Note: Descriptions are shown in the official language in which they were submitted.
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A BOILER PLANT, A SUPPORT STRUCTURE AND A METHOD FOR
SUPPORTING THE WALLS OF A STEAM BOILER OF A BOILER
PLANT
Field of the invention
The invention relates to a boiler plant, a support structure, as well as a
method for supporting the walls of a steam boiler.
Background of the invention
The boilers of typical boiler plants comprise tubular walls, where water
and/or steam circulates. Combustion takes place inside the boiler in a
furnace, and as a result of the combustion and gas flows negative
pressures and positive pressures may occur in different areas of the
boiler. The pressure effect is directed at the walls of the boiler and the
walls tend to move. For this reason, different support structures are
made in the walls. Typically a support structure is a horizontai
buckstay, which circles the outer wall of the boiler. Typically the
support ring is formed of a strong steel beam, which is attached to the
wall of the boiler in a suitable manner. One known support structure
solution is disclosed in US 5,557,901. The boilers of large boiler plants
may be several tens of meters high, in which case several support
structures are needed. Thus, a great deal of steel is needed for the
structures, which causes costs.
Brief summary of the invention
Now a solution has been invented for a combined horizontal support
system of a boiler and a boiler building for supporting the walls of a
boiler without heavy ring structures. The purpose of the support is to
control the pressure effects directed at the boiler wall during use and at
the same time the powers directed at the boiler house.
To attain this purpose, the boiler plant according to the invention
comprises a recovery boiler, a frame of a boiler house surrounding the
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recovery boiler, wherein the boiler plant in addition comprises support
structures, by which the walls of the boiler are supported laterally to the
frame of the boiler house. The support structure of a wall of a recovery
boiler of a boiler plant is arranged to be attached to the wall of the
boiler, wherein the support structure is also arranged to be attached to
the frame of the boiler house surrounding the recovery boiler laterally.
In the method according to the invention the walls of the recovery boiler
are supported laterally to the frame of the boiler house by a support
structure.
The different embodiments of the invention can be used in different
configurations and in different environments and in connection with
boilers using different boiler techniques.
The basic idea of the invention is to integrate the support structures of
the boiler walls to the frame of the boiler house. This is provided in
such a manner, that the boiler walls are supported laterally to the frame
of the boiler house by a support structure.
In an advantageous embodiment the support structure comprises
attachment areas for attaching the support structure to the boiler wall
and the attachment areas allow the horizontal movement of the support
structure in relation to the boiler wall. The horizontal movement tends
to be created by the thermal expansion of the boiler, and the pressure
effects. Preferably the support structure allows the thermal expansion,
but substantially prevents movement created by the pressure effect.
In an embodiment the support structure comprises attachment
structure for attaching the support structure to the frame of the boiler
house and the attachment structures allow the vertical movement of
the boiler wall in relation to the frame of the boiler house. In the height
direction the change in the height of the boiler created by thermal
expansion can be, for example, 20 to 300 mm.
In an embodiment the support structure comprises attachment
structure for attaching the support structure to the frame of the boiler
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house and the attachment structures allow the support structure to turn
vertically in relation to the frame of the boiler house. Thus, the boiler
wall can move vertically in relation to the frame, for example, due to the
effect of changed in the temperature of the boiler.
In an embodiment a boiler plant comprises a service platform and a
support structure is used as a bearing structure. Thus, separate
support structures are not needed for the service platform.
The different embodiments of the above-described arrangement, taken
separately and in various combinations, provide several advantages.
One significant advantage of an embodiment is that the structures of a
boiler house provide a multiple advantage, because they operate both
as a horizontal bracing of both the pressurized frame and the building,
and as a structure of a service platforms.
The entire membrane wall of the boiler becomes significantly simpler in
comparison to the present structure, because the horizontal support
rings are eliminated, and at the same time the isolation and plating of
the wall become significantly simpler.
In an embodiment the span lengths and buckling lengths of steel
columns necessary in the frame of a boiler house become significantly
shorter. Thus, the bending moments of the columns become smaller.
Buckling and transverse buckling do not significantly decrease the
allowed bearing stresses either. Due to the solution the amount of steel
needed for the columns decreases due to the new structure.
