Particle Separation Efficiency Research Articles

Fly Ash Penetration through Electrostatic Precipitator and Flue Gas Condenser in a 6 MW Biomass Fired Boiler

The effects of an electrostatic precipitator and a flue gas condenser on size resolved fly ash particle concentration and composition were studied in a 6 MW biomass combustion unit, fired with moist forest residue. The boiler was of moving grate type. The fly ash particles were sampled upstream and downstream of the electrostatic precipitator and flue gas condenser, respectively. Fine particle number size distributions were measured using an electric mobility spectrometer (SMPS) and coarse particle number size distributions were measured using a time-of-flight instrument (APS). The mass size distributions were measured using a multi-jet low pressure cascade impactor (DLPI). For chemical analyses of the impactor substrates particle induced X-ray emission analysis (PIXE) was used. After the flue gas passed the electrostatic precipitator (ESP), the fly ash particle concentration was reduced by approximately 96% by number and 83% by mass. After the particles passed the flue gas condenser, particle number concentration was only marginally altered, whereas the mass concentration was reduced by half. Both the ESP and the condenser showed, size dependent particle separation efficiency. The main elements (Z > 12) in the fine fly ash fraction were K, S, and Cl, whereas the main elements in the coarse fraction were Ca, K, S, and Cl. After passing the ESP the mass ratio of Ca decreased in the coarse fraction, while the ratios of K, S, and Cl increased, indicating transference of fly ash material from the fine to the coarse particle fraction. There was no significant difference in the elemental composition for any particle size fraction sampled upstream or downstream of the condenser.

Synthesis and performance of organic-coated magnetite particles

Polymeric-coated magnetite particles with an adsorbed layer of extractant have been synthesized and are being evaluated for application in the separation and recovery of low concentrations of europium from water solutions. Physical characterizations of the extractant adsorbed particles were performed by X-ray diffractometry, Scanning Electron Microscopy and FT-IR spectrometry. Metal separations have been performed at various HNO 3 concentrations. Separation efficiency of the polymeric magnetic particles and the equilibrium adsorption isotherm of europium were investigated. Moreover, the magnetic field effect in the separation using a magnet was also verified.

Flow structures in a dissolved air flotation pilot tank and the influence on the separation of MBBR floc

The objective of the study was to find ways of improvement of the dissolved air flotation process by studying the flow structure. The paper presents experimental data on flow structures and the relation between the flow structure and the removal efficiency. Measurements have been performed in a pilot plant with an Acoustical Doppler Velocimeter. The water velocity was measured in a grid net, giving insight into the flow structure. The removal efficiency was analysed at Malmö wastewater treatment plant in Sweden. The pilot plant separated biological floc from a Kaldnes Moving Bio-Bed Reactor (MBBR). The efficiency of the separation was analysed by measurements of suspended solids in the influent and the effluent. Air content was measured inside the tank and in the re-cycle. The result showed that basically two flow structures existed; the stratified and the short-circuit flow structure. The stratified flow structure seemed correlated to efficient separation of particles while the short-circuit flow structure seemed to have a negative effect, especially when the flow structure was affected by varying the re-cycle rate, i.e. the air content. Conclusively, the flow structure seemed to be correlated to type of flow structure. However, studies with higher concentration of suspended solids for verification were suggested.

Predicting the performance of air cyclones

Many empirical models for predicting the particle separation efficiency of cyclone separators have been presented by different investigators, but they are often limited in their use to the particular type of cyclones on which they were developed. This paper describes theoretical models and a numerical model for the analysis of the fluid flow and particle separation of cyclones and how they may be used in the design of new types of cyclones. The governing fluid and particulate flow equations have been analysed and numerically solved in order to predict the fluid flow and particle separation in cyclones. In addition, the key design parameters for the cyclones have been discussed as to their effect on the overall performance of the cyclone and general recommendations for the engineering design of cyclones have been suggested. Copyright © 2002 John Wiley & Sons, Ltd.

Modelling of magnetodensimetric separation in two high gradient magnetic separation axial cells

Two magnetodensimetric cells with high gradient magnetic separation (HGMS) axial structure are presented. The method of magnetodensimetric separation is based on the buoyant force exercised by a magnetic fluid, particularly a ferrofluid, on a solid particle when it is placed in a nonuniform magnetic field. The equations of motion of the particles entering cells through a well-delimited surface are solved. By studying the trajectories of the particles we prove the possibility of efficient separation of particles with different densities.

