EP0009857A2 - Dispositif d'agglomération de cendre volante, conduit équipé de ce dispositif et procédé pour enlever des particules chargées en suspension, de dimensions variables, d'un volume de gaz - Google Patents

Dispositif d'agglomération de cendre volante, conduit équipé de ce dispositif et procédé pour enlever des particules chargées en suspension, de dimensions variables, d'un volume de gaz Download PDF

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Publication number
EP0009857A2
EP0009857A2 EP79300858A EP79300858A EP0009857A2 EP 0009857 A2 EP0009857 A2 EP 0009857A2 EP 79300858 A EP79300858 A EP 79300858A EP 79300858 A EP79300858 A EP 79300858A EP 0009857 A2 EP0009857 A2 EP 0009857A2
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EP
European Patent Office
Prior art keywords
particles
charged
electric field
suspended
gas
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP79300858A
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German (de)
English (en)
Other versions
EP0009857A3 (fr
Inventor
Owen James Tassicker
Morton Mitchner
Leland Frederick Collins
Sidney Albert Self
Masaaki Kobashi
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Electric Power Research Institute Inc
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Electric Power Research Institute Inc
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Publication date
Application filed by Electric Power Research Institute Inc filed Critical Electric Power Research Institute Inc
Publication of EP0009857A2 publication Critical patent/EP0009857A2/fr
Publication of EP0009857A3 publication Critical patent/EP0009857A3/fr
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/34—Constructional details or accessories or operation thereof
    • B03C3/38—Particle charging or ionising stations, e.g. using electric discharge, radioactive radiation or flames

