chemical reaction is not yet available. Two phase (liquid – solid)
inverse fluidized beds are used for anaerobic biological processes due to their high mass
transfer potential.
The studies on the hydrodynamics and mass transfer of two-phase inverse
fluidization were performed only in the last few decades one of the most important recent
applications of inverse fluidized beds is in the field of bioreactor engineering. Inverse
fluidization is used in biotechnology as the basics of a new type of bioreactor, the so
called inverse fluidized bed bioreactor are among the most efficient application for
aerobic and anaerobic wastewater treatment Penicillin Production and Phenol
degradation.
The inverse fluidization system gained significant importance during the last few
decades in the field of environmental, biochemical engineering, and oil water separation.
The hydrodynamics of the inverse fluidization have been studies by Karamanev
and Nikolov (1996), Ulaganathan and Krishnaiah (1996), Ramos et al. (1998), Banerjee
et al. (1999), Vijaya Lakshmi et al. (2000), and Renganathan and Krishnaiah (2003, 2004,
2007) using water-solid system. They proposed empirical correlations to predict the
minimum inverse fluidization velocity. Fan et al. (1982), Karamanev and Nikolov (1992),
Biswas and Ganguly (1997), Bendict (1998), Lee (2001), Renganathan and Krishnaiah
(2005) reported the bed expansion characteristics in two phase downward fluidization
and predicted their bed expansion data in terms of Richardson and Zaki equation.
It is very much essential to study on hydrodynamic characteristics such as
pressure drop and minimum inverse fluidization velocity for successful analysis, design
and operation of inverse fluidization bed.
Experiments will be carried out using four polyethylene particles having different
densities, different diameter and sphericity with different concentrated aqueous solutions
of SCMC as fluidizing liquid. Minimum fluidization velocity will be estimated from the
experimental data. An empirical correlation will be developed for the minimum
fluidization velocity as a function of physical and dynamic variables of the system.

This review presents the state of the art regarding the possible intensification of desorption processes by use of microwave irradiation. The most important experimental and modeling results reported in the literature on the laboratory... more

This review presents the state of the art regarding the possible intensification of desorption processes by use of microwave irradiation. The most important experimental and modeling results reported in the literature on the laboratory scale as well as on the industrial scale were collected in this paper. It follows from the review that microwave heating is a powerful novel method proving many advantages when utilized for regeneration of loaded adsorbents. In general, a short penetration depth could be a drawback of this very efficient heating method. Hence, it seems that the fluidized bed adsorbers are better choice than the fixed-bed ones when the microwave-assisted desorption step is carried out because more homogenous temperature distribution would be guaranteed. 7 8 9 10 11 12

Phase holdups were measured in the riser section of a gas-liquid-solid circulating fluidized bed (GLSCFB). Electrical resistance tomography (ERT) as a non-invasive imaging technique, pressure transducers (PTs) and fibre optic probes were... more

Phase holdups were measured in the riser section of a gas-liquid-solid circulating fluidized bed (GLSCFB). Electrical resistance tomography (ERT) as a non-invasive imaging technique, pressure transducers (PTs) and fibre optic probes were employed. Water was used as continuous and conductive phase, air as the gas phase and glass beads as solid nonconductive phases. ERT technique is based on conductivity measurement of the continuous phase (water in this study), which provides color-coded cross-sectional view of phases with a frequency of up to 250 images per second. The local conductivity measured by a number of electrodes located at the periphery of the plane was then further converted into a local phase concentration distribution based on Maxwell's relation. The results obtained by PTs, when combined with ERT results, were used to determine gas and solid holdups. Fibre optic probe was also employed to measure gas holdup independently. To measure gas and solid holdup, a model was introduced to exploit the fibre optic data in differentiating gas bubbles from solid particles in the riser. Radial profiles of the phase holdups were determined.

