Icarys
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For those of you who are actually interested in the thread and haven't come to argue.
http://www.distributedenergy.com/november-december-2005/better-cogeneration-chemistry.aspxOrganic
Organic Rankine Cycle Engines
So what makes an Organic Rankine Cycle (ORC) engine so special? Like a standard steam engine, the ORC utilizes heated gas to drive a turbine. However, this gas is a heated organic chemical instead of superheated water steam. The organic chemicals used by an ORC include freon and most of the other traditional refrigerants—iso-pentane, CFCs, HFCs, butane, propane, and ammonia.
Refrigerants seem like an odd choice for a heat engine’s working fluid. However, these gases boil at extremely low temperatures. For example, a typical refrigerant will boil at a mere 150°F, generating significant pressures. The cycle of pressurization with a pump—expansion resulting from applied heat, using the heat to turn a turbine to create energy, and condensation of the fluid back to its liquid state—is identical to the steam engine. It just occurs at much lower temperatures. There are a few differences. Heating and expansion occurs with the application of heat to an evaporator, not a boiler. The condenser can utilize ambient air temperatures to cool the fluid back into a liquid. There is no need for direct contact between the heating source at the evaporator or the cooling source at the condenser.
For those applications where higher temperatures are available to heat the organic working fluid, a regenerator is often added to increase the efficiency of the system. Regenerators are typically constructed of a wire metal mesh or a series of closely spaced thin metal plates. The void spaces between the metal wires and plates allow for easy flow of the working fluid through the regenerator. The relatively large surface area of the metal permits conduction of heat. As the heated organic fluid leaves the boiler it passes through the regenerator, and some of its heat remains. When the cooled organic fluid leaves the condenser it passes through the regenerator in the opposite direction, acquiring some of the previously deposited heat, and preheating the fluid before it enters the boiler. Less heat is needed to boil the liquid, which increase the efficiency of the engine, since it is doing the same amount of work.
Though the amount of work performed by a typical ORC cannot compare with its steam-engine big brother, the ORC has many advantages. First, it has a very high cycle efficiency. For the relatively small amount of waste heat used to drive the engine a comparatively high amount of work can be performed. This results in high turbine efficiency—as high as 85%. That is, the amount of electricity generated by the turbine can be equal to 85% of the equivalent energy generated by the engine. This is the result of the relatively low peripheral speed of the turbine. Again, though the amount of electricity generated is small compared to the behemoth steam-driven turbines, the turbines driven by ORC engines operate at much higher efficiencies.
The low peripheral speed has several other advantages. First, it results in less mechanical stress on the turbine and no erosion of the turbine blades (though this is also a result of the lack of moisture corrosion). Low speeds allow for direct drive of the turbine, as there is no need for a reduction gear. All of the above result in a long operating life, less maintenance, and fewer repairs. Most ORC systems are essentially self running and do not need the constant supervision of a human operator.
http://en.wikipedia.org/wiki/Organic_Rankine_Cycle
< Message edited by Icarys -- 5/10/2011 3:10:34 PM >
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