Perforated Plate Distributor Research Articles

Study on the uniform flow in adsorption device with perforated plate distributor

The adsorption device is widely used in the purification of impurity-containing wastewater, which is of great significance. However, the problem of non-uniform distribution of liquid in the packed bed has a large impact on the adsorption process. In the current study, CFD is used to simulate the fluid flow state during the adsorption process based on the physical modelling of the adsorption device, where the packed bed is modelled as a porous medium. By studying the effect of hole distribution, perforation rate, thickness and installation position of the perforated plate on flow uniformity and bed pressure drop, the influencing factors affecting the uniform distribution of fluid and pressure drop are discussed. Results show that changing the hole array did not have a significant effect on the fluid uniformity. When the perforation rate of the distributor is 15–29.4 %, the pressure drop is smaller and the flow distribution uniformity is better. The non-uniformity of flow field decreases first and then increases continuously with the increasing of the thickness. When the thickness of the perforated plate is between 10 and 30 mm, the overall performance is the best. Increasing the distance between the perforated plate and the inlet can reduce the impact strength of high-speed fluid on the perforated plate and improve the flow uniformity and increasing the inlet flow rate of the fluid can improve the uniformity of the flow field within a certain range, but it will increase the fluid flow loss.

Structural Improvement and Numerical Simulation of a Perforated Distributor in an Adsorption Tower

AbstractA “closed” perforated plate distributor was proposed to improve the gas distribution in an industrial adsorption tower. Compared with the industrial perforated plate distributor, the designed distributor restricts the space for the disordered movement of gas under the perforated plate. The new distributor effectively converts the gas from the initial axial flow on the inlet section to the axial flow on the tower section to improve the gas uniformity. In addition, the gas velocity at the edge of the inlet cross section of the adsorbent bed is increased by opening holes on the bottom plate. The uniformity of gas distribution is further improved. The simulation method in this study and the distribution performance of the “closed” perforated plate distributor have been verified by experiments.

Gas holdup, bubble size distribution, and mass transfer in an airlift reactor with ceramic membrane and perforated plate distributor

AbstractThe airlift reactor is one of the most commonly used gas–liquid two‐phase reactors in chemical and biological processes. The objective of this study is to generate different‐sized bubbles in an internal loop airlift reactor and characterize the behaviours of the bubbly flows. The bubble size, gas holdup, liquid circulation velocity, and the volumetric mass transfer coefficient of gas–liquid two‐phase co‐current flow in an internal loop airlift reactor equipped with a ceramic membrane module (CMM) and a perforated‐plate distributor (PPD) are measured. Experimental results show that CMM can generate small bubbles with Sauter mean diameter d32 less than 2.5 mm. As the liquid inlet velocity increases, the bubble size decreases and the gas holdup increases. In contrast, PPD can generate large bubbles with 4 mm < d32 < 10 mm. The bubble size and liquid circulation velocity increase as the superficial gas velocity increases. Multiscale bubbles with 0.5 mm < d32 < 10 mm can be generated by the CMM and PPD together. The volumetric mass transfer coefficient kLa of the multiscale bubbles is 0.033–0.062 s−1, while that of small bubbles is 0.011–0.057 s−1. Under the same flow rate of oxygen, the kLa of the multiscale bubbles increases by up to 160% in comparison to that of the small bubbles. Finally, empirical correlations for kLa are obtained.

Computational fluid dynamics simulations to improve performance characteristics of a manifold having a central inlet and outlet

