Perforated Distributor Research Articles

PIV investigation on the effect of gas distributor design for fluidization of Geldart A spherical particles

This is a hydrodynamics study on gas distribution during fluidization of the industrially relevant Geldart A type particles. The impact of 10 different distributor designs comprising perforated distributors (pitch and orifice arrangement pattern varied) and nozzle distributors (nozzle size varied) were studied experimentally on a bench-scale unit. Particle flow homogeneity in air was determined by a novel Particle Image Velocimetry (PIV) analysis of the freeboard velocity field. Over 50 PIV particle phase vector field images are presented and analysed. Bed expansion, Particle attrition with and without fines, velocity profiles with and without fines and effect of fines on bed expansion were ascertained. Best distributor design for a unit such as Fluid Catalytic Cracking (FCC) regenerator and FCC riser were found to be 0.8 cm and 0.6 cm nozzle plates distributors respectively. Confirmation with previous study revealed a correlation between homogeneous distribution of particulate flow and lower number of turbulence zones.

Investigating the Influence of Distributor Type, Particle Size and Rice Husk Percentage on Fluidized Beds through Cold Fluidization Experiments

This work studies a fluidization system through cold experiments by using a mixture of rice husk and sand to investigate three parameters: type of bed distributor (perforated plate and plate with Tuyere-type injectors), sand granulometry (mean diameters of 324 µm and 647 µm) and rice husk mass ratio (from 1% to 10% of rice husk). The results reveal that the perforated distributor plate achieved a lower minimum fluidization velocity. However, the plate with Tuyere injectors generated better mixing, thus reducing possible stagnation points. An increase in the mean diameter of the sand raises the minimum fluidization velocity but also facilitates the formation of preferential channels. As for the rice husk mass ratio, values of over 5% cause stagnation points and preferential channels. It was also found that the relation between minimum fluidization velocity and rice husk ratio follows an exponential behavior, and an equation was developed to better describe their relation.

Optimizing Design and Operational Parameters for Enhanced Mixing and Hydrodynamics in Bubbling Fluidized Bed Gasifiers: An Experimental and CFD-Based Approach

An experimental investigation of hydrodynamics of gas-solid flow is carried out by engaging different designs of air distributor plates. An analysis of three different plates, i.e., perforated, 45° slotted and novel hybrid plate, revealed the difference in pressure drop and minimum fluidization velocities (Umf) for varying input operational variables. Umf is found to be lowest for perforated and highest for 45° slotted plate, whereas pressure drop is found to be highest for 45° slotted plate and lowest for novel hybrid distributor plate. The bubbles rise velocity ratio (Umf,b/Umf,f) is noticed minimum for 45° slotted plate due to relatively larger bubbles originating from the bigger slot openings and maximum for perforated distributor plate owing to smaller bubbles with dominant axial rise. Furthermore, the bed height rise ratio (h/L) is observed as a minimum for perforated distributor and maximum for 45° slotted plate due to larger bubbles through 45° slots rupturing the bed surface, causing more bed expansion. Furthermore, CFD analysis is also carried out to observe the insight flow dynamics using the distributor plates. The simulations use a two-fluid model (TFM) and K-Epsilon turbulence models. CFD model shows promising results in agreement with the experimental results. CFD results revealed that the lower portion enhanced lateral dispersion/mixing of solid particles due to 45° angular openings of an air inlet. In contrast, the perforated plate exhibited a straight upward motion of small air bubbles, causing no radial/lateral mixing. CFD results for the hybrid plate show the mixed axial as well as lateral mixing of solids by revealing velocity distribution; therefore, the novel hybrid plate is found to be an optimum distributor plate due to its lowest pressure drop, adequate Umf, intermediary bed height rise ratio and moderate bubble rise velocity ratio across the bed.

