Get Industrial electrostatic precipitation Books now! Many industrial, power generation and chemical processes produce unwanted fine particulate material as a consequence of their operation. Electrostatic precipitation is a highly efficient method of removing entrained particulate contaminants from exhaust gases and is extensively used in these industries to limit particulate emissions. New legislation aimed at improving the. It presents the newest developments in electrostatic precipitation, flue gas desulphurization FGD , selective catalytic reduction SCR , and non-thermal plasma techniques for multi-pollutants emission control.
Almost all outstanding scientists and engineers world-wide in the field will report. The electrostatic precipitator ESP is an effective device for industrial air pollution control.
Electrostatic precipitation technology has been around for over years and, within the last few decades, a push for new technology and applications of this device has been experienced. Hylsky, published by Unknown which was released on The latent image creates an electric field abovethe photoreceptor that attracts toner to the photoreceptor surface.
The calculation of an electric field due to an arbitrary charge pattern is a classic problem in electrostatics. The electric fields due to three latent images are discussed, a solid area, a single line, and a series of parallel lines. The proper charging of toner particles is anessential requirement of a good development system. Yet the contact charging of insulators, i. It appears that the high density limit of the surface state model, which postulates that charge is exchanged to create an electric field during the contact, can explain the data.
But identification of the physical significance of the electric field remains an unsolved problem. Therefore toner material choicesare generally made by empirical means. Finally, toner development, the process step that determines the best image quality that electrophotography can produce, has been shown to SCHEZN be dominated by electrostatic considerations. Inthe dual component insulative magnetic brush developmentsystem, the buildup of charge oncarrier beads, as toner develops onto the photoreceptor, limits toner development.
In monocomponent developmentsystems, a field stripping model, in which the Coulomb force due to the latent image overcomesthe adhesion force of toner to the roller, appears to account for the data. An electronic model of triboelectrification of two-component electrophotographic developers. Bauser, H. Static electrification of organic solids. Dechema A-Monogr. Klopffer, and H. Rabenhorst On the charging mechanism of insulating solids. Electrification, 1, 2 Cobine, J.
Gaseous Conductors. Dover, New York. Cottrell, G. Hatto, C. Reed, and A. Rose-Innes Contact charging of ideal insulators: experiments on solidified rare gases. D: Appl. Physics, 17, Crowley, Joseph M. Davies, D. Charge generation of dielectric surfaces. Gallo, C. Coronas and gas discharges in electrophotography: a review.
Corona-a brief status report. Harper, V. Contact and Frictional Electrification. Oxford University Press, Oxford. Hays, D. Contact electrification between mercury and polyethylene: effect of surface oxidation. Kao, C. Electric field, transfer, and spread function in xerographic image studies. Kittaka, S. Murata Photoelectric emission and contact charging of vacuum irradiated polymers. Kmpp, H. Physical modelsof static electrification of solids.
Static Electrification. Lee, 1. A surface interaction modelof triboelectrification of tonercamer pairs. Lowell, J. Contact electrification. Advances in Phys. Medley, J. The electrostatic charging of some polymers by mercury. Nature, , Neugebauer, H. Electrostatics fields of xerographic images.
InXerography and Related Processes J. Dessauer and H. Clark, eds. Focal Press, New York, Chap. Focal Press, New York. Electrophotographyand DevelopmentPhysics. Springer Verlag, New York.
Cranch The static electrification of mixtures of insulating powders. Fowler Physics of development in the IBM electrophotographic printer. Castle, and A. Dean Theory of monocomponent development. Beardsley, and M. Moore Development efficiency in electrophotography. LaHa, and D.
Novotny Theory of insulator charging. A , , Shahin, M. Characteristics of corona discharge and their application to electrophotography. Sci Eng. Shaw, P. Jex Tribo-electrocity and friction solid elements and textiles. London, , Takahashi, T. Hosono, J. Kanbe, and T. Toyono Mechanism of canon toner projection development. Vyverberg, R. Charging photoconductive surfaces. In Xerography and Related Processors J. Canada 1.
Displays are currently experiencing a revolutionary phase in their development, because new requirements call for flat panels that are capable of high resolution color display.
