U.S. patent application number 09/533194 was filed with the patent office on 2001-12-06 for apparatus and methods of reheating gas turbine cooling steam and hp steam turbine exhaust in a combined cycle power generating system.
Invention is credited to Smith, Raub Warfield, Tomlinson, Leroy O..
Application Number | 20010047646 09/533194 |
Document ID | / |
Family ID | 24124896 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010047646 |
Kind Code |
A1 |
Tomlinson, Leroy O. ; et
al. |
December 6, 2001 |
Apparatus and methods of reheating gas turbine cooling steam and hp
steam turbine exhaust in a combined cycle power generating
system
Abstract
In a combined cycle system having a multi-pressure heat recovery
steam generator, a gas turbine and steam turbine, steam for cooling
gas turbine components is supplied from the intermediate pressure
section of the heat recovery steam generator supplemented by a
portion of the steam exhausting from the HP section of the steam
turbine, steam from the gas turbine cooling cycle and the exhaust
from the HP section of the steam turbine are combined for flow
through a reheat section of the HRSG. The reheated steam is
supplied to the IP section inlet of the steam turbine. Thus, where
gas turbine cooling steam temperature is lower than optimum, a net
improvement in performance is achieved by flowing the cooling steam
exhausting from the gas turbine and the exhaust steam from the high
pressure section of the steam turbine in series through the
reheater of the HRSG for applying steam at optimum temperature to
the IP section of the steam turbine.
Inventors: |
Tomlinson, Leroy O.;
(Niskayuna, NY) ; Smith, Raub Warfield; (Ballston
Lake, NY) |
Correspondence
Address: |
Richard G Besha
Nixon & Vanderhye PC
1100 North Glebe Road
8th Floor
Arlington
VA
22201-4714
US
|
Family ID: |
24124896 |
Appl. No.: |
09/533194 |
Filed: |
March 23, 2000 |
Current U.S.
Class: |
60/772 ;
60/39.182 |
Current CPC
Class: |
Y02E 20/16 20130101;
F01K 23/106 20130101 |
Class at
Publication: |
60/39.02 ;
60/39.182 |
International
Class: |
F02C 006/18 |
Claims
What is claimed is:
1. In a combined cycle system including a gas turbine, a steam
turbine and a heat recovery steam generator wherein gas turbine
exhaust is used in the heat recovery steam generator for heating
steam for the steam turbine, a method of operating the combined
cycle system comprising the steps of: supplying steam from the
intermediate pressure section of the heat recovery steam generator
to the gas turbine to cool component parts thereof; supplementing
the steam from the intermediate pressure section of the heat
recovery steam generator by supplying a first portion of steam from
a high pressure section of the steam turbine to the gas turbine to
cool component parts thereof; combining spent cooling steam from
said gas turbine and a second portion of steam from the high
pressure section of the steam turbine; reheating the combined spent
cooling steam and said second steam portion in said heat recovery
steam generator; and flowing the reheated combined spent cooling
steam and said second steam portion to an intermediate pressure
section of the steam turbine.
2. A method according to claim 1 including flowing steam from a
high pressure superheater in the heat recovery steam generator to
an inlet for the high pressure turbine.
3. A method according to claim 1 including controlling the flow of
the supplemental steam supplied from the high pressure section of
the steam turbine to the gas turbine.
4. A method of operating a combined cycle system comprising the
steps of: supplying steam from an intermediate pressure section of
a heat recovery steam generator to a gas turbine to cool component
parts thereof; supplementing the steam from the intermediate
pressure section of the heat recovery steam generator by supplying
a first portion of cooling steam from an ancillary steam turbine to
the gas turbine for cooling component parts thereof; combining a
second portion of cooling steam from the ancillary turbine and
spent cooling steam from the gas turbine for flow through the heat
recovery steam generator heated by exhaust gases from the gas
turbine; and flowing the heated combined cooling steam to another
section of the ancillary turbine.
5. A method according to claim 4 including controlling the flow of
the supplemental steam supplied from the ancillary steam turbine to
the gas turbine.