Definitions

  • coal often contains inorganic minerals such as silica and alumina to the extent of up to 10% of its weight.
  • inorganic minerals such as silica and alumina
  • fly ash When pulverized coal is used, substantially all of the ash is emitted, but even with coarsely crushed coal, approximately 20% of the ash present is emitted from the furnace.
  • the exhaust gases from a coal-fired central station electrical plant contain large amounts of fly ash. Fly ash particles range down in size to the sub- micron region.
  • an electrostatic precipitator removes suspended particulate matter from a gas stream by causing the particles to become electrically charged, and sweeping them out of the gas stream by means of an electrostatic field, normally transverse to the flow direction.
  • the high voltage DC corona is almost universally used in electrostatic precipitators.
  • the corona is most often established between one or more fine wires, normally at a large negative voltage, and a grounded smooth electrode.
  • the particles passing through the corona field are charged according to two mechanisms, bombardment (or field) charging and diffusion charging. Both of the charging mechanisms take place at the same time, but, theoretically, diffusion charging is predominant for particles smaller than 0.2 microns in diameter, while bombardment charging is predominant for particles larger than 0.5 microns in diameter. If all the corona wires are operated at the same polarity, the charging is said to be unipolar. Under such conditions, it still may be very difficult to convert all the particles to the same polarity, especially when the dust loading is high.
  • the charged particles then start to move toward collector plates according to a high voltage DC field.
  • the electrodes for providing the collection field are the same as the corona electrodes.
  • precipitators are called single stage precipitators.
  • Most precipitators used for air cleaning applications are two-stage precipitators in which the contaminated gas stream is first passed through a charger, such as a high intensity ionizer, and then passed through a separate collector in which the collecting field is maintained. In either type of precipitator, the charged particles drift towards an electrode of the opposite sign and out of the gas stream.
  • electrostatic precipitators are highly efficient in removing the larger particles having diameters above about 1 micron, and the very small particles having diameters below about 0.1 microns, they are considerably less efficient in the removal of particles in the 0.1-1.0 micron range.
  • the problem is compounded by the fact that efforts to reduce the emission of certain gaseous pollutants by using low sulphur coal have led to highly resistive fly ash. It has been found that the efficiency of a given electrostatic precipitator decreases as the electrical resistivity of the fly ash increases.
  • One of the main approaches to the problem of increasing the efficiency of the electrostatic precipitator, especially for particles in the sub-micron region, is to increase the size of the electrostatic precipitator itself.
  • Precipitators are already very large devices, typically requiring between 100 and 500 square feet of collection plate area per 1,000 cubic feet per minute throughput. Given that a big power plant typically has a throughput in the range of several million cubic feet per minute, it can be seen that acres of plate are required. Therefore, an improvement along this line is relatively expensive. Additionally, an increase in size is not the kind of change that is readily made to an existing system.
  • precipitator efficiency could be improved by first subjecting the entrained..particles to so-called bipolar charging wherein some of the particles become charged positively and others negatively. The amounts of positive and negative charge would be equal. Then, coulomb attraction between oppositely charged particles would.tend to cause agglomeration, thereby resulting in fewer submicron particles. Since a lot of neutralization of charge could occur, the particles might have to be recharged before collection. A description of this process is found in J.F. Melcher and K.S. Sachar, "Electrical Induction of Particulate Agglomeration", Final Report to Air Pollution Control Office, APTD-0869, National Technical Information Services PB-205188 (August 1971).
  • the present invention provides a method and apparatus for improving the efficiency of electrostatic precipitators, to allow a reduction in the size and cost of the units.
  • the invention can be added to many existing electrostatic precipitator facilities to comply with increasingly stringent regulations with a minimum of disruption. Further, the invention does not result in any significant pressure drop, thereby avoiding the need for additional fans, and it achieves the increased efficiency without a substantial increase in energy expenditure.
  • the invention provides a fly ash agglomerator through which the contaminated gas is passed after passage through the charger and before passage through the collector.
  • the agglomerator includes a plurality of parallel plates aligned with the flow direction and connected to an AC voltage source to subject the charged particles to a high voltage AC field. This AC field causes the larger-sized particles to sweep past the smaller-sized particles.
  • the invention can be used with unipolar or bipolar charging.
  • the AC field tends to overcome the long-range coulomb repulsion and produces large short-range attractive forces which help the smaller particles adhere to the larger particles.
  • the AC field promotes mixing and enhances the short-range attractive forces. By thus removing a significant fraction of the smaller particles from the stream, the overall collection efficiency is improved.
  • the invention could have other applications, such as in the carbon black industry. Additionally, the agglomerator of the present invention need not be used with an electrostatic precipitator, but could be used to increase the efficiency of cyclone collectors.
  • the present invention is directed to increasing the particles' average migration velocity.
  • the migration velocity depends on many variables, including the properties of the particles and the gas. However, the relation can be simplified and still remain illuminating.
  • the migration velocity w is given by:
  • the overall efficiency (corresponding to the mean migration velocity) could be increased by increasing either the charging field, the collecting field or the mean particle radius, as suggested by Equation 4.
  • the present invention increases the average migration velocity by causing the smaller particles to adhere to the larger ones, thereby effectively increasing the mean particle radius. This is done by subjecting the particles to an AC electric field E given by: where
  • each charged particle subjected to the field of Equation 5 undergoes oscillatory motion characterized by a displacement x given by: where q, E, a, ⁇ and ware as defined in Equations 2 and 5.
  • Equation 3 the particle displacement x is given by: sinwt where Eo , E a , a, ⁇ and w are as defined in Equations 2, 3 and 5.
  • Eo , E a , a, ⁇ and w are as defined in Equations 2, 3 and 5.
  • the AC field promotes mixing and increases the shor-range force of attraction.
  • Equation 8 shows the amplitude of oscillation to be inversely proportional to frequency, it must be noted that the number of oscillations undergone is proportional to frequency. Thus, the total path length swept out by a particle in a given time is independent of frequency, subject to the underlying simplifying assumptions.
  • the particulate laden gas first passes through a charger 10, in which the suspended particles become charged, the particles being charged generally with the same polarity.
  • the gas then passes through an agglomerator 15 which subjects the gas stream and suspended charged particles to a high voltage AC field aligned transverse to the direction of gas flow.
