Fluidization Air Flow Rate Research Articles

Fluidized spray driven polymer mediated ultra stable Aluminum metal coating with enhanced dielectric properties

In this work, a novel method for coating the polymeric substrate with an aqueous metallic powder (Aluminum) solution was developed. In the modified fluidized bed, assisted bottom spray coater was used to achieve the strong interfacial coating of the aluminum on the fluidized spherical expanded polystyrene (EPS) substrate and polyvinyl alcohol (PVA) as a binder. The coated aluminum metal exhibits a layered thickness of 340 ± 50 µm. The effect of fluidization airflow rate, spray rate, atomization air pressure, and inlet air temperature on the aluminum coating on the EPS spheres was investigated for the first time. The substantial integrity, interfacial bonding and surface morphology of aluminum coating were confirmed through XRD, FTIR, shaking test and SEM analysis. In addition, a remarkably high dielectric constant of 12,000 compared to the dielectric constant of the pristine EPS sphere of 60 at low frequency was observed.

Optimization of Fluidized-Bed Process Parameters for Coating Uniformity and Nutrient-Release Characteristics of Controlled-Release Urea Produced by Modified Lignocellulosic Coating Material

Controlled-release fertilizers are employed in precision agriculture to optimize technology-enabled farming without environmental deterioration. In this study, almond-shell lignocellulosic waste particles are chemically processed to synthesize a coating suspension for the production of controlled-release urea (CRU) in a Wurster fluidized-bed reactor. The interactive effect of process parameters such as atomizing air pressure (Pair), fluidized-bed temperature (Tfb), spray rate (Rspray), and fluidizing-air flow rate (Qair) on the (i) coating-film uniformity of CRU particles and (ii) longevity of nutrient-release from CRU is reported. CCRD is used with RSM to design the experiments for the optimization of nutrient-release performance and coating-film uniformity in terms of a coefficient-of-variance (CoV) of film thickness. The regression models indicate a good prediction of coating-film uniformity and nutrient-release time, with R2 = 0.971 and R2 = 0.98, respectively. The optimum conditions for coating-film uniformity are determined to be Pair = 3.5 bar, Tfb = 80 °C, Rspray = 0.15 mL/s, and Qair = 72 m3/h, with a predicted CoV film thickness of 11.5%. Similarly, Pair = 3.2 bar, Tfb = 78 °C, Rspray = 0.125 mL/s, and Qair = 75 m3/h are the optimum conditions for nutrient-release performance, with a prediction nutrient-release time = 56 h. The experimental validation yields a CoV of film thickness = 12.6% and a nutrient-release time = 49.5 h, indicating good agreement between predicted and experimental values. In addition, Tfb appears to be the most significant parameter.

Evaluation of the effect of maltodextrin and hydroxyethyl cellulose solution containing ZnO and Fe2O3 nanoparticles on the CO2 release in sodium bicarbonate coating process

Coating is a rapidly extending technology; especially in food and pharmaceutical industries. The coating process of sodium bicarbonate using ZnO and Fe2O3 nanoparticles (NPs) in aqueous solutions of maltodextrin (MD) and hydroxyethylcellulose (HEC) as wall materials has been studied in this work. The best operating conditions obtained by factorial design were the fluidization air flow rate of 100 m3/h, spraying pressure of 4 bars, drying air temperature of 60 °C, MD concentration of 30 % and HEC concentration of 0.1 %. The introduction of the NPs into the coating solution provides a heterogeneous surface, which enforces the wall material to a more uniform and faster crystallization. The applied conditions have been shown to be efficient for the coating process investigated in this study since they improve the coating characteristics such as CO2 release reduction, which is the most important one. CO2 release was reduced from 4 % for coated powders with no NPs in the coating solution to 2.4 % and 3.5 % for coated powders with Fe2O3 and ZnO NPs in the coating solution, repectively. The adsorption–desorption of N2 gas implies that the pore sizes of the coating layer surface have been significantly decreased by adding NPs to the coating solution.

