U.S. patent application number 13/376469 was filed with the patent office on 2012-03-29 for continuous evaporator.
Invention is credited to Jan Bruckner, Joachim Franke.
Application Number | 20120073520 13/376469 |
Document ID | / |
Family ID | 43069748 |
Filed Date | 2012-03-29 |
United States Patent
Application |
20120073520 |
Kind Code |
A1 |
Bruckner; Jan ; et
al. |
March 29, 2012 |
CONTINUOUS EVAPORATOR
Abstract
A continuous evaporator for a horizontal waste heat steam
generator is provided. The continuous evaporator includes a first
evaporator heating surface that has a number of essentially
vertically arranged first steam generating tubes wherein the
circulation takes place from the bottom to the top, and another
second evaporator heating surface located downstream of the first
evaporator heating surface on the side of the flow medium, the
second evaporator heating surface including a number of other
essentially vertically arranged second steam generating tubes
wherein the circulation takes place from the bottom to the top is
provided. In order to provide a continuous evaporator with an
especially simple structure and an especially long service life, a
number of second steam generator tubes have an inner profiled
element.
Inventors: |
Bruckner; Jan; (Uttenreuth,
DE) ; Franke; Joachim; (Nurnberg, DE) |
Family ID: |
43069748 |
Appl. No.: |
13/376469 |
Filed: |
April 30, 2010 |
PCT Filed: |
April 30, 2010 |
PCT NO: |
PCT/EP10/55886 |
371 Date: |
December 6, 2011 |
Current U.S.
Class: |
122/7R |
Current CPC
Class: |
F22B 37/103 20130101;
F22B 1/1815 20130101; F22B 29/062 20130101 |
Class at
Publication: |
122/7.R |
International
Class: |
F22B 1/00 20060101
F22B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2009 |
DE |
10 2009 024 587.1 |
Claims
1-9. (canceled)
10. A once-through evaporator for a horizontal-type waste heat
steam generator, comprising: a first evaporator heating surface
comprising a first plurality of essentially vertically disposed
first steam generator tubes through which a flow medium flows from
bottom to top; and a second evaporator heating surface connected
downstream of the first evaporator heating surface with respect to
the flow medium direction and comprising a second plurality of
essentially vertically disposed second steam generator tubes
through which the flow medium flows from bottom to top, wherein the
second plurality of second steam generator tubes each include an
internal profile.
11. The once-through evaporator as claimed in claim 10, wherein the
internal profile is helical-spring-shaped.
12. The once-through evaporator as claimed in claim 10, wherein the
profile geometry of the respective internal profile is selected
such that a specified frictional pressure drop of the flow medium
is obtained via a respective second steam generator tube.
13. The once-through evaporator as claimed in claim 10, wherein the
respective internal profile is provided as a kind of internal
finning in a respective second steam generator tube.
14. The once-through evaporator as claimed in claim 10, wherein the
respective internal profile is installed as a fitted component in a
respective second steam generator tube.
15. The once-through evaporator as claimed in claim 10, wherein the
plurality of second steam generator tubes is connected in series as
tube rows in a heating gas direction.
16. The once-through evaporator as claimed in claim 10, wherein the
first evaporator heating surface is connected downstream of the
second evaporator heating surface with respect to the heating gas
direction.
17. A waste heat steam generator, comprising: a once-through
evaporator as claimed in claim 10.
18. The waste heat steam generator as claimed in claim 17, wherein
a gas turbine is disposed upstream of the waste heat steam
generator with respect to a heating gas direction.
19. The waste heat steam generator as claimed in claim 17, wherein
the internal profile is helical-spring-shaped.
20. The waste heat steam generator as claimed in claim 17, wherein
the profile geometry of the respective internal profile is selected
such that a specified frictional pressure drop of the flow medium
is obtained via a respective second steam generator tube.
21. The waste heat steam generator as claimed in claim 17, wherein
the respective internal profile is provided as a kind of internal
finning in a respective second steam generator tube.
22. The waste heat steam generator as claimed in claim 17, wherein
the respective internal profile is installed as a fitted component
in a respective second steam generator tube.
23. The waste heat steam generator as claimed in claim 17, wherein
the plurality of second steam generator tubes is connected in
series as tube rows in a heating gas direction.
