U.S. patent application number 14/523134 was filed with the patent office on 2015-04-30 for feedwater preheating system and method.
The applicant listed for this patent is ALSTOM Technology Ltd. Invention is credited to Joerg DIETZMANN, Paul DROUVOT, Francois DROUX, Torbjorn STENSTROM.
Application Number | 20150114319 14/523134 |
Document ID | / |
Family ID | 49517316 |
Filed Date | 2015-04-30 |
United States Patent
Application |
20150114319 |
Kind Code |
A1 |
DROUVOT; Paul ; et
al. |
April 30, 2015 |
FEEDWATER PREHEATING SYSTEM AND METHOD
Abstract
The feedwater preheating system includes a feedwater tank and a
constant volume recirculation pump. The feedwater tank is adapted
to store the feedwater. The feedwater tank includes feed and return
lines. The feed line is adapted to feed the feedwater to the HRSG,
and the return line enables returning of the feedwater into the
feedwater tank. The return line precludes a control valve, and is
configured to the feedwater tank to reduce component loss while
feedwater recirculation. The constant volume recirculation pump is
configured in the feed line to recirculate the feedwater between
the HRSG and the feedwater tank. The pump is capable of
recirculating the feedwater at constant speed and volume to reduce
heat loss while feedwater recirculation, as against the prior art
feedwater preheating systems.
Inventors: |
DROUVOT; Paul;
(Village-Neuf, FR) ; STENSTROM; Torbjorn; (Baden,
CH) ; DIETZMANN; Joerg; (Baden, CH) ; DROUX;
Francois; (Oberrohrdorf, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALSTOM Technology Ltd |
Baden |
|
CH |
|
|
Family ID: |
49517316 |
Appl. No.: |
14/523134 |
Filed: |
October 24, 2014 |
Current U.S.
Class: |
122/441 |
Current CPC
Class: |
F22D 1/325 20130101;
Y02E 20/16 20130101; F22D 3/06 20130101; F22D 3/00 20130101; F01K
23/10 20130101 |
Class at
Publication: |
122/441 |
International
Class: |
F22D 1/32 20060101
F22D001/32; F22D 3/06 20060101 F22D003/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2013 |
EP |
13190995.4 |
Claims
1. A feedwater preheating system for preheating feedwater to be fed
into a Heat Recovery Steam Generator (HRSG), the feedwater
preheating system, comprising: a feedwater tank to store the
feedwater, the feedwater tank having a feed line to feed the
feedwater to the HRSG, and a return line to enable returning of the
feedwater into the feedwater tank, wherein the return line
precludes a control valve and is configured to the feedwater tank
to reduce component loss while feedwater recirculation; and a
constant volume recirculation pump configured in the feed line to
recirculate the feedwater between the HRSG and the feedwater tank,
wherein the constant volume recirculation pump is capable of
recirculating the feedwater at constant speed and volume to reduce
heat loss while feedwater recirculation, thereby increasing
efficiency of the HRSG.
2. The feedwater preheating system as claimed in claim 1, wherein
the feedwater is maintained at or above a minimum set
temperature.
3. The feedwater preheating system as claimed in claim 2, further
comprising a pegging steam source line configured to the feedwater
tank to supply pegging steam to preheat the feedwater as and when
the temperature of the feedwater in the feedwater tank reaches
below the minimum set temperature.
4. The feedwater preheating system as claimed in claim 3, further
comprising a control valve configured in the pegging steam source
line to close and open the pegging steam source line to supply the
pegging steam.
5. The feedwater preheating system as claimed in claim 4, further
comprising a temperature control circuit configured to the control
valve of the pegging steam source line and to the feedwater tank,
to send signals to open and close the control valve based on the
temperature of the feedwater tank in order to maintain the minimum
set temperature of the feedwater.
6. The feedwater preheating system as claimed in claim 1, wherein
the feedwater is maintained at a temperature, a required minimum
temperature, as required by the HRSG.
7. The feedwater preheating system as claimed in claim 6 further
comprising a pegging steam source line configured to the feedwater
tank to supply pegging steam to preheat the feedwater as and when
the temperature of the feedwater in the feedwater tank reaches
below the required minimum temperature.