3D numerical simulation of a directly irradiated bubbling fluidized bed with SiC particles

Abstract This paper presents the numerical results obtained in a directly irradiated fluidized bed. The numerical model was implemented using CPFD-Barracuda software coupled with a P-1 radiation model. The bed consists of a cylindrical geometry containing SiC particles, with a diameter of 7.62 cm and a fixed bed height of 8 cm. The irradiation on the top of the bed was implemented by including a high temperature surface that directly irradiated on the top of the bed, with a uniform radiation flux of 3 × 1 0 4 kW ∕ m 2 . The work studies the influence of the airflow rate and the thermal behavior of the irradiated bed. The results show that increases in the airflow rate (up to 2.5 times the minimum fluidization conditions) notably enhance the mixing rate and the agitation levels on the top of the bed, reducing the appearance of hot spots on the top surface, with the bed exhibiting a more uniform temperature in its upper half. At higher airflow rates, the maximum temperature of the directly irradiated particles is reduced from 454 K to 384 K when the airflow rate is increased from 1.5 to 2.5 times the minimum fluidization airflow rate. In contrast, the mean temperature of the whole bed of particles rises (from 315.9 K to 327.5 K), increasing the storage efficiency.

Pollutant emissions released during sewage sludge combustion in a bubbling fluidized bed reactor

The combustion of dry sewage sludge particles in a bubbling fluidized bed was studied in detail, analyzing the composition of the exhaust gases by means of a FTIR equipment. The operating conditions of the fluidized bed, i.e., the bed temperature and mass flow rate of fluidizing air, were varied to quantify their effect on the exhaust gas composition. The bed material was also varied, using sepiolite, silica sand and braunite particles, to evaluate the effect of different bed densities on the pollutant emissions. The results obtained for the combustion of sewage sludge particles in the different fluidized beds tested were compared to combustion tests run for the same operating conditions and bed materials using Cynara cardunculus L. as a fuel. Pollutant emissions derived from sludge combustion are much higher than those obtained from combustion of Cynara. The operating conditions also affect the emissions, e.g., the concentration of CO in the exhaust fumes decreased substantially when increasing bed temperature and air flow rate. The bed density has an effect on the combustion efficiency of sludge, obtaining higher efficiencies in low-density beds for high temperature and air flow rates, while the efficiency was increased in high-density beds for low bed temperature and fluidizing air flow rate. The effects of ash accumulation and agglomerates formation were also analyzed.

Studies on fluidization characteristics of a continuous gas-solid fluidized bed with dynamic scrapers

Scrapers are important inner components in continuous fluidized beds in the state where they are most commonly used industry. Dynamic scrapers have significant effects on fluidization characteristics. A lab-scale continuous air dense medium fluidized bed (CADMFB) was designed, and the influences of operational parameters were studied. Moving scrapers lead to velocity gradients in the horizontal direction among magnetite particles in different bed heights, which assisted in loosening of the dense medium bed. Hence, bed pressure drop and minimum fluidization airflow rate were lower than those in beds with static scrapers. If the scraper velocity is kept constant, minimum fluidization airflow rate increases with increasing scraper distance. But the ratio of standard deviation to average bed pressure drop increases with the increase in the scraper distance, which indicates a decrease in bed stability. Minimum fluidization airflow rates also increased with increasing scraper velocities, but a fast scraper speed may also cause bed pressure fluctuations. Dynamic scrapers can inhibit the generation of big gas bubbles. Optimum scraper velocities for various scraper distances can be calculated by v>Lg0.6π0.21.43Q0.2. Results indicate that 50 mm was the ideal scraper distance, and the optimum scraper velocity was about 0.35 m/s. Results also show that fluidization in boundary zones between dynamic scrapers and static sidewalls was worse than that of middle zones of CADMFB.