We studied the gasification of two wastes in a fluidised-bed pilot plant aiming at finding sustainable methods for the utilisation of the ash produced. Two objectives were pursued: (1) optimisation of the operating conditions to achieve... more

We studied the gasification of two wastes in a fluidised-bed pilot plant aiming at finding sustainable methods for the utilisation of the ash produced. Two objectives were pursued: (1) optimisation of the operating conditions to achieve better ash quality while keeping reasonably high energy efficiency and (2) assessment of the ash quality in order to explore potential utilisation options for the ash. An extensive characterisation of the raw ash produced was carried out, finding that, in most cases, the existing fly ash utilisation methods are not applicable. The high concentrations of unburned carbon and harmful soluble compounds restrict ash utilisation or normal disposal, making pretreatment necessary prior to use in agriculture and construction. The only alternative that allows material recycling and energy recovery without the need of pretreatment is the use of the ash in cement kilns. However, competition with other fuels makes this option uncertain. Therefore, we further investigated more innovative utilisation concepts where pretreatment is not necessary, like the addition of ash in the manufacture of lightweight wall board and bricks with special properties. These utilisation options are based on low-cost preparation methods using ash in significant proportions, yielding a notably high-value product. We show that they are promising new applications with high market potential.

Numerous subconcordant andesite sheets occur in the Ordovician Borrowdale Volcanic Group of N.W. England. Many have brecciated tops and bases in which andesite fragments are enclosed in a fine volcaniclastic matrix. Previously, all have... more

Numerous subconcordant andesite sheets occur in the Ordovician Borrowdale Volcanic Group of N.W. England. Many have brecciated tops and bases in which andesite fragments are enclosed in a fine volcaniclastic matrix. Previously, all have been interpreted as block lava flows with interstitial downwashed sediment. Eight well-exposed sheets are described whose field and textural relations indicate that they were intruded into wet sediment with formation of peperite.

A mathematical model of biomass gasification in bubbling fluidized gasifier has been developed. It is a one-dimensional, two-phase (bubble and emulsion), two-zone (bottom dense bed and upper freeboard), steady state model. The model is... more

A mathematical model of biomass gasification in bubbling fluidized gasifier has been developed. It is a one-dimensional, two-phase (bubble and emulsion), two-zone (bottom dense bed and upper freeboard), steady state model. The model is based on global reaction kinetic, mass and energy balances and is capable of predicting temperature, solid hold ups and gas concentration along the reactor's major axis. The overall model has sub-models to deal with biomass pyrolysis, gasification, bed hydrodynamics, material classification and property calculation. A sub-model for tar generation and cracking is included in this study. The model is capable of dealing with wide variety of biomasses and fluidizing agents, i.e. air, oxygen, steam or a mix of these gases. Results show that during devolatilization step, gases release and mixing are sensitive and critical parameters. They have a strong influence on the overall performance of a gasifier. A comparison with experimental data from numerous literature works was done, which showed fairly good agreement. The model can be used to study and optimize the operation of bubbling fluidized bed gasifier. However, further validation with diverse data will help to fine-tune the model.

Biomass is considered an environmentally friendly energy source for the future. However, the transition from fossil fuels to clean sustainable energy sources will require a comprehensive understanding of the technical and socioeconomic... more

Biomass is considered an environmentally friendly energy source for the future. However, the transition from fossil fuels to clean sustainable energy sources will require a comprehensive understanding of the technical and socioeconomic dynamics of renewables. In Malaysia, the annual production of palm oil generates large quantities of lignocellulosic biomass which can be converted into nonpolluting renewable energy. Therefore, scientists are exploring the prospects of valorizing palm waste via thermochemical routes such as gasification using gasifier reactors for energy production. Consequently, this study is aimed at proposing a methodology for the design and fabrication of a bubbling fluidized bed gasifier (BFBG) for Empty Fruit Bunch (EFB) briquettes gasification. It will employ established theoretical knowledge on fluidized beds and literature studies for application in biomass gasification. The proposed gasifier system consists of three main parts; feeding, gasification and effluent zones for syngas production. The results presented in this study are limited to the feedstock properties, bed hydrodynamic calculations and fluidization parameters such as fluidizing velocities; bed height and pressure drop in the gasification zone of the gasifier.

petroleum refining engineering

Reçu le 20 décembre 1999, accepté le 24 janvier 2000)

This paper studies thermal and mechanical sand reclamation system. It emphasizes the need of compact thermal sand reclamation process for smart foundry. This paper generates alternative ideas and conceptual design for foundry sand... more

This paper studies thermal and mechanical sand reclamation system. It emphasizes the need of compact thermal sand reclamation process for smart foundry. This paper generates alternative ideas and conceptual design for foundry sand reclamation. A fluidised bed combustor is good alternative for foundry sand reclamation process. Fluidized bed combustor consist of internal chamber, heating coil, insulation and nozzle for develop conceptual model. FBC system contains selection or design of fluidized bed structure, design and selection heating coil such as furnace coil heating technique. selection or design of Suitable insulation for 550 to 800 degree Celsius temperature and nozzle selection or design for sand bubbling process. Homogeneous heating of sand take place with the help of fluidized bed also Nozzle design is such a way that sand does not enter inside the nozzle. The requirement of such reclamation unit are very important than previously developed sand reclamation unit. It generates alternative for foundry sand reclamation.

