Evaluation and Comparison of Different Blade Cooling Solutions to Improve Cooling Efficiency and Gas Turbine Performances

Abstract

The performance increase for Heavy Duty (HD) gas turbines requires very high R&D efforts to improve life and reliability of the hot components. In fact the maximum temperature increase is the most important factor for the HD gas turbines development. Blade cooling of hottest and most loaded turbine stages becomes a fundamental key for R&D process in gas turbine design. Several innovations have been realised in last years about blade cooling and many industrial manufacturers have recently proposed new coolants, like steam or water. In this paper a detailed comparison among different cooling systems and coolants is proposed. Therefore performances of the most important HD gas turbine models are predicted and applications of the various cooling solutions are evaluated. An advanced cooling scheme based on air cooling closed loop is also studied. The simulations have been made from the point of view of blade cooling design and of global plant performances prediction. Interesting results have been obtained to confirm the present trend of R&D of HD gas turbines. Finally a wide comparison between different cooling solutions for several gas turbine models is presented.

Mathematical Model Based on Newton’s Laws and in First Thermodynamic Law of a Gas Turbine

“…The next equation is the equation that involves the temperature in the system and by adding some terms relate of the shear forces expressed everything in a vector form is the equation well known as the energy balanced equation [12,15,16]:…”

The methodology of the gas turbine efficiency calculation

“…Limitations of these temperatures result from the application of thermal barrier coatings (TBC), which cover elements exposed to the highest temperatures. Assumed that currently used TBC allow for continuous operation at a temperature not exceeding 1200 • C. Presently used cooling technologies allow for the flue gas temperature reduction at the cooled surface by ∆t = 300-400 K, therefore the highest temperature (COT or TIT) can reach 1500-1600 • C. Raising TIT by 100 to 200 K is associated with the increase in ∆t, i.e., to the value ∆t = 500-600 K. Such actions were the object of scrutiny of producers more than 10 years ago [10,11], but there is no information in the literature about their realization. An exception is the paper Hada et al [12], from Mitsubishi Heavy Industries, Ltd., which indicates that the key to the creation of a J-class turbine with T IT = 1600 • C (M701J and M501J for 50 Hz and 60 Hz, respectively), i.e., the temperature higher by 100 • C than the reference G-class, was to improve cooling technology and search for materials with lower thermal conductivity of TBC.…”

An experimental investigation of heat transfer characteristics for steam cooling and air cooling in a rectangular channel roughened with parallel ribs

“…Corman [12] proposed the basic design strategy of steam cooling gas turbine. Facchini [13] analyzed the advantages of the closed-loop cooling technology for double mediums (air and steam) and its contribution to the system efficiency. The research results indicated that the cooling efficiency of the closed-loop steam cooling blade can be significantly improved at the same combustion temperature compared with air cooling blade.…”