U.S. patent application number 12/646201 was filed with the patent office on 2011-06-23 for method of starting a steam turbine.
This patent application is currently assigned to General Electric Company. Invention is credited to Steven Dipalma, Dileep Sathyanarayana.
Application Number | 20110146276 12/646201 |
Document ID | / |
Family ID | 43566990 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110146276 |
Kind Code |
A1 |
Sathyanarayana; Dileep ; et
al. |
June 23, 2011 |
METHOD OF STARTING A STEAM TURBINE
Abstract
The present invention has the technical effect of reducing the
start-up time associated with starting a steam turbine. Embodiments
of the present invention provide a new methodology for reducing the
steam-to-metal temperature mismatch present during the start-up of
a steam turbine. Essentially, embodiments of the invention may
raise the pressure of the steam upstream of an admission valve
associated with a High Pressure (HP) section of a steam turbine.
The initial high pressure of the steam may reduce the enthalpy of
steam, reducing temperature of the steam admitted to the HP
section.
Inventors: |
Sathyanarayana; Dileep;
(Clifton Park, NY) ; Dipalma; Steven; (Sterling,
MA) |
Assignee: |
General Electric Company
|
Family ID: |
43566990 |
Appl. No.: |
12/646201 |
Filed: |
December 23, 2009 |
Current U.S.
Class: |
60/646 ;
60/660 |
Current CPC
Class: |
F05D 2270/301 20130101;
F01D 19/02 20130101; F05D 2270/3032 20130101; F01D 17/145 20130101;
F01K 13/02 20130101 |
Class at
Publication: |
60/646 ;
60/660 |
International
Class: |
F01K 13/02 20060101
F01K013/02 |
Claims
1. A method of starting a powerplant machine, the method
comprising: providing a steam turbine configured for converting
steam to a mechanical torque; wherein the steam turbine comprises
an HP section; and increasing a pressure of steam upstream of an
admission valve to a pressure matching range, wherein the admission
valve is located upstream of the HP section; wherein the step of
increasing the pressure of the steam decreases a temperature of the
steam prior to admission into the HP section.
2. The method of claim 1 further comprising the step of initiating
a start-up of the steam turbine if a start-up permissive is
satisfied.
3. The method of claim further comprising the step of opening the
admission valve to allow the steam to enter the HP section.
4. The method of claim 2 further comprising the step of determining
whether a rotor stress is within an acceptable range.
5. The method of claim 4 further comprising the step of maintaining
a current load on the steam turbine until the rotor stress is
within the acceptable range.
6. The method of claim 5 further comprising the step of decreasing
the pressure of the steam upstream of the admission valve.
7. The method of claim 6 further comprising the step of increasing
a temperature of the steam in an HP bowl region of the HP
section.
8. The method of claim 5 further comprising the step of increasing
a temperature of the steam in an HP bowl region of the HP
section.
9. The method of claim 8 further comprising the step of decreasing
the pressure of the steam upstream of the admission valve.
10. A method of starting a powerplant comprising a steam turbine,
the method comprising: providing a steam turbine configured for
converting steam to a mechanical torque; wherein the steam turbine
comprises an HP section and a bypass system; determining whether a
cold start of the steam turbine is requested; increasing a pressure
the steam upstream of an admission valve to a pressure matching
range, wherein the admission valve is located upstream of the HP
section; determining whether the steam upstream of the admission
valve is within the pressure matching range; initiating a start-up
of the steam turbine if a start-up permissive is satisfied; and
modulating the admission valve such that allow the steam flows into
the HP section; wherein the step of increasing the pressure of the
steam decreases a temperature of the steam before steams flows into
the HP section.
11. The method of claim 10, wherein the step of increasing the
pressure of the steam upstream of the admission valve to a pressure
matching range, further comprises the step of modulating a bypass
valve of the bypass system.
12. The method of claim 11 further comprising the step of
determining whether a rotor stress is within an acceptable
range.
