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
  • B03C3/02—Plant or installations having external electricity supply
  • B03C3/04—Plant or installations having external electricity supply dry type
  • B03C3/14—Plant or installations having external electricity supply dry type characterised by the additional use of mechanical effects, e.g. gravity
  • B03C3/155—Filtration

Definitions

• the present invention relates to a filter for separating particles from gases by screening, comprising bag-shaped filter members made of filter material, each filter member having at least one opening for discharging the gases flowing through the filter medium of said filter member, and pervious stiffening means arranged inside said filter members.
• the gaseous impurities not separated in the contact reactor can be separated in the filter, and the degree of separation is naturally due to the sojourn time of the gases in the dust cakes.
• the pressure drop across the filter increases as well. Since the energy consumption by the fans of the plant increases, and since the fans are not capable of pressing the gases through the filter at very high pressure drops, the cake thickness will thus be limited by the pressure drop which in turn is determined by the magnitude of the resistance which the dust cakes exert on the gas flow.
• the filter operating temperature is in this case at a level too low for the remaining process.
• a powdery catalyst material is applied to the outsides of the filter members, and ammonia is added to the gases ahead of the filter, the latter may be used for catalytic reduction of nitrogen oxides in the gases.
• the catalyst material in many cases has such a high density that the catalyst material layers formed on the outsides of the filter members become so heavy that they fall off the filter members before they have become thick enough for a satisfactory nitrogen oxide reduction.
• the object of the present invention is, therefore, to provide a gas cleaning filter which imparts to the dust cakes or the catalyst material layers a sufficient thickness to obtain a satisfactory separation of the particulate and gaseous impurities of the gases in all filter applica ⁇ tions, i.e. also in a plant for cleaning flue gases from a refuse in- cineration plant.
• the electrically conductive means inside the filter members consist of the said stiffening means, while the electrically conductive means outside the filter members consist of electrodes.
• a voltage of 0-50 kV, especially 20 kV, has been applied between the stiffening means and the electrodes.
• the stiffening means may be earthed, and to the electrodes a voltage of 0-50 kV, preferably 20 kV, may be applied.
• the electrodes may be earthed, and to the stiffening means a voltage of 0-50 kV, preferably 20 kV, may be applied.
• the filter medium consists of textile material which, preferably, is of PTFE (TEFLON).
• the fibres hanging loosely from the filter medium preferably consist of PTFE (TEFLON) and usually have a length of 10-50 mm, preferably 30 mm, and a thickness smaller than or equalling 0.2 mm, preferably 0.1 mm.
• Fig. 1 is a longitudinal sectional view of a bag filter according to the invention.
• Fig. 2 is an enlarged part sectional view of Fig. 1.
• the bag filter 1 shown in Fig. 1 comprises a filter housing 2, an inlet 3 for the gases, e.g. flue gases from a refuse incineration plant, to be cleaned, and an outlet 4 for the cleaned gases.
• a plate 5 divides the inside of the filter housing into a raw gas chamber 2a and a clean gas chamber 2b communicating with the inlet and the outlet, respectively.
• the bag filter usually comprises 100-500, especially 300, filter bags 7 arranged in longitudinal and transverse rows. At their upper open end, these filter bags are detachably mounted in holes 6 in the plate 5 by means of a conventional attachment (not shown).
• the length of the filter bags is 3-5 m, usually 5 m, and their diameter is 100-200 mm, usually 125-130 mm.
• the longitudinal distance between two adjacent filter bags 7 is 300-500 mm, usually 400 mm.
• the transverse spacing is 300-500 mm, usually 400 mm.
• Electrodes 8 are arranged between the filter bags such that one electrode is positioned at each point of intersection between the diagonal lines of four longitudinally and transversely adjacent filter bags. As is apparent from Fig. 1, the electrodes have the same length, but are thinner than the filter bags and in the form of round rods. Their diameter is 20-40 mm, usually 30 mm. The electrodes are inserted through holes (not shown) in the plate 5 and are kept in place by means of hol ⁇ ders (not shown), such that they have no contact with the plate 5. A voltage of 20 kV has been applied to the electrodes via their holders. Nozzle tubes 9 with nozzles 10 are transversely arranged over the filter bags 7, such that one nozzle is positioned over the upper open end of each filter bag.
