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This year’s PowerGen conference featured a number of big announcements on the turbomachinery front. Siemens launched a 37 MW GT, showcasing it in a surround-sound dome in the exhibit hall. And Pratt & Whitney Power Systems announced the imminent arrival of the long-anticipated FT4000 gas turbine which is derived from the PW4000 turbofan jet engine.

Siemens SGT-750

With a capacity of 37 MW, the SGT-750 has been released to close the gap in the Siemens portfolio, which previously jumped from 5 to 50 MW. It can be employed for power generation and as a mechanical drive. In the latter use case, this twin-shaft turbine can reach an efficiency level of 40%. The SGT-750 can be used for peak or baseload operation, and like all recent Siemens releases, it can accommodate fast startup and cycling.

According to the company, offsite maintenance work accounts for 17 days of downtime over a 17-year span.

“This is achieved by utilizing a spare gas generator, since the SGT-750 package is designed for a 24-hour gas generator exchange,” said Anders Hellberg, the SGT- 750 ProductManager.

Scheduled maintenance stops occur at 34,000 and 102,000 hours for two days each, with a major 5-day overhaul in between at the 68,000-hour mark, and additional days for borescope inspections. The rotors utilize axial blade grooves for easy replacement. Long-life tilting pad bearings have been incorporated. Rotor balancing can be accomplished on site without the need for disassembly.

Easy access for borescope inspection is another feature. “A new design method using Studio 3D visualization enabled service personnel to offer valuable input on the accessibility of the working environment,” said Hellberg.

Instead of all-new design and parts from scratch, the company selected proven components from other Siemens GTs. It comes with a dry low emission (DLE) combustion system with dual-fuel switchover capabilities. Temperaturemonitoring of the blades is done using infrared. The turbine spins up to 6,100 rpm and comes with two variable guide vanes.

“This is the first Siemens gas turbine where the best technology has been used, taken from our whole range, 5 to 375 MW,” said Hellberg. “The package has a great deal in common with the SGT- 600/700 package.”

The compressor is a 13-stage axial flow machine with a 24-to-1 pressure ratio. It is built up from a number of electron-beamwelded disks. The intermediate shaft is welded onto the compressor and the two gas-generator turbine disks are bolted onto the intermediate shaft. The low pressure section is manufactured in low alloy steel. Inconel 718 is used for the disks in the high pressure section.

The compressor section uses a conventional horizontally split design, while the remainder of the unit uses vertically split, single-piece, circular stator components. The reason for this is to eliminate loss of circularity and keep aerodynamic losses to aminimum. These sections can be removed as modules for permiting easy access and simple maintenance.

Horizontal split design

“A horizontal split design means that the upper compressor casing can be lifted off for maintenance inside the gas turbine enclosure and single blades/vanes can be exchanged if needed,” said Hellberg. “The electron beam (EB) welded rotor where the disks are welded together is very stable in operation with low vibrations since the disks can't move.”

The combustion chamber system consists of eight cans with double-skin serialcooled design, and eight transition ducts of double-skin parallel cooled design, suitable for both liquid and gaseous fuels. The can design is said to provide for excellent maintainability and exchangeability.

The power turbine is a two-stage axialflow turbine, aero-dynamically connected to the gas generator. The first stage (stator with guide vanes) is cooled by a combination of internal convective cooling and film cooling whereas the second-stage (rotor assembly bolted to the compressor rotor) is cooled by internal convective cooling.

Siemens predicts a marked increase in demand for gas turbines with ratings between 35 and 40MWup to 2020.

“Since the power from a GT is reduced at hot ambient temperatures, the SGT-750 is optimized at these temperatures,” said Hellberg. “Today’s engines in the 30-35 MW class have a heritage from the 20-30 MWclass, where growth has been constant for the last few decades.”

Siemens is offering a complete package for the SFT-750. The GT is mounted on a foundation frame with single-lift capability, with a skid split between driver and driven equipment. Driven equipment can also be located on a concrete foundation for onshore applications. The lubrication oil system is installed inside the GT package.All the auxiliary systems, except for the liquid fuel system, the water injection system and the fire extinguishing system, are mounted on the base frame.