In an embodiment the support solution significantly increases the
space for vertical pipe, duct and cable drafts and stairs in the area
between the outer wall lines of the house and the boiler stanchions.
In an embodiment the total volume of the house and the side
dimensions decrease due to a decrease in the dimensions of the
stanchions. Thus, the boiler plant is easier to place in the environment.
In addition, the wind area of the boiler plant can be decreased.
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In an embodiment significant cost savings are provided when
horizontal support rings and their heavy fastening parts are left out of
the boiler. -
A solution according to the invention is primarily intended for
supporting large, tens of meters high steam boilers. The solution is
especially advantageous when the boiler plant comprises service
platforms. Specifically, the invention is advantageous for supporting
large recovery boilers. In large recovery boiler plant applications the
present solution may provide significant total weight savings in the
structures of the boiler pressure parts and structures of the boiler
house.
Description of the drawings
In the following, the invention will be described in more detail with
reference to the appended principle drawings, in which
Fig. 1 shows a frame of a boiler house and a boiler according to the
invention
Fig. 2 shows a vertical cross-section of an embodiment of a support
structure
Fig. 3 shows a horizontal cross-section of the embodiment
according to Fig. 2 on level F3-F3, i.e. seen from above
Fig. 4 shows a detail of a support structure in a vertical cross-section
Fig. 5 shows a part of the embodiment according to figure 4 in a top
view
Fig. 6 shows an embodiment of a support structure
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For the sake of clarity, the figures only show the details necessary for
understanding the invention. The structures and details that are not
necessary for understanding the invention but are obvious for anyone
skilled in the art have been omitted from the figures in order to
5 emphasize the characteristics of the invention.
Detailed description of the invention
Figure 1 shows only those parts of a boiler plant that are necessary for
describing the invention. These are the frame 1 of a boiler house, a
boiler 2 and a support structure 3. In addition, other structures are
required in the boiler plant, inter alia for supplying fuel and air, and for
processing flue gases. In addition, there are often different structures
for use and maintenance work. In figure 1 the frame 1 of the boiler
plant is for clarity shown only on one side, i.e. side A, even though the
frame in practice is on each side. Correspondingly, the support
structure 4 of an outer screen is shown only on side B of the boiler
house, even though such a frame is advantageously on every
screened side. Sides C and D of the boiler house do not show the
frame 1 of the boiler house, nor the screening frame 4, in order to
shown the location of the support structures 3 more clearly. The frame
1 of the boiler house comprises vertical boiler columns 5. The
screening frame 4 comprises vertical outer wall columns 6. In figure 3,
which shows a horizontal cross-section of the embodiment according to
Figure 2 on level F3-F3, i.e. seen from above, can be seen the location
of the screening frame 4, the frame 1 and the support structure 3
around the boiler 2 in an embodiment. Thus, the above-mentioned
structures surround the boiler 2 horizontally on each side A, B, C and
D. Figure 2, in turn, shows that the screening frame 4 can be attached
to the frame 1 by a differently dimensioned spacing than the support
structures 3.
The frame 1 of the boiler house is a support structure, to which the
other structures of the boiler plant can be attached. For example, it is
possible to suspend the boiler 2 from the upper part of the frame 1
above the boiler. The frame 1 is generally made of steel beams and
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columns. The frame 1 generally comprises vertical, horizontal and
diagonal beam and columns parts. For example, a boiler plant with a
boiler 2 that is 18 x 18 meters in its bottom area, in an application
comprises boiler columns 5 with a six meter spacing. Horizontal truss
beams 3, in turn, are placed with approximately a 3 meter spacing. The
stanchions are supported vertically with a significantly denser spacing
than in traditional boiler plant houses, where horizontal bracing levels
are typically every 12 meters (10...18 m) vertically.
The walls of a boiler 2 of a boiler plant are typically membrane walls,
where a medium can be circulated. Due to the great height of the wall,
in order to reach a sufficient bracing and pressure endurance, support
structures 3 supporting the wall 2 of the boiler laterally are necessary.
In the example according to figure 1 the walls of the boiler 2 are
supported laterally to the frame 1 of the boiler house by support
structures 3. The support structures 3 are advantageously formed in
such a manner that they allow the thermal expansion of the walls of the
boiler 2.
