U.S. patent application number 14/905412 was filed with the patent office on 2016-05-26 for method for operating a combined cycle power plant.
This patent application is currently assigned to Siemens Aktiengesellschaft. The applicant listed for this patent is SIEMENS AKTIENGESELLSCHAFT. Invention is credited to Edwin Gobrecht, Matthias Heue.
Application Number | 20160146060 14/905412 |
Document ID | / |
Family ID | 48914057 |
Filed Date | 2016-05-26 |
United States Patent
Application |
20160146060 |
Kind Code |
A1 |
Gobrecht; Edwin ; et
al. |
May 26, 2016 |
METHOD FOR OPERATING A COMBINED CYCLE POWER PLANT
Abstract
A method for operating a combined cycle power plant, according
to which shortly before the planned start-up of a parked load, the
steam turbine is lowered to a very low output, the gas turbine is
then operated in parked load, and next the steam turbine is powered
up to a parked output. The GT operating power can be the rated
power of the gas turbine. The ST operating power can be the rated
power of the steam turbine.
Inventors: |
Gobrecht; Edwin; (Ratingen,
DE) ; Heue; Matthias; (Bochum, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SIEMENS AKTIENGESELLSCHAFT |
Munchen |
|
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
Munich
DE
|
Family ID: |
48914057 |
Appl. No.: |
14/905412 |
Filed: |
July 3, 2014 |
PCT Filed: |
July 3, 2014 |
PCT NO: |
PCT/EP2014/064182 |
371 Date: |
January 15, 2016 |
Current U.S.
Class: |
60/774 |
Current CPC
Class: |
F01K 23/101 20130101;
F22B 1/1815 20130101; F01K 7/24 20130101; Y02E 20/16 20130101; F01K
13/02 20130101 |
International
Class: |
F01K 23/10 20060101
F01K023/10; F01K 13/02 20060101 F01K013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 2013 |
EP |
13177932.4 |
Claims
1. A method for operating a combined cycle power plant, comprising:
operating the gas turbine at a GT operating power and operating the
steam turbine at an ST operating power, reducing the power of the
steam turbine to an ST part power, wherein the ST part power is
lower than the ST operating power, reducing the power of the gas
turbine to a GT parked power, wherein the GT parked power is lower
than the GT operating power, wherein once the GT parked power of
the gas turbine has been reached, increasing the power of the steam
turbine to an ST parked power.
2. The method as claimed in claim 1, wherein the ST part power is
5%-40%, 5%-30%, 5%-20%, or 5%-10% of the ST operating power.
3. The method as claimed in claim 1, wherein the GT parked power is
20%-60% of the GT operating power.
4. The method as claimed in claim 1, wherein the ST parked power is
20%-60% of the ST operating power.
5. The method as claimed in claim 1, wherein the power of the steam
turbine is reduced by reducing the pressure of the steam.
6. The method as claimed in claim 1, wherein the steam turbine
comprises a HP, IP and LP turbine section and wherein the HP
turbine section, the HP turbine section and the IP turbine section,
the IP turbine section, the IP turbine section and the LP turbine
section or the LP turbine section is/are not charged with
steam.
7. The method as claimed in claim 6, wherein the pressure of the
steam in the turbine sections not charged with steam is reduced to
below a limit value.
8. The method as claimed in claim 1, wherein the drain, evacuation
lines, start-up lines or process steam lines are opened.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2014/064182 filed Jul. 3, 2014, and claims
the benefit thereof. The International Application claims the
benefit of European Application No. EP13177932 filed Jul. 25, 2013.
All of the applications are incorporated by reference herein in
their entirety.
FIELD OF INVENTION
[0002] The invention relates to a method for operating a combined
cycle power plant, wherein the gas turbine is operated at a GT
operating power and the steam turbine is operated at an ST
operating power, wherein the power of the steam turbine is reduced
to an ST part power, wherein the ST part power is lower than the ST
operating power.