13. The method of claim 12 further comprising the step of adjusting
a loading rate of the steam turbine until the rotor stress is
within the acceptable range.
14. The method of claim 13 further comprising the step of
modulating the bypass valve to decrease the pressure of the steam
upstream of the admission valve.
15. The method of claim 14 further comprising the step of
increasing a temperature of the steam in an HP bowl region of the
HP section.
16. The method of claim 13 further comprising the step of
increasing a temperature of the steam in an HP bowl region of the
HP section.
17. The method of claim 16 further comprising the step of
modulating the bypass valve to decrease the pressure of the steam
upstream of the admission valve.
18. A system configured for starting a steam turbine, the system
comprising: a steam turbine configured for converting steam to a
mechanical torque; wherein the steam turbine comprises an HP
section; and a control system configured for starting the steam
turbine, wherein the control system performs the steps of:
determining whether a cold start of the steam turbine is requested;
increasing a pressure the steam upstream of an admission valve to a
pressure matching range, before the steam flows into the HP
section, wherein an admission valve is located upstream of the HP
section; determining whether the steam upstream of the admission
valve is within the pressure matching range; initiating a start-up
of the steam turbine if a start-up permissive is satisfied; and
opening the admission valve to allow the steam to flow into the HP
section; wherein the step of increasing the pressure of the steam
decreases a temperature of the steam prior to admission into the HP
section.
19. The system of claim 18, wherein the control system performs the
step of modulating a bypass valve of the bypass system to increase
the pressure of the steam upstream of the admission valve.
20. The system of claim 19, wherein the control system further
performs the steps of: modulating the bypass valve to decrease the
pressure of the steam upstream of the admission valve in order to
increase a temperature of the steam in an HP bowl region of the HP
section.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to the operation of
a turbomachine, and more particularly, to a method of reducing the
start-up time of a steam turbine.
[0002] The start-up and loading process of some known steam
turbines, typically involves a plurality phases occurring at
different load ranges. One reason for this method of starting and
loading the steam turbine is rotor stress control. A rotor of the
steam turbine can experience an overstress event during the
start-up and the initial loading phases. Overstressing can degrade
the material properties of the rotor. A rotor stress control may
stage the loading of the steam turbine with the goal of maintaining
the rotor stress within an allowable range.
[0003] Known methods of reducing the likelihood of an overstress
event involve maintaining the temperature of the steam exiting a
boiler, such as, but not limiting of, a Heat Recovery Steam
Generator (HRSG) at a relative low temperature. For example, but
not limiting of, on a combined cycle powerplant the gas turbine is
held at a low load spinning reserve, or the like, to ensure that
the temperature of the steam generated within the HRSG is
acceptable to the steam turbine. For a cold start, this temperature
may around 700 degrees Fahrenheit. A cold start may be considered
the start-up of the steam turbine after a period on in
operation.
[0004] On combined cycle applications, the steam pressure is
typically related to gas turbine load. On a cold start, the gas
turbine may limited to operate at a load equivalent to
approximately 40% of rated pressure prior to steam turbine start.
Due to the relatively low initial upstream pressure, when steam is
admitted to the steam turbine, the upstream steam enthalpy is also
relatively high. In addition, when steam is admitted to the steam
turbine, the pressure ratio across the upstream and downstream
admission valves is relatively high. These operational factors may
result in steam temperature inside a section of the steam turbine,
at the turbine bowl, to be roughly 40-50 degrees Fahrenheit lower
than the upstream temperature of the steam. During a cold start of
the steam turbine, this reduction in steam temperature may be
insufficient to prevent an overstressing event on the turbine
rotor.
[0005] Therefore, there is a desire for an improved method of
starting a steam turbine. The method should reduce the start-up
time. This method should also eliminate or reduce or the level of
overstressing experienced by the rotor.
