siemens sgt-700 gas turbine performance upgrade …
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Copyright © Siemens AG 2009. All rights reserved. 1
SIEMENS SGT-700 GAS TURBINE PERFORMANCE UPGRADE YIELDS
MORE POWER AND HIGHER EFFICIENCY
Anders Hellberg Georg Nordén
Siemens Industrial Turbomachinery AB
Finspong, Sweden
Copyright © Siemens AG 2009. All rights reserved.
POWER-GEN Europe 2009 – Cologne, Germany May 26-29, 2009
Copyright © Siemens AG 2009. All rights reserved. 2
Summary
It is ten years since the Siemens SGT-700 was launched on the market in 1999 and several
units are now in commercial operation. The turbine is installed in various applications such
as mechanical drive, power generation, onshore and offshore. SGT-700 is derived from the
25 MW SGT-600 and utilizes technology from the 47 MW SGT-800.
The SGT-700 was initially designed for over 31 MW but was introduced at 29 MW. With five
units each having achieved more than 24,000 hours of operational experience, and after a
period of extensive testing, the time has come to release the improvements. The SGT-700,
together with the new rating, extended maintenance plan and fuel flexibility, will better fulfil
the market requirements. The new rating should not be considered as a new product, but the
incorporation of some minor improvements into the basic design. It is also possible to
upgrade existing units.
Copyright © Siemens AG 2009. All rights reserved. 3
Improved performance
The SGT-700 gas turbine was originally designed for 31 MW but it was introduced at 29 MW
electric power and 36% efficiency. For the initial rating there has been an extensive program
feeding back fleet data and maintenance activities. The result from these, together with
component improvements, has led to the new rating of 31.2 MW, i.e. a power increase of over
7%, and 36.4% efficiency (9882 kJ/kWh), see figure 1. The increase in exhaust gas
temperature by 10 deg C to 528 deg C will benefit the combined-cycle with an improvement
to 44.4 MW and 52.3% efficiency.
20
22
24
26
28
30
32
34
36
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-40 -30 -20 -10 -5 0 5 10 15 20 25 30 35 40
Compressor inlet temperature, °C
Gen
erat
or o
utpu
t, M
W
9,6
9,8
10
10,2
10,4
10,6
10,8
Hea
t rat
e, M
J/kW
h
PowerHeat rate
Figure 1. Compressor inlet temperature vs generator output and heat rate
The SGT-700 is equipped with Dry Low Emissions (DLE) technology as standard, so all
SGT-700’s are DLE. The DLE system offers dry emission control on both liquid and gaseous
fuel, with dual-fuel capability, and fuel can be changed in both directions during operation.
The 3rd generation DLE burner, also used in the SGT-800 gas turbine, can limit NOx to
15ppmV dry (at 15% O2) when operating on gaseous fuel. CO emission is limited to 25ppmV
(at 15% O2) for both gas and liquid fuel. These values apply to 70-100% load.
Copyright © Siemens AG 2009. All rights reserved. 4
On liquid fuel the SGT-700 can operate in a DLE mode without any water injection at
42ppmV dry (15% O2), see table 1.
Introductory Mature Power generation: 29.06 31.21 MWe
Frequency: 50/60 Hz
Electrical efficiency: 36.0 36.4 %
Heat rate: 9999 9882 kJ/kW-hr
Heat rate: 9477 9367 btu/kW-hr
Turbine speed: 6500 rpm
Compressor pressure ratio: 17,6:1 18:01
Exhaust gas flow: 92 94 kg/s
Exhaust gas flow: 203 208 lbs/s
Temperature: 518 528 °C
Temperature: 964 983 °F
NOx emissions (gas fuel): 15 ppmV (15% O2)
NOx emissions(liquid fuel): 42 ppmV (15% O2)
Power CC 41 44.35 MWe
Efficiency CC 51.5 52.3 %
Table 1, SGT-700 data
Five units have been validated (until Dec 2008) thru mechanical running test (emissions,
vibration, performance) and all are in line with expected performance.
Basic Design
The SGT-700 is a twin-shaft machine, see figure 2, with two main modules, the gas generator
and the power turbine, each of which can be exchanged. The SGT-700 is derived from the
proven 25 MW SGT-600.
The compressor has 11 stages. The first two stages have variable inlet guide vanes and the
compressor has two bleed valves. The rotor is composed of disks which are electron-beam-
welded to a single robust unit which requires a minimum of maintenance.
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The combustor is of the annular type and is made of welded sheet metal. Its inner surface has
a thermal barrier coating (TBC), which reduces the level of heat transfer and extends the
lifetime of the unit. The 18 burners are easily removable from the outside for fast assembly
and maintenance.
Figure 2. SGT-700 cross section
The first stage of the compressor-turbine inlet guide-vanes has convection cooling with film-
cooled edges. Shrouded blades and honeycomb seals are introduced in the second stage. The
two-stage uncooled free power turbine has the disks bolted to the shaft for ease of
maintenance. The inlet guide vane to the power turbine can be set to different angles to
optimize the performance for different ambient conditions.