Steady state operational data from a pilot scale circulating fluidized bed bioreactor (CFBBR) during biological treatment of landfill leachate, at empty bed contact times (EBCTs) of 0.49, and 0.41 d and volumetric nutrients loading rates... more

Steady state operational data from a pilot scale circulating fluidized bed bioreactor (CFBBR) during biological treatment of landfill leachate, at empty bed contact times (EBCTs) of 0.49, and 0.41 d and volumetric nutrients loading rates of 2.2-2.6 kg COD/(m 3 d), 0.7-0.8 kg N/(m 3 d), and 0.014-0.016 kg P/(m 3 d), was used to calibrate and compare developed process models in BioWin ® and AQUIFAS ® . BioWin ® and AQUIFAS ® were both capable of predicting most of the performance parameters such as effluent TKN, NH 4 -N, NO 3 -N, TP, PO 4 -P, TSS, and VSS with an average percentage error (APE) of 0-20%. BioWin ® underpredicted the effluent BOD and SBOD values for various runs by 80% while AQUIFAS ® predicted effluent BOD and SBOD with an APE of 50%. Although both calibrated models, confirmed the advantages of the CFBBR technology in treating the leachate of high volumetric loading and low biomass yields due to the long solid retention time (SRT), both BioWin ® and AQUIFAS ® predicted the total biomass and SRT of CFBBR based on active biomass only, whereas in the CFBBR runs both active as well as inactive biomass accumulated.

Quality of fluidization is an important criterion for efficient heat and mass transfer in gas–solid fluidized beds. Knowledge of voidage distribution in fluidized bed is essential when exothermic reactions are carried out in fluidized... more

Quality of fluidization is an important criterion for efficient heat and mass transfer in gas–solid fluidized beds. Knowledge of voidage distribution in fluidized bed is essential when exothermic reactions are carried out in fluidized beds. Quality of fluidization is often expressed in terms of time average local void-faction distribution. Gamma ray transmission technique is one of the techniques used to study the quality of fluidization. In the present study, Gamma ray transmission technique was explored to study the quality of fluidization in a unary fluidized bed and packed fluidized bed, in which small particles are fluidized in the interstitial void space of relatively large and stationary pebbles. Gamma ray photons were allowed to pass through a unary fluidized bed of silica and lithium–titanate particles at different angular and axial positions of the bed. Experiments were conducted in packed-fluidized bed of silica particles in the interstices of large size alumina pebbles and lithium–titanate particles in the interstitial void space of large size lithium titanate pebbles. It was observed, that packed fluidized bed provides better quality of fluidization or more homogeneous fluidization compared to that of a unary fluidized bed. Operating principle, experimental details and results are discussed in this paper.

This research deals with the design and analysis of the nozzle and bed materials required for fluidized bed boiler. The design parameters (Diameter of the bed particle, Range of the terminal velocities, Minimum Fluidization /Bubbling... more

This research deals with the design and analysis of the nozzle and bed materials required for fluidized bed boiler. The design parameters (Diameter of the bed particle, Range of the terminal velocities, Minimum Fluidization /Bubbling velocities, Maximum amplitude and steady velocities) were calculated using Microsoft Excel by interpreting and solving various formulas. Best bed material was selected on the basis of their various characteristics like porosity, adhesive or cohesive properties, resistance to flow etc. An important characteristic change of air distributor velocity with combustion chamber temperature has been established. ANSYS was used as a simulation tool for the analysis. Static Structural solver was used to carry out the strength analysis of the designed wind box. Likewise, computational fluid dynamics (CFD) was carried out using FLUENT solver. Air flow inside the wind box and fluidization phenomena was verified using FLUENT. Furthermore, the designed system was checked for its validity by comparing the results from the Excel sheets and theoretical calculations with simulation results. Lastly, correlation between temperature and velocity inside combustion temperature were determined to identify their relationship with each other.

