55 Rankine Cycle Microturbines

The Rankine cycle is most commonly known from its application in large steam-driven power plants. In its simplest form, this closed cycle consists of

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Specific power, KJ/Kg

FIGURE 5.18

Efficiency map (85% effective recuperator).

FIGURE 5.19

Highly recuperated, two-shaft microturbine. (Courtesy of Ingersoll-Rand Energy Systems, with permission.)

a boiler, turbine, condenser, and feed pump, as shown in Figure 5.20. Heat is transferred to the Rankine cycle working fluid in the boiler, producing saturated or superheated vapor for the turbine. As the vapor is expanded through the turbine, shaft power is extracted. The low density fluid then passes through the condenser, where it is cooled and converted to liquid which is then pressurized by the feed pump to supply liquid to the boiler, thus completing the cycle.

While the Rankine cycle is best known from steam power plants, it has been used successfully in geothermal and solar binary power systems and waste heat power systems. Figure 5.21 shows a small, high-speed turbine-alternator-pump unit used in a solar-powered Rankine system. In this application, the turbine,

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FIGURE 5.20

Rankine cycle schematic diagram.

FIGURE 5.21

Integrated turbine-alternator-pump for solar Rankine cycle.

feed pump, and power generator were all mounted on the same shaft. The feed pump supplied working fluid through the alternator cooling passages, thus preheating the feed water before moving to the boiler.

When combined with other engines, the Rankine cycle engine can increase overall system efficiency by utilizing the exhaust heat stream typically discarded from the primary engine to produce power with no additional fuel expense. Studies show the output of a recuperated gas turbine can be increased 15 to 30%, and the output of diesel and gasoline engines can be increased 12 to 25% by exhaust gas heated Rankine cycle engines (Angelino and Moroni, 1973; Morgan and David, 1974). Thus, Rankine cycle engines can be used to improve the operating cost basis of these primary engines in the distributed generation market.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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