Conventional Fluidized Bed Research Articles

Biodiesel production in a magnetically-stabilized, fluidized bed reactor with an immobilized lipase in magnetic chitosan microspheres

Biodiesel production by immobilized Rhizopus oryzae lipase in magnetic chitosan microspheres (MCMs) was carried out using soybean oil and methanol in a magnetically-stabilized, fluidized bed reactor (MSFBR). The maximum content of methyl ester in the reaction mixture reached 91.3 (w/v) at a fluid flow rate of 25ml/min and a magnetic field intensity of 150 Oe. In addition, the MCMs-immobilized lipase in the reactor showed excellent reusability, retaining 82% productivity even after six batches, which was much better than that in a conventional fluidized bed reactor. These results suggested that a MSFRB using MCMs-immobilized lipase is a promising method for biodiesel production.

A Novel Configuration For Fluidized Bed

A novel configuration for fluidized bed has been developed. It is basically a bubbling fluidized bed furnished with a spouted jet in the upper part of the bed. A part of gases is fed through the distributor to fluidize bed solids. The remaining part is fed through a vertical pipe creating a jet-fountain zone. A distinct feature of the novel configuration different from previous spouted bed patents and configurations is that the jet spout height is independent of the bed height. The experiments carried out using the novel configuration furnish promising results. The power consumption in delivering gases is found much lower when applying the novel configuration. Moreover, bubble sizes reduce considerably in the main bed as only a part of gases passes through it. Tests on combustion of a gaseous fuel indicate that the novel configuration enables smooth combustion of gaseous fuels and a rapid reliable method for initial heating of fluidized bed combustor. Staged air combustion technique is also applied. Drying silica gel has been tested in the novel configuration and in the conventional fluidized bed. Results demonstrate that the overall mass transfer rate is considerably higher in the novelconfiguration, particularly, at higher air flowrate. Keywords: Fluidized Bed, Jet, Combustion, Gaseous Fuels, Staged air, Drying, Silica Gel, Mass Transfer.

Corn Drying with Zeolite in The Fluidized Bed Dryer under Medium Temperature

Drying is an important step to find high quality of corn. Based on Standard of National Industry, populer as SNI, number 01-3920-1995, the corn was well stored at moisture content 14% or below (wet basis). However, conventional corn drying dealed with in-efficient energy process and corn quality degradation. This research evaluated the performance of corn drying assisted by zeolite as moisture adsorbent. In this process, the zeolite and corn were placed in the dryer fluidized by warm air as drying medium under 40 - 50oC. The air evaporated water product from corn, and at same time the zeolite adsorbed moisture in air. So, the relative humidity of air in dryer can be kept low in which enhanced the driving force for drying. Beside that, the moisture adsoprtion by zeolite was exothermic process that can supply the energy for drying or keep the dryer temperature. Thus, the drying rate can be faster. This work foccussed to observe the effect of drying temperature, air velocity, and corn to zeolite ratio on drying time as well as corn quality. As indicators, the drying rate was estimated and the proxymates content such as protein, fat, and carbohydrate content were analyzed. The results showed that compared with conventional fluidised bed dryer, corn drying with zeolite, can speed up drying time as well as improving the constant of drying rate. In addition, the corn proximate nutrition content can be well retained. At operating temperature 40oC, air velocity 9 m.s-1, and zeolite to corn ratio 1:2, the drying time can be 60 minutes shorter compared to that without zeolite.

Enhanced Methanation over Aerogel NiCo/Al2O3Catalyst in a Magnetic Fluidized Bed

CO methanation reaction over a nanosized NiCo aerogel catalyst (NiCo) for synthetic natural gas production was investigated in a magnetic fluidized bed (MFB) reactor. The results indicated that the NiCo catalyst showed poor fluidization behavior, while the fluidization quality of the catalyst can be greatly improved by introducing an axial uniform magnetic field. The catalyst in the MFB reactor afforded higher conversion of CO and higher selectivity and yield of CH4 than those in the conventional fluidized bed, which was attributed to the MFB reactor improved gas-solid contract efficiency and inhibited axial back-mixing of the product gas. The catalytic performance in the MFB reactor was quite stable during a 100 h reaction. Such good stability is attributed to the superior property of the catalyst and the improved gas-solid contact efficiency in the MFB reactor. Furthermore, the particle agglomeration was inhibited when the catalyst was explored to a magnetic assisted fluidized bed. The combination of magnetic nanosized catalyst and MFB intensification as a promising route was developed for synthetic natural gas production.

