Cooling Systems

High-performance gas turbine models feature turbine inlet gas operating temperatures that exceed allowable operating metal temperatures. Hence, carefully controlled cooling

Fig. 10-24 Power Turbine Module in Foreground; Gas Generator in Background. Source: ABB STAL

Fig. 10-25 High-Pressure Compressor-Drive Turbine Featuring Two Axial-Flow Stages. Source: MAN GHH

Fig. 10-26 Turbine Section Design for Large-Capacity Heavy-Duty Turbine. Source: ABB
Fig. 10-27 Turbine Section on Large Heavy-Duty Gas Turbine. Source: General Electric Company

Fig. 10-28 Vanes and Blades of High-Pressure Compressor-Drive Turbine. Source: MAN GHH

Fig. 10-25 High-Pressure Compressor-Drive Turbine Featuring Two Axial-Flow Stages. Source: MAN GHH

is essential for the gas turbine's hot section. Temperature limits are maintained by cooling air, diverted from the compressor and passed through critical parts to carry excess heat into the turbine exhaust stream. The use of air for cooling, however, may involve a turbine efficiency penalty.

Figure 10-30 shows the hot section of an industrial gas turbine. Generally, at maximum cooling flow rates, basic convective cooling can limit turbine rotor inlet gas temperature to a maximum of about 2,050°F (1,121°C). To counterbalance the high heat transfer at the leading

Fig. 10-28 Vanes and Blades of High-Pressure Compressor-Drive Turbine. Source: MAN GHH

Fig. 10-29 Turbine Rotor with Four-Stage Blading for Large-Capacity Gas Turbine. Source: Siemens Power Corporation
Fig. 10-30 Industrial Gas Turbine Hot Section. Source: Solar Turbines

Fig. 10-31 Cooling Process for Four-Stage Power Turbine Section of Large-Capacity Gas Turbine. Source: Siemens Power Corp.

edge, more advanced cooling techniques, such as film cooling for the entire airfoil, have been applied. Internal airfoil cooling is accomplished by introducing cooling air at the root, or tip, of the air foil. It is then discharged at the opposite end of the blade through the trailing edge or ejecting holes. Currently available cooling systems have brought the high-end limit for turbine inlet gas temperature to about 2,400°F (1,316°C).

Figure 10-31 illustrates the cooling process and shows the flow of cooling air for vane and blade rows of a four-stage power turbine section of a large-capacity, heavy-duty industrial gas turbine. With the exception of the last stage rotating blades, all turbine stationary and rotating blades are air-cooled. Cooling air is provided at different pressure and temperature levels from compressor extraction to optimize cooling effect and thermal performance.

Figure 10-32 shows a typical turbine blade cooling passage for a small-capacity industrial gas turbine. Figure 10-33 is a gas turbine bucket design showing air-cooled passages. In this turbine, the first- and second-stage buckets, as well as all three nozzles, are air-cooled. The first-stage bucket is convectively cooled by means of an aircraft-derived serpentine arrangement. Cooling air exits through axial airways located on the bucket's trailing edge and sidewalls for film cooling.

Fig. 10-32 Typical Turbine Blade Cooling Passage for Small-Capacity Turbine. Source: Solar Turbines

Fig. 10-31 Cooling Process for Four-Stage Power Turbine Section of Large-Capacity Gas Turbine. Source: Siemens Power Corp.

Fig. 10-32 Typical Turbine Blade Cooling Passage for Small-Capacity Turbine. Source: Solar Turbines

Fig. 10-33 Gas Turbine Bucket Design Showing Air-Cooled Passages. Source: General Electric Company
Fig. 10-34 Air Foil Cooling Techniques Using Combinations of Impingement, Convection and Film Cooling. Source: Solar Turbines

Fig. 10-35 Illustration of Typical Nozzle Vane Showing Isotherms. Source: General Electric Company

Figure 10-34 illustrates airfoil-cooling techniques using combinations of impingement, convection, and film cooling. Figure 10-35 illustrates a typical nozzle vane pitch cross-section with lines of constant temperature superimposed upon it. Design considerations focus not only on maximum temperature, but also on thermal gradients in the material, since the thermal stress associated with these gradients causes fatigue damage.

Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment