The first 9FB gas turbine has achieved first firing at the Group III of the Arcos de la Frontera combined cycle plant in Spain, marking a milestone in the development of GE’s F technology.

Siân Green

n May 2003, Spanish utility Iberdrola Generacion awarded GE Energy contracts to provide 9FB-based combined cycle power systems for two power projects in Spain. Just two years later, in August 2005, GE Energy announced that first firing of one of the gas turbines had taken place, marking the first time that a 9FB machine had been fired for a commercial project.

The first firing took place at the Arcos de la Frontera Grupo III (Group III) combined cycle project in Cadiz, Spain, where GE Energy has supplied a S209FB multi-shaft combined cycle system consisting of two Frame 9FB gas turbines, one D11 steam turbine with 48” last-stage buckets, three 330H hydrogen-cooled generators and two three-pressure heat recovery steam generators (HRSGs). The company has supplied a second S209FB combined cycle system for Iberdrola’s Escombreras power plant in Murcia, Spain.

The first 9FB at the 800 MW Group III plant was fired on August 27 and was synchronized to the grid on September 5, with the second unit following soon after. The first firing marked the beginning of a test phase at the Group III site that will lead up to commercial operation by the end of the year.

Located between Sevilla and the Campo de Gibraltar – two areas with a growing demand for electricity – the Group III plant is part of Iberdrola’s plans to add 1700 MW of new capacity to the Spanish grid this year. Engineering, procurement and construction (EPC) for the project is being carried out by Iberdrola’s engineering subsidiary, Iberdrola Ingenieriá y Construccion SAU (Iberinco).

Evolutionary design

GE describes the first firing at the Group III power plant as a “milestone” for its 9FB technology, which was launched to market in mid-2002. The company describes the 9FB as one of the world’s most advanced air-cooled 50 Hz gas turbines. It is the latest evolution in GE’s F technology, which has accumulated more than 13 million hours of commercial service around the world.

The 9FB is the 50 Hz version of the 60 Hz 7FB gas turbine – introduced in 1999 – the first unit of which was installed at a Reliant Energy project in Hunterstown, Pa., USA. Configured with GE’s advanced steam turbine technology in combined cycle operation (one 9FB plus one steam turbine), the 9FB is designed to produce 412 MW and achieve a net plant efficiency of 58 per cent. By comparison, GE’s 9FA gas turbine has a combined cycle output of 390 MW and a net plant efficiency of 56.7 per cent.

The improved output and efficiency has been achieved by increasing firing temperatures and the use of advanced materials, including those developed for GE’s H System. The original Frame 7F machine, introduced in 1989, fired at 1260°C, while the 9FB fires at more than 1370°C.


The Group III project in Spain is scheduled for start up in early 2006. The 9FB is the latest evolution in GE’s F technology, which has accumulated over 13 million operating hours in projects around the world
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The FB compressor is based closely on the FA compressor. It is an 18-stage, axial flow unit with variable inlet guide vanes to maintain high part-load efficiency and low emissions over a wide operating range. Variable vanes also improve low-speed surge characteristics, make startups easier, and provide good part-load performance in combined cycle applications. Closing the vanes keeps exhaust temperature up at reduced loads, thus retaining steam-raising capabilities if the gas turbine is running at less than 100 per cent load.

Throughout the compressor blade path, all airfoil material is high chromium-stainless steel. While the FA units operate at compressor pressure ratios of 15.5 to 1, the FB machines run at 18.5 to 1. The compressor rotor tie bolts material is changed to IN718 alloy to provide improved clamp load for the higher torque margins of the FB.

Compressor bleed air extraction manifold configurations cast into the casings have been modified to provide better transient clearance control to the outer compressor flow path.

Three-stage turbine

An advancement for the FB compared to the FA series comes in the design of the three-stage turbine. With the increase in firing temperature, the gas path airfoils for the FB were redesigned and new materials were specified. Advanced, three-dimensional aerodynamics have been applied to the turbine design, using computational fluid dynamics to optimize gas flow, resulting in higher efficiency and lower cooling air consumption.

The higher firing temperature required the application of single crystal N5 in the first stage bucket, with thermal barrier coating. Second and third stage buckets are comprised of directionally solidified GTD444 materials, replacing the DS GTD111 material of the FA units. First and second stage nozzles for the FB utilize GTD111, while earlier F units used the older, cobalt-based FSX414.

The GTD111 alloy, originally developed for buckets, offers higher creep strength and is used in the FB to maintain the same hot gas path inspection intervals of the 7FA. Utilizing high-pressure air supply bled from the compressor, the FB turbine bucket rows 1 and 2 are fully air cooled, using a combination of impingement, convection and film cooling. A similar system is used to cool nozzle rows 1 and 2.

Since launching the 9FB in 2002, GE has made one modification to the unit’s combustion system design, says Gregory Beggs, 9FB product line manager at GE Energy. “Initially when launched, the 9FB was fitted with a Dry Low NOx (DLN) 2+ combustion system, which had been used extensively on the 9FA machines. It is now equipped with a DLN2.6+ combustion system,” says Beggs.


The FB consists of an 18-stage compressor and a three-stage gas turbine. Validation of the units at the Group III power plant in Spain was completed in November
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The DLN2.6+ is a blend of the 9FA’s DLN2+ combustion system and the DLN2.6 system from GE’s 7FA gas turbine series. The 2.6+ design consists of GE’s patented “swozzle” technology – a combination of a swirler and a nozzle – with an additional nozzle in the centre. This design promotes flame stability and improves fuel staging capability, says Beggs: “We took the best features of both systems and combined them for use in the 9FB”.

Validation

In order to fully validate the 9FB units at Group III, one of the units was instrumented with over 1100 gas turbine sensors and over 300 controls, accessory and packaging sensors. Over 170 hours of testing was performed, and validation ended on 22 November 2005, says Beggs.

“We validated output, heat rate, emissions, component dynamics, aeromechanics, operational clearances, transient operability, and the controls and accessory operability,” says Beggs. “Testing was performed over the whole operating range of the product, from minimum downturn to baseload. We basically tested for anything that the plant might experience under real operating conditions.”

“The gas turbines have met all our expectations so far,” adds Beggs. “GE is very pleased with the product.”

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A smooth validation and commissioning period is important for both GE Energy and Iberinco as the plant is officially scheduled for commercial operation in early 2006. But according to Beggs, validation and commissioning is going to plan. Both gas turbines have achieved full speed full load (FSFL) operation, and the steam turbine has also been operational. Beggs was expecting the plant as a whole to achieve FSFL in November. “We will be ready to supply power to the grid when needed.”

One of the 9FB units at Group III remains instrumented for validation, and a number of additional activities, including the reliability run, need to be carried out at the plant before the PAC is issued, says Beggs.

In addition to supplying the Group III and the 815 MW Escombreras combined cycle plants in Spain for Iberdrola, GE has undertaken an additional three contracts for the supply of six 9FB machines in Europe: two in Spain and one in Italy. While the Escombreras plant is slated for commercial operation by the end of 2006, these other 9FB projects are scheduled for start-up in early 2007.