Geothermal Gas Emission From Hellisheidi and Nesjavellir Power Plants

Emission of geothermal gases is an inevitable part of high temperature geothermal utilization. Annually Hellisheiði and Nesjavellir Power Plants Iceland emit 61800 tons CO2 and 28200 H2S. New regulation set by the government of Iceland in 2010 on H2S concentration in air puts high demands on the geothermal industry in Iceland to lower H2S emission from their power plants. Reykjavík Energy has been working on solution to lower gas emission from its power plants since commissioning of hot water production in Nesjavellir power plant in 1990. Since commissioning of Hellisheiði Power Plant in 2006 that was followed by an increase in H2S concentration in nearby town and communities more focus was put on H2S abatement. Three experimental pilot scale projects have been in planning and operation since 2006. Gas separation station involves separating geothermal gas into soluble (CO2 and H2S) and non-soluble gases (H2, N2, Ar) and two experimental gas re-injection projects SulFix and CarbFix have been or are being carried out. The geothermal gases are dissolved in water and injected into the bedrock. In SulFix the target zone is the >200°C high temperature geothermal system below 800 m and in Carbfix the target zone is 30-80 °C between 400-800 m. Industrial scale injection of geothermal gases is planned in 2014 where around 15% of H2S from Hellisheiði Power Plant will be injected into >200°C formations along with CO2 after dissolution in condensate water from the power plant. Further increase in gas injection from Hellisheiði Power Plant will then be planned based on the experience of that injection. Injection of H2S back into the geothermal system where it came from has to be considered an environmentally benign method of H2S abatement