The most important markets include computer monitors and high definition TV HDTV , which is now the new standard for the next generation of television systems. Requiring lines of vertical picture resolution and screen sizes of over 1 m2, current CRT and flat panel technologies are not yet at the point of meeting the needs of HDTV, which willgenerate an enormous market for the successful color display. This chapter will focus on display technologies that have application for flat panels, which are expected to make significant inroads into CRT dominated areas.
However, another potential candidatefor flat panels is a flat CRT, which will be examined first. FLAT CRTs The CRT,in retrospect, is a very elegant means of addressing many -lo6 discrete pixels by deflecting an electron beam that is accelerated to high energies KeV , allowing it to impart considerable energyto phosphor materialon the screen.
In order to use this idea in a flat paneldisplay, two basic approaches are possible. The first Pankove, steers or guides an electron beam across the back of the panel and then deflects it toward the screen through a 90" angle by means of an array of closely spaced electrostatic deflection electrodes as shown inFig.
Periodic focusing prevents the electron beam from expandingdue to space charge repulsion betweenelectrons. This is achieved usingapertures held at high and low voltages alternately, allowing a low energy eV beam to remain intact.
Disadvantages of this structure include the need for a vacuum envelope, complexelectrode structures, and difficulty achieving high resolution color displays. More recently, another approach has been taken, using field emission of electrons from a conducting needle to form a cold cathode Stowell, If a dense array of such tips is placed behind the phosphor screen, electrons may be generated when and where they are needed. The field emission process Spindt et al.
The structure of a typical deviceis shown in Fig. The calculated emitting area of a tip is only -I x cm2, whichsuggests that only a fewatomic sites on the tip contribute to the emission, allowing the electrons to be collected by an anode, not shown in Fig. By placing arrays of such tips behind a phosphor screen, over foot lamberts of apparent brightness may be obtained with an anode voltage of under V.
The glass envelope is supported by micropillars that remove the need for thick glass, and color pixels per inch may be realized. In either case, field-excited ions collide with each other and give rise to visible light emission, or alternatively uv light generated by the plasma excites visibleemitting phosphors Pankove, In a typical ac PD, two glass substrates are spaced to form a chamber containing a neon gas mixture.
Each substrate holds a set of parallel conductors that are covered by a transparent dielectric. Selected intersections of the mutually orthogonal conductors emit localized neon-colored light when suitably driven.
A firing voltage Vf is necessary to initiate the discharge, and a lower sustain voltage V, of alternating polarity follows. Typical values of Vf and V, are V and 90 V respectively. A proper model of the device includesthree capacitors in series, namely a wall capacitor, a gas capacitor, and another wall capacitor, which allowstransient response to be determinedif the gas discharge current is included. To improve optical efficiency, a slotted electrode may be used that avoids covering the plasma by the electrode, as shown in Fig.
A typical front-to-rear electrode separation is pm. Plasma panels are capable of displaying over lo6 pixels, although resolution is inherently limited to below pixels per inch and color is hard to achieve.
Nevertheless, plasma panels are mass produced for portable computers and banking terminals. In essence, HFEL devices initialize a strong electric field to generate hot electrons that are able to excite luminescence centers. Hence these electrons must have at least eV of kinetic energy to allow them to excite visible luminescence. The most important material for achieving such luminescence is ZnS: Mn.
ZnS has a large band gap 3. The means of applying such large fields has several variations. In the s, powder devices were popular Ivey, These contained km diameter grains of ZnS usually doped with copper. The copper acted as a luminescent center although other metals such as Mn could also be used , but more importantly copper in the form of CuzS segregated at dislocations within such grains to yield tiny conductive needles buried within the grain.
These needles wereable to produce an enhancedelectric field at their tips, which resulted in comet-shaped luminescent regions of the ZnS at the ends of the needles. See Fig. Such devices are used as backlights and touch-sensitive panels. This enables such devicesto be flexible. More recently Inoguchi et al. Here, as shown in Fig.
From Chadha, The mechanism is a combination of tunneling, in which electrons trapped at surface states at the interfaces tunnel into the conduction band of ZnS and then gain kinetic energy, and avalanching, in which additionalelectrons are generated that increase the hot electron density. A band model is shown in Fig. Thin film HFEL devices have found application in matrix-addressed flat panel displays.
