Fluidization Air Research Articles

Multiscale Simulation of the Fluidized Bed Granulation Process

AbstractA novel multiscale modeling approach was developed, implemented as basis of a simulation environment and applied to the fluidized bed spray granulation process. The high detailing level of the simulation is based on the process description on different time and length scales which are coupled by interscale communication laws. This allows considering a higher amount of process parameters, compared to the semi‐empirical models which are typically used. The developed concept represents the production plant as flow sheet, with its further dynamic simulation on the macroscale. The influence of parameters such as viscosity of the sprayed suspension, nozzle positions, and temperature of the fluidization air on the whole process can be considered on the microscale.

Fluidized bed gasification of a packaging derived fuel: energetic, environmental and economic performances comparison for waste-to-energy plants

A comparison of possible solutions for small scale (0.2–1MWe) waste-to-energy gasification-based industrial application is presented. A pilot scale bubbling fluidized bed air blown gasifier, having a capacity of 500kWe, provided experimental data: the syngas complete composition as well as the characterization of the bed material and contaminants downstream of the cyclone and wet scrubber. Mass and energy balances and material and substance flow analyses have been drawn to assess and compare design solutions utilizing a packaging derived fuel (PDF) obtained as scrap by food industrial processes. The related environmental, energetic and economic performances have been estimated on the basis of the experimental data and manufacturer’s specifications. In the scale range analyzed, the best solution is that of a power gasification coupled with an internal combustion engine, which provides high reliability and high internal rate of return.

Effect of heat, pH and coating process with stearic acid using a fluidized bed granulator on viability of probiotic Lactobacillus reuteri C 10

This study was conducted to investigate the use of a fluidized bed granulator to coat a probiotic Lactobacillus reuteri C 10 with stearic acid with a view to enhance its survival rate during storage. L reuteri C 10 cells of two treatments, namely, freeze-dried cells incorporated with trehalose and sucrose as cryoprotectants prior to freeze-drying, and freeze-dried cells without any incorporation of cryoprotectants were evaluated. Since the pH of stearic acid is 5.5 and the melting point is 57.23°C, and the inlet temperature of the fluidized bed granulator could be as high as 70°C, a preliminary study was initiated to determine the tolerance of L. reuteri C 10 cells to heat exposure from 58 to 70°C and acidic conditions of pH 4 to 6 for 60 min, during which the cell viabilities were determined every 15 min. In the coating process, 2:3 ratio of freeze-dried L. reuteri C 10 cells and stearic acid, fluidization air of 20 to 50 rpm, coating rate of 40 to 80 g/min and inlet and outlet temperatures of between 50 to 70°C were assessed for optimization of the fluidized bed granulator. Results of the preliminary study showed that freeze-dried L. reuteri C 10 cells incorporated with cryoprotectants exhibited significantly (P < 0.05) less cell loss than cells without cryoprotectants when exposed to 62°C for 15 to 60 min, 64 °C for 15 to 30 min, 66°C for 30 min and 68°C for 15 to 30 min. Freeze-dried L. reuteri C 10 cells with cryoprotectants were also able to survive for 15 min at 70°C, but not freeze-dried L. reuteri C 10 cells without cryoprotectants. Freeze-dried L. reuteri C 10 cells with or without cryoprotectants could tolerate acidic conditions and there was growth and increase in cell viability at pH 4, 5 and 6. However, cells with cryoprotectants had significantly (P < 0.05) more growth when exposed to pH 5 for 30 to 60 min, and pH 6 for 15 to 60 min than cells without cryoprotectants. The application of a fluidized bed granulator to coat L. reuteri C 10 cells with or without cryoprotectants with melted stearic was not successful in this study because the fluidized bed granulator could not maintain the temperature of stearic acid above its melting point which led to clogging of the tube and spray nozzle of the fluidized bed granulator or resulted in the formation of a big lump of stearic acid and L. reuteri C 10 cells instead of uniform coated cell granules. Installation of a temperature jacket on the fluidized bed granulator may be necessary to control the temperature of stearic acid in the tube and spray nozzle above melting point. Key words : Coating, fluidized bed granulator, Lactobacillus reuteri C10, stearic acid.