BACKGROUND OF INVENTION
[0003] Combined cycle power plants are used to generate electrical
energy for communal energy supply. In general, a combined cycle
power plant supplies electrical energy to a supply grid, the energy
requirement being dependent on the time profile. This means that
the energy requirement is not constant over the course of a day.
The electrical supply grid is supplied with electrical energy by
multiple power plants. Thus, use is made for example of
conventional power plants and power plants which convert renewable
energies into electrical energy. Feeding-in of the renewable
energies is subject to fluctuations, which leads to increasing
demands on the conventional power plants. This means that
conventional power plants must be operated longer and lower in what
are termed part loads or parked loads. In combined cycle power
plants, such low part loads are associated--depending on the
configuration of the gas turbine--with reduced gas turbine outlet
temperatures.
[0004] As a result, the steam turbine inlet temperature also drops.
Thus, as soon as the plant is operated in part load, the steam
inlet temperature is reduced. However, this means that the hot
components of the steam turbine are exposed to cold steam, which
leads to thermal stresses.
[0005] If the parked load is then abandoned again, the steam
temperatures rise again, which once again leads to thermal
stresses. In order to prevent these thermal stresses, it is
possible not to run the gas turbine so far in part load in order
that the steam temperature does not drop so much. It is also
possible to slowly reduce the steam temperature by spraying prior
to the actual load reduction. Then, the load change takes place at
a lower--but therefore more constant--temperature. After increasing
the load, the steam temperature is once again raised slowly to the
rated temperature.
[0006] Another possibility for preventing thermal stresses consists
in running the steam turbine down prior to reducing the gas turbine
power. Then, the components of the steam turbine will cool down
with very low thermal stresses. Once the components have cooled
sufficiently, the steam turbine could be started up again at a
reduced gas turbine power and thus at a low steam inlet
temperature. This would lead to very low service life
consumption.
SUMMARY OF INVENTION
[0007] The invention is based on an object of indicating another
possibility for reducing thermal stresses.
[0008] This object is achieved by a method for operating a combined
cycle power plant, wherein the gas turbine is operated at a GT
operating power and the steam turbine is operated at an ST
operating power, wherein the power of the steam turbine is reduced
to an ST part power, wherein the ST part power is lower than the ST
operating power, wherein the power of the gas turbine is then
reduced to a GT parked power, wherein the GT parked power is lower
than the GT operating power.
[0009] Once the GT parked power of the gas turbine has been
reached, the power of the steam turbine is increased to an ST
parked power, wherein the ST parked power is 20% to 60% of the ST
operating power.
[0010] The invention thus proposes indicating an operating method
wherein the steam turbine is involved in the parked load. Thus, for
the purposes of grid stability, the steam turbine rotor keeps as
much rotating mass as possible on the grid.
[0011] The ST power of the steam turbine is reduced to a very low
power shortly before the planned commencement of the parked load.
The gas turbine is then operated in parked load. On account of the
markedly lower heat transfers between steam and steam turbine
components in part load, service life consumption is significantly
lower as a consequence of lowering the steam temperature. In that
context, the steam turbine cools down slowly.
[0012] Advantageous developments are specified in the dependent
claims. Thus, in a first advantageous development, the ST part
power is set at 5% to 40%, 5% to 30%, 5% to 20%, or 5% to 10% of
the ST operating power.
[0013] In another advantageous refinement, the GT parked power is
20% to 60% of the gas turbine operating power.
[0014] It is thus proposed to once again take up load after the
steam turbine has cooled down slowly at a reduced gas turbine power
and thus a low steam inlet temperature.
[0015] In one alternative embodiment, the steam turbine could be
held in this low part load until the end of the parked load.