They have the advantages of completely stable brightness with time and simple structure. Current difficulties includethe lack of suitable phosphorsfor red, green, and blue color displays andthe high cost of high voltage drivers for rows and columns. Nevertheless, HFEL is regarded as the ideal flat panel display because it is solid state, inherently light emitting, and rugged with respect to thermal and mechanical abuse.
From Hurd et al. From Smith, The near future will see widespread use of LCDs for color computer and data terminals, indicating the degree of development of this technology. Under the application of an electric field, polar liquidcrystal molecules will rotate or tilt so as to affect the polarization of the light shining through the medium, or alternatively so as to change the index of refraction of the medium along a particular axis.
By suitable incorporation of the LC medium in an optical system, light may be efficiently modulated. Matrix addressing may be used to make high resolution displays of this type. Liquid crystal displays consist of a thin layerof liquid crystal material. Liquid crystals are organic materials that possess an intermediate phase between solid and isotropic liquid Pankove, , in which molecules interact with each other to produce various kinds of ordered states. The nematic phase has the molecules with major axes parallel to each other; the cholesteric phase hasa helical structure of molecular ordering; andthe smectic phases show layeredstructures with the major axes of molecules parallel within each layer.
Since the materials are liquids, little energyis required to produce large changes in molecular ordering see Fig. Hence, a torque is exerted by E to rotate d to minimize w d. Figure 13 shows a nematic material. Abovea critical field,the molecules will align verticallyas shown in Fig. Liquid crystals have two valuesof refractive index, no for light polarized perpendicularto d and ne for light polarized parallelto d. The optical birefringence ne - no may be as high as 0.
Most popular is through altering the polarization vector of light as it passes through the birefringement material. By placing polarizers oneither side of the LC, light may be allowed to pass or may be blocked, depending upon the director orientations. Ina scattering state, light is reflectedor scattered many times within the LC, and the device is opaque.
Application of an electric fieldremoves the random refraction, andlight passes through. Here, rather than having a film of LC, a polymer that has micron sized pores filled with LC material the is active medium. Whenthe refractive indexof the LC is different fromthat of the polymer, light is scattered. Figure 12 a Nematic, b smectic, and c cholesteric liquid crystal phases. From Lerner, Finally, it is possible to use the LC to orient molecules of dissolved dichroic dye, whose molecules reflect light with different spectral reflectivities depending upon the relative orientation of the molecule to the optical electric field.
The advantage of the two latter techniques is that no polarizers are necessary. More complexelectric field effects also exist in liquid crystal materials Helfrich, For example, in nematics, if the liquid is slightly conducting, the field E can induce an instability.
First, the molecular alignmentis slightly deformedby a thermal fluctuation. Powder electroluminescence. In Solid State Luminescence A. Kitai, ed. Chapman and Hall, London, Destriau, G. Helfrich, W. Conduction-induced alignment of nematic liquid crystals: basic model and stability considerations. Hurd, J. King Physical and electrical characterization of co-deposited ZnS:Mn electroluminescent thin film structures.
Electronic Materials, 8, Inoguchi, T. Digest of Technical Papers, 86, Ivey, H. Electroluminescence and Related Effects. Advances in Electronics and Electron Physics. Academic Press, New York, Suppl. Lerner, R. Trigg Concise Encyclopediaof Solid State Physics.
Addison-Wesley, Reading, Mass. Pankove, J. Display Devices. Springer-Verlag, Berlin; New York. Smith, D. Luminescence, 23, Spindt, C. Brodie, L. Humphrey, and E. Westerberg Physical properties of thin film field emission cathodes. Stowell, R. Recent progress in low voltage field emission cathode development. Kanagawa, Japan 1. Equipment using many different methods of separation are applied in these processes. Electrostatic separation including electrostatic classification is one separation method.
This method, relying on the differences of electrostatic characteristics inherent in different materials, has an unexpectedly long history, with initial patents to remove impurities from grain Murata, having been awarded years ago.
