Classifications

• • 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
  • B03C3/40—Electrode constructions
• • 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
  • B03C3/36—Controlling flow of gases or vapour
• • 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
  • B03C3/74—Cleaning the electrodes

Definitions

• the invention relates to an electrostatic filter for separating particles from a gas, which has at least one electrode connected to a high-voltage source and at least one grounded or oppositely polarized electrode, between which the gas loaded with the particles can be passed.
• the invention further relates to a method for separating particles from a gas by means of an electrostatically operating filter.
• Electrostatic filters of the generic type are known, for example, from EP 0 847 806 B1. They are used for the electrostatic separation of any particles and droplets from different gases in many process engineering processes, especially for gas dedusting.
• the gas to be cleaned flows through a lane-shaped register of precipitation electrodes, each of which is essentially shaped as a plate.
• Spray electrodes are arranged in the center of each alley formed by the precipitation electrodes.
• a high DC voltage is applied between the spray electrodes and the precipitation electrodes, which is above the corona threshold voltage.
• the spray electrodes emit electrons, which are accelerated in the immediate vicinity of the high-voltage spray electrodes due to the high electric field strength there so that their kinetic energy is sufficient to knock out more electrons from neutral gas atoms and / or molecules and in this way to generate an electron cloud.
• the electric field strength quickly decreases, so that the kinetic energy of the electrons falls below the limit at which the electrons are bound again by neutral gas molecules or atoms with the formation of negative gas ions.
• these negative gas ions preferentially attach to the dust particles and thus impart an electrical charge to them, so that the dust particles charged in this way experience an accelerating force effect in the direction of the precipitation electrode in the electrical field.
• they are collected in a dust layer through which the charge carriers flow to the grounded precipitation electrode, agglomerated and preferably cleaned by vibrations of the electrodes, for example caused by knocking, and fed to the dust collection and dust discharge device by gravity.
• a special design of an electrostatically operating filter is described in DE 3 723 544 A1.
• a “structured separation electrode” is shown as the precipitation electrode, which is opposite the spray electrode.
• the structuring can be developed in various ways. It is always used for mechanical binding and storage of the electrostatically separated dust particles.
• the structure-forming elements of the deposition electrode are placed in front of a closed metal plate, then a field-free space is created within the deposition electrode, but its dimensions are not described because it is irrelevant for the function of the deposition electrode: a Faraday cage is created by accident due to the design.
• the decisive factor for the function of this type of filter are the porous structure-forming elements, which are intended to ensure binding and storage of the separated dust.
• HS unit voltage source
• EP 0 847 806 B1 proposes a method in which the dust particles are charged and separated in procedural terms in decoupled substeps.
• a first charging zone the dust particles are electrically charged when the number of charge carriers is as high as possible - even if high gas turbulence is accepted.
• the separation zone the electrically charged dust particles are separated in an electrical field, the voltage of which is below the corona threshold voltage. This avoids the excitation of the electric wind.
• electrostatically operating filters which are also referred to as electrostatic filters
• a relatively high expenditure of energy is required for efficient separation of the particles or droplets from the gas.
• the electrical wind generated creates separation-inhibiting turbulence.
• the dust layer on the precipitation electrodes increasingly acts as a limiting factor for the current and the separation efficiency.
• the invention is therefore based on the object of eliminating the abovementioned disadvantages and proposing an electrostatic filter and a method for its operation which are distinguished by a high separation efficiency with low energy expenditure.
• the generation of electric wind should be minimized and the limiting effect of the specific electrical dust resistance should be eliminated.
• the construction is to be carried out in such a way that a continuous or quasi-continuous removal of the separated particles is ensured during the ongoing filter operation.
• the solution to this problem by the invention is characterized in that at least one of the electrodes of the electrostatically operating filter comprises a space into which the particles can enter and in the extension of which there is no electrical potential difference when the filter is in operation.
• a space is therefore provided on the electrode that is largely free of electrical fields.
• a spray electrode that is, an electrode on which extreme field strength peaks are generated by small radii or other geometric tapering. Since the electrodes of both polarities then act as precipitation or deposition electrodes, it is therefore only necessary to distinguish conceptually between the high-voltage and the grounded electrode.
• the positive or negative electrode can be highly excited.
• only the at least one electrode connected to the high-voltage source preferably all electrodes connected to the high-voltage source
• contains such a space it can also be provided that only the at least one grounded electrode, preferably all grounded electrodes, contains such a space.
