Conventional Fluidized Bed Research Articles

Oxidation of Hydrocarbons in anin SituRedox Fluidized Bed Reactor

Methanol to Gasoline (MTG) process transforms methanol to hydrocarbons within the boiling point range of gasoline. The result is a wide spectrum of products (olefins, paraffins, aromatics and naphthenics, among others), with the total conversion of methanol to hydrocarbons and water. Catalyst deactivation by coke is a main problem in this process. This work aims to determine the feasibility of carrying out the production of gasoline from methanol in a two-zone fluidized bed reactor (TZFBR). The hypothesis is that the formation of carbonaceous deposits (coke) on the catalyst particles can be counteracted by its combustion in the regeneration zone that this novel reactor presents, thus achieving stable and continuous operation. In this way, both processes (reaction and regeneration) would be being carried out simultaneously in the same reactor (process intensification). The comparison of results between a conventional fluidized bed reactor and a TZFBR shows that the second one actually provides a better stability over time.

Linear, nonlinear small-amplitude, steady and shock waves in magnetically stabilized liquid-solid and gas-solid fluidized beds

The propagation of solid concentration disturbances in fluidized beds in an external magnetic field is considered. Both solid particles and the liquid phase are assumed to be simultaneously magnetizable. The total fluid-particle interaction force is supposed to include the inertial component proportional to the relative acceleration of fluid and particles. The effect of simultaneous magnetization of particles and fluid as well as the influence of the inertial component of interphase interaction force on the resulting criterion of stability of the uniform fluidization are analysed. Consideration is given to the dispersion phenomena in the wave propagation process. The model of propagation of nonlinear waves is developed in approximation of small finite-amplitude waves. The basic equations are reduced to the Korteweg-de Vries-Burgers equation for the departure of solid concentration from the uniform state. Possible configurations of the concentration wavefront are studied, including the oscillating wavefronts and small-amplitude shocks. The conditions of realization of each possible configuration are obtained. The propagation of a long finite-amplitude nonlinear steady wave is considered. The conditions for the existence of the steady concentration wave are derived. The structure of the wavefront is studied and the thickness of the front is calculated as a function of magnetic and other physical parameters and the concentrations ahead of and behind the front. The conditions across the concentration shock in the fluidized bed of magnetic particles are obtained. The shock speed is calculated. The obtained results can be used to analyse structures of boundaries of bubbles, slugs and solid clusters formed in magnetically stabilized fluidized beds. In conclusion the analogy between the basic equations of magnetic fluidized beds and equations of the “particle bed” model by Foscolo & Gibilaro is briefly discussed in order to analyse the possibility to apply the developed approach to the study of the considered classes of nonlinear waves in conventional fluidized beds.

Application of fuzzy logic to bed height control in agitation-fluidized bed granulation

Development of a new technique for producing spherical and well-compacted granules, and the application of fuzzy control to a fluidized bed granulation process are described. An agitation-fluidized bed, a type of fluidized bed equipped with an agitator blade, was used for granulation; bed height was controlled by fuzzy logic based on a linguistic algorithm employing IF—THEN rules, to maintain a constant bed height and impart effective agitation to the granules. It was shown that bed height control was effective in preventing defluidization and channeling, and was necessary for automatic operation. The effects of bed height and agitator rotational speed on granule properties, such as apparent density, and on granule shape were investigated. A new technique is proposed for utilizing bed height control to produce spherical and well-compacted granules, which cannot be done using conventional fluidized bed techniques.

A novel fluidised bed bioreactor for fermentation of glucose to ethanol using alginate immobilised yeast

A novel fluidised bed bioreactor has been developed which avoids the problems of particle flotation and gas logging seen in such bioreactors by arranging for the bed to be simultaneously fluidised from the top and bottom with fluid removal from a side port. With alginate immobilised yeast, the bed converted glucose to ethanol at a 27% higher rate than a similar conventional fluidised bed bioreactor using similar conditions.

Degradation of aromatic compounds by Pseudomonas putida

AbstractThe influence of different process kinetics on the course of phenol degradation has been studied as well as the influence of axial dispersion in the liquid phase on the reactor height with relatively large biofilm thickness in a conventional fluidized bed and air‐lift bioreactor. The object of this was to achieve a high conversion of substrate in a device of real size in real process time. For calculating the mathematical model, the method of orthogonal collocation with the STIFF integration routine has been used.