Evaluation of pellet cycle times in a Wurster chamber using a photoluminescence method

Particle cycle time variation in a fluid bed coater is an important parameter that affects inter-particle coating uniformity. For the purpose of analyzing the pellet circulation process, a tracer particle photoluminescence detection system was developed and used in a laboratory scale fluid bed Wurster chamber. In order to tackle the problem of optically dense flow within the Wurster tube, transitions of a photoluminescent pellet were recorded in the down-flow region. Tracer pellets were representative for evaluated populations of pellets in terms of size and density. Pellet cycle time distributions were assessed for processes with varying particle size, gap, fluidizing air flow rate and loading mass. A higher air flow rate and gap decreased the distribution mode whereas a decrease in gap and an increase in the air flow rate and loading mass decreased the magnitude of pellet cycle time variation. Additionally, the variation in the position of tracer pellet successive passes was assessed and the change in transition azimuth was connected to stability of gas–solids flow. We also estimated that for the homogeneous spray case the average circulation process variability contribution to the total coating mass variability is relatively small.

Using response surface methodology to optimize the operating parameters in a top-spray fluidized bed coating system

The fluidized bed coating system is a conventional process of particles coating in various industries. In this work, an experimental investigation was conducted using Response Surface Methodology (RSM) to optimize the coating mass of particles in a top-spray fluidized bed coating. The design of experiments (DOEs) is a useful tool for controlling and optimization of products in industry. Thus, DOE was conducted using MINITAB software, version 16. This process used a sodium silicate solution for coating the sodium percarbonate particles. The effect of the fluidization air flow rate, atomization air flow rate and liquid flow rate on the coating mass in the top-spray fluidized bed coating was investigated. The experimental results indicated that the coating mass of particles is directly proportional to the liquid flow rate of the coating solution and inversely proportional to the air flow rate. It was demonstrated that the flow rate of the coating solution had the greatest influence on the coating efficiency.

Use of experimental design to investigate the coating process of sodium bicarbonate in a conical fluidized bed

Sodium bicarbonate is a white crystalline powder that is used as the active chemical compound in industrial processes. To maintain its properties against environmental effects, it must be coated. Thus, the spray coating of sodium bicarbonate in a pilot plant conical fluidized bed was studied to determine the effect of the operating conditions on the process performance and product quality. A 2(5-1) fractional factorial design was developed with the following independent variables: fluidization air flow rate (100–140m3/h), spray pressure (4–6bar), drying air temperature(40–60°C), maltodextrin concentration (10–30% w/v) and hydroxyethylcellulose concentration (0–0.2% w/v). The bulk porosity, flowability, moisture content, dissolution time, volume of carbon dioxide release and powder morphology were evaluated. The results show that a fluidization air flow rate of 100m3/h, spray pressure of 4bar, inlet temperature of 60°C, maltodextrin concentration of 30% and hydroxyethylcellulose concentration of 0.1% led to higher flowability and, a lower dissolution time, moisture content and CO2 release. The proposed conditions were shown to be efficient for the coating process evaluated in this study, reducing CO2 release from 8% for raw materials to 2% for coated powder.

Tribo-aero-electrostatic separation of micronized mixtures of insulating materials using “back-and-forth” moving vertical electrodes

The existing industrial tribo-electrostatic separators have proved their efficiency for sorting mixtures of millimeter-sized granular plastics. The objective of this paper is to validate a new tribo-aero-electrostatic separator designed for processing granular mixtures of insulating materials (average size: 10–100 μm). The device consists of two vertical plate electrodes of dimensions 20 cm × 30 cm, connected to two DC high voltage supplies of opposite polarities. Both electrodes perform “back-and-forth” motions inside a fluidized bed containing the micronized materials to be separated. Fluidization is achieved by injection of air using a variable speed air blower. The experimental study is carried out with samples of white PVC and gray PVC having an average size of 50 μm, and enables the analysis of the effects of several factors on the separation efficiency: the linear speed of the electrodes, the electric field, the mass of processed materials and the fluidization air flow rate. The new separation process is characterized by high product recovery rates. The purity of the separated products, estimated by visual examination, exceeds 90% in all experiments.