00/03224 Low temperature CFB gasifier conceptual ideas and applications

A novel Circulating Fluidized Bed (CFB) gasification process for volatile fuels such as biomass and many waste materials are described. The fuel is pyrolyzed at e.g. 550 C in the CFB reaction chamber and the char residue is converted at e.g. 650 C in a separate Bubbling Fluidized Bed (BFB) char gasification chamber located in the particle recirculation path. Due to the tendency for char particles to segregate to the upper part of the BFB they achieve a high retention time in the slowly fluidized BFB by recirculating mainly inert particles from the bottom. In a simple version of the process essentially all of the air is added to the bottom of the BFB and the produced char gas serves as fluidizing gas in the CFB reaction chamber. This way the product gas leaving the CFB reaction chamber obtains a higher heating value at around 11 MJ/Nm{sup 3} when using a biomass fuel with around 15% moisture. In combination with the low process temperature, and not needing building height for char conversion in the CFB reaction chamber, this means that the CFB reactor and off-gas system becomes very compact. The low temperatures also means that agglomeration can be avoided evenmore » when using fuels such as unweathered straw with a high content of alkaline and chlorine. Furthermore, the alkaline and chlorine in the raw gas will mainly be in the solid state meaning that a high retention can be obtained simply by efficient particle separation. The paper mentions a number of possible applications for the gasifier including as an example a simple and compact system for co-firing biomass and waste at power plants.« less

Operational analysis of ash-agglomerating fluidized bed gasifiers

The operational characteristics of ash-agglomerating fluidized bed gasifiers are analyzed through a simplified approach. Based on the simple theoretical analysis, true steady state operations in ash-agglomerating fluidized bed gasifiers require that the ash concentration in the bottom ash withdrawal be equal to the steady state ash concentration dictated by the kinetics of coal combustion and gasification, and other process variables in the fluidized bed gasifiers. There are only three steady state operational modes possible depending on the coupled effects of ash agglomeration rate and the particle separation efficiency of char and ash agglomerates. Without precise knowledge of the ash agglomeration rate, the combustion and gasification kinetics, and the rate and degree of particle separation between char and ash agglomerates, experimental trial and error is required to approach the true steady state. Locating the true steady state or the lack of it may seem unimportant in a pilot plant operation, where solids samples are obtained hourly so that correctional steps can be implemented quickly, its implication for the commercial operation can be serious.

NUMERICAL MODELLING OF THE FLUID AND PARTICLE PENETRATION THROUGH SMALL SAMPLING CYCLONES

In this paper, the numerical modelling of the fluid flow and the particle dynamics in small sampling cyclones is addressed. The presence of the particles is assumed not to affect the fluid flow in the cyclone due to the light particle loads which are normally encountered in most small air sampling cyclone applications. The governing fluid flow equations, along with the RNG turbulent model equations, are solved using the control volume method in a body-fitted coordinate system. A particle tracking technique is used to track the motion of the particles in the cyclone. We have found reasonable agreement between the present numerical results and the experimental data of Kim and Lee (1990) for the particle separation efficiency of a small sampling cyclone even though the turbulent effects of the fluid flow have not been included in the particle tracking procedure. Further, the effects of changing various geometrical dimensions and operating conditions on the performance of the cyclone have been discussed. The predictions of the cyclone separation efficiency using the Barth (1956) and the Dietz (1981) empirical models are also presented.

A Numerical Simulation of Hydrocyclones

A numerical method is presented for the calculation of the three-dimensional flow and separation efficiency for particles with low concentrations in a hydrocyclone. Multi-block curvilinear grids in the frame of a cylindrical coordinate system are used to represent accurately the hydrocyclone geometry. Turbulence is represented by a modified k — ɛ model which adds a curvature correction term with a single empirical constant in the dissipation equation. Both three- and two-dimensional axisymmetric computations are carried out and are compared with experimental data. It is shown that the standard k — ɛ model can produce large errors which result in incorrect predictions of the flow patterns. The three-dimensional calculations using the modified k — ɛ model produce results in good agreement with experimental data. The two-dimensional axisymmetric calculations can predict approximate flow patterns, but are inadequate to predict the separation efficiency of hydrocyclones. To analyse the separation efficiency, a three-dimensional model, as developed in the present study, is required.

Separation of aerosol fine particles by high-power ultrasound

The application of high-intensity acoustic fields to an aerosol can produce the agglomeration of the suspended particles, shifting their size distribution to a large range. Acoustic agglomeration is a process in which acoustic forces cause particles to interact and eventually to collide. The complex mechanism of this process involves orthokinetic and hydrodynamic effects. The orthokinetic effect refers to direct collisions produced among particles of different size and/or density which are differently entrained by the acoustic field. The hydrodynamic effects refer to particle interactions generated through the surrounding fluid by hydrodynamic forces induced by the acoustic field. One important hydrodynamic effect is the acoustic wake effect which is related to the asymmetry of the flow field around the moving particles. Acoustic agglomeration has a potential use in the separation of fine particles (smaller than 2.5 μm) which are emitted from industrial and residential combustion and from vehicle exhaust. In this paper recent theoretical and experimental advances in the knowledge of the basic mechanisms of acoustic agglomeration are presented, together with some results about the improvement of fine particle separation efficiency of conventional filters when the aerosol is previously treated with high-power ultrasound. [The authors acknowledge the support of CICYT-AMB96-A211-C02.]

