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
  • B03C3/16—Plant or installations having external electricity supply wet type
• • 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
  • B03C3/01—Pretreatment of the gases prior to electrostatic precipitation
  • B03C3/014—Addition of water; Heat exchange, e.g. by condensation
• • 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
  • B03C3/06—Plant or installations having external electricity supply dry type characterised by presence of stationary tube electrodes

Definitions

• the invention relates to a method and a device for separation of particles from a gas flow, of the kind indicated by the preambles of the attached independent method claim and device claim respectively.
• Heat may for example be extracted primarily for some useful purpose, e.g. district heating, which entails the flue gas being cooled to, for example, 5O 0 C, e.g. by conventional heat exchange or by water sprayed directly into the flue gas flow and drawn off in a hot state at various points along the gas line for direct or indirect heat exchange against a district heating flow.
• the flue gas still contains particles of various kinds which need substantially removing before the flue gas flow can or may be discharged directly to the environment. It is of course also desirable, at least as far as economically possible, to extract residual heat from the gas flow after the extraction of thermal energy for the primary purpose, before the gas flow is discharged to the environment.
• One object of the invention is therefore to indicate a simple technique which at relatively low cost makes it possible to substantially clean flue gas and also makes it possible to recover heat from it easily and effectively in conjunction with said clea- ning.
• a particular object is to extract heat and clean flue gas at a low temperature in order to achieve particularly effective cleaning of it.
• flue gas after primary heat extraction is at a relatively low temperature, e.g. 5O 0 C or lower.
• care is taken to ensure that the flue gas is substantially saturated before it is led through a special heat exchanger comprising a plurality of parallel separate tubes which are cooled on the outside by a flow of a fluid such as ambient air, whereby the heat absorbed by the fluid, and possibly also the fluid itself, can be utilised, e.g. as preheated combustion air for a biof ⁇ el boiler which produces the flue gas flow.
• the tubes may be surrounded by a vessel with an inlet and an outlet for the cooling fluid, e.g. a liquid such as water, or ambient air, which is thus heated, making it possible for the heat content of the fluid to be utilised in a conventional manner.
• the tubes are substantially vertical and each comprise a coaxial electrode supplied with an electrical potential which differs greatly from earth potential, while the tubes are maintained at earth potential.
• the electrode and its power supply are with advantage so disposed and designed as to cause corona arcs in the saturated gas flow which passes through axially, in order to charge and/or treat the particles therein, the gas flow being preferably led downwards so that it remains substantially saturated during its movement along the tubes, despite being progressively cooled.
• the amount of particles in the flue gas may be reduced to, for example, 30 mg/m 3 in cases where the gas flow is cooled to a temperature of about 3O 0 C, e.g. against ambient air.
• the invention thus makes it possible in practice, by cooling the flue gas flow to low temperature levels of, for example, about 3O 0 C, to free the flue gas from pollutants which are otherwise particularly difficult to deal with, such as certain types of salts. It certainly might be possible to remove pollutants of the dioxin type by the technique according to the invention. Further cooling of the gas flow, e.g. down to 1O 0 C or 5 0 C, makes it possible for the separation to be still more effective for certain pollutants and/or might enable further pollutants to be separated effectively.
• the condensate with associated pollutants from the inside walls of the tubes is produced in relatively small flows, and effective and relatively low cost techniques are now available for the separation and final treatment of pollutants from the condensate flow.
• Fig. 1 depicts schematically a combustion installation comprising a particle- separating flue gas cooler according to the invention.
• Fig. 2 depicts schematically a sectioned sideview through a tubular heat exchanger whose tubes are intended to have flue gas or process gas flowing through them with a view to separation of pollutants from the flue gas flow with simultaneous extraction of heat from it.
• Fig. 3 depicts a sectioned view along the line III-III in Fig. 2.
• Figs. 4 and 5 depict schematically a sideview and an end view respectively of a group of electrodes fitted in the heat exchanger tubes.
• Fig. 6 depicts schematically a transverse section through the heat exchanger's tubes and electrodes and illustrates the positioning of liquid injection pipes in intermediate spaces between groups of mutually adjacent heat exchange tubes.
• Fig. 7 illustrates schematically a section along the line VII-VII in Fig. 6.
