Air Distributor Research Articles

INFLUENCE OF COMPRESSED HEATED AIR ON EFFECTIVE PERFORMANCE OF THE PNEUMOENGINE WORKFLOW

The experimental data on the change in speed characteristics of effective indicators of the four-cylinder piston air motor D/S = 76/66 mm with a spool air distributor with unheated and heated compressed inlet air are considered. It is shown that heating the compressed air has a positive effect on the energy and economic performance of the workflow: increased power and torque, reduced hours and specific air consumption significantly increases the effective efficiency.

Position and posture determination of a large dense object in a fluidized bed

An innovative method using a micro-three-dimensional acceleration sensor and a micro-three-dimensional gyroscope to trace the motion behavior of a large object in the dense zone of a fluidized bed is proposed here. By placing a self-designed particle spy module, namely particle tracing sensor (PTS), inside an object, the translational velocity and angular velocity, as well as the posture of the object during the motion process can be detected. The method is validated by testing the displacements of a spherical object with diameter of 40mm during freefall and by testing its attitude angles during rotation. Then several PTSs, served as object spies delivering in situ information they detect, are utilized to study the motion behavior of spherical and non-spherical objects on the inclined air distributor of a fluidized bed. Findings indicate that the method is capable of tracing the motion behavior of dense objects in the bottom of a bed. The smallest size of the object it can detect is 30mm×20mm×20mm and the maximum tracking time is 10min.

Air Distributor Designs for Fluidized Bed Combustors: A Review

Air Distributor Designs for Fluidized Bed Combustors: A Review

Air Distributor Designs for Fluidized Bed Combustors: A Review

Fluidized bed combustion (FBC) has been recognized as one of the suitable technologies for converting a wide variety of biomass fuels into energy. One of the key factors affecting the successful operation of fluidized bed combustion is its distributor plate design. Therefore, the main purpose of this article is to provide a critical overview of the published studies that are relevant to the characteristics of different fluidized bed air distributor designs. The review of available works display that the type of distributor design significantly affects the operation of the fluidized bed i.e., performance characteristics, fluidization quality, air flow dynamics, solid pattern and mixing caused by the direction of air flow through the distributors. Overall it is observed that high pressure drop across the distributor is one of the major draw backs of the current distributor designs. However, fluidization was stable in a fluidized bed operated at a low perforation ratio distributor due to the pressure drop across the distributor, adequate to provide uniform gas distribution. The swirling motion produced by the inclined injection of gas promotes lateral dispersion and significantly improves fluidization quality. Lastly, the research gaps are highlighted for future improvement consideration on the development of efficient distributor designs.

Simulation of air velocity in a vertical perforated air distributor

Perforated pipes are utilized to divide a fluid flow into several smaller streams. Uniform flow distribution requirement is of great concern in engineering applications because it has significant influence on the performance of fluidic devices. For industrial applications, it is crucial to provide a uniform velocity distribution through orifices. In this research, flow distribution patterns of a closed-end multiple outlet pipe standing vertically for air delivery in the horizontal direction was simulated. Computational Fluid Dynamics (CFD), a tool of research for enhancing and understanding design was used as the simulator and the drawing software SolidWorks was used for geometry setup. The main purpose of this work is to establish the influence of size of orifices, intervals between outlets, and the length of tube in order to attain uniformity of exit flows through a multi outlet perforated tube. However, due to the gravitational effect, the compactness of paddy increases gradually from top to bottom of dryer, uniform flow pattern was aimed for top orifices and larger flow for bottom orifices.

Particle Image Velocimetry of a Swirling Fluidized Bed at Different Blade Angles

AbstractThe particle motion within a stable swirling operation regime of a fluidized bed is investigated. Particle image velocimetry was used to elaborate the hydrodynamics of multi‐sized particles fluidized at different air distributor blade angles. The experimental results revealed that the superficial velocity is the most prominent aspect affecting the hydrodynamics of a swirling fluidized bed (SFB) followed by the bed weight, particle shape, and blade inclination angle. Particles of different sizes and shapes fluidized well in the SFB which emphasizes its superiority over contemporary techniques. The slug‐wavy regime in the SFB is promising and has considerable potential, especially for diffusion‐controlled reactions and processes in the industry. The particle velocity increased with air flow rate at shallow bed height but decreased with bed weight.