Continuous separation of solids in a mechanically fluidized bed

The separation of flotsam and jetsam particles fed continuously to a mechanically-fluidized bed was studied using both two- and three-component systems. The two-component system consisted of sand and magnetite, and the three-component system consisted of a fluidizing medium (sand), together with larger particles of jetsam (glass) and flotsam (nylon or acrylic resin). A mechanically fluidized bed was agitated with a stirrer while supported by frictional forces due to upwardly flowing gas [1]. Under favourable conditions separation was complete with the three-component systems, but was relatively poor with the magnetite/sand system, which otherwise segregates strongly in a conventional fluidized bed.

Anaerobic Treatment of Domestic Sewage under Moderate Climatic (Dutch) Conditions Using Upflow Reactors at Increased Superficial Velocities

This paper describes experiments with domestic sewage using a 120 litre expanded granular sludge bed (EGSB) reactor and a 205 litre fluidised bed (FB) reactor. Presettled domestic sewage was used in the experiments, because these reactor systems are inadeguate in removing SS. Compared to conventional UASB reactors, the advantage of EGSB systems is the significantly better contact between sludge and wastewater. A batch recirculation system was used to assess the maximum achievable removal of the different COD fractions under EGSB and UASB conditions. The results obtained with the EGSB reactor reveal a removal efficiency of 90% with respect to the maximum obtainable efficiency of the soluble COD fraction under dry weather conditions. This efficiency can be obtained at hydraulic retention times (HRT) exceeding 3 hours. Even at HRT's ranging from 2 - 1.5 hours, still 84% - 77% of the maximum possible removal efficiency as assessed in batch recirculation experiments can be achieved at temperatures exceeding 13°C. The advantage of EGSB systems is the high volumetric loading rate that can be applied while maintaining a high removal of the dissolved COD fraction. Moreover, little if any accumulation of inert suspended solids occurs in the sludge bed. On the other hand, the poor removal of suspended solids can be considered as a disadvantage of these systems in treating domestic sewage. Conventional FB systems using sand as carrier material were shown to have little prospect for treating settled domestic sewage, because hardly any methanogenic activity will develop in such a system. However, it was also found that a very satisfactory guality granular sludge developed on settled sewage when operating FB systems in a mode similar to EGSB systems. This granular sludge appeared to be of a guality egual or even better than that of granular seed sludge, cultivated in a UASB reactor treating papermill wastewater.

Synthesis of AlN/SiC composite powders by floating-type fluidized-bed CVD

Floating-type fluidized-bed CVD was studied with the aim of synthesizing fine particulate composites having a high uniformity of dispersion. SiC powder was floated into the reactor with an N 2NH 3 gas mixture. The behavior of the floating SiC particles was observed, and it was found possible to steadily float finer particles in the floating-type fluidized-bed as compared with conventional fluidized-beds. AlCl 3 was fed into the reactor to deposit AlN particles onto the floating SiC particles at 800 to 1 100 °C. The composite ratio of AlN to SiC can be controlled by controlling the synthesis temperature, the AlCl 3-feeding rate, and the flow rate of the gas mixture for flotation.

EFFECT OF VIBRATION ON THE DRYING RATE DURING THE FALLING RATE PERIOD

ABSTRACT The results of an experimental study on the drying characteristics in vibrated fluidized beds of corn plumule, silica gel and citric acid are presented. Application of vibration was found to enhance the drying rate during the falling rate period. In the optimum range of vibration parameters, the critical moisture content decreased significantly as compared with that in conventional fluidized beds of the same material.

Studies in magnetochemical engineering: Part VI. An experimental study of screen-packed and conventional fluidized beds in axial and transverse magnetic fields

This paper describes the results from an experimental study of fluidization characteristics and magnetic stabilization of screen-packed and conventional ( i.e., unpacked) beds of solids subjected to external magnetic fields applied axially or transversely relative to the fluidizing gas flow. The beds consist of either entirely ferromagnetic iron particles or admixtures of iron and paramagnetic manganese(II) oxide, MnO. Key variables investigated include superficial gas velocity, presence of screen packing, particle type and shape, magnetic field intensity and orientation, and fraction of ferromagnetic particles in the fluidizing admixture. This study of screen-packed magnetofluidized beds (SPMFBs) has fundamental importance to the development of fluidized-bed high-gradient magnetic separation (FBHGMS) and of magnetic valve for solids (MVS) and magnetic distributor-downcomer (MDD). This study also extends the concept of magnetically stabilized beds (MSBs) to admixtures of ferromagnetic and paramagnetic particles by examining the role of internal screen packing in both axial and transverse magnetic fields. The results show that screen packing significantly alters the fluidization behavior of magnetofluidized beds of iron and MnO particles. In addition, by adding a small fraction of iron, magnetic stabilization ( i.e., bubble elimination) of conventional beds of MnO is achievable with an axial or a transverse field. Magnetized screens tend to serve as distributor plates in SPMFBs of iron and MnO in moderate field intensities (20–100 Oe), creating a staged bed appearance. The tendency to exhibit bed staging increase with increasing field intensity and with increasing volume fraction of iron in MnO. Gas velocities at the transition to bubbling and at the onset of staging ( i.e., transition and staging velocities) increases with increasing field intensity. As the magnetic field orientation changes from transverse to axial, transition and staging velocities decrease and staged behavior is less likely. These results have two practical implications. First, in magnetofluidized-bed operations impaired by bed staging, such as dry coal desulfurization by FBHGMS, the magnetic field should be applied axially. Second, in operations aided by bed staging, such as MVS/MDD, the magnetic field should be applied transversely. To date, reported work in MVS/MDD technology employs only axial fields. This work presents quantitative data comparing the fluidization behavior and magnetic stabilization in axial and transverse fields. For beds of ferromagnetic particles and of ferromagnetic-paramagnetic admixtures, the results show a wider range of gas velocities for magnetic stabilization in an axial field compared to a transverse field. Such results validate the claim that MSB operations should utilize an axial, rather than a transverse, field to maximize the bubble-free gas throughput.

