Note: Descriptions are shown in the official language in which they were submitted.
CA 02507821 2005-05-30
2002P02955WOUS / PCT/EP2003/012250
1
Description
Method for producing a continuous steam generator and a
continuous steam generator
The invention relates to a method for producing a continuous
steam generator, having an enclosing wall formed from steam
generator pipes welded together in a gas-tight fashion, said
wall being prefabricated in modules in the workshop, said
modules being welded together during final assembly. It also
relates to a continuous steam generator that is particularly
suitable for production by such a method.
In a continuous steam generator a number of steam generator
pipes, which together form the gas-tight enclosing wall of the
combustion chamber, are heated to evaporate a fluid medium in
the steam generator pipes completely in one passage. The fluid
medium - generally water - is fed after evaporation to the
superheater pipes connected after the steam generator pipes
and superheated there. The steam generator pipes of the
continuous steam generator can thereby be arranged vertically
or in a spiral fashion and therefore at an angle.
In contrast to a natural circulation steam generator, a
continuous steam generator is not subject to pressure
limitation so that it can be designed for live steam pressures
well above the critical pressure of water (Pkrit = 221 bar),
where it is impossible to differentiate between the water and
steam phases and phase separation is therefore not possible. A
high live steam pressure favors a high level of thermal
efficiency and therefore lower CO2 emissions from a fossil-fuel
power plant.
CA 02507821 2005-05-30
2002P02955W0US / PCT/EP2003/012250
2
The enclosing walls of large combustion chambers - for example
for continuous steam generators with a design output of more
than 100 MWel - cannot be manufactured whole in the workshop
for transport reasons. In such instances final assembly is
required at the actual site of deployment, during which
process the parts or even modules provided to form the
enclosing wall of the combustion chamber are welded together
directly on site. To facilitate production, a modular
structure can be provided, with which the enclosing wall is
prefabricated in modules, which have to be welded together
during final assembly. Such a structure however significantly
restricts the selection of materials that can be used, as when
using materials that are subject to comparatively high thermal
and mechanical loading, a subsequent heat treatment may be
essential when welding.
Subsequent heat treatment of the weld seams involves a
significant technical outlay and can therefore generally only
be undertaken in the workshop and not on site during final
assembly. Therefore when producing enclosing walls for large
combustion chambers of continuous steam generators until now
only materials that did not require subsequent heat treatment
of the weld seams were used.
However to increase the efficiency and therefore reduce the 002
emissions of a fossil-fuel power plant, it is desirable to
design continuous steam generators for particularly high live
steam pressures and temperatures. The production of such
continuous steam generators requires materials which withstand
loading due to high heat flow densities at high steam
temperatures and therefore high material temperatures. However
these are the materials that require subsequent heat treatment
of the weld seams.
CA 02507821 2010-05-19
54106-59
3
A possible alternative to these materials would be nickel-based
materials, which despite their ability to withstand a high thermal load do not
require
subsequent heat treatment of the weld seams, the use of which would however
significantly complicate production and render it more expensive.
The object of some embodiments of the invention is therefore to
specify a method of the type mentioned above for producing a continuous steam
generator that can operate at high steam pressures, which is cost-effective
and
involves simple technology. Also a suitable continuous steam generator for
production using such a method is to be specified.
With regard to the method, according to an embodiment of the
invention a number of pipe segments provided to form the steam generator pipes
and made from a material of a first material category are combined into a
number of
modules, each module being provided with an adapter at a number of connection
points provided for connection to a further module, said module being made
from a
material of a second material category.
An aspect of the invention relates to method for producing a
continuous steam generator, having an enclosing wall formed from steam
generator
pipes welded together in a gas-tight fashion, a number of pipe segments made
from
a material of a first material category and provided to form the steam
generator
pipes being combined into a number of modules, each module being provided
respectively with an adapter made from a material of a second material
category at
a number of connection points provided for connection to a further module,
wherein
the pipe segments are combined into modules such that each module respectively
forms a surface, out of which the respective adapters curve such that the
adapters
provided to connect two adjacent modules are weldable together in a plane that
is
offset in respect of the respective surface, and wherein the enclosing wall is
comprised of the modules.
The invention is thereby based on the consideration that technical
outlay and cost can be kept low when producing the continuous steam generator,
in
that the continuous steam generator is designed for the consequent processing
of
conventional materials rather than expensive nickel-based materials which are
CA 02507821 2010-05-19
54106-59
3a
difficult to process. The continuous steam generator to be produced should
thereby
be designed in a suitable fashion for loading due to high live steam pressures
and
temperatures. Primary consideration is given to the fact that the essential
components of the steam generator pipes
CA 02507821 2009-08-21
20365-4971
4
forming the enclosing wall are made from a material that is
suitable for this purpose.