The paper introduces the phenomenon of fluidization as a process. Fluidization occurs when a fluid (liquid or gas) is pushed upwards through a bed of granular material. This may make the granular material to behave like a liquid and, for... more

The paper introduces the phenomenon of fluidization as a process. Fluidization occurs when a fluid (liquid or gas) is pushed upwards through a bed of granular material. This may make the granular material to behave like a liquid and, for example, keep a level meniscus on a tilted container, or make a lighter object float on top and a heavier object sink to the bottom. The behavior of the granular material, when fluidized, depends on the superficial gas velocity, particle size, particle density, and fluid properties resulting in various regimes of fluidization. These regimes are discussed in detail in the paper. This paper also discusses the application of fluidized beds from its early usage in the Winkler coal gasifier to more recent applications for manufacturing of carbon nano-tubes. In addition, Geldart grouping based on the range of particle sizes is discussed. The minimum fluidization condition is defined and it is demonstrated that it may be registered slightly different when particles are being fluidized or de-fluidized. The paper presents discussion on three numerical modelling techniques: the two fluid model, unresolved fluid-particle model and resolved fluid particle model. The two fluid model is often referred to Eulerian-Eulerian method of solution and assumes particles as well as fluid as continuum. The unresolved and resolved fluid-particle models are based on Eulerian-Lagrangian method of solution. The key difference between them is the whether to use a drag correlation or solve the boundary layer around the particles. The paper ends with the discussion on the applicability of these models.

An a priori reactor model for an adiabatic spouted bed reactor has been developed. This model uses first-principles mass and energy balances to predict the concentration and temperature profiles in the spout, annulus and fountain regions... more

An a priori reactor model for an adiabatic spouted bed reactor has been developed. This model uses first-principles mass and energy balances to predict the concentration and temperature profiles in the spout, annulus and fountain regions of the reactor. The particle circulation and voidage profiles in the spout are calculated using previously developed analytical techniques. Particle circulation patterns in the annulus are determined by a minimum path-length analysis, The spout and fountain are shown to contribute significantly to the overall conversion in the bed. Predicted and experimental conversions at flowrates up to 1.2Um show that extension of the fountain reaction zone and increased particle circulation with increasing inlet flow makes up for the higher average voidage in the spout and fountain. Experimental data confirm the calculated results for a stably spouting bed with CO oxidation over a Co,O,/cr . AI,O, catalyst. The effects of flowrate and inlet reactant concentration are confirmed.

The effect of operating conditions on product yields and compositions has been studied in the catalytic cracking of polyolefins (high-and low-density polyethylene and polypropylene) in a conical spouted bed reactor. The catalyst has been... more

The effect of operating conditions on product yields and compositions has been studied in the catalytic cracking of polyolefins (high-and low-density polyethylene and polypropylene) in a conical spouted bed reactor. The catalyst has been prepared by agglomerating an HZSM-5 zeolite (SiO 2 /Al 2 O 3 = 30) with bentonite and alumina. The study has been carried out in continuous mode, in the 450À570°C range, with polyolefin flow rates between 1 and 2 g min À1 and feeding up to 1 kg of polyolefin into a 30 g catalyst bed. The result is an excellent performance of the reactorÀcatalyst pairing for continuous catalytic pyrolysis, given that the yields obtained in the pyrolysis of high-density polyethylene at 500°C without defluidization problems and very low catalyst deactivation are as follows: 60 wt % C 2 ÀC 4 olefins, 15 wt % nonaromatic C 5 ÀC 11 hydrocarbons, 10 wt % single-ring aromatics, and 14 wt % C 4-alkanes. Only small differences are observed in the pyrolysis of the different polyolefins.

