Learning from experience

Industry, especially in the Middle East, places much importance on reliability and mature design. MEE looks at early operating experience with Siemens Power Generation’s newly commercialized SGT-700 industrial gas turbine at a site in Egypt.

Siemens’ 30 MW SGT-700 gas turbine (launched as the GT10C) is now a fully commercial product and living up to the expectations of the market. Globally, seven delivered units are now in commercial operation, in applications as diverse as mechanical drive, power generation, offshore and onshore. A further eighth unit has recently been ordered and is due to come on line in December 2007. Two more units have been produced as spares, one being kept at the manufacturing site in Finspong, Sweden, and the other placed in Egypt.

The first two SGT-700 turbines to be delivered and to be put into commercial operation were for the UGDC Port Said Nile Gas project. The turbines operate on both single and dual fuel.


Figure 1. Development of ST-700 from SGT-600
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These two fleet leaders in Port Said have been running at over 98 per cent reliability during their initial period of operation and have provided excellent operating experience for units to follow.

Design features

The robust design of the SGT-600, which has accumulated over three million hours of operation, was utilized to maintain high availability and reliability and has been an excellent platform for the SGT-700 introduction. The concept of the SGT-700 is based on the 25 MW two-shaft SGT-600 but with third-generation DLE (Dry Low Emissions) combustion technology taken from the more recent 45 MW SGT-800.

Comparison with SGT-600:

ࢀ¢ SGT-700 airflow has been increased from 80 to 91 kg/s by extending the compressor blading profile and introducing an additional compressor stage.


Figure 2. The first SGT-700 string test was performed in the presence of the customer
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ࢀ¢ The third generation combustion system was taken from the 45 MW SGT-800 and demonstrates 15ppm NOx on gaseous fuel and 42 ppm NOx on liquid fuel without introduction of water or steam.

ࢀ¢ The turbine inlet temperature (TIT) has increased by a moderate 27à‚°C (from 1115à‚°C to 1142à‚°C, mixture temperature according to ISO). The compressor turbine has a modified cooling design in order to handle the increased TIT.

ࢀ¢ The pressure ratio has been increased from 14 to 18.

ࢀ¢ The power turbine has been designed for a lower speed (from 7700 r/min to 6500) in order to increase the efficiency. Since speed was reduced and output increased, the turbine now has a larger diameter.

ࢀ¢ The efficiency has increased from 34 to 37 per cent.

Market introduction

In late 2001 verification tests were initiated and the turbine underwent a number of different development stages in the Finspong test facility. Complete disassembly and visual inspection of each component were standard procedure during this first year to validate the design. During these comprehensive tests, 1200 additional measuring points were installed, and the control system was additionally equipped with data acquisition systems.


Figure 3. Port Said plant, Egypt
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In April 2003 the turbine was launched commercially for partial release. The three orders taken that year for the first five units were the basis for the evaluation and introduction programme which has been applied in 2004 and 2005.

Focus has changed during the past year from intensive quality assurance of the internal engineering to external focus on the customer and his applications, concentrating mainly on raising availability and reliability. The introduction programme includes a maximized extended inspection schedule to secure stable and reliable operation, main activities being:

ࢀ¢ Inspections of fleet leader every 2500 operating hours.

ࢀ¢ Continuous updating of back-up plans such as preventive, operational and emergency spares

ࢀ¢ Resident engineering support on site and continuous feedback

ࢀ¢ Review of feedback from sites and identification of potential improvements for other sites

ࢀ¢ Failure mode and effect analysis to judge new and potential findings

ࢀ¢ Condition monitoring with on-line evaluation direct from site.

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Two inspections at 2500 hours were performed on Port Said unit 2 (Egypt, mechanical drive) and Sochi unit 2 (Russia, power generation). Two findings were reported, one transpiring to be an artefact on the blade surface and the other related to an abnormal amount of debris inside the engine. Neither finding was related to normal operation. Inspection was also performed on the fleet leader, Port Said unit 1, after approximately 4500 equivalent operation hours (EOH): results were entirely satisfactory.

An extended disassembly and inspection is also planned to be carried out after 10 000 EOH for the fleet leader, which will be in early 2006.

Port Said Nile Gas project

The first two SGT-700 turbines to be delivered and to be put into commercial operation were for the UGDC Port Said Nile Gas project. Two identical trains were ordered in November 2002 for delivery to a natural gas liquids (NGL) plant in Port Said, Egypt, owned by UGDC (United Gas Derivatives Company), a special-purpose company owned in equal parts by the oil & gas majors AGIP, BP Egypt and Gasco.


Figure 4. SGT-700 in enclosure
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The Port Said Nile Gas project, for two residue gas compressor sets, is an explicit example of the evolution in compressor drive with gas turbines. It is one of many where the end user has to pay for the gas feed stock, i.e. he pays directly for the gas burnt in the turbine, therefore efficiency is extremely important. With its high speed power turbine, the SGT-700 requires no step-up gearbox. The turbine is designed to match the overall fuel consumption of the aero-derivatives, offering high peak efficiency, very good off-design efficiency and low degradation.

