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Scientists experiment with lime to accumulate and store the heat of the sun

Ivanpah Solar Power Facility, USA: The heat, even on the scale of large solar energy reactors, is suitable for lime as well. Photo: Aioannides / Wikimedia Commons

Implementation could increase demand of limestone / image upgrade for stone branch

Use of limestone for thermal storage is an idea currently under investigation by German scientists at the German Aerospace Center (DLR). The method provides for the overly abundant heat of the sun to be converted chemically and stored in the stone deposits. The method is almost as old as mankind itself: it is based on the principle of lime mortar, to which water is added resulting in a hardening adhesive substance.

Perhaps demand for limestone will increase as a result. But certainly the natural stone branch can boast helping to resolve the energy dilemma.
Scientists are not so much interested in the adhesive properties of quicklime chemically translated into three phases: CaO, Ca(OH)2, and CaCO3.

All eyes are set on the heat-emitting properties when lime comes into contact with water, or slaked. The heat released was previously stored when the lime was fired.

Slaking reverses the procedure freeing the stored energy.

Research projects aim to optimize the chemical reaction and release of thermal energy.

Under laboratory conditions the calcium carbonate is brought into contact with steam on a milligram scale. „What is the best temperature under which pressure to result in optimal conversion?“ are two of the main questions asked by Dr. Antje Seitz of the DLR-Institute of Technical Thermodynamics.

Just as important: how much steam is needed to optimize the reaction. This avoids waste of energy and water.

In the reactor – large scale thermal conversion – more questions arise, i.e. how should the quicklime be spread to optimize contact with steam? What type of heat exchanger is best suited for the job?

Large thermal energy collectors already exist for solar reactors but these operate on the basis of salts. Lime is being examined because its use is much less complex and the substance readily available.

German Aerospace Center, DLR (German)

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(21.09.2016, USA: 09.21.2016)