Measurement of particle concentration in a Wurster coater draft tube using light attenuation

Particle concentration in a coating zone of fluid bed coater is important to ensure appropriate coating uniformity and process yield. A transmissive optical setup at the top of the Wurster draft tube was used in a lab scale coater. Measured transmittances were converted to particle chord average volume fraction distributions using results of Monte Carlo calculations. The ranges of measured transmittances were from 0.002 to 0.285 and the range of particle chord average volume fraction was from 1.36% to 5.44%. The effect of gap between the draft tube and distribution plate, fluidizing air flow rate, particle size and load was studied. Comparisons of particle chord average volume fraction results with results of global particle volumetric fraction in the draft tube and particle cordal fraction obtained from CFD simulations are shown. In order to study the dynamics of the system as a function of different process parameters frequency analysis of transmittance signals was performed. Four distinct frequency responses were identified. Findings indicate presented local light attenuation method as suitable for assessing particle chord average volume fraction at the top of Wurster draft tube and with a potential for in-line method development.

Use of experimental designs to optimize fluidized bed granulation of maltodextrin

The goal of this study was to use the experimental design approach in order to determine which process parameters are the most influent to granules properties. The agglomeration process was performed with a fluidized bed processor equipped with a top-spray tilted nozzle. The granules were obtained by binding fluidized particles of maltodextrin (DE 12) with an aqueous solution of maltodextrin. The variables considered in the experimental design were fluidization air flow rate, drying air temperature, spraying pressure and binder flow rate. The physical properties of the granules were evaluated in terms of granule size, particle size distribution, dissolution time and flowability. Moreover, the amount of binder for each experiment was noted. The statistical analysis performed with Statgraphics® Centurion version XVI software indicated that the best operating conditions were found for low fluidization air flow rate, high drying air temperature, high spraying pressure and high binder flow rate. The study also revealed the difficult task of acquiring all the optimum properties at the same time.

Product design based on discrete particle modeling of a fluidized bed granulator

Fluidized bed agglomeration is a process commonly used to construct powdered food or pharmaceutical products to improve their instant properties. This works analyzes the influence of a wide range of operating parameters (i.e., fluidization air flow rate, temperature, and liquid injection rate) on growth rate, process stability, and product particle structure. Different granulator configurations (i.e., top spray, Wurster coater, spouted bed) are compared using identical process parameters. The impacts of both process variables and granulator geometry on the fluidization regime, the particle and collision dynamics, and the resulting product structure and corresponding properties are studied in detailed simulations using a discrete particle model (DPM) and lab-scale agglomeration experiments with amorphous dextrose syrup (DE21). The combination of numerical and experimental results allows to correlate the kinetics of micro-scale particle interactions and the final product properties (i.e., agglomerate structure and strength). In conclusion, detailed DPM simulations are proven as a valuable tool for knowledge-based product design.

Numerical simulation of two-phase flow in a Wurster coating chamber and comparison with experimental results

Pellet coating is commonly performed in a fluid bed coater such as a Wurster coater. Computational fluid dynamics (CFD) simulations and experimental measurements of laboratory-scale Wurster coating were performed. CFD simulations were performed in a 2D axisymmetric space using the two-fluid model. The effect of the Wurster gap and fluidizing airflow rate on gas–solid flow was analyzed in both simulations and experiments. Experimentally, the draft tube two-phase flow was evaluated by measuring the volume fraction of pellets within the draft tube and local particle velocities at the tube exit and by monitoring the local pressure drop fluctuations. A rather good agreement between the simulated and experimental results was observed and thus it can be assumed that this particular simulation setup represents a computationally reasonable tool that provides a valuable insight into the Wurster coating process due to the impact of two-phase flow properties on the process.