PADDY DRYING IN MIXED ADSORPTION DRYER WITH ZEOLITE: DRYING RATE AND TIME ESTIMATION

Recently, the main problem of the rice stock and distribution in Indonesia is the quality degradation as indicated in unpleasant odor (smelly), stained, yellowness, and high percentage of broken rice. This is due to the low of paddy quality dried by from either direct sunlight or conventional fluidized bed dryer. As a result, the paddy cracks and breaks easily during milling in which causes the storage life being shorter as the enzymatic degradation by germ or fungi occurs. Air dehumidified with zeolite at drying medium temperature is potential to improve the quality of paddy. Zeolite is a material having high affinity to water vapor. In this case, the paddy and zeolite was mixed and fluidized with the air. The air will evaporate water from paddy, and at same time, the zeolite will adsorb water from air. Hence, the humidity of dryer can be kept low in which improves the driving force for drying. This work discusses the effect of presence of zeolite in the dryer, operational drying temperature, air velocity and relative humidity on drying rate of paddy. The results showed that increasing of zeolite as well as operational temperature increased the drying rate. In addition, using the model, the air dehumidification with zeolite and increase of air velocity can speed up drying time significantly at operational temperature below 80oC. This condition is very suitable for paddy drying since the quality degradation can be avoided.

Drying of Biomass Particles: Experimental Study and Comparison of the Performance of a Conventional Fluidized Bed and a Rotating Fluidized Bed in a Static Geometry

The performance of a conventional fluidized bed and a rotating fluidized bed in a static geometry (RFB-SG) for the drying of woody biomass is experimentally studied. The performance with respect to the specific biomass drying rate, product uniformity, and air utilization is evaluated. RFB-SGs are shown to intensify the drying process by easily one order of magnitude, due to a combination of increased gas–solid slip velocities and improved particle bed density and uniformity. The cost in terms of increased and less efficient air utilization can be minimized by optimizing the RFB-SG drying chamber design.

Characteristics of a Pressurized Gas‐Solid Magnetically Fluidized Bed

AbstractThe hydrodynamic, heat and mass transfer characteristics of a pressurized co‐current gas‐solid magnetically fluidized bed (MFB) were systematically investigated considering major influence factors, such as magnetic field strength, superficial gas velocity, and operating pressure. It was shown that this pressurized gas‐solid MFB has the advantages of a wider operation range of the superficial gas velocity under bubble‐free particulate fluidization, a larger bed voidage with smaller pressure drop across the bed, and larger heat transfer efficiency, compared with a conventional fluidized bed. Moreover, the minimum bubbling velocity, gas‐solid mass, and heat transfer coefficients were correlated at high accuracy within the investigated range of operating conditions.

Particle transport and separation in inclined channels subject to centrifugal forces

A novel experimental system was established in order to investigate the effect of centrifugal forces on the hydrodynamic transport of particles through planar channels inclined at 70° to the axis of rotation. The device, consisting of a fluidized bed housing attached to a system of parallel inclined channels, was mounted inside a 2m diameter centrifuge. Fluidization water was directed to the outer periphery of the system, entering the base of the housing. The water then flowed in a direction towards the centre of the centrifuge, through an open chamber 150mm long, and then through the system of planar channels, 160mm long. The channels had a perpendicular spacing of z=1mm. The water then emerged via an overflow weir, 400mm from the centre of the centrifuge. Semi-batch elutriation experiments were conducted on a silica feed, 0–0.060mm in diameter, achieving separations defined in terms of the particle diameter, d, and centrifugal acceleration gG, where g is the magnitude of the acceleration due to gravity. The throughput advantage achieved using G=73 over a conventional fluidized bed with G=1 ranged from 845 to 3094. The extraordinary results were in reasonable agreement with the theoretical throughput advantage described in the paper. It was concluded that the hydrodynamic benefits of the inclined channels and the centrifugal force multiplied. The centrifugal force produced further synergy with the system hydrodynamics, resulting in the suppression of the effects of particle size, and hence a powerful separation on the basis of the particle density. This physical arrangement offers the potential to separate ultrafine particles in coal and mineral processing on the basis of density, offering an alternative to flotation.