• Fig. 1 illustrates a process in which flue gas from a biofuel boiler is led out along a flow path 2 along which it is cooled in a cooler 3 by local injection of water sprays at separate points along the flow path.
• the resulting flows of hot water and condensate are drawn off locally along the flue path, have correspondingly different temperature levels and are subjected to heat exchange at respective corresponding temperature levels against a flow path which has flowing through it a fluid, e.g. district heating water, which is to be heated as a primary purpose of the biofuel boiler.
• coarse pollutants such as ash, soot particles and the like are washed out of the flue gas flow.
• the outgoing flue gas After the primary energy extraction from the flue gas flow, the outgoing flue gas, which is in a saturated state, are at a temperature of about 6O 0 C and is then led into a heat exchanger 4.
• the heat exchanger 4 comprises a bundle 41 of mutually separate axially parallel cylindrical tubes 42 made of thermally conductive material, e.g. acid-resistant stainless steel.
• the tubes are preferably of circular cross-section and are disposed substantially vertically, and the flue gas flow is distributed to the tubes 42 via an inlet box 45 and is led in at the lower ends of the tubes and led out at the upper ends of the tubes 42 to an outlet box 46, and thence to, for example, the environment.
• the tubes 42 are cooled externally by a forced flow 50 of a fluid such as, preferably, ambient air 58.
• the fluid may be a liquid flowing through a casing which surrounds the heat exchanger 4.
• the cooling air 58 is heated and its energy content is utilised in a heat consumer 56 and/or is introduced as combustion air into the boiler 1.
• Each of the circular cylindrical tubes 42 has extending along its centre a respective electrode 43 which may be provided with protrusions distributed along the length of the electrode and around the circumference of the electrode.
• the electrodes 43 are supplied via a distribution system 44 with electric current which has a potential of, for example, 50,000 volts relative to earth potential.
• the tubes 42 are with advantage maintained at earth potential.
• the electrodes are with advantage negatively charged relative to earth potential.
• Each electrode is preferably so powered and designed as to generate corona effects in the gas flow along the respective tube.
• An electrical field is also established between the electrode and the tube wall.
• Particles in the gas flow passing through the respective tube will thus become charged and be deposited on the inside wall of the tube, on which water from the saturated gas condenses, l ne condensate washes down the pollutants deposited on the inside wall of the tube.
• the electrical field and/or the corona effects may possibly break down certain types of pollutants in the gas flow.
• the condensate with accompanying solid and loose pollutants washed down in it accumulates in the box 45 and is led out to a cleaner 60 in which the condensate undergoes some form of conventional cleaning not described in more detail, after which the condensate can be recirculated to some part of the process concerned.
• liquid tubes 70 with a diameter of, for example, 25 mm may be placed in respective intermediate spaces between groups of mutually adjacent condensation tubes 42 and extend parallel with the tubes 42.
• the liquid tubes 70 may be supplied via a water supply system and have small perforations 71 distributed along and around the tubes 70 and serving as spray nozzles for finely divided delivery of pressurised water/liquid.
• the resulting water sprays saturate the cooling air 58 and cool the condensation tubes 42, with the result that the cooling air acquires a power energy content at relatively low temperature and that the flue gas/process gas can be effectively cooled to a low temperature despite a relatively small heat exchange surface, while the condensate which forms on the inside of the tubes 42 is used for washing down solid pollutants which become deposited on the inside of the tubes 42.
• the flow direction selected for the process gas results in advantageous washdown conditions and limits recontamination of the process gas.
• the cooling air can be utilised, e.g. as combustion air for the fuel boiler.
• the liquid tubes 70 constitute a humidifier for the condenser tubes 42 and provide a high transfer rate and an advantageous large temperature difference across the wall of the condenser tubes 42.
• the condenser tube heat exchanger 4 according to Figs. 1 and 2 has a heat exchange area of about 100 m 2 (the local wall area of the tubes 42) and the air velocity across the condenser tubes 42 is, for example, about 14 m/s.

Landscapes

• Electrostatic Separation (AREA)
• Treating Waste Gases (AREA)
• Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (3)

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Family Cites Families (6)

• 2004
  • 2004-07-05 SE SE0401751A patent/SE526864C2/sv unknown
• 2005
  • 2005-06-16 EP EP05752729A patent/EP1765505A1/en not_active Withdrawn
  • 2005-06-16 WO PCT/SE2005/000927 patent/WO2006004490A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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