Environmental Engineering Reference
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Kühlturm
Turbine
Generator
Cooling tower
Flash-Behälter
Flash vessel
G
Kondensator
Condenser
Sepa-
ration
of gases
Gasab-
scheidung
Feinfilter
Filter
Fig. 10.16 Simplified schematic diagram of a geothermal power production facility operat-
ing according to single flash technology with condensation
Production well
Injection well
Förderbohrung
Injektionsbohrung
Double flash process with condensation. The disadvantage of the relatively low
utilisation ratio of the overall produced geothermal energy within single flash
processes can be remedied by a simple appendage to the single flash system. The
pressure of the boiling water drained from the first flash vessel (separator) is re-
lieved a second time and the generated steam is again separated within another
vessel. Subsequently, the separated steam is then used by another (low-pressure)
turbine or within a complementary low-pressure part of the high-pressure turbine
(Fig. 10.17).
The efficiency of the additional pressure reduction within the second flash ves-
sel depends on the temperature level inside the condenser and the starting point of
the pressure reduction above the atmospheric pressure.
At a temperature of approximately 160 °C the maximum resource exploitation
varies between 130 (t/h)/MW and 40 (t/h)/MW at a geothermal fluid temperature
of approximately 240 °C (Fig. 10.15). It is thus considerably higher than the utili-
sation of single flash plants.
Although flash systems at temperatures above 175 to 180 °C are no longer ap-
plied, double flash systems are especially suitable to control the difficulties related
to low resource temperatures, such as a low flash pressure and a low specific
steam volume. Hence, due their simple design, low operation and maintenance
costs and their ability to produce their own cooling tower water, double flash sys-
tems are characterised by considerable advantages, especially when compared to
binary systems. However, double flash systems need to be optimised economi-
cally, as they present higher investment costs when compared to alternative sys-
tems due to the needed additional turbine or turbine stages, additional vessels,
pipelines, control systems, etc.
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