[0016] The invention thus proposes reducing the power of the steam
turbine to an ST part power. The ST part power is lower than the ST
operating power. Reducing to the ST part power is effected by
closing a steam inlet valve. In that context, the steam inlet valve
is controlled such that almost no fresh steam flows through the
steam turbine. In that context, a bypass station is formed such
that there results a fluidic connection between the steam inlet and
the condenser. Thus, downstream of the steam generator, steam is
not fed to the steam turbine but directly to the condenser, which
has a disadvantageous effect on the efficiency. The steam turbine
then cools down. After this, the power of the gas turbine is
reduced to a GT parked power. This affects the steam inlet
temperature. That means that the steam inlet temperature drops.
After a certain time, the steam inlet valve is then once again
opened and the fluidic connection between the steam inlet and the
condenser is interrupted. Thus, all of the steam generated in the
steam generator is then fed through the steam turbine.
[0017] In one advantageous development, the steam turbine comprises
a high-pressure, intermediate-pressure and low-pressure turbine
section, wherein--the high-pressure turbine section,--the
high-pressure turbine section and the intermediate-pressure turbine
section,--the intermediate-pressure turbine section,--the
intermediate-pressure turbine section and the low-pressure turbine
section or--the low-pressure turbine section is/are not charged
with steam.
[0018] Thus, ideally, one pressure stage is completely closed. In
the switched-off turbine section, the service life consumption is
even lower since here the components cool down naturally.
Advantageously, the pressure in the steam turbine or in the
remaining operational turbine sections is reduced as much as
possible, which is made possible by drains, evacuation lines,
start-up lines or also process steam lines.
[0019] Thus, the significant reduction in the pressure in the steam
turbine reduces the heat transfer and significantly reduces the
service life consumption during part load.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The invention will now be explained in more detail with
reference to an exemplary embodiment. In the drawing:
[0021] FIG. 1 shows a schematic representation of a combined cycle
power plant.
DETAILED DESCRIPTION OF INVENTION
[0022] FIG. 1 shows a schematic representation of a combined cycle
power plant. In essence, a combined cycle power plant 1 comprises a
gas turbine 2 that can be operated with fossil fuels. This gas
turbine 2 comprises a compressor part 3 in which air is heated and
compressed, a combustion chamber 4 in which the air from the
compressor part 3 is mixed with fuel and ignited, and a turbine
part 5 in which--in various stages consisting of guide vanes and
rotor blades that are not shown--the hot exhaust gases turn a
rotor. A shaft 6 transfers this rotation to a generator 7. The
generator 7 then supplies a supply grid with electrical energy (not
shown).
[0023] The hot exhaust gases from the gas turbine 2 are fed into a
steam generator 8. In this steam generator 8, fresh steam is
generated by means of a line 9 and is then fed via a steam turbine
fresh steam line 10 into a high-pressure turbine section 11. An HP
valve 12 is arranged in the steam turbine fresh steam line 10. The
steam leaving the HP turbine section 11 is conveyed to an
intermediate superheater 13. This takes place via the cold
intermediate superheater line 14. Once the steam has been heated in
the intermediate superheater 13, the hot intermediate superheater
line 15 supplies steam to an intermediate-pressure turbine section
16. From the intermediate-pressure turbine section 16, the steam
flows via an overflow line 17 into two low-pressure turbine
sections 18. After the low-pressure turbine section 18, the cold,
expanded steam flows into a condenser 19 where it condenses to
water which is conveyed, via a pump 20, back into the fresh steam
generator 8 via the fresh steam line 9.
[0024] The steam turbine fresh steam line 10 is fluidically
directly connected to the condenser 19 via a redirection station
21. An overflow valve 22 is arranged in the overflow line 21. An
electric generator 23 is connected, in a torque-transmitting manner
via a common shaft 24, to the high-pressure turbine section 11, the
intermediate-pressure turbine section 16 and the low-pressure
turbine section 18. The HP turbine section 11, the IP turbine
section 16 and the LP turbine sections 18 form the steam turbine
25.
