U.S. patent application number 14/433395 was filed with the patent office on 2015-08-27 for boiler structure and method of assembly.
The applicant listed for this patent is DOOSAN BABCOCK LIMITED. Invention is credited to Dewan Shamsuz Zaman.
Application Number | 20150241054 14/433395 |
Document ID | / |
Family ID | 47225657 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150241054 |
Kind Code |
A1 |
Zaman; Dewan Shamsuz |
August 27, 2015 |
BOILER STRUCTURE AND METHOD OF ASSEMBLY
Abstract
A support structure for a boiler envelope, for example being the
boiler envelope of a boiler thermal plant, a boiler structure so
supported, and a method of supporting a boiler, are described. The
support structure includes a support platform structure, comprising
a part of the primary load bearing boiler cold structure for the
boiler envelope, and adapted to engage with and thereby carry at
least a major part of the static load of the boiler envelope. The
support platform structure is provided surroundingly about the
boiler envelope at a support platform level substantially below
full envelope height and provided with associated further boiler
cold structure in such manner that at least the substantial
majority of the boiler cold structure is at or below the support
platform level and preferably such that essentially all the boiler
cold structure is at or below the support platform level and only
elements of the boiler hot structure and the boiler pressure parts
extend above the support platform level supported by the boiler
cold structure.
Inventors: |
Zaman; Dewan Shamsuz;
(Crawley, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DOOSAN BABCOCK LIMITED |
Crawley Suuex |
|
GB |
|
|
Family ID: |
47225657 |
Appl. No.: |
14/433395 |
Filed: |
September 27, 2013 |
PCT Filed: |
September 27, 2013 |
PCT NO: |
PCT/GB2013/052521 |
371 Date: |
April 3, 2015 |
Current U.S.
Class: |
122/493 ;
122/496; 122/510; 29/890.051 |
Current CPC
Class: |
Y10T 29/49387 20150115;
F22B 37/242 20130101; F22B 37/24 20130101 |
International
Class: |
F22B 37/24 20060101
F22B037/24 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 4, 2012 |
GB |
1217746.5 |
Claims
1. A support structure for a boiler envelope, for example being the
boiler envelope of a boiler thermal plant, comprising: a support
platform structure, comprising a part of the primary load bearing
boiler cold structure for the boiler envelope, and adapted to
engage with and thereby carry at least a major part of the static
load of the boiler envelope; wherein the support platform structure
is provided surroundingly about the boiler envelope at a support
platform level substantially below full envelope height and
provided with associated further boiler cold structure in such
manner that at least the substantial majority of the boiler cold
structure is at or below the support platform level.
2. A support structure in accordance with claim 1 comprising: a
boiler support cold structure including a support platform
structure and a boiler support hot structure supported via the
boiler support cold structure; wherein the support platform
structure is provided surroundingly about the boiler envelope at a
support platform level substantially below full envelope height and
configured such that at least the substantial majority of the
boiler cold structure is at or below the support platform
level.
3. A support structure in accordance with claim 1 wherein
essentially all the boiler cold structure is at or below the
support platform level and only elements of the boiler hot
structure and the boiler pressure parts extend above the support
platform level supported by the boiler cold structure.
4. A support structure in accordance with claim 1 wherein the
support platform structure comprises a substantially horizontal
framework of structural members extending around and supporting the
boiler envelope at a height substantially below the boiler maximum
height.
5. A support structure in accordance with claim 1 further
comprising suitable secondary and tertiary structural elements,
including suitable cross members, beams, ties, buckstays, tensile
members and the like.
6. A support structure in accordance with claim 1 wherein the
support platform structure is provided in association with a boiler
at a height above the burners of the boiler but below the heating
surfaces of the boiler.
7. A support structure in accordance with claim 1 wherein the
support platform structure is provided in association with a boiler
such that all the boiler cold structure sits at or below a maximum
height level which maximum height level is above the burners of the
boiler but below the heating surfaces of the boiler.
8. A support structure in accordance with claim 1 wherein the
support platform structure is provided in association with a boiler
at a height of around 40 to 60 per cent of a boiler envelope
maximum height.