P&W FT4000 SwiftPac

Anewaeroderivative industrial gas turbine is arriving on the scene. The FT4000 SwiftPac is based on the widely utilized PW4000 turbofan aircraft engine,which has flown for 26 million hours on more than 850 engines for the Airbus A330 and Boeing 777. This new GT will be available for simple cycle, combined cycle or cogeneration.

“In terms of price, power output, efficiency, emissions and availability, we’re confident that the FT4000 SwiftPac will be an attractive solution for utilities and power providers,” said Peter Christman, president, Pratt &Whitney Power Systems.

The company incorporated modular design features and lessons learned from its FT8 SwiftPac and MobilePac products. Intended for use as in peaking and base-load power, it will be sold either as a 60 MW single engine or a 120 MW dual engine.

The FT4000 utilizes a modified core compressor and turbine from its aero parent. However, it maintains more than 90% part commonality with the PW4170 and PW4090 jet engines. The package will include wet compression as a means of power augmentation.

Currently in development, the company anticipates the first prototype will be available in 2013, and full scale production will be underway by 2014.

“In the early 1960s, Pratt & Whitney was the first to look at the aerospace fleet and see how we could redesign those engines for industrial applications,” said Chuck Levey, vice president of Pratt & Whitney Power Systems.

He explained the sequence of action on this new model. Engineers first took the PW4000 compressor and optimized the flow to match industrial turbine speed and torque requirements.

With that accomplished, they then designed the power turbine to take the thrust energy and convert it to rotational energy connected to a generator. The lube oil, fuel oil and control systems were also redesigned and packaged to operate safely in a power plant.

“Aircraft engines start and stop a lot, so aeroderivatives are good at that,” said Levey. “This machine will be good for load following and will offer simple cycle efficiency greater than 41%.”

The company has very high hopes for this new machine. “The FT4000 has economic advantages on a dollars per kW basis and will directly compete with the LMS100,” said Levey. “At 120 MW, it will also compete with the E-class, but be more flexible.”

Alliance with Wood group

But PowerGen wasn’t all about new turbines for Pratt & Whitney Power Systems (PWPS). The company also presented a new alliance withWood Group GTS for Fclass services. Both companies will jointly service the GE Frame 7FA industrial gas turbine aftermarket.

GTS has an exclusive 10-year license for sale and distribution of PWPS manufactured combustion hardware, hot gas path components and repair services. GTS will gain access to parts which will enhance its ability to support power plant owners and operators via long-term maintenance agreements.

The relationship is exclusive in North America and Saudi Arabia for GTS to use PWPS parts. Other zones are not included in the deal.At the same time, PWPS is not restricted from directly selling parts and repair services on what it calls a transactional basis.

“If you just want a part or repair, Power Systemswill do it,” said Levey. “But for bundled services for repair contracts, lifecycle management and so on, we would serve those customers via GTS.”

PWPS, then, prefers to stick to its core competency of part manufacture and repair manufacturing. This arrangement enables the company to leverageWoodGroupGTS’s expertise in lifecycle management.

“Our agreement builds on the successful collaboration between GTS and PWPS supporting aero-derivative machines,” said Peter Christman. “The F technology market demands a comprehensivemaintenance solution, and through partnership with GTS, we are able to meet this need. The combination of PWPS’s engineering, new part manufacturing and repair technology and GTS’s service experience and risk management strategies is a compelling proposition.”

Mitigating F-class risk

As with the Chromalloy announcement (see p. 28), the lure of the F-class aftermarket has proved to be a powerful draw. Of the over 1000GE F-classmachines in operation,70% are 7FAunits.Aswell as servicing its F-class clientele via maintenance actions, GTS can now add parts and repair into the mix.

“This package provides a truly independent and high quality solution for F technology units to mitigate the technical and commercial risk of turbine operation,” said Mark Papworth, CEOWood Group GTS.

Frank Avery, president of power plant services at Wood Group GTS, laid out his company’s service credentials. We have 18,000 MW of long-term contracts and another 12,000MWfalling within its operations and maintenance services scope.

“Our core capabilities are the servicing of GE GTs from Frame 5 to Frame 9 machines, as well as 7FA,” saidAvery. “7FA operators demand choice so this alliance provides a viable OEM alternative and a means for users to control future costs. With many existing service agreements expiring over the next several years, this presents a big opportunity.”