Force characteristic of a large dense object in a fluidized bed equipped with an inclined air distributor

Large dense objects are easily stagnated over the distributor during fluidization, having serous influence on bed performance. In this study, three-dimensional modeling of the gas–solid flow in a fluidized bed equipped with an inclined air distributor is conducted by means of two-fluid model to explore the characteristics of the force acting on a stagnant object in bottom bed. Images of the instantaneous particle concentration demonstrate the inhomogeneity of transverse gas–solid flow in bottom bed. The influences of gas velocities on the force fluctuation characteristic for object in various positions of the bottom bed are evaluated. Statistical, spectral and wavelet analysis methods are applied to disclose the time-averaged and instantaneous characteristic of the forces. Results show that with the increasing of gas velocity, the transverse movements of bubbles and particles are both intensified, and the latter is more significant. The dominant frequency of the forces on an object along the inclined direction is 0.3–0.5Hz, which is smaller than that perpendicular to the distributor of 1.2Hz.

高Flux 型中空糸膜モジュール「ピューリア®GL」

Kuraray has developed and launched a new hollow fiber membrane module, “GL”. This module consists of high permeability hydrophilic PVDF membrane and accordingly is expected to enable higher design flux. Moreover, the physical cleaning process has been improved by employing the one–end–free fiber structure and an air and water distributor located at the center of the module. It was proven in a verification test using river surface water that “GL” had twice as high operating flux as conventional modules.

Design and Analysis of Air Distributors and Bed Materials of Fluidized Bed Boiler

This research deals with the design and analysis of the nozzle and bed materials required for fluidized bed boiler. The design parameters (Diameter of the bed particle, Range of the terminal velocities, Minimum Fluidization /Bubbling velocities, Maximum amplitude and steady velocities) were calculated using Microsoft Excel by interpreting and solving various formulas. Best bed material was selected on the basis of their various characteristics like porosity, adhesive or cohesive properties, resistance to flow etc. An important characteristic change of air distributor velocity with combustion chamber temperature has been established. ANSYS was used as a simulation tool for the analysis. Static Structural solver was used to carry out the strength analysis of the designed wind box. Likewise, computational fluid dynamics (CFD) was carried out using FLUENT solver. Air flow inside the wind box and fluidization phenomena was verified using FLUENT. Furthermore, the designed system was checked for its validity by comparing the results from the Excel sheets and theoretical calculations with simulation results. Lastly, correlation between temperature and velocity inside combustion temperature were determined to identify their relationship with each other.

Research of device for air distribution with swirl and spread air jets at variable mode

The research deals with solving the urgent problem of improving the efficiency of air distribution with the swirl and spread air jets to ensure regulatory parameters of the air in industrial premises. The mathematical model of air supply with the swirl and spread air jets in these premises is improved. It is shown that for maximum air distribution efficiency, air should be supplied with the jets that are intensively damped before entering the working area. The design of the air distributor with the formation of swirl and spread air jets, providing intense damping of the velocity and excess temperature of the resulting air flow is developed and investigated. The feature of this design is the ability to feed two supply air jets, the swirl air jet, formed after having passed through plates, and the spread air jet, which comes from the annular slot. This ensures intense mixing of supply air jets of the ambient air and provides the variable mode. Graphic dependencies are built, and theoretical dependencies are derived based on experimental studies that can be used in further engineering computations. The designs of air distributors for air supply with swirl and spread air jets and feeding the supply air jets in the variable mode are developed and protected by patents Ukraine. The economic efficiency of double-jet air distributors compared to the alternatives is shown, specific performance of air distribution is presented.