9. A support structure in accordance with claim 1 wherein the
support platform structure is provided in association with a boiler
such that all the boiler cold structure sits at or below a maximum
height level which maximum height level is around 40 to 60 per cent
of a boiler envelope maximum height.
10. A boiler apparatus comprising a support structure in accordance
with claim 1 in conjunction with and providing at least a major
part of the static load support for a boiler envelope of a
boiler.
11. A boiler apparatus in accordance with claim 10 wherein the
boiler is a utility boiler for thermal power generation.
12. A thermal power generation plant including at least one boiler
apparatus in accordance with claim 10.
13. A method of assembly of a boiler structure comprising the steps
of: providing a support structure for a boiler envelope in
accordance with the above described first aspect of the invention;
assembling a boiler envelope so as to be mechanically supported
thereon in such a manner that at least the major part and
preferably substantially all of the boiler cold structure is at or
below the support platform level.
14. The method of claim 13 wherein the boiler envelope is supported
such that there is essentially no boiler cold structure above the
support platform level and essentially only elements of the boiler
hot structure and the boiler pressure parts extend above the
support platform level.
15. The method of claim 13 wherein the steps of providing a support
structure, and assembling in a supporting manner thereon a boiler
envelope structure, are performed progressively in parallel.
Description
[0001] The invention relates to a boiler structure, for example for
a thermal power generation plant, and in particular to a support
structure for a boiler envelope and to a boiler apparatus
incorporating such a support structure. The invention further
relates to a method of assembly of a boiler structure and in
particular a method of assembly of a support structure for a boiler
envelope and of a boiler envelope supported by such a support
structure.
[0002] Thermal power plant driven by combustion of carbonaceous
fuel for the generation of steam within a boiler system (which term
as used herein encompasses subcritical and supercritical systems)
remains a major source of generation of electrical power. Large
scale boiler systems, especially fuelled by combustion of
carbonaceous fuel, also have other industrial applications.
[0003] Boiler systems for a thermal power plant or other industrial
apparatus on a comparable scale are large and complex apparatus
requiring complex assembly and extensive structure. Although small
industrial boilers, for example up to around 30 MW generating
capacity, may practically be self-supporting, larger boilers, for
example utility boilers of 60 MW generating capacity and above,
typically require extensive supporting structures. In particular,
extensive support structures are required to provide a mechanical
support for and structural stability to the boiler envelope. Such
structures are necessary to carry the high static mechanical loads
associated with the boiler envelope and to transmit those loads to
the ground, and also to provide stability and to accommodate
operational load factors, such as those which might be attributable
to thermal expansion effects and environmental influences such as
weather and seismic influences on the large boiler envelope
structures. Such support structures can be expensive both in terms
of the structural materials used and in terms of the build
complexity. Support structures for the boiler envelope can have a
very large footprint.
[0004] In a typical prior art construction, a boiler house is first
constructed including a large primary support structure which
incorporates as part of the primary support structure a suspension
deck in the vicinity of the boiler house roof and above the boiler
envelope maximum height. The boiler envelope and associated
structures are then supported on the primary suspension deck by
suitable secondary and tertiary structural elements. The primary
load carrying structure for the entire boiler envelope, including
the heating surfaces within the boiler envelope and the boiler
envelope structural elements themselves, is primarily supported via
the suspension deck, and the associated load primarily transmitted
to the ground via the suspension deck and associated supporting
primary structure.
[0005] As the skilled person will understand, it is conventional in
the art to consider the elements of a boiler envelope and support
structure to fall into one of three classifications: boiler
pressure parts; boiler hot structures; and boiler cold structures.
In particular it is conventional to classify the structural support
elements into boiler hot structures and boiler cold structures. The
distinction will be well understood by the skilled person but can
perhaps be expressed simply by defining boiler hot structures as
those support structures which are designed to expand and contract
thermally with the boiler, and boiler cold structures as those
support structures which do not.
[0006] In the typical prior art construction above described the
suspension deck comprises a generally horizontally extending
primary support structure which sits at full height above the
maximum height of the boiler envelope in the boiler house roof.