A double helical gearbox is connected to the power turbine via a flexible coupling. The
gearbox reduces the turbine speed from 6500rpm to 1500rpm/1800rpm (50 or 60 Hz). The
gearbox is then connected to the AC-generator.
The SGT-700 has the same package as the SGT-600. The package is designed to meet
customer requirements and there are different options to suit different markets. The turbine is
skid-mounted, with the auxiliaries placed in the auxiliary room in front of the gas turbine. All
systems are assembled at the Siemens workshop and pre-tested in order to reduce time at site.
The gas-turbine driver layout is basically the same for mechanical drive and power generation
and meets the market requirements for compactness, short erection and commissioning times
and ease of maintenance.
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Figure 3. SGT-700 package
The gas-turbine-driver skid is built from steel beams and carries the gas turbine, auxiliary
systems and starter motor. The gas turbine skid is bolted to the gear and alternator skid or kept
as a single driver package for mechanical drive applications
Fleet experience
The SGT-600/700 fleet has to date accumulated more than 5 million operating hours, with the
fleet leader for the SGT-600 achieving more than 120,000 hours. SGT-700 has been in
operation since 2003 and the SGT-700 fleet leader has achieved more than 30,000 operating
hours. During the operation a number of scheduled inspections have been carried out. The
turbines have shown high reliability during their very successful operation.
Electrical & control module
AC generator
Speed reduction gear
Lubricating oil cooler
Ventilation air outlet
Exhaust air silencer
Air intake filter
Ventilation air inlet
Auxiliary room
Gas turbine enclosure
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Figure 4. SGT-700 combined-cycle in Miskolc, Hungary
To date 33 SGT-700’s have been sold. They are located in different environments and are
used in different applications, such as single cycle, cogeneration and combined cycle, both
onshore and offshore, see figure 4. The experience from all these different sites has revealed
no generic or design faults. A number of level B inspections (20,000 hours) have been
performed with no unexpected results. The hot section has been in good condition and parts
have been reconditioned according to the
maintenance plan.
Of all SGT-700 sold, five have the mature
rating, see figure 5. They target different
applications such as base load and frequent start.
All of the gas turbines are supplied with a
condition-monitoring system, which
significantly improves the quality of the
feedback from the fleet. Two engines with
mature rating are now in operation and the rest
will come into operation early this year. The first
units will be closely followed by condition
monitoring and extra scheduled inspections.
Figure 5. SGT-700 mature rating installation at site
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Key features towards increased power output and efficiency
The operating experience of the past years has been essential for the next step towards
increased power and efficiency. More than 150,000 hrs and several B-level inspections have
formed the basis for improving the design. In coordination with customers of the SGT-700
fleet-leaders, extended inspections have been performed.
Validation of the first rating at 29 MW included the extensive crystal test using 700
measuring points on turbine blading in order to find base-load temperatures, ref 2, and ref 3.
Evaluation shows areas with improvement and fine tuning of secondary air system (SAS).
The new rating is one step towards a more optimized design to redistribute air and still
maintain maximum allowed temperatures. Component lifetime has been reworked to fit
an extended maintenance program to lower life cycle cost (LCC).
The scope of the new 31 MW SGT-700 is limited to the stationary components in the
compressor turbine and its cooling scheme, see figure 6. Risk has been kept lower by
maintaining initial design for following parts, compressor turbine (rotating blades), PT
blading (vane/blade), core casings/stator, fuel injector, combustion chamber and shaft
bearings.
Previous tests and experience has strengthened the strategy to take a minor step with a limited
number of new risks.
Figure 6 Improvements for mature rating
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The DLE combustion system has been updated with a more even burner airflow (See figure 7)
in order to improve the overall temperature distribution factor (OTDF) to lower highest
temperature. An even temperature distribution is essential for stator lifetime, extended
maintenance program and improved durability to operate on low NOx.
Figure 7. 3rd generation DLE fuel injector Thermal barrier coating (TBC) on stationary vanes and lower OTDF are the two new key
features and a part of the proven technology from other Siemens gas turbines. Risk level
according to strategy is kept low by maintaining blade #1, blade #2 (CT) and all material
selections unchanged in flow path. Airfoil geometry also maintains unchanged flow path.
Increased power is created by less cooling flow due to lower OTDF and TBC on compressor
turbine vane #1 and #2. Turbine vane #1 (platforms) and vane 2 (platform/airfoil) have a
design philosophy for a slow damage sequence. Critical areas such as the leading edge of the
airfoil can maintain full inspection intervals despite deterioration of TBC. Durability is
essential for the extended maintenance program during the 30,000 hours.
Part-load operation extends intervals since equivalent operating hours (EOH) is set down to
0.65 EOH per operating hour (OH). It is an essential benefit for the customers, mainly
operating on part load, to increase availability and lower service cost. New components can
be retrofitted on all SGT-700 if these features (more power and an extended maintenance
program) are attractive.