[0025] In one alternative embodiment, the combined cycle power
plant comprises a redirection system. This redirection system
comprises a high-pressure redirection station 22 and a
high-pressure redirection valve 21 arranged in the high-pressure
redirection station 22, wherein the high-pressure redirection
station 22 establishes a fluidic connection between the steam
turbine fresh steam line 10 and the cold intermediate superheater
line 14. Furthermore, the redirection system comprises an
intermediate-pressure redirection station 22a and an
intermediate-pressure redirection valve 21a arranged in the
intermediate-pressure redirection station 22a, wherein the
intermediate-pressure redirection station 22a establishes a fluidic
connection between the hot intermediate superheater line 15 and the
condenser 19.
[0026] Thus, steam can flow from the steam turbine fresh steam line
10 to the condenser 19, via the redirection system comprising the
high-pressure redirection station 22 and the intermediate-pressure
redirection station 22a.
[0027] Furthermore, the combined cycle power plant comprises an
intermediate-pressure valve 12a arranged in the hot intermediate
superheater line 15.
[0028] Now, according to the invention, the combined cycle power
plant is operated as follows. First, the gas turbine 2 is operated
at a gas turbine operating power. Equally, the steam turbine 25 is
operated at an ST operating power. The power of the steam turbine
25 is reduced to an ST part power, wherein the ST part power is
lower than the ST operating power. Then, in this context, the ST
part power is 5% to 40%, 5% to 30%, 5% to 20%, or 5% to 10% of the
ST operating power.
[0029] This is achieved by nearly closing the HP valve 12 and the
intermediate-pressure valve 12a, such that almost no steam flows
through the steam turbine 25. Thus, the components in the steam
turbine 25 cool down. After a certain time, the power of the gas
turbine 2 is then reduced to a GT parked power, wherein the GT
parked power is lower than the GT operating power. In this case,
the GT parked power is 20% to 60% of the gas turbine operating
power. As a result, the temperature of the hot exhaust gas from the
gas turbine 2 is lower, leading to a reduction in the temperature
of the fresh steam which is generated in the steam generator 8 and
passes through the steam turbine fresh steam line 10 and the hot
intermediate superheater line 15.
[0030] Once the HP valve 12 is almost closed, the overflow valve 22
or the redirection system 22, 21; 22a, 21a is opened such that the
majority of the steam generated in the steam generator 8 is fed
directly into the condenser 19. However, this is disadvantageous
for the overall efficiency of the combined cycle power plant.
[0031] Once the GT parked power of the gas turbine 2 has been
reached, the power of the steam turbine 25 is increased to an ST
parked power. This ST parked power is 20% to 60% of the ST
operating power. This is achieved by opening the HP valve 12 and
the intermediate-pressure valve 12a. The overflow valve 22 in the
overflow line 21 is closed again. Thus, the steam--now conveyed in
the steam turbine fresh steam line 10 and in the hot intermediate
superheater line 15 as a consequence of the reduced steam inlet
temperature of the steam--can be fed into the HP turbine section
11. As a consequence of the lower fresh steam temperature, the
volumetric flow of fresh steam is also lower.
[0032] The power of the steam turbine 25 is reduced by reducing the
pressure of the steam. It is now possible, once the ST part power
and the GT parked power have been reached, to operate the steam
turbine 25 as follows. The steam turbine 25 comprises a
high-pressure turbine section 11, an intermediate-pressure turbine
section 16 and a low-pressure turbine section 18, wherein the
high-pressure turbine section 11, the high-pressure turbine section
11 and the intermediate-pressure turbine section 16, the
intermediate-pressure turbine section 16, the intermediate-pressure
turbine section 16 and the low-pressure turbine section 18 or the
low-pressure turbine section 18 is/are not charged with steam. The
remaining turbine sections remain closed and can cool down
naturally.
[0033] The pressure of the steam in the turbine sections not
charged with steam is then reduced as far as possible. To that end,
drains, evacuation lines, start-up lines or process steam lines are
opened.
* * * * *