The Kalina cycle is a thermodynamic cycle for converting thermal energy to mechanical power, optimized for use with thermal sources which are at a relatively low temperature compared to the heat sink (or ambient) temperature. The cycle uses a working fluid with at least two components (typically water and ammonia) and a ratio between those components is varied in different parts of the system to increase thermodynamic reversibility and therefore increase overall thermodynamic efficiency. There are multiple variants of Kalina cycle systems specifically applicable for different types of heat sources. Several proof of concept power plants using the Kalina cycle have been built.
The Kalina cycle was invented by the Russian engineer Alexander Kalina. Waste heat recovery plants using the Kalina Cycle technology are in operation at a Sumitomo Metal steelworks and Fuji Oil's refinery in Tokyo Bay. Geothermal plants exist in Husavik, Iceland, and Unterhaching, Germany, recently built by Siemens. The Kalina Cycle trademark and patents are owned by Global Geothermal Ltd, the parent of Recurrent Engineering Inc.
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Since the phase change from liquid to steam is not at a constant temperature, the temperature profiles of the hot and cold fluids in a heat exchanger can be made closer, thus making the global efficiency of the heat transfer bigger. For this reason, this cycle is increasingly popular in geothermal power plants, where the hot fluid is very often below 100ºC. Up to now, in the binary plants (where a heat exchanger is used to produce steam instead of directly employing the steam underground), the most common cycle had been the ORC (Organic Rankine Cycle). Example of this is the Landau-Pfalz power plant in Germany, rated 3.8 MW of electrical power and 8 MW of thermal power.
http://www.geothermie.de/gte/gte46/geothermal_power_plant.htm
http://www.google.com/patents?id=PwgQAAAAEBAJ&dq=6820421+-+Low+temperature+geothermal+system
Diagram of Kalina Cycle for Geothermal Energy: http://www.mannvit.com/GeothermalEnergy/GeothermalPowerPlants/Kalinacyclediagram/
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   | Overview of the Kalina cycle - Heat Recovery in Kalina Systems |
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