8. The feedwater preheating system as claimed in claim 7 further
comprising a Continuous Emission Monitoring System (CEMS) circuit
configured to the pegging steam source line and to the HRSG to
enable calculation of the required minimum temperature, based on
parameters of the HRSG, at which the feedwater is required to be
kept for recirculation in the HRSG, to enable the pegging steam
source line to supply the pegging steam in the feedwater tank to
reheat the feedwater to the required minimum temperature calculated
by the CEMS circuit.
9. The feedwater preheating system as claimed in claim 8, further
comprising a control valve configured in the pegging steam source
line to close and open the pegging steam source line to supply the
pegging steam.
10. The feedwater preheating system as claimed in claim 9, further
comprising a temperature control circuit configured to the control
valve of the pegging steam source line and to the feedwater tank,
to send signals to open and close the control valve based on the
temperature of the feedwater tank in order to maintain the required
minimum temperature of the feedwater.
11. A feedwater preheating system for preheating feedwater to be
fed into a Heat Recovery Steam Generator (HRSG), the feedwater
preheating system, comprising: a feedwater tank to store the
feedwater, the feedwater tank having a feed line to feed the
feedwater to the HRSG, and a return line to enable returning of the
feedwater into the feedwater tank, wherein the return line
precludes a control valve and is configured to the feedwater tank;
and a constant volume recirculation pump configured in the feed
line to recirculate the feedwater between the HRSG and the
feedwater tank, wherein the constant volume recirculation pump is
capable of recirculating the feedwater at constant speed and volume
to reduce heat loss while feedwater recirculation, and maintain a
minimum set temperature of the feedwater.
12. The feedwater preheating system as claimed in claim 11, further
comprising a pegging steam source line configured to feedwater tank
to supply pegging steam to preheat the feedwater as and when the
temperature of the feedwater in the feedwater tank 110 reaches
below the minimum set temperature.
13. The feedwater preheating system as claimed in claim 12, further
comprising a control valve configured in the pegging steam source
line to close and open the pegging steam source line to supply the
pegging steam.
14. The feedwater preheating system as claimed in claim 13, further
comprising a temperature control circuit configured to the control
valve of the pegging steam source line and to the feedwater tank,
to send signals to open and close the control valve based on the
temperature of the feedwater tank in order to maintain the minimum
set temperature of the feedwater.
15. A feedwater preheating system for preheating feedwater to be
fed into a Heat Recovery Steam Generator (HRSG), the feedwater
preheating system, comprising: a feedwater tank to store the
feedwater, the feedwater tank having a feed line to feed the
feedwater to the HRSG, and a return line to enable returning of the
feedwater into the feedwater tank, wherein the return line
precludes a control valve and is configured to the feedwater tank;
a constant volume recirculation pump configured in the feed line to
recirculate the feedwater between the HRSG and the feedwater tank,
wherein the constant volume recirculation pump is capable of
recirculating the feedwater at constant speed and volume to reduce
heat loss while feedwater recirculation; a pegging steam source
line configured to feedwater tank to supply pegging steam to
preheat the feedwater; and a Continuous Emission Monitoring System
(CEMS) circuit configured to the pegging steam source line and to
the HRSG, to enable calculation of a required minimum temperature
at which the feedwater is required to be kept for recirculation in
the HRSG, based on parameters of the HRSG, and to enable the
pegging steam source line to supply the pegging steam in the
feedwater tank to reheat the feedwater to the required minimum
temperature calculated by the CEMS circuit.
16. The feedwater preheating system as claimed in claim 15, further
comprising a control valve configured in the pegging steam source
line to close and open the pegging steam source line to supply the
pegging steam as and when the temperature of the feedwater in the
feedwater tank reaches below the required minimum temperature.
17. The feedwater preheating system as claimed in claim 16, further
comprising a temperature control circuit configured to the control
valve of the pegging steam source line and to the feedwater tank,
to send signals to open and close the control valve based on the
temperature of the feedwater tank in order to maintain the required
minimum temperature of the feedwater.