  • the larger charged particles sweep back and forth past the smaller ones, thereby overcoming the long range coulomb repulsion and causing the smaller particles to adhere to the larger ones.
  • the gas then passes through a collector 20 in which the gas stream is subjected to a transverse high voltage DC field which causes the charged particles to be swept out of the gas stream.
  • the gas stream is first passed through a bipolar charger 25 under the influence of which the suspended particles become charged, some negatively and some positively. Some processes give rise to particles that are naturally bipolarly charged, as for example grinding or dispersion processes which charge the particles triboelectrically. If such is the case, no charger is required.
  • the gas stream then passes to an agglomerator 30 where it is subjected to a transverse AC field. The AC field causes the larger particles to sweep by the smaller ones, thereby enchancing attractive coulomb forces and overcoming repulsive coulomb forces. Thus agglomeration is achieved. Since substantial charge neutralization often tends to occur, the gas stream may then be passed through a recharger 35 and thereafter through collector 40.
  • Recharger 35 may be of a similar design to that of charger 10, or it can be incorporated with collector 40 as a single stage precipitator. Recharger 35 is preferably unipolar since some charge neutralization occurs when bipolar charging is used, and this could significantly impair collection efficiency.
  • Charger 10 may be of any conventional design. Since migration velocity and hence collection efficiency are improved through using as high a charging field as practical, as discussed in Equations 1 and 4, any improvements allowing the use of a high field are preferably incorporated into charger 10 (or 25). Increasing the charging field also increases the agglomeration, as indicated by Equation 7.
  • One example of such an improvement relating to chargers is set forth in the copending commonly owned United States Patent Application Serial No. 784,196, filed April 18, 1977, and entitled "Resistive Anode for Electrostatic Precipitation".
  • collector 20 (or 40) will not be described herein in detail. However, for the purpose of describing the relevant parameters for the agglomerator, it is helpful to note some basic parameters and design considerations for collectors more generally.
  • the collector typically consists of a series of grounded parallel plates and an interleaving series of electrodes at high voltage.
  • the high voltage electrodes are the same wires that provide the corona field; in two-stage precipitators the high voltage electrodes may be wires or plates.
  • the grounded electrode plates are where the collection occurs, and a dust layer having a thickness of a centimeter or more can be expected to form.
  • the plates are typically designed with the collecting surface shielded from the gas flow to prevent the once collected particles from becoming re-entrained in the gas stream.
  • the preferred spacing between electrodes results from a compromise.
  • a smaller spacing would require a lower voltage for the same field and provide a larger plate area for a given overall width.
  • too small a spacing leads to problems with collected dust layers bridging the gap and causing a short circuit.
  • Expense is also a problem with smaller spacing, since more material is required.
  • the optimum duct spacing (the distance between adjacent ground plates, there being a high voltage wire plane therebetween) can be shown to be in the range of 10 inches. See White at pp. 177-180.
  • the mechanical structure of agglomerator 15 typically resembles that of plate type collectors.
  • the agglomerator includes an outer grounded shell 50 which extends along the direction of gas flow 60 and defines a transverse cross sectional area of gas flow.
  • Shell 50 is provided with a plurality of high voltage electrode plates 70 aligned parallel to the direction of gas flow, and an interleaved plurality of grounded plates 75.
  • a high voltage A C field is set up between adjacent electrode pairs, each such pair having a grounded electrode and a high voltage electrode.
  • an electric field amplitude E a differ depending on whether the collisions are between like-charged or unlike-charged particles. For like-charged particles one should choose as high a field E a as possible so as to overcome coulomb repulsion. For collisions between unlike-charged particles, there is a trade-off between higher fields E a that promote both a larger relative velocity (and hence collision frequency) between particles as well as an enhanced short-range attraction and mixing, and lower fields E a that better allow for the beneficial effects of long-range coulomb attraction. Again, there is the static breakdown field limit on E a , with practical con- siderations dictating a lower peak amplitude in the range of 5-15 kv/cm.
  • the agglomerator is not a collecting stage, plate spacing and design may be varied in order to optimize other considerations. In contrast to the situation in the collection stage, agglomeration efficiency is not increased by increasing the plate area (for a given plate length). Thus, the main advantage of using a smaller plate spacing is the feasibility of using a lower voltage source for a given field. This can be directly balanced against the cost of an increased nubmer of plates.
  • the plates need not be designed to avoid re- entrainment, since collection is undesirable. Thus, flat plates are suitable. However, the edges should be rounded to avoid local field enhancement and resultant corona emission which can reduce the charge on the particles. A "Rogowski" shape is preferred.
  • agglomerator field frequency is relatively simple. As was discussed in connection with Equation 8, the path length swept out to produce agglomeration is independent of frequency. Thus, there is great freedom on the choice of frequency at which the agglomerator can be operated. Since nearly all power is distributed at 60 cycles (cps) per second, most agglomerators will operate at that frequency. Other frequencies, such as the 400 cps frequency encountered on aircraft and the like, can be employed when practicing the present invention. A preferred frequency range is 30-500 cps, since inertial effects could become significant at higher frequencies. At frequencies much lower, the agglomerator could act as a collector, especially with respect to the larger particles. This would undercut the agglomerator function.
  • the length of a typical agglomerator stage depends on the length of time it takes for agglomeration to occur.
  • This characteristic time referred to as residence time, can be shown to be inversely proportional to the charging field E 0 , the agglomerator (AC) field E a , the collision cross section or efficiency, and the dust loading.
  • the charging field has been maximized, and furthermore recognizing that the dust loading is likely to be a given quantity in a specific application, it becomes an object to increase the product of E a and collision efficiency which depends on E a . Whether this is necessary clearly depends on a given situation, for example, the properties of the suspended particles in question.
  • Bipolar charging improves collision efficiency since positive and negative particles are attracted to one another, thereby enchancing the agglomeration. Bipolar charging is not without its detrimental characteristics since it may become necessary to recharge the suspended particles if considerable charge neutralization occurs. This would require additional precipitator length, and could undercut some of the advantage to be gained by agglomeration. Additionally, it is more of a routine procedure to run ionizers with negative polarity than it is to run them with positive polarity. Thus the choice between unipolar and bipolar charging will depend on the particular application.