24. The waste heat steam generator as claimed in claim 17, wherein
the first evaporator heating surface is connected downstream of the
second evaporator heating surface with respect to the heating gas
direction.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the U.S. National Stage of International
Application No. PCT/EP2010/055886, filed Apr. 30, 2010 and claims
the benefit thereof. The International Application claims the
benefits of Getman application No. 10 20009 024 587.1 DE filed Jun.
10, 2009. All of the applications are incorporated by reference
herein in their entirety.
FIELD OF INVENTION
[0002] The invention relates to a once-through evaporator for a
horizontal-type waste heat steam generator, having a first
evaporator heating surface comprising a plurality of essentially
vertically disposed first steam generator tubes through which a
flow medium flows from the bottom to the top, and another second
evaporator heating surface disposed downstream of the first
evaporator heating surface in respect of the flow medium direction
and comprising a plurality of other essentially vertically disposed
second steam generator tubes through which the medium flows from
the bottom to the top.
BACKGROUND OF INVENTION
[0003] In a gas and steam turbine plant, the heat contained in the
expanded working medium or heating gas from the gas turbine is used
to generate steam for the steam turbine. Heat transfer takes place
in a waste heat steam generator mounted downstream of the gas
turbine and in which a plurality of heating surfaces for water
preheating, steam generation and steam superheating are normally
disposed. The heating surfaces are connected into the water/steam
circuit of the steam turbine. The water/steam circuit nonually
contains a plurality of, e.g. three, pressure stages, each pressure
stage possibly having an evaporator heating surface.
[0004] For the steam generator mounted downstream of the gas
turbine in the heating gas path as a waste-heat steam generator, a
number of alternative design concepts are suitable, namely
configuration as a once-through steam generator or as a
recirculating steam generator. In the case of a once-through steam
generator, the heating of steam generator tubes provided as
evaporator tubes results in evaporation of the flow medium in the
steam generator tubes in a single pass. In contrast, in the case of
a natural or forced circulation steam generator, the circulating
water is only partly evaporated as it passes through the evaporator
tubes, the water that is not evaporated being is re-fed to the same
evaporator tubes for further evaporation after separation of the
generated steam.
[0005] In contrast to a natural or forced circulation steam
generator, a once-through steam generator is not subject to any
pressure limitation. A high live steam pressure promotes high
thermal efficiency and therefore low CO.sub.2 emissions from a
fossil-fired power plant. In addition, a once-through steam
generator has a simple type of construction compared to a
recirculating steam generator and can therefore be manufactured
particularly inexpensively. Using a steam generator of once-through
design as the waste heat steam generator of a gas and steam turbine
plant is therefore particularly advantageous for achieving a high
overall efficiency of the gas and steam turbine plant without
constructional complexity.
[0006] A once-through steam generator designed as a waste heat
steam generator can basically be implemented in one of two
alternative types of construction, namely vertical or horizontal. A
horizontal-type once-through steam generator is designed to provide
an approximately horizontal flow path for the heating medium or
heating gas, e.g. the exhaust gas from the gas turbine, whereas a
vertical-type once-through steam generator is designed to provide
an approximately vertical flow path for the heating medium.
[0007] In contrast to a once-through steam generator of vertical
design, a horizontal-type once-through steam generator can be
manufactured using particularly simple means and with particularly
low production and assembly costs. In both types, particularly in
the downstream (in flow medium direction) steam generator tubes of
the second evaporator heating surface, an uneven distribution of
the two-phase flow medium to the steam generator tubes may occur
within each individual row of tubes, resulting in temperature
imbalances and mechanical stresses caused by differential thermal
expansion. In order to prevent damage to the waste heat steam
generator, expansion bends, for example, have therefore hitherto
been fitted to compensate for these stresses. However, this measure
can be comparatively complex technically in the case of a
horizontal-type waste heat steam generator.
SUMMARY OF INVENTION
[0008] The object of the invention is therefore to specify a
once-through evaporator for a waste heat steam generator as
described in the introduction, which permits a particularly simple
type of construction while providing a particularly long service
life.
[0009] This object is achieved according to the invention by
providing a plurality of second steam generator tubes with an
internal profile.
