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  • 1. Hellström, Göran
    et al.
    Larson, Sven
    Department of Geology, Earth Sciences Centre, Göteborg.
    Seasonal thermal energy storage: the HYDROCK concept2001In: Bulletin of Engineering Geology and the Environment, ISSN 1435-9529, E-ISSN 1435-9537, Vol. 60, no 2, p. 145-156Article in journal (Refereed)
    Abstract [en]

    A method for seasonal storage of heat or cold in the bedrock (the HYDROCK concept) is presented and its thermal performance discussed. It involves the use of a fractured bedrock at shallow depths (ca. 50-250 m), where existing fractures are stimulated or new fractures artificially created and used as flow-paths for a heat/cold carrier (usually water). The fracture surfaces are used as heat exchangers and the bedrock is loaded and unloaded to suit the energy needs. Propants are injected into the fractures to keep them open and reduce the energy needed for pumping water through the system. Field tests confirm that stacked parallel fractures can be produced by hydraulic fracturing. The thermal performance of the store is modelled and compared with a ducted ground heat store. It is shown that the HYDROCK store may yield 10-20% more energy during extraction than a ducted ground heat store for similar amounts of injected energy. This indicates that the HYDROCK concept is competitive as a seasonal energy store and may be of particular importance as an alternative energy source where existing methods cannot be economically justified.

  • 2.
    Loorents, Karl-Johan
    et al.
    VTI - Statens väg-och transportforskningsinstitut.
    Johansson, Eva
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Arvidsson, Håkan
    VTI - Statens väg-och transportforskningsinstitut.
    Free mica grains in crushed rock aggregates2007In: Bulletin of Engineering Geology and the Environment, ISSN 1435-9529, E-ISSN 1435-9537, Vol. 66, no 4, p. 441-447Article in journal (Refereed)
    Abstract [en]

    Enrichment of free mica (i.e. as monomineralic grains) in the fine fraction of crushed rock aggregates affects the quality of the aggregate end product. Granitoid rock from the Svecofennian Province were used as being representative of crushed rock aggregates commonly used for construction purposes. The results reveal a general trend of enrichment of mica for finer fractions. For the coarse grained rock a peak occurs at 0.25-0.5 mm followed by a decrease in the amount of free mica; for grains <0.063 mm there is an increase. The general trend and peak are correlated to the microstructural characteristics of the samples.

  • 3.
    Loorents, Karl-Johan
    et al.
    Swedish Road Administration, Gothenburg.
    Kondelchuk, Dimitri
    Trends of enrichment of free mica grains in crushed rock aggregates2009In: Bulletin of Engineering Geology and the Environment, ISSN 1435-9529, E-ISSN 1435-9537, Vol. 68, no 1, p. 89-96Article in journal (Refereed)
    Abstract [en]

    The paper reports a study of the behaviour of free mica grains in crushed rock aggregates of metamorphic origin undertaken to identify any typical trends of enrichment with grain size. The mineralogical composition of the various grain size fractions was obtained using a polarizing microscope and point counting. Two general trends of enrichment of mica are presented: Type I (isotropic source rock) and Type A (anisotropic source rock). Type I is associated with a general increase in free mica towards the finer fraction, with or without a peak for "coarser" grain fractions. Type A is associated with an increase in free mica up to a certain grain fraction, after which there is a decrease with progressively smaller grain size.

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