BRIEF DESCRIPTION OF THE INVENTION
[0006] In an embodiment of the present invention, a method of
starting a powerplant machine, the method comprising: providing a
steam turbine configured for converting steam to a mechanical
torque; wherein the steam turbine comprises an HP section; and
increasing a pressure of steam upstream of an admission valve to a
pressure matching range, wherein the admission valve is located
upstream of the HP section; wherein the step of increasing the
pressure of the steam decreases a temperature of the steam prior to
admission into the HP section.
[0007] In an alternate embodiment of the present invention, a
method of starting a powerplant comprising a steam turbine, the
method comprising: providing a steam turbine configured for
converting steam to a mechanical torque; wherein the steam turbine
comprises an HP section and a bypass system; determining whether a
cold start of the steam turbine is requested; increasing a pressure
the steam upstream of an admission valve to a pressure matching
range, wherein the admission valve is located upstream of the HP
section; determining whether the steam upstream of the admission
valve is within the pressure matching range; initiating a start-up
of the steam turbine if a start-up permissive is satisfied; and
modulating the admission valve such that allow the steam flows into
the HP section; wherein the step of increasing the pressure of the
steam decreases a temperature of the steam before steams flows into
the HP section.
[0008] In an another alternate embodiment of the present invention,
a system configured for starting a steam turbine, the system
comprising: a steam turbine configured for converting steam to a
mechanical torque; wherein the steam turbine comprises an HP
section; and a control system configured for starting the steam
turbine, wherein the control system performs the steps of
determining whether a cold start of the steam turbine is requested;
increasing a pressure the steam upstream of an admission valve to a
pressure matching range, before the steam flows into the HP
section, wherein an admission valve is located upstream of the HP
section; determining whether the steam upstream of the admission
valve is within the pressure matching range; initiating a start-up
of the steam turbine if a start-up permissive is satisfied; and
opening the admission valve to allow the steam to flow into the HP
section; wherein the step of increasing the pressure of the steam
decreases a temperature of the steam prior to admission into the HP
section.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic illustrating a HP section of a steam
turbine representing an environment within which an embodiment of
the present invention may operate.
[0010] FIG. 2 is a chart illustrating operating curves in
accordance with a known method of starting a steam turbine.
[0011] FIG. 3 is a block diagram illustrating a method used to
start-up a turbomachine, in accordance with an embodiment of the
present invention.
[0012] FIG. 4 is a block diagram illustrating a method used to
start-up a turbomachine, in accordance with an alternate embodiment
of the present invention.
[0013] FIG. 5 is a chart illustrating operating curves in
accordance with a method of starting a steam turbine in accordance
with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The present invention has the technical effect of reducing
the start-up time associated with starting a steam turbine.
Embodiments of the present invention provide a new methodology for
reducing the steam-to-metal temperature mismatch present during the
start-up of a steam turbine. Essentially, embodiments of the
invention may raise the pressure of the steam upstream of an
admission valve associated with a High Pressure (HP) section of a
steam turbine. The initial high pressure of the steam may reduce
the enthalpy of steam, thus reducing temperature of the steam
admitted to the HP section.
[0015] Detailed example embodiments are disclosed herein. However,
specific structural and functional details disclosed herein are
merely representative for purposes of describing example
embodiments. Example embodiments may, however, be embodied in many
alternate forms, and should not be construed as limited to only the
embodiments set forth herein.
[0016] Accordingly, while example embodiments are capable of
various modifications and alternative forms, embodiments thereof
are illustrated by way of example in the drawings and will herein
be described in detail. It should be understood, however, that
there is no intent to limit example embodiments to the particular
forms disclosed, but to the contrary, example embodiments are to
cover all modifications, equivalents, and alternatives falling
within the scope of example embodiments.
[0017] It will be understood that, although the terms first,
second, etc. may be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another. For example, a first
element could be termed a second element, and, similarly, a second
element could be termed a first element, without departing from the
scope of example embodiments. As used herein, the term "and/or"
includes any, and all, combinations of one or more of the
associated listed items.