18. A feedwater preheating system for preheating feedwater to be
fed into a Heat Recovery Steam Generator (HRSG), the feedwater
preheating system, comprising: a feedwater tank to store the
feedwater, the feedwater tank having a feed line to feed the
feedwater to the HRSG, and a return line to enable returning of the
feedwater into the feedwater tank, wherein the return line
precludes a control valve and is configured to the feedwater tank;
a constant volume recirculation pump configured in the feed line to
recirculate the feedwater between the HRSG and the feedwater tank,
wherein the constant volume recirculation pump is capable of
recirculating the feedwater at constant speed and volume to reduce
heat loss while feedwater recirculation; and a pressure control
means configured to a steam turbine inlet at an evaporator of the
HRSG to increase an operational pressure of steam in the evaporator
to shift heat to the feed line to increase heat gain in the
feedwater and maintain a minimum set temperature of the feedwater,
thereby increasing the efficiency of the HRSG.
19. The feedwater preheating system as claimed in claim 18, further
comprising a temperature control circuit configured to the pressure
control means of the evaporator and to the feedwater tank, to send
signals to increase or decrease the operational pressure of the
steam in the evaporator based on the temperature of the feedwater
tank in order to maintain the minimum set temperature of the
feedwater.
20. A method for preheating feedwater to be fed into a Heat
Recovery Steam Generator (HRSG), the method comprising: circulating
the feedwater in a feed line and a return line of a feedwater tank
at constant speed and volume to reduce heat loss while feedwater
recirculation to maintain a minimum set temperature of the
feedwater, wherein the return line precludes a control valve and is
configured to the feedwater tank to reduce component loss while
feedwater recirculation, thereby increasing the efficiency of the
HRSG.
21. The method as claimed in claim 20, further comprising supplying
pegging steam to preheat the feedwater as and when the temperature
of the feedwater reaches below the minimum set temperature.
22. A method for preheating feedwater to be fed into a Heat
Recovery Steam Generator (HRSG), the method comprising: circulating
the feedwater in a feed line and a return line of a feedwater tank
at constant speed and volume to reduce heat loss while feedwater
recirculation, wherein the return line precludes a control valve
and is configured to the feedwater tank to reduce component loss
while feedwater recirculation; calculating a required set
temperature of the HRSG at a last stage; and supplying pegging
steam to preheat the feedwater in the feedwater tank as and when
the temperature of the feedwater reaches below the required minimum
temperature.
23. A method for preheating feedwater to be fed into a Heat
Recovery Steam Generator (HRSG), the method comprising: circulating
the feedwater in a feed line and a return line of a feedwater tank
at constant speed and volume to reduce heat loss while feedwater
recirculation, wherein the return line precludes a control valve
and is configured to the feedwater tank to reduce component loss
while feedwater recirculation; and increasing an operational
pressure of steam in an evaporator of the HRSG to shift heat to the
feed line to increase heat gain in the feedwater and maintain a
minimum set temperature of the feedwater, thereby increasing the
efficiency of the HRSG.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to European application
13190995.4 filed Oct. 31, 2013, the contents of which are hereby
incorporated in its entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to Combined Cycle Power
Plants (CCPP), and, more particularly, to feedwater preheating
system and method for preheating feedwater to be fed into a Heat
Recovery Steam Generator (HRSG) in the CCPP.
BACKGROUND
[0003] Where equipped, in Combined Cycle Power Plants (CCPP),
feedwater heating systems are generally used to preheat water
delivered Heat Recovery Steam Generators (HRSG) to up to or above a
fixed minimum temperature required at the HRSG. Preheating the
feedwater reduces the irreversibilities involved in steam
generation in the HRSG and improves the thermodynamic efficiency of
the CCPP. Among various others advantages of the preheating
feedwater, such preheating also helps avoiding corrosion caused by
flue gas condensation on outer tubes surface in inside the
HRSG.
[0004] For the CCPP equipped with the feedwater heating systems,
the preheating is achieved by different heating source, such as,
pegging steam extracted from the HRSG, steam turbine extraction
either in a condensate preheater, a separate feedwater preheater,
feedwater recirculation from an economizer extraction or
recirculation of feedwater in a dedicated HRSG coil at a cold end
of the HRSG. A philosophy of the mentioned state of the art
concepts is to control a fixed temperature, generally, in the
feedwater tank.
