ORGANIC RANKINE CYCLES (ORC)

Organic Rankine Cycles (ORC) are used for the generation of power from heat recovery, e.g. heat recovery from geothermal sources or waste heat recovery from industrial processes. Several tons of HFCs (e.g. HFC-245fa, HFC-365mfc, HFC-134a,) are contained in each system

The Rankine cycle

The basic system, called the Rankine cycle, is similar to the process used for power generation in steam turbines, but operates at lower temperatures (dependent on the working fluid properties) and so can make use of heat from geothermal sources or rejected from industrial processes. When HFCs are used as the working fluid, these systems are called Organic Rankine Cycles (ORC). The Rankine cycle uses heat to evaporate the working fluid (HFCs) at relatively high pressure. The resultant gas is passed through an expansion engine which does useful work, usually driving an alternator to produce electrical power. The conversion rate from thermal to electrical power varies with the pressure differences and the expansion engine efficiency, but typically is between 10% and 15%, including the electrical power required to drive fans and pumps in the system. [UNEP 2014 Report of the Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee 2014 Assessment]

HFCs used in Organic Rankine Cycles

Some ORC systems use HFC-134a as the working fluid, but it has a low critical temperature and so cannot take full advantage of higher temperature heat sources. Other systems use HFC-245fa or HFC-236fa, which have significantly higher critical temperatures. The GWP of HFC-245fa is approximately 858, whereas for HFC-236fa it is approximately 8060.