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Microstructural and chemical variation in silica-rich precipitates at the Hellisheiði geothermal power plant

Published online by Cambridge University Press:  05 July 2018

D. B. Meier ,
E. Gunnlaugsson ,
I. Gunnarsson ,
B. Jamtveit ,
C. L. Peacock  and
L. G. Benning
D. B. Meier*
Affiliation:
Cohen Geochemistry Group, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
E. Gunnlaugsson
Affiliation:
Reykjavik Energy, 110 Reykjavik, Iceland
I. Gunnarsson
Affiliation:
Reykjavik Energy, 110 Reykjavik, Iceland
B. Jamtveit
Affiliation:
Physics of Geological Processes, Department of Geoscience, University of Oslo, 0316 Oslo, Norway
C. L. Peacock
Affiliation:
Cohen Geochemistry Group, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
L. G. Benning
Affiliation:
Cohen Geochemistry Group, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK GFZ German Research Centre for Geosciences, Helmholz Centre Potsdam, Telegrafenberg, 14473 Potsdam, Germany
*
* E-mail: eedbm@leeds.ac.uk
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Abstract

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Precipitation of amorphous silica (SiO2) in geothermal power plants, although a common factor limiting the efficiency of geothermal energy production, is poorly understood and no universally applicable mitigation strategy to prevent or reduce precipitation is available. This is primarily due to the lack of understanding of the precipitation mechanism of amorphous silica in geothermal systems.

In the present study data are presented about microstructures and compositions of precipitates formed on scaling plates inserted at five different locations in the pipelines at the Hellisheiði power station (SW-Iceland). Precipitates on these plates formed over 6 to 8 weeks of immersion in hot (120 or 60ºC), fast-flowing and silica-supersaturated geothermal fluids (~800 ppm of SiO2). Although the composition of the precipitates is fairly homogeneous, with silica being the dominant component and Fe sulfides as a less common phase, the microstructures of the precipitates are highly variable and dependent on the location within the geothermal pipelines. The silica precipitates have grown through aggregation and precipitation of silica particles that precipitated homogeneously in the geothermal fluid. Five main factors were identified that may control the precipitation of silica: (1) temperature, (2) fluid composition, (3) fluid-flow regime, (4) distance along the flow path, and (5) immersion time.

On all scaling plates, a corrosion layer was found underlying the silica precipitates indicating that, once formed, the presence of a silica layer probably protects the steel pipe surface against further corrosion. Yet silica precipitates influence the flow of the geothermal fluids and therefore can limit the efficiency of geothermal power stations.

Keywords

silicaprecipitatesscalinggeothermal powerIceland
Type
Research Article
Information
Mineralogical Magazine , Volume 78 , Issue 6 , November 2014 , pp. 1381 - 1389
Creative Commons
Creative Common License - CCCreative Common License - BY
© [2014] The Mineralogical Society of Great Britain and Ireland. This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY) licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2014

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