[0010] The invention is based on the consideration that a
particularly simple design of the waste heat steam generator or
more specifically of the once-through evaporator could be achieved
by dispensing with the hitherto customary expansion bends. In doing
so, however, another way must be found of reducing the mechanical
stresses caused by temperature imbalances in the parallel connected
steam generator tubes of each individual tube row. These occur
particularly in the second evaporator heating surface to which the
water/steam mixture is applied. The temperature imbalances are
caused by different proportions of water and steam in the flow
medium at the inlet of the individual tubes of a tube row and a
resultant differential flow through these tubes. It was realized
that this differential flow in the tubes is caused by the
frictional pressure drop in the steam generator tubes being low
compared to the geodetic pressure drop. In fact, a flow with a high
proportion of steam in the flow medium flows comparatively quickly
through individual steam generator tubes with low frictional
pressure drop, whereas a flow with a high proportion of water is
disadvantaged because of its higher geodetic pressure drop due to
weight and may tend to stagnation. In order to make the flows
uniform, the frictional pressure drop must therefore be increased.
This can be achieved by a plurality of second steam generator tubes
having an internal profile which causes an additional frictional
pressure drop of this kind.
[0011] In order to a achieve a particularly high additional
frictional pressure drop, the laminar boundary layer on the inside
of the tubes must be reduced. This can be achieved by producing
turbulence in the tube. This effect can be amplified still further
by swirling of the flow medium. Swirling of this kind can be
produced by advantageously making the internal profile
helical-spring-shaped.
[0012] Said frictional pressure drop must be appropriately
determined using the normal operating parameters such as tube
geometry, the dimensions of the heating gas path and the
temperature conditions. Advantageously, the geometry of the
particular internal profile must then be selected such that the
predefined frictional pressure drop of the flow medium is obtained
via the respective second steam generator tube. This provides an
even better means of preventing temperature imbalances.
[0013] In an advantageous embodiment, the particular internal
profile is provided in the respective second steam generator tube
as a kind of internal finning, thereby allowing a particularly
simple once-through evaporator or rather waste heat steam generator
design.
[0014] In order to facilitate retrofitting to existing steam
generators and/or achieve greater flexibility in the design of
steam generators in respect of the tube geometries, the particular
internal profile is advantageously inserted in the respective
second steam generator tube as a fitted component. The internal
profile is therefore implemented as a separate component and
disposed in the steam generator tubes.
[0015] In an advantageous embodiment, a plurality of second steam
generator tubes are connected in series in the heating gas
direction as tube rows. This enables a larger number of parallel
connected steam generator tubes to be used for an evaporator
heating surface, which means a better heat input due to the
enlarged surface. However, the steam generator tubes disposed in
series in the heating gas flow direction will be differentially
heated in this case. The flow medium will be comparatively strongly
heated particularly in the steam generator tubes on the heating gas
inlet side. However, as a result of the described design of the
second steam generator tubes with an internal profile, a
through-flow matched to the heating can also be achieved in these
steam generator tubes, thereby ensuring a particularly long service
life for a waste heat steam generator of simple constructional
design.
[0016] In an advantageous embodiment, the first evaporator heating
surface is connected downstream of the second evaporator heating
surface in respect of the heating gas direction. The advantage of
this is that the second evaporator heating surface connected
downstream in respect of the flow medium direction and therefore
designed for further heating of already evaporated flow medium is
also in a comparatively more strongly heated region of the heating
gas path.
[0017] A once-through evaporator of this kind can be usefully
installed in a waste heat steam generator and the waste heat steam
generator employed in a gas and steam turbine plant. Said steam
generator is advantageously connected downstream of a gas turbine
in respect of the heating gas direction. In this configuration,
supplementary firing equipment can be usefully connected downstream
of the gas turbine to increase the heating gas temperature.
[0018] The particular advantages achieved by the invention consist
in that, by providing the second evaporator tubes with an internal
profile, an improvement is achieved in the distribution of the flow
and therefore a reduction in the temperature differences between
parallel connected second steam generator tubes and in the
resultant mechanical stresses, thereby ensuring a particularly long
service life of the waste heat steam generator. The appropriate
provision of the internal profile enables other complex technical
measures such as expansion bends to be dispensed with, while at the
same time allowing a particularly simple, cost-saving design of the
waste heat steam generator or more particularly of a gas and steam
turbine power plant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] An exemplary embodiment of the invention will now be
explained in greater detail with reference to the accompanying
drawings in which:
[0020] FIG. 1 shows a simplified view in longitudinal section
through a horizontal-type steam generator,
[0021] FIG. 2 shows a longitudinal section through a steam
generator tube with internal finning,
[0022] FIG. 3 shows a longitudinal section through a steam
generator tube with fitted components,
[0023] FIG. 4 shows a plot of tube temperature versus steam content
at the heating tube inlet without internal profile and
[0024] FIG. 5 shows a plot of tube temperature versus steam content
at the heating tube inlet with internal profile
[0025] Identical parts are denoted by the same reference characters
in all the figures.