Each compressor set features a SGT-700 gas turbine and a STC-SV centrifugal compressor, both supplied by Siemens. The compressor features a fully parametric, five-stage, inline impeller line-up housed in fabricated steel casing. The casing is supported by a flexible leg support structure to ascertain true centre-line support. The bolted removable end head facilitates easy maintenance. The unit is equipped with tandem dry gas seals and oil lubricated bearings. The lubrication is provided by the gas turbine lube oil console.

These compressors handle residue gas from the UGDC C2/C3-refinery in Port Said, and boost it to 72 bar[a] discharge pressure for further use by the end users. The unit is site rated at 20 315 kW at 6163 r/min. The units are installed with a horizontal exhaust containing a waste heat recovery unit. As the package is compact, with virtually no separate auxiliaries arranged outside the confines of the skid, installation is straightforward.

The equipment was string-tested in Finspong in October 2003, incidentally the first full string-test to be performed with a fully Siemens-owned gas turbine-compressor train, enabled by Siemens’ purchase of Alstom’s industrial turbine businesses earlier in the year.

Port Said plant

The Port Said plant has receiving facilities, pre-treatment, NGL recovery, fractionation and residue gas compression as its main processing areas. It is very important for the Egyptian national economy, being designed to process 1100 million standard cubic feet of gas per day (21.17 million m3) from the Egyptian national gas grid to produce commercial propane, future ethane for the petrochemical industry, sales gas, liquefied propane gas and condensate for a variety of commercial applications. The plant is at sea level and its mechanical design is for an ambient temperature of 45à‚°C. All equipment and instrumentation is protected against the highly corrosive marine climate by tropicalization of electric components. Because of the nature of the plant, health, safety and environmental considerations are paramount in all aspects of the site work.

Installation proceeded on site during the first six months of 2004, and commissioning began in the summer. Both turbine-compressor sets were commissioned at the end of 2004, and taken over by the customer successively after thorough performance testing. By the end of December 2005 the two turbines had jointly accumulated 14 843 operating hours. These two fleet leaders in Port Said have exceeded all expectations, running at over 98 per cent reliability during their initial operation.

Since customer takeover Siemens has two resident engineers on site as part of the service contract with the customer.

Two other mechanical drive projects are in commercial operation. In Eischleben, Germany, two SGT-700 compressor trains are installed in a pipeline compressor station, having come on line in May 2005. A further SGT-700 for mechanical drive is running on a platform offshore Qatar. This site required special considerations to enable the turbine to handle the hot environment (+48à‚°C).

SGT-700 as compressor driver

The SGT-700 is the ideal compressor driver. Like the SGT-600, it has a two-stage compressor turbine and a two-stage power turbine, and its gas generator can be assembled together with the new or existing power turbine. The compressor rotor and the two-stage bolted compressor turbine module form a single shaft, which rests in two standard hydrodynamic bearings of the tilting pad type. The separate high speed (6500 r/min) two-stage power turbine also forms a single unit resting in two standard hydrodynamic bearings of the same type as the gas generator rotor. The power turbine is then coupled to driven equipment.

In contrast to the older type of industrial turbine, which had a relatively low power turbine speed (3600-4700 r/min), the new generation industrial gas turbine has a 6500 r/min design speed, i.e. on a par with the aeroderivatives which run at 5500-6100 r/min. The speed of the power turbine is chosen to give a high total efficiency in compressor drive applications: both SGT-600 and SGT-700 gas turbines have a high power turbine speed which results in a high train efficiency for compressor drives.


Figure 5. SGT-700 is installed on an offshore platform, Qatar
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Installation for these turbines meets stringent requirements for compactness, short erection and commissioning times and ease of maintenance. The turbine is skid-mounted, with the auxiliaries grouped in self-contained modules placed in the auxiliary room. The whole compression package can also be designed to form a single lift unit. The layout is basically the same for both power generation and mechanical drive applications.

The turbine was designed with the flexibility to be both driver and generator. Its design and heritage also make it a powerful machine for electrical generation in terms of efficiency and environmental performance. The first two SGT-700 gensets are now generating power and district heating for the town of Sochi, Russia’s major resort on the Black Sea Coast, and a further unit has recently been ordered for a combined cycle plant at Miskolc in Hungary, where it will boost the output of an existing power plant.

Operating performance

As of December 2005 some 36 000 running hours have been accumulated with six units in operation, the fleet leader, Unit A in Port Said, having accumulated approximately 9000 operation hours, and Unit B having accumulated 6500 hours. In December, the seventh unit, the installation offshore Qatar, also began to operate commercially.

Because the gas turbine units are integrated in a larger infrastructure (pipeline or process), availability and reliability are prioritized parameters. The reliability factor during the first year of operation has been 98.9 per cent and the corresponding availability figure 97.7 per cent. Start reliability has been particularly high. In addition, the combustion system has shown good durability over time with stable emission levels.

Limited outage occurred, related entirely to non-standard delivery or extended scope. Some outage was due also to the additional inspection and follow-up which has been a part of the introduction programme. As a result of the investigations, all delivered units have been updated with a pulsation governing system to secure reliable operation and fulfillment of lifetime predictions. All new units have this system as standard.

Conclusion

The introduction of the SGT-700 has passed the first critical phase and been given market acceptance. The SGT-700 can now be considered a mature product and the number of delivery slots has been extended accordingly to meet the required number of units in the coming years.

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