Jökull - 01.12.1961, Side 58

U. N. CONFERENCE ON NEW SOURCES OF ENERGY, ROME 1961:
Utilization of Geothermal Energy for Heating Purposes
and Combined Schemes Involving Power Generation,
Heating and/or By-Products1)
BY GUNNAR BODVARDSSON
(1) JNTRODUCTION.
The following report has been compiled for
the purpose of giving a brief review of the cur-
rent development in the utilization of geother-
mal energy for space and industrial heating
including combinecl schemes involving power
generation and the recovery of by-products.
The report is largely based on papers presented
for agenda item II. A. 3 of the Conference.
The coverage of the papers presented for
agenda item II. A. 3 is rather restricted. Some
interesting topics are not discussed. The present
report is therefore going somewhat beyond the
coverage of the papers and contains a few sup-
plementary remarks and sections.
(2) GEOTHERMAL RESOURCES AND
THE MARKET FOR HEAT.
Thermal areas are sources of energy which in
many cases can be produced at low cost, but
which is characterized by relatively low tempera-
tures and especially by a low transportability.
These properties are fundamental to any dis-
cussion of the utilization of geothermal resour-
ces.
Inclividual thermal areas are characterized by
the reservoir temperature. This figure repre-
sents the upper limit to the temperature of the
fluid that can be producecl by drilling. The
production temperature will, in fact, always be
below the reservoir temperature.
The highest reservoir temperatures have been
recorded in the large thermal areas in Iceland,
Italy and New Zealand. It is remarkable that
three major thermal areas now being exploited,
that is, the Hengill in Iceland, Larderello in
1) General Report on Conference Agenda Item II.A.3.
Italy and Wairakei in New Zealand, all appear
to have a reservoir tempreature in the range
230° C to 250° C. The geologial conditions in
the areas are nevertheless quite different. These
areas, having the highest temperatures on re-
cord, are potent sources of natural stearn at pres-
sures up to around 20 atomspheres and tempera-
tures up to arouncl 200° C.
Other thermal areas have considerably lower
temperatures. Two important large tliermal
areas in Iceland, which will be mentioned be-
low, produce water at an average as low as 87°
C and 114° C respectively.
The geothermal energy is therefore applicable
only to low-temperature industries as space
heating, low-pressure power generation and
some low-temperature process heating.
Space heating can be carried out bv means of
water at a temperature as low as 50° C. Any
large scale generation of power, on the other
hand, has to be carriecl out by natural steam.
Also, process lieating in the chemical industry
would in most cases require steam or water at
temperatures around or above 100° C.
It is therefore clear that space heating is a
very suitable market for geothermal energy.
Moreover, heat for this purpose can also be
made available as a by-product to power gener-
ation processes basecl on geothermal energy.
The low transportability of geothermal fluids
constitutes the greatest diffculty encountered in
space heating by means of geothermal resources.
This is illustratecl by the fact that one kilo-
gramme of natural steam at one atomsphere abs.
and 100° C contains only 540 kilogramme cal-
ories of latent heat. The implications will be
discussed below.
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