LIQUID-SOLID MASS TRANSFER IN A THREE PHASE DRAFT TUBE FLUIDIZED BED REACTOR

Abstract Liquid-solid mass transfer coefficients in a three phase draft tube fluidized bed reactor have been measured using spherical ion exchange particles. The particle diameters ranged from 655 to 1119μm and solids volume fractions of approximately 5 and 10% were employed in water at 28°C. The experimental data can be successfully correlated using a Reynolds number derived using Kolmogoroffs theory of isotropic turbulence, although it is doubtful whether isotropic turbulence actually prevails in the fluidized bed over the range of conditions employed. Comparison with correlations determined for bubble columns and gas-liquid fluidized beds is performed. A model which considers the draft tube reactor as comprising two distinct fluid mechanical regions is developed to explain the apparently lower values of mass transfer coefficients obtained in a draft tube as opposed to conventional fluidized bed reactor.

Development of a unique laboratory scale fluidized bed wear testing unit

Significant wastage of internal bed components in fluidized bed combustors has been widely experienced throughout the industry. A major probable contribution to heat exchanger tube wastage in bubbling fluidized beds is mechanical in nature. It arises from the impact of blocks of defluidized particles thrown against tube undersides during either the passage of rising bubbles or the collapse of ‘teardrop’ like voids that form periodically under tubes. In an effort to investigate this process, isolated from other erosive or corrosive effects, a novel wear testing rig has been designed and built. This device simulates the particle block impact environment by the fast movement of a specimen rod vertically within a minimally fluidized bed. Data from initial room temperature tests indicate that rods exposed in the rig suffered losses which were similar in both magnitude and circumferential distribution to those experienced by tubes in other cold model studies that utilized more conventional fluidized bed units. The worn surface regions of the tested metallic rods were composed of a relatively hard multilayered composite of bed material and base metal that resulted from deposition of fine particle fragments and considerable surface deformation. Removal of material from this composite probably occurred primarily through a process of three-body microabrasion. For pure aluminum, a secondary process of layer spallation was active at circumferential locations where an exceptionally thick composite layer developed.

都市ごみ燃却用流動床炉の燃焼制御

A fluidized bed incinerator for municipal solid wastes (MSW) has excellent characteristics with a high combustion rate. But they sometimes burn incompletely when the wastes supplied to the bed change greatly in feed rate and properties. As a countermeasure for this, a fluidization at the center of the bed, where wastes were supplied, was kept rather weak and that at the both side was made strong and weak alternately. Then the heat transfer coefficient to the wastes was decreased and pyrolysis was delayed. At the same time by blowing secondary air to the freeboard at the optimum position and flow rate, a stable combustion could be realized. At the test of the actual MSW fluidized bed incinerator, it was confirmed that the frequency of high CO emisson spike was decreased and that visual smoke was suppressed than the conventional fluidized bed incinerator.

マイクロコンテナ粒子の流動層によるサブミクロンセラミックス微粉の合成

The concept of a fluidized bed of microcontainer particles is proposed. Although conventional fluidized beds are not good at handling cohesive submicron particles, the use of microcontainer particles enables us to produce and process them in fluidized beds. To examine the proposed concept, the syntheses of nitrogen ceramic powders (Si3N4, TiN and AlN) through carbothermal reduction and nitridation were performed in a thin fixed bed and a fluidized bed at 1300-1550°C. In every case, submicron powders were successfully obtained. For Si3N4 synthesis, the SiO(g) loss from the fixed bed and the degrees of silica reduction and nitridation were determined as functions of time and temperature. Though the deposition of SiO vapor increased the stickiness of the bed, the bed was fluidized with no problems when the gas flow rate was sufficiently high for bubbling. The SiO vapor deposition in the freeboard was found to be controllable by adjusting particle size and the gas flow rate.

