flow compressors sometimes combined with a centrifugal compressoras the last stage， operated by axial turbines.
2.
Medium-sized gas turbines between 5-50M认 are a combination of aero-derivative and frame type turbines. These gas turbines have axial flow compressors and axial flow turbines.
3.
Largepowerturbinesover50-480M认，theseareframe-typeturbines， the new large turbines are operating at very high firing temperatures about 2400 oF (1315 oc) with cooling provided bysteam， at pressure ratios approaching 35:1.
Plant Location and Site .onfiguration
The location of the plant is the principal determination of the type of plant best configured to meet its needs. Aero-derivatives are used on offshoreplatforms. Industrial turbines are mostly used in petrochemical applications， and the frame type units are used for large power production.
Other important parameters that govern the selection and location ofthe plant are distance from transmissionlines， location from fuel port orpipe lines， and type of fuel availability. Site configuration is generally not aconstraint. Periodically， sites are encountered where one plant configuration or another is best suited.
Plant Type. The determination to have an aero-derivative type gas turbine or a frame-type gas turbine is the plant location. In most cases if the plant is located off-shore on a platform then an aero-derivative plant isrequired. On most on-shore applications， if the size of the plant exceeds100M认 then the frame type is best suited for the gas turbine. In smallerplants between 2-20 M认， the industrial type small turbines best suit theapplication， and in plants between 20-100M认， both aero-derivative or frame types can apply. Aero-derivatives have lower maintenance and havehigh heat-recovery capabilities. In manycases， the type of fuel and service facilities may be the determination. Natural gas or diesel no. 2 would besuited for aero-derivative gasturbines， but heavy fuels would require a frame type gas turbine.
Gas Turbine Size and Efficiency
Gas turbine size is important in the cost of the plant. The larger the gasturbine the less the initial cost perk认. The aero-derivative turbines have traditionally been higher inefficiency however， the new frame type tur-bines have been closing the gap in efficiency. Figure 4-3 shows typical gas turbine cost and efficiency as a function of gas turbine output for an industrial type turbine. Industrial turbines range from micro-turbines of20k认 at an installed cost of nearly $1000jk认 and an efficiency of about15-18%， to turbines rated at about 10M认 at a cost of$500jk认 and an efficiency of about 28-32%. The efficiency in these figures is a simple cycle gas turbine efficiency. These efficiencies can be increased by regeneration or other techniques dealt with in detail in chapter 3. Figure 4-4 shows theaero-derivative turbines rated between 10M认 to 40M认 with an installed
1200
35 30 1000
25 800
20
600 15
400 10
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00
0 24 6 810 12 GAS TURBINE-INDUSTRIAL TYPE-RATED POWER (MW)
Figure 4-.. Installed cost and efficiency of industrial type turbines.
500 450 400 350 300 250 200 150 100 50
0
39.5 39
38.5 38
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152025 30 3540 45 GAS TURBINE-AERODERIVATIVE-RATED POWER (MW)
cost of$400jk认 and an efficiency of about 40%. Figure 4-5 is for a frametype turbines. These turbines range from about 10 M认 to about 250M认with an installed cost for the larger units at$350jk认， and efficiencies of the newer units reaching 40%.
Type of Fuel
The type of fuel is one of the most important aspects that govern the selection of a gas turbine. chapter 12 handles the type of fuels and their effect in detail. Natural gas would be the choice of most operators if natural gas was available since its effects on pollution is minimal and maintenance cost would also be the lowest. Table 4-1 shows how the maintenance cost would increase from natural gas to the heavy oils.
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