Comparison of mass and energy balances for air blown and thermally ballasted fluidized bed gasifiers

Abstract The objective of this study was to compare the mass and energy balances for a conventional air blown fluidized bed gasifier and a ballasted fluidized bed gasifier developed at Iowa State University. The ballasted gasifier is an indirectly heated gasifier that uses a single reactor for both combustion and pyrolysis. Heat accumulated in high-temperature phase change material during the combustion phase is released during the pyrolysis phase to generate producer gas. Gas composition, tar and char contents, cold gas efficiency, carbon conversion, and hydrogen yield per unit biomass input were determined as part of these evaluation. During the pyrolysis phase of ballasted gasification, higher volumetric concentrations of hydrogen and methane were obtained than during air blown gasification. Hydrogen yield for ballasted gasification was 14 g kg −1 of biomass, which was about 20% higher than that obtained during air blown gasification. The higher heating value of the producer gas also reached higher levels during the ballasted pyrolysis phase than that of air blown gasification. Heating value for air blown gasification was 5.2 MJ m −3 whereas the heating value for the ballasted pyrolysis phase averaged 5.5 MJ m −3 , reaching a maximum of 8.0 MJ m −3 . The ballasted gasifier was expected to yield producer gas with average heating value as high as 15 MJ m −3 but excessive use of nitrogen to purge and cool the fuel feeder system greatly diluted the producer gas. Relatively simple redesign of the feeder system would greatly reduce the use of purge gas and may increase the heating values to about 17.5 MJ m −3 . Higher char production per kilogram of biomass was associated with the ballasted system, producing 140 g kg −1 of biomass compared to only 53 g kg −1 of biomass during air blown gasification. On the other hand, tar concentrations in the producer gas were 6.0 g m −3 for ballasted gasification compared to 11.7 g m −3 for air blown gasification. On balance, carbon conversion was found to be higher for air blown gasification. Cold gas efficiencies were somewhat higher for air blown gasification compared to ballasted gasification, although the difference did not appear to be significant.

CO2 gasification of coal cokes using internally circulating fluidized bed reactor by concentrated Xe-light irradiation for solar gasification

For the solar thermochemical gasification of coal coke to produce CO + H2 synthetic gas using concentrated solar radiation, a windowed reactor prototype is tested and demonstrated at laboratory scale for CO2 gasification of coal coke using concentrated Xe light from a 3-kWth sun simulator. The reactor was designed to be combined with a solar reflective tower or beam-down optics. The results for gasification performance (CO production rate, carbon conversion, and light-to-chemical efficiency) are shown for various CO2 flow rates and ratios. A kinetics analysis based on homogeneous and shrinking core models and the temperature distributions of the prototype particle bed are compared with those for a conventional fluidized bed reactor tested under the same Xe light irradiation and CO2 flow-rate conditions. The effectiveness and potential impacts of internally circulating fluidized bed reactors for enhancing gasification performance levels and inducing consistently higher bed temperatures are discussed in this paper.

Numerical Investigation of Air Flow Distribution in a Swirling Fluidized Bed

Swirling fluidized bed (SFB) is one of the recent technologies developed in fluidization to overcome various drawbacks in the conventional fluidized beds, particularly poor lateral mixing and relatively high distributor pressure drop. Though a number of beds operating with similar technique are commercially available, very little has been published on the subject, particularly on the distributor design. The distributor of the SFB is formed by an array of blades which are inclined to the horizontal, with a centre body in the middle of the bed. Air flow investigation was carried out on the empty bed via CFD approach. The study focused on the effects of number of blades and its inclination angle on the flow distribution and pressure drop, so as to arrive at an optimum choice of the distributor design. The findings indicate that higher number of has lower open area which resulted higher jet velocity of air from the distributor. Blade inclination has significant effect on the flow distribution where lower blade inclination produces higher magnitude of tangential velocity that creates intense swirling but at an expense of higher pressure drop. In conclusion, the distributor with 30 blades and 15º inclination was found to meet the design criterion outlined.

Simulation and Validation of Microwave-Assisted Fluidized Bed Drying of Soybeans

A general mathematical model of heat and mass transfer was developed to simulate the microwave-assisted fluidized bed drying of bulk grain. The model was solved using the well-known Runge-Kutta-Gill method. The model is capable of predicting the moisture content of soybean as well as the drying air parameters (i.e., drying air temperature and moisture content) during drying. The values of mean relative deviation (MRD) were less than 8 and 10% for prediction of grain moisture content and outlet air parameters, respectively, which reflects an acceptable accuracy. In comparison with conventional fluidized bed drying of soybean, microwave-assisted fluidized bed drying led to 83.39–98.07% savings in drying time and 82.07–95.22% savings in specific energy consumption when reducing soybean moisture content from 18.32 to 12% (db).

