Supercritical water

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Supercritical water (also supercritical water or scH 2 O , from English supercritical ) is water in a fluid state above its critical temperature and its critical pressure - i.e. beyond the critical point .

Above the critical point, it is not possible to differentiate whether a substance is liquid or gaseous; it is dense like a liquid, but has the same viscosity as a gas. In order to reach the supercritical state, the water must have a temperature of at least 374.12 ° C and a pressure of at least 22.1 MPa (221 bar) - around 218 times normal air pressure.

Phase diagram of water. At temperatures and pressures above the critical point, one speaks of supercritical water .

Properties and use

Supercritical water has significantly different properties than under normal conditions . It has the density of normal water and the viscosity of water vapor.

It is used as a solvent in the decomposition of electronic waste, radioactively contaminated soil, many organic compounds and other problematic substances. Salts that dissolve in normal water are not soluble in supercritical water.

Supercritical water is used in the steam process in around 500 coal-fired power plants worldwide . The live steam reaches temperatures of up to 580 ° C and pressures of around 270 bar and thus the supercritical state. Power plants with supercritical live steam temperatures of 700 ° C and pressures of 350 bar are under development. The use of supercritical water in nuclear power plants is still the subject of research, cf. supercritical light water reactor .

history

The phenomenon of supercritical fluids has been known since 1822. At that time, Baron Charles Cagniard de la Tour discovered the existence of a critical temperature above which the liquid / gaseous phase boundary of a liquid enclosed in a pressure vessel disappears. In 2005, supercritical water was found in the Atlantic Ocean where it emerges from two hydrothermal vents.

literature

  • M. Bernabei, A. Botti, F. Bruni, MA Ricci, AK Soper: Percolation and three-dimensional structure of supercritical water . In: Physical Review E . tape 78 , no. 2 , 2008, p. 021505 , doi : 10.1103 / PhysRevE.78.021505 .
  • AG Kalinichev, SV Churakov: Size and topology of molecular clusters in supercritical water: a molecular dynamics simulation . In: Chemical Physics Letters . tape 302 , no. 5-6 , 1999, pp. 411-417 , doi : 10.1016 / S0009-2614 (99) 00174-8 .
  • Katharina Truninger: Supercritical water. In: Horizons. No. 83, 2009, p. 28, PDF ( Memento from October 29, 2013 in the Internet Archive ).

Web links

Individual evidence

  1. ↑ a b Marc-Denis Weitze: Surprises from 374 degrees Celsius ( memento from October 6, 2011 in the Internet Archive ). Neue Zürcher Zeitung, September 13, 2006.
  2. ↑ welt.de: Supercritical water dissolves electronic waste , May 6, 1997.
  3. ↑ Klaus Jacob: Energy generation - energy from the devil's kitchen. In: Zeit Online. August 3, 2009, accessed March 17, 2012 .
  4. ↑ a b Modern steam power plants. Section 700 ° C technology . In: BINE Information Service. Fachinformationszentrum (FIZ) Karlsruhe, accessed on March 17, 2012 .
  5. ^ Vogt Bastian: Analysis of a pressurized water reactor with supercritical water as a coolant. Dissertation Univ. Stuttgart, 2009.
  6. ↑ Catherine Brahic: Found: The hottest water on Earth , New Scientist, August 4, 2008