U.S. patent application number 09/905982 was filed with the patent office on 2002-01-10 for apparatus and methods for supplying auxiliary steam in a combined cycle system.
Invention is credited to Carberg, William George, Gorman, William G., Jones, Charles Michael.
Application Number | 20020002819 09/905982 |
Document ID | / |
Family ID | 22794344 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020002819 |
Kind Code |
A1 |
Gorman, William G. ; et
al. |
January 10, 2002 |
Apparatus and methods for supplying auxiliary steam in a combined
cycle system
Abstract
To provide auxiliary steam, a low pressure valve is opened in a
combined cycle system to divert low pressure steam from the heat
recovery steam generator to a header for supplying steam to a
second combined cycle's steam turbine seals, sparging devices and
cooling steam for the steam turbine if the steam turbine and gas
turbine lie on a common shaft with the generator. Cooling steam is
supplied the gas turbine in the combined cycle system from the high
pressure steam turbine. Spent gas turbine cooling steam may augment
the low pressure steam supplied to the header by opening a high
pressure valve whereby high and low pressure steam flows are
combined. An attemperator is used to reduce the temperature of the
combined steam in response to auxiliary steam flows above a
predetermined flow and a steam header temperature above a
predetermined temperature. The auxiliary steam may be used to start
additional combined cycle units or to provide a host unit with
steam turbine cooling and sealing steam during full-speed no-load
operation after a load rejection.
Inventors: |
Gorman, William G.;
(Ballston Spa, NY) ; Carberg, William George;
(Ballston Spa, NY) ; Jones, Charles Michael;
(Ballston Lake, NY) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
8th Floor
1100 North Glebe Road
Arlington
VA
22201
US
|
Family ID: |
22794344 |
Appl. No.: |
09/905982 |
Filed: |
July 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
09905982 |
Jul 17, 2001 |
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|
09640667 |
Aug 18, 2000 |
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09640667 |
Aug 18, 2000 |
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09213253 |
Dec 17, 1998 |
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Current U.S.
Class: |
60/784 ;
60/39.182 |
Current CPC
Class: |
F01K 23/106 20130101;
Y02E 20/16 20130101; Y02E 20/14 20130101 |
Class at
Publication: |
60/39.07 ;
60/39.182 |
International
Class: |
F02C 006/18 |
Claims
What is claimed is:
1. Apparatus for supplying auxiliary steam to an end user
comprising: a combined cycle system including a steam-cooled gas
turbine, a steam turbine and a heat recovery steam generator in
heat transfer relation with hot products of combustion from said
gas turbine, said heat recovery steam generator including a low
pressure heater for generating steam and driving said steam
turbine; a reheater for flowing spent cooling steam from said gas
turbine to said steam turbine; a low pressure control valve for
diverting at least a portion of the low pressure steam generated by
the low pressure heater for flow through a first conduit for
auxiliary steam use; a high pressure control valve for diverting at
least a portion of the spent high pressure cooling steam from said
gas turbine for flow thereof through a second conduit; a third
conduit for receiving the low pressure and high pressure steam
flows of said first and second conduits, respectively, and defining
an auxiliary steam conduit for flow thereof to an end user; and a
water attemperator in said third conduit for controlling the
temperature of the auxiliary steam.
2. Apparatus according to claim 1 including a measuring device for
measuring flow of steam in said third conduit, said attemperator
being activated in response to a measurement of a predetermined
steam flow in said third conduit provided by the steam flowing
through said first conduit into said third conduit.
3. Apparatus according to claim 1 including a second combined cycle
system including a second gas turbine, a second steam turbine and a
second heat recovery steam generator in heat transfer relation with
hot products of combustion from said second gas turbine for
generating steam for the second steam turbine, steam seals in said
second combined cycle system for the second steam turbine and a
fourth conduit for connecting the third conduit to said steam
seals.
4. Apparatus according to claim 1 including a second combined cycle
system having a second gas turbine, a second steam turbine and a
second heat recovery steam generator in heat transfer relation with
hot products of combustion from said second gas turbine for
generating steam for the second steam turbine, a steam sparger in
said second combined cycle system for sparging water in a condenser
of the second steam turbine and a fourth conduit for connecting the
third conduit to said sparging device.