ABSORPTIVE SEPARATION OF NO FROM DILUTE OFF-GAS

ABSTRACT With regard to its negligible absorption properties, the separation of nitrogen monoxide from dilute off-gas is limited to bench-scale experiments. Investigation has been centered on improving the rate of absorption by the use of complex-forming additives based on iron(II) compounds. Further efforts have been made to improve the separation efficiency by the use of reactive additives. Due to the low reactivity of nitrogen monoxide, these attempts did not succeed. The oxidation of moderately concentrated off-gas with ozone and the absorption of the so-formed nitrogen dioxide have been reported. Technical as well as economical considerations do not permit the application of the process to the treatment of dilute off-gas. The principle underlying this process led to the investigation of direct oxidation of the off-gas under electrical discharge followed by absorption with aqueous diamide solution. Temperature and moisture of the off-gas have been considered, in addition to various feed contents of nitrogen monoxide. The results of this investigation show that direct oxidation of nitrogen monoxide by corona discharge is possible. The rate of conversion increases with increasing gas velocity, accompanied by a decreasing specific energy consumption. Applied to tunnel off-gas purification, the direct oxidation route seems to offer promising technical boundaries as it is accompanied by efficient particle separation.

Separation of metal oxides from supercritical water by crossflow microfiltration

Low-shear crossflow microfilters rated for 34.5 MPa and 455°C were evaluated for their ability to remove α-alumina particles from supercritical water. The crossflow microfilters were tested in conjunction with a 2.5 L/h bench-scale apparatus and a 150 L/h pilot plant. The filter elements were made of sintered Stainless Steel 316L tubes with a nominal pore size of 0.5 μm. Process variables included volumetric feed concentration, feed flow rate, temperature, and fluid density and viscosity. The mean particle diameter was about 1.6 μm. Filtration characteristics were similar at supercritical water conditions to those at ambient conditions: Increased shear rates and decreased fluid viscosity resulted in increased filtrate fluxes. Filtrate flow deterioration over time and the required transfilter pressure drop were about 40% less at supercritical water conditions as compared to the performance obtainable at ambient conditions. Higher shear rates delayed the establishment of steady state operating conditions. Filtrate flux could be augmented by pressure swings or periodic increases in the shear rate. Particle separation efficiencies typically exceeded 99.9%. A modified concentration polarization model for turbulent flow yielded steady state filtrate fluxes that were within a factor of two of the experimental results. Back diffusion was modeled as a process-in-series of molecular diffusion and eddy diffusion. The proposed model was consistent with findings of numerical diffusion studies and the theory of concentration polarization as recently presented in the literature. To save on energy costs it might be possible to achieve the benefits of filtration at supercritical conditions at near-critical subcritical conditions: viscosity and mass diffusion coefficients are similar but the density of subcritical water is 3 to 4 times higher than supercritical water thus increasing the filtrate mass flow rate by a factor of 3 to 4 for a given filter.

Transport and Deposition of Spherical Particles and Fibers in an Improved Virtual Impactor

ABSTRACT Flow velocity in an improved virtual impactor was calculated for a Reynolds number of 4000 using a finite-element method. The governing equations of motion for spherical particles and fibers were used along with flow field information to calculate transport and losses in the impactor. The calculated separation efficiency and loss fraction for spherical particles agreed with experimental results reported in the literature. For fibers, separation efficiency curves were obtained in terms of fiber Stokes number and aspect ratio. The calculated collection efficiency curve moved to higher Stokes numbers with increasing fiber aspect ratio. All fiber sizes showed significant losses at the tip of the collecting probe of the impactor. As a result, the separation efficiency never reached 100%. The computational approach illustrated here can be used for predicting separation characteristics, which will lead to improved and cost-effective design of the impactor.