DETAILED DESCRIPTION OF INVENTION
[0026] The once-through evaporator 1 for the waste heat steam
generator 2 as shown in FIG. 1 is connected downstream of a gas
turbine (not shown in greater detail) in respect of the exhaust gas
direction. The waste heat steam generator 2 has an enclosing wall 3
which forms a heating gas path 5 for the exhaust gas from the gas
turbine which can flow through it in an approximately horizontal
heating gas direction indicated by the arrow 4. A plurality of
evaporator heating surfaces 8, 10 of once-through design are
disposed in the heating gas path 5. Although in the exemplary
embodiment in FIG. 1 two evaporator heating surfaces 8, 10 are
shown, a larger number of evaporator heating surfaces can also be
provided.
[0027] The evaporator heating surfaces 8, 10 shown in FIG. 1 each
comprise, in the manner of a tube bundle, a plurality of tube rows
11 and 12 respectively, disposed in series in the heating gas
direction. Each row of tubes 11, 12 in turn comprises a plurality
of steam generator tubes 13 and 14 respectively, disposed in
parallel with one another in the heating gas direction, only one of
which is visible for each tube row 11, 12. Said approximately
vertically disposed first steam generator tubes 13 of the first
evaporator heating surface 8 which are connected in parallel for
the passage of a flow medium W are connected on the output side to
a common outlet header 15. The likewise approximately vertically
disposed second steam generator tubes 14 of the second evaporator
heating surface 10 which are connected in parallel for the passage
of a flow medium W are likewise connected on the output side to a
common outlet header 16. A comparatively more complex header system
can also be provided for the two evaporator heating surfaces 8, 10.
A downcomer system 17 connects the steam generator tubes 13 of the
first evaporator heating surface 8 to the downstream (in terms of
flow medium) steam generator tubes 14 of the second evaporator
heating surface 10.
[0028] The flow medium W which can be applied to the evaporator
system constituted by the evaporator heating surfaces 8, 10 is
evaporated in one passage through the evaporator system and, after
exiting the second evaporator heating surface 10, is discharged as
steam D. The evaporator system formed by the evaporator heating
surfaces 8, 10 is connected into the water/steam circuit (not shown
in greater detail) of a steam turbine. In addition to the
evaporator system comprising the evaporator heating surfaces 8, 10,
a number of other heating surfaces 20 schematically indicated in
FIG. 1 can be connected into the water/steam circuit of the steam
turbine. Said heating surfaces 20 can be, for example,
superheaters, medium pressure evaporators, low pressure evaporators
and/or preheaters.
[0029] The second steam generator tubes 14 now have a
helical-spring-shaped internal profile 22 which is illustrated in
FIGS. 2 and 3. The profile geometry thereof is selected such that
the swirl- and turbulence-induced frictional pressure drop of the
flow medium W in the steam generator tubes 14 is accordingly high
enough to ensure an even through-flow within a tube row 11, thereby
reducing temperature imbalances. Said internal profile 22 can be
directly incorporated in the steam generator tubes 14 as a kind of
internal finning 23. Alternatively, fitted components 24 can be
used as the internal profile 22, which in particular allows
retrofitting to existing once-through evaporators 1.
[0030] The effect of the internal profile 22 on the temperature
differences is illustrated in the graphs in FIGS. 4 and 5 which
plot the average tube wall temperature 25 and the tube outlet wall
temperature 27 against the steam component 29 of the flow medium at
the tube inlet. FIG. 4 shows the situation without internal profile
22. Here the average tube wall temperature 25 varies between
approximately 460.degree. C. and 360.degree. C., the tube outlet
wall temperature 27 between 480.degree. C. and 370.degree. C., as a
function of the steam content 29. In FIG. 5 which explains the
situation with internal profile 22 it is shown that these
variations are reduced to approximately 440.degree. C. to
390.degree. C. and 470.degree. C. to 405.degree. C. respectively.
The temperature differences between tubes with different steam
content at the inlet are therefore significantly reduced.
[0031] By reducing the temperature differences of tubes with
differing steam content at the flow inlet, the mechanical stress
loading of the waste heat steam generator 2 is reduced and a
particularly long service life is ensured, while at the same time
allowing a simple type of construction by eliminating the hitherto
customary expansion bends.
* * * * *