In the present work, performance/flow characteristics (namely, the effect of operating parameters like pressure on flow patterns, pressure drop, and the extent of flow uniformity) and transport phenomena of a manifold (header tube assembly) having an inlet and outlet at the center are carried out on a macroscale geometry using CFD simulations. In this study, an existing design available in the published literature (with high flow non-uniformity) was considered and an optimized design (with minimum flow non-uniformity) was developed. The optimization is performed by incorporating a perforated plate (distributor) inside the top header of the manifold. First, CFD simulations for different configurations of the existing design with the perforated plate have been performed for a pressure of 10 bar with steam as a working fluid, and an optimized configuration having a minimum flow non-uniformity of less than 3% is obtained. CFD simulations for both the existing design and optimized design are then performed for a pressure range (10 ≤ p ≤ 70 bar) and the corresponding Reynolds number (Re) range (2.82E+05 ≤ Re ≤ 2.82E+06) with steam as the working fluid. The extent of non-uniformity (ENU) and pressure drop for the existing design (without a distributor) and optimized design (with a distributor) have been analyzed and compared. The optimized design gives the near uniform flow (∼1–4%) for all pressures and Reynolds numbers considered. An empirical correlation relating the friction factor (as per the Chilton–Colburn analogy) and Re has been developed for both designs (with and without a distributor). The predicted friction factors are compared with the present CFD predictions, and experimental data of the shell and tube heat exchanger are available in the published literature. A good agreement within a 10–15% deviation has been observed. Based on the Chilton–Colburn analogy, a correlation for the Nusselt number is obtained from the friction factor correlations for both with and without distributor cases. The correlations for friction factors were found to be valid under any operating conditions for a pressure drop range within 0.05 < ∆p < 1.8 bar irrespective of the design of the distributor, assuming that the manifold is able to withstand the pressure drops in the given range.

Flow characteristics of air separation in VPSA process with radial flow adsorber

Radial flow adsorbers are widely applied to large-scale air separation. The low pressure drops and flow uniformity in radial flow adsorbers (RFAs) are of great importance for high quality O2 enrichment. However, the insufficient consideration of annular channel structure and simplification of perforated plate distributor in existing methods limit a further optimization of uneven flow in the RFAs. In this study, the detailed perforated plate distributor configuration (hole arrangement and porosity) is adopted to investigate the flow field in the RFAs more deeply. In addition, the effects of three types of annular channels on pressure drop profiles rarely studied intensively in previous publications are also discussed. The simulated results agree well with static and dynamic experiments in terms of N2 adsorbed amount and breakthrough time, indicating the feasibility of proposed model for RFAs simulation. Thereafter, it can be found that for the adsorber with a convergent annular channel, the utilization ratio of the adsorbent and desorption efficiency can reach up to 27.58% and 91.64% respectively, accompanied by average 96.61% pressure drop uniformity. Moreover, the impact of hole arrangement is insignificant in the case of a regular arranged cylindrical holes on the distributor. However, the nonuniform porosity makes the adsorption area shift from the bottom to upper of the adsorber by changing the flow resistance. For the adsorber with convergent annular channel and optimized arrangement of distributor, the whole flow uniformity can be improved by 24.69%.

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.

Attrition rate of CO2 adsorbent in bubbling fluidized beds

Particle attrition induced by bubbles in a bubbling fluidized bed was investigated with CO2 adsorbent particles (0.128 mm in diameter, 1770 kg/m3 in apparent density). The theoretical relationship between the rate of attrition by gas jets on the perforated plate distributor (Ra,j) and the rate of attrition by bubbles (Ra,b) in the bed was revealed that the rate constant of attrition by bubbles (Ka,b) was the product of the rate constant of attrition by gas jets (Ca) and dimensionless particle diameter (dpbc). An attrition tube (0.035 m-i.d.) using the perforated-plate distributor designed for reducing the attrition by gas jets was employed as the fluidized bed, and the air as the fluidizing gas. The mode of attrition by bubbles was identified as abrasion. The rate of attrition by bubbles (Ra,b) was linearly proportional to the power given to the bed solids by bubbles. The top size of the fine particles formed by attrition (dpm,ab) increased exponentially with an increase of bed mass and gas velocity. The effects of temperature, pressure, and area of internal surface contacting particle bed on the Ra,b and dpm,ab were negligible under the tested condition. Empirical relationships on Ra,b and dpm,ab were proposed based on the experimental data. When both jet and bubble attrition were significant, there existed the static bed heights that gave respectively the minimum attrition rate and the minimum of the top size of fine particles formed by attrition. Each optimal static bed heights increased with an increase of the orifice jet velocity of the perforated plate distributor.