In high boilers 2 the height direction distance of the adjacent support
structures 3 can be 2 to 5 meters, advantageously 3 to 3 meters.
Preferably the distance of the support structures is selected to
correspond to the spacing of the horizontal beams of the frame 1.
Thus, the support structure 3 is substantially located on the same level
as the horizontal beam of the frame 1. The distances of the support
structures 3 may also vary. For example, the support structures 3 may
be positioned more densely in those areas, where a larger load is
directed, for example, due to pressure fluctuations.
It is advantageous to place the support structures 3 on a horizontal
plane on all walls. In some cases it may be necessary to place support
structures 3 only on some of the walls, but still, a support structure 3
can be placed between the frame 1 of the boiler house, preferably the
boiler stanchions 5, and the wall of the boiler 2.
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The support structures 3 can be provided in various ways. In one
application the support structure 3 is substantially as wide as the wall
of the boiler 2. In one application the part of the support structure 3
placed against the boiler 2 wall substantially has the width of the boiler
wall and the part located further away from the wall is wider. For
example, figure 3 shows such an embodiment, where the ends of the
support structure 3 are in a angle of approximately 45 in relation to the
wall line, in which case the ends of the support structures placed on
adjacent walls are parallel.
In an embodiment the support structure 3 is a truss structure. In one
case the truss structure is formed of two beams located parallel to the
wall of the boiler 2, between which there are diagonal beams. In
addition, the truss structure may comprise beams that are
perpendicular to the wall of the boiler. The beams are connected to
each other in a suitable manner, such as, for example, by welding
and/or with bolted joints. Preferably the beams are, for example,
rectangular pipes, in which case the strength in relation to their weight
is advantageous.
The support structure 3 can be connected to the boiler 2 wall in
different ways. In the example, the support structure 3 comprises
attachment areas 7, to which areas the wall of the boiler 2 is connected
from the attachment points 8 on the boiler walls in the height direction.
The distance between the adjacent attachment areas 7 and attachment
points 8 depends on the application. Advantageously the distance
between the attachment areas 7 and the attachment points 8 is 0,5 to 2
meters horizontally, preferably approximately 1 meter, and of the boiler
the above-mentioned 2 to 5 meters, preferably 3 to 4 meters. The
dimensioning is affected by, inter alia, the bracing of the walls of the
boiler 2 and pressure loads.
In the example the attachment areas 7 of the support structure 3
comprise flanges. The attachment points 8 of the boiler walls, in turn,
also comprise flanges. In addition to, or instead of the flanges the
attachment areas 7 and the attachment points 8 may comprise different
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brackets, cavities, grooves, dents, pins, possibly springs, or other
solutions suitable for connecting. Now, flanges are used as an
example, because they have been found advantageous as they
provide versatile application possibilities.
The overall dimensions of the wall of the boiler 2 change due to the
effect of temperature, especially in the corner areas. In the height
direction the change in the height of the boiler 2 can be, for example,
20 to 300 mm. Laterally the change in the width of the boiler 2 can be,
for example, 5 to 30 mm. It is advantageous to take into account the
changes in the dimensions of the boiler 2 walls in the support structure
3 and/or its attachment to the boiler wall.
The vertical changes in the dimensions of the boiler 2 can be taken into
account, inter alia, by attaching the support structure 3 by means of
hinges or articulations to the boiler and the frame 1. Thus the
hinge/articulation enables the movement of the boiler 2 wall in relation
to the frame 1. One such an attachment structure 9 is shown in figure
4. In the example the attachment structure 9 is between the support
structure 3 and the frame 1 of the boiler house and it allows the vertical
turning of the support structure in relation to the attachment structure 9.
In order to take the vertical change into account, the support structure
3 can originally be placed diagonally, in which case it is substantially
horizontal when the boiler 2 operates. In one embodiment, where the
boiler 2 is suspended from above, the lower support structures 3 of the
support system are more diagonal than the upper support structures
when the boiler is cold. When the boiler 2 is hot, all the support
structures 3 are substantially horizontal when the lower part of the
boiler has moved more in relation to the frame 1 than the upper part.
The support structure 3 can originally be placed horizontally as well, in
which case it is slightly diagonal when the boiler 2 operates.