A novel process for coating of silica aerogel microspheres for controlled drug release applications

Aerogels are nanoporous materials with an open-pore structure and high specific surface area. Because of their outstanding properties they have been investigated in immense fields of applications like novel insulation materials, catalysts and catalysts carrier, optics, waste treatment and drug delivery systems. However, the limitation of aerogels (specially hydrophilic ones) in a number of applications is their open-pore structure, allowing the penetration of liquids therein resulting in destruction of their textural properties. Applying a polymeric coating layer on aerogels surface can be a solution for this problem and can open a wide window of new applications for aerogels, especially in pharmaceutical industry. This work suggests a novel process for coating of aerogels with polymeric materials using spouted bed technology. Firstly, spherical silica aerogel particles with a high surface area up to 1100m2/g and particles diameter ranging from 200μm to few millimetres were produced. Then, the aerogel particles were loaded with a model drug (Ibuprofen) by adsorption from supercritical CO2 phase. The loaded aerogel particles were coated with different polymeric materials in a slit-shaped spouted fluidized bed with two horizontal gas inlets and adjustable gas supply. The corresponding polymers were sprayed as an aqueous suspension or as melts. The process conditions for coating (coating material, fluidization air flow rate, temperature, etc.) were optimized accordingly. The physical, mechanical, structural and release properties of the resulting formulations were evaluated. This technology allows to provide a specific release mechanism of pharmaceuticals (thermal, pH-sensitive or enzyme triggered release) from aerogels and to broaden aerogel applications in pharmaceutical technology.

An experimental investigation of L-valve operation in an interconnected circulating fluidized bed system

Control of solid flow rate is an essential parameter in various fluidized bed processes involving circulation of particles. L-valve is a common non-mechanical valve used to control solid flow rate pneumatically. Gas flow around the elbow of an L-valve together with particles properties determines the amount of solids transported through the L-valve of known geometry.The L-valve operation in an interconnected fluidized bed system is presented in this work. Helium was used to trace gas flow rate across the standpipe of an L-valve with 0.017 m i.d. Ilmenite and sand particles were used with corresponding density of 4750kg/m3 and 2650kg/m3 and average diameters of 128 and 368μm. 0.3vol.% of Helium in the fluidization air was used to trace gas flow rate across the standpipe of the L-valve. The average voidage of the non-fluidized solid flow across the standpipe was measured for packed bed and transitional packed bed flow. Moreover, the L-valve was operated alternatively with Helium and air to investigate gas properties effect on the L-valve operation. Accordingly, gas density had a minimum effect on the solid flow rate in the L-valve. Finally, the limiting operation of the L-valve was investigated in batch and continuous solid circulation operations. The overall pressure balance was found to play an important role in stability of the solid flow rate in the standpipe by imposing gas flow rate across this section.

Particle surface moisture content estimation using population balance modelling in fluidised bed agglomeration

The objective of this study was to investigate the effect of particle surface moisture content on growth rate during fluidised bed agglomeration. In order to establish the relationship between process conditions and particle surface moisture content, the combined population balance and thermodynamic model, as described by Ronsse et al. (2007a,b), was used but was modified to include the degree of wetting and surface moisture content as variables in the population balance. Growth kinetics were experimentally verified by fluidised bed agglomeration tests using 100μm glass beads and maltodextrin based aqueous binder solutions, under varying process conditions. Studied process variables included binder concentration, fluidisation air temperature, liquid binder feed rate and liquid binder atomisation pressure. With the exception of varying binder concentrations, it was observed that a clear correlation existed between the model-predicted surface moisture content and the experimentally obtained growth rates. This work clearly demonstrates that, in population balance modelling of fluidised bed agglomeration, constant rate agglomeration kernels are insufficient and need to be sensitised to surface moisture content and binder concentration.

Effect of agglomeration/defluidization on hydrogen generation during fluidized bed air gasification of modified biomass

This study presents the effect of particle agglomeration on syngas emission during the biomass air gasification process. Various operating conditions such as operating temperature, equivalence ratio (ER), and amount of bed materials are employed. The concentrations of H2 and CO increase along with the operating time as agglomeration begins, while CO2 decreases at the same time. However, there is no significant change in the emission concentration of CH4 during the defluidization process. The lower heating value increases while the system reaches the agglomeration/defluidization under various operating parameters. When the system reaches the agglomeration/defluidization process, the LHV value sharply increases. The results are obtained when the system reaches agglomeration/defluidization. The temperature increases while bed agglomeration occurs. A higher temperature increases the production of H2 and CO, contributing to the LHV calculation.

