Environmental Engineering Reference
In-Depth Information
within the underground and not during ordinary circulation and thus production of
the hot geothermal fluid. In seismic unstable areas, this microseism may produce
small earthquakes before the natural event. However, this situation is very
unlikely to occur as such sites would not be chosen due to their history or would
be eliminated at least after the stress has been detected at site. For this reason, also
the slightest acoustic signals are recorded, which occur when rocks burst during
stimulation /10-1/.
Due to the relatively low temperatures, varying between 150 and 250 °C, the
efficiency of geothermal power generation is relatively low when compared to
conventional power plants. This is a result of the high quantities of waste heat to
be released into the atmosphere and thus pollute the environment. However, if
there is a certain demand for low-temperature heat in the locality of the power
plant, the heat might be used to substitute other environmental harmful heat provi-
sion systems (e.g. coal oven). Furthermore, waste heat could also be returned into
the underground.
Geothermal generation facilities are characterised - compared to other power
plants based on renewables and conventional energy carrier - in general by little
land demand depending on the reservoir and generation conditions only. Addi-
tional space is required for the pipelines that transfer the geothermal fluid from
the well head to the power plant. In the case that the pipes are installed above-
ground they also affect the landscape visually. Additional space is required for
cooling towers and power stations. However, these space requirements do not
differ essentially from those of fossil fuel-fired power plants.
For normal operation, altogether only very few environmental effects can be
expected. From the current viewpoint no significant detrimental effect on humans
and the natural environment is likely to occur.
Malfunction.
Due to the salt and mineral contents, in case of a malfunction, minor
environmental impacts may result from heat transfer medium leakage at the
earth's surface (i.e. hot water or hot steam). However, the environmental impacts
are low compared to those observed in the volcanic areas of the earth. Further
environment impacts may result from a possible pressure relief of the heat transfer
medium within the power plant (due to a malfunction (e.g. leakage) of the circuit).
Small amounts of gases may be released; however, such a release can be pre-
vented by appropriate safety measures which are well known from the conven-
tional power plant technology /10-1/. As for any other technical plant, environ-
mental impacts are thus by all means possible; however, they are always limited to
a restricted area and do not have global effects. From our current knowledge they
only have very little impact.
End of operation.
To prevent unwelcome environmental impacts, at the end of
operation the wells need to be properly sealed to permanently exclude penetration
of harmful substances from and to the earth's surface and to prevent a hydraulic
short-circuit of various subterranean layers. Disposal of plant components, in
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