Experimental study of cluster properties in a two-dimensional fluidized bed of Geldart B particles

The paper presents an analysis of measurement results on cluster properties in a two-dimensional lab-scale cold fluidized bed operating in turbulent and circulating fluidized bed modes. Experiments were carried out with Geldart B particles of (Sauter mean) diameters varying from 0.256mm to 0.440mm. Different particle size distributions and bed mass were used along with different superficial gas velocities in the range of 2.75m/s to 4.00m/s. High-speed images of the bed were taken in a controlled lighting environment. Analysis of the experimental images was conducted to determine the horizontal length scale distribution of the solid clusters along the 3m high CFB. Additionally, the solid hold-up inside the clusters was evaluated. The effects of particle size, bed mass and superficial gas velocity on the measured cluster properties were determined. The solid hold-up of the clusters was correlated to the horizontal length scales of the clusters to estimate the importance of each cluster size in terms of the mass fraction of solids residing in clusters of a specific width range. In the bottom region up to 0.2m from the air distributor, about 5% of the solid mass in clusters was found to reside in structures with horizontal length scales less than 1cm while at 1.2m height the corresponding share was about 10%. This information is relevant for determination of the mesh resolution required to describe all the significant cluster sizes in CFD simulations. The findings of the study on the width distributions of the clusters and the solid concentrations inside the clusters may also be used as a point of comparison with corresponding measures observed in simulations, by which a quantitative validation of CFD results could be made.

Modeling of thermal stresses in a microtubular Solid Oxide Fuel Cell stack

A modeling study was carried out to analyze thermal stresses in a microtubular Solid Oxide Fuel Cell (mSOFC) stack and to estimate thermal expansion of the fuel cells inside the stack. A joint analysis by Computational Fluid Dynamics (CFD) and Computational Structural Mechanics Finite Element Method (FEM) was performed. Temperature profiles generated by the thermo-hydrodynamic model were applied in the thermo-mechanical model to calculate thermal stress distributions in the mSOFC stack. The results yield maximum thermal axial elongation equal to 1.34 mm for the mSOFC stack, while the maximum radial elongation was equal to 0.496 mm. Modeled maximum equivalent (von Mises) stress was equal to 538 MPA in the contact areas of the cylindrical housing and manifold on the fuel inlet side. Based on comparison of the total axial stresses and the residual ones with the material strength it was noticed that the anode and electrolyte layers should not be critically deformed, but there is a risk of damage for cathode layers at chosen fuel cell configurations. A high risk of damage was also noticed for the outer housing, near contact points with manifolds as well as at the air distributor due to large number of cut-outs in the material.

Density-based segregation/separation performances of dense medium gas–solid fluidized bed separator (DMFBS) for coal cleaning and upgrading

Dense medium gas–solid fluidized bed separator (DMFBS) is recognized as a new, alternative technique for coal cleaning and upgrading. Characteristics of the used dense medium (magnetite powder) were studied, and washability of the feeding coal sample was analyzed. A double-layer, stable-pressure air distributor was designed to ensure uniform air distribution for the bed. Fluidization characteristics, including bed pressure drop ΔPB, overall stability of the bed, fluctuation of the bed density, were investigated and the results indicate that the bed can provide favorable fluidization stability and uniform density distribution with suitable gas velocities that allow for coal separation. Segregation/separation performances of DMFBS are mainly dependent on operating gas velocity. Density-based segregation occurred, with optimum segregation efficiency Sash values of 0.65, 0.68, 0.72 and 0.75 were achieved at U = 1.6 Umf for various sized coals. The laboratory-scale separator reduced the ash content from 39.56 to 10.96% and rejected sulfur content from 1.07 to 0.41% for 3–25 mm sized coal. The probable error EP values of 0.075, 0.070, 0.060 and 0.058 g/cm3 were obtained at the separating densities of 1.605, 1.69, 1.76 and 1.83 g/cm3, respectively for various sized coals, indicating that a notable separation performance was achieved.