6. A combined cycle system comprising: a gas turbine, a steam
turbine and a multi-pressure heat recovery steam generator wherein
gas turbine exhaust gas is used in the heat recovery steam
generator for reheating steam for the steam turbine; a supply
passage for supplying gas turbine cooling duty steam from an
intermediate pressure section of said heat recovery steam generator
supplemented by a portion of the steam exhausting from a high
pressure section of the steam turbine to the gas turbine for
cooling turbine parts; a first passage in communication with said
high pressure steam turbine section for supplying the supplemental
steam portion to said supply passage; a reheater in said heat
recovery steam generator; a second passage for flowing spent
cooling steam from said gas turbine to said reheater; a third
passage for flowing another portion of steam exhausted from said
high pressure turbine section to said reheater; the spent cooling
steam and exhaust steam being combined for flow through the
reheater; and a fourth passage in communication with said reheater
and said intermediate pressure section of the steam turbine for
flowing the reheated combined steam flows exiting the reheater to
said intermediate pressure section of the steam turbine.
7. A system according to claim 6 wherein said first passage and
said third passage are in communication with one another, and a
bypass control valve in said third passage for modulating the flow
of steam along said first passage.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a combined cycle land-based
power generating system in which the heat content of the exhaust
gases from the gas turbine is recovered in a heat recovery steam
generator for heating steam for expansion through the steam
turbine. The invention particularly relates to reheating spent
cooling steam from the gas turbine and exhaust steam from the HP
steam turbine outlet in the heat recovery steam generator for use
in the IP steam turbine.
[0002] In prior combined cycle power generating systems, hot
component parts of the gas turbine are cooled by introducing a
fluid medium, for example, cooling steam, from the intermediate
pressure section of the heat recovery steam generator supplemented
by steam exhausting from the steam turbine into the gas turbine.
Typically, cooling steam is provided from the intermediate pressure
section of the heat recovery steam generator supplemented by a
controlled portion of the steam from the exhaust from the HP
section of the steam turbine only to the extent the steam is needed
to cool the component parts of the gas turbine. The balance of the
steam from the steam turbine HP section not needed for cooling
purposes in the gas turbine is conventionally forwarded to the
reheat section of the heat recovery steam generator for reheating.
The energy for reheating the unneeded steam from the steam turbine
is obtained from the exhaust gases of the gas turbine flowing
through the heat recovery steam generator. The reheated steam is
then typically combined with the spent cooling steam from the gas
turbine for flow into the inlet of another portion of the steam
turbine, e.g., the intermediate pressure (IP) steam turbine
inlet.
[0003] The system described above is set forth in U.S. Pat. No.
5,428,950, of common assignee herewith. At that time, the cooling
cycle duty and steam flow was believed sufficient to provide a mix
of spent cooling steam from the gas turbine and the reheat steam at
a temperature at or near the required inlet temperature for the IP
steam turbine section for optimum performance. Increased steam
cooling steam flow requirements of the gas turbine, however, have
significantly and substantially reduced the temperature of the mix
of spent cooling steam exiting the gas turbine and the reheat steam
exiting the heat recovery steam generator to a temperature well
below the optimum temperature of the steam supplied to the IP steam
turbine inlet. With this reduced temperature of the mix, reduced
performance of the combined cycle system results. It is this
performance penalty which the present invention addresses.
BRIEF SUMMARY OF THE INVENTION
[0004] In accordance with a preferred embodiment of the present
invention, and in a combined cycle system where the temperature of
the mix of spent cooling steam exiting the gas turbine is
significantly lower than the optimum temperature of the steam at
the IP steam turbine inlet, the spent cooling steam and exhaust
steam from the HP steam turbine section are combined for flow
through the reheat section of the heat recovery steam generator
prior to delivery to the IP steam turbine inlet. It will be
appreciated that the parallel flow arrangement of heat recovery in
the aforementioned prior system disclosed in U.S. Pat. No.
5,428,950, i.e., (i) recovering heat from the exhaust gases of the
gas turbine in the reheat section to reheat the exhaust steam from
the HP section of the steam turbine, and (ii) generating heat from
steam cooling the hot component parts of the gas turbine to provide
heated spent cooling steam and combining the reheated exhaust steam
and the spent cooling steam for flow to the IP section of the steam
turbine is penalized by the greater of the pressure drops of the
parallel flow paths. Consequently, if the steam temperature of the
mix is comparable to or even slightly below the desired inlet
temperature to the IP section of the steam turbine, the parallel
arrangement is advantageous. However, as the cooling steam flow
requirements increase for the gas turbine, the temperature of the
mix of spent cooling steam and reheat steam becomes significantly
and substantially lower than the desired input temperature to the
IP steam turbine. In accordance with a preferred embodiment, a
series arrangement for the reheat and spent cooling steam is
provided to raise the temperature of the mix of steam provided to
the IP section of the steam turbine. Moreover, a net increase in
combined cycle performance is obtained by mixing the spent cooling
steam and HP steam turbine exhaust for combined passage through the
reheat section of the HRSG to substantially maintain the desired
steam temperature at the intermediate pressure turbine inlet when
the steam cooling flow requirements are high. The pressure loss
caused by the combined pressure drops through the gas turbine and
reheater, when the spent cooling steam and HP section exhaust steam
are combined in series and pass through the reheater of the heat
recovery steam generator, comprise the penalty for maintaining the
mixed steam at the IP inlet of the steam turbine at the desired
temperature. However, where the steam cooling requirements of the
gas turbine are substantial and there is a consequential
substantial reduction in temperature of the mixed cooling steam and
reheat steam at the IP inlet of the steam turbine, the combined
cycle system employing series reheat rather than the parallel
reheat as set forth in the prior U.S. Pat. No. 5,428,950 affords
improved overall performance.
