Jökull - 01.12.1961, Page 62

does not precipitate much scale if free of oxy-
gen. However, contamination with air may
result in a rather rapid scaling, e g. clogging
of radiators after a period of a few years. The
scale appears to be formed by a corrosion of
the steel piping. Pitting is also observed in the
pipes. Steel-plate radiators appear especially
vulnerable, ancl should not be used in any
heating system with clirect use of thc thermal
water.
Third, water issued at 100° C or at higher
temperatures contains silica in excess of 150
ppin. Water of this type may precipitate scale
rather rapidly and should not be used directly.
On the other hand, the mixure of water and
steam issued by wells in the high-temperature
thermal areas does not appear to cause much
corrosion of steel piping and other equipment
built of steel. The external corrosion of the
equipment is more of a problem. Special care
shoulcl be taken in preventing leaks.
Some thermal waters in Iceland are conta-
minatecl by sea-water and contain several hund-
red ppm of sodium chloride. These waters are
more corrosive than the ordinary thermal waters.
(5) PROCESS HEATING.
Process heating is a possible market for geo-
thermal energy. But development in this íield
is impeded by the low transportability of the
geothermal energy as well as of the necessary
raw materials. The geothermal resources are
generally located in areas with no supply of
raw materials suitable for an economical low-
temperature processing.
Lindal (G/59) discusses briefly the problems
involved and concludes that the transportability
of the energy is less than that of the possible
raw materials and products.
As of now tliere are no reports on important
practical uses of geothermal energy for process
heating. On the other hand, the possibilities
in this field have been the subject of a study
carried out by the State Electricity Authoritv in
Iceland. Some of the cases investigated are dis-
cussed by Linclal (G/59). The following gives a
brief review of these and other possibities in this
field.
(a) Production of heavy water.
The production of heavy water (D20) by the
dual temperature H2S process is no doubt one
of the chemical processes that should constitute
the best market for geothermal energy. The raw
material is water and the unit price of the pro-
duct is very high. The consumption of heat by
the process is exceptionally high, or about 6,000
units weight of steam per unit weight of the
product. The steam lias to be available at about
6 atmospheres abs.
A study carried out by the Iceland Nuclear
Science Commission indicates that it should be
possible to operate a large heavy water plant in
Iceland. The estimated price of the product is
considerably below the price estimated for sim-
ilar plants if erected in Western F.urope ancl
operated by ordinary fuel.
However, as of now the future market for
heavy water is rather uncertain. The erection of
a plant does not appear to be warranted at the
present situation.
(b) Production of fresh water.
Another rather obvious use of geothermal
energy is the production of fresh water in arid
regions where unpotable water and geothermal
energy are available. This is a relatively simple
process and does not need further comments.
(c) Production of salt and other materials from
brines and sea-water.
There has been some interest in Japan and
Iceland in the production of salt and other
materials from sea-water by means of geother-
mal 'energy. Both conuntries have to import
considerable quantities of salt.
i) Salt production in Japan. Mizutani (G/7)
gives a review of the development in Japan.
Salt production by geothermal energy was
initiated in 1940 and reached in 1958 its maxi-
mum output of 21,000 tons/year. However,
production cost turned out quite liigh, i. e. 16
to 22 S/ton which is above the price of imported
salt. The industry is now largely abandoned.
Most of the Japanese salt plants are open
systems where the sea-water is evaporated in
open pans or ponds, depending wheather hot-
water or natural-steam is used as the heating
medium. The ponds are used as crystallizers.
A typical pond operating with natural-steam is
10 to 20 meters long, 4 to 5 rneters wide and
0.3 to 0.5 meters deep. Optimum evaporation is
one ton/hour for 50 to 80 square meters of
surface.
A few Japanese salt plants use triple-effect
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