RU2176561C1 - Method and device for cleaning gas - Google Patents

Abstract

FIELD: gas cleaning devices. SUBSTANCE: method consists in treatment of gas flow between receiving electrodes coated with layer of homogeneous dielectric and perforated over working surface; electrode gas is filled with unipolar space charge extracted from plasma zone of barrier discharge. Barrier discharge plasma is activated in form of plasma columns above perforations of one of receiving electrodes. Device is provided with additional plate-type electrodes: one electrode is made in form of metal plate with needles whose pointed edges lie above centers of perforations of receiving electrodes at equal distance from surface of receiving electrode; other additional electrode coated with layer of homogeneous dielectric is mounted at before-breakdown distance from surface of opposite receiving electrode. Elevated temperature in plasma columns formed at pointed edges of needles of one of additional electrodes prevents formation of ozone molecules increasing concentration of changed particles in plasma discharge; position of plasma columns of discharge above perforations of receiving electrode provides for coincidence of directions of motion of charge carriers with direction of field lines of electric field between receiving electrodes, thus facilitating extraction of charge carriers into electrode gap during voltage half- wave, higher discharge of dispersed dielectric admixture and enhanced settling on receiving electrodes during respective period of time. EFFECT: enhanced efficiency. 5 cl, 1 dwg

Description

 The invention relates to the purification of gas from dielectric impurities and can be used in metallurgical, chemical, oil refining and other industries.

 A known method of gas purification, based on the transmission of the medium to be cleaned through a constant electric field created between the plate deposition electrodes and ionizing electrodes, which was used as a system of crossed rows of bare and dielectric coated wires. When an alternating voltage was applied to the ionizing electrodes, a barrier discharge plasma arose in the areas of their overlap. Carriers are removed from the plasma zone under the influence of a constant electric field, dust particles are charged by them and deposited on the precipitation electrodes.

 (USSR Author's Certificate N 956019, M.C. B 03 C 3/08, 09/07/82).

 The disadvantage of this method of gas purification is the presence of a high probability of spark breakdowns between the bare ionizing wires and the precipitation electrode, also without a dielectric coating. The probability of spark breakdowns increases with the capture of dielectric impurities due to the occurrence of "reverse corona" in the dust layer on the precipitation electrode.

 There is also a method of purifying gas from a dielectric impurity, comprising treating a gas stream with an alternating voltage electric field between flat deposition electrodes coated with a uniform dielectric layer and perforated over the working surface, in which the interelectrode gap is filled with a unipolar space charge by removing charge carriers from the barrier discharge plasma zone excited between precipitation electrodes and plate additional electrodes, also covered with a layer of die ktrika.

 (RF patent N 2098191, CL B 03 C 3/08, 12/10/97).

 This method has a low efficiency of cleaning gas flows at a high concentration of dielectric impurity due to the low degree of extraction of charge carriers from the plasma zone, which is not formed in the volumes above the perforation openings - regions of the discharge from the charge carrier plasma. In addition, the formation of a large number of ozone molecules in a discharge plasma requires additional equipment for its catalytic decomposition.

 The problem solved by the invention is to increase the efficiency of capture of dielectric impurities.

 To solve the problem according to a method of gas purification from a dielectric impurity, which includes treating a gas ceiling with an alternating voltage electric field between flat deposition electrodes coated with a uniform dielectric layer and perforated over the working surface, in which the interelectrode gap is filled with a unipolar space charge extracted from the barrier discharge plasma zone excited between the precipitation and additional electrodes, the plasma of the barrier discharge is excited in the form of a change columns over the perforations of one of the precipitation electrodes.

 A device for cleaning gas from a dielectric impurity is known, comprising a housing, a system of plane-parallel deposition electrodes coated with a uniform dielectric layer and perforated along the working surface, additional plate electrodes also coated with a dielectric layer, and an alternating current source.

 (RF patent N 2098191, CL B 03 C 3/08, 12/10/97).

 However, this device is also not effective enough.

 Improving the cleaning efficiency of the device according to the invention is achieved by the fact that in the device for gas purification from a dielectric impurity, comprising a housing, a system of plane-parallel precipitation electrodes coated with a uniform dielectric layer and perforated along the working surface, additional plate electrodes and an alternating current source, one of the additional electrodes is performed in the form of a metal plate with needles, which is installed over one of the precipitation electrodes, providing the position of sharp edges ok needles above the centers of the perforations at an equal distance from the surface of the precipitation electrode, and another additional electrode coated with a layer of a uniform dielectric is installed at a fractional distance from the surface of the opposite precipitation electrode. The distance of the sharp edges of the needles from the surface of the precipitation electrode is selected in the range of 0.05 - 0.15 m. The diameter of the perforation holes in the precipitation electrodes is selected in the range of 0.02 - 0.1 m.

 Precipitation electrodes are connected to opposite terminals of the AC source, and the corresponding additional electrodes are connected to these terminals of the source in the reverse order.