To keep production costs low still, the continuous steam
generator should thereby be prefabricated to a particularly
large extent in the workshop, so that in particular any
subsequent heat treatment required for weld seams can take
place in relatively simple conditions and with recourse to the
plurality of resources available there. The prefabricated
modules can therefore be formed from pipe segments of a
material suitable for high live steam pressures and
temperatures.
To allow final assembly of the modules, which have been
prefabricated in a suitable fashion, in respect of these
criteria, thereby consequently avoiding the need for
subsequent treatment, the modules should be provided with
corresponding adapters, which allow welding during final
assembly without subsequent heat treatment of the weld seams.
To this end, in contrast to the pipe segments, the adapters
are made from a material with correspondingly different
characteristics.
The materials for the pipe segments on the one hand and the
adapters or adapter units formed therefrom on the other hand
are preferably selected specifically in respect of the
criterion whether subsequent heat treatment of the weld seams
is required. A particularly suitable criterion for assessing
whether a material requires subsequent heat treatment of the
weld seams is the so-called Vickers hardness (DIN 50 133).
CA 02507821 2009-08-21
20365-4971
3
A possible alternative to these materials would be nickel-based
materials, which despite their ability to withstand a high thermal load do not
require subsequent heat treatment of the weld seams, the use of which would
however significantly complicate production and render it more expensive.
The object of some embodiments of the invention is therefore to
specify a method of the type mentioned above for producing a continuous steam
generator that can operate at high steam pressures, which is cost-effective
and
involves simple technology. Also a suitable continuous steam generator for
production using such a method is to be specified.
With regard to the method, according to an embodiment of the
invention a number of pipe segments provided to form the steam generator pipes
and made from a material of a first material category are combined into a
number
of modules, each module being provided with an adapter at a number of
connection points provided for connection to a further module, said module
being
made from a material of a second material category.
An aspect of the invention relates to method for producing a
continuous steam generator, having an enclosing wall formed from steam
generator pipes welded together in a gas-tight fashion, a number of pipe
segments made from a material of a first material category and provided to
form
the steam generator pipes being combined into a number of modules, each
module being provided respectively with an adapter made from a material of a
second material category at a number of connection points provided for
connection to a further module.
The invention is thereby based on the consideration that technical
outlay and cost can be kept low when producing the continuous steam generator,
in that the continuous steam generator is designed for the consequent
processing
of conventional materials rather than expensive nickel-based materials which
are
difficult to process. The continuous steam generator to be produced should
thereby be designed in a suitable fashion for loading due to high live steam
pressures and temperatures. Primary consideration is given to the fact that
the
essential components of the steam generator pipes
CA 02507821 2005-05-30
2002P02955WOUS / PCT/EP2003/012250
The parts of the combustion chamber walls of the continuous
steam generator subject to a high level of loading due to high
heat flow densities are therefore expediently made from a
material of a first material category, the Vickers hardness of
which is higher than the Vickers hardness of the parts of the
combustion chamber walls subject to a lower level of loading.
The latter are expediently made from a material of the second
material category, the Vickers hardness HV10 of the materials
of the second material category thereby preferably being less
than around 350 to 400.
Adjacent steam generator pipes connected parallel to the flow
of a fluid medium are advantageously connected together via
fins, in particular to ensure a high specific heat input into
the steam generator pipes. These fins are advantageously made
from a material of the second material category. As has been
proven, as the fins are components of the continuous steam
generator through which there is no flow, they are not subject
to excessive loading due to the lack of internal pressure,
with the result that the material specifications relating to
them are by comparison not so stringent. These less stringent
material specifications are also met by materials of the
second material category. Such fins also allow the individual
modules to be connected without any problem in a horizontal
direction during final assembly when the pipes of the
continuous steam generator are vertical. To this end half-
width fins are preferably welded onto the modules at the
points provided for connection to other modules in the
workshop and are used for connection purposes during final
assembly.
CA 02507821 2010-05-19
54106-59
6
The individual modules are expediently connected in a vertical
direction via adapter units comprising a number of adapters and if necessary
additional bend couplings. An adapter made from a material of the second
material
category for example is thereby welded in the workshop to a pipe segment made
from a material of the first material category and the weld seam is
subsequently
heat-treated. During final assembly two pipe segments produced in this fashion
are
for example connected directly or by means of a bend coupling, which is also
made
from the material of the second material category. The weld seams applied
during
final assembly do not have to undergo subsequent heat treatment, because the
material used does not require this.
With regard to the continuous steam generator at least some of the
steam generator pipes respectively are formed from a number of pipe segments
connected one behind the other on the fluid medium side and that pipe segments
of a
steam generator pipe connected one after the other in the direction of flow
are each
connected via an adapter unit made from a material of a second material
category.
