METHOD AND DEVICE FOR CLEANING FAN IMPELLERS

Abstract: In a method of cleaning fan impellers bursts of solid material are thrown towards the impeller blades or other parts of the impeller, subjected to deposits, by means of pulses of compressed air, shot from a compressed air cannon. A device for cleaning fan impellers comprised of at least one compressed air cannon for directing shots in the form of pulses of compressed air towards the impeller blades or other parts of the impeller, subjected to deposits. The outlet cylinder (28) of the cannon is loaded with a charge of solid material (4) to be thrown towards the impeller blades or said other parts of the impeller, when shooting a pulse of compressed air.

Description: Method and device for cleaning fan impellers The present invention relates to a method and a device for cleaning fan impellers, said device comprising at least one compressed air cannon for directing shots in the form of pulses of compressed air towards the impeller blades or other parts of the impeller, subjected to deposits. In Swedish Patent Application No. 8902335-2 a method and a device is described for producing a shock wave by means of a compressed air cannon to unstick deposits on fan impeller blades. This technique is applicable to fans used under heavy environment conditions, like in dusty spaces such as in kilns of cement plants where deposits of dust on the impellers can cause severe vibration problems. Figure 1 shows an example of a device according to this prior art with a compressed air cannon disposed at the fan inlet. In some applications the hardness of the deposits on the blade surfaces will be so high that the deposits can not be efficiently removed by pulses of compressed air. The purpose of the present invention is to improve the efficiency of removing such hard deposits from impeller blades or other parts of a fan impeller. This purpose is obtained by a method according to claim 1 and a device according to claim 6. According to the invention hard deposits are removed by throwing bursts of solid material towards the impeller blades or other parts of the impeller, subjected to deposits. According to advantageous embodiments of the method according to the invention the bursts of solid material are thrown periodically or are controlled as a function of the level of vibration of impeller bearings. According to another advantageous embodiment of the method according to the invention the bursts of solid ma¬ terial are thrown towards diametrically opposite blades of the impeller by means of two compressed air cannons to avoid excessive unbalance due to unsticking of the deposits. According to still another advantageous embodiment of the method according to the invention the instant of shooting bursts of solid material is controlled as a function of the blade positions of the rotating impeller to provoke unstick- ing of deposits on the different blades in a selected order to reduce the unbalance created by this removal of deposits. According to an advantageous embodiment of the device ac¬ cording to the invention the solid material is contained in a cylindrical cartridge, intended to be positioned in the out- let cylinder of the cannon, the ends of the cylindrical cart¬ ridge being closed by a material, brittle enough to be broken by the compressed air pulse. Thus the cartridge has to be of sufficient strength to keep the material during transporta¬ tion, while the ends of the cartridge has to be so brittle that it is broken, when used in the air cannon, by the shot of compressed air from the cannon. The solid material used is chosen according to the hard¬ ness of the deposits and the fans liability to damages. The chosen solid material must be of sufficient strength to crush the deposits and at the same time be friable enough to elimi¬ nate the risk of damage or wearing of the impeller blades or other parts of the impeller. Thus, according to still another advantageous embodiment of the device according to the in¬ vention the solid material is formed of a coarse-grained material, the size of the grains being preferably between 5 and 50 mm, which coarse-grain material is friable without hard contents, and is preferably formed of gypsum stones. The solid material can also comprise an explosive which will explode when hitting the impeller blades or other parts of the impeller, subjected to deposits. With such a material a still more efficient cleaning effect can be obtained. An exemplifying embodiment of the device according to the invention will now be described more in detail with reference to the enclosed drawings on which Fig. 1 shows an embodiment of a device of the type used in the present invention with a movable compressed air cannon located at the impeller inlet. Fig. 2 in an axial section a portion of the outlet cylin¬ der of the air cannon charged with a cartridge containing solid material. Fig. 3 a cross-section through the plane A-A in fig. 2, and Fig. 4 a perspective view of the outlet cylinder of the air cannon with the retainer cylinder for the cartridge partly swung out. Fig. 1 shows a fan comprising an impeller 10 mounted inside a fan casing or fan scroll 18. A compressed air cannon 26 is located at the impeller inlet. The outlet cylinder 28 of the cannon 26 can be orient¬ ed in the axial direction of the fan or in any inclined di¬ rection to deliver compressed air pulses towards the impeller blades 24. The compressed air cannon which can be of the type described in the Swedish Patent Application 8902335-2 is shown in Fig. 1 in two different orientations by solid lines and dashed lines, respectively. A portion of the outlet cylinder 28 is shown in Fig. 2-4. A cartridge 2 containing solid material 4 is placed in the bore of the outlet cylinder 28. The cartridge 2 is formed of a material of sufficient strength to keep the material during transportation without damages. The ends of the cylinder are closed by a material 3 which is broken by the pressure pulse from the air cannon 26, such that the material 4 is thrown through the outlet cylind- er 28 to hit the impeller blades 24 or possibly other parts of the impeller subjected to deposits. The end walls 3 of the cartridge 2 can be formed e.g. of an expanded polystyrene composit or formed as cover plates of a thickness of up to 2 cm which plates are stuck with a proper adhesive to the cart- ridge cylinder. As another exemple the end walls 3 could be formed of paper of suitable quality. The outlet cylinder 28 comprises a removable portion 5 in the form of a half cylinder in which a retainer cylinder 6 for the cartridge 2 is mounted. The half cylinder 5 is articuledly mounted by a hinge 30 to the remaining part of the outlet cylinder 28, such that the half cylinder 5 can be swung along the hinge axis 8 out of the bore of the outlet cylinder 28. In this way the retainer cylinder 6 mounted in the half cylinder 5 can be removed from the bore of the out- let cylinder to allow removal of used cartridges 2 and in¬ sertion of new ones containing the solid material 4, where¬ upon the new cartridge 2 is swung into the bore of the out¬ let cylinder 28. As a closing device for the movable half cylinder 5 a suitable clamping device 32 is used. A sealing 7 is disposed between flanges 34 and 36 formed on the half cylinder 5 and the outlet cylinder 28 respectively to avoid air leakage with the half cylinder 5 positioned in the bore of the outlet cylinder 28. Other embodiments are possible for introducing the cart¬ ridges containing the solid material into the bore of the outlet cylinder. Thus e.g. a construction with guide bars can be used to allow removal of the removable portion from the outlet cylinder by a translational motion, or a revolver system can be associated with the outlet cylinder to allow loading of several cartridges. The opening of the outlet cylinder to remove used cart¬ ridges and inserting new ones is not dangerous for the operator, even if the fan is operating with hot gases. For such applications the fan is operating at a pressure below atmospheric pressure, and therefore when opening the outlet cylinder air is flowing from the atmosphere into the fan. As a consequence the removable part of the outlet cylinder is then cleaned from dust and cooled rapidly. The solid material 4 is a rather friable, coarse-grained material with a typical grain size of 5 to 50 mm. The materi¬ al is selected depending on the application such that depo¬ sits are effectively crushed and then blown away as a powder while the material is friable enough for eliminatig any risk of damage or wearing of the impeller blades. As an exemple gypsum stones can be used without any hard content that could give rise to wear. The solid material can also be formed of an explosive which will explode when hitting the impeller blades or other parts of the impeller subjected to deposits.