Application of powder coatings: Viscosity and density measurements in a conventional fluidized bed

AbstractThe values of dynamic viscosity characteristic of the different stages in a fluidized bed were determined using a torsional viscometer (Dragge Eppretch Rheometer type STVK) with a specially designed cup. Experiments were made with three kinds of rotor: a full paddle, a cylinder and a split paddle.Apparent densities have been determined by measuring differential pressures across known heights in an experimental fluidized bed. A modified Matheson equation has been developed to determine the values of maximum bed density and minimum bed porosity, associated with the inset of fluidization.The experimental determinations were made with a white powder coating in which the granulometric distribution and composition were previously established.

Heat Transfer and Pressure loss of a very shallow fluidized-bed heat exchanger Part 1. Experiment with a single row of tubes

A novel gas fluidized-bed heat exchanger with a very small static bed height has been developed for a heat-exchanging system using a low-pressure fan. This fluidized bed is composed of a multislit distributor, a single row of 8 mm diameter tubes, and glass beads 48–195 μm in diameter. The measured performance of heat transfer is excellent and that of fluidization is satisfactory, in spite of the static bed height being as small as 13 mm. In the best case, the test fluidized bed exhibited a heat transfer performance comparable to that of a conventional fluidized bed with a perforated plate distributor and a static bed height of 150 mm, and showed one-fourteenth the pressure loss.

On partial fluidization in rotating fluidized beds

In a rotating fluidized bed, unlike in a conventional fluidized bed, the granules are fluidized layer by layer from the (inner) free surface outward at increasing radius as the gas velocity is increased. This is a very significant and interesting phenomenon and is extremely important in the design of these fluidized beds. The phenomenon was first suggested in a theoretical analysis and recently verified experimentally in the authors' laboratory. However, in the first paper, the equations presented are too cumbersome and the influence of bed thickness is not clearly stated. In this note the authors present simplified equations, based on that paper, for the pressure drop and the minimum fluidizing velocities in a rotating fluidized bed. Experimental data are also shown and compared with the theoretical model, and the effect of bed thickness is shown. Furthermore, an explanation for the observation of a maximum in the pressure drop vs. velocity curve instead of the plateau derived by Chen is proposed.

Contacting modes and behaviour classification of gas—solid and other two‐phase suspensions

AbstractAn attempt is made to extend schemes for classifying the behaviour of gas—solid contacting modes and other two‐phase systems. The regime diagram approach of Reh (1971) is modified and extended to cover the operating regions of common reactors and contactors where a gas flows upwards through a bed of solids including fixed and moving packed beds, conventional fluidized beds, circulating beds, spouted beds, and pneumatically conveyed suspensions. New boundaries are proposed between groups A and B and between groups B and D of the Geldart (1972, 1973) powder classification scheme. These boundaries reflect more recent data and allow the classification scheme to be used for gases other than air and for temperatures and pressures other than atmospheric.

Hydrodynamic aspects of conventional and vibrofluidized beds —a comparative evaluation

A simple power law type correlating equation based on Anderson's correlation for homogeneous fluidization velocity in a vibrofluidized bed is proposed. Comparison of the calculated minimum fluidization velocities in the presence of vibration with experimental data was found to be favourable. An empirical correlation is given to relate the basic flow parameters in conventional fluidized beds with those in corresponding vibrated fluidized beds.

A COMPARATIVE STUDY OF WHIRLING- AND CONVENTIONAL-FLUIDIZED BEDS IN THEIR APPLICATION TO DEHYDRATION. I. HEAT AND MASS TRANSFER ANALYSIS

Heat and mass transfer characteristics of conventional- and whirling-flui-dized beds were compared in order to determine their suitability in dehydration applications. Results obtained for the particular case of wheat dehydration indicated that whirling beds present a better design with higher heat and mass transfer coefficients than conventional-fluidized beds. In fact, studies carried out in two-stage fluidized beds showed that whirling beds had approximately 1.9 times higher heat transfer coefficients in the first stage and 1.7 times higher in the second stage than conventional-fluidized beds. Moreover, mass transfer coefficients were 1.9 and 2.8 times higher in the first and second stages, respectively, as compared to conventional-fluidized beds. Conventional-fluidized beds were observed to exhibit a tendency for pulsating fluidization, resulting in slugging, channeling, and bubbling, factors that impair heat and mass transfer. This behavior was seldom found in whirling beds for the conditions investigated.