For example, when the attachment point of a 3000 mm wide support
structure 3 and/or one edge of the platform changes 50 mm in height
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direction, the inclination of the support structure and/or the platform
changes about one degree.
The horizontal changing of boiler 2 dimension can be take into account
in different ways in the support structure. For example, the support
structure 3 may allow the movement in relation to the support structure
caused by the thermal expansion of the boiler 2 wall. Different solutions
allowing the movement can be provided in the support structure 3 and
advantageously movement into a certain direction only is allowed. For
example, different slide solutions can be used, where the wall of the
boiler 2 may move in relation to the support structure 3 on a certain
path defined by the slide. In an embodiment the thermal expansion of
the boiler 2 wall is taken into account by elongated holes 10 of the
attachment area 7 of the support structure 3 and/or the flanges of the
attachments points 8 of the boiler, such as shown, for example, in
figure 5. The holes 10 are advantageously diagonal in the direction of
change of the dimensions, in which case the hole 10 enables the
movement of the wall of the boiler 2 in relation to the frame 1. Figure 6
shows how the inclination of the holes 10 may change depending on
what point of the boiler 2 wall they are located at. In the example the
direction of movement allowed by the attachment area located in the
middle of the boiler wall is mainly perpendicular to the wall, while on
the edge areas movement in the direction of the wall is allowed in
addition to the perpendicular movement. When the hole 10 is diagonal
in relation to the wall of the boiler 2, the hole prevents a sudden
perpendicular movement of the wall, i.e. such a movement typically
caused by a pressure effect.
In addition, other functions may be connected to the support structure,
or it may be used to for other purposes besides supporting. In one
embodiment the support structure 3 operates as a bearing structure for
service platforms 11. Figure 1 shows a boiler plant, where two support
structures 3 operate as a bearing structure for service platforms 11.
Thus, a suitable platform may be placed on the support structure 3,
such as, for example, a grate or a plate, which enables moving in the
area. In addition, the service platform 11 may comprise the necessary
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auxiliary and shielding structures, such as rails, attachment points and
toe mouldings. The service platform 11 may circle around the boiler 2
being placed on its every wall. It is also possible to make a partial
service platform 11, in which case the service platform may be, for
5 example, on one or more walls of the boiler 2 and/or only on a part of
the boiler wall. Advantageously the service platform 11 is at the
location of the target to be serviced.
Due to the support structure the isolation and cladding of the
10 membrane wall of the boiler 2 becomes simpler in comparison to the
solutions with buckstays. Since the boiler 2 wall is substantially
straight, its outer surface can be isolated and cladded relatively simply.
Only holes at the attachment points 8 are needed in the cladding.
Sheet metal cladding is typically used as cladding. Figures 4 and 5
show one manner for placing the insulator 12 and the cladding 13.
The support structures 3 can be formed in the construction phase at
the construction site. Advantageously the support structures 3 are
ready modules, which are attached to the boiler 2 wall and the frame 1
of the boiler house at the construction site. Thus, the time used in
constructing the boiler house can be decreased. Figure 6 shows a
support structure module 3, which comprises attachment areas 7 and
attachment structures 9. The attachment areas 7 are for attaching the
support structure 3 to the wall of the boiler 2. The attachment
structures 9 are for attaching the support structure 3 to the frame 1 of
the boiler house. The attachment areas 7 advantageously enable the
horizontal movement of the support structure 3 in relation to the wall of
the boiler 2, for example in order to allow the thermal expansion of the
boiler wall. The attachment structures 9 advantageously enable the
vertical movement of the boiler wall 2 in relation to the frame 1 of the
boiler house. For example, the attachment structures 9 allow the
vertical turning of the support structure 3 in relation to the frame 1 of
the boiler house. It is possible to form the support structure 3 of several
modules as well, in which case the support structures around large
boilers can be manufactured elsewhere and transported easily to the
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construction site, where they are assembled into a larger support
structure.
By combining, in various ways, the modes and structures disclosed in
connection with the different embodiments of the invention presented
above, it is possible to produce various embodiments of the invention
in accordance with the spirit of the invention. Therefore, the above-
presented examples must not be interpreted as restrictive to the
invention, but the embodiments of the invention may be freely varied
within the scope of the inventive features presented in the claims
hereinbelow.
