Technical Field
[0001] 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.
Background Art
[0002] 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.
Disclosure of the Invention
[0003] 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.
[0004] 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.
Brief Description of the Drawings
[0005] 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:
Fig. 1 schematically shows a combustion plant, in which the present invention is implemented,
fig. 2 schematically shows a cleaning head in cross-section, and
fig. 3 schematically shows a hose reel with a drive unit for controlled lowering and
raising of the cleaning head and a pump unit for delivering the cleaning fluid to
the flexible hose.
Description of the Preferred Embodiment
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
1. Apparatus for cleaning the open draft boiler (17, 18, 19) surfaces in a combustion
or incineration plant in service, said apparatus comprising
- a nozzle head (4) with several nozzles (5),
- means for rotating the nozzle head (4),
- means for providing a mainly linear movement of the nozzle head (4) inside the open
draft (17, 18, 19), and
- means for supplying a cleaning fluid to the rotating and linearly moving nozzle
head (4), whereby the cleaning fluid exiting the nozzles (5) hits the surfaces to
be cleaned,
characterized by
the nozzle head (4) being mounted on the end of a flexible hose (7), delivering the
cleaning fluid to the nozzles (5), at least one opening (16) being provided in the
top of each open draft (17, 18, 19) to be cleaned, said opening (16) allowing the
insertion, lowering and raising of the nozzle head (4) inside the open draft (17,
18, 19).
2. Apparatus in accordance with claim 1, characterized by the cleaning fluid being water
3. Apparatus in accordance with claim 1 or 2, characterized by the means for rotating the nozzle head (4) being provided as a drive unit (2, 3)
mounted on the end of the flexible hose (7), said drive unit (2, 3) being driven by
the cleaning fluid delivered to the nozzles (5) through the flexible hose (7).
4. Apparatus in accordance with claim any of the preceding claims, characterized by the means for providing a mainly linear movement of the nozzle head (4) inside the
open draft (17, 18, 19) comprising a hose reel (6) with a drive unit (8) for lowering
and raising the nozzle head (4) on the end of the flexible hose (7) downward and upward
inside the open draft (17, 18, 19).
5. Apparatus in accordance with claim 4, characterized by the drive unit (8) for the hose reel (6) being a speed controlled (15) gear motor
(9, 10).
6. Apparatus in accordance with any of the preceding claims, characterized by the means for supplying the cleaning fluid to the nozzle head (4) comprising a feed
water pump (11) delivering the cleaning fluid at a pre-determined pressure level through
the flexible hose (7).
7. Apparatus in accordance with claim 6, characterized by the feed water pump (11) being pressure controlled (15).
8. Apparatus in accordance with any of the preceding claims, characterized by the pressure level of the cleaning fluid delivered to the nozzles (5) being less
than 10 bar.
9. Apparatus in accordance with any of the preceding claims, characterized by the nozzles (5) of the nozzle head (4) being of a type which keeps the outflowing
jet from the nozzles concentrated with only minor dissolving into droplets.
10. Apparatus in accordance with any of the preceding claims, characterized by the rotational speed of the rotating nozzle head (4) being between 1 and 50, preferably
between 5 and 10, revolutions per minute.
11. Apparatus in accordance with any of the preceding claims, characterized by the flexible hose (7) being a flexible bellows-type metal hose (7), preferably of
stainless steel material.