Experimental investigation on the distribution uniformity and pressure drop of perforated plate distributors for the innovative spray-type packed bed thermal storage

As an innovative thermal energy technology, the spray-type packed bed has advantages of high efficiency and low cost. A liquid distributor is the key component for the spray-type packed bed for scattering heat-transfer liquid drops evenly. In this study, the distribution performance and pressure drop of the perforated plate distributors of different orifice diameters were studied experimentally. The experimental results indicate that orifice diameter has a greater effect on the distribution performance compared to flow rate. With an increase in flow rate, the flow pattern through the distributor changes from the uncovered drop to the covered drop and then to the jet flow. The covered drop pattern shows the best performance with a good distribution and a small pressure drop simultaneously, which is the design and optimization principle of the distributor for a spray-type packed bed.

Rate of CO2 adsorbent attrition induced by gas jets on perforated plate distributors in bubbling fluidized beds

Particle attrition is a major challenge when handling bulk solid materials with fluidized beds due to its ability to cause particle loss. Herein, the particle attrition induced by the gas jets on a perforated plate distributor in a bubbling fluidized bed was investigated for CO2 adsorbent particles. An attrition tube, which used air as the fluidizing gas, was used as the fluidized bed. At a constant fluidizing velocity, the initial static bed height and orifice gas velocity were considered as variables. It was confirmed that abrasion dominated the particle attrition. The trend indicating the change in the maximum size of the particles (dpm,a) formed by attrition followed that of the attrition rate (i.e., the formation rate of fine particles via attrition). A new stirring factor that combined the model developed by Werther and Xi with the original stirring factor adequately explained the effect of the static bed height on both the attrition rate and dpm,a when the initial static bed height was greater than the length of the orifice gas jet that penetrated the bed. The attrition rate increased linearly with the new stirring factor. However, dpm,a increased exponentially with the new stirring factor. Relationships were successfully proposed to enable the estimation of the attrition rate and dpm,a for the CO2 adsorbent particles. This study provided the evidence indicating the significance of the effect of bed height on particle attrition induced by the gas jet on the distributor. Moreover, proper models for correlating the attrition rate and the maximum size of the fine particles formed by attrition in the bubbling fluidized bed were provided.

CFD Analysis of the Fluidised Bed Hydrodynamic Behaviour inside an Isothermal Gasifier with different Perforated Plate Distributors

The hydrodynamic behaviour of gas-solid mixtures inside Bed Fluidised Beds (BFB) gasifiers has a major impact on the gasification process due to particles - gas and particle - particle contact mechanisms. The Discrete Phase Model DPM with Multiphase Particle-in-Cell method MPPIC was used as a CFD approach to study the hydrodynamic behaviour of an 800 height x 83 mm φ prototype fluidised bed gasifier with 4 different perforated plate distributors. In terms of bubble forming, pressure drop and superficial velocity, the type D distributor, i.e. triangular, had the best performance among the other types and in turn better bed height and bed movement, thus allowing best fluidisation performance as a consequence of better flow distribution.

Experimental investigation of maldistribution in vertical plate falling film tower

ABSTRACTFalling film towers are popular in process industries due to moderate air side pressure drop, less energy ingesting liquid distribution and easy cleanup features. Two major limitations of falling film towers are the uneven distribution of liquid across solid surfaces (maldistribution) and contraction of falling liquid film on the solid surface (poor wetting). Maldistribution of liquid is primarily dependent on the type of liquid distributor and scope of liquid flow (slit opening) across solid surfaces. In the current communication; the influence of liquid distributor on maldistribution problem for vertical plate falling film tower has been experimentally investigated. Four types of liquid distributors: plain tube, spray nozzle, perforated plate, and branch tube distributor have been tested. Effect of parameters: slit opening, liquid flow rate, and the number of plates on maldistribution are also explored. It is found that branch tube distributor is best suited for vertical plate falling film tower application.