Effects of Mixing Using Side Port Air Injection on a Biomass Fluidized Bed

Fluidized beds are being used in practice to gasify biomass to create producer gas, a flammable gas that can be used for process heating. However, recent literature has identified the need to better understand and characterize biomass fluidization hydrodynamics, and has motivated the combined experimental-numerical effort in this work. A cylindrical reactor is considered and a side port is introduced to inject air and promote mixing within the bed. Comparisons between the computational fluid dynamics (CFD) simulations with experiments indicate that three-dimensional simulations are necessary to capture the fluidization behavior of the more complex geometry. This paper considers the effects of increasing side port air flow on the homogeneity of the bed material in a 10.2 cm diameter fluidized bed filled with 500-600 μm ground walnut shell particles. The use of two air injection ports diametrically opposed to each other is also modeled using CFD to determine their effects on fluidization hydrodynamics. Whenever possible, the simulations are compared to experimental data of time-average local gas holdup obtained using X-ray computed tomography. This study will show that increasing the fluidization and side port air flows contribute to a more homogeneous bed. Furthermore, the introduction of two side ports results in a more symmetric gas-solid distribution.

Analysis of Optimal Control Problems and Plant Debottlenecking for Urea Granulation Circuits

The optimal control of a complete urea granulation circuit is studied in this work. The dynamic circuit operation is modeled by means of population, mass, and energy balances for the equipment of an industrial urea granulation flowsheet. The objective for the optimal control of the granulation circuit is to drive the process from a given steady-state (corresponding to the nominal capacity of a large-scale plant) to another one, by maximizing the throughput during the transient. To this aim, realistic operating constraints are taken into account and, based on an analysis of the active physical limitations, different optimal control variables are selected (i.e., urea melt flow rate, granulator discharge area, and granulator fluidization air temperature and mass flow rate). The results provide new promising operating points, which can be achieved by tracking the calculated optimal time-trajectories for the selected control variables, and give insights into the main plant bottlenecks.

Tribocharging and electrostatic separation of mixed granular solids in fluidized bed devices

Granular materials, when fluidized by air or other gaseous medium, acquire electrostatic charge by inter-particle and particle-wall collisions. The effectiveness of particle tribocharging achieved with such fluidization process is crucial for establishing the feasibility of electrostatic separation of mixed granular solid wastes in the recycling industry. The present paper aims at a crude evaluation of the effects of the main factors that influence the efficiency of such a tribocharger, in the presence of an electric field orthogonally oriented to the direction of the fluidization air. The experiments were carried out on binary mixtures taking combinations of two of the three polymeric materials in different tests: (a) virgin polyamide, (b) polycarbonate and (c) polyacetal granules. The variables investigated were the duration of the tribocharging process, the level of the high-voltage applied to the electrode and the composition of the mixture. The analysis of the experimental data revealed the effects of each variable on the mass and the charge of the granules collected at the electrodes.

Effect of alkali concentrations and operating conditions on agglomeration/defluidization behavior during fluidized bed air gasification

Biomass gasification plays an important role in finding a solution to the energy crisis, and the fluidized bed (FB) is recognized as an important technique for using biomass. However, this process significantly tends toward bed material agglomeration. Accordingly, the aim of this study is to emphasize the effects of operating conditions and different Na concentrations on agglomeration behavior during FB air gasification. Defluidization time decreases as Na concentration increases from 0.8 to 3%. Defluidization time decreases as temperature and the amount of bed materials increase. In addition, no significant change in the trend for this process occurs as the equivalence ratio increases. Adding CaO and Al2O3 can significantly prolong this process, and the inhibition level follows the sequence: Al2O3>CaO. The same observations are noted during both incineration and air gasification in the FB at various operating conditions.

Tribocharging of Mixed Granular Plastics in a Fluidized-Bed Device

The output of any electrostatic separation process is strongly dependent on the effectiveness of particle charging. The aim of the present paper is to evaluate the effects of several factors that might influence the efficiency of a fluidized bed tribocharger, in the presence of an electric field orthogonally oriented to the direction of the fluidization air. The experiments were carried out on several synthetic mixtures of binary granular mixtures. The velocity of the fluidization air, the duration of the tribocharging process, and the composition of the mixture were the three process variables investigated. Whenever possible, the effects of these variables on the output of the process (i.e., the mass and the charge of the granules collected at the electrodes), were evaluated using the experimental design methodology. The results of full- and composite-factorial experimental designs were analyzed with a commercial software (MODDE 5.0, Umetrics). The effectiveness of the charging process was found to depend significantly on each of these factors. The propitious aerodynamic design of the device is a prerequisite for the successful industry application of the technique.

