Utilisation of Geothermal Energy - Renewable Energy: Technology, Economics and Environment - page 442

tion and the injection well. Additionally, the damage of the production reservoir
with contaminated geothermal fluid, for instance due to the use within public
swimming pools, is impossible. Limitations of such so-called two layer systems
are due to the nonexistent mass balance compensation, and thus to an expected
change within the reservoir pressure. Experience has shown that for reduced pro-
duction volumes of 30 to 60 m 3 /h, production and injection of geothermal fluid
can be performed by a single well.

Uphole part. The aboveground geothermal fluid circuit, i.e. the actual geothermal
heating station connected to the production and injection well, links the available
geothermal energy to the demand for heating, warm water and process heat, which
is subject to significant local and temporal variations. The aboveground geother-
mal fluid circuit has to meet the following requirements:
− production and transfer of geothermal fluid,
− heat transfer to a secondary thermal loop,
− geothermal fluid processing to ensure appropriate injection water quality,
− pressure increase prior to injection,
− injection of geothermal fluid and
− process safety.
The following discussions contain a description of the specific aspects, dimen-
sions and the operation of the aboveground plant, as well as illustrations of the
main components. Fig. 10.5 shows a diagram of the general system layout. How-
ever, we need to keep in mind that the system layout largely depends on the char-
acteristics of the respective geothermal reservoir and thus on the characteristics of
the extracted geothermal fluid.

Fine-mesh filter

M

Heat
ex ch anger

Pressure
maintenance

Coarse filter

M

Injection
pumps

Slop pits

M

Injection well

Production well

Fig. 10.5 Operation principle of the uphole part of the geothermal fluid circuit

Production of geothermal fluid. Geological conditions often require the use of a
pump to produce geothermal fluid. The two basic solutions are either a gas lift,
operating as a siphon, or mechanical pumps.
The use of gas lift according to the siphon principle based on ambient air is
necessarily associated with a ventilation of the geothermal fluids. This might re-
sult in a change of chemical properties and maybe the precipitation of solids.
Therefore gas lifts based on ambient air are generally limited to tests conducted