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Maintenance program
In order to increase availability and lower LCC an extended maintenance program coincides
with the launch of increased power output. Engine swap in 24 hours is also available to
increase availability further. The extended maintenance program ends at 120kEOH but is not
the full lifetime for the product.
We have focused on reducing major overhauls from five to three. Power-turbine blading is
extracted from the replacements scheme due to lower turbine (PT) inlet temperature. No PT
blading will be replaced during the first 120kEOH, see figure 8. Experience has been essential
for this preventive maintenance. A trial with an extended time of 27,000 hours to level B
inspection has given a very good result (normally level B is at 20 000 hours).
Le
Level A - Borescope inspection
Level B – Hot-section overhaul
Level C - Level B and non-destructive testing (NDT)
Figure 8. Maintenance program
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Validation
The first unit was fully instrumented late 2007 and went into the new test facility as first unit.
Commissioning took place in winter/spring 2008, validation was performed and finalized in
June 2008. The unit was provided with 150 measuring points, metal/air temperature and
pressure gauges. These were additional points outside the normal performance test made for
new units. A number of different power turbine inlet guide vane setting, matchings, have been
validated in order to validate different ambient conditions.
Online measurements and an extensive evaluation afterwards show confidence in life
prediction and the quality of the new product.
Agreements are in place with the first customers for a closer interval inspection to ensure the
quality during the first years of operation. The 29 MW rating is also of interest since there
will be a C-level inspection (40 kEOH) during 2009. A program is in place to ensure field
feedback during the coming years from all types of customers (turbines with base and
frequent start units) and different ratings.
Gas Turbine Test Facility
A new test facility has been built to handle higher delivery capacity, see figure 9. Ability to
run SGT-600 or SGT-700 is set up with a flexible system. Preparation can be made outside
the test cell to maintain the highest capacity. The target turnaround time for a mechanical
running test is 3 days. The rig is equipped with auxiliary systems for both gas and oil
operation which are derived from a standard installation.
The test facility is set up with full capacity for normal operation and full-load mechanical
running tests can be done according to API. Normal transient conditions such as start
sequence, stop or trip can be performed for a quality assurance of all products.
Copyright © Siemens AG 2009. All rights reserved. 12
Figure 9. Siemens test rig for mechanical running Fuel flexibility
There is a growing market for gas turbines which can handle gases with high content of inert
gases such as nitrogen and carbon dioxide. To meet this market, tests have been made with
the standard DLE-combustion system. Different types of tests have been carried out such as
single-burner and engine tests with nitrogen-rich fuel mixtures. Tests have been very positive,
confirming a wide fuel-range possibility for the burner which is common to both SGT-700
and the 47 MW SGT-800.
A full engine test has been performed at the Siemens test facility in Finspong, Sweden. The
SGT-700 DLE has been tested with up to 40 vol-% nitrogen in natural gas. A mobile nitrogen
supply unit was connected to the LNG system, see figure 10, and a buffer tank was used for
mixing.
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Figure 10. Nitrogen test
A standard SGT-700 with a standard gas-fuel system was used, with no changes made. The
DLE system has only three (pilot, main, central) gaseous fuel control valves. As these can be
set from the operator station in the control room, the test could easily be handled as a normal
SGT-700 mechanical running test. Different loads over the whole load range were tested and
the nitrogen content increased from zero up to 40%. The stability of the gas-turbine operation
was very good, in fact, the same as for natural gas fuel. This was proven at low load, medium
and full load, with no limiting indications noted. The engine can be easily started with high
nitrogen content as long as the starting fuel composition is known.
The test was not done specifically to achieve low emissions, but it was noted that emissions
levels were in the range of normal guarantees. Since combustion is very stable, emissions are
also very stable.
As a test, the nitrogen to the buffer tank was shut off and the buffer volume was enough for 1
minute operation. A rapid change of nitrogen content was tested successfully at different
loads, both shutting off the nitrogen and turning the nitrogen on shows operability in transient
conditions.
LNG tank
Nitrogen tank
Mobile nitrogen unit
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Conclusion
Ten years have passed since the market introduction of SGT-700 (at that time GT10C) and
SGT-700 now has five years of operation experience. It is now time to release the mature
rating of 31.2 MW. The new rating, extended maintenance plan and fuel flexibility, will better
fulfil the market requirements. The new rating should not be considered as a new product, but
the incorporation of some minor improvements into the basic design.
References
1. Hellberg A., Results and experience from operation and testing of the 30 MW GT10C
gas turbine, ASME 2003 38676
2. Hellberg A., Experience of the 29 MW SGT-700 gas turbine in power generation
applications, Power Gen International 2006
3. Norden G., Report on the first operational experience of the newly commercialized
29 MW SGT-700 (GT10C) gas turbine, PowerGen Middle East Abu Dhabi, 2006
Copyright © Siemens AG 2009. All rights reserved. 15
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