5. Apparatus according to claim 1 including a second combined cycle
system including a second gas turbine, a second steam turbine and a
second heat recovery steam generator in heat transfer relation with
hot products of combustion from said second gas turbine for
generating steam for the second steam turbine, a steam cooling
circuit for the second steam turbine and a fourth conduit for
connecting the third conduit to said steam cooling circuit.
6. In a combined cycle system having a steam cooled gas turbine, a
steam turbine and heat recovery steam generator in heat transfer
relation with hot products of combustion from said gas turbine and
including a heater for generating steam and driving the steam
turbine, a method of generating auxiliary steam for use by an end
user, comprising the steps of: diverting at least a portion of the
steam generated by the heater supplied to said steam turbine for
flow through a first conduit; diverting at least a portion of the
spent cooling steam from said gas turbine for flow through a second
conduit; combining the steam flows through the first and second
conduits in a third conduit for flowing auxiliary steam to an end
user; and reducing the temperature of the steam in said third
conduit.
7. A method according to claim 6 including reducing the temperature
of the steam in said third conduit in response at least in part to
a predetermined flow of steam in said third conduit.
8. A method according to claim 6 including reducing the temperature
of the steam in said third conduit in response, at least in part,
to a predetermined temperature of the steam in said third
conduit.
9. A method according to claim 6 including reducing the temperature
of the steam in said third conduit in response to a predetermined
flow of steam and the temperature of the steam in the third
conduit.
10. A method according to claim 6 including a second steam turbine
having seals, and flowing the auxiliary steam in said third conduit
to said steam seals prior to start-up of said second steam
turbine.
11. A method according to claim 6 including a second steam turbine
and a condensor, and flowing the auxiliary steam in said third
conduit to said condensor for use as sparging steam.
12. A method according to claim 6 including a second steam turbine
having a steam cooling circuit, and flowing the auxiliary steam in
said third conduit to said steam cooling circuit for cooling said
second steam turbine at startup thereof.
Description
TECHNICAL FIELD
[0001] The present invention relates to apparatus and methods for
supplying auxiliary steam in a combined cycle system employing a
gas turbine having steam cooling and particularly relates to a
combined high pressure/low pressure system for extracting auxiliary
steam from the combined cycle system and supplying the auxiliary
steam to an end user, for example, steam seals and sparging devices
for starting one or more additional combined cycle systems.
BACKGROUND OF THE INVENTION
[0002] In a typical combined cycle system, a gas turbine combusts a
fuel/air mixture which expands to turn the turbine and drive a
generator for the production of electricity. The hot gases of
combustion exhaust into a heat recovery steam generator in which
water is converted to steam in the manner of a boiler. Steam thus
produced drives a steam turbine, typically comprising high,
intermediate and low pressure turbines, in which additional work is
extracted to drive a further load such as a second generator for
producing additional electric power. In some configurations, the
gas and steam turbines drive a common generator and, in others,
drive different generators.
[0003] In a conventional combined cycle system where additional
similar combined cycle systems are employed, auxiliary steam is
often generated by a host system and applied to such second or
additional systems for use during startup, for example, to provide
auxiliary steam to the steam seals and sparging devices of such
additional units. Auxiliary steam is typically extracted from the
exhaust of the high pressure steam turbine and supplied directly to
a header which, in turn, supplies auxiliary steam to the
sub-systems of the additional unit(s). Auxiliary steam may also be
utilized for other end purposes, for example, as process steam in
co-generation applications.