• each filter bag when being cleaned, re ⁇ ceives a direct injection of cleaning air supplied to the nozzles from a pressure tank (not shown) via the nozzle tubes.
• the cleaning air is supplied to one nozzle tube at a time, in the form of a short strong pulse of com- pressed air.
• the nozzle tubes are detachably mounted in the clean gas cham ⁇ ber 2b for exchange of filter bags.
• the top of the filter housing 2 is provided with a number of doors 11 positioned over the nozzle tubes 9.
• the bottom of the filter housing 2 is funnel-shaped to serve as a dust pocket for collecting the dust separated from the raw gas.
• the dust is then fed to a dust container (not shown) by means of a screw conveyor (not shown).
• the filter bags 7 are mounted round stiffening means 12 in the form of cages which, in conventional manner, are shaped such that they do not interfere with the movement of the gas flow through the filter bags. Furthermore, these cages are earthed via the plate 5.
• Fig. 2 It is also apparent from Fig. 2 that the outsides of the filter bags are provided with fibres 13 hanging loosely from the filter material of the filter bags. These fibres are usually made of the same textile material as the filter. Since such materials can withstand higher operating temperatures, when surrounded by thick dust cakes, the choice of the material is determined by the filter operating temperature and the thickness of the dust cake 14 forming round the fibres 13.
• Acryl is a suitable material for operating temperatures of 60-130°C polyester for temperatures of 130-150°C RYT0N for temperatures of 150-180°C, and TEFLON for temperatures of 180-240°C.
• the length of the fibres is 10-50 mm, preferably 30 mm, and the thickness is smaller than or equalling 0.2 mm, preferably 0.1 mm.
• the bag filter operates as follows. The dust-laden gases to be cleaned in the bag filter are conducted, under a certain excess pressure, into the raw gas chamber 2b of the filter housing 2 via the inlet 3. Since the inlet is positioned at the upper end of the filter bags, the gases will flow vertically downwards along the outsides thereof (see
• the bag filter according to the invention has the same pressure drop as a conventional bag filter, although it has far thicker dust cakes than the conventional filter.
• the present bag filter thus ob ⁇ tains a higher degree of separation than a conventional bag filter at the same pressure drop. Then, the cleaned gases flow from the inside of the filter bags to the clean gas chamber 2b and, via the outlet 4, to a chimney (not shown) and are discharged into the atmosphere (see Fig. 1).
• the fibres hanging loosely on the outsides of the filter bags will also have a reinforcing effect on the dust cakes of the filter bags, such that the heavy dust cakes usually formed on the outsides of the filter bags when the filter is used as a N0 ⁇ -catalyst, will remain on the filter bags.
• the invention is not restricted to the embodiment de ⁇ scribed above, and it can be modified in several different ways within the scope of the accompanying claims.
• a different voltage than 20 kV may of course be applied between the electrodes and the cages, but it should preferably be 0-50 kV to make it possible to obtain maximum results. It would, for example, be possible to replace the electrodes arranged between the filter bags by cylindrical, gas-pervious electrodes round each filter bag.
• the round rod electrodes may, of course, also be of square or spiral form.

Landscapes

• Filtering Of Dispersed Particles In Gases (AREA)
• Electrostatic Separation (AREA)

Priority Applications (1)

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Publications (2)

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• 1989
  • 1989-01-03 SE SE8900017A patent/SE462615B/sv not_active IP Right Cessation
• 1990
  • 1990-01-02 EP EP90901699A patent/EP0452387B1/de not_active Expired - Lifetime
  • 1990-01-02 DE DE90901699T patent/DE69007611D1/de not_active Expired - Lifetime
  • 1990-01-02 AU AU48362/90A patent/AU4836290A/en not_active Abandoned
  • 1990-01-02 JP JP2501820A patent/JPH04502577A/ja active Pending
  • 1990-01-02 WO PCT/SE1990/000002 patent/WO1990007382A1/en not_active Ceased
  • 1990-01-02 CA CA002045146A patent/CA2045146A1/en not_active Abandoned

Non-Patent Citations (1)

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