[0018] The terminology used herein is for describing particular
embodiments only and is not intended to be limiting of example
embodiments. As used herein, the singular forms "a", "an" and "the"
are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises", "comprising", "includes" and/or
"including", when used herein, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
[0019] It should also be noted that in some alternative
implementations, the functions/acts noted might occur out of the
order noted in the FIGS. Two successive FIGS., for example, may be
executed substantially concurrently or may sometimes be executed in
the reverse order, depending upon the functionality/operations
involved.
[0020] Referring now to the FIGS., where the various numbers
represent like parts throughout the several views. FIG. 1 is a
schematic illustrating a HP section 120 of a steam turbine 100
representing an environment within which an embodiment of the
present invention may operate. Typically, a steam turbine 100
typically comprises multiple sections, such as, but not limiting
of, a High-Pressure (HP), an Intermediate-Pressure (IP), and a
Low-Pressure (LP). Embodiments of the present invention may control
the steam flow into the HP section 120. Therefore, FIG. 1 and the
following discussion focus on the HP section 120 which is
integrated with a condensor 140. For simplicity, the IP drum and IP
section, the LP drum and LP section, and reheat components are not
illustrated in FIG. 1. However, embodiments of the present
invention may apply to a steam turbine 100 comprising some or all
of those sections and components, or the like.
[0021] A control system 190 applying known methods of starting up
the steam turbine 100 may perform the following steps. Steam from
an IP drum may be admitted to the IP section of the steam turbine
100. Next, the steam turbine 100 may accelerate to
full-speed-no-load (FSNL). Next, the steam turbine 100 may
synchronize with a grid system, or the like. Next, turbine transfer
of the steam from the IP section to full flow to the HP section 120
may occur. Here, an admission valve 115 may begin to open, allowing
steam to from the HP drum 105 to the HP section 120. Concurrently,
the control system 190 monitors the rotor stress. If the rotor
stresses exceed an allowable range then the control system 190 may
hold or reduce the steam flow into the HP section 120, for a
predetermined waiting period. After, the rotor stresses decrease to
an allowable range, the control system 190 may continue to admit
steam into the HP section 120 via the admission valve 115 until
full steam flow is achieved or the steam turbine load meets a load
set point.
[0022] FIG. 2 is a chart 200 illustrating operating curves in
accordance with a known method of starting a steam turbine 100, as
described in FIG. 1. A first vertical axis represents Temperature
(in deg. F.) and Pressure (in psia). A second vertical axis
represents stress (in percentage). The first and second vertical
axes are versus the start-up time (in minutes) on the horizontal
axis. Data series 205 represents the actual HP rotor stress and
data series 210 represents the allowable stress limit. Data series
215 and 220 represent HP upstream pressure and temperature
respectively. The upstream area is illustrated as the upstream
location 130 in FIG. 1. Data series 225 may represent the HP bowl
temperature, illustrated as HP bowl 125 in FIG. 1.
[0023] The upstream area 130 may be considered a region upstream
and adjacent to the admission valve 115. The downstream area 135
may be considered a region downstream and adjacent to the admission
valve 115:
[0024] FIG. 2 illustrated that from approximately 8 minutes to
approximately 24 minutes, the HP rotor stress 205 exceeded the
allowable stress limit 210. To correct this situation the control
system 190 may modulate the admission valve 115 towards a closed
position for a predetermined waiting period. As illustrated in FIG.
2, at approximately 25 minutes, the rotor stresses decreases to an
allowable range. Here, the control system 190 may modulate the
admission valve 115 towards an open position to continue to admit
steam into the HP section 120, as described. The period that the HP
rotor stress 205 exceeded the allowable stress 210, approximately
16 minutes, prevented the steam turbine 100 from completing the
start-up process.
[0025] As will be appreciated, the present invention may be
embodied as a method, system, or computer program product.
