Tackling the Challenge of H2S Emissions

Bjarni Mar JULIUSSON, Ingvi GUNNARSSON, Kristin Vala MATTHIASDOTTIR, Sigurdur H. MARKUSSON, Bjarni BJARNASON, Oli Gretar SVEINSSON, Thor GISLASON, Hildigunnur H. THORSTEINSSON

[Reykjavik Energy, Iceland]

Tackling the Challenge of H2S Emissions Although geothermal power plants produce renewable energy with very little emissions compared to their fossil fuel counterparts, emission of non-condensable gases is an inevitable part of high temperature geothermal power production. The major gases in geothermal fluids are CO2, H2S, H2, N2, CH4 and Ar. Concentration of these gases varies from one geothermal field to another and depends on temperature, composition of fluid and geological setting. Hydrogen sulfide (H2S) levels have been measured in Iceland’s capital, Reykjavik, since 2006 and concentration levels have increased as the Hellisheiđi geothermal power plant, located 27 km east of the city, has expanded. The Hellisheiđi geothermal field was developed in stages with the first units coming online in 2006 and the last in 2011. Hellisheiđi’s nameplate capacity is 303 MWe and 133 MWth. About 1000 kg/sec of geothermal fluid is used in the production cycle and the concentration of non-condensable gases in the steam phase is about 0.4%. In 2014 regulation will take effect in Iceland that lowers the allowable of atmospheric hydrogen sulfide (H2S). The H2S levels stipulated in the regulation are significantly lower than the current World Health Organization guidelines and require the Icelandic geothermal industry to take action to reduce its H2S emissions. To tackle this challenge, three Icelandic energy companies that all produce power from high temperature geothermal fields, Reykjavik Energy, Landsvirkjun and HS Orka, joined forces to develop the best abatement solution. Conventional abatement processes are available where the emitted gases are turned into sulfur and sulfuric acid, for which there is a little demand in Iceland. These conventional solutions are considered to be an expensive option for the Icelandic geothermal industry. It was therefore decided to build on research and development of reinjection methods for CO2 at Reykjavik Energy to develop an abatement method called SulFix. The aim of the SulFix project is to develop a sustainable and environmentally friendly H2S abatement method with lower operation costs than commercially available abatement options. The process dissolves H2S in condensate water and injects it back into the high temperature geothermal reservoir. Once injected, water-rock reactions taking place in the high temperature geothermal reservoir will mineralize the H2S. The method will be tested at industrial scale at the Hellisheiđi Power Plant.

        Topic: Environmental and Societal Aspects Paper Number: 02062
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