An aspect of the invention relates to a continuous steam generator
with an enclosing wall formed from steam generator pipes welded together in a
gas-
tight fashion and connected in parallel to allow the passage of a fluid
medium,
wherein at least some of the steam generator pipes are each formed from a
number
of pipe segments connected one behind the other on the fluid medium side and
made from a material of a first material category and with pipe segments of a
steam
generator pipe arranged one after the other in the direction of flow being
connected
together via an adapter unit made from a material of a second material
category,
and wherein a number of adapter units, each comprising a number of adapters
made from a material of the second material category, are arranged such that a
weld seam applied to connect two adapters of the same adapter unit together is
outside a wall surface provided by the pipe segments.
Adjacent steam generator pipes are expediently connected together in
a gas-tight fashion via fins, the fins also being made from a material of the
second
material category.
CA 02507821 2005-05-30
2002P02955W0US / PCT/EP2003/012250
7
The advantages achieved with the invention are in particular
that by using different materials in the enclosing wall of the
combustion chamber, i.e. for the pipe segments on the one hand
and for the adapters and the adapter units formed therefrom on
the other hand, with characteristics, which are tailored to
the respective thermal loading of the steam generator pipes,
the production method for continuous steam generators for high
steam pressures can be kept particularly simple. The use and
combination of different types of material allows this in
particular in that the steam generator pipes are prefabricated
in the workshop from a material of the first material
category, welded to form modules, subjected to subsequent heat
treatment and provided with adapters made from a material of
the second material category, which does not require
subsequent heat treatment, at the points provided for
connection to other modules during assembly. Suitable
arrangement of these adapters outside the area exposed to high
heat flow densities prevents the material being subjected to
excessive loading. The weld seams resulting from welding the
individual modules together during assembly do not require
subsequent heat treatment, as only materials of the second
material category have to be welded during final assembly.
An exemplary embodiment of the invention is described in more
detail below with reference to a drawing, in which:
FIG 1 shows a schematic illustration of a continuous steam
generator with vertically arranged evaporator pipes,
FIG 2 shows two pipe segments connected together by means
of an adapter unit,
FIG 3 shows two pipe segments connected together by means
of an alternative embodiment of an adapter unit,
CA 02507821 2005-05-30
2002P02955W0US / PCT/EP2003/012250
8
FIG 4 shows two pipe segments connected together by means
of a further alternative embodiment of an adapter unit and
FIG 5 shows a cross-section through evaporator pipes
connected together via fins.
Identical parts are marked with the same reference characters
in all the figures.
Figure 1 shows a schematic illustration of a continuous steam
generator 1, the vertical gas duct of which is surrounded by
an enclosing wall 4 and forms a combustion chamber, with a
bell-shaped base 6 at the lower end. The base 6 encloses an
outlet opening 8 (not shown here) for ash.
In the area A of the gas duct a number of burners 10, of which
only one is shown, are attached in the enclosing wall of the
combustion chamber formed from vertically arranged steam
generator pipes 12. The vertically arranged steam generator
pipes 12 are welded together via fins 14 to the gas-tight
enclosing wall 4.
During operation of the continuous steam generator 1 a body of
flame 16 results in the combustion chamber during combustion
of a fossil fuel. This body of flame 16 exposes the area
marked A of the continuous steam generator 1 to a very high
heat flow density during its operation. The body of flame 16
has a temperature profile, which decreases in a vertical
direction starting from the area of the burner. Below the area
A is an area B that is remote from the flame and above the
area A is a further area C also remote from the flame, both of
CA 02507821 2005-05-30
2002P02955W0US / PCT/EP2003/012250
9
which are exposed to a comparatively low level of heat due to
the resulting temperature profile.
The continuous steam generator 1 is designed to be suitable
for operation at high live steam pressures and temperatures
and therefore for a particularly high level of efficiency even
with quite limited production outlay. To this end the steam
generator pipes 12, in particular in the area of high heat
flow densities and high material temperatures, are made from a
material, which withstands loading due to high heat flow
densities. To keep production outlay and cost low at the same
time, the enclosing wall 4 of the combustion chamber is
prefabricated in modules 17 in the workshop. During
prefabrication of the modules 17 in the workshop specific use
is made of the fact that a large number of resources are
available there without further outlay, so that it is possible
in particular to process materials that can be subjected to a
high level of thermal loading despite the associated outlay in
particular during the subsequent heat treatment of weld seams.
To produce the modules 17 therefore finished pipe segments 18
made from a material of a first material category, that can in
particular be subjected to a high level of thermal loading,
are welded together. The pipe segments 18 are thereby selected
such that after final assembly a plurality of pipe segments 18
connected one behind the other on the fluid medium side
respectively form a steam generator pipe 12.