Effect of distributor on fluidized bed hydrodynamics

In this work, the effect of distributor type on fluidized bed hydrodynamics was studied by taking into account time, frequency, and state space domains. For this purpose, pressure fluctuations were measured in a fluidized bed with 0.15 m diameter and the experiments were carried out for three different types of distributors (perforated plate, bubble cap, and porous plate) at different sizes and various superficial gas velocities and particle sizes. Time domain analysis demonstrated that while the initial bubble size on the bubble cap distributor is greater than that on the perforated plate, the standard deviation of pressure fluctuations is greatest in a bed equipped with the porous plate, followed by the perforated plate and then the bubble cap distributor. Based on the current analysis and in view of the frequency domain analysis, it was found that the contribution of finer structures (small bubbles and clusters) is highest for a porous plate, followed by a bubble cap and then a perforated plate distributor. Also, according to the S‐statistic method, it was concluded that the S‐test is a reliable method for detection of differences between hydrodynamic situations of fluidized beds, while different types of distributors were used.

Study on recovery of valuable metals from waste mobile phone PCB particles using liquid-solid fluidization technique

In this paper, an effort was made to separate the valuable metals from waste mobile phone printed circuit board (PCB) particles using liquid-solid fluidization technique. Based on the mechanical liberation characteristics of waste mobile phone PCBs, four closely sieved particles having a granularity, respectively, of 0.075–0.106, 0.106–0.18, 0.18–0.25 and 0.25–0.35mm were chemically analyzed and charged into the fluidized bed to study the fluidization separation behavior. The minimum fluidization velocities and terminal settling velocities of single components were served as an important tool for the evaluations of the experimental data. The results showed that, in the process configuration, the fluidization separation was effective within each limited range of particle size with proper control on water velocity. When the water velocity was in the appropriate range, higher metal yield and grade could be obtained. The calculated minimum fluidization velocities and terminal settling velocities of waste mobile phone PCB particles were in reasonable agreement with the actual operating water velocities. Additionally, the influence of the porosity of perforated plate distributor and the height of the fluidized bed on the metal grade and yield was also discussed. The application of liquid-solid fluidization technique in beneficiation of waste mobile phone PCB particles is expected to be one of the important developmental directions.

Investigation of the radial effect on the transition velocities in a bubble column based on the modified Shannon entropy

A new parameter for flow regime identification in a bubble column based on the calculation of the Shannon entropy (SE) from different parts of the signal was developed. The bubble column (0.15m in ID) was equipped with a perforated plate distributor (14 holes, Ø 4×10−3m) and operated with an air-deionized water system at ambient conditions. The newly introduced dimensionless ratio of minimum SE to maximum SE was capable of identifying the main transition velocities Utrans at three different dimensionless radial positions (r/R): 0.0 (core), 0.63 (inversion point of axial liquid velocity) and 0.88 (annulus).In the column’s core the new dimensionless SE ratio identified successfully three Utrans values at 0.034, 0.089 and 0.134m/s. They marked the end of the gas maldistribution regime, the onset and the end of the churn-turbulent flow regime, respectively. Three Utrans values (at 0.045, 0.089 and 0.124m/s) were also identified in the annulus. However, the second Utrans value identified the boundary between the first and second transition sub-regimes. The third Utrans value distinguished the onset of the churn-turbulent flow regime. It was found that in the core both the transition and churn-turbulent flow regimes started earlier.At r/R=0.63 the end of the gas maldistribution regime was shifted to a somewhat higher Utrans value (0.067m/s). The second transition sub-regime began at 0.101m/s, whereas the onset of the churn-turbulent regime occurred at 0.124m/s.