Typically, the whole boiler house primary structure goes up to the
level of this full height suspension deck, and supports the
suspension deck at roof height to complete the primary load bearing
structure. Thus, in the typical design, the boiler cold structures
extend to a full height above the maximum height of the boiler
envelope whereby the boiler hot structures and thereby the boiler
pressure parts are supported.
[0007] Such an arrangement produces a boiler cold structure with a
large footprint extending fully above the height of the boiler
envelope and extensively beyond the boiler envelope footprint and
requires a large quantity of high strength structural steel to make
up the extensive full height boiler cold structure.
[0008] Moreover such an arrangement typically requires the boiler
house, and in particular at least the boiler cold structure
including the suspension deck, to be constructed in its entirety
first, before any boiler envelope structure, heating surfaces etc
can be brought into position and supported upon it. The prior art
support system does not lend itself to progressive parallel
construction from the ground upwards.
[0009] The invention is directed at providing a support structure
for a boiler envelope and a method of assembly of a boiler support
structure which mitigate some or all of the above
disadvantages.
[0010] In a particular preferred case the invention is directed at
the provision of a support structure for a boiler envelope which
offers simplicity of fabrication and/or a reduction in the
structural material requirement and/or a reduction in the overall
structural envelope.
[0011] In a particular preferred case the invention is directed at
a method of assembling the support structure which facilitates the
progressive parallel construction of the support structure and of a
supported boiler envelope.
[0012] Thus, in accordance with the invention in a first aspect a
support structure for a boiler envelope, for example being the
boiler envelope of a boiler thermal plant, comprises:
[0013] a support platform structure, comprising a part of the
primary load bearing boiler cold structure for the boiler envelope,
and adapted to engage with and thereby carry at least a major part
of the static load of the boiler envelope;
[0014] wherein the support platform structure is provided
surroundingly about the boiler envelope at a support platform level
substantially below full envelope height and provided with
associated further boiler cold structure in such manner that at
least the major part and preferably substantially all of the boiler
cold structure is at or below the support platform level.
[0015] That is to say in the alternative, in accordance with the
invention in a first aspect a support structure for a boiler
envelope, for example being the boiler envelope of a boiler thermal
plant, comprises:
[0016] a boiler support cold structure including a support platform
structure and a boiler support hot structure supported via the
boiler support cold structure;
[0017] wherein the support platform structure is provided
surroundingly about the boiler envelope at a support platform level
substantially below full envelope height and configured such that
at least the major part and preferably substantially all of the
boiler cold structure is at or below the support platform
level.
[0018] The support platform structure of the invention is in broad
structural terms the equivalent to the primary load bearing
structure provided in the prior art by the full height suspension
deck. The support platform structure of the invention performs an
equivalent mechanical function. It is a primary loaded bearing
structure to carry at least a static load of the boiler envelope.
It is a primary load bearing part of the boiler cold structure by
means of which the boiler hot structures and thereby the boiler
pressure parts are supported.
[0019] However the support platform structure of the invention can
be contrasted with a prior art suspension deck at roof height,
above the entire boiler structure, in that it eliminates the need
for boiler cold structure above the support platform level. At
least the substantial majority and preferably essentially all the
boiler cold structure is at or below the support platform level,
and only elements of the boiler hot structure and the boiler
pressure parts extend above the support platform level supported by
the boiler cold structure.
[0020] Advantages can accrue over a prior art design with boiler
cold structure including a suspension deck which sits at full
height above the maximum height of the boiler envelope in the
boiler house roof in two ways in particular. First, the boiler cold
structure of the present invention is all at substantially below
full height. Second, in consequence, whereas the prior art cold
structure extends across and over the boiler envelope footprint, in
the present invention that the support platform structure surrounds
the boiler envelope, the boiler envelope passing through it via an
apertured portion. This can reduce the overall footprint. Both of
these may produce a significant reduction in the overall structural
requirement, and in particular in the requirement for higher
strength structural materials.
[0021] The Invention further provides as an advantage that the
boiler envelop may expand thermally upward and downward from the
support platform structure, providing a qualitative change to the
way boiler is supported and expanded, adding core value to the
design by removal of much of the variable and constant spring
requirements that are found in prior art designs.