 The increased temperature of the gas in the plasma columns formed on the sharp edges of the needles of the additional electrode prevents the formation of ozone molecules and contributes to a higher density of charged particles.

 The location of the columns of the discharge plasma above the perforation holes of the precipitation electrode ensures that the directions of motion of the charge carriers coincide with the direction of the electric field lines between the precipitation electrodes.

 The drawing shows a schematic diagram of the implementation of a method of purification of gas from a dielectric impurity, also depicting a cross section of a device for its implementation.

 The device comprises a housing (not shown in the drawing) in which plate-like precipitating electrodes 1 and 2 are located. The depositing electrodes are coated with a uniform dielectric layer 3 (for example, glass, fluoroplastic) and have perforations 4. An additional plate electrode 5 is coated with a uniform dielectric layer and installed at a fractional distance from the precipitation electrode 1. Another additional electrode 6 is made in the form of a metal plate with needles 7 and is mounted above the opposite precipitation electrode 2, at The sharp edges of 8 needles 7 are located above the centers of the perforations at an equal distance from the surface of the precipitation electrode. Precipitation electrodes have a polymer protective mesh 9 on the gas stream side with a mesh size that is not permeable to dispersed dielectric impurities.

 The method of gas purification is as follows.

 A gas stream containing a dielectric impurity is passed through the gap between the precipitation electrodes 1 and 2. When an alternating high voltage is applied to the electrodes between the precipitation electrode 2 and the sharp edges 8 of the needles 7 of the additional metal electrode 6, a one-way barrier discharge plasma is formed, which is collected near the sharp edges of the needles in the form of a high-temperature plasma column, which then decomposes into multiple curved streamer channels in the vicinity of the opposite opening in the precipitation m electrode.

 The charge carriers extracted by the electric field between the precipitation electrodes from the plasma column through the perforations 4 in the precipitation electrode 2 fill the gap between the precipitation electrodes with a unipolar space charge. Particles of a dielectric impurity falling into the region of the space charge with a gas stream are charged by charges of the corresponding sign and move to the precipitation electrode 1 during the half-wave voltage. When the polarity of the electric potential on the precipitation electrodes changes, carriers of the opposite charge are removed into the region between the precipitation electrodes and particle deposition continues.

 The dielectric impurity is also deposited on the precipitation electrode 2 due to incomplete removal of impurity particles charged during the half-wave voltage from the region between the precipitation electrodes.

 The method of gas purification was carried out in the following example.

In the experimental device containing a system of plane-parallel precipitation electrodes coated with glass, a gas was supplied containing high-resistance flue gas ash from TPPs. The total deposition area was 2.0 m ² , the distance between the precipitation electrodes was 0.4 m. Removing the sharp edges of the needles of the metal additional electrode from the surface of the perforated precipitation electrode was 0.1 m. The diameter of the perforations was 0.05 m. The distance between the centers perforations - 0.2 m. An additional plate electrode covered with glass was located at a distance of 0.5 - 0.7 m from the surface of another precipitation electrode. The alternating voltage between the electrodes is 35 kV. The gas flow rate is 2 m / s.

 With the selected test parameters, the capture efficiency was 80%, and for the same conditions, when using a plasma of a barrier discharge between plane-parallel precipitation and additional electrodes coated with glass, with a distance between them of 0.02 m, the cleaning efficiency was 50%.

 The low adhesion of many dielectric coatings improves the conditions for removal of the deposited dielectric impurities from the precipitation electrodes.

 The device according to the proposed method of gas purification has high reliability and stability when working in aggressive environments and carries out the deposition of both solid and liquid dielectric impurities with high concentrations in gas streams.

Claims (5)

 1. A method of purifying a gas from a dielectric impurity, comprising treating a gas stream with an alternating voltage electric field between plane-parallel deposition electrodes coated with a uniform dielectric layer and perforated over the working surface, in which the interelectrode gap is filled with a unipolar space charge extracted from the plasma discharge barrier region excited between precipitation and additional electrodes, characterized in that the plasma of the barrier discharge is excited in the form of plasma olbov perforations over one of the collecting electrodes.  2. A device for gas purification, comprising a housing, a system of plane-parallel precipitation electrodes coated with a uniform dielectric layer and perforated along the working surface, additional plate electrodes and an alternating current source, characterized in that one of the additional electrodes is made in the form of a metal plate with needles, which set over one of the precipitation electrodes, ensuring the position of the sharp edges of the needles above the centers of the perforations at an equal distance from the surface a single electrode, and another additional electrode coated with a layer of a uniform dielectric, is installed at a fractional distance from the surface of the opposite precipitation electrode.  3. The device for gas purification according to claim 2, characterized in that the distance of the sharp edges of the needles from the surface of the precipitation electrode is selected in the range of 0.05-0.15 m  4. The device for gas purification according to claim 2, characterized in that the diameter of the perforation holes is selected in the range of 0.02-0.1 m  5. The gas purification device according to claim 2, characterized in that the precipitation electrodes are connected to opposite terminals of the AC source, and the corresponding additional electrodes are connected to these terminals of the source in the reverse order.