Study of the Hydrodynamics and Mass Transfer Coefficient in a 2D Mimicked FT Slurry Bubble Columns for Alternative Clean Energy and Chemical Production

Abstract Bubble columns are widely used for contacting gas–liquid and gas–liquid–solid mass transfer/chemical reactions. Gas distributor is the most important accessory because it decides the bubble size/rise velocity and gas distribution. In this study, the effect of distributor design on hydrodynamics and mass transfer coefficient are studied at different operating conditions of height to diameter ratio, solid loading, and superficial gas velocity The overall gas holdup, is studied experimentally using a rectangular slurry bubble column operating at ambient temperature and pressure, using liquid paraffin (C9–C11), three heights to diameter ratios (6, 7.5 and 10) and silica as a solid phase (0 %, 9 % and 25 %) with oxygen as gas phase. Two types of distributor were used, perforated plate and ring type. The results showed that the overall gas holdup increased by increasing gas velocity and decreased by increasing height to diameter ratio and solid loading. Also, it is found that the perforated plate distributor gave a higher gas hold up than ring distributor at gas velocity higher than 0.03 m/sec. The following correlations are obtained: Plate distributor at presence of silica particles: ε g = 1.343 U g 0.0612 − 0.00891 ε s − 0.374 − 0.702 L D 0.041 4.904 − 0.0251 $$\eqalign{{{\rm{\varepsilon}}_{\rm{g}}} =& {\left({1.343{\rm{U}}_{\rm{g}}^{0.0612} - 0.00891{\rm{\varepsilon}}_{\rm{s}}^{- 0.374} - 0.702{{\left({{{\rm{L}} \over {\rm{D}}}} \right)}^{0.041}}} \right)^{4.904}}\cr& - 0.0251}$$ Ring distributor at presence and absence of silica particles: ε g = 0.216 U g 0.297 − 0.354 ε s 1.4671 − 0.127 L D 0.147 1.1206 + 0.058 $$\eqalign{{{\rm{\varepsilon}}_{\rm{g}}} = &{\left({0.216{\rm{U}}_{\rm{g}}^{0.297} - 0.354{\rm{\varepsilon}}_{\rm{s}}^{1.4671} - 0.127{{\left({{{\rm{L}} \over {\rm{D}}}} \right)}^{0.147}}} \right)^{1.1206}} \cr&+ 0.058}$$ There is a good agreement between experimental and predicted values with a percent of error less than 2 %. It has been found that the mass transfer coefficient is higher for ring distributor than the perforated plate and growing higher for heterogeneous flow regime and higher solid loading.

Mixing Characteristics and Bubble Behavior in an Airlift Internal Loop Reactor with Low Aspect Ratio

The present study summarizes the results of macro- and micro-mixing characteristics in an airlift internal loop reactor with low aspect ratio (H/D≤5) using the electrolytic tracer response technique and the method of parallel competing reactions respectively. The micro-mixing has never been investigated in airlift loop reactors. The dual-tip electrical conductivity probe technique is used for measurement of local bubble behavior in the reactor. The effects of several operating parameters and geometric variables are investigated. It is found that the increase in superficial gas velocity corresponds to the increase in energy input, liquid circulation velocity and shear rate, decreasing the macro-mixing time and segregation index. Moreover, it is shown that top clearance and draft diameter affect flow resistance. However, the bubble redistribution with a screen mesh on the perforated plate distributor for macro-mixing is insignificant. The top region with a high energy dissipation rate is a suitable location for feeding reactants. The analysis of present experimental data provides a valuable insight into the interaction between gas and liquid phases for mixing and improves the understanding of intrinsic roles of hydrodynamics upon the reactor design and operating parameter selection.