[0022] The support platform structure performs otherwise a similar
role, within the boiler cold support structure, as the prior art
suspension deck structure, and aspects of the of the support
platform structure of the invention may consequently be inferred
from the prior art by analogy. In particular, the support platform
structure of the invention preferably comprises a substantially
horizontal framework of structural members, for example structural
steel members, extending around and supporting the boiler envelope
at the desired height substantially below the boiler maximum
height. The support platform structure forms part of the primary
load bearing boiler cold structure which boiler cold structure will
include vertical structural elements which support the boiler hot
structure and transmit the primary load directly from the support
platform structure to the ground in familiar manner. Suitable
secondary and tertiary structural elements, including suitable
cross members, beams, ties, buckstays, tensile members and the like
as applicable will complete the load transmitting structure in a
manner which will be generally familiar to the skilled
engineer.
[0023] In accordance with the invention, the support platform
structure is provided at a height level substantially below the
full height of the boiler envelope and there is preferably
essentially no cold structure above this height. In a particular
preferred case the support platform structure is provided at a
height above the burners (and typically for example above any
overfire airports if present, and typically for example just below
or level with any cage ring main if present) but below the heating
surfaces (and typically therefore below the soot blowers etc.). In
a typical boiler design embodying the principles of the invention a
preferred support platform structure level will be at around 40 to
60 per cent of the boiler envelope maximum height, and this level
may be referred herein below for convenience as "half height".
However, the skilled person will appreciate that the principles set
out above are the ones that are important for determining an ideal
location in conjunction with the particular boiler structure to
which the support structure of the invention is to be
associated.
[0024] The invention takes advantage of the fact that in typical
burner design a significant majority of the equipment within the
boiler house is below the half height level. By providing a primary
support platform structure at this level it may be possible to
substantially reduce or eliminate the requirement for any boiler
cold structure at all above this level. The support platform
structure performs a similar role, within the boiler cold
structure, as the prior art suspension deck structure, and as a
result a full height suspension deck structure and associated
boiler cold structure comparable with that in the prior art is not
required. It is not necessarily for the boiler cold structure to
extend to the full boiler house height and to the full extent of
the footprint, as is required in the prior art. The extent of the
boiler cold structure can be reduced in terms of height and/or
footprint, with a potential for simplification of construction and
for reduction in the quantity of structural steel requirement. Both
of these can confer significant savings. It is possible to dispense
with boiler cold structure altogether above the level of the
suspension deck structure, relying only on boiler hot structural
elements above this level.
[0025] A further potential advantage of the support structure in
accordance with the invention may accrue in relation to flexibility
of construction. If, in accordance with the invention, the boiler
cold structure extends only up to the half height support platform
structure, it ceases to be necessary to construct the boiler house
and all of the associated full height structural support elements
before considering assembly of the boiler envelope and associated
structures. It is possible to construct and support the boiler
assembly on the half height suspension deck and through the
aperture therein, and to develop a method of assembly of a support
structure and boiler envelope in integrated manner which is at
least to some extent progressively effected. It is not necessary to
build support structures to full height of the suspension deck
structure before commencing assembly of the boiler envelope, but
merely to the half height of the support platform structure. It is
necessary only to complete that part of the support platform
structure and associated cold structure and hot structure that
directly bears on the boiler envelope structure before beginning
construction of the side walls. The structure that is required
before parallel construction of the boiler can start may be
relatively much reduced. The roof can be built as a separate module
away from the site. This parallel construction option may confer
significantly increased flexibility in practice.