Bed agglomeration characteristics of palm shell and corncob combustion in fluidized bed

Abstract Bed particle agglomeration was studied experimentally in an atmospheric laboratory scale fluidized bed combustor using quartz sand as bed material. Palm shell and corncob were tested. The objectives of the study were (i) to describe the contributions of the biomass ash properties and the operating conditions on the bed agglomeration tendency in term of the bed defluidization time (tdef) and the extent of potassium accumulation in the bed (K/Bed) and (ii) to further elucidate the ash inorganic behaviors and the governing bed agglomeration mechanisms. Defluidization caused by the bed agglomeration was experienced in all experiments during combustion of these biomasses, as a consequence of the presence of potassium in biomass. The experimental results indicated that biomass ash characteristics were the significant influence on the bed agglomeration. The increasing bed temperature, bed particle size and static bed height and the decreasing fluidizing air velocity enhanced the bed agglomeration tendency. The SEM/EDS analyses on the agglomerates confirmed that the agglomeration was attributed to the formation of potassium silicate liquid enriched on the surface of quartz sand particles in conjunction with the high surface temperature of the burning biomass char particles. Thermodynamic examination based on the phase diagram analysis confirmed that the molten phase formation was responsible for the agglomeration. In this study, the high molten ash fraction resulting from the high potassium content in biomass promoted the agglomeration and thus defluidization.

CFD study of solids concentration in a fluidised-bed coater with variation of atomisation air pressure

The solids volume fraction inside a tapered fluidised bed coater was simulated with the use of an Eulerian computational fluid dynamics (CFD) model with atomisation nozzle sub-model. The drag force, describing momentum transfer between the gas and solid phases was calculated using the drag model proposed by [1]. In order to account for the particle size distribution of the fluidised solid materials, a 4-phase Eulerian model was used. The model-predicted results for different atomisation air pressures were verified using published experimental data [2]. It was shown that the model proved to be highly sensitive to changes in the fluidisation air flow rate with regard to the model-predicted solids volume distribution.

Effects of fluidization number and air factor on the combustion of mixed solid waste in a fluidized bed

Abstract Combustion behavior of mixed solid waste in a fluidized bed was studied. Bed, surface and freeboard temperatures were monitored continuously for that purpose. The effect of fluidization number and air factor on the combustion behavior of mixed solid waste of high moisture content in a fluidized bed combustor was investigated. Mixed solid waste was used as a sample which was formulated from four major waste compositions found in Malaysia namely food, paper, plastic and vegetable waste (green). Combustion study was carried out in a rectangular fluidized bed with sand of mean particle size of 0.34 mm as a fluidization medium. The range of fluidization numbers investigated was 3–11 U mf . The first part of the combustion study was carried out at stoichiometric condition. Results showed that the best fluidization number was 5 U mf in which the bed temperature was sustained in a much longer period. The second part of the study dealt with the effect of air factor on the combustion behavior conducted at 5 U mf . The chosen range of air factor was 0.4–1.2. It was revealed that the best air factor was in the range of 0.8–1. Energy balance was also performed to determine the thermal efficiency of the combustion. It was concluded that the thermal efficiency was significantly increased at higher air factor.

A techno-economic comparison of fluidized bed gasification of two mixed plastic wastes

A comparison between the most promising design configurations for the industrial application of gasification based, plastics-to-energy cogenerators in the 2–6 MWe range is presented. A pilot scale bubbling fluidized bed air gasifier, having a feeding capacity of 100 kg/h, provided experimental data: the syngas complete composition, the characterization of the bed material, the entrained fines collected at the cyclone and the purge material from the scrubber. Mass and energy balances and material and substance flow analyses have been therefore drawn to assess and compare design solutions utilizing two mixed plastic wastes (MPW) obtained from separate collection of plastic packaging, after different levels of pre-treatments. The related techno-economic performances have been finally estimated on the basis of the manufacturer’s specifications. The study concludes that the MPW obtained after a very simple pre-treatment and fed to a gasifier coupled with a steam turbine is the solution that currently offers the higher reliability and provides the higher internal rate of return for the investigated range of electrical energy production.