[0004] Combined cycle systems also typically employ air-cooled gas
turbines. The auxiliary steam conventionally extracted from the
high pressure steam turbine exhaust is sufficiently cool for direct
auxiliary use without attemperation. In more recent advanced design
combined cycle systems, however, steam-cooled gas turbines are
employed. Thus, steam from the high pressure steam turbine flows
through the steam-cooling circuit of the gas turbine and the spent
cooling steam is reheated for return to the steam turbine, for
example, the intermediate pressure steam turbine. Low pressure
steam is, of course, also supplied from the low pressure heater in
the heat recovery steam generator to the steam turbine. Given the
necessity of maintaining the flow of cooling steam through the gas
turbine, it no longer remains practical to use steam from the high
pressure steam turbine for use as auxiliary steam because to do so
reduces the necessary cooling steam for the gas turbine, causing
overheating and attendant problems. Consequently, the problem
addressed is the provision of auxiliary steam in a combined cycle
system employing a steam-cooled gas turbine.
BRIEF SUMMARY OF THE INVENTION
[0005] In accordance with an embodiment of the present invention,
there is provided a combined cycle system employing a steam-cooled
gas turbine wherein low pressure steam from the low pressure
superheater of the heat recovery steam generator and normally
supplied to the intermediate pressure steam turbine is diverted, at
least in part, for flow through a first conduit by opening a
pressure-responsive control valve. The diverted flow of steam flows
into a header for flowing steam to another combined cycle system
during startup to steam seals, for use as sparging steam, and, when
applicable, steam turbine cooling steam at startup. When additional
steam flow is required, spent cooling steam exhausting from the
cooling circuit of the gas turbine may also be diverted in part
from its return to the reheater by opening a pressure responsive
high pressure control valve for flowing steam in a second conduit.
These first and second steam flows are combined in a third conduit,
also containing a flow nozzle for measuring the flow. A water
attemperator is disposed in the third conduit and a thermocouple
measures the steam temperature in the header. The attemperator is
responsive to the measured flow and header steam temperature to
reduce the temperature of the combined flows when the flow in the
third conduit obtains a predetermined minimum flow and the header
temperature exceeds a predetermined temperature. Thus, low pressure
steam from the heat recovery steam generator and high pressure
spent cooling steam are combined and attemperated at a
predetermined flow and header steam temperature to produce an
auxiliary steam flow. The attemperator is consequently used only
when a predetermined minimum steam flow and temperature have been
established. The low pressure flow does not usually require
attemperation and establishes the predetermined minimum flow. The
valve positions and, consequently, the flow through the first and
second conduits is determined by the auxiliary steam pressure in
the header to which the auxiliary steam is supplied.
[0006] There are many different types of end uses for the generated
auxiliary steam. For example, auxiliary steam can be used as
process steam for co-generation purposes. Another use of the
auxiliary steam is for starting other off-line combined cycle
units. That is, in power generating stations having multiple
combined cycle units, it is desirable to supply auxiliary steam
from one operating unit to another unit during startup of the
second unit. Auxiliary steam is necessary during startup of a
second combined cycle unit, for example, for purposes of activating
the steam seals, sparging the condenser and commencing delivery of
cooling steam to the steam turbine when the gas turbine and steam
turbine use a common generator. Otherwise, another source of steam
must be utilized, for example, from an additional boiler, which may
not always be available. Consequently, the auxiliary steam
generated by the host unit can be supplied to a second unit header
for supplying auxiliary steam to the steam seals and sparging
devices and for cooling the steam turbine of the second unit, if
applicable. Because the auxiliary steam temperature may be too high
for use in certain devices, attemperation or temperature reduction
is desirable.
[0007] It will be appreciated from the foregoing-described system
that one or more additional off-line units can be started using
auxiliary steam from the host unit as described and wherein the
additional units may be started seriatim with short time intervals
between starts. Additionally, the high pressure/low pressure system
of this invention does not impact the steam-cooling requirements of
the gas turbine of any one or more of the combined cycle units.
This is significant because it is critically important that the
steam flow for the cooling circuit in each gas turbine be
maintained for proper cooling of the steam-cooled components
thereof. Additional advantages of the present system include the
use of low temperature steam from the LP HRSG system to establish a
minimum flow level before the attemperator is used for the higher
temperature supplemental steam. This minimizes the potential for
water-related damage due to inadequate mixing of the steam and
attemperating water. Further advantages include the use of reduced
cost headers, for example, carbon steel headers instead of alloyed
headers necessary for higher temperature steam. Still further, each
unit is provided its own steam turbine cooling, when a common
generator is used, and sealing steam during full speed no-load
operation after a load rejection.