Heat Transfer of Alumina Sands in Fluidized Bed Combustor with Novel Circular Edge Segments Air Distributor

Fluidized bed combustor, which consists of a reaction chamber, an air distribution plate, uses inert particles, as its bed material. In order to ensure stable operation, it is apparent that the operating velocity of the air should be sufficiently large so that the flow rate through it is relatively undisturbed by the bed pressure fluctuation above it. However, high distributor pressure drop in fluidized bed system is undesirable because it will lead to high energy input in the blower to supply the fluidization air to fluidize the inert sand particles. Thus, the new novel designs of air distributor that consists of circular edge segments that contributed to low pressure drop and improvement of heat and mass transfer in fluidized bed combustor is introduced and will become primary interest of this research. The effects of temperature variations between an electrically heated tube immersed vertically in fluidized bed and alumina particles of various sizes were experimentally studied. In this paper, the data for heat transfer coefficient for an electrically heated vertical tube immersed vertically in fluidized bed combustor consists of alumina particles diameter ranging from (▪= 100, 177 and 250μm) is reported at temperature from 50 oC to 250 oC.

Experimental investigation of hydrodynamics of gas‐solid flow in an internally circulating fluidized bed

Hydrodynamic study of gas and solid flow in an internally circulating fluidized bed (ICFB) is made in this paper using a high‐speed camera and pressure probes for the laboratory 0.3 m × 0.27 m column having an internal draft tube. Experiments were conducted using sand particles of Geldart B and Geldart B‐D groups. At each run the standard pressure‐flow curves for both the draft tube and annular region beds, and the moving wall particle velocity in the annular bed region were measured. The effects of superficial gas velocity, static bed height, and draft tube gap height on pressure drop profiles, solid circulation patterns, and gas bypassing dynamics for the ICFB were investigated extensively. Unlike the conventional CFB, the pressure drop in ICFB is further decreased with superficial gas velocity after the minimum spouting fluidization, followed by yielding a cross‐over in the pressure drop of the annular bed compared to the draft tube. Pressure drop in the draft tube increases with an increase of static bed height and gap height between the draft tube bottom and the air distributor. The gas bypassing fraction increases with an increase in gap height and decreases with increased bed height and mean particle size. The mechanism governing the solid circulation and the pressure losses in an ICFB has been elaborated based on gas and solid dynamics obtained from the experimental data.

Effect of inclined distributor on the motion behavior of a large spherical object in the bottom zone of a fluidized bed

In many applications of the fluidized bed, large and dense objects may be captured in a stagnant zone over the air distributor, having paramount influence on the performance of the bed. Inclined air distributor was commonly used to induce the objects to the discharging hole, ensuring the normal operation of this type of fluidized bed.A set of experiments was carried out to study the residence time distribution (RTD) of the large objects in four lab-scale fluidized beds, each equipped with a certain inclined angle of the air distributor, for various fluidizing velocities. The objects were far larger than the fine particles of the dense phase and their densities ranged from 2 to 3.5 times of the fixed bed density. Results show that increasing the inclined angle decreases the residence time of the object in a fluidized bed, and the effect becomes significant at a low fluidization velocity. Numerical simulations based on Eulerian–Eulerian model were taken to investigate the characteristic of the dynamic force acted on the stagnant objects over the air distributors. It indicates that the transverse bubble and particle movements due to the existence of the inclined air distributor and the oriented air caps primarily cause the periodical force fluctuation on the object along the inclination direction. The drag force and buoyancy force acted on the object from the surrounding gas–solid flow and the friction force from the distributor vary with the inclined angles, resulting in larger motion velocities and longer residence times for the objects in the fluidized beds with small inclined angle distributors.

CFD Simulation of Air Flow through the Annular Distributor of a Swirling Fluidized Bed

Fluidized beds are widely used in a variety of industrial processes. The air distributor being an integral part of the fluidized bed, the air flow characteristic through it is of great importance as far as the design and working of it is concerned. Inappropriate design will lead to an incomplete fluidization and improper mixing of the air and bed particles. The current study was carried out to investigate the flow characteristics and predict non-uniformity in flow through the annular distributor of a Swirling Fluidized Bed and its variation with various aspects of the distributor like blade overlap angle and blade inclination. In this study, the commercial CFD package FLUENT 6.3 was used for analysis. The velocity and pressure profiles for various blade designs were investigated at the distributor outlet based on several operating variables including air inlet velocities, blade overlap angles (9o, 12o, 15o, and 18o), blade inclinations (10oand 15o), along with variations in the opening between the distributor blades. The most significant finding of this work is that the fluid tends to flow through a path with least resistance. The flow path with the largest cross section area and shortest path length has been identified and explains the velocity profile at blade exit.

