Environmental Engineering Reference
In-Depth Information
460
change under otherwise unchanged framework conditions (such as installed ther-
mal capacity) with customers showing a demand behaviour different from the
household customers assumed here. Heat supply to industrial enterprises with a
heat consumption constant throughout the overall year (e.g. a dairy) permits for
example to increase the provided heat dramatically (i.e. the number of full load
hours) and reduce the heat production costs accordingly (see Fig. 10.9). Interest
rate and depreciation period also have a major impact on the production costs of
geothermal heat supply systems. In contrast, operation and fuel costs are of minor
importance.
Environmental analysis.
As with any other form of geotechnical utilisation, also
hydrothermal energy generation constitutes an intervention into the natural bal-
ance of the earth's upper crust. The intervention causes energetic and material
changes, mechanical fracture events and, to a lower extent, also mass displace-
ments /10-3/. However, since there are no cavities created by hydro-geothermal
exploitation, the created environmental effects are considerably lower when com-
pared, for instance, to the exploitation of an oil field or even an open top mine.
On this basis, for hydrothermal energy utilisation the following environment
effects are identified /10-5/. For this purpose, it is distinguished between the con-
struction of a geothermal heating station, its normal operation and possible acci-
dents (malfunction) and the end of operation.
Construction.
For well drilling the same processes as for mineral oil and natural
gas exploration or exploitation and water procurement are applied. However,
when constructing a hydrothermal plant this process is the one that is connected
with the greatest environmental dangers. Due to well depths up of to 3,000 m and
above, there is the danger of a hydraulic short circuit of various layers and aqui-
fers, respectively. However, by observing the corresponding regulations devel-
oped for the oil and gas industry, the environmental effects resulting from such a
short circuit can be minimised. The moderately perceptible noise during well drill-
ing only occurs during this time-limited process and not during the operation of
the geothermal heating plant. The additional environmental impacts due to the use
of appliances, intermediate storage of the drilling mud, space consumption for the
drilling rig etc. are restricted to a short period of time and to the site. After drilling
and completion of the well the original state of the area around the well head is
restored.
Normal Operation.
No substances or particles are released during normal opera-
tion of a hydro-geothermal heating plant. All emissions possibly released during
the operation of the heating station at the site of the geothermal plant are attribut-
able to fossil fuel-fired additional plant components or peak-load boilers.
During the operation of geothermal heating stations the water balance within
the used aquifer can theoretically be affected by improper re-injection. This may
lead to a modification of the pore pressure
and - as a consequence - microseisms
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