[0008] In a preferred embodiment according to the present
invention, there is provided apparatus for supplying auxiliary
steam to an end user comprising a combined cycle system including a
steam-cooled gas turbine, a steam turbine and a heat recovery steam
generator in heat transfer relation with hot products of combustion
from the gas turbine, the heat recovery steam generator including a
low pressure superheater for generating steam and driving the steam
turbine, a reheater for flowing spent cooling steam from the gas
turbine to the steam turbine, a low pressure control valve for
diverting at least a portion of the low pressure steam generated by
the low pressure heater for flow through a first conduit for
auxiliary steam use, a high pressure control valve for diverting at
least a portion of the spent high pressure cooling steam from the
gas turbine for flow thereof through a second conduit, a third
conduit for receiving the low pressure and high pressure steam
flows of the first and second conduits, respectively, and defining
an auxiliary steam conduit for flow thereof to an end user and an
attemperator in the third conduit for controlling the temperature
of the auxiliary steam.
[0009] In a further preferred embodiment according to the present
invention, there is provided in a combined cycle system having a
steam cooled gas turbine, a steam turbine and heat recovery steam
generator in heat transfer relation with hot products of combustion
from the gas turbine and including a heater for generating steam
and driving the steam turbine, a method of generating auxiliary
steam for use by an end user, comprising the steps of diverting at
least a portion of the steam generated by the heater supplied to
the steam turbine for flow through a first conduit, diverting at
least a portion of the spent cooling steam from the gas turbine for
flow through a second conduit, combining the steam flows through
the first and second conduits in a third conduit for flowing
auxiliary steam to an end user and reducing the temperature of the
steam in the third conduit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic illustration of an apparatus for
supplying auxiliary steam in a combined cycle system in accordance
with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Referring to the single drawing FIGURE, there is illustrated
a combined cycle system, generally designated 10, which employs a
gas turbine 12 for combusting a fuel/air mixture in a combustor 14
and supplying the hot gases of combustion to turn the turbine and
generate work, for example, to drive a generator 16 for the
production of electricity. The turbine, of course, has a compressor
18 for supplying compressed air as is conventional. In a combined
cycle system, the hot gases of combustion exhausting from the gas
turbine exhaust to a heat recovery steam generator (HRSG) 20 in
which water is converted to steam in the manner of a boiler. The
steam thus produced drives a steam turbine, in this case
represented by high pressure, intermediate pressure and low
pressure turbines 22, 24 and 26, respectively, where additional
work is extracted to also drive the generator or a second
generator, not shown, for producing electricity.
[0012] A heat recovery steam generator typically comprises HP, IP
and LP evaporators, as well as various heaters, i.e., economizers
and superheaters, generally referred to as heaters, whereby the
exhaust gases from the gas turbine at high temperature convert the
water in the HRSG to steam for use in driving the steam turbine.
When there are multiple combined cycle systems in a plant, steam is
also commonly extracted for use in other combined cycle systems,
for example, starting the steam turbines whereby auxiliary steam is
supplied to the steam seals and sparging devices of additional
steam turbines. The HRSG, therefore, under normal operating
conditions supplies low pressure, intermediate pressure and high
pressure steam to the LP, IP and HP steam turbines via suitable
piping arrangements, not all of which are shown.
[0013] In advanced gas turbine design, however, the gas turbine 12
is steam cooled and most steam from the high pressure steam turbine
is normally supplied to a cooling steam circuit 30 of the gas
turbine via piping 32 from the high pressure steam turbine 22. As
will be appreciated from the drawing FIGURE, the spent cooling
steam exhausted from the gas turbine 12 via line 34 is normally
supplied a reheater 36 via line 38 for use in the intermediate
pressure turbine 24. Steam exhausting the intermediate pressure
turbine 24 is supplied the low pressure turbine 26 via line 39.
