The utility of waters from the high-temperature areas in Iceland for space heating as determined by their chemical composition

Abstract

Geothermal waters from the high-temperature areas in Iceland cannot, as a rule, be used directly for space heating or domestic purposes. It is their chemical composition which makes them unsuitable for direct use and the components that are relevant include silica, hydrogen sulphide, carbon dioxide, calcium, and, for three high-temperature areas, too high salinity. In order to exploit the thermal energy from the high-temperature waters for space heating, this energy has to be transferred into fresh ground water by means of heat exchangers. Pilot plant tests and chemical thermodynamic calculations indicate that suitable thermal water for space heating can be produced by mixing steam flashed from high-temperature waters directly with fresh ground water. The fresh water must be heated to 110–130°C so it can be degassed by subsequent flashing to 100°C. The quality of the heated water formed by this method depends on the hydrogen sulphide and carbon dioxide content of the steam and the overall composition of the fresh water. The components in the fresh water that are particularly significant include total carbonate and pH. Fresh water heated directly with steam from the typical non-saline high-temperature hydrogen sulphide bearing waters would be too high in hydrogen sulphide to be suitable for domestic use as suggested by the thermodynamic calculations. Possibly the fresh water could be treated after heating to lower its hydrogen sulphide content to an acceptable level.