All-air-cooled J attracts interest

Mitsubishi Hitachi Power Systems (MHPS) reports seven “technical selections” over the past few months by power plant project developers (utilities and independent power producers) for the new JAC gas turbine, an all-air- cooled version of its J-series machine (a technical selection meaning that JAC gas turbines will be used if the project goes ahead, subject to financing/permitting, etc).

MHPS says the JAC turbine offers a combined cycle efficiency of 63%, with an installed capacity of 540 MW and 680 MW (single shaft combined cycle), respectively, for 60 Hz and 50 Hz.

While “other suppliers led the industry with F-class installations”, MHPS concedes, it claims to have “more advanced-class gas turbines (ACGT) operating around the globe than the next two competitors combined” (GE and Siemens). MHPS says that “following up on the success of its steam- cooled and air-cooled G-series gas turbines” – the G and the GAC – it has “already sold 45 steam-cooled J-series turbines, with 21 turbines currently in operation having racked up more than 335 000 hours of commercial operation at an unprecedented 99.3% reliability.”

The G-series employs a turbine inlet temperature of around 1500°C, while in the J the turbine inlet temperature is increased to 1600°C for increased efficiency.

The J-series gas turbines employ steam cooling in the combustors. In the JAC (J Air Cooled) version the steam cooling is eliminated (as in the GAC), providing enhanced flexibility.

According to Paul Browning, who, interestingly, was with GE when it moved away from steam cooling and launched its all air cooled advanced turbine platform, initially called FlexEfficiency, now known as HA, and is currently president and CEO of MHPS Americas, “MHPS is revolutionising the advanced class...with an air-cooled J-series that’s larger and more efficient than any other turbine.”

To convert the J-series from steam cooling to air cooling, modifications were made to the combustor and thermal barrier coatings were enhanced in the turbine section to allow for a higher firing temperature.

At its Takasago Machinery Works in Japan, “the highly instrumented T-Point facility has conducted full speed full load testing of the JAC, followed by thousands of hours of reliability verification in commercial operation”, says MHPS, claiming that “no other gas turbine manufacturer conducts this combination of short term performance testing and long term reliability verification for turbine designs before they are made available to customers.”

According to MHPS, the JAC gas turbine has now accumulated more than 11 000 hours of commercial operation, at a “record” 99.5% reliability.

“Our fundamental approach at MHPS is to use a combination of highly instrumented short term testing at different speeds and loads, followed by long-term reliability verification at T-Point before we release a first of kind product enhancement. This differentiates us from other turbine manufacturers,” suggests Akimasa Muyama, head of turbine products, MHPS.

“There are a number of potential reliability issues, such as creep, low cycle fatigue and thermal barrier coating deterioration that require thousands of operating hours before they start to become apparent. We’re the only turbine OEM to have research and development, design, manufacturing, short term performance testing and long term reliability verification in a single location.”

MHPS JAC units are being built at and shipped from the Savannah Machinery Works in Georgia, USA as well as the Takasago Works in Japan.

The JAC machine maintains the long standing MHPS advanced gas turbine features of a compressor shaft end drive, two-bearing rotor structure, axial flow exhaust, bolt-connected discs with torque pins on the compressor rotor and CURVIC couplings on the turbine rotor discs.

M501Js for Greensville

Meanwhile, on 1 December, Dominion Virginia Power held a groundbreaking ceremony for its 1588 MW Greensville County combined cycle plant, which will use three MHPS M501J gas turbines.

This is the third combined cycle project in the past five years in which MHPS has partnered with Dominion to supply gas turbines. The other two plants, Warren County and Brunswick County, employ M501GAC gas turbines, a total of six.