Co-firing of pressed sugar beet pulp with coal in a laboratory-scale fluidised bed combustor

Relatively cheap, poor quality, unprepared biomass materials can be difficult to burn efficiently on a large commercial scale because of their variable composition, relatively low calorific values and high moisture contents. Consequently it is often necessary to co-fire these materials with a hydrocarbon support fuel to ensure stable and efficient combustion. Fluidised bed combustion (FBC) is a promising method for burning mixtures of fuels with widely differing individual characteristics although there is a need for further information on the “optimum” conditions for efficient operation as well as on the proportions of support fuel which should be used in particular applications. This paper is therefore concerned with co-firing of coal with pressed sugar beet pulp, (a solid biomass with an average moisture content of 71%), in a lab scale (<25kW net thermal input) fluidised bed combustor.The project was undertaken in collaboration with British Sugar plc. who operate a large coal-fired fluidised bed, with a nominal thermal rating of 40MW, to generate hot combustion gases for use in subsequent drying applications. The combustion characteristics of different coal and pressed pulp mixtures were investigated over a wide range of operating conditions. For stable combustion the maximum proportion of pulp by mass in the blended fuel was limited to 50%. However under these co-firing conditions a fixed bed temperature can be achieved with 20% lower fluidising air (when compared with coal alone) since evaporation of the moisture in the pressed pulp provides additional cooling of the bed. This reduction in excess air will be beneficial for the output of the full scale plant at British Sugar since at present the flow rate of the fluidising air and hence the amount of coal which can be burnt is limited by high pressure drops in the bed air distributor system. The pressed pulp has relatively low nitrogen levels and hence a further benefit of co-firing is that NOx emissions are reduced by about 25%.Agglomeration of the bed can be a problem when co-firing biomass because of the formation of “sticky” low melting point alkali metal silicate eutectics which result in subsequent adhesion of the ash and sand particles. Consequently, longer term co-firing tests were undertaken with a 50/50 blended fuel by mass. Problems of bed agglomeration were not observed over the duration of these tests and moreover, scanning electron microscopy (SEM) studies indicated that the levels of alkali metals in the ash were relatively low.

Residence time distribution study in a pilot-scale gas–solid fluidized bed reactor using radiotracer technique

This paper describes a radiotracer study carried out to measure residence time distribution (RTD) of coal particles in a pilot-scale gas–solid fluidized bed reactor (FBR). Gold-198 labelled on coal particles was used as radiotracer. RTD measurements were conducted for selected operating conditions and mean residence times (MRTs) of the coal particles were determined. Gamma function model was used to simulate the measured RTD data and mixing of coal particles in the reactor was investigated. Based on the results, the performance of the air distributor used in the reactor was evaluated.

Identify of flow patterns in bubbling fluidization

Bubbling fluidization has been widely applied in process industries, such as power generation from coal, renewable energy production, gasification and pyrolysis. In this study, we attempted to predict solid flow patterns in a bubbling fluidized bed based on operational conditions, the air distributor and particle velocity. We first investigated the effect of operational conditions and the air distributor on solid/gas flow patterns, and investigate the correlations between solid/gas flow patterns with the solid mixing, solid and gas contact, and bubble behaviour within bubbling fluidized beds by using positron emission particle tracking (PEPT). A ‘Flow Pattern Parameter (FPP)’ is then proposed to identify the solid flow pattern in a bubbling fluidized bed. The ‘Flow Pattern Parameter (FPP)’ consists of particle kinetic energy, bed aspect ratio (H/D), pore size of air distributor, minimum fluidization velocity, and superficial gas velocity. The results show that solid flow patterns in the bubbling fluidized bed can be clearly classified based on the Flow Pattern Parameter. Different flow pattern corresponds to a certain range of the Flow Pattern Parameter.