Magnetic resonance studies of jets in a gas–solid fluidised bed

Magnetic resonance imaging (MRI) has been used to study the behaviour of jets at the distributor of a 50mm diameter fluidised bed of 0.5mm diameter poppy seeds. Two perforated-plate distributors were examined, containing either 10 or 14 holes, each 1mm diameter. Ultra-fast MR imaging was able to show the transient nature of the upper parts of the jets, where discrete bubbles are formed. Imaging in 3D showed that the central jets were the longest for flow rates below minimum fluidisation. Above minimum fluidisation, the outer jets, nearest the wall of the fluidised bed, arched inward towards the central axis. In this latter case, interpretation of the time-averaged 3D image required the use of ultra-fast MR imaging to identify the approximate height above the distributor at which discrete bubbles were formed. The apparently continuous void extending along the central axis above this height in the time-averaged 3D image was thus identified, using ultra-fast MR imaging, as representing the averaged paths of released bubbles. Time-averaged MR velocity mapping was also used to identify dead zones of stationary particles resting on the distributor between the jets. The dead zones could be observed when the superficial velocity of the gas approached minimum fluidisation, but they were smaller than those observed at lower gas superficial velocity. Comparable images of a single jet through 1.2mm diameter poppy seeds from MRI and electrical capacitance volume tomography (ECVT) are also demonstrated.

Two dimensional fluidised bed reactor: Performance of a novel multi-vortex distributor

The influence of the distributor configuration on interphase mass transfer, gas axial dispersion and bubble size was studied in a pseudo 2-D fluidised bed reactor for two types of distributor configurations; a novel multi-vortex (MV) distributor with tubes directed vertically and horizontally at different heights and a standard perforated plate distributor (baseline). The linear inlet velocity ( U 0) ranged between 0.1 m/s and 0.35 m/s, with air as fluidising medium at ambient conditions. The ozone decomposition reaction over Fe 2O 3 impregnated FCC catalyst was used as an indirect measure for the performance of the FBR and it was found that the MV distributor causes a significant improvement (15% average) in the conversion efficiencies at all velocities tested. Bubble size measurements (using two separate techniques) indicated larger bubbles for the MV distributor, while the visual bubbling to turbulent transition boundary ( U c ) for the MV distributor was found to be lower than the baseline distributor. The interphase bubble-emulsion mass transfer was quantified using the model derived by Thompson et al. [32] and was found to be 52% higher for the MV distributor than the baseline distributor. In addition the MV distributor exhibited near plug flow characteristics at velocities exceeding U c , while this was not the case for the baseline distributor.

Motion of a large object in a bubbling fluidized bed with a rotating distributor

This work studies the effect of a low-frequency rotating distributor on the motion of a large object immersed in a bubbling fluidized bed. The object size and density differ from those of the inert solids that conform the bed. Examples of objects moving in a bubbling fluidized bed include passive particles, catalysts and reactants. The rotation modifies the bed dynamics in the surroundings of the distributor and affects the motion of the object within the bed. A set of experiments was carried out in a lab-scale cylindrical bed, equipped with a perforated plate distributor that can rotate at around 1 Hz, for different bed aspect ratios, gas velocities, and object characteristics. Sizes were far larger than that of the solids of the dense phase and densities ranged from half the bed density to values around it. The experiments were video recorded, capturing the surface of the bed from above. As have often been noted, objects might remain in stagnant regions near the distributor and be “lost” or precluded to circulate. This can be avoided in most practical cases forcing the distributor to rotate. Also, the effect of rotation on the circulation time of the objects is presented, showing a general reduction of large circulation times.

CFD studies of solids hold-up distribution and circulation patterns in gas–solid fluidized beds

Numerical results for a gas-fluidized bed using a 2D Eulerian model including the kinetic theory for the particulate phase were provided. The circulation patterns for various operating conditions were discussed. Modeling parameters of drag function, algebraic and transport equations of granular temperature, frictional stress model, turbulent model and discretization scheme were investigated for a bed with different gas distributors and a slotted draft tube. CFD results showed that the drag model is an important hydrodynamics parameter for gas-fluidized beds with various gas distributors. Transport and algebraic equations for granular temperature should be utilized, respectively, for beds including partial and complete sparging at U g = 2.18 m/s. Frictional stresses play an important role for the beds containing partial sparging with and without draft tube. Discretization schemes should be examined to achieve better results. The Simonin and k– ε turbulent models can improve the CFD results at high gas velocities. Considering perforated plate distributor improves the results.