Since then the method has found application mainly in the separation of impurities in raw ore. After an initial overviewof the electrostatic technique, this paperwill discuss a number of interesting applicationsof the technique inthe fields of ore, coal, food, and scrap processing.
Finally, a few new applications will be discussed. Some examples are particle size using sieves; density using wind, water or another liquid, or magnetic fluidforce; surface phenomenon characteristics using float separation or oil agglomeration; and electromagnetic characteristics using electrostatics, magnetics, or eddy currents. The electrostatic separation method utilizes inherent differences in friction charge characteristics, electric conductivity, and dielectricconstants between substances.
Since individual particles behave differently under the application of electrostatic, gravitational, and centrifugal forces, separation is possible. Electrostatic force is proportional to the surface area available for surface charge, while gravity is proportional to the mass of Figure 1 Representative methods of electrostatic separation.
From Kasai, For electrostatic separation, particles mustfirst be chgrged. A number of methods are currently used to charge the particles, including contact and collision friction charge; induced charge, electron or ion collision charge; pyroelectric effect; and field emission by light and radiation.
An electrostatic force Coulomb, image,or gradient is then applied along with gravity, wind,or an alternatingcurrent. Three typical implementationsof the technique are illustrated in Fig. Miningindustry Electrostatic separation has long been used toseparate dry ore.
Charging has primarily been by means of corona discharge, induced charge, or contact charge. Separation relies on the differences in conductivity between ores. Various processes depending on the composition of the ore are utilized to create a large variationin surface resistance from particle to particle. A number of these processes are summarized in Table 1 Beddow, In addition, the pyroelectric effect is usedin the separation of feldspar from rockcrystal, and gradientforce acting of the polarized dielectric is used to separate rutile from vinyl chloride Murata, Recently, many researchers have been studyingnew methods of electrostatically classifying inorganic substances.
The apparatus consists of two plate electrodes with some inclination angle to which are applied an alternating high voltage. As the electric field between the two electrodes is bent in an arc, moving particles experience a centrifugal force, being deflected toward the wide gap. Asseen from the experimental results shown in Fig. A classification method utilizing three-phase alternating current charging equipment usingthe principle of the boxer charger is illustrated in Fig. From Murata et al.
Separating characteristics of smaller particles F from bigger particles A to E with weight ratio 1to 1. From Ashizawa et al.
When an alternating voltage is applied between adjacent electrodes, charged particlesare forced to vibrate. Results relatingto the HAGA particle size: diameter small 0. Reproduced with permission from Law and Cooper, Copyright, AmericanSociety of Agricultural Engineers. Mills, ; Herzog et al. Figure 12 pictures a University of Georgia developed embedded electrode induction nozzle and associated electronics specifically designedfor charging conductive water-borne pesticide sprays Law, This isthe key component facilitating the commercial development of greenhouse Fig.
Reproduced with permission from Law, Copyright, Institute of Electrical and Electronics Engineers. Figure 15 documents the two-fold improvement in deposition efficiency of Captan fungicide applied to strawberry plants using this aerodynamic-electrostaticmachine Giles and Blewett, In addition, the persistence of the disease-preventing deposits wasidentical over the subsequent day period viz.
Spraying of tree-size plants in orchards requires spray droplets to be dispensed in large volume, high velocityair carrier streams ca. Photograph courtesy of Electrostatic Spraying Systems, Inc. While several prototype and commercial electrostatic orchard sprayer machines have been introduced over the past decade, limited success has been achieved mainly duethe to great dominance of aerodynamic forces over electrostatic.
Deposition improvements mainly within low air velocity regions hold promise Inculet et al. In all cases, the maximum current density corona current distribution along the axis at the surface of the for the central needle is greater than that of the lateral one.
On the other hand, modification of the interelectrode conductivity of the air, was accompanied by an increase of distance at constant total current causes a significant change the corona current Fig. All these effects were expected, as in the distribution of current density Fig. Finally, the effect already documented for other corona electrode configurations.
In these installations, the particles are forced the development of certain electrostatic technologies. This is through the electric field along well-defined trajectories.
Further experi- ments are necessary in order to optimize the new design. Atten and Dr. The laboratory model of the matrix-type multiple-needle electrode was built by M.