Investigation and scale-up of hot-melt coating of pharmaceuticals in fluidized beds

This study was performed to investigate and scale-up the hot-melt coating process in fluidized beds. A series of well-designed experiments was carried out in a pilot scale unit with 20 kg product capacity to investigate the effects of process variables on the efficiency of the coating of Cefuroxime Axetil with stearic acid. Results showed that the efficiency is at the highest when the fluidization air flow rate is adjusted by considering the changes in the amount of materials present in the unit as well as the changes in the terminal velocities of particles during the process. With the objective to scale-up the hot-melt coating process from pilot to production scale, a dynamic thermodynamic model based on conservation equations of mass and energy was developed. Predictive accuracy of the model was assessed by applying it to the pilot scale unit and comparing its predictions with the online measurements taken on the same unit. Results showed that the predictions of the model agree well with the measurements. Utilizing this model and taking several experiments performed in the pilot scale unit as a basis, scaling up of the hot-melt coating process was carried out. Comparisons of the model predictions with the measurements taken on the production scale unit (200 kg product capacity) revealed that the model is able to reproduce the product attributes and the outlet air temperatures across scales. Therefore, it proves to be a promising tool that can be used in the scale-up of the hot-melt coating processes in fluidized beds.

Germinated Brown Rice Drying by Hot Air Fluidization Technique

Germinated brown rice containing moisture content of 52% dry basis (db) needs to be dried in a reasonable time in order to prevent the growth of microorganisms. Fluidized bed drying is a possible method because this drying technique provides a high mass and heat transfer rate and high-temperature drying can be used. However, such a high-performance dryer may affect the quality of the finished product. The effect of fluidized bed drying temperatures (90, 110, 130, and 150°C) on the quality of germinated brown rice, that is, cooked rice textural property, γ-aminobutyric acid (GABA) level, fissured grain, and microorganisms was therefore investigated. The germinated brown rice was dried to the moisture contents of 18–20% (db), tempered for 30 min, and ventilated by ambient air until the sample moisture content reached 13–15% (db). The experimental results showed that the drying rate increased with increasing drying temperature. The high drying rate, in particular drying at 130°C or higher, caused severe fissuring on the kernel and this fissuring subsequently affected the cooked rice shape and textural property of rice; that is, hardness. The GABA contents of germinated brown rice insignificantly changed with drying temperatures and did not depend on the rice varieties. The populations of attached bacteria, yeast, and mold on the surface of the dried samples were less than 104 colony-forming units (CFU)/g, which is safe for food.

The influence of the density of a gas–solid fluidized bed on the dry dense medium separation of lump iron ore

A gas–solid fluidized bed was used for dry dense medium separation of lump iron ore particles based on their floating and sinking in the fluidized bed. The density of the bed was adjusted to different values using mixtures of zircon sand and iron powder as the fluidized media. Float–sink experiments using 30 mm diameter density adjusted spheres in the range of 2100–4500 kg/m 3 in density increments of 100 kg/m 3 were carried out to determine the partition curves, the density of the bed and the probable error ( Ep). It was found that the density could be adjusted in the range of 2500–4200 kg/m 3, when the bulk volume fraction of iron powder and the fluidizing air velocity were varied. The Ep values were less than or equal to 0.05, if suitable fluidizing air velocities were chosen. The density of the bed determined using the spheres floating–sinking corresponds to that measured using the height of the fluidized bed. The float–sink performance of lump iron ore particles in the size range of +25–31.5 mm agrees well with the spheres’ float–sink performance. The partition curves, separation density and the Ep values were determined for the lump iron ore particles. The Ep value for the ore particle separation was around 0.03. The theoretical Fe-grade recovery (washability) curve for the ore was determined for separation densities between 2500 and 4200 kg/m 3 from the density distribution and Fe content of the lump iron ore particles. The actual Fe-grade and recovery were calculated from the partition curves of the ore particle separation and compared to the theoretical maximum obtainable Fe-grade and recovery.

CFD simulation and experimental analysis of flow dynamics and grinding performance of opposed fluidized bed air jet mill

This paper presents a three dimensional Computational Fluid Dynamics (CFD) model to investigate the flow dynamics of solid–gas phases during fine grinding in an air jet mill. Alpine 100AFG fluidized bed air jet mill is considered for the study and the jet milling model is simulated using FLUENT 6.3.2 using a standard k-ε model. The model is developed in GAMBIT 2.3.16 and meshed by tet/hybrid (T-Grid) and Triangular (Pave) meshes. The effects of operating parameters such as solid feed rate, grinding air pressure and internal classifier speed on the performance of the jet mill are analyzed. The CFD simulation results are presented in the forms of dual phase vector plot, volume fraction of phases and particle trajectories during fine grinding process. The mass of ground feed entering and leaving the cyclone (underflow) is also computed by simulation. The proposed model gives realistic predictions of the flow dynamics within the jet mill. Experiments are conducted on the Alpine 100AFG jet mill to study the particle size, morphology and mass of the ground product. The numerical results are found in good agreement with the experimental results.