CFD Studies on Velocity Distribution of Air in a Swirling Fluidized Bed

This paper presents computational fluid dynamics (CFD) studies to characterize air velocity distribution for various bed configurations in a swirling fluidized bed (SFB). Unlike conventional fluidized beds, a SFB provides radial mixing which is desirable is fluidization. Three velocities components were observed, the tangential velocity, radial velocity and axial velocity. These velocities were created as a result of using annular blade type distributor which mimics the turbine blades. In actual industrial applications, the axial velocity will create fluidization while the tangential velocity provides swirling effect. The presence of radial velocity can be explained as a consequence of centrifugal force generated by the swirling gas. Understanding these velocity distributions will enable optimization of the annular blade distributor design towards a high efficient fluidized bed system.

Heat transfer in a swirling fluidized bed with geldart type-D particles

A relatively new variant in fluidized bed technology, designated as the swirling fluidized bed (SFB), was investigated for its heat transfer characteristics when operating with Geldart type D particles. Unlike conventional fluidized beds, the SFB imparts secondary swirling motion to the bed to enhance lateral mixing. Despite its excellent hydrodynamics, its heat transfer characteristics have not been reported in the published literature. Hence, two different sizes of spherical PVC particles (2.61 mm and 3.65 mm) with the presence of a center body in the bed have been studied at different velocities of the fluidizing gas. The wall-to-bed heat transfer coefficients were measured by affixing a thin constantan foil heater on the bed wall. Thermocouples located at different heights on the foil show a decrease in the wall heat transfer coefficient with bed height. It was seen that only a discrete particle model which accounts for the conduction between the particle and the heat transfer surface and the gas-convective augmentation can adequately represent the mechanism of heat transfer in the swirling fluidized bed.

Fluidization of Geldart Type-D Particles in a Swirling Fluidized Bed

Geldart Type-D particles are often associated with poor fluidization characteristics due to their large sizes and higher densities. This paper reports the hydrodynamics of various Geldart Type-D particles when fluidized in a swirling fluidized bed (SFB). Four different sizes of particles ranging from 3.85 mm to 9.84 mm with respective densities ranging from 840 kg/m3 to 1200 kg/m3 were used as bed material to study the effect of various bed weights (500 gram to 2000 gram) and centre bodies (cone and cylinder) for superficial velocities up to 6 m/s. The performance of the SFB was assessed in terms of pressure drop values, minimum fluidization velocity, Umf and fluidization quality by physical observation on regimes of operation. The swirling fluidized bed showed excellent capability in fluidizing Geldart Type-D particles in contrast to the conventional fluidized beds. The bed pressure drop of increased with superficial velocity after minimum fluidization as a result of increasing centrifugal bed weight. It was also found that the particle size and centre body strongly influence the bed hydrodynamics.

TAP studies of Pt–Sn–K/γ-Al 2O 3 catalyst for propane dehydrogenation

A Pt–Sn–K/γ-Al 2O 3 catalyst was prepared by incipient wet impregnation and studied with a temporal analysis of products (TAP) reactor for propane dehydrogenation. Previously to TAP analyses, the catalyst samples were used for propane dehydrogenation in two different reactors: a conventional fluidized bed reactor (FBR) where the catalyst was deactivated in time; and a two zone fluidized bed reactor (TZFBR) where propane and oxygen are fed at different levels, providing separated zones for the reaction and catalyst regeneration thus allowing a continuous mode operation. Several operating conditions were also investigated: different times on stream in the FBR, and in TZFBR at steady state the temperature, the oxygen flow rate and the location of the propane feeding point. Samples of catalyst were obtained at several axial positions in the bed. The amount of coke deposited on the catalyst surface has been determined by thermogravimetric analysis. TAP results show that activation energies for propane conversion are markedly different for catalysts used in FBR and TZFBR; these differences have been related to the different nature of coke present on the catalyst surface.

Experimental Studies on a Swirling Fluidized Bed with Annular Distributor

This paper reports the experimental findings on a swirling fluidized bed which operates with an annular-blade distributor. Spherical PVC particles (which fall under type D in Geldart’s classification) with two different sizes (5.75 mm and 9.84 mm) were used as bed material to study different bed configurations, taking into account the variation of fraction of open area (12.9% and 17.2%), blade overlapping angles (9° and 12°) and bed weight (500 gram to 2000 gram) for superficial velocities is from 1 m/s to 8 m/s. The performance of the swirling fluidized bed was assessed in terms of pressure drop values, minimum fluidization velocity and fluidization quality by physical observation on regimes of operation. The most significant finding is that the pressure drop of the bed increased with superficial velocity after minimum fluidization, in contrast with a conventional fluidized bed. It was also found that the blade geometry has less effect on bed performance, compared to fraction of open area and particle size. New regimes of operation were discovered, and designated as wave regime and two-layer bed regime. The best configuration obtained in the current work, which provides stable swirling at lower pressure drops, is the one with 60 distributor blades and 12° overlapping angle, operating with 9.84 mm particles.

