The present invention relates to an apparatus for cleaning the open draft boiler surfaces in a combustion or incineration plant of the kind set forth in the introductory portion of claim 1.
In apparatuses for cleaning boiler surfaces in a combustion or incineration plant of this kind, it is known to use a nozzle head with several nozzles for supplying a cleaning fluid to the boiler surfaces to be cleaned, said nozzle head being rotated and moved linearly in a direction in and out of the combustion chamber. An apparatus of this kind is known from US 5,579,726, which describes such a device for cleaning a boiler in service, said device comprising a lance and a rotating cleaning head mounted on the end of the lance and means for providing a linear movement in and out of the combustion chamber and means for rotating the cleaning head. The lance in this device is a stiff construction and the rotational and linear movements are provided by means of motors mounted externally of the combustion chamber to be cleaned. In all constructions shown and described in said document, the linear movement is in a horizontal direction, thus requiring that the lance is of a stiff construction. Another cleaning apparatus which comprises all the technical features of the preamble of claim 1 is known from DE-1 262 496.
It is the object of the present invention to provide an apparatus for cleaning the open draft boiler surfaces in a combustion or incineration plant of the kind referred to above, which is of a simplified but yet effective construction compared to the prior art apparatuses, and this object is achieved with an apparatus of said kind which, according to the present invention, also comprises the features set forth in the characterizing clause of claim 1. With this arrangement the nozzle head on the end of the flexible hose can simply be lowered through the opening provided in the top of the open draft to be cleaned and moved downward while supplying cleaning fluid to the nozzles for delivery to the surfaces to be cleaned in an efficient way. Since the apparatus is positioned inside the open draft only during cleaning operations, the construction can be relatively simple as the cleaning fluid will keep the construction cool during the cleaning operation and the construction, thus, will not have to suffer the high temperatures inside the open draft of the combustion or incineration plant in service. Furthermore, the flexible hose construction reduces the amount of space required for introducing the cleaning apparatus into the open draft, thereby enabling the use of the apparatus in connection with existing plants substantially without any modifications thereof.
Preferred embodiments of the cleaning apparatus in accordance with the present invention, the advantages of which will be disclosed in the following detailed part of the present description, are revealed in the subordinate claims.
In the following detailed part of the present description, the invention will be explained more in detail with reference to the exemplary embodiment of an apparatus for cleaning the open draft boiler surfaces in a combustion or incineration plant according to the invention shown in the drawings, in which:
The combustion or incineration plant shown in fig. 1 comprises three successive open drafts 17, 18, 19 in which heat is transferred from the flue gasses to boiler tubes covering the walls of the open drafts 17, 18, 19. After the open drafts 17, 18, 19 a superheater 20 or several such superheaters and other boiler constructions are positioned.
In such a plant it is desired to keep clean the heat exchange surfaces in the open drafts 17, 18, 19 in order to reduce the heat transfer resistance from the flue gasses to the boiler tubes.
The cleaning apparatus implemented in the combustion or incineration plant shown in fig. 1 comprises a cleaning head 1 mounted on the end of a flexible hose 7 for insertion and lowing inside the open draft 17 through an opening 16 centrally positioned in the top of the open draft 17. The linear movement of the cleaning head 1 inside the open draft 17 is provided by rotating the hose reel 6 upon which the hose 7 is mounted.
The rotation of the nozzle head 4, as shown in fig. 2, is provided by means of a turbine 2 driven by the cleaning fluid entering the cleaning head 1 from the flexible hose 7. In order to reduce the speed of the rotation of the nozzle head 4, a gear train 3 is provided between the turbine 2 and the nozzle head 4. Several nozzles 5 are mounted on the nozzle head 4 in order to distribute the cleaning fluid in different directions during rotation of the nozzle head 4.
As shown in fig. 3, the hose reel 6 is mounted for rotation on an axle driven by a drive unit 8 for the hose reel 6, said drive unit 8 comprising an electric motor 9 and a reduction gear mechanism 10. As likewise shown in fig. 3, the electric motor 9 is controlled from a control unit 15 controlling the motor speed and rotational direction of the motor 9.