Experimental study of the performance of open–type refrigerated display cabinet

<p>This paper presents experimental investigations of the efficiency of an open-type refrigerated display cabinet used to store food at temperatures between –1 and +7 °C. The purpose of the study was to increase the efficiency of the open-type cabinet by improving its design. The cabinet has five shelves for food products with lengths of 350-600 mm. The spacing between the base and the first shelf is 280 mm, and between the other shelves it is 250 mm. The air enters the cabinet from the return air grille (RAG) at the bottom of the front panel, fans blow air through the evaporator, and the cooled air travels through a tunnel to the top of the refrigerator. The perforated distributor at the top distributes the cooled air, and part of the air is blown through the perforated back panel and the other part passes through the air-off honeycomb (dimensions (WH) are 12020 mm) at the front top of the cabinet, thus forming an air curtain between the inside of the refrigerator and the ambient warm air to protect the chilled food products. The cooled air entering through the perforated back panel into the display area helps maintain the required food temperature. In this study, two versions of the refrigerated cabinet were analyzed. The first version is the standard refrigeration cabinet and the second version is the same cabinet but with a change in the angle of inclination of the honeycomb and a reduction in the depth of the shelves. Air and test product temperatures were measured with thermocouples, and electrical energy consumption was measured with the Carel MT300W1100 energy meter. The experimental results show that the infiltration ratio decreases from 38.7 to 27.7%, and the 24-hour electrical consumption decreases from 24.91 to 19.22 kWh in the case of the modified cabinet. The average air temperature in the return air grille (RAG) decreased from 7.5 to 6.52 °C with the same temperature settings. The average temperature of the M packages decreased by 0.2-2.2 °C depending on the position in the refrigerator.</p>

Drying Performance of Piper Nigrum in a Swirling Fluidized Bed Dryer: An Experimental Study

Sun drying is widely used in drying agricultural products such as piper nigrum because of its ability to dry a high volume in one batch. However, this conventional method of drying has many disadvantages, especially on the hygienic issue. This study investigates the drying performance of piper nigrum by using conventional sun drying and a new dryer called Swirling Fluidized Bed Dryer. Swirling fluidized bed dryer is operated using two inclination angles of air distributors, namely 45°, 67° and one perforated plate distributor. The drying performance is accessed in terms of drying time and moisture content reduction at three different operating temperatures. The results show that the drying time of piper nigrum using a swirling fluidized bed dryer is reduced as compared to conventional sun drying. Besides, the drying performance between different distributors in swirling fluidized bed shows that the moisture content reduction of piper nigrum using 45° angle of air distributor shows the most reduction compared to 67° angle distributor and followed by the perforated distributor. In conclusion, results show that the drying of piper nigrum in a swirling fluidized bed operated with 45° inclination angle of the distributor at high operating temperature gives the best performance.

Computational Analysis of the Hydrodynamic Behavior for Different Air Distributor Designs of Fluidized Bed Gasifier

Fluidized bed gasification has proven to be an appropriate technique for converting various biomass feedstocks into helpful energy. Air distributor plate design is one of the critical factors affecting the thermochemical conversion performance of fluidized bed gasifiers. The present study is proposed to investigate the mixing pattern and pressure drop across different configurations of air distributors using a two-fluid model (TFM) of finite volume method-based solver ANSYS FLUENT. The pressure drop across the bed and mixing pattern have been investigated through qualitative and quantitative analysis of CFD results using three diverse distributor plate designs: perforated plate, 90° slotted plate, and 45° swirling slotted plate. The pressure drop by employing the perforated distributor plate reveals the highest pressure drop due to the smallest open area ratio. However, the pressure drop in the case of 90° slotted plate is found to be 7% and 4% lesser than perforated and 45° slotted plate respectively due to a smaller velocity head developed through the wider open area of the straight slotted plates. The distributor design configuration having a 45° slotted plate exhibits considerable pressure drop compared to the 90° slotted plate due to the longer path length of the slot. Numerical pressure drop results across the bed with different types of distributor plates prove reasonable agreement with the experimental results available in the literature. Mixing behavior in perforated distributor plates exhibits lower portion solid volume fraction of around 0.58. However, it falls rapidly as go up the riser (7.7% of column height); 90° slotted plate shows bottom region solid volume fraction of around 0.5. In addition, it exhibits an even broader range of sand volume fraction and column height (13.46% of column height). Finally, the 45° distributor plate reveals the highest range of volume fraction through the riser height (17.3% of column height), indicating the better mixing characteristics of the fluidized zone.

