U.S. patent application number 12/216196 was filed with the patent office on 2010-01-07 for steam turbine overload valve and related method.
This patent application is currently assigned to General Electric Company. Invention is credited to Gregory L. DiAntonio, Douglas C. Hofer, William Parry.
Application Number | 20100000216 12/216196 |
Document ID | / |
Family ID | 41396914 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100000216 |
Kind Code |
A1 |
Hofer; Douglas C. ; et
al. |
January 7, 2010 |
Steam turbine overload valve and related method
Abstract
A steam turbine operating system includes at least a high
pressure turbine section and a low pressure section; one or more
control valves arranged to admit steam from a boiler to the high
pressure turbine section; a condenser arranged to receive steam
exhausted from the low pressure section and to convert the steam to
a liquid; a top heater arranged to receive liquid from the
condenser and to heat the liquid via heat exchange with steam from
the high pressure section, and to return the heated liquid to the
boiler; and an overload bypass valve arranged to supply steam
bypassed around the one or more control valves directly to the top
heater.
Inventors: |
Hofer; Douglas C.; (Clifton
Park, NY) ; DiAntonio; Gregory L.; (Marietta, GA)
; Parry; William; (Rexford, NY) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
41396914 |
Appl. No.: |
12/216196 |
Filed: |
July 1, 2008 |
Current U.S.
Class: |
60/645 ;
60/652 |
Current CPC
Class: |
F01K 13/02 20130101 |
Class at
Publication: |
60/645 ;
60/652 |
International
Class: |
F01K 13/00 20060101
F01K013/00 |
Claims
1. A steam turbine operating system comprising at least a high
pressure turbine section and a low pressure section; one or more
control valves arranged to admit steam from a boiler to the high
pressure turbine section; a condenser arranged to receive steam
exhausted from the low pressure section and to convert the steam to
a liquid; a top heater arranged to receive liquid from the
condenser and to heat said liquid via heat exchange with steam from
the high pressure section, and to return the heated liquid to the
boiler; and an overload bypass valve arranged to supply steam
bypassed around said one or more control valves directly to said
top heater.
2. The operating system of claim 1 wherein bypass steam from the
overload valve and steam from the high pressure turbine section are
drained from said top heater.
3. The operating system of claim 1 wherein said overload bypass
valve is moveable between open and closed positions.
4. The operating system of claim 3 wherein said overload bypass
valve is moveable incrementally in a throttling manner.
5. The operating system of claim 3 wherein said bypass overload
valve is moveable manually at the discretion of operating
personnel.
6. The combination of claim 3 wherein said bypass overload valve is
moveable automatically in response to a signal indicative of
turbine load.
7. A method of operating a steam turbine delivering power to a
connected load and adapted to receive steam from a steam generating
source, the turbine having one or more control valves for
controlling the admission of steam to higher pressure stages of the
turbine; a condenser 134 arranged to receive steam exhausted from
said turbine and convert the steam to a liquid; and a bypass
overload valve connected to receive steam from the steam source,
the method comprising the steps of: (a) maintaining said bypass
overload valve closed while controllably positioning said control
valves to admit steam to the turbine to sustain a preselected power
load; (b) at least partially opening said bypass overload valve;
and (c) returning steam passing through said bypass overload valve
to said top heater.
8. The method of claim 7 wherein said bypass overload valve is
manually caused to be opened and closed at an operator's
discretion.
9. The method of claim 7 wherein said bypass overload valve is
automatically caused to be opened and closed in response to a
signal indicative of turbine load.
Description
[0001] This invention relates to the operation of a steam turbine
using turbine reserve capacity for operation at elevated loads.
BACKGROUND OF THE INVENTION
[0002] Large steam turbines of the type used in the electrical
power generating industry are liberally designed to provide some
additional load capability beyond the nominal rated capacity, an
operating point commonly referred to as the "guarantee point." The
nominal rated capacity is stated in terms of power output, and
conventionally, this condition is achieved with one or more control
valves less than fully open so that the additional capability is
obtained by opening the control valves fully. If the turbine design
is such that the nominal rated capacity occurs with the steam
admission valves fully open, the turbine efficiency at that point
will be improved significantly in terms of energy utilization or
heat rate. However, with the control valves fully open, there are
limited means by which reserve capacity of a steam turbine can be
achieved.
