GT10C targets the 30 MW gap

6 May 2002

An upgrade of the proven GT10B, the new 30 MW GT10C gas turbine will be commercially available in June 2002. With the emphasis very much on robustness and reliability rather than novelty, the first GT10C is currently under test on a new rig in Finspong. James Varley

There has been a big gap in the market for years, but it now seems to be filling up", said Bertil Nilsson, Manager, Strategic Development, Alstom Power, Sweden. He was speaking in Finspong in April at the press launch of Alstom's new GT10C industrial gas turbine.

The gap he was talking about is around the 30 MW power level, where he sees growing demand and a "new focus emerging", with other gas turbine vendors also active (GE and the Frame 5E, Rolls Royce and its upgraded RB211, Pratt & Whitney with the FT8+).

Alstom is hoping the GT10C, which will be commercially available in June, will put it ahead of the pack.

Currently, it seems to be the oil and gas market which is driving up demand in the 27-34 MW gas turbine sector. But Bertil believes that opportunities in power generation will follow. This is a pattern he has seen before, for example with the GT10B, where sales started on the oil and gas side, with the power generation market developing a little later.

Uprated version

Understandably, in view of recent well known "teething" problems with the introduction of new gas turbine technologies, buyers are wary of the novel and desperate for dependability. Alstom is therefore not ashamed to admit, indeed anxious to emphasise, that many features of the GT10C are not new, but carried forward from the GT10B. The GT10C is in effect an uprated version of this proven earlier machine, with major goals being robustness, higher efficiency, reduced emissions and lower life cycle cost.

The table attached compares the performance of the B and C machines, while the upper diagram (please refer to issue) summarises some of the key design differences. These include the addition of a compressor stage, taking the number of stages from ten in the GT10B to 11 for the GT10C, with an increased air flow, and improved compressor blade profiles.

The GT10C also uses removable AEV (Advanced Environmental Vortex) burners (identical to those employed in Alstom's GTX100 gas turbine), rather than the EV burners used on the GT10B. The number of burners in the GT10C is 18 (the same as the GT10B) but they are angled, which means that they can be removed without dismantling the gas turbine.

Like its predecessor, the GT10C is designed for dual fuel (gas and oil) use. The AEV burner, a dry low emissions (DLE) system, is expected to be able to limit NOx emissions down to 15 ppm (at 15 per cent O2) on gas, compared with 25 ppm for the GT10B. On liquid fuel, the expected NOx figure for the GT10C is less than 42 ppm, without water injection. The GT10B can achieve the same low level on liquid fuel, but only with water injection. CO is limited to 25 ppm on gas and oil for both the GT10C and the earlier machine.

Improvements have also been made to the combustion turbine blade cooling. The first stage of the GT10C turbine inlet guide vanes has convection cooling with film cooled edges, with shrouded blades and honeycomb seals introduced in the second stage. The GT10B has shrouded blades in all stages and no film cooled edges.

The basic configuration of the GT10C is of course, however, essentially the same as the GT10B. It is a twin-shaft machine. The first two compressor stages have variable inlet guide vanes. The rotor is composed of discs electron-beam welded to a single robust unit (as in the GT10B). Also like the GT10B, the GT10C combustion chamber (combustor) is annular and of sheet metal construction, with thermal barrier coating on the inner surface. The two-stage power turbine is a free-shaft turbine, with discs bolted onto the shaft.

The GT10C package has exactly the same layout and footprint as the GT10B and it is designed so that the auxiliaries have considerable commonality with those of the GT10B. The maintenance schedule for the two machines is identical. The GT10C package (like the GT10B) is skid mounted, with single-lift capability.

Building a test rig

Full scale testing of the combustor has been carried out at a facility near Moscow (Central Institute of Aviation Motors), while testing of the complete GT10C package has been conducted (and is still underway) at a new dual fuel full-load test facility in Finspong.

Unlike the GTX100, where testing of the first unit was done as a joint project with a utility (at Helsingborg), a decision was made to perform the GT10C testing "at home", says Alstom's Anders Hellberg, GT10C product manager.

The small problem of there being no gas in Finspong was solved by installing an LNG facility, with 17 m high tank of 100 m3 capacity. The LNG is imported from Russia.

There are 1200 measuring points on the GT10C package under test at Finspong. Test milestones to date have included (on gas fuel): 100 per cent load (1 March); blade dynamic tests; power turbine variable speed test; normal cold start (12+5 minutes) and stop; peak test (31 MW on cold morning); emissions (less than 15 ppm NOx at 31 MW); 25 starts; 50 hours of operation. The test programme, which will also include operation on fuel oil, and a paint test, is due to be completed in early September.

Going commercial

The concept of the GT10C was launched in 1998, at the Asme annual turbine event. This summer will see the culmination of the effort when the machine becomes commercially available and the second unit leaves the factory.

Alstom's research suggested there was a gap in its industrial gas turbine range, and in the market, at 30 MW. Over the next few months the company will be hoping to find a market in the gap.

Performance comparison, GT10B and GT10C (baseload power generation on natural gas)

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