Biomass gasification with pure steam in a fluidized bed is a highly endothermal process that has been connected in several ways to a fluidized-bed combustor to burn the char that is generated in the gasifier. This resulted in what... more

Biomass gasification with pure steam in a fluidized bed is a highly endothermal process that has been connected in several ways to a fluidized-bed combustor to burn the char that is generated in the gasifier. This resulted in what currently is called dual fluidized-bed (DFB) biomass gasifiers. This review starts by describing the pioneering DFB biomass gasifiers that were operated during the period of 1975-1990 by Kunii's group in Japan, Battelle-Columbus and FERCO in the United States, TNEE in France, AVSA in Belgium, etc., ... and Corella and Herguido's gasifier, which was operated during the period of 1989-1991. A description of the gasifiers operated today in Europe (TU Wien and Güssing in Austria and ECN in The Netherlands), Japan (IHI Co., EBARA, AIST-Tsukuba), and the People's Republic of China (Dalian, Hangzhou, and Beijing) then is given. Their most-relevant operation data, and the results from these gasifiers (mainly, the gaseous hydrogen (H 2 ) and tar contents in the raw produced gas), are finally presented briefly.

The application of the Ergun equation to predict the expansion of filter media during backwashing is investigated. Fluidization data from the literature have been analyzed and the values k1 =3.519 and k2 =0.266 have been found to give a... more

The application of the Ergun equation to predict the expansion of filter media during backwashing is investigated. Fluidization data from the literature have been analyzed and the values k1 =3.519 and k2 =0.266 have been found to give a very good fit to the data in the range of Reynolds numbers of interest in filter backwashing. An empirical equation that is applicable over a wider range of Reynolds numbers than the Ergun equation is also developed. New experiments have been carried out with glass spheres, plastic spheres, silica sand, and crushed glass. The effect of particle shape on expansion behaviour is investigated. It is found that the influence of particle shape is larger than previously recognized. Furthermore, the shape effect depends on the Reynolds number based on the backwash velocity. The advantages, limitations, and range of applicability of each method of calculation are delineated.

A two-phase model is proposed for describing the behavior of a fluidized bed reactor used for polyethylene production. In the proposed model, the bed is divided into several sequential sections where flow of the gas is considered to be... more

A two-phase model is proposed for describing the behavior of a fluidized bed reactor used for polyethylene production. In the proposed model, the bed is divided into several sequential sections where flow of the gas is considered to be plug flow through the bubbles and perfectly mixed through the emulsion phase. Polymerization reactions occur not only in the emulsion phase but also in the bubble phase. Voidages of the emulsion and bubble phases are estimated from the dynamic two phase structure hydrodynamic model. The kinetic model employed in this study is based on the moment equations. The hydrodynamic and kinetic models are combined in order to develop a comprehensive model for gas-phase polyethylene reactor. The results of the model are compared with the experimental data in terms of molecular weight distribution and polydispersity of the produced polymer. A good agreement is observed between the model predictions and actual plant data. It has been shown that about 20% of the polymer is produced inside the bubble phase and as such cannot be neglected in modeling such reactors. ᭧

Numerous equations can be found in the literature for the prediction of bed expansion during liquid–solid fluidization. There is no general agreement regarding which equation is the most accurate. In this work, fluidization experiments... more

Numerous equations can be found in the literature for the prediction of bed expansion during liquid–solid fluidization. There is no general agreement regarding which equation is the most accurate. In this work, fluidization experiments have been carried out with plastic and glass spheres of 11 different sizes, varying from 1.11 mm to 6.01 mm. Water was used as the fluidizing medium in all the experiments. Widely used correlations are compared and evaluated using the data collected in this work and certain long-standing data from the literature. A new equation with a simple and meaningful form is developed for the prediction of bed expansion in liquid fluidized beds of spheres. The proposed correlation is based on an extension of the fixed-bed friction factor concept to fluidized beds. The new equation has a number of advantages such as a wider operating range, improved accuracy, simple and continuous form, and a fundamental basis.

a b s t r a c t CO 2 capture system based on the carbonation/calcination loop, still in its infancy, has gained rapid interest due to promising carbonator CO 2 capture efficiency, low sorbent cost and the fact that no flue gases... more