[0005] A prior art FIG. 4 depicts a typical outline of the
feedwater preheating system 10 utilized for preheating and
controlling the fixed temperature of the feedwater. The system 10
includes a feedwater tank 12 having a feed line 14 and a return
line 16 to feed the preheated water to the HRSG, such as, a HRSG
30. The feed line 14 includes a pump 18 to convey the feedwater to
the HRSG 30, and the return line 16 may include a control valve 20
to throttle the flow of the feedwater. The control valve 20
throttles the flow to adjust the recirculation mass flow and
therefore adjust the heat input to the feedwater tanks to maintain
required temperature. Alternatively, the feedwater flow is
controlled by using the pump 18, where the feedwater recirculation
mass flow is variable. Nevertheless, for certain load cases of the
CCPP, the heat integrated by the feedwater recirculation system
operating at full load (e.g. 130 kg/s) may not be enough to
maintain the required minimum temperature set point, which may
usually be 60.degree. C. or above. For that, as depicted in FIG. 4,
the system 10 includes the heating source, such as a pegging steam
circuit 22, to supply heated steam to maintain and control the
minimum feedwater temperature set point in the feedwater tank
12.
[0006] Using any such heating source may constantly affects the
CCPP efficiency since the energy used to heat the feedwater is
usually derived from a main steam source (CRH, LP, etc.) or
extracted between the stages of the steam turbine. Therefore, the
steam that would be used to perform expansion work in the turbine
(and therefore generate power) is not utilized for that purpose.
The percentage of the total cycle steam mass flow used for the
feedwater heating must be carefully optimized for maximum CCPP
efficiency since increasing in fraction of this steam causes a
decrease in the CCPP efficiency.
[0007] Accordingly, there exists a need to minimize or preclude the
need of utilizing such heating stream to heat the feedwater for
heating HRSG to maximize efficiency of the CCPP.
SUMMARY
[0008] The present disclosure describes improved feedwater
preheating system and method, that will be presented in the
following simplified summary to provide a basic understanding of
one or more aspects of the disclosure that are intended to overcome
the discussed drawbacks, but to include all advantages thereof,
along with providing some additional advantages. This summary is
not an extensive overview of the disclosure. It is intended to
neither identify key or critical elements of the disclosure, nor to
delineate the scope of the present disclosure. Rather, the sole
purpose of this summary is to present some concepts of the
disclosure, its aspects and advantages in a simplified form as a
prelude to the more detailed description that is presented
hereinafter.
[0009] An object of the present disclosure is to describe improved
feedwater preheating systems and methods, which may minimize or
preclude the need of utilizing high energetics heating stream to
heat the feedwater to maximize efficiency of a Combined Cycle Power
Plants (CCPP). Such improved feedwater preheating systems and
methods may equally be capable in preventing corrosion caused by
flue gas condensation on outer tubes surface in inside the HRSG.
Further, object of the present disclosure is to describe an
improved feedwater preheating systems and methods, which may be
convenient to use in an effective and economical way. Various other
objects and features of the present disclosure will be apparent
from the following detailed description and claims.
[0010] The above noted and other objects, in one aspect, may be
achieved by an improved feedwater preheating system. The feedwater
preheating system is adapted to preheat feedwater to be fed into a
Heat Recovery Steam Generator (HRSG). The feedwater preheating
system includes a feedwater tank and a constant volume
recirculation pump. The feedwater tank is adapted to store the
feedwater. The feedwater tank includes a feed line and a return
line. The feed line is adapted to feed the feedwater to the HRSG,
and the return line adapted to enable returning of the feedwater
into the feedwater tank. The return line precludes a control valve
to reduce component loss while feedwater recirculation. Further,
the constant volume recirculation pump is configured in the feed
line to recirculate the feedwater between the HRSG and the
feedwater tank. The constant volume recirculation pump recirculate
the feedwater at constant speed and volume to reduce heat loss
while feedwater recirculation, thereby increasing efficiency of the
HRSG.