5502243 Hydrocarbonylation of dimethyl ether

This study evaluated the separation of particles suspended in power law fluids by applying a 10 mm hydrocyclone. Al2O3 particles were added to an aqueous polyacrylic acid solution to prepare 0.1 vol% suspensions with different flow behaviors. The effects of operating conditions, such as the inlet velocity, pressure drop, split ratio, and fluid flow behavior, on the fluid velocity distribution, particle trajectory, and particle separation efficiency were studied. The study applied a simulation in which the governing equations were coupled using the SIMPLE algorithm; the Reynolds stress model served as a turbulence model. The distributions of the fluid velocity and pressure were simulated using a segregated, steady-state, three-dimensional implicit numerical solver provided by ANSYS 15.0 software. The tangential velocity increased with the flow behavior index, n, at a fixed inlet velocity and split ratio. This effect was attributed to a lower molecular viscosity. The particle trajectories were simulated using a Lagrangian frame. The particle migration in the cylindrical part of the hydrocyclone dominated the particle separation efficiency. A reduction in the fluid n-value engendered a higher effective viscosity and lower tangential velocity, which caused fewer particle rotations and lower centrifugal effects, consequently lowering the opportunity for particles to collect in the underflow. The separation efficiency increased with the inlet velocity and particle size because of a higher centrifugal effect, but the influence of the inlet velocity was extremely small for a low fluid n-value. The total separation efficiency increased by approximately 40% as the n-value increased from 0.51 to 1.00. The simulated particle separation efficiency was highly consistent with experimental data. This verified the reliability of the simulation method and the validity of this method for understanding the effects of fluid flow behavior on particle separation performance.

Effect of dense medium properties on the separation performance of a dense medium cyclone

Extensive separation tests were carried out on a 6″ dense medium cyclone loop with the use of density tracers to study the effects of medium stability and rheology on the separation of fine particles. The medium properties were modified by changing the magnetic particle size and medium density. Four magnetite samples with RRB size modulus d 63.2 ranging from 4.7 to 33 μm were used, and the medium densities were varied from 1.2 to 1.7 s.g. It was found that, while the separation efficiency and cutpoint shift for coarse particles (>2.0 mm) were mainly determined by the medium stability, the separation performance of fine particles (<0.5 mm) was more sensitive to the change in medium rheology.

Characteristics of an electro-acoustic precipitator (EAP)

Results of a laboratory scale investigation to remove sub-micron particles from a gas stream, using a combined acoustic module and electrostatic precipitator (ESP), are presented. In these experiments, 1kW of electrical power is required per 1000m 3 of gas treated to increase the particle separation efficiency of the ESP from 90 to 95%.

Separation Efficiency of Particles in Low Pressure Virtual Impactor

Click to increase image sizeClick to decrease image sizeKEYWORDS: molecular laser isotope separationuraniumvirtual impactorcompressible inviscid flowseparation efficiencyparticle sizepressure dependence

Separation Efficiency of Particles in Low Pressure Virtual Impactor

The separation of 235UF6 particles from gas by an impactor has been studied in the research and development of molecular laser isotope separation of uranium (MLIS). The virtual impactor(1) is an inertial separator containing a 'virtual' surface instead of a solid impaction plate used in the conventional impactor. Therefore, it makes continuous operation possible in the separation of UF5 particles from gas. In this study, a theoretical investigation for estimation of the separation efficiency of particle in a virtual impactor was carried out in order to design and develop the separation process of particles from gas in MLIS.

Simulation of flow in a low-pressure impactor and separation efficiency of particles.

Simulation of flow in a low-pressure impactor and separation efficiency of particles.

A numerical model for the inviscid flow of a fluid in a hydrocyclone to demonstrate the effects of changes in the vorticity function of the flow field on particle classification

A numerical model for the inviscid flow of a fluid in a conical hydrocyclone is presented. Validity of the model is demonstrated by successful spatial simulation of the three velocity components determined experimentally by Kelsall (1952). Although the simulation of Kelsall's experimental findings is subject to certain limitations, the results are acceptable and they can be used to form a basis for further work. An important feature of the model described is the vorticity function of the flow field, being defined in terms of the Stokes' Stream Function. This vorticity function forms a term of the flow equation solved and provides a useful degree of freedom for the programmer, whereby he is afforded the opportunity to investigate the effect of changes made to this function on the spatial solution for ψ, initially, and ultimately on the shape of a quasi-viscous representation of the particle separation efficiency curve. The writer's numerical solution for ψ is discussed together with a simulated particle classification efficiency function with which any given spatial solution for ψ will be consistent. This latter model then provides a basis for the investigation of the effect which the vorticity function of the flow field has on the former quasi-viscous particle classification efficiency curve. It is further shown that some types of vorticity function give rise to sharper theoretical efficiency functions than do others. A method for deriving the relationship between the vorticity function and the physical scenario in the inlet of the cyclone which gives rise to such is developed in the paper. This further lays the foundation for a practical study involving changes made to the velocity profile of the slurry in the inlet to a 76.2 mm diameter cyclone, and the quantification of the effect which these changes have on the experimental particle separation efficiency curve. The results demonstrate that it is possible to modify the shape of the efficiency curve by changing the velocity profile of fluid in the inlet and these results further confirm the predictions obtained using the numerical model.