Fluidized bed agglomeration of skim milk powder: Analysis of sampling for the follow-up of agglomerate growth

Skim milk powder agglomeration was investigated by spraying water in a conical batch fluidized bed at lab scale. Evolution of powder water content and particle size distribution along a “long” agglomeration process (33 min) was followed by taking samples (~ 4 g) at different times (every ~ 5 min). Then “short” agglomeration experiments, with the same operating conditions, were stopped after the same times. The water content and the particle size distribution of the whole powder were compared to that of the sample taken at the same times during the “long” process. Samples were found to be representative of the whole powder for the size and particle size distribution, but not for the water content, due to non homogeneous distribution of humidity in the fluid bed. From the evolution of the particle size distribution, agglomerates formation and growth were found to occur in stages with the appearance of intermediate population till reaching a maximum size depending on conditions, especially the fluidizing air flow rate. During batch fluidized bed agglomeration of skim milk powder in a conical bed, samples were representative of the whole powder for the size and particle size distribution, but not for the water content. Agglomerates formation occurred in stages and depended on the fluidizing air flow rate.

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.

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.

Effect of operating conditions and particle properties on performance of vertical air-lift

The effect of the fluidization air flow rate and the transport air velocity on the solids mass flow rate and the pressure drop along the transport pipe was investigated in a vertical air-lift. The use of two different materials, glass (150μm) and zirconium oxide (260μm) particles (Geldart's B class), enabled to estimate the effect of particle properties on the air-lift performance. Different levels of the solids mass flow rate were obtained by varying the fluidization air flow rate while keeping the transport air velocity constant. The solids loading ratio varied between 2 and 16 for both types of particles. The pressure drop was non-linearly related to the solids mass flow rate at most of the transport air velocities tested. State diagrams presenting the relationship between the transport air velocity, the solids mass flow rate, and the pipeline pressure drop were constructed to characterize the flow pattern and to compare the behavior of the glass and zirconium oxide particles. Owing to the larger size and higher density, the zirconium oxide particles displayed higher pressure drop values than the glass beads and the minimum pressure drop shifted towards higher transport air velocities. The velocity at the transition between dilute and dense phase conveying was approximately in the range of 7 to 10m/s for glass beads and 10 to 12m/s for zirconium oxide, at the solids mass flow rates tested. The flow patterns could be also effectively characterized from the analysis of the pressure drop fluctuations at different transport air velocities.

Dynamics of an Industrial Fluidized-Bed Granulator for Urea Production

Granulation is one of the fundamental operations in particulate processing; however, there is still need to provide insight into the complex dynamic state behavior of these units. The unsteady state of an industrial multichamber fluidized-bed granulator for urea production, with variable mass holdup, is studied under different imposed step changes in key operating variables. For the assayed disturbances, the unit dynamics is considerably slow. In fact, many important state variables (e.g., bed height, pressure drop, solid mass flow, etc.) required more than 1 h to achieve the new steady state. The observed nonsteady behavior indicates the need of an efficient control to return the system rapidly to the desired operational point. The discharge area, fluidization air flow rate, and temperature were determined to be the more appropriate manipulative variables, for granulator stability control purposes.

A novel cartridge type powder feeder

In the present work, a novel cartridge type powder feeder is developed by applying ‘subliminal fluidization’, which is defined as partial aeration to the bed below minimum fluidization, but only for a limited region above the distributor, and by discharging solids together with the air through the tube located at the centre of the distributor. The distinct advantage of cartridge type feeder developed in this work lies in its simplicity of construction and operation giving quite an advantage for particulate material handling, transportation and metric feeding. Temporal solid efflux rates were measured for charcoal of mean sizes 220, 290 and 430 μm, glass beads of 265, 535 and 930 μm and spherical activated alumina (Neo beads) of 145 and 595 μm and density in the range of 1250 to 2500 kg/m 3. Temporal flow rates of solids indicated that the solids efflux was independent of time and amount of material inside the bed and was only determined by the air supply from the distributor plate. Solids efflux rate was found to decrease with increased particle size and internal friction and reduced fluidization air flow rate. Solids efflux was found to vary slightly with the change in air humidity. A dimensionless correlation for solids efflux was developed as a function of fluidization number and the internal friction angle.