[0011] In one embodiment of the present disclosure, the feedwater
is maintained above or at a minimum set temperature, defined during
the design based on the sulphur/water content in the flue gas. In
such embodiment, preclusion of the control valve from the return
line and inclusion of the constant volume recirculation pump,
instead of variable volume recirculation pump, enable the feedwater
preheating system to recirculate the feedwater at constant speed
and volume, reducing heat loss while feedwater recirculation, and
maintaining the minimum set temperature of the feedwater, as set
during designing.
[0012] In further embodiment of the present disclosure, instead of
defining the minimum set temperature during the design, as in the
above embodiment, the feedwater is maintained at a temperature, a
required minimum or above set temperature, as required by the HRSG
during operation. As per this embodiment, a Continuous Emission
Monitoring System (CEMS) circuit or any other measuring device,
such as dedicated water/acid dew point measurement device, is
configured to the HRSG to enable calculation of the required
minimum set temperature, based on parameters of the HRSG, at which
the feedwater is required to be kept for recirculation in the HRSG.
In this embodiment, preclusion of the control valve from the return
line and inclusion of the constant volume recirculation pump, to
recirculate the feedwater at constant speed and volume, reduce heat
loss while feedwater recirculation, and maintain the required
minimum set temperature of the feedwater, as calculated by the CEMS
circuit.
[0013] In both the embodiments, the feedwater preheating system
includes an optional provision of a pegging steam line source to
supply pegging steam to the feedwater tank to preheat the feedwater
up to the minimum temperature set during the designing or up to the
required minimum set temperature calculated by the CEMS circuit. As
and when the temperature of the feedwater in the feedwater tank
reaches below the minimum set temperature or below the required
calculated minimum set temperature, the pegging steam line source
may be activated to attain the feedwater temperature requirement.
Such control and reduced use of the pegging steam is capable of
increasing efficiency of the HRSG and hence of the CCSS.
[0014] Both embodiments of the feedwater preheating system includes
a control valve configured in the pegging steam source line to
close and open the pegging steam source line to supply the pegging
steam. Both the embodiments of the system also further includes a
temperature control circuit configured to the control valve of the
pegging steam source line and to the feedwater tank, to send
signals to open and close the control valve based on the
temperature of the feedwater tank in order to maintain the minimum
set temperature of the feedwater.
[0015] In further aspect of the present disclosure, instead of
minimizing the pegging steam for preheating the feedwater, it is
complete precluded from the feedwater preheating system. In this
aspect, the feedwater preheating system includes a feedwater tank,
a constant volume recirculation pump and a pressure control means.
The feedwater tank includes a feed line and a return line. The feed
line is configured to feed the feedwater to the HRSG; and the
return line is configured to enable returning of the feedwater into
the feedwater tank. The return line precludes the control valve and
is configured to the feedwater tank. Further, the constant volume
recirculation pump is configured in the feed line to recirculate
the feedwater between the HRSG and the feedwater tank. The constant
volume recirculation pump is configured to recirculate the
feedwater at constant speed and volume to reduce heat loss while
feedwater recirculation. Furthermore, the pressure control means is
configured to an evaporator of the HRSG to increase an operational
pressure of steam in the evaporator to shift heat to the feed line
to increase heat gain in the feedwater and maintain a minimum set
temperature of the feedwater, thereby precluding the pegging steam
requirement for preheating the feedwater as and when required in
the above two embodiments, thereby increasing the efficiency of the
HRSG.
[0016] The feedwater preheating system may further includes a
temperature control circuit configured to the pressure control
means of the evaporator and to the feedwater tank, to send signals
to increase or decrease the operational pressure of the steam in
the evaporator based on the temperature of the feedwater tank in
order to maintain the minimum set temperature of the feedwater.
[0017] In further aspect, methods are disclosed in the present
disclosure to be operable in view of the respective feedwater
preheating systems.