As also shown in fig. 3, the cleaning fluid is supplied to the hose 7 by means of a pump unit 11 comprising an electric motor 12 driving a pump 13. The electric motor 12 is controlled by the control unit 15 in order to be able to control the pressure of the cleaning fluid delivered to the flexible hose 7. The connection between the pump 13 and the hose reel 6 comprises a rotational coupling 14 in order to allow the hose reel 6 to rotate relative to the fixedly positioned pump 13.
As can be seen in fig. 1, each of the open drafts 17, 18, 19 have a centrally positioned opening 16 for insertion of the cleaning head 1 and the flexible hose 7 and for lowering and raising the cleaning head 1 downward and upward through the open drafts 17, 18, 19. During lowering and raising of the cleaning head 1, cleaning fluid is supplied through the flexible hose 7 whereby the nozzle head 4 is rotated and cleaning fluid is supplied to the internal surfaces of the open drafts 17, 18, 19 through the nozzles 5. These nozzles 5 are dimensioned to supply a concentrated jet of cleaning fluid to the internal surfaces of the open drafts 17, 18, 19, substantially without any dissolving into droplets of the concentrated jets. Preferably, the cleaning fluid is water which, when hitting the inner surfaces in the open drafts 17, 18, 19, evaporates whereby the water expands to a volume of approximately 1,500 times its original volume, said expansion providing the forces necessary for removing dirt from the surfaces hit. As already mentioned the cleaning is performed in service, i.e. the combustion or incineration plant is burning off fuel and producing heat and the surfaces to be cleaned are at a high temperature, necessary for providing the evaporation of the cleaning fluid.
Due to the fact that cleaning is performed during function of the plant, the cleaning can be performed whenever this is considered necessary, e.g. as detected by rising temperature of the flue gasses entering the superheater 20, because of dirt on the boiler surfaces reducing the heat transfer from the flue gasses in the open drafts 17, 18, 19. Thus, it is possible, in a controlled manner, to keep the temperature of the flue gasses entering the superheater 20 below a desired maximum temperature of e.g. 600 - 650 °C.
In this way corrosion on the superheater tubes is reduced and, furthermore, a reduction in temperature of the flue gasses in the superheater 20 results in less sticky deposits on the superheater surfaces. In a typical incineration plant the cleaning of each open draft 17, 18, 19 is performed approximately every week, e.g. one of each of the open drafts 17, 18, 19 is cleaned every second day. In this way it has proven possible to reduce the temperature of the flue gasses entering the superheater 20 by approximately 100 °C.
In a test setup, the cleaning fluid used was water and supplied to the flexible hose 7 at a pressure of approximately 4 - 5 bar on the top of the open drafts 17, 18, 19 and the nozzle head was provided with 6 nozzles. The time involved in cleaning a single open draft 17 was approximately 5 - 10 minutes and approximately 1,000 I of water were used for the cleaning.
Due to the fact that the cleaning system is only to be used approximately once a week, a single cleaning system may service several open drafts 17, 18, 19 by providing suitable means for introducing the cleaning head 1 and the flexible hose 7 through the corresponding openings 16.
Although the invention has been described above in connection with a preferred embodiment of the invention, as shown in the figures, it will be evident for a person skilled in the art that several deviations may be envisaged within the scope of the following claims, such deviations comprising among others the provision of several openings 16 for each of the open drafts 17, 18, 19 to be cleaned, in order to have the cleaning head 1 moved up and down closer to the surfaces, said openings 16 being positioned at a distance from the central part of each open draft 17, 18, 19, the provision of automatic means for opening and closing the openings 16, the provision of several cleaning systems, e.g. one cleaning system for each open draft 17, 18, 19, each such cleaning system comprising its respective cleaning head 1, flexible hose 7 and hose reel 6, etc.