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Supercritical Water Oxidation
Supercritical Water Oxidation Technology
Safely Disposes Of Hazardous Wastes
A safer, more economical approach to the
disposal of
wastewater, chlorinated wastes, chemical
weapons,
explosives, and other hazardous materials
has been
discovered. Called Assisted Hydrothermal
Oxidation (AHO),
the process was developed by SRI
International (Menlo Park,
CA), and will be licensed first to
Mitsubishi Heavy
Industries.
Mitsubishi will receive an exclusive
field-of-use license in
Japan for AHO, where the technology will
be used to destroy
polychlorinated biphenyls (PCBs) in large
volumes.
Currently, these hazardous wastes are
disposed by
incineration-a relatively expensive
process that can release
harmful dioxins and other chemicals into
the air. SRI and
Mitsubishi have been collaborating to
commercially advance
AHO since 1995.
The AHO oxidation technology uses a
unique variation of
supercritical water oxidation, an
approach that has been
ardently pursued as an alternative to
incinerators for the
disposal of hazardous waste and military
ordnance for more
than 15 years. However, corrosion of such
disposal units
from acidic gases and salt deposits had
prevented the
widespread commercial or military
adoption of such an
approach, as measures to address the
corrosion problem
were prohibitively expensive.
SRI's patented innovation exploits the
special properties of
pressurized, superheated liquid water
("supercritical"
water) to decompose hazardous wastes to
undetectable
amounts. This process is augmented by
adding nontoxic
sodium carbonate: an inexpensive, readily
available
catalyst/reagent. This enhancement to the
technology
eliminates corrosion and accelerates
oxidation rates within
the reaction chamber such that smaller
and less-expensive
units may be constructed. Additionally,
the SRI design is
constructed from inexpensive materials
and operates at a
lower temperature than conventional
supercritical water
oxidation processes. Because of this, the
technology is
cheaper to operate than current
incineration methods.
In a pilot plant, Mitsubishi Heavy
Industries successfully
demonstrated that the AHO technology
could destroy PCBs.
By heating PCBs in water to 380°C at 270
atm and
introducing certain inexpensive
catalysts, harmful chlorine
was recovered as sodium chloride (common
table salt) and
organic carbon was converted to carbon
dioxide and water.
Mitsubishi will use the technology in
commercial plants to
decompose very large volumes of PCBs in
concentrated form
and in solution with other materials such
as transformer oil.
Mitsubishi's current designs reduce these
substances to
concentrations of three ppb at greater
than 99.9999%
removal efficiency. Designs for future
plants are expected
to achieve detection limits of 0.5 ppb in
the near future.
Mitsubishi also anticipates lower overall
operating costs, as
the SRI system uses easily obtainable
parts and consumes
less electricity than do conventional
waste-disposal
methods.
SRI International is one of the world's
largest independent
research, technology development, and
consulting
organizations. Founded in 1946 as the
Stanford Research
Institute, SRI has been meeting the needs
of strategic,
global markets for more than 50 years. As
part of its
strategy to bring its technologies to the
marketplace, SRI
licenses technologies, forms strategic
technology
partnerships, and creates spin-off companies.
For more information, call 650-859-4042.