[0003] One known method of achieving excess capacity in a turbine
when the nominal rated capacity occurs with the control valves
fully open, is to provide a bypass valve and thereby pass extra
steam around the control valves to a later lower pressure stage of
the turbine. This method (as used in the past) has three
disadvantages. First, it has been considered necessary to integrate
the bypass valve into the turbine control system, in effect making
the bypass valve an additional control valve which is throttled in
a controlled and coordinated manner with the admission control
valves. This adds significantly to the complexity of the control
system. Second, to meet industry incremental regulation
requirements with a throttling type bypass valve, it has been
necessary to provide some overlap between the control valves and
the bypass valve. In other words, it becomes necessary to begin
opening the bypass valve before the control valves are fully open.
This degrades the efficiency of the turbine at its nominal rated
capacity. Third, because of the small capacity of such a bypass
valve, considerable valve stroking motion is required to have the
turbine participate in frequency control in the power system to
which it is connected. This large motion may cause heavy wear and
lead to early failure of the valve.
[0004] In another method, a bypass overload valve is employed to
achieve reserve capacity of the turbine with no substantial change
to the turbine control system, with the diverted or bypass steam
reintroduced into a downstream turbine stage. This method is
described in commonly-owned U.S. Pat. No. 4,403,476.
BRIEF DESCRIPTION OF THE INVENTION
[0005] In the exemplary but non-limiting embodiment disclosed
herein, the steam supplied by the boiler and diverted toward the
overload valve upstream of the steam turbine inlet is redirected to
the top heater rather than to a downstream turbine stage.
[0006] Accordingly, in one aspect, the present invention relates to
a steam turbine operating system comprising at least a high
pressure turbine section and a low pressure section; one or more
control valves arranged to admit steam from a boiler to the high
pressure turbine section; a condenser arranged to receive steam
exhausted from the low pressure section and to convert the steam to
a liquid; a top heater arranged to receive liquid from the
condenser and to heat the liquid via heat exchange with steam from
the high pressure section, and to return the heated liquid to the
boiler; and an overload bypass valve arranged to supply steam
bypassed around the one or more control valves directly to the top
heater.
[0007] In still another aspect, the invention relates to a method
of operating a steam turbine delivering power to a connected load
and adapted to receive steam from a steam generating source, the
turbine having one or more control valves for controlling the
admission of steam to higher pressure stages of the turbine and
having a bypass overload valve connected to receive steam from the
steam source, the method comprising the steps of: (a) maintaining
the bypass overload valve closed while controllably positioning the
control valves to admit steam to the turbine to sustain a
preselected power load; (b) at least partially opening the bypass
overload valve; and (c) returning steam passing through the bypass
overload valve to the top heater.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a simplified schematic illustration of a steam
turbine generator power plant in which the turbine utilizes a
bypass overload valve in accordance with a known arrangement;
and
[0009] FIG. 2 is a supplied schematic illustration similar to FIG.
1, but modified to incorporate the subject matter of the exemplary
but non-limiting embodiment disclosed herein.
DETAILED DESCRIPTION OF THE INVENTION
[0010] In the electrical power generating plant of FIG. 1, a boiler
10 serves as the source of high pressure steam, providing the
motive fluid to drive a reheat steam turbine 12 which includes high
pressure (HP) section 14, intermediate pressure (IP) section 16,
and a low pressure (LP) section 18. Although the turbine sections
14, 16 and 18 are illustrated to be tandemly coupled to each other
and to generator 20 by shaft 22, other coupling arrangements may be
used. It will also be appreciated that the invention disclosed
further herein applies equally and well to non-reheat turbines
which do not have an IP section.
[0011] The steam flow path from boiler 10 is through steam conduit
24 from which steam may be taken to HP turbine 14 through one or
more admission control valves (plural valves are shown at 25-28).
