Fate of Hydrogen Sulfidefrom the Nesjavellir and Hellisheidi Power Plants

Sigurður Magnús GarðarssonProfessor, Civil and Environmental Engineering, University of Iceland

Co-AuthorsSnjólaug Ólafsdóttir, Ph.D., Andrými Consulting

Hrund Ólöf Andradóttir, Professor, University of Iceland

GEORG Geothermal WorkshopReykjavik, 24-25th Nov. 2016

Main Objectives

• Understand what happens to the H2S after it is emitted to the environment from Hellisheidi and Nesjavalla Power Plants

- Which environmental factors have the most impact on the distribution and fate of H2S

• Impacts of meteorological factors on H2S concentration• Spatial distribution of H2S • Natural near field sinks of H2S

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Meteorological Impacts on H2S Concentration

• Concentration at Grensasvegur Measuring Station analyzed

• Focus on events with easterly winds for 2 hours or more

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Impacts of Weather Grensasvegur Measuring Station

• Highest H2S concentration – wind direction from the

east, 54-125°– wind speed < 4 m/s (~2-4

m/s)– temperature < 0°C– very stable air

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Olafsdottir, S., and Gardarsson, S.M. (2013). Impacts of Meteorological Factors on Hydrogen Sulfide Concentration downwind of Geothermal Power Plants. Atmospheric Environment, 77, 185-192. DOI 10.1016/j.atmosenv.2013.04.077

Spatial distributionDownwind of the power plants

• Point measurements • Downwind• 3-4 days each month

2009• Total 44 days measured• 18 events selected for

further analysis

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Northwestward distribution

• Eight events analyzed• Self-similarity• Overlapping• High concentration

− Low wind speed− Stable air− Lack of precipitation

Eastward distribution

• Four events analyzed• Self-similarity• Higher concentration

with smooth surface • Wider plume with

rough surface

Southward distribution

• Six events analyzed• Highest concentration

– Inversion– At bottom of slope

• Concentration rise correlated with end of a mountain pass

• Plumes − followed landscape− deviated from initial

path

Southward distribution

View from Hellisheidi to the SouthOlafsdottir, S., Gardarsson, S.M., and Andradottir, H.O. (2014). Spatial distribution of Hydrogen Sulfide from two Geothermal Power Plants in Complex Terrain. Atmospheric Environment, 82, 60-70. DOI 10.1016/j.atmosenv.2013.10.013

Natural near Field Sinks of H2S

• Identification of main sinks

• 35 km radius • Emission 2012:

20,684 tons

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Box Model

Idealized box model• Center of mass of

emission• Standard Gaussian plume• L = 35 km• A = 110 km2

• Cair = 72 µg/m3

Sink Estimation

Oxidation

• Depleted:143 tons/year (0.69%)

Surface water uptake

• Lake Thingvallavatn• Depleted: 70 tons/year (0.34%)

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Washout

• Henry’s law• Depleted: 46 kg/year

(<0.001%)

Vegetation uptake

• Depleted: 32 tons/year (0.15%)

Soil uptake • Fick’s law• Depleted: 9 tons/year (0.04%)

Five sinks modelled

Sink EstimationTotal depleted within 35 km radius

=> About 99% of the H2S is transported out of the area

  Amount

(tons/year)% of 2012 emission

Oxidation 143 0.69Washout 0.046 < 0.001Dissolved in steam 1.9 0.009Vegetation 32 0.15Soil 9 0.04Lake Thingvallavatn

70 0.34

Total 256 1.2%

Olafsdottir, S., Gardarsson, S.M., Andradottir, H.O. (2014). Natural near Field Sinks of Hydrogen Sulfide from two Geothermal Power Plants. Atmospheric Environment, 96, 236-244. DOI 10.1016/j.atmosenv.2014.07.039

Summary

Point measurements of H2S• Overlapping of the two plumes • Self-similarity on measurement road• Narrower plumes over water• Maximum concentration measured during an

inversion• Plume pathways effect by the terrain

Estimation of H2S sinks• Total H2S depleted: about 250 tons/year • About 99% of H2S transported out of the area• Largest: Oxidation and uptake in Lake

Thingvallavatn• Smallest: Washout with precipitation

Publications

Olafsdottir, S., Gardarsson, S.M., Andradottir, H.O. (2014). Natural near Field Sinks of Hydrogen Sulfide from two Geothermal Power Plants. Atmospheric Environment, 96, 236-244. DOI 10.1016/j.atmosenv.2014.07.039

Olafsdottir, S., Gardarsson, S.M., and Andradottir, H.O. (2014). Spatial distribution of Hydrogen Sulfide from two Geothermal Power Plants in Complex Terrain. Atmospheric Environment, 82, 60-70. DOI 10.1016/j.atmosenv.2013.10.013

Olafsdottir, S., and Gardarsson, S.M. (2013). Impacts of Meteorological Factors on Hydrogen Sulfide Concentration downwind of Geothermal Power Plants. Atmospheric Environment, 77, 185-192. DOI 10.1016/j.atmosenv.2013.04.077

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AcknowledgementsReykjavik Energy Landsvirkjun Energy Research Fund ISORThe Icelandic Meteorological Office The Environment Agency of Iceland The Icelandic Road Administration The Icelandic Institute of National History Belgingur - Institute for Meteorological Research Vedurvaktin – Meteorological consultancy Innovation Center IcelandThe United Nations University Geothermal Training Program The Faculty of Earth Sciences of the University of Iceland The Agricultural University of Iceland The Department of Environment in the City of Reykjavik The Environmental and Health Protection Department of Hafnafjordur, Kopavogur and Gardabaer.

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Andrými ConsultingSnjólaug Ólafsdóttir, Ph.D.

• Environmental Consulting• Assist company and employees in

understanding environmental impact and finds ways to reduce the impact

• andrymi.is

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Thank you

AERMOD Modeling

• Nesjavellir plume partly over water

• Narrower plume • Highest concentration

further from the power plant

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Sink EstimationOxidation

• k = 5.10-12 cm3/molecule.sec• COH = 2.75 .105 molecule/cm3 • Depleted:143 tons/year

(0.69%)• Compared to emission:

insignificant

Surface water uptake

• kw = 36.9 cm/h • Lake Thingvallavatn• Depleted: 70 tons/year

(0.34%)• Compared to emission:

insignificant

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Sink EstimationWashout

• Henry’s law• pH = 5.6, pKa = 6.99• H2S unreactive• Low partial pressure • Total precipitation:

2.27.108 m3/year• Depleted: 46 kg/year

(<0.001%)• Compared to emission:

insignificant

Sulfur in precipitation at Irafoss

2005: Nesjavellir PP increased production; 2006: Hellisheidi PP started production

Sink EstimationVegetation uptake

• Sulfur measured in moss• Depleted: 32 tons/year

(0.15%)• Compared to emissions:

insignificant

Soil uptake

• Fick’s law• Depleted: 9 tons/year

(0.04%)• Compared to emission:

insignificant

Measured S in moss - exponential fit

Olafsdottir, S., Gardarsson, S.M., Andradottir, H.O. (2014). Natural near Field Sinks of Hydrogen Sulfide from two Geothermal Power Plants. Atmospheric Environment, 96, 236-244. DOI 10.1016/j.atmosenv.2014.07.039

Summary of Near Field Sinks

- About 99% of the H2S leave the area