a b s t r a c t CO 2 capture system based on the carbonation/calcination loop, still in its infancy, has gained rapid interest due to promising carbonator CO 2 capture efficiency, low sorbent cost and the fact that no flue gases desulphurization unit is needed before entering the system. The sum of these features results in a competitively low cost CO 2 capture system. There are different options to design the carbonation loop. In this work, a basic configuration that makes use of two interconnected circulating fluidized beds (carbonator and calciner) has been studied. Among the key variables that influence the performance of these systems, the carbonation conversion of the sorbent and the heat requirement at calciner are the most relevant. Both variables are mainly influenced by CaO/CO 2 ratio and make-up flow (purge) of solids. A purge is necessary in order to reduce the sorbent deactivation and to compensate the formation of CaSO 4 from the SO x content in the flue gas. Large CaO/CO 2 ratios improve the carbonation conversion but also increase the cost of the system due to a more intensive solid circulation. High make-up flow also improves the carbonation conversion and hence the CO 2 capture, but increases the heat demand at calciner and the fresh sorbent cost. The aim of this paper is to calculate the optimum make-up flow and CaO/CO 2 ratio in order to minimize the capture cost of the system. Independent variables are make-up flow of fresh CaCO 3 and CaO/CO 2 ratio. The constraint equations are experimental data on carbonation reaction, mass and energy balances, oxygen requirement and fuel composition.

The impact of biomass shape factor on the fluidization characteristics is demonstrated. The axial distribution profile of biomass is obtained by RPT, bed freezing and simulation. The reliability of the "frozen bed" technique to quantify... more

The impact of biomass shape factor on the fluidization characteristics is demonstrated. The axial distribution profile of biomass is obtained by RPT, bed freezing and simulation. The reliability of the "frozen bed" technique to quantify the mixing state of the bed contents is assessed by RPT. The capability of NEPTUNE_CFD software to predict the distribution and velocity profiles of biomass particles is demonstrated. The plausible reasons of some discrepancies between the experimental and simulation results are discussed.

The study explored the heat transfer properties in an air-fluidized bed of sand, heated with an immersed heat transfer tube positioned at several angles of inclination. Operating with fluidizing velocity up to 0.5 m/s; and particles of... more

The study explored the heat transfer properties in an air-fluidized bed of sand, heated with an immersed heat transfer tube positioned at several angles of inclination. Operating with fluidizing velocity up to 0.5 m/s; and particles of 150–350 μm diameter, the effect of air velocity and particle size on the average and maximum achieved heat transfer coefficient was examined for the heat transfer tube at angles of inclination in the range 0–90°. Experimental results showed that the angle of inclination altered the bubble size and behavior close to the heat transfer tube hence the expected heat transfer coefficient, with the influence of tube inclination being less pronounced for smaller particles. The optimum angle of inclination was in the range of 10–15° relative to the direction of the flow, while the heat transfer coefficient had its lowest values at the angle of 45°, and thereafter improved upon transition to 90°. Upon comparison with existing correlations, a correction factor is proposed to account for the impact of the angle of inclination on the heat transfer coefficient calculated by the Molerus–Wirth semi-empirical correlation.

Soft-sediment deformational structures are important diagnostic features of paleoseismic studies. These seismites result from local vigorous fluidization and hydroplastic deformation formed during liquefaction as a direct consequence of... more

Soft-sediment deformational structures are important diagnostic features of paleoseismic studies. These seismites result from local vigorous fluidization and hydroplastic deformation formed during liquefaction as a direct consequence of permanent deformation of ground surface due to earthquakes of large magnitude.

Numerical results for a gas-fluidized bed using a 2D Eulerian model including the kinetic theory for the particulate phase were provided. The circulation patterns for various operating conditions were discussed. Modeling parameters of... more

Numerical results for a gas-fluidized bed using a 2D Eulerian model including the kinetic theory for the particulate phase were provided. The circulation patterns for various operating conditions were discussed. Modeling parameters of drag function, algebraic and transport equations of granular temperature, frictional stress model, turbulent model and discretization scheme were investigated for a bed with different gas distributors and a slotted draft tube. CFD results showed that the drag model is an important hydrodynamics parameter for gas-fluidized beds with various gas distributors. Transport and algebraic equations for granular temperature should be utilized, respectively, for beds including partial and complete sparging at U g = 2.18 m/s. Frictional stresses play an important role for the beds containing partial sparging with and without draft tube. Discretization schemes should be examined to achieve better results. The Simonin and k-ε turbulent models can improve the CFD results at high gas velocities. Considering perforated plate distributor improves the results.