Steam from the low pressure superheater portion of the HRSG 20 is
supplied via line 40 to the intermediate turbine 24. Thus, in
normal operation of the combined cycle system, high pressure
superheated steam is normally supplied the high pressure turbine 22
via valve 90 from the high pressure superheater, not shown, of the
HRSG 20 for driving the high pressure steam turbine. Most of the
steam exhausting from the high pressure turbine 22 is supplied to
the gas turbine steam cooling circuit 30 for cooling the gas
turbine. The spent cooling steam is supplied via reheater 36 to the
intermediate pressure turbine 24 which, in turn, supplies steam to
the low pressure turbine 26 via line 39.
[0014] Each combined cycle system 10, CC2, CC3, etc. includes a
unit header 42, 42a, 42b (42a and 42b are not completely shown),
etc. Connected to each header, for example, a host header 42 via
piping 44, 46 and 48 are a steam seal valve 50, a sparging valve 52
and a cooling steam valve 54 (for a common GT/ST generator
application). The steam seal valve 50 couples the piping 44 to the
steam seals of the steam turbine. The steam valve 52 couples the
steam of the header 42 to a sparging device for the condenser.
Finally, the valve 54 couples the steam in the header 42 to a steam
cooling circuit for the steam turbine for use during startup when a
common generator is used for the gas turbine and steam turbine.
[0015] The following description of the combined cycle system 10 is
considered as a description of the additional systems CC2, CC3,
etc., which are identical to combined cycle system 10. As
illustrated, low pressure steam from the HRSG superheater is
provided via line 40 to the intermediate pressure turbine 24. To
extract auxiliary steam from the combined cycle system, and supply
auxiliary steam to the header 42, or to the headers 42a and 42b of
systems CC2 and CC3, respectively, a conduit 60 lies in
communication with conduit 40 through a pressure control valve 62.
Conduit 60 also lies in communication through a check valve 64 with
a conduit 66 in communication with a conduit 68 for directly
supplying auxiliary steam to the header 42. During normal
operation, the control valve 62 is closed whereby steam flows from
the HRSG 20 via conduit 40 to the intermediate turbine 24. The
steam flowing in the low pressure conduit 40 has a pressure level
which is suitable for a header system design. The steam flowing in
the low pressure conduit 40 has a temperature which generally meets
the auxiliary steam use temperature requirements for starting
additional combined cycle units and does not require cooling by
attemperation. However, the low pressure supply system may not have
adequate capacity to meet all of the auxiliary steam supply
requirements. Consequently, the auxiliary steam supplied from the
low pressure superheater of the HRSG 20 may be supplemented by a
high pressure auxiliary steam source.
[0016] To accomplish this, a conduit 70 is coupled to the conduit
34 of the steam cooling circuit downstream of the gas turbine 12
and upstream of the reheater 36 for combining the spent cooling
steam from the gas turbine from conduit 34 with the low pressure
steam flowing via line 60. Thus, the low pressure steam in first
conduit 60 is supplemented with the high pressure steam in second
conduit 70 for flow in the third conduit 66. Because the high
pressure steam supply temperature is too high for auxiliary use
during starting, and the temperature of the high pressure auxiliary
steam flowing in line 70 is too hot for auxiliary use purposes, a
temperature reduction to the steam use temperature is necessary. To
reduce the temperature of the supplementary steam for the off-line
units, e.g., CC2 or CC3, a water attemperator 74 is provided in the
third conduit 66. A water attemperator is used because a suitable
steam attemperator source is not available with steam-cooled gas
turbine combined cycle systems. A flow nozzle 76 for measuring the
flow in third conduit 66 is also provided. The attemperator 74 is
responsive to a predetermined minimum measured flow in conduit 66
and a predetermined temperature of the steam in header 42 to effect
cooling of the auxiliary steam flowing in line 66. That is, the
attemperator is not turned on until a minimum flow through nozzle
76 and a predetermined temperature in header 42 are established.
