Oxidation of hazardous waste in supercritical water: A comparison of modeling and experimental results for methanol destruction Page: 4 of 18
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Oxidation of organics in supercritical water is a promising technology for the
detoxification of contaminated groundwater and industrial waste streams. Recent
experiments at Sandia National Laboratories conducted in conjunction with an industrial
partner have demonstrated successful clean-up of contaminated water in a supercritical
water reactor.1 These experiments targeted wastes of interest to Department of Energy
(DOE) production facilities and the electronics industry. Because current supercritical
water reactor designs are based on global models and limited experimental data, scale-up
and design optimization remain pressing issues hindering technology development.
Detailed computational models can provide valuable information in these areas.
In supercritical water oxidation (SCWO), organics are oxidized in the presence of a
high concentration of water, at temperatures and pressures above the critical point of water
(374°C and 22.1 MPa). Above its critical point, water has properties that make it an ideal
medium for the oxidation of organic compounds: nonpolar organic molecules are
completely miscible; many inorganic salts become virtually insoluble and may be
precipitated in a controlled manner; oxidation reactions occur at considerably lower
temperatures than in conventional combustion systems; and gas-like transport properties
and liquid-like densities lead to rapid fluid dynamic mixing and compact designs. These
characteristics have been exploited for the destruction of a variety of compounds in several
different SCWO configurations.2-9 An historical review of both supercritical and
subcritical water oxidation is given in Ref. 10, which also presents preliminary system
design and economic analyses for several possible system configurations.
In practice, supercritical oxidation is usually conducted at 400 to 650°C ana
approximately 25 MPa. For treatment of aqueous wastes, SCWO is energetically more
efficient than incineration. More importantly, however, SCWO technology has been
shown1 to be applicable to mixed wastes (wastes that contain chemically toxic organic,
inorganic, and radiological components). These wastes constitute one of the most serious
problems facing DOE production facilities. Cost estimates for long-term storage of one
such mixed waste at Hanford are on the order of fifteen billion dollars. Currently, no
commercial technology exists that will treat mixed waste.
Because of the extremely promising nature of SCWO technology as a technique for
destroying hazardous wastes, a feasibility demonstration was conducted at Sandia National
Laboratories, Livermore in collaboration with several DOE/DP production facilities and
private industry. The objectives of the study were: (1) to determine the feasibility of
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Butler, P.B. (Iowa Univ., Iowa City, IA (United States)); Bergan, N.E.; Bramlette, T.T. (Sandia National Labs., Albuquerque, NM (United States)); Pitz, W.J. & Westbrook, C.K. (Lawrence Livermore National Lab., CA (United States)). Oxidation of hazardous waste in supercritical water: A comparison of modeling and experimental results for methanol destruction, article, March 17, 1991; [Livermore,] California. (https://digital.library.unt.edu/ark:/67531/metadc1093067/m1/4/: accessed March 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.