Accordingly, the present invention may take the form of an entirely
hardware embodiment, an entirely software embodiment (including
firmware, resident software, micro-code, etc.) or an embodiment
combining software and hardware aspects all generally referred to
herein as a "circuit", "module," or "system". Furthermore, the
present invention may take the form of a computer program product
on a computer-usable storage medium having computer-usable program
code embodied in the medium. As used herein, the terms "software"
and "firmware" are interchangeable, and include any computer
program stored in memory for execution by a processor, including
RAM memory, ROM memory, EPROM memory, EEPROM memory, and
non-volatile RAM (NVRAM) memory. The above memory types are
exemplary only, and are thus not limiting as to the types of memory
usable for storage of a computer program.
[0026] Any suitable computer readable medium may be utilized. The
computer-usable or computer-readable medium may be, for example but
not limited to, an electronic, magnetic, optical, electromagnetic,
infrared, or semiconductor system, apparatus, device, or
propagation medium. More specific examples (a non exhaustive list)
of the computer-readable medium would include the following: an
electrical connection having one or more wires, a portable computer
diskette, a hard disk, a random access memory (RAM), a read-only
memory (ROM), an erasable programmable read-only memory (EPROM or
Flash memory), an optical fiber, a portable compact disc read-only
memory (CD-ROM), an optical storage device, a transmission media
such as those supporting the Internet or an intranet, or a magnetic
storage device. Note that the computer-usable or computer-readable
medium could even be paper or another suitable medium upon which
the program is printed, as the program can be electronically
captured, via, for instance, optical scanning of the paper or other
medium, then compiled, interpreted, or otherwise processed in a
suitable manner, if necessary, and then stored in a computer
memory. In the context of this document, a computer-usable or
computer-readable medium may be any medium that can contain, store,
communicate, propagate, or transport the program for use by or in
connection with the instruction execution system, apparatus, or
device.
[0027] The term processor, as used herein, refers to central
processing units, microprocessors, microcontrollers, reduced
instruction set circuits (RISC), application specific integrated
circuits (ASIC), logic circuits, and any other circuit or processor
capable of executing the functions described herein.
[0028] Computer program code for carrying out operations of the
present invention may be written in an object oriented programming
language such as Java7, Smalltalk or C++, or the like. However, the
computer program code for carrying out operations of the present
invention may also be written in conventional procedural
programming languages, such as the "C" programming language, or a
similar language. The program code may execute entirely on the
user's computer, partly on the user's computer, as a stand-alone
software package, partly on the user's computer and partly on a
remote computer or entirely on the remote computer. In the latter
scenario, the remote computer may be connected to the user's
computer through a local area network (LAN) or a wide area network
(WAN), or the connection may be made to an external computer (for
example, through the Internet using an Internet Service
Provider).
[0029] The present invention is described below with reference to
flowchart illustrations and/or block diagrams of methods,
apparatuses (systems) and computer program products according to
embodiments of the invention. It will be understood that each block
of the flowchart illustrations and/or block diagrams, and
combinations of blocks in the flowchart illustrations and/or block
diagrams, can be implemented by computer program instructions.
These computer program instructions may be provided to a processor
of a public purpose computer, special purpose computer, or other
programmable data processing apparatus to produce a machine, such
that the instructions, which execute via the processor of the
computer or other programmable data processing apparatus, create
means for implementing the functions/acts specified in the
flowchart and/or block diagram block or blocks.
[0030] These computer program instructions may also be stored in a
computer-readable memory. These instructions can direct a computer
or other programmable data processing apparatus to function in a
particular manner. The such that the instructions stored in the
computer-readable memory produce an article of manufacture
including instruction means which implement the function/act
specified in the flowchart and/or block diagram block or blocks.
The computer program instructions may also be loaded onto a
computer or other programmable data processing apparatus. These
instructions may cause a series of operational steps to be
performed on the computer or other programmable apparatus to
produce a computer implemented process. Here, the instructions,
which execute on the computer or other programmable apparatus,
provide steps for implementing the functions/acts specified in the
flowchart and/or block diagram blocks.
