Fluidization

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...

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 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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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