バイナリー発電

If the geothermal fluid’s temperature is medium to low (about 150 ° C or less), it is not possible to turn the turbine directly with the steam separated from geothermal fluids.
In that case, a method of heating and evaporating a secondary fluid having a boiling point lower than that of water (such as CFCs, a mixture of water and ammonia, etc.) with a heat exchanger and turning the turbine with the vapour of the secondary fluid, called binary generation is employed. Since there are two working fluids (geothermal fluids and secondary fluid), this method is thus called binary generation.
Considered to greatly expand the possibility of geothermal power generation, small and medium-sized power plants employing this power generation method are increasing year by year.
The first full-scale binary power plant in Japan is installed in the Hatchobara power station.
In addition, the Sugawara binary power station in Kokonoe-cho, Oita Prefecture boasts the largest scale of binary power generation system in Japan.

Hachobaru Power Station Source: Kyushu Electric Power Co., Ltd.

Overview of major binary power stations

Hot spring binary power generation

In hot spring areas where hot spring water temperature is high, hot water above 50°C has to be cooled down before it can be used for bathing.
However, with binary power generation system installed, hot water at high temperature (70 ~ 120°C) can be used for electricity generation without its the chemical components affect, while ultimately ending up as cooled down hot spring water perfect for bathing, killing two birds with one stone.

Mechanism of Binary power generation

Point: Binary power generation is a living organism
Steam flow, hot spring flow, hot water flow, cooling water flow
HFC245fa Secondary Fluid flow

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Dry steam plants

地熱貯留層にある高温（200〜300℃）の天然蒸気で直接タービンを回す方法が蒸気発電

Single Flash plants

地下で減圧沸騰(フラッシュ)した地熱流体から蒸気を1回だけ分離しタービンを回す方法。日本の地熱発電所のほとんどがこの方式

Double flash plants

地下水がマグマの熱で加熱されて高温・高圧になった蒸気や熱水を取り出し発電するのが地熱発電