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EP79300858A 1978-09-15 1979-05-17 Dispositif d'agglomération de cendre volante, conduit équipé de ce dispositif et procédé pour enlever des particules chargées en suspension, de dimensions variables, d'un volume de gaz Withdrawn EP0009857A3 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US94258278A 1978-09-15 1978-09-15
US942582 1978-09-15

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EP0009857A2 true EP0009857A2 (fr) 1980-04-16
EP0009857A3 EP0009857A3 (fr) 1980-04-30

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JP (1) JPS5539289A (fr)
AU (1) AU4621379A (fr)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3238793A1 (de) * 1982-10-20 1984-04-26 Robert Bosch Gmbh, 7000 Stuttgart Verfahren und vorrichtung zum reinigen von gasen
EP0253056A1 (fr) * 1986-03-26 1988-01-20 BBC Brown Boveri AG Méthode de chargement électrostatique de particules solides ou fluides en suspension dans un courant gazeux, utilisant des ions
WO1997034701A1 (fr) * 1996-03-16 1997-09-25 Pifco Limited Traitement de polluants particulaires
US5707428A (en) * 1995-08-07 1998-01-13 Environmental Elements Corp. Laminar flow electrostatic precipitation system
WO2000065150A1 (fr) * 1999-04-23 2000-11-02 The Babcock & Wilcox Company Procede de gazeification de liqueur residuaire a haute temperature et haute pression
WO2001034854A2 (fr) 1999-11-11 2001-05-17 Indigo Technologies Group Pty Ltd Procede et appareil d'agglomeration de particules
US7300496B2 (en) 2004-12-10 2007-11-27 General Electric Company Methods and apparatus for air pollution control
CN105855045A (zh) * 2016-05-20 2016-08-17 武汉大学 可调控的湍流产涡超细颗粒物凝并装置
US11123752B1 (en) * 2020-02-27 2021-09-21 Infinite Cooling Inc. Systems, devices, and methods for collecting species from a gas stream
US11298706B2 (en) 2019-08-01 2022-04-12 Infinite Cooling Inc. Systems and methods for collecting fluid from a gas stream

