Deep Aquifere
Overview
If sufficient groundwater is
present in a depth of 1 to 3 km, it can be worthwhile itself to directly
use the warmth from it. If the temperature reaches or exceeds 100° C,
even the possibility exists of producing electricity!
The opening and use of deep Aquifers to gain warmth for the urban
long-distance heating pipeline nets began in Europe in the 70's, whereby
in France the strongest development of this usage of geothermal energy was
registered. In the other Switzerland-surrounding countries, numerous
plants in Germany, as well as in Austria and Italy can be found.
In regions with normal geothermal gradients, about 30 °C/km, which is
the case in central Switzerland, the temperature in the deep Aquifer of
1km depth is about 40 °C and approximately 70 °C in 2 km depth.
If the water in this depth is only easily mineralized (less than 2 g/l)
and is there the possibility given to derive the water cooled down after
the extraction of heat into a waterstream - river or lake - or a pile then
only one supply-drilling, a so-called Singlette is sufficient. If the
water in this depth should exhibit however a mineral content of over 2
g/l, the cooled-down water must be injected back into the underground with
the help of a second drilling (doublet).
Promoted by a drilling risk warranty of the federation, in the years
1987 to 1998 12 geothermal deep-wells in Switzerland were opened.
Altogether there were five successes, one partial success and six failures
in the sense of the risk warranty - that means “dry” drillings or to
small amount of water supply. One drilling of the six failures could
nevertheless be supplied to a geothermal usage: the drilling in Weissbad
(Canton of Appenzell) was developed as “deep” terrestrial heat probe.
With successfully run of the deep wells the energetically meaningful
use is in the main focus. With the Thermalwatersupply for therapeutic
baths, should be proceeded for example according to the “cascade
principle”. After the use for the actual bath usage (with decreasing
temperatures) also the health establishments themselves and the heating of
greenhouses as a last step, can be done e.g. in Schinznach-Bad
(Canton of Aargau).
Schematic diagram of a geothermal doublet plant
for the use of a deep Aquifer.
Function mode of a doublet plant
Over a supply drilling, warm Thermalwater is pumped with the help of a
submerged pump to the surface, where a heat exchanger and a downstreamed
heat pump are used for the rise to the desired heating temperature. The
heating cycle supplies the consumer in form of a long-distance heating
pipeline. The cooled down water is led back with a injection-drilling into
the Aquifer.
|