Environmental Engineering Reference
In-Depth Information
482
In all these different options the steam pressure of the working fluid is reduced in
work machines (such as steam turbines, screw or piston expansion machines). The
generated mechanical energy of the rotating axle is then transformed into electric
energy by means of an electric generator.
The related thermodynamic process is the Clausius Rankine process (see Chap-
ter 5.1) that is state of the art within conventional power plant technology. Steam
is heated at the same pressure (i.e. isobaric heat supply) and evaporated, relieved
isentropically producing work, and subsequently condensed isobarically followed
by an isentropic compression.
The different processes used for electricity generation from geothermal fluid
based on this Clausius Rankine process are explained throughout the following
sections. They differ with regard to the achievable efficiency and in terms of ex-
ploitation of the geologic resource. Fig. 10.15 thus illustrates average specific
data.
500
500
ORC
Single flash-system
Double flash-system
Single flash-system / ORC
Kalina
ORC
Single flash-system
Double flash-system
Single flash-system / ORC
Kalina
ORC
Single flash-System
Double flash-System
Single flash-System /
ORC
Kalina
ORC
Single flash-System
Double flash-System
Single flash-System /
ORC
Kalina
450
450
400
400
350
350
300
300
250
250
200
200
150
150
100
100
50
50
0
0
100
100
120
120
140
140
160
160
180
180
200
200
220
220
240
240
Temperature of the produced thermal waters in °C
Temperature of the produced thermal waters in °C
Fig. 10.15
Specific average resource utilisation of different cycles suitable for geothermal
power production (ORC - Organic Rankine Cycle; Kalina - Kalina Cycle)
Open systems.
Depending on the characteristics of the geothermal resource either
direct steam utilisation systems or flash systems are possible. Flash systems are
further divided into single flash systems without condensation, single flash sys-
tems with condensation and double flash systems. They will be explained as fol-
lows.
Direct steam utilisation.
This process applies to geothermal resources where su-
perheated steam is directly produced or where steam constitutes a high portion of
the produced geothermal energy. After separation of particulate matter and water
droplets, the steam pressure is directly transferred to a turbine where work it pro-
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