[0026] In the preferred case, a support platform structure in
accordance with the invention is provided at a support platform
level generally above the burners but below the heating surface of
a typical boiler structure. All the boiler cold structure is at or
below the support platform level. Only elements of the boiler hot
structure and the boiler pressure parts extend above the support
platform level supported by the boiler cold structure. In a typical
boiler structure to which the support structure of the invention is
intended to be applied, the majority of associated functional
components within the boiler house will similarly be below this
level, including for example the secondary air duct and other
secondary structures. There are some functional structures above
this level, notably including the heating surfaces and other boiler
envelope structures, soot blowers and the like which may require
some support structure to transmit residual static loads and to
stabilise against dynamic load variations, in particular, for
example against lateral movement, but the structural requirement
above the half height level is substantially reduced. Any such
additional support structure need extend only across the horizontal
extent of the boiler envelope/hot structures not to the full extent
of the boiler house to full height as is the case with prior art
designs. For both these reasons, there will be a significant
reduction in the structural material requirement above the half
height support platform structure. In particular, there is no
requirement for a full height suspension deck as such, as the
primary static load bearing role it performs in the prior art
boiler cold structure is at least in major part performed in the
invention by the half height support platform structure.
[0027] The invention does not preclude the provision of support
structure elements above the height of the primary support platform
structure, and in particular considers that structural elements
forming part of the boiler hot structure may be provided above this
height, for example to stabilise/support the envelope/heating
surfaces above mid height and/or accommodate expansion, stabilise
the structure laterally against environmental dynamic loads etc.
However, the invention is characterised in that it substantially
eliminates the need for boiler cold structure above the primary
support platform structure level.
[0028] Regardless of such provision of boiler hot structure above
the support platform structure level the general principle of the
invention is maintained, in which an integrated structure is
provided which seeks to take the boiler cold structure down to half
height. The skilled person will readily appreciate that the limited
hot structure which may optionally be provided above this support
platform structure level is not in engineering terms in any way
equivalent to the full height suspension deck and associated boiler
cold structure in the prior art.
[0029] Additional lateral stabilisation may be provided as required
in a familiar manner.
[0030] In a particular preferred case, additional structural
elements associated with the support structure of the invention may
include buckstay arrangements such as are described in
International Publication WO2010/0730030.
[0031] In accordance with a more complete aspect of the invention,
a boiler apparatus comprises a support structure as hereinbefore
described in conjunction with and providing at least a major part
of the static load support for a boiler envelope, in particular of
a boiler apparatus comprising part of a thermal power generation
plant.
[0032] In particular the boiler is a utility boiler for thermal
power generation on a utility scale, for example with 60 MW
generating capacity and above. Such boilers in the prior art
typically have boiler cold structures which in conventional design
extend to and beyond the full boiler envelope height and have a
large footprint. The invention when applied to such boilers offers
significant constructional advantages as above described.
[0033] In a further more complete embodiment, a thermal power
generation plant includes at least one such boiler apparatus.
[0034] In accordance with the invention the further aspect, a
method of assembly of a boiler apparatus comprises the steps
of:
[0035] providing a support structure for a boiler envelope in
accordance with the above described first aspect of the
invention;
[0036] assembling a boiler envelope so as to be mechanically
supported thereon in such a manner that at least the major part and
preferably substantially all of the boiler cold structure is at or
below the support platform level and there is essentially no boiler
cold structure above the support platform level; that is, only
elements of the boiler hot structure and the boiler pressure parts
extend above the support platform level supported by the boiler
cold structure.
[0037] The invention further comprises by analogy a method of
assembly of provision of a thermal power generation plant including
at least one such boiler apparatus.
[0038] As has been previously noted, it is a particular preferred
feature of the support structure in accordance with the invention,
and in particular of the fact that the full height suspension deck
and associated boiler cold structure is dispensed with, and instead
a boiler cold structure at less than full height is provided which
includes a support platform apertured to surroundingly support the
boiler envelope, that it lends itself to parallel assembly of
supporting structure and boiler envelope structure.
[0039] Thus, in a preferred embodiment of the method, the steps of
providing a support structure, and assembling in a supporting
manner thereon a boiler envelope structure, are performed
progressively in parallel. This can be contrasted with typical
prior art methods, where it is necessary to assemble the entire
support structure, and indeed the entire boiler house, before
suspension of the boiler envelope from the primary suspension deck
structure can be commenced.