[0018] Such improved feedwater preheating systems, either minimize
or preclude the need of utilizing heating stream to heat the
feedwater for heating a Heat Recovery Steam Generator (HRSG) to
maximize efficiency of a Combined Cycle Power Plants (CCPP). Such
improved feedwater preheating systems and methods may equally be
capable in preventing corrosion caused by flue gas condensation on
outer tubes surface in inside the HRSG. Further, the improved
feedwater preheating systems may be convenient to use in an
effective and economical way.
[0019] These together with the other aspects of the present
disclosure, along with the various features of novelty that
characterize the present disclosure, are pointed out with
particularity in the present disclosure. For a better understanding
of the present disclosure, its operating advantages, and its uses,
reference should be made to the accompanying drawings and
descriptive matter in which there are illustrated exemplary
embodiments of the present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The advantages and features of the present disclosure will
be better understood with reference to the following detailed
description and claims taken in conjunction with the accompanying
drawing, wherein like elements are identified with like symbols,
and in which:
[0021] FIG. 1 illustrates an example line diagram of a feedwater
preheating system, in accordance with first exemplary embodiment of
the present disclosure; and
[0022] FIG. 2 illustrates an example line diagram of a feedwater
preheating system, in accordance with second exemplary embodiment
of the present disclosure;
[0023] FIG. 3 illustrates an example line diagram of a feedwater
preheating system, in accordance with third exemplary embodiment of
the present disclosure; and
[0024] FIG. 4 illustrates an example line diagram of a feedwater
preheating system as per prior art.
[0025] Like reference numerals refer to like parts throughout the
description of several views of the drawings.
DETAILED DESCRIPTION
[0026] For a thorough understanding of the present disclosure,
reference is to be made to the following detailed description,
including the appended claims, in connection with the above
described drawings. In the following description, for purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of the present disclosure. It will
be apparent, however, to one skilled in the art that the present
disclosure can be practiced without these specific details. In
other instances, structures and apparatuses are shown in block
diagrams form only, in order to avoid obscuring the disclosure.
Reference in this specification to "one embodiment," "an
embodiment," "another embodiment," "various embodiments," means
that a particular feature, structure, or characteristic described
in connection with the embodiment is included in at least one
embodiment of the present disclosure. The appearance of the phrase
"in one embodiment" in various places in the specification are not
necessarily all referring to the same embodiment, nor are separate
or alternative embodiments mutually exclusive of other embodiments.
Moreover, various features are described which may be exhibited by
some embodiments and not by others. Similarly, various requirements
are described which may be requirements for some embodiments but
may not be of other embodiment's requirement.
[0027] Although the following description contains many specifics
for the purposes of illustration, anyone skilled in the art will
appreciate that many variations and/or alterations to these details
are within the scope of the present disclosure. Similarly, although
many of the features of the present disclosure are described in
terms of each other, or in conjunction with each other, one skilled
in the art will appreciate that many of these features can be
provided independently of other features. Accordingly, this
description of the present disclosure is set forth without any loss
of generality to, and without imposing limitations upon, the
present disclosure. The terms "a" and "an" herein do not denote a
limitation of quantity, but rather denote the presence of at least
one of the referenced item.
[0028] Referring now to FIGS. 1 to 3, various examples of feedwater
preheating systems illustrated in accordance with various exemplary
embodiments of the present disclosure. In as much as the
construction and arrangement of the feedwater preheating systems
and its arrangement with respect a Heat Recovery Steam Generator
(HRSG) 200 to maximize efficiency of a Combined Cycle Power Plants
(CCPP), various associated elements may be well-known to those
skilled in the art, it is not deemed necessary for purposes of
acquiring an understanding of the present disclosure that there be
recited herein all of the constructional details and explanation
thereof. Rather, it is deemed sufficient to simply note that as
shown in FIGS. 1 to 3, the feedwater preheating systems 100, only
those components are shown that are relevant for the description of
various embodiments of the present disclosure.
[0029] As shown in FIG. 1, according to first aspect the present
disclosure, the feedwater preheating system 100 includes a
feedwater tank 110 and a constant volume recirculation pump 120.
The feedwater tank 110 is adapted to store the feedwater. The
feedwater tank 110 includes a feed line 112 and a return line 114.