[0005] In a preferred embodiment according to the present
invention, there is provided in a combined cycle system including a
gas turbine, a steam turbine and a heat recovery steam generator
wherein gas turbine exhaust is used in the heat recovery steam
generator for heating steam for the steam turbine, a method of
operating the combined cycle system comprising the steps of
supplying steam from the intermediate pressure section of the heat
recovery steam generator to the gas turbine to cool component parts
thereof, supplementing the steam from the intermediate pressure
section of the heat recovery steam generator by supplying a first
portion of steam from a high pressure section of the steam turbine
to the gas turbine to cool component parts thereof, combining spent
cooling steam from the gas turbine and a second portion of steam
from the high pressure section of the steam turbine, reheating the
combined spent cooling steam and the second steam portion in the
heat recovery steam generator and flowing the reheated combined
spent cooling steam and the second steam portion to an intermediate
pressure section of the steam turbine.
[0006] In a further preferred embodiment according to the present
invention, there is provided a method of operating a combined cycle
system comprising the steps of supplying steam from an intermediate
pressure section of a heat recovery steam generator to a gas
turbine to cool component parts thereof, supplementing the steam
from the intermediate pressure section of the heat recovery steam
generator by supplying a first portion of cooling steam from an
ancillary steam turbine to the gas turbine for cooling component
parts thereof, combining a second portion of cooling steam from the
ancillary turbine and spent cooling steam from the gas turbine for
flow through the heat recovery generator heated by exhaust gases
from the gas turbine and flowing the heated combined cooling steam
to another section of the ancillary turbine.
[0007] In a still further preferred embodiment according to the
present invention, there is provided a combined cycle system
comprising a gas turbine, a steam turbine and a multi-pressure heat
recovery steam generator wherein gas turbine exhaust gas is used in
the heat recovery steam generator for reheating steam for the steam
turbine, a supply passage for supplying gas turbine cooling duty
steam from an intermediate pressure section of the heat recovery
steam generator supplemented by a portion of the steam exhausting
from a high pressure section of the steam turbine to the gas
turbine for cooling turbine parts, a first passage in communication
with the high pressure steam turbine section for supplying the
supplemental steam portion to the supply passage, a reheater in the
heat recovery steam generator, a second passage for flowing spent
cooling steam from the gas turbine to the reheater, a third passage
for flowing another portion of steam exhausted from the high
pressure turbine section to the reheater, the spent cooling steam
and exhaust steam being combined for flow through the reheater and
a fourth passage in communication with the reheater and the
intermediate pressure section of the steam turbine for flowing the
reheated combined steam flows exiting the reheater to the
intermediate pressure section of the steam turbine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic flow diagram of a multi-pressure
reheat combined cycle system with a steam cooled gas turbine
employing series reheat in accordance with a preferred embodiment
of the present invention; and
[0009] FIG. 2 is a chart illustrating a comparison of series and
parallel reheat as a function of net power.
DETAILED DESCRIPTION OF THE INVENTION
[0010] Referring now to FIG. 1, there is illustrated a combined
cycle power generation system, generally designated 10. The gas
turbine portion of the combined cycle system 10 includes a
compressor 12, a turbine section 14 and a combustion system 16. The
steam turbine portion of the combined cycle system includes a steam
turbine 18 having high pressure (HP), intermediate pressure (IP)
and low pressure (LP) sections 20, 22 and 24, respectively. As
schematically illustrated, the gas turbine and steam turbine are
connected one to the other on a common shaft 26 for driving a
generator 28. Multiple shaft arrangements and multiple generators
can also be employed.