Claims: Claims 1. A method of cleaning fan impellers, c h a r a c t e r¬ i z e d in that bursts of solid material are thrown towards the impeller blades or other parts of the impeller, subjected to deposits, by means of pulses of compressed air shot from a compressed air cannon. 2. The method according to claim 1, c h a r a c t e r¬ i z e d in that the bursts of solid material are thrown periodically. 3. The method according to claim 1, c h a r a c t e r¬ i z e d in that the throwing of bursts of solid material is controlled as a function of the level of vibration of impeller bearings. 4. The method according to claim 1, c h a r a c t e r- i z e d in that the instant of shooting bursts of solid material is controlled as a function of the positions of the blades of the rotating impeller. 5. The method according to any of the claims 1 - 4, c h a r a c t e r i z e d in that bursts of solid material are thrown towards diametrically opposite blades of the impeller by means of two compressed air cannons. 6. A devide for cleaning fan impellers, comprising at least one compressed air cannon for directing shots in the form of pulses of compressed air towards the impeller blades or other parts of the impeller, subjected to deposits, c h a r a c t e r i z e d in that the outlet cylinder of the cannon is loaded with a charge of solid material to be thrown towards the impeller blades or said other parts of the impeller subjected to deposits, when shooting a pulse of compressed air. 7. The device according to claim 6, c h a r a c t e r¬ i z e d in that the solid material is contained in a cylind¬ rical cartridge, intended to be positioned in the outlet cylinder of the cannon, the ends of the cylindrical cartridge being closed by a material brittle enough to be broken by the compressed air pulse. 8. The device according to to claim 7, c h a r a c t e r¬ i z e d in that the material closing the ends of the cylin ¬ drical cartridge is formed of an expanded polystyrene compo- sit. 9. The device according to claims 7 or 8, c h a r a c t¬ e r i z e d in that the ends of the.cylindrical cartridge are covered by plates stuck to the cartridge cylinder. 10. The device according to any of the claims 7 through 9, c h a r a c t e r i z e d in that the outlet cylinder of the air cannon comprises a removable portion for allowing insertion of the cartridge containing the solid material into the outlet cylinder of the air cannon. 11. The device according to claim 10, c h a r a c t e r¬ i z e d in that the removable portion of the outlet cylinder is mounted to the remaining part of the outlet cylinder by a hinge allowing said removable portion to be swung out of the bore of the outlet cylinder along an axis parallel to the axis of the outlet cylinder. 12. The device according to claim 10, c h a r a c t e r¬ i z e d in that a construction of guide bars is provided to allow removal of the removable portion out of the bore of the outlet cylinder by a translational motion. 13. The device according to any of the claims 7 through 9, c h a r a c t e r i z e d in that a revolver system is coupled to the outlet cylinder of the compressed air cannon to allow loading of several cartridges containing solid material. 14. The device according to any of the claims 6 through 13, c h a r a c t e r i z e d in that the solid material is formed of a coarse-grained material, the size of the grains being preferably between 5 and 50 mm. 15. The device according to claim 14, c h a r a c t e - i z e d in that the coarse-grained material is friable and without hard contents, and preferably formed of gypsum stones. 16. The device according to any of the claims 6 through 15, c h a r a c t e r i z e d in that the solid material is an explosive which will explode when hitting the impeller blades or said other parts of the impeller.

Inventors: GODICHON ALAIN, GODICHON, ALAIN
Applicants: FLAEKT AB, ABB FLAEKT AB
Application year: 1991
Main classification: F04D29
IPC codes: B08B5, F04D29, F24F7