Pop, to whom the authors express their most sincere thanks. Moore, Electrostatics and Its Applications. New York: Wiley, Comparison between the current-density distributions average val- [2] J. Cross, Electrostatics: Principles, Problems and Applications.
Dascalescu, An Introduction to Ionized Gases. S Chang, A. Kelly, and J. Crowley, Eds. New York: Marcel Dekker, Indeed, some particles cross the electric field [5] S. Masuda and I. Static Electrification. Hughes, Electrostatic Powder Coating.
New York: Research [e. With a hexagonal-grid electrode, Studies Press, Inculet, Electrostatic Mineral Separation. Iuga, L. Dascalescu, R. Morar, I.
Csorvassy, and V. Neamtu, of nonzero current density [Fig. Electrostatics, vol. McDonald, M. The design of Desalter may be influenced by factors, including process requirements, economics and safety. In this guideline, there are tables that assist in making these factored calculations from the vary reference sources. Include in this guideline is a calculation spreadsheet for the engineering design. All the important parameters use in the guideline are explained in the definition section which help the reader understand the meaning of the parameters or the terms used.
The theory section explains the type of Desalter single stage, two stage and dual polarity , troubleshooting and emulsion drop theory. The application section of this guideline with the examples will make the user understand a Desalter and its operation. These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. General Design Consideration Heavy crude oil is becoming an increasingly more important option in terms of crude oil refining due to the fact that this type of feedstock is generally cheaper in the international market.
Crude oil production is usually associated with the co-production of varying amounts of water, formation solids, and corrosion products. The water frequently contains sizeable concentrations of dissolved salts with the chlorides, sulfates, and bicarbonates of alkali metals and in which alkaline earths predominate.
Separation processes are applied at the production site in order to minimize the unnecessary transportation costs and to prevent corrosion in the transportation system. When crude oil is processed in the refinery, salt can cause numerous operating and maintenance problems.
Salt occurs naturally in all crudes but can vary significantly in concentration and makeup between crudes. The salt content of crude oil is highly variable and results principally from production practices used in the field.
Salt may be derived from reservoir, aboard tankers, ballast water of varying salinity, formation waters or from other waters used in secondary recovery operations.
The bulk of the salt present will be dissolved in coexisting water and can be removed in Desalter, but small amounts of salt may be dissolved in the crude oil itself. The salts that are most frequently found present in crude oil feed stocks are sodium, calcium and magnesium chlorides NaCl, CaCl2 and MgCl2 although other forms of salt can be present in smaller quantities.
If these compounds are not removed from the oil several problems arise in the refining process. Below are some effects of salts. During flash vaporization of crude oil certain metallic salts, the high temperatures that occur downstream in the process could cause water hydrolysis that can be hydrolyzed the metallic salts to hydrochloric acid which extremely corrosive.
NaCl on the other hand has a high hydrolyzation temperature not normally reached in a crude charge furnace. For this reason Caustic or NaOH can be injected into the Desalter crude stream to lower overhead chlorides. Salts and evolved acids can contaminate both overhead and residual products, and certain metallic salts can deactivate catalysts.
Salt cakes out inside equipment, cause poor flow and plugging 4. If a certain amount of salt remains it may cause fouling problems in pipes and reduces heat transfer rates in exchangers, and cause high heater tube-wall temperatures. Plugged fractionators trays and burned-out fire tubes 6. Metals from salts can also cause catalyst deactivation and sintering which result in lower catalyst activity. Sodium has been found to be the most harmful metal for catalysts Metals from salts can also cause catalyst deactivation and sintering which result in lower catalyst activity.
Sodium has been found to be the most harmful metal for catalysts. This decrease in activity implies that used catalyst must be replaced more often to maintain a given activity level. This accumulations takes place in heating tubes and may cause the following problems 2 : 1. Reduction in heat transfer rate, which leads to more fuel consumptions and thus higher operating cost. Creation of "Hot Spots" in heating tubes, which reduces tubes' operational expected lives.
Development of blockages inside tubes and thus lowering their capacities and efficiencies. Since facilities are designed for a specific corrosion allowance it is critical that salt and corrosion to be controlled and to stay at or below the design limits.
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