[0040] The invention will now be described by way of example only
with reference to the accompanying drawings in which:
[0041] FIG. 1 is a schematic side view in elevation of a typical
prior art thermal power plant boiler and support structure;
[0042] FIG. 2 is a schematic side view in elevation of an
embodiment of support structure in accordance with the invention as
applied to a boiler such as that in FIG. 1;
[0043] FIG. 3 is a plan view of the support structure of FIG. 2 at
primary support platform structure level;
[0044] FIG. 4 is a plan view of the support structure of FIG. 2 at
roof level;
[0045] FIG. 5 is a more detailed end elevation of the framework
structure below support platform structure level;
[0046] FIG. 6 is a sectional view of a possible embodiment by means
of which thermal expansion and contraction may be accommodated by
the roof indicating movement of walls, buckstays, roof, heating
surface supports and galleries when the roof is designed to move
upwards when the wall expands horizontally and vertically.
[0047] FIG. 1 is a representation of a typical boiler structure to
which a support structure in accordance with the invention might be
applied, but shown in the case of FIG. 1 in side elevation with a
prior art supporting structure including a conventional suspension
deck. It will be appreciated that this is an example only of a
boiler structure which the invention might be applicable, and that
the invention might confer advantages to any boiler structure with
similar structural considerations. It will also be appreciated that
where example dimensions for the structures of FIG. 1 and FIG. 2
are given herein, they are for exemplification only.
[0048] FIG. 1 illustrates a typical vertical boiler assembly with a
typical prior art primary support structure with the boiler cold
structure extending to full height and supporting the boiler hot
structure and pressure parts from above maximum boiler envelope
height. For simplicity, most structural elements other than primary
structural elements have been omitted.
[0049] The primary structure consists of a primary boiler support
structure 1 and a SCR support structure 3. The boiler support
structure consists of a suspension deck 5 at approximately 15
metres above the boiler roof level. In the example embodiment, the
suspension deck is thus at approximately 82 metres above the
ground. The suspension deck 5 forms the main load bearing part of
the boiler cold structure. The boiler hot structure and thereby the
envelope and the heating surfaces are all supported from this deck
via slings 7.
[0050] The deck typically consist of several very large structural
steel beams, usually around 5 metres to 6 metres deep depending on
boiler width and on loads spanning across the boiler lateral plain.
Interconnecting beams, designed as secondary structure and laid out
in boiler fore and aft directions, are arranged to suit the sling
positions.
[0051] With this arrangement, the boiler vertical expansion is
entirely downward from the roof. The boiler framing designed to
restrain the boiler envelope in the horizontal plane is supported
by the boiler envelope.
[0052] As can be seen from the figure, the primary structural
framework making up the boiler cold structure extends to the full
extent of the boiler house and to the full height of the suspension
deck 5 at 82 metres.
[0053] The boiler cold structure as a result has a substantial
footprint, and requires primary structural elements to the full
height of the boiler house. This imposes a significant structural
steel requirement. Estimated structural steel requirements for the
typical prior art design illustrated in FIG. 1 are in excess of
11,000 tonnes.
[0054] A side elevation of a modified support structure embodying
the principles of the invention, employed in association with an
equivalent boiler to that shown in FIG. 1, is presented in FIG.
2.
[0055] In FIG. 2, the full height primary structure suspension deck
is dispensed with. Instead, the primary support platform 15 is
provided at mid height, above the burners 17 but below the heating
surfaces 19. This carries a substantial part of the static load of
the boiler envelope and associated structures.
[0056] In the embodiment, the boiler support platform is provided
at a 42 metre level, and the boiler cold support structure
associated with the boiler support platform, and required to
transmit the load from the boiler support platform to the ground,
consequently only needs to rise to this 42 metre level, rather
than, as in FIG. 1, to the full height and full extent of the
boiler house at the 83 metre level. This eliminates the need for
boiler cold structure above the 42 metre level. All the boiler cold
structure is at or below the 42 metre level. Only elements of the
boiler hot structure and the boiler pressure parts extend above the
42 metre level supported by the boiler cold structure.
[0057] Secondary supporting structure 21 is provided above the 42
metre platform level. All horizontal forces above this supporting
platform level are transmitted to the boiler envelope via braces
and tie bars, and then transmitted to the structure below support
level by appropriate links. The wall lateral stiffness is
maintained by a buckstay system, such as described in International
Patent Publication WO2010/073030.