[0011] The steam turbine system 18 includes an unfired,
multi-pressure heat recovery steam generator (HRSG), generally
designated 30. The HRSG 30 includes an LP economizer 32, an LP
evaporator 34, an HP and IP economizer 36, a low pressure
superheater 38, an IP evaporator 40, an HP economizer 42, an IP
superheater 44, an HP evaporator 46, a first HP superheater 48, an
HP reheater 50 and a second HP superheater 52, all of which is
conventional.
[0012] Steam exhausting from the low pressure steam turbine section
24 is condensed in a condenser 54 and the condensate is supplied
via a pump 56 and conduit 58 to the HRSG 30. The condensate passes
through the LP economizer 32 and into the LP evaporator 34. Steam
from the low pressure evaporator 34 is fed to the LP superheater 38
via conduit 60 and then returned to the low pressure section 24 of
the steam turbine 18 via conduit 62. Feed water is pumped by a pump
64 through the LP evaporator 34 and the HP and IP economizer 36 by
way of a conduit 66 and then to the HP economizer 42 via conduit
68; and through the HP and IP economizer 36 via conduit 70 and then
to the IP evaporator 40 via conduit 72.
[0013] Steam from the IP evaporator 40 passes through the IP
superheater 44 via conduit 74 and is then passed to a steam cooling
duty conduit 76 via conduit 78. As noted below, the steam from the
IP superheater 44 combines with a portion of the exhaust steam in
conduit 102 from the high pressure section 20 of the steam turbine
in the steam cooling duty conduit 76. Thus, conduits 76 and 78 form
a supply passage for supplying gas turbine cooling duty steam from
intermediate pressure section 44 and conduits 96 and 102 form a
first passage in communication with the HP turbine section 20 for
supplying supplemental steam to the supply passage 76, 78.
[0014] Condensate in the HP economizer 42 is passed to the HP
evaporator 46 via conduit 80. Steam exiting the HP evaporator 46
via conduit 82 passes through the first superheater 48 and then
through the second superheater 52 via conduit 84. Superheated steam
from superheater 52 is then returned to the high pressure section
20 of the steam turbine 18 via conduit 86. As well known, heat is
provided to the HRSG 30 by the exhaust gases from the gas turbine
14 introduced into the HRSG via conduit 90. Those exhaust gases
exit the HRSG 30 via a stack 92.
[0015] As illustrated, the cooling steam conduit 76 is supplied
with steam from the IP superheater 44 and a portion of the exhaust
from the high pressure section 20 of the steam turbine 18 via
conduits 96 and 102. The heated cooling steam exiting the gas
turbine section 14 via conduit or second passage 94 combines with a
portion of the steam exiting the high pressure section 20 of steam
turbine 18 via conduit or third passage 104 for combined flow to
the reheater 50 of the HRSG via conduit 98. The portion of steam
exhausting from the HP section 20 of the steam turbine that is
supplied to the cooling steam through conduit 102 is modulated by
the bypass control valve 103 in conduit 104. The reheated steam
from reheater 50 is supplied via conduit or fourth passage 100 to
the inlet of the IP section 22 of the steam turbine 18. Thus,
instead of a parallel arrangement in which cooling steam heated by
the gas turbine and reheated exhaust steam from the HP section of
the steam turbine are combined for input to the IP section of the
steam turbine, the IP section of the steam turbine is provided with
steam in series from the combined spent cooling steam and the HP
steam turbine exhaust steam passed through the reheater 50.
[0016] As a consequence of this series arrangement and instead of
the parallel arrangement, a net performance gain is achieved by
substantially maintaining the desired steam temperature to the IP
steam turbine inlet by passing the spent cooling steam and HP
turbine exhaust steam in combination through the reheater and
accepting the higher pressure drop penalty. This increase in net
performance is graphically illustrated with reference to FIG. 2
which presents a performance comparison for a typical combined
cycle unit with a steam cooled gas turbine in which the gas turbine
cooling duty is constant and cooling steam flow is varied. It can
be seen that where the steam cooling duty requirement is less than,
e.g., about 64% of the exhaust from the HP section of the steam
turbine, a parallel arrangement of steam delivery to the IP steam
turbine as disclosed in the prior U.S. Pat. No. 5,428,950 is
advantageous. However, when increased cooling steam flow or reduced
gas turbine cooling duty reduces the temperature of steam
discharged from the gas turbine such that the temperature of the
steam supplied to the intermediate pressure section of the steam
turbine is lower than that required for optimum performance, net
power output is improved by maintaining the steam temperature to
the IP section inlet of the steam turbine at a desired level and
accepting the higher pressure drop penalty by using the series
reheat of the present invention.
[0017] 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.
* * * * *