siemens sgt-700 gas turbine performance upgrade …

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


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.


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

38

-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.


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.


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.


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


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


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


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.


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


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.


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.


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


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


Permission for use

The content of this paper is copyrighted by Siemens and is licensed to PennWell for

publication and distribution only. Any inquiries regarding permission to use the content of

this paper, in whole or in part, for any purpose must be addressed to Siemens directly.

Disclaimer

These documents contain forward-looking statements and information – that is, statements

related to future, not past, events. These statements may be identified either orally or in

writing by words as “expects”, “anticipates”, “intends”, “plans”, “believes”, “seeks”,

“estimates”, “will” or words of similar meaning. Such statements are based on our current

expectations and certain assumptions, and are, therefore, subject to certain risks and

uncertainties. A variety of factors, many of which are beyond Siemens’ control, affect its

operations, performance, business strategy and results and could cause the actual results,

performance or achievements of Siemens worldwide to be materially different from any

future results, performance or achievements that may be expressed or implied by such

forward-looking statements. For us, particular uncertainties arise, among others, from changes

in general economic and business conditions, changes in currency exchange rates and interest

rates, introduction of competing products or technologies by other companies, lack of

acceptance of new products or services by customers targeted by Siemens worldwide, changes

in business strategy and various other factors. More detailed information about certain of

these factors is contained in Siemens’ filings with the SEC, which are available on the

Siemens website, www.siemens.com and on the SEC’s website, www.sec.gov. Should one or

more of these risks or uncertainties materialize, or should underlying assumptions prove

incorrect, actual results may vary materially from those described in the relevant forward-

looking statement as anticipated, believed, estimated, expected, intended, planned or

projected. Siemens does not intend or assume any obligation to update or revise these

forward-looking statements in light of developments which differ from those anticipated.

Trademarks mentioned in these documents are the property of Siemens AG, its affiliates or

their respective owners.

siemens sgt-700 gas turbine performance upgrade …

Documents