The low pressure flowing from conduit 60 establishes the necessary
minimum flow. The flow through the conduit 70 prior to combining in
conduit 66 with the flow through first conduit 60 from the low
pressure source is controlled by a high pressure control valve 78.
High pressure valve 78 is controlled to open at a slightly lower
set point than the set point for the low pressure control valve 62.
A thermocouple 79 measures the steam temperature in header 42 and
provides a signal via line 81 to the attemperator should the steam
temperature in header 42 exceed a predetermined temperature.
[0017] It is essential that the steam cooling of the gas turbine be
maintained at all times. Thus, to maintain pressure at the inlet to
the gas turbine cooling system when extracting steam from the
reheat system, the intercept control valves 78 and 62 are
responsive to the pressure in the header 42.
[0018] In operation, and to start, for example, off-line unit CC2
using auxiliary steam from a host unit 10, the host unit 10 is
presumed operating at a suitable load. Where the units to be
started are in a warm or hot condition, it is usually not necessary
to attemperate the low pressure steam supply when supplying
auxiliary steam. For starting unit CC2, the low pressure valve 62
is opened to prewarm the header system 42 and valve 43a is opened
to prewarm header 42a. Sealing steam to CC2 is initiated by opening
steam seal valve 50a. The host unit 10 low pressure control valve
62 will respond to provide the additional flow. Similarly, as the
sparging valve 43a is opened to provide sparging steam for starting
unit CC2, low pressure control valve 62 responds by providing
additional low pressure steam. The low pressure steam does not need
to be attemperated and establishes a minimum flow requirement for
attemperation if and when needed. As CC2 steam use continues, such
as opening steam cooling valve 54, on a unit with a common
generator for the gas and steam turbine, or as CC3 unit is brought
on-line, all of the low pressure steam flow will ultimately be
utilized. The additional steam flow required is provided from
conduit 70 by opening high pressure control valve 78. The high
pressure steam temperature is too hot for the steam uses and is
cooled by the attemperator 66 by measuring the header temperature
using thermocouple 79. Water attemperation of the high temperature
steam is acceptable because the low pressure flow has established
the minimum flow requirement to ensure adequate mixing of steam and
water. Control valve 78 provide the necessary additional steam flow
as needed.
[0019] For starting a cold unit, the temperature of the low
pressure steam may be too hot for the starting unit's steam seals.
In this case the low pressure steam also needs to be cooled.
Cooling of the low pressure steam is accomplished by opening the
host unit's sparging valve 52 and admitting steam flow to the
condenser. This will establish a minimum flow in the attemperator
to ensure adequate steam to water mixing. Once this steam flow has
been established, the low pressure steam can be attemperated to the
proper temperature and the steam seal valve 50a of the starting
unit can then be opened. Sparging valve 52a of the starting unit
can then also be opened establishing additional steam flow through
the host unit attemperator. Once the minimum flow in the
attemperator has been established, the host unit's sparging valve
46 can be closed and the use of the auxiliary steam system
continues in the normal manner.
[0020] The high pressure control valve 78 is reduced and closed
when the steam demand is reduced. The low pressure control valve 62
provides steam without attemperation. As the steam demand for the
additional unit CC2 reduces, the low pressure control valve is
closed. The additional unit CC3 may be similarly started using
auxiliary steam from the host unit 10 or from the second unit CC2
in a similar manner.
[0021] The host unit and one or more of the additional units may
operate continuously at full speed no-load (FSNL) after a load
rejection to provide steam for sealing and steam turbine cooling
for a single-shaft system. With respect to unit 10, at FSNL after a
load rejection, the steam turbine main control and reheat intercept
valves 90 and 92 are closed and cooling steam is admitted, using
the low pressure admission valve 94 to prevent overheating. The
source of steam is the low pressure conduit 40 from the HRSG. If
the amount of low pressure steam via conduit 40 is insufficient,
low pressure steam can be admitted to the header 42 through valve
62 with the cooling steam valve 54 open and the high pressure steam
system used to supplement the low pressure steam. For steam seal
supply, at FSNL after a load rejection, intermediate pressure steam
for sealing steam may be used.
[0022] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *