R&D for 1700C-class Turbine Closed Loop Cooled Blades

K. Sagae, N. Kizuka, K. Kawaike ,
S. Anzai, S. Marushima and T. Ikeguchi

Power Industrial Systems R&D Division
Hitachi Ltd., Ibaraki, 312-0034, Japan
(Fax.) 81-29-276-5647 (e-mail) sagae@erl.hitachi.co.jp

KEYWORDS: Hydrogen-Fueled Combustion, Closed Water-Cooling, Closed Steam Cooling

Introduction

The turbine cooled blades for 1700C-class hydrogen-fueled combustion gas turbine are being developed in the World Energy NET Work ( WE-NET ) program under a contract with New Energy and Industrial Technology Development Organization (NEDO). This research and development work in above-mentioned program has been directly entrusted by the Japan Power Engineering and Inspection Corporation (JAPEIC). The goal is achieving a thermal plant with an efficiency of greater than 60% high heating value (HHV) at a turbine inlet temperature of 1,700C. We are taking part in research and development program to develop an effective cooling system for hydrogen-fueled combustion gas turbines. In addition, water cooling was considered for the stationary nozzle blades, which is superior to steam cooling as a cooling medium. As for the moving rotor blades, closed-circuit internal steam cooling was chosen to avoid the expectable problems such as water leakage and difficulty in recovering water through the turbine rotor.

COOLING SYSTEM

The effect of three types of cooling systems on the calculated operating performances of a hydrogen-fueled thermal power plant with a 1700℃-class gas turbine were studied with the goal of attaining a thermal efficiency of greater than 60%. The combination of a closed-circuit water cooling system for the nozzle blades and a steam cooling system for the rotor blades was found to be the most efficient. The gas path and cooling circuits of the compressor, combustor and IP turbine based on this system were conceptually designed as shown in Fig.1. The HP turbine, compressor and IHP turbine are operated at the rotational speed of 6,500 rpm and the ILP and LP turbines are operated at 3,000 rpm. Water for cooling the nozzle blades is externally supplied from the bottoming cycle through the outer casing and the heat exchanged water is returned to the bottoming cycle. Steam for cooling rotor blades of the IHP turbine is externally supplied from the bottoming cycle into the rotor shaft end through the outer casing and it flows through the inner paths of the rotor disks to each rotor blade.


Figure 1. Schematic view of gas path and cooling circuits of gas turbine

DESIGN OF COOLED BLADES

The cooling configuration of the water cooled first-stage nozzle and the steam cooled first-stage rotor blade needed to apply closed-circuit cooling system were designed. The cooling design concepts for the first-stage nozzle blade ( Fig.2 ) were (1) having a blunt leading edge to reduce the thermal load at the leading edge region; (2) applying a copper alloy containing Cr and Zr (CZ-Cu), whose thermal conductivity is about 15 times greater than that of conventional nickel base alloys, to reduce the metal temperature and thermal stress; (3) allocating many circular cooling holes as close to the blade surface as possible to keep the temperature below the allowable temperature of copper alloy of about 400℃; (4) having water cooling of outer and inner endwalls by drilled cooling passages; and (5) having a thermal barrier coating (TBC) to reduce the thermal load and protect the metal surface.

Figure 2. The first-stage nozzle blade design concepts

To achieve closed-circuit cooling with steam for the rotor blades, intensified internal cooling techniques were required. The cooling design concepts for the first-stage rotor blade (Fig. 3) were (1) having a blunt leading edge to reduce thermal load at the leading edge region as well as the nozzle blade; (2) applying V-shaped staggered turbulence promoter ribs1),2) in the serpentine cooling passage to enhance internal heat transfer; (3) minimally allocating film cooling holes at only the leading edge region to achieve closed-circuit cooling as much as possible; and (4) having a TBC to reduce the thermal load and protect the metal surface.


Figure 3. The first-stage rotor blade design concepts

Conclusion

The results indicated closed-circuit water cooling system for nozzle blades and steam cooling system for rotor blades were most effective for achieving high efficiencies than conventional open-circuit cooling systems. Based on the results, the water cooled first-stage nozzle blade and the steam cooled first-stage rotor blade were designed. The former features array of circular cooling holes close to the surface and uses a copper alloy taking advantage of recent coating technologies such as thermal barrier coatings (TBCs) to decrease the temperature and protect the blade core material. The later has cooling by serpentine cooling passages with V-shaped staggered turbulence promoter ribs which intensify the internal cooling.