To be able to avoid subsequent heat treatment during final
assembly of the modules 17, said modules 17 are then provided
- still in the workshop - at the connection points provided
for connection to a further module 17 with an adapter 19 made
from a material of a second material category. The material of
CA 02507821 2005-05-30
2002P02955W0US / PCT/EP2003/012250
the second material category is thereby selected such that it
is suitable for welding without subsequent heat treatment.
During attachment to the respectively assigned pipe segment 18
- also still in the workshop - said weld seam is subjected to
a subsequent heat treatment, in order to satisfy the
requirements of the material forming the respective pipe
segment 18. The materials of the second material category
thereby have a lower Vickers hardness than the materials of
the first material category.
During final assembly on site the individual modules 17 are
finally welded together at horizontal joints 20 and vertical
joints 21 respectively via the adapters 19, with only
components made from a material of the second material
category being connected together so that no subsequent heat
treatment is required.
At the vertical joints 21 a connection is achieved via fins 14
and at the horizontal joints 20 via adapter units 22 formed
from a plurality of adapters 19 welded together.
Figure 2 shows an exemplary embodiment of the transition area
at a horizontal joint 20, which is particularly suitable for
use in the area A in proximity to the flame. Two steam
generator pipes 12, provided for use in the area A, in which
the heat flow density is particularly high, are connected
there via an adapter unit 22 in the direction of flow. The
adapter unit 22 thereby comprises two adapters 19 and a bend
coupling 23, each made from a material of the second material
category. Two connectors 24 made from a material of the first
material category are provided to connect the adapters 22 to
the steam generator pipes 12.
CA 02507821 2005-05-30
2002P02955W0US / PCT/EP2003/012250
11
A weld seam 25 between a pipe segment 18 and a connector 24 is
executed in the workshop, because it requires subsequent heat
treatment due to the characteristics of the material of the
pipe segments 18; the same applies to a weld seam 26 between a
connector 24 and an adapter 19. A weld seam 27 between an
adapter 19 and a bend coupling 23 on the other hand can be
executed during final assembly, as it does not require
subsequent heat treatment due to the material characteristics
of the adapters 19 and the bend coupling 23.
The fins 14 are not subject to internal pressure from a fluid
medium and can therefore be made from a material of the second
material category, even if they are in the area A. A weld seam
28 between fins 14 can therefore be executed without any
problem during final assembly.
Figure 3 shows an alternative embodiment of the adapter unit
22, which is also used in the area A, comprising two adapters
19 made from a material of the second material category. The
pipe segments 18 are thereby bent at the points provided for
welding during final assembly such that they curve out from
the surface formed by the pipe segments 18 combined to form a
module 17. A separate connector 24 is therefore not required
with this exemplary embodiment. A weld seam 26 between a pipe
segment 18 and an adapter 19 is executed in the workshop, as
it requires subsequent heat treatment, while a weld seam 27
between two adapters 19 can be executed during final assembly.
The fins 14 can also be welded together here without any
problem at a weld seam 28 during final assembly, as the lack
of internal pressure from a fluid medium means that they can
be made from a material of the second material category, which
does not require subsequent heat treatment.
CA 02507821 2005-05-30
2002P02955W0US / PCT/EP2003/012250
12
Figure 4 shows two pipe segments 18, which are connected
together via an adapter unit 22, which can be attached in the
areas B and C. The adapter unit 22 thereby comprises two
adapters 19 made from a material of the second material
category. The weld seams 26 between the pipe segments 18 and
the adapters 19 are executed in the workshop, while the weld
seam 27 can be executed during final assembly, as it is
between two materials of the second material category, which
do not require subsequent heat treatment. In this exemplary
embodiment the adapter unit 22 is not configured for the
adapters 19 to be welded together in a plane outside the wall
surface provided by the pipe segments 18, as the heat input in
the areas B and C that are remote from the flame is low and
the arrangement of components made from a material of the
second material category in the actual plane of the wall can
therefore be permitted.
Figure 5 shows a cross-section through pipe segments 18
combined into a module 17, which are connected together via
fins 14 and form the steam generator pipes 12. The steam
generator pipes 12 are made from a material of the first
material category, while in contrast the fins 14 are made from
a material of the second material category. Weld seams 29
between a steam generator pipe 12 and a fin 14 are executed in
the workshop, as they require subsequent heat treatment due to
the material characteristics of the steam generator pipes 12.
In contrast weld seams 30, via which two modules 17 are
connected together at vertical joints 21, can be executed
during final assembly, as they do not require subsequent heat
treatment. During final assembly two modules 17 are welded
together at the vertical joints 21 via half-width fins 31.