Simultaneous PM2.5 and moisture removal from wet flue gas by a gas-liquid cross flow array

A gas-liquid cross-flow array (GLCA) system is proposed as the direct condensing technique for PM2.5 and moisture simultaneous removal from the wet flue gas. Such a GLCA with huge surface area is formed by numerous vertically down-flowing wastewater films along a number of wires through a perforated distributor. And each falling film acts as an independent sink to remove PM2.5 and moisture. Analytical models are developed to predict PM2.5 and moisture removal efficiency of a GLCA, based on the differential equation of convection diffusion with diffusiophoresis (DP), the only considering mechanism of PM2.5 removal. The models indicate that PM2.5 removal efficiency is proportional to the moisture removal amount, and PM2.5 removal efficiency can be increased sharply due to moisture condensation. Experiments with a lab-scale GLCA are carried out with variable humidity of inlet gas, and a constant gas (60℃) and water (20℃) temperature. The experimental measurements for PM2.5 and moisture removal generally compare satisfactorily with the model predictions.

Fluidized bed drying of stingless bee pot-pollen: Performance of swirling distributor

Pot-pollen is pollen collected by stingless bee, mixed with honey and bee secretion, and then stored in cerumen pots. Raw pot-pollen contains high moisture content which can lead to excessive fermentation and spoilage. Drying of pot-pollen is needed to preserve them. Typically, elevated temperature can increase the drying performance. However as pot-pollen is heat sensitive, heating above 40 °C is not preferable. Hence, the objective of this study is to explore drying performance of fluidized bed dryer with swirling distributor. The experiment was conducted using three different distributors, a perforated distributor, 45° and 67° swirling distributor, at 1.0 m/s and 1.5 m/s superficial air velocities. The weight of pot-pollen used in this experiment is 50 grams. The drying experiment was conducted at ambient conditions, with no heating being applied to the pot-pollen samples. It was found that 67° swirling distributor at 1.5 m/s superficial air velocity has the highest improvement in terms of drying performance, able to reduce the moisture content from 30.5 % to 18 % for 30 minutes drying time. Hence, using swirling distributor is a suitable enhancement to fluidized bed drying especially for heat sensitive food materials.

A CFD‐based design scheme for the perforated distributor with the control of radial flow

AbstractIn the present study, flow homogenization by distributors in chemical apparatus is studied as a process of flow control and its mechanism is reconsidered from the model of resistance to the model of radial flow. This process is composed of four consecutive behaviors: the generation, distribution, conversion of the radial flow and the momentum transfer of axial flow. Based on these flow behaviors, the novel distributor is designed as the combination of perforated plate in the center area and vertical guiding baffles around. Taking the wire‐screen catalytic reactor as a case study, numerical simulation is employed to optimize the structure of distributor and a CFD‐based design scheme called “flow field analysis scheme” is proposed. Numerical simulation is conducted in the apparatus with a diffuser (inlet D0 = 500 mm, main part D1 = 3,000 mm) under the gas velocity of 3.6 m/s (corresponding Re ≈ 12,000). The numerical results from optimized distributor show that compared with the traditional perforated plate, the flow field adjusted by the novel distributor can achieve a better flow uniformity with lower energy consumption. The theoretical analysis and numerical results are also validated and proved by the experimental results.

Analysis of micro-holes shape in a textile terminal using optical microscopy

Currently, development and improvement of ventilation and air conditioning systems efficiency is related with the use of new devices for air transportation and distribution. These include micro perforated air distributors made of textile which are installed both at the level of the indoor working area and directly near the workplace. Air terminals of this type are made of polymer composite material – fabric based on synthetic fibers. To make such a fabric, modern laser technology to produce micro-holes is used which allows burning in the fabric holes of a given diameter and pitch with melted edges. Results of studies on shape and size of micro-holes in the micro perforated textile terminal are described in this paper. A conclusion is made that the micro–holes shape is irregular and the holes boundaries have uneven edges. Data on micro-holes area range are given. Actual diameter of the micro-holes declared by manufacturer is defined more exactly.

CALCULATION OF THE DRAINAGE SYSTEM OF LEAVING FLUE GASES FROM THE TURBINE THROUGH THE COOLING TOWER

The article presents result of a research a system of the venting of exhaust gases of the recovery boiler the gas turbine plant through the natural draft cooling tower in the environment. The use of this scheme allows the fl ue gases to lower the temperature of the circulating water at the outlet of the cooling tower to provide a deeper vacuum in the condenser steam turbine combined cycle power plant with simultaneous reduction of capital to build chimneys. As a result of the application of this scheme, an increase in the absolute electric effi ciency of turbines is achieved. As stated in Article method of calculating the removal of exhaust fl ue gas systems with a perforated distributor ring allows to determine the level of engineering design and volume requirements of these systems.

