Binary cycle

[1] Binary cycles permit electricity generation even from low temperature geothermal resources (<180°C) that would otherwise produce insufficient quantities of steam to make flash power plants economically viable.

[1] The geothermal reservoir's hot in-situ fluid (or geofluid) is produced to the surface via a wellbore, if necessary assisted by a pump.

[1] The earliest example of a binary cycle geothermal power plant is thought to have been located on Ischia, Italy, between 1940-1943.

The plant is thought to have used Ethyl Chloride as the working fluid at an effective capacity of 250 kW.

[3] Another binary cycle geothermal power plant was taken into operation in 1967 near Petropavlovsk on the Kamchatka peninsula, Russia.

It was rated at 670 kW and ran for an unknown number of years, proving the concept of binary cycle geothermal power plants.

[5] Two secondary cycles are operated in tandem, each with a separate working fluid and boiling point.

The equation below can be used to determine the condenser duty and mass flow rate of coolant required.

The equation below can be used to determine the primary heat exchanger duty and mass flow rate of geofluid required.

For this reason, a geothermal power plant producing hot geofluid at 180°C (≈450 K) and rejecting heat at 25°C (≈298 K) has a maximum efficiency of just 34%.

[1] The working fluid plays a pivotal role in any binary cycle and must be selected with care.