The feed line 112 is adapted to feed the feedwater to the HRSG 200.
Further the return line 114 is adapted to enable returning of the
feedwater into the feedwater tank 110. As compared to the prior art
feedwater preheating system 10, shown in FIG. 4, the return line
114 of the present embodiment precludes a control valve 20, and
that the return line 114 is directly configured to the feedwater
tank 110 to reduce component loss while feedwater recirculation.
Further, the constant volume recirculation pump 120 is configured
in the feed line 112 to recirculate the feedwater between the HRSG
200 and the feedwater tank 110. The constant volume recirculation
pump 120 is fully redundant to recirculate the feedwater at
constant speed and volume to reduce heat loss while feedwater
recirculation, as against the prior art feedwater preheating system
10 that recirculate feedwater with variable speed and volume.
[0030] In one embodiment of the present disclosure as shown in FIG.
1, the feedwater is maintained at minimum or above a set
temperature, defined during the design based on the sulphur/water
content in the flue gas of the CCPP. In this embodiment, preclusion
of the control valve 10 (as shown in prior art FIG. 4) from the
return line 114 and inclusion of the constant volume recirculation
pump 120 instead of the variable speed and volume pumps 18 (as
shown in prior art FIG. 4), make the feedwater preheating system
100 fully redundant to recirculate the feedwater at constant speed
and volume, reduces heat loss while feedwater recirculation and
maintain the minimum set temperature of the feedwater, as set
during designing.
[0031] In further embodiment of the present aspect as shown in FIG.
1, the feedwater preheating system 100 may further include an
optional provision of a pegging steam line source 130 to supply a
pegging steam in the feedwater tank 110 to reheat the feedwater to
up to the minimum set temperature set during the designing. As and
when the temperature of the feedwater in the feedwater tank 110
reaches below the minimum set temperature, the pegging steam line
source 130 may be activated to attain the feedwater temperature
requirement. Such control and reduced use of the pegging steam is
capable of increasing efficiency of the HRSG and hence of the
CCSS.
[0032] In further embodiment, the feedwater preheating system 100,
as shown in FIG. 1, includes a control valve 140 configured in the
pegging steam source line 130 to close and open the pegging steam
source line 130 to supply the pegging steam as and when required.
Further, the system 100 also includes a temperature control circuit
150 configured to the control valve 140 of the pegging steam source
line 130 and to the feedwater tank 110, to send signals to open and
close the control valve 140 based on the temperature of the
feedwater tank 110 in order to maintain the minimum set temperature
of the feedwater.
[0033] Referring now to FIG. 2, a second aspect of the present
disclosure, where instead of defining the minimum set temperature
during the design, as in the first aspect described with respect to
FIG. 1, the feedwater is maintained at or above a required
temperature, herein after referred as "required minimum
temperature," as required by the HRSG 200 during the operation. As
per this aspect, shown in FIG. 2, a Continuous Emission Monitoring
System (CEMS) circuit 160 is configured to the HRSG 200 to
calculate the required minimum temperature for the feedwater, based
on parameters of the HRSG 200., at which the feedwater is required
to be kept for recirculation in the HRSG 200 to avoid corrosion
thereof. However, without departing from the scope of the present
disclosure, apart from the CEMS, any other measuring device, such
as dedicated water/acid dew point measurement device may also be
used to for calculation of the required minimum temperature.
Further, in this second aspect (as shown in FIG. 2), similar to the
first aspect (as per FIG. 1), preclusion of the control valve 10
from the return line 114 and the constant volume recirculation pump
120, makes the feedwater preheating system 100 fully redundant to
recirculate the feedwater at constant speed and volume, reduce heat
loss while feedwater recirculation, and maintain the required
minimum temperature of the feedwater, as calculated by the CEMS
circuit 160.
[0034] Similar to the first aspect (shown in FIG. 1), the second
aspect (shown in FIG. 2) of the feedwater preheating system 100
also includes the optional provision of the pegging steam line
source 130 to supply the pegging steam in the feedwater tank 110 to
reheat the feedwater to up to the required minimum temperature
calculated by the CEMS circuit 160. As and when the temperature of
the feedwater in the feedwater tank 110 reaches below the required
calculated minimum temperature, the pegging steam line source 130
may be activated to attain the feedwater temperature requirement.