Bubble properties measurement in bubble columns: From homogeneous to heterogeneous regime

Bubble properties, such as local gas holdup, bubble frequency, bubble velocity, bubble size, and interfacial area concentration, are of great significance for the design and scale-up of bubble columns. In the present study, bubble properties in a 0.15m in diameter bubble column were measured by a dual-tip conductivity probe. A new method was proposed to establish the relationship between chord length distribution (CLD) and bubble size distribution (BSD) without the assumption of fixed bubble aspect ratio. The bubble velocity and BSD measured by the probe were validated by a high speed camera in a square column. The results indicate that considering the decreasing of bubble aspect ratio with bubble diameter is required to obtain accurate BSD from measured CLD. Furthermore, the measured bubble properties at different axial positions show that the flow development is much more rapid in the churn-turbulent regime than that in the homogeneous regime. It is also found that the bubble breakage is dominant over the bubble coalescence in the homogeneous regime due to the large bubbles generated at the perforated distributor. The measured results provide a benchmark data for validation of CFD simulation.

Evaluation of hydrodynamic behavior of the perforated gas distributor of industrial gas phase polymerization reactor using CFD-PBM coupled model

A 2D computational fluid dynamics (Eulerian–Eulerian) multiphase flow model coupled with a population balance model (CFD-PBM) was implemented to investigate the fluidization structure in terms of entrance region in an industrial-scale gas phase fluidized bed reactor. The simulation results were compared with the industrial data, and good agreement was observed. Two cases including perforated distributor and complete sparger were applied to examine the flow structure through the bed. The parametric sensitivity analysis of time step, number of node, drag coefficient, and specularity coefficient was carried out. It was found that the results were more sensitive to the drag model. The results showed that the entrance configuration has significant effect on the flow structure. While the dead zones are created in both corners of the distributors, the perforated distributor generates more startup bubbles, heterogeneous flow field, and better gas–solid interaction above the entrance region due to jet formation.

Model-based analysis of the impact of the distributor on the hydrodynamic performance of industrial polydisperse gas phase fluidized bed polymerization reactors

A two dimensionally Eulerian–Eulerian multiphase flow model coupled with a population balance modeling (CFD–PBM) simulation was implemented to investigate the fluidization structure in an industrial scale gas phase polymerization reactor (FBR). Direct quadrature method of moments (DQMOM) was employed in this model to solve the PBM. Two cases including perforated distributor and complete sparger have been applied to examine the flow structure through the bed. A simulation of the reactor with perforated distributor was performed first to validate and evaluate the impact of distributor's characteristics on the fluidization behaviors. The predicted results were in good agreement with the industrial data in terms of pressure drop and bed height. The results showed that different heterogeneous flow patterns were created in a perforated distributor, due to more kinetic energy and jet formation above the distributor. A dead zone is expected to be formed near the corners of the perforated distributor. In addition, the cluster formation is expected to be decreased in comparison with the complete sparger plate distributor. Furthermore, the results predicted bigger bubble diameter in the case of the perforated distributor by using an image processing technique. The information obtained from this study could be important to assure efficient industrial operations of FBRs.

Fluid bed characterization using Electrical Capacitance Volume Tomography (ECVT), compared to CPFD Software's Barracuda

Being able to accurately predict the performance and operation of multiphase flow systems continues to be a significant challenge. In order to continue the advancement of knowledge and to develop better models, a 10 cm diameter fluidized bed of 185 μm glass beads was used along with an Electrical Capacitance Volume Tomography (ECVT) sensor and high speed pressure measurements. Three dimensional images of the gas–solid flow structure were obtained and analyzed as well as frequency information from the high speed pressure transducers. The experimental data was then compared to four computational models performed with CPFD Software's Barracuda code exploring different techniques to handle the perforated distributor plate. • Barracuda CFD model results were compared to ECVT and pressure measurements. • Four different methods were used to model the distributor plate. • The results indicate that modeling the plenum produces the most accurate model as compared to experiments.