[0031] Embodiments of the present invention provide a new start-up
methodology. As described below, embodiments of this methodology
may increase the pressure of the steam upstream of the HP section
120. This may reduce the temperature of the steam prior to
admission into the HP section 120; which may reduce the rotor
stresses. Then, during initial steam turbine loading, the
methodology may reduce the upstream steam pressure. This may
increase the temperature of the steam flowing into the HP section
120 to a normal operating range at the HP bowl 125.
[0032] Referring again to the Figures, FIG. 3 is a block diagram
illustrating a method 300 used to start-up a steam turbine 100, in
accordance with an embodiment of the present invention. The method
300 may be operated by the control system 190, as illustrated in
FIG. 1. The control system 190 may provide a graphical user
interface (GUI), or the like, that allows an operator to interact
with the method 300.
[0033] In step 305, the method 300 may determine the initial steam
turbine metal temperatures. Here, the control system 190 may
receive data on the metal temperatures from a temperature sensing
devices integrated with the rotor of the steam turbine 100.
[0034] In step 310, the method 300 may determine if a cold start of
the steam turbine 100 is required. A cold start may be considered a
start-up of a steam turbine 100 that has been idle for a certain
period. Components of the steam turbine 100 typically require
longer warming periods when operating under a cold start. The
control system 190 may comprise an operating timer, or the like,
which determines when a cold start is required. If a cold start is
required, then the method 300 may proceed to step 315; otherwise
the method 300 may proceed to step 325.
[0035] In step 315, the method 300 may increase the pressure of the
HP steam at the upstream location 130 to a matching pressure range.
Referring again to FIG. 1, embodiments of the present invention may
modulate the bypass valve 110 to a position allowing for the
matching pressure range. In an embodiment of the present invention,
the pressure range may be from approximately 1200 deg. F. to
approximately 1500 deg. F.
[0036] In step 320, the method 300 may determine whether the
pressure of the steam at the upstream location 130 is within the
matching pressure range. If the pressure of the steam is within the
matching pressure range, then the method 300 may proceed to step
325; otherwise the method 300 may revert to step 315.
[0037] In step 325, the method 300 may determine whether a start-up
permissive is satisfied. Here, the control system 190 may include
start-up permissives that serve to ensure that various systems of
the steam turbine 100 are ready and/or enable for the start-up
process. If the start-up permissive is satisfied, then the method
300 may proceed to step 330; otherwise the method 300 may revert to
step 325 until the start-up permissive is satisfied.
[0038] In step 330, the method 300 may initiate the start-up
process of the steam turbine 100. Here, steam from an IP drum may
be admitted to the IP section of the steam turbine 100. Next, the
steam turbine 100 may accelerate to full-speed-no-load (FSNL).
[0039] In step 335, the method 300 may synchronize the steam
turbine 100. Here, the steam turbine 100 may be electrically
connected with a grid system, or the like.
[0040] In step 340, the method 300 may begin to modulate the
admission valve 115. This may allow steam from the HP drum 105 to
fill and warm the piping adjacent the HP section 120.
[0041] In step 345, the method 300 may transfer to full flow of the
steam from the IP section to the HP section 120. Here, the
admission valve 115 may further open, allowing steam to enter the
HP section 120.
[0042] In step 350, the method 300 may determine if the rotor
stress level is allowable. Here, the control system 190 may monitor
the rotor stress in real-time and compare the actual rotor stress
to the allowable stress limit. If the rotor stresses are not in the
allowable range, then the method 300 may proceed to step 355;
otherwise the method 300 may proceed to step 360.
[0043] In step 355, the method 300 may maintain or reduce the steam
flow into the HP section 120, for a predetermined waiting period.
After, the rotor stresses decrease to the allowable range; the
control system 190 may continue to admit steam into the HP section
120 via the admission valve 115.
[0044] In step 360, the method 300 may increase the temperature of
the steam at the upstream location 130 to approximately a rated
temperature. Here, the control system 190 may modulate the bypass
valve 110 to a position allowing for decreasing the pressure of the
steam, allowing for an increasing the steam temperature, as
described.
