Power Generation :: Combined Cycle
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| King’s Lynn Power Plant using Siemens V94.3 GT and SSS Clutch |
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| Taranaki Power Plant using Alstom GT26 GT and SSS Clutch |
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| Single Shaft CCGT Arrangement using an SSS Clutch |
Overview
Combined Cycle Gas Turbine (CCGT) Power Plant suppliers configure turbine generators in a number of different arrangements.
Single shaft arrangements where a gas turbine and a steam turbine drive a single generator are often preferred because they offer a more compact plant at a lower cost.
Many include an SSS Clutch to disconnect the steam turbine and to allow the gas turbine/generator to be operated separately.
Also on this page...
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| The start up sequence of a CCGT Plant with SSS Clutch. |
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| The shutdown sequence of a CCGT Plant with SSS Clutch. |
The advantages of this arrangement include...
A - Simplified startup
• Standard GT Start
• Reduced time to generation
• No cooling steam required
• Reduced starting power
• Reduced emissions
• Standardised design
• Simplified torsional analysis
B - Increased flexibility
• Simplified commissioning
• Steam turbine trips do not stop power generation
• Maintenance of GT is possible during ST cooling
C - Optimised shutdown
• Shutdown ST at reduced GT power
For more information refer to the following articles reprinted from various
magazines...
 86kb |
SSS
Clutch: Key to combined cycle flexibility NR9905_2.pdf Overview of the use of SSS Clutches in CCGT Plant from various manufacturers. |
129kb |
Blackstone: flexible
and environmentally friendly power plant NR0207_1.pdf How an Alstom KA26 CCGT plant uses SSS Clutches to achieve flexibility and to reduce emissions. |
152kb |
Siemens on fast
track to commission Santa Rita NR0003_2.pdf How an SSS Clutch in Siemens V84.3A CCGT plant speeds complete plant commissioning. |
163kb |
One year on:
Enfield is the definitive GT26B NR0111_5.pdf An SSS Clutch in Alstom KA26 CCGT plant simplifies regular GT inspections. |
 PDF files require the Adobe Acrobat Reader. Download your free copy by clicking here. |
A - Simplified startup
The start up sequence of a CCGT Plant with SSS Clutch.
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• Standard GT Start
The SSS Clutch allows the GT to be run up independent from the ST.
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• Reduced time to generation
The time from start initiation to synchronising the generator to the grid
is reduced and can be accurately predicted as it is independent of steam
turbine temperature.
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• No cooling steam required
During the GT startup sequence no steam is available from the HRSG and
so unless the steam turbine is uncoupled a steam supply is needed to cool
the steam turbine blades and provide sealing during the run up.
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• Reduced starting power
The power required to start the machine is reduced as only the gas turbine
and generator are rotated by the gas turbine starting system.
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• Reduced emissions
The reduced starting time of the gas turbine results in reduced emissions
during the start sequence when emissions may be higher than at efficient
high loads.
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• Standardised design
As the steam turbine is mounted with its own axial bearing there are less
constraints on the turbine and a more standard design can be utilised.
Where differing steam cycles are offered various steam turbine designs
can be accommodated more readily.
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• Simplified torsional analysis
The steam turbine is disconnected during gas turbine acceleration therefore
the condition when the gas turbine is driving the steam turbine does not
have to be considered.
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B - Increased flexibility
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• Simplified commissioning
Assuming that the plant has a 100% steam bypass facility the GT can be
commissioned as a simple cycle machine without rotating the steam turbine.
Gas turbine performance can be proven and quantified before commissioning
of the steam turbine is begun.
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• Steam turbine trips do
not stop power generation
Because the steam turbine can be shutdown independently from the GT any
tripping of the steam turbine system does not necessarily entail a GT
trip. Clearly GT trips are a particular concern because of the total loss
of power generation capability and their effect on maintenance schedules.
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• Maintenance of GT during
ST cooling
An important option that can be provided when using an SSS Clutch is to
allow the gas turbine to be stopped whilst the steam turbine continues
to be rotated by its own turning gear. This feature can be important as
generally the time that the steam turbine must remain on turning gear
after shutdown is significantly longer than the time required by the gas
turbine. Outage times could be reduced by starting gas turbine maintenance
whilst still turning the steam turbine.
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C - Optimised shutdown
The shutdown sequence of a CCGT Plant with SSS Clutch.
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• Shutdown ST at reduced
GT power
During a normal shutdown of the machine the steam turbine can be shutdown
before the gas turbine. This is generally arranged whilst there is some
load remaining on the gas turbine to prevent the reduced gas turbine exhaust
temperatures causing the steam turbine temperatures to drop and therefore
delaying any subsequent starts.
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