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57152828A (en) * 1981-03-16 1982-09-21 Engei Gijutsu Center Kk Cultivation in greenhouse
JPS63148163U (fr) * 1987-03-18 1988-09-29

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1102109B (de) * 1957-08-13 1961-03-16 Georg Ronge Verfahren zur Saeuberung staubhaltiger und verunreinigter Gase
US3717977A (en) * 1971-04-05 1973-02-27 Freeman W Smoke pollutant concentrator
FR2167504A1 (fr) * 1972-01-14 1973-08-24 Nippon Kogei Kogyo Co
DE2329344A1 (de) * 1973-06-08 1975-01-09 Haupt & Pusch Gmbh Kombiniertes entstaubungs-aerosolfilterund klimatisationsverfahren
US4154585A (en) * 1977-03-28 1979-05-15 Massachusetts Institute Of Technology Fluidized bed particulate collectors

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1102109B (de) * 1957-08-13 1961-03-16 Georg Ronge Verfahren zur Saeuberung staubhaltiger und verunreinigter Gase
US3717977A (en) * 1971-04-05 1973-02-27 Freeman W Smoke pollutant concentrator
FR2167504A1 (fr) * 1972-01-14 1973-08-24 Nippon Kogei Kogyo Co
DE2329344A1 (de) * 1973-06-08 1975-01-09 Haupt & Pusch Gmbh Kombiniertes entstaubungs-aerosolfilterund klimatisationsverfahren
US4154585A (en) * 1977-03-28 1979-05-15 Massachusetts Institute Of Technology Fluidized bed particulate collectors

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3238793A1 (de) * 1982-10-20 1984-04-26 Robert Bosch Gmbh, 7000 Stuttgart Verfahren und vorrichtung zum reinigen von gasen
EP0253056A1 (fr) * 1986-03-26 1988-01-20 BBC Brown Boveri AG Méthode de chargement électrostatique de particules solides ou fluides en suspension dans un courant gazeux, utilisant des ions
CH669341A5 (fr) * 1986-03-26 1989-03-15 Bbc Brown Boveri & Cie
US5707428A (en) * 1995-08-07 1998-01-13 Environmental Elements Corp. Laminar flow electrostatic precipitation system
AU715203B2 (en) * 1995-08-07 2000-01-20 Environmental Elements Corp. Laminar flow electrostatic precipitation system
WO1997034701A1 (fr) * 1996-03-16 1997-09-25 Pifco Limited Traitement de polluants particulaires
WO2000065150A1 (fr) * 1999-04-23 2000-11-02 The Babcock & Wilcox Company Procede de gazeification de liqueur residuaire a haute temperature et haute pression
WO2001034854A3 (fr) * 1999-11-11 2002-04-18 Indigo Technologies Group Pty Procede et appareil d'agglomeration de particules
WO2001034854A2 (fr) 1999-11-11 2001-05-17 Indigo Technologies Group Pty Ltd Procede et appareil d'agglomeration de particules
US6872238B1 (en) 1999-11-11 2005-03-29 Indigo Technologies Group Pty Ltd. Method and apparatus for particle agglomeration
US7300496B2 (en) 2004-12-10 2007-11-27 General Electric Company Methods and apparatus for air pollution control
CN105855045A (zh) * 2016-05-20 2016-08-17 武汉大学 可调控的湍流产涡超细颗粒物凝并装置
US11298706B2 (en) 2019-08-01 2022-04-12 Infinite Cooling Inc. Systems and methods for collecting fluid from a gas stream
US11786915B2 (en) 2019-08-01 2023-10-17 Infinite Cooling Inc. Systems and methods for collecting fluid from a gas stream
US11123752B1 (en) * 2020-02-27 2021-09-21 Infinite Cooling Inc. Systems, devices, and methods for collecting species from a gas stream
US20210370318A1 (en) * 2020-02-27 2021-12-02 Infinite Cooling Inc. Systems, devices, and methods for collecting species from a gas stream

Also Published As

Publication number Publication date
JPS5539289A (en) 1980-03-19
EP0009857A3 (fr) 1980-04-30
AU4621379A (en) 1980-03-20

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Inventor name: SELF, SIDNEY ALBERT