• This space is advantageously at least partially delimited by a grid, mesh or the like and a separating plate, which are connected to one another in an electrically conductive manner and form the electrode.
• the grid has inlet openings for the particles.
• the quasi field-free space formed between the grid, mesh or the like and the separating plate is designed in such a way that the entering particles are braked to such an extent that they do not adhere to the separating plate for a longer period of time, but instead fall continuously downwards and are removed ,
• the grid, net or the like can be formed from a number of interconnected rods arranged parallel to one another, these being electrically conductively connected to the plate-shaped separating plate.
• the grid is formed from a number of interconnected rings which are arranged parallel to one another and which, when electrically connected to a cylindrical or hollow-cylindrical separating plate, form the electrode.
• the electrostatically operating filter can be designed as a “plate electrostatic filter”, in which a number of flat, box-shaped electrodes are arranged parallel to one another. It is also possible that it is designed as a tubular electrostatic filter, in which at least two electrodes are cylindrical or hollow-cylindrical are arranged coaxially to each other.
• At least one electrode has a discharge channel for particles, which adjoins the largely electrically field-free space.
• the method for separating particles from a gas by means of an electrostatically operating filter which has at least one electrode connected to a high-voltage source and at least one grounded or an oppositely polarized electrode, is characterized in that the gas laden with particles is passed between the electrodes, wherein the particles are deflected to one of the electrodes, and that the particles enter a space of the electrode, in the extension of which there is no electrical potential difference.
• the high voltage and the grounded electrodes can be constructed in the same way.
• a quasi-homogeneous electric field is therefore formed between the electrodes perpendicular to the direction of flow of the particle-laden gas - without a field strength peak, as in the previously known systems with spray electrodes.
• particles can be separated from the gas at the electrodes of both polarities in the same way.
• the proposed method uses the effect of an electric field between two electrodes on dust particles not ionized by a technical device or on specifically ionized dust particles in a gas stream.
• the electrodes are preferably under a voltage that is below the corona threshold voltage. Depending on the polarity, the particles in the electric field are deflected towards one of the two electrodes.
• the electrostatic filter can be constructed as a horizontally flowed filter, in which a cascade of box-shaped electrodes is used. Every second box-shaped electrode is either connected to the high-voltage source or grounded or with opposite polarity.
• a design can also be provided which leads to a vertically flowed through tube or honeycomb electrostatic precipitator.
• the proposed principle is equally applicable to a wet electrostatic precipitator.
• the invention makes use of the fact that, in the proposed design of the electrodes with a quasi-electric field-free space, dust particles can enter the space due to their kinetic energy, but are then not exposed to any further external electrostatic force and are therefore separated and removed using gravity be carried out continuously in the system.
• the proposed electrostatic filter has a highly efficient ability to separate particles and droplets from any gas stream, with only a small amount of energy being required. The occurrence of an electric wind is largely avoided.
• the electrodes are cleaned automatically, as described. If, on the other hand, the particles have adhesive or adhesive properties, the filtered particles can be cleaned from the walls of the electrostatic filter and / or the electrodes in a manner known per se by tapping the electrodes, the particles falling down predominantly in a largely electrically field-free space he follows. Depending on the properties of the particles, rinsing - i.e. wet filtering - is also possible during operation.
• the deposition of particles on / in the electrodes is also essentially dependent on the field strength that prevails between the high-voltage electrode and the grounded electrode.
• the field line of maximum field strength is perpendicular between the electrodes according to the polarity; this also applies in principle to known filters with grounded separating plates and spray electrodes at high voltage potential.
• the aim is to increase the distance between the electrodes of different polarity.
• Electrodes connected in a conductive manner, bodies - eg wires - protrude into the space between the electrodes. These bodies can be arranged parallel or perpendicular or obliquely to the flow direction of the gases to be cleaned.
• the maximum field strengths depend on the structural arrangement and can therefore have different values and directions.
• the angles between the maximum field strengths can assume all values between 0 ° and 180 °.
• Figure 1 is a perspective view of an electrostatic filter, which is designed as a horizontal flow filter.
• Figure 2 is a perspective view of a vertical flow through a tube filter.
• Fig. 4 is a perspective view of a filter lane of a horizontally flowed filter, the electrodes of which are provided with field-free spaces and with additional bodies (here wire brackets)
• FIG. 1 shows an electrostatic filter which is suitable for filtering particles and / or droplets from a gas stream.
• the gas contaminated with particles and flowing into the filter is identified by an arrow with the reference number 1.
