M501G at Ilijan Power Plant

The 1200MW Ilijan Power Plant is the first M501G application outside of Japan. The plant is composed of two blocks in a 2x1 configuration. each gas turbine unit is site rated at 198.66MW at an ambient condition of 32 C and 85% R.H. The units exhaust to a Three-Presure level Heat Recovery Steam Generator, which supplies steam to two 240MW Mitsubishi steam turbines.

The 501G is a cold-end drive machine with 17 stages of axial-flow compressor resulting in a 19:1 pressure ratio. The combustion section is of the can-annular type with 16 individual Dry Low Nox (DLN) combustors that utilizes a closed-circuit steam cooling. This results in a much higher firing temperature at approx. 1500 C. The turbine is an air-cooled, 4-stage reaction type turbine. The first and second stage vanes and blades are TBC (Thermal Barrier Coating)-coated to reduce base metal temperatures to an acceptable level.

Compress0r

The 501G utilizes a 17-stage axial flow compressor capable of producing a pessure of ratio of 19:1. It has a Varaible Inlet Guide Vane which allows a constant exhaust temperature at all loads and controls surge during run-up and coast-down. Stages 1-3 utilizes a Multiple Circular Arc (MCA) profile on the blade and a Controlled Diffusion Arc (CDA) airfoil on the nozzle while Stages 4-7 fully utilize a CDA profile on blades and nozzles. The remaining stages utlize the NACA65C design. The flow path of the compressor decraeses in cross-sectional area towards the discharge. This allows a uniform axial velocity as the air is compressed. The compression process increases the temperature and pressure of the air. At compressor discharge, the temperature is at the range of 400 C -450 C. Air bleeds are also provided for surge control and cooling of hot gas path parts. Bleeds are at the 6th (Low Pressure / LP) and 11th (Intermediate Pressure / IP) stages. High pressure bleed is taken directly from the discharge (17th stage).

Combustor

The combustor is of the dry-low NOx type (DLN) having a dual fuel capability, either natural gas or distillate fuels. Multiple nozzles supply pre-mixed fuel for lean burn combustion. The transition piece / liner utilizes a unique cooling scheme to acheive a firing temperature of 1500 C. Closed-circuit steam cooling is used to cool the liner. Steam is extracted from the IP economizer and is circulated in the liner reheating of the steam at the same time prior to admission in the IP section of the steam turbine. Such technique improves thermal efficiency and power output.

Turbine

The turbine is a 4-stage axial-flow reaction type. It utilizes a Directionally Solidified (DS) blade material, which has improvements in creep and fatigue strength over Equi-axed blades. Advanced air-cooling is used coupled with thermal barrier coatings on the 1st and 2nd stage blade. This allows lower base metal temperature, permitting a higher turbine creep life usage.