Application of fluidized bed film coating for membrane encapsulation of catalysts

Fluidized bed film coating is considered as an efficient method to coat membranes onto catalytic particles producing a micro/mesoporous composite structure. These composite materials described as Membrane Encapsulated Catalysts (MECs) have the potential to increase reaction yield and selectivity by controlling the diffusion of products and reactants to and from the catalytic core. MECs were synthesized by film coating spherical zeolite particles with a nano-alumina suspension in hydroxylpropyl cellulose (HPC) using a conventional fluidized bed (Mini-Glatt). Coated particles were subsequently calcined in a furnace to remove the HPC leaving a porous alumina membrane. The fluidized bed coating process was evaluated by its ability to coat uniformly and defect-free as well as to control the membrane coating thickness. Scanning electron microscopy (SEM), Near Infrared Spectroscopy (NIR), and surface area and pore size distribution analysis (BET) were used to characterize the coated catalyst. Results show that membrane coatings were uniformly applied and free of defects upon optimization of fluidization parameters for the range of membrane thicknesses (6.0 μm–26.0 μm) produced in this study. The coating thickness estimated from the experimental techniques was in good agreement with the theoretically predicted thickness demonstrating the precision and controllability of the process. The alumina membrane was also shown to adhere well to the catalyst after removal of HPC and its thickness remained unchanged after calcining. Analysis of the membrane coated zeolite showed both microporous and mesoporous properties which may be particularly advantageous in separation processes. It was shown that NIR spectroscopy may be used as a method to replace image analysis for fast characterization of the membrane thickness. NIR spectra were shown to correlate coating thickness with absorbance at 1184 nm (R 2 = .9920).

Two- and three-dimensional CFD modeling of Geldart A particles in a thin bubbling fluidized bed: Comparison of turbulence and dispersion coefficients

A comprehensive understanding of turbulence and dispersion is essential for the efficient design of a conventional fluidized bed reactor. However, the available information is restricted to that in a two-dimensional (2-D) plane, because of the experimental and simulation limitations. It is, therefore, of importance to evaluate the remaining third dimension of the system and compare these results with the corresponding data obtained from the 2-D analysis for validation. In this study, computational fluid dynamics (CFD) based upon the kinetic theory of granular flow with a modified interphase exchange coefficient was successfully used to compute the system hydrodynamics of fluid catalytic cracking (FCC) particles in a thin bubbling fluidized bed with 2-D and three-dimensional (3-D) computational domains. In addition, the shortcoming of the current CFD model was evaluated. With respect to the bed height, the bed expansion ratio and solid volume fraction revealed similar results from both 2-D and 3-D computational domains. The turbulent granular temperature was higher than that of the laminar ones in the lower section of the bed while the laminar granular temperature dominates the system in the upper section. However, the granular temperatures obtained from the 3-D computational domain were slightly lower than that from the 2-D computational domain. The computation also showed that the dispersion coefficients are in good agreement with the literature measurements and so the 2-D computational domain can be used to simulate the bubbling fluidized bed system. Finally, all the evaluated system hydrodynamic values in the thin radial system direction were lower in the 3-D computational domain than in the thick radial system direction.

Fluidized bed granulation of an ordered powder mixture

The phenomenon of ordered unit segregation is of paramount importance in determining the homogeneity of an ordered mixture. This problem can be avoided by using a monodisperse carrier, but it is uneconomic. The fluidized bed granulation of a 0.1% ordered mixture has been studied as a method of reducing the effects of segregation. The ordered units were stable when fluidized and no significant loss of the microfine adsorbed material occurred during processing. The distribution of the minor component in the granules was significantly more uniform than in the original ordered mixtures. The demixing potential (formula: see text) (where p = proportion of cohesive minor component and w is the weight % of carrier material in a particular size range) was used to quantify the distribution of the minor component as a function of particle size. DP is a coefficient of variation and can be directly compared with the specification standard deviation sigma A. Batches of granules were compressed into 100 or 350 mg tablets, containing approximately 100 and 350 micrograms of model drug substance. The weight and content coefficients of variation (c.v.) were determined for 20 tablets. All batches had a weight c.v. less than or equal to 1.5% and a content c.v. less than or equal to 4.6%. Granulation of an ordered mixture greatly reduces the potential for segregation to decrease the mixture homogeneity. It also provides a solution to the problems which may be encountered when the mixing of small quantities of cohesive materials during conventional fluidized bed granulation is attempted.