Each control valve 25-28 is connected to discharge steam to the HP
section 14 either through circumferentially arranged nozzle arcs in
a partial admission configuration or to a single space ahead of the
first stage nozzles in a single admission configuration. Both of
these configurations are well known in the art. Further, the
control valves of a turbine with the partial admission arrangement
may be operated either simultaneously, in the full arc mode in
which case steam is admitted to the HP section 14 in an assembly
uniform circumferential pattern so that the turbine operates like a
single admission turbine, or they may be operated sequentially, in
the partial arc mode, in which case steam is admitted first to one
or more nozzle arcs and then to the others in sequence as the
turbine load is increased.
[0012] Steam exhausted from the HP section 14 passes through
reheater 30 wherein the temperature of the steam is increased.
Subsequently, steam from the reheater is passed to IP section 16
then, through crossover conduit 32, to LP section 18. Steam
exhausted from the LP section 18 flows to the condenser 34 which
changes the state of the fluid from a vapor, i.e., steam, to a
liquid, i.e., water. The water is then returned to the boiler where
it is changed back to steam and returned to the turbine through the
one or more control valves.
[0013] Although control of a steam turbine is a very complex and
complicated process, with the turbine operating at essentially
steady state the principal considerations are to maintain the
turbine's speed and load. With reference to FIG. 1, these variables
are controlled by feedback control system 38 which positions (i.e.,
determines the degree of opening of) control valves 25-28 to admit
more or less steam to the turbine 12. Such control systems are well
known and control system 38, for example, may be of the type
disclosed by U.S. Pat. No. 3,097,488.
[0014] Virtually every turbine is designed to provide reserve
capacity for producing power over the nominal rated capacity. For
gaining additional power from the turbine after the control valves
have reached their limit or fully open position, a bypass overload
valve 40 is connected between the steam supply conduit 24 and the
reheat point ahead of reheater 30. For control of the bypass
overload valve 40, a simple open-closed (manual or automatic)
control 42 is provided that actuates valve 40 to be opened whenever
the load demand is greater than the nominal rated capacity. For
manual operation of the overload valve 40, a simple switching
arrangement may be used and the valve 40 opened at the discretion
of operating personnel whenever the control valves 25-28 are fully
open.
[0015] For example, with the control valves 25-28 fully open and
the turbine 12 operating at its nominal rated capacity, additional
power is attained by subsequently opening the overload bypass valve
40. This allows a quantity of steam to bypass the higher pressure
sections of the turbine and enter the low temperature side of the
reheater 30. Alternatively, however, the bypassed steam through
overload 40 may be admitted to a lower pressure stage of the high
pressure section 14 as indicated by the dashed line 44. In either
case, there is an increase in total steam flow into the turbine,
which, if maintained, enables the turbine 12 to produce a greater
output.
[0016] With reference now to FIG. 2, where similar reference
numerals are utilized, but with a prefix 1 added, to indicate
corresponding components, the steam diverted from the boiler 110
toward the overload valve 140 is not redirected to a downstream
turbine stage as in the FIG. 1 arrangement, but rather, is
redirected via line 46 to the turbine top heater 48. Thus, steam
input to the top heater 48 from the HP section 114 (or steam
extracted from a location part way through the HP turbine
expansion), and the bypass steam entering the top heater via line
46 combine to heat the liquid condensate from the condenser 134.
The heated condensate returns to the boiler 110 where it is
converted back to steam and recycled to the turbine, while the
now-cooled steam from the HP section 114 and line 46 are simply
drained from the top heater. It will also be appreciated that the
overload valve may be opened and/or closed incrementally (as
opposed to simple on/off operation) by any suitable known control
arrangement, i.e., used in a throttling manner and thus be more
responsive to cycle conditions.
[0017] The exemplary but non-limiting arrangement solves problems
associated with the more conventional arrangements. For example,
this arrangement eliminates the need for another control stage
within the steam turbine which is normally very costly. Bypassing
the steam to the top heater directly also prevents the steam path
from being disrupted. The arrangement also eliminates problems
associated with temperature mis-match in the turbine structure
which causes thermal distortion at the point where the bypass flow
enters the steampath. Thermal distortions can result in larger
clearances between rotating and stationary components leading to
increased steam leakage and lower efficiency.
[0018] 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.
* * * * *