Design methodology for fluidized bed carbon nanotube synthesis

Carbon nanotubes constitute a unique class of carbon materials with exceptional mechanical and thermal properties by virtue of which significant breakthroughs have been possible in various fields. The increasing breadth of applications necessitates the mass production of high-quality nanotubes and a viable technology to accomplish the same. Fluidized bed technology has demonstrated significant potential to cater to high-volume nanotube production by virtue of its benefits such as isothermal operation with high heat and mass transfer rates. A suitable design approach for the fluidized bed reactor is necessary to realize its manifold advantages. The present paper proposes an organized methodology for the design of a fluidized bed synthesis of carbon nanotubes by taking into consideration the complex hydrodynamics and the diffusion of carbon into the nanosized iron catalyst to nucleate nanotubes. The authors further extend the calculations to the design of a perforated gas distributor to ensure uniform fluidization so as to enhance mass transfer to the catalyst support. The authors present typical results obtained using the methodology for nanotube synthesis and depict the distributor design for the same.

EXPERIMENTAL STUDY OF COATING IN A BOTTOM SPRAYED FLUIDIZED BED

Several investigations have been devoted towards understanding the coating process in fluidized beds. Most of these studies focused on spraying liquid droplets over the bed. However, due to the complexity of these systems, more investigations are still required to quantify the effect of operating conditions on the coating criteria. The present work aims at fundamentally understanding and precisely determining the effect of different operating conditions on coating quality in a jetting fluidized bed where the coating agent is sprayed as liquid droplets into the bed. A 3-D fluidized bed with a spraying nozzle situated in the middle of a perforated distributor plate was used for the experimental study of the effect of the operating condition on the coating quality. Results from the experimental part showed that at maximum jet gas flow rate which the jet didn't turn into a spout and turbulent stage of fluidization the coating quality improves, but there is a limitation for the binder flow rate(NAR=4.0E-5) which is recognized in this study and could be use for any fluidized bed coater in the same condition. Based on the experimental results, an empirical function was derived to predict the coating efficiency in different operating conditions and this function also could be used in the mathematical model.

Bed Expansion – Extending Correlations for Fluidized Beds with Inserts to Open Fluidized Beds

AbstractBed expansion occurs during the operation of gas‐fluidized beds and is influenced by particle properties, gas properties and distributor characteristics. It has a significant bearing on heat and mass transfer phenomena within the bed. A method of predicting bed expansion behavior from other fluidizing parameters would be a useful tool in the design process, dispensing with the need for small‐scale trials. This study builds on previous work on fluidized beds with vertical inserts to produce a correlation that links a modified particle terminal velocity, minimum fluidizing velocity and distributor characteristics with bed voidage in the relationship with P as the pitch between holes in the perforated distributor plate.

Experimental study and particle population modeling of coating in a jet-fluidized bed

The present work focuses on the study of a bottom-spray fluidized-bed coater in the absence of any liquid (solvent) evaporation. The main objective is to point out and model the effect of operating conditions on the coating efficiency and the coating mass content distribution of particles. A fluidized bed with a bottom-placed spraying nozzle situated in the middle of a perforated distributor plate was used. The experimental results showed that increasing the jet and fluidizing gas flow rates improve the quality of coating, but there is a limitation for the binder flow rate which is dependent on the bed size and jet gas flow rate. Based on the experimental results, an empirical function was derived to predict the coating efficiency in different operating conditions and this function was also used in the mathematical model. Furthermore, a mathematical model was derived based on the population balance equations for two different zones in the bed. The model could predict the coating mass content distribution and the effect of different operating conditions during the process.

Effect of air distributor on the fluidization characteristics in conical gas fluidized beds

The effect of an air distributor on the fluidization characteristics of 1 mm glass beads has been determined in a conical gas fluidized bed (0.1 m-inlet diameter and 0.6 m in height) with an apex angle of 20‡. To determine the effect of distributor geometry, five different perforated distributors were employed (the opening fraction of 0.009–0.037, different hole size, and number). The differential bed pressure drop increases with increasing gas velocity, and it goes from zero to a maximum value with increasing or decreasing gas velocity. From the differential bed pressure drop profiles with the distributors having different opening fractions, demarcation velocities of the minimum and maximum velocities of the partial fluidization, full fluidization, partial defluidization and the full defluidization are determined. Also, bubble frequencies in the conical gas fluidized beds were measured by an optical probe. In the conical bed, the gas velocity at which the maximum bed pressure drop attained increases with increasing the opening fraction of distributors.