[0045] In step 365, the method 300 may increase the temperature of
the steam in the HP bowl 125. Here, the control system 190 may
modulate the bypass valve 110 to a position allowing for decreasing
the pressure of the steam, allowing for an increasing the steam
temperature, as described.
[0046] In step 370, the method 300 may increase the load to a base
load, or other load setpoint. Here, the control system 190 may
continue to admit steam into the HP section 120 via the admission
valve 115 until the desired load is reached.
[0047] In step 375, the method 300 may maintain the load setpoint.
Here, the method 300 may modulate the admission valve 115 as needed
to maintain the load.
[0048] FIG. 4 is a block diagram illustrating a method 400 used to
start-up a turbomachine, in accordance with an alternate embodiment
of the present invention. The majority of the steps described in
FIG. 3 may be repeated. Therefore, the discussion of FIG. 4 will
focus on the differences between the methods 300 and 400. Steps 360
and 365 of the method 300 are swapped in the method 400. Here, the
method 400 prioritizes the step of increasing the temperature of
the steam in the HP bowl 125, in step 460, over the step of
increasing the temperature of the steam at the upstream location
130. This approach in the method 400 is opposite to the approach
used in the method 300; and may be used to further mitigate the
rotor stress level.
[0049] Embodiments of the present invention reduce the enthalpy of
the steam upstream of the admission valve 115. In addition, the
pressure ratio across the admission valve 115 may be reduced.
Together, these actions may collectively reduce the temperature
inside the HP bowl 125. In an embodiment of the present invention,
the temperature reduction across the admission valve 115 may range
from approximately 125 deg. F. to approximately 150 deg. F. In
comparison, the method described in conjunction with FIG. 2, may
merely provide a temperate reduction of up to approximately 50 deg.
F. The increased temperature reduction that may be provided by an
embodiment of the present invention may reduce the steam-metal
temperature mismatch and, thus mitigate rotor stress.
[0050] FIG. 5 is a chart 500 illustrating operating curves in
accordance with method 300 of FIG. 3 and 400 of FIG. 4 in
accordance with embodiments of the present invention. A first
vertical axis represents Temperature (in deg. F.) and Pressure (in
psia). A second vertical axis represents stress (in percentage).
The first and second vertical axes are versus the start-up time (in
minutes) on the horizontal axis. Data series 505 represents the
actual HP rotor stress and data series 510 represents the allowable
stress limit. Data series 515 and 520 represent HP upstream
pressure and temperature respectively. The upstream area may be
adjacent the upstream location 130 (illustrated in FIG. 1). Data
series 525 may represent the HP bowl temperature, illustrated as HP
bowl 125 in FIG. 1.
[0051] FIG. 5 illustrates that throughout the start-up of the steam
turbine 100, the HP rotor stress 505 did not exceed the allowable
stress limit 510. Here, the bypass valve 110 was modulated to
increase the pressure at the upstream location 130 to approximately
1400 psig. In FIG. 5 the HP bowl temperature 525 is approximately
575 deg. F. In contrast, the HP bowl temperature of FIG. 2 is
approximately 725 deg. F. FIG. 5 also illustrates increases in the
HP upstream pressure and temperature, 520, 525 respectively as the
upstream pressure 515 is decreased, as described.
[0052] As one of ordinary skill in the art will appreciate, the
many varying features and configurations described above in
relation to the several exemplary embodiments may be further
selectively applied to form the other possible embodiments of the
present invention. Those in the art will further understand that
all possible iterations of the present invention are not provided
or discussed in detail, even though all combinations and possible
embodiments embraced by the several claims below or otherwise are
intended to be part of the instant application. In addition, from
the above description of several exemplary embodiments of the
invention, those skilled in the art will perceive improvements,
changes, and modifications. Such improvements, changes, and
modifications within the skill of the art are also intended to be
covered by the appended claims. Further, it should be apparent that
the foregoing relates only to the described embodiments of the
present application and that numerous changes and modifications may
be made herein without departing from the spirit and scope of the
application as defined by the following claims and the equivalents
thereof.
* * * * *