Such control and reduced use of the pegging steam is capable of
increasing efficiency of the HRSG 200 and in turn the efficiency of
the CCSS.
[0035] Similar to first aspect as shown in FIG. 1, the feedwater
preheating system 100 of the second aspect (shown in FIG. 2), also
includes the control valve 140 configured in the pegging steam
source line 130 to close and open the pegging steam source line 130
to supply the pegging steam as and when required. Further, the
system 100 of second aspect also includes the temperature control
circuit 150 configured to the control valve 140 of the pegging
steam source line 130 and to the feedwater tank 110, to send
signals to open and close the control valve 140 based on the
temperature of the feedwater tank 110 in order maintain the
required minimum temperature of the feedwater calculated by the
CEMS circuit 160.
[0036] Referring now to FIG. 3, third aspect of the feedwater
preheating system 100 is depicted. As per this aspect, the
feedwater preheating system 100, instead of minimizing the pegging
steam for preheating the feedwater which may optionally be required
in the feedwater preheating system 100 of the first and second
aspects, such use of the pegging steam is completely precluded. In
this aspect, the feedwater preheating system 100 includes a
feedwater tank 110, a constant volume recirculation pump 120 and a
pressure control means 170. The feedwater tank 110 includes a feed
line 112 and a return line 114, as similar to the first and second
aspects of the feedwater preheating system 100, and excluded herein
from explanation for the sake of brevity. Further, the constant
volume recirculation pump 130 of the third aspect is similar to the
first and second aspects of the feedwater preheating system 100,
and excluded herein from explanation for the sake of brevity. The
third aspect of the feedwater preheating system 100 includes the
pressure control means 170, which is configured at a steam turbine
inlet, specifically to an evaporator 210 of the HRSG 200, to
increase an operational pressure of steam in the evaporator 210 to
shift heat to the feed line 112 to increase heat gain in the
feedwater and maintain the minimum set temperature of the
feedwater. Since the heat required for preheating the feedwater to
up to the minimum set temperature is gained by the evaporator 210
by shifting its heat to the feed line 112, the pegging steam
requirement for preheating the feedwater as and when required in
the above two aspects is excluded in the third aspect of the
present disclosure, thereby increasing the efficiency of the HRSG
200.
[0037] The feedwater preheating system 100 as shown in FIG. 3 may
include a temperature control circuit 180 configured to the
pressure control means 170 of the evaporator 210 and to the
feedwater tank 110, to send signals to increase or decrease the
operational pressure of the steam in the evaporator 210 based on
the temperature of the feedwater tank 110 in order to maintain the
minimum set temperature of the feedwater.
[0038] The invention of the present disclosure is advantageous in
various scopes. Such improved feedwater preheating systems, either
minimize or preclude the need of utilizing heating stream to heat
the feedwater for heating a Heat Recovery Steam Generator (HRSG) to
maximize efficiency of a Combined Cycle Power Plants (CCPP). Such
improved feedwater preheating systems and methods may equally be
capable in preventing corrosion caused by flue gas condensation on
outer tubes surface in inside the HRSG. Further, the improved
feedwater preheating systems may be convenient to use in an
effective and economical way. Various other advantages and features
of the present disclosure are apparent from the above detailed
description and appendage claims.
[0039] The foregoing descriptions of specific embodiments of the
present disclosure have been presented for purposes of illustration
and description. They are not intended to be exhaustive or to limit
the present disclosure to the precise forms disclosed, and
obviously many modifications and variations are possible in light
of the above teaching. The embodiments were chosen and described in
order to best explain the principles of the present disclosure and
its practical application, to thereby enable others skilled in the
art to best utilize the present disclosure and various embodiments
with various modifications as are suited to the particular use
contemplated. It is understood that various omission and
substitutions of equivalents are contemplated as circumstance may
suggest or render expedient, but such are intended to cover the
application or implementation without departing from the spirit or
scope of the claims of the present disclosure.
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