Kalina Cycle

The next one among geothermal cycles is called "Kalina Cycle". It has been given name by its inventor, Russian engineer Alexander Kalina. Beside Organic Rankine Cycle (ORC), Kalina Cycle is another cycle used in power facilities fueled by geothermal water streams of lower temperature.

In comparison with Organic Rankine Cycle, the main advantage of Kalina Cycle lies in higher thermodynamic efficiency. In addition, there is also so called "New Kalina Cycle" that can be characterized as one producing less emissions and requiring less energy while being used. There are various variations of Kalina Cycle, each one suitable for concrete mixture of geothermal water properties - working fluid.

Similarly to Organic Rankine Cycle, Kalina Cycle uses a working fluid comprised of at least two different components - typically water and ammonia. Unlike Organic Rankine Cycle, condensation of ammonia-water mixture typically permits additional heat recovery, so this fluid of much lower temperature can be repeatedly used in order to produce additional energy. Surely, the amount of additional energy is quite low and depends on the concrete ratio of water and other items included in working fluid.

Kalina Cycle trademark and patents are owned by Global Geothermal Ltd.

Organic Rankine Cycle – ORC

Like we mentioned that the principle of geothermal power plant lies in thermodynamic cycles, we would like to write briefly about one of them, so called Organic Rankine Cycle (ORC).

Firstly, what is a Rankine Cycle? In general, it is a thermodynamic cycle used in turbines in order to produce electricity. It is one of practical approaches to Carnot Cycle, which refers to ideal type of turning heat into work without any energy losses. Rankine Cycle is used in steam turbines exploiting so called waste heat. In other words, once the “primary” heat is used for some purpose and the part of it was consumed, the waste heat can be a source of energy for Rankine Cycle.

“Organic” means using high molecular mass fluid, which has lower boiling point than water. Very simplified, geothermal water stream heats closed high molecular mass fluid loop, turned into steam and fueling steam turbine. In practice, ORC uses chemical fluid consisting of butane, propane, ammonia or some of new environmental friendly refrigerants. The main advantage of refrigerant is that it boils at a temperature below the temperature of frozen ice. Moreover, additional heating, although by low temperature geothermal stream, increases the pressure in closed loop.

Organic Ranking Cycle is therefore suitable to be used in geothermal power plants established on wells producing water streams of lower temperature, which means especially the range from 50 to some 100 Celsius degrees, or in combination with other thermodynamic cycles producing the waste heat. On the other hand, the efficiency of ORC is low in general.