As a preliminary overview, this work provides first a broad tutorial on the fluidization of discrete event dynamic models, an efficient technique for dealing with the classical state explosion problem. Even if named as continuous or... more

As a preliminary overview, this work provides first a broad tutorial on the fluidization of discrete event dynamic models, an efficient technique for dealing with the classical state explosion problem. Even if named as continuous or fluid, the relaxed models obtained are frequently hybrid in a technical sense. Thus, there is plenty of room for using discrete, hybrid and continuous model techniques for logical verification, performance evaluation and control studies. Moreover, the possibilities for transferring concepts and techniques from one modeling paradigm to others are very significant, so there is much space for synergy. As a central modeling paradigm for parallel and synchronized discrete event systems, Petri nets (PNs) are then considered in much more detail. In this sense, this paper is somewhat complementary to . Our presentation of fluid views or approximations of PNs has sometimes a flavor of a survey, but also introduces some new ideas or techniques. Among the aspects that distinguish the adopted approach are: the focus on the relationships between discrete and continuous PN models, both for untimed, i.e., fully non-deterministic abstractions, and timed versions; the use of structure theory of (discrete) PNs, algebraic and graph based concepts and results; and the bridge to Automatic Control Theory. After discussing observability and controllability issues, the most technical part in this work, the paper concludes with some remarks and possible directions for future research.

Liquid holdup in a turbulent contact absorber was determined experimentally. Experiments were performed in a 44.7 cm diameter Perspex column. Hollow spherical high-density polyethylene balls were used as packing. The effect of liquid and... more

Liquid holdup in a turbulent contact absorber was determined experimentally. Experiments were performed in a 44.7 cm diameter Perspex column. Hollow spherical high-density polyethylene balls were used as packing. The effect of liquid and gas velocities, static bed height, diameter and density of packing on liquid holdup was investigated for the range of gas velocities greater than minimum fluidization velocities. Also, the effect of gas and liquid distributors on liquid holdup was studied. Correlations for liquid holdup were developed and compared with those in the literature. It was observed that liquid holdup increased with the increase in liquid velocity, packing density, and the decrease in static bed height. Liquid holdup also increased with gas velocity when the gas distributor section was included, while no effect was observed for the bed. Lack of information on the contribution of liquid and gas distributors seems to be the logical explanation for the wide variation in data reported in the literature.

Fluidization experiments have been carried out with glass spheres, plastic spheres and several sieved fractions of silica sand, garnet sand, perlite and crushed glass. The effect of particle shape on expansion behavior is investigated.... more

Fluidization experiments have been carried out with glass spheres, plastic spheres and several sieved fractions of silica sand, garnet sand, perlite and crushed glass. The effect of particle shape on expansion behavior is investigated. Sphericity as determined using the Ergun equation and fixed-bed head loss data is employed to quantify the shape effect. It is found that the influence of particle shape depends on the Reynolds number based on backwash velocity. A new equation that accounts for particle shape is proposed. For the materials studied, the proposed equation gives excellent agreement with both the spherical and the non-spherical particle data.

Analysis of fluid flow in a liquid-solid circulation fluidized bed (LSCFB) is necessary to understand its behavior under different operating parameters. In this work, ample parametric studies have been carried out numerically, which... more

Analysis of fluid flow in a liquid-solid circulation fluidized bed (LSCFB) is necessary to understand its behavior under different operating parameters. In this work, ample parametric studies have been carried out numerically, which provides a view how an LSCFB operates under different operating parameters, and the numerical model has been validated using the experimental data. This study aims to get an insight of the behavior of LSCFB under different operating parameters, which include solids circulation rate, primary and auxiliary liquid velocity. In addition to this task, numerical modeling has also been carried out to predict the behavior of different particles with different densities upon fluidization in an LSCFB, which resolves the problem of experimentation with a wide spectrum of new particles that might have a wide variety of applications in an LSCFB. LSCFBs always involve high Reynolds number flow and dense solids concentration, which demands for proper modeling of the turbulent flow, liquid-solid interactions and particle-particle interactions. Kinetic theory based on Eulerian-Eulerian two-phase model is used to account for particle interactions and is applied to model the solids viscosity and solids pressure, which takes into account the particle-particle collisions.

The partial or complete bed defluidization is an undesired phenomenon in industrial application involving fluidized bed operations. In the process of particle coating, the defluidization can be prevented by increasing the gas velocity... more

The partial or complete bed defluidization is an undesired phenomenon in industrial application involving fluidized bed operations. In the process of particle coating, the defluidization can be prevented by increasing the gas velocity and/or decreasing the coating suspension flow rate, if the changes in the hydrodynamics of the fluidization are early detected. For industrial applications, the use of a technique