• the gas flow flows through the filter, the particles in the gas being filtered out and removed.
• the outflowing cleaned gas is indicated by the arrow with the reference number 2.
• the stream of separated particles 3 emerges from the filter downwards.
• a cascade of electrodes is used to clean a larger gas flow.
• a number of box-shaped electrodes 4 and 5 are arranged parallel to one another. Between the electrodes 4, 5 there are alleys 8 through which the gas 1 to be cleaned is passed.
• the electrodes 4, 5 are alternately either connected to a high voltage source (namely the electrodes 4) or grounded (namely the electrodes 5).
• all electrodes 4, 5 are provided with a space, not designated here, into which the particles to be filtered out can enter, but in the extension of which there is no electrical potential difference; it is therefore referred to here as a quasi electrical field-free space.
• This space is created in the electrodes 4, 5 in that the separating plate 7 is surrounded by a grid 6. Separation plate 7 and grid 6 are electrically conductively connected.
• the grid 6 consists of a number of rods arranged parallel to one another.
• the gas loaded with particles first flows between the electrodes 4, 5 (cf. gas stream 1) and there it comes under the effect of the quasi-homogeneous electric field.
• the particles are deflected towards the electrodes and enter through the grid openings. This means that they are located in a quasi-electric field-free room, where they are no longer exposed to any further external electrostatic force. They fall down due to gravity and can be continuously removed from the filter while the filter is in operation.
• the cleaned gas leaves the filter in a horizontal direction via an outlet hood (see gas flow 2).
• the electrodes 4, 5 according to FIG. 1 show, by way of example, the creation of the electrical field-free space by the grid 6, which is made up of interconnected rods and is electrically conductively connected to the internal separating plate 7.
• the electrodes 4, 5 can have a modular structure and can be arranged one above the other and one behind the other, as shown in FIG. 1. In this example, the electrodes have a field-free space on both sides of the separating plate. Marginal electrodes or, in the case of a filter with only one passage for the gas passage, the electrodes can also be constructed such that they have a field-free space only on one side of the separating plate. In any case, the depth of the field-free space depends on the requirements for continuous particle removal.
• the grounded electrode 5 contains the quasi-field-free space 9, which is delimited here by a ring grating 6 and the cylindrical separating plate 7.
• the grid 6 is formed here by a number of interconnected metal rings arranged parallel to one another, these being electrically conductively connected to the separating plate 7 and together forming the electrode 5.
• the aim is for the electrically field-free spaces 9 to be designed as flow-calmed zones in order to prevent dust from entering the gas flow again.
• This can be achieved by a corresponding geometric arrangement of the lattice bars or lattice rings and / or a corresponding design of the gas inlet and the gas outlet.
• 3a and 3b show some details of the design of the electrodes 4, 5 with the separating plate 7, the grating 6 and the quasi electrically field-free spaces 9 defined thereby.
• the separating plates 7 are plate-shaped and surrounded by rod-shaped grating elements which form the grating 6.
• the largely electrically field-free space 9 is formed in the electrodes 4, 5 between the separating plates 7 and the grid 6.
• the filtered particles move downward in the direction of the arrow 3 (direction of gravity) and can be removed from the electrostatic filter.
• 3b shows a double-walled design of the electrodes 4, 5 to support the discharge of the particles from the filter.
• the particles located in the largely electrically field-free space 9 sink due to the force of gravity and are guided through guide plates and slots of the double-walled separating plate 7 into an internally protected intermediate space, namely into a discharge channel 10. There they can be led out of the electrostatic filter unaffected by the external gas flow.
• the structure of the electrodes shown can in principle be provided in the case of an electrostatic filter with a horizontal and vertical flow, wherein straight, curved, edged or round electrodes can be used.
• the design of the electrodes and the level of the voltage are matched to one another in such a way that there is no increase in the electric field strength, which leads to a corona or to external partial discharges.
• the bodies 11 are shown between the grids 6. They are made up of wire brackets that are conductively connected to the respective electrodes (4, 5).
• the straight wires are arranged perpendicular to the gas flow.
• the bodies can also be arranged parallel to the gas flow or at all angles between perpendicular and parallel to the gas flow.

Applications Claiming Priority (3)

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• 2002
  • 2002-09-30 DE DE10245902A patent/DE10245902A1/de not_active Withdrawn
• 2003
  • 2003-09-30 AT AT03750661T patent/ATE333942T1/de active
  • 2003-09-30 DE DE50304383T patent/DE50304383D1/de not_active Expired - Lifetime
  • 2003-09-30 ES ES03750661T patent/ES2268407T3/es not_active Expired - Lifetime
  • 2003-09-30 AU AU2003270294A patent/AU2003270294A1/en not_active Abandoned
  • 2003-09-30 WO PCT/EP2003/010830 patent/WO2004030825A1/fr not_active Application Discontinuation
  • 2003-09-30 DK DK03750661T patent/DK1545785T3/da active
  • 2003-09-30 EP EP03750661A patent/EP1545785B1/fr not_active Expired - Lifetime
• 2005
  • 2005-03-03 ZA ZA200501859A patent/ZA200501859B/xx unknown

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