[0058] In the embodiment, boiler hot structural elements and a roof
structure 23 are shown at 75 metre level. Alternatively, at least
the boiler envelope may be self-supporting above the 42 metre
level. However, it will be appreciated even in the embodiment where
boiler hot structural elements and a roof structure 23 are present
that this is in engineering terms a very different structure from
the suspension deck 5 and associated cold structure in the prior
art illustration of FIG. 1. None of the structure above the 42
metre level is cold structure. Only elements of the boiler hot
structure and the boiler pressure parts extend above the 42 metre
level. There is a substantial saving, both in terms of footprint
and in terms of material requirement, above the platform level of
42 metres. In the proposed design, the structural steel requirement
may be reduced to below 8000 tonnes. This is because the boiler
cold structure has both reduced footprint and reduced height, and
the structural steel requirement above the 42 metre platform level
is substantially reduced.
[0059] FIG. 3 illustrates the 42 metre level platform structure in
more detail in plan view, and in particular illustrates the manner
in which it surroundingly supports the boiler envelope. Even at
this level, the design allows for a reduction in footprint.
[0060] FIG. 4 illustrates in plan view the roof level support at 75
metres, and shows the much reduced footprint and structural
requirement at this level when a half height support platform
structure 15 and associated boiler cold structure at or below this
height is provided in accordance with the invention.
[0061] FIG. 5 illustrates in end elevation the open frame primary
structural support arrangement by which load is transmitted from
the support platform 15 at the 42 metre level to the ground. The
use of cross bracings 35 in addition to conventional horizontal and
vertical framework elements opens up the framework below the
platform level, providing at its widest opening of 21.5 metres.
This can be contrasted by the conventional framework structure in
FIG. 1 which has a maximum dimension of 12 or 13 metres. This open
framework, together with the requirement to construct the primary
support platform only to the half height 42 metre level, combined
to facilitate the simultaneous progressive assembly of the support
structure and the boiler envelope. It is only necessary to develop
the support structure up to platform level to the extent sufficient
to support the boiler side walls before it becomes possible to
begin to assemble the boiler envelope within, through and upwardly
from the aperture defined by the 42 metre platform support. The
possibility of jacking from below rather than below using large
cranes from above may further simplify the assembly process.
[0062] FIG. 6 illustrates a possible embodiment by means of which
thermal expansion and contraction may be accommodated by
incorporating the roof into the boiler hot structure. The figure
illustrates movement of walls, vertical buckstays, gallery and roof
due to boiler expansion.
[0063] With reference to FIG. 6, the increase in wall temperature
will result in boiler wall expansion outward. In the embodiment an
assumed expansion is in the y direction (i.e. a boiler lateral
direction) and the magnitude is 63 mm and assuming that the wall is
supported at 42000 mm level and free to expand upward (as well as
downward) from this level. It follows that when the wall expand
horizontally outwards, the wall and the roof intersection will tend
to expand upward by 140 mm and the central part of the roof will
need to move upward by the same amount if the stress level at the
roof and the heating surface is to be negligible.
[0064] In the illustrated embodiment this is enabled by supporting
the roof and the heating surface by angulated links L4 and L5. The
diagram indicates the link cold positions marked by C which will
move to their corresponding hot positions marked by H when the
vertical buckstay is moved outward by 63 mm as a result of boiler
expansion. This is controlled by the movement of horizontal
buckstays such as for example are described in International Patent
Publication WO2010/073030 incorporated herein by reference. The
diagram also indicates two spring units marked as S1 and S2.
However it is noted that the system will work with other
arrangements for example using other link systems. The system
further indicates gallery support and other structure which are
integral part of the total system.
[0065] Thus, the design in accordance with FIGS. 2 to 6 represents
a potentially significant improvement over the prior art design in
FIG. 1. There is a potential reduction in structural weight, and an
associated cost reduction, of around 30 per cent when compared to
conventional support structures having substantial boiler cold
structure to full height. Parallel construction may be enhanced
leading to a significant reduction in construction lead time. The
overall footprint of the boiler may be reduced.
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