Alstom GT24 gas turbine boosts operational flexibility

The next generation of the Alstom GT24 gas turbine has been designed to deliver over 230 MW at 40% efficiency (heat rate of 8'571 Btu/kWh). The corresponding KA24 CCPP can achieve 700 MW output in a 2-on-1 configuration and operate at greater than 60% efficiency and a heat rate of less than 5,714 Btu/KWh.

The main technology differentiator of Alstom's GT24/GT26 is the 'sequential combustion' principle. The EV (EnVironmental) burner in a first annular combustor, followed by the high pressure (HP) turbine, SEV (Sequential EnVironmental) burners in the second annular combustor, and the low pressure (LP) turbine.

Since its introduction, the GT24 has been through three upgrades:

1) In 1999, as part of the conversion from A-configuration to B-configuration where the first combustor (EVcombustor) was modified to incorporate standard EV-burners.

2) In 2002, with the introduction of the first compressor redesign to increase mass flow and CCPP output by around 5%. This was accomplished through airfoil redesign without change to the rotor and stator flow path contour. Hence the design was retrofitable.

3) In 2006, a new rating with a second compressor upgrade with a slight
turbine inlet temperature increase and the staged EV-burner was introduced. This time, the compressor was restaggered in the front stages to increase the mass flow further. Some restagger was also carried out in the high-pressure part of the compressor.

However, the flow path as defined by the outer casing and the rotor profile remained unchanged. Additionally, a stepped increase of the turbine inlet temperature for the LP turbine took place to improve gas turbine and plant efficiency. Finally, the staged EV-burner was introduced into the GT24/GT26 gas turbines.

More in Turbomachinery International magazine Nov. /Dec. 2011.