Binary systemIn a plant using a
binary system, geothermal fluid, either hot water (also called brine) or
steam, or both, is extracted from an underground reservoir. It flows
from the wellhead through a gathering system of insulated steel
pipelines to a heat exchanger, which heats a secondary working fluid
which has a low boiling point. This is typically an organic fluid such
as isopentane or isobutane, which is vaporized and used to drive the
turbine. The organic fluid is then condensed in a condenser which may be
cooled by air or by water from a cooling tower. The condensed fluid is
then recycled back to the heat exchanger, closing the cycle within the
sealed system. The cooled geothermal fluid is reinjected back into the
reservoir.
The binary technology is depicted in the graphic below.
The binary technology is depicted in the graphic below.
Flash design system
In a plant using flash design, geothermal fluid is
extracted from the underground reservoir and flows from the wellhead
through a gathering system of insulated steel pipelines to flash tanks
and/or separators. There, the steam is separated from the brine and sent
to a demister in the plant, where any remaining water droplets are
removed. This produces a stream of dry steam, which drives a turbine
generator to produce electricity. In some cases, the brine at the outlet
of the separator is flashed a second time (dual flash), providing
additional steam at lower pressure used in the low pressure section
steam turbine to produce additional electricity. Steam exhausted from
the steam turbine is condensed in a surface or direct contact condenser
cooled by cold water from a cooling tower. The non-condensable gases
(such as carbon dioxide) are removed through the removal system in order
to optimize the performance of the steam turbines. The condensate is
used to provide make-up water for the cooling tower. The hot brine
remaining after separation of steam is injected back into the geothermal
resource through a series of injection wells. The flash technology is
depicted in the graphic below.
In some instances, the wells directly produce dry
steam (the flashing occuring under ground). In such cases, the steam is
fed directly to the steam turbine and the rest of the system is similar
to the flash power plant described below.
