As indicated, this process has only been demonstrated in the laboratory at a scale of 4 L/day organic throughput. However, a 190 L/day pilot reactor is being developed jointly by MODAR for field tests with actual wastes.
Since the process is still in the bench scale stage, costing of a reasonable scale plant is difficult. For a facility, with a capacity of 10 000 L/day of organic material initial estimates are that minimum capital cost would be approximately $5 200 000 (US). Unit processing costs would be $0.13 - 0.53 minimum for each kg of organic liquid destroyed in the reactor. This process as it pertains to the destruction of hazardous and toxic wastes is in its early development stage; its reliability at a reasonable scale remains to be demonstrated. The technology has been operated at bench scale for the past two years and will undergo pilot plant tests in 1982-83.
The impacts of this technology await further development. However, a significant environmental advantage claimed for the process is that process effluents are minimized; only salt, H2O, CO2 and a small portion of feed organic exit the oxidizer. The salts have been washed in the supercritical fluid and oxygen and should be disposable by ordinary means. (Fluid stream from the oxidizer contains N2 as well if air has been used as the oxidant). The feed organic material in the output steam stream can be managed to very low levels by control of reaction conditions in the oxidizer. Relatively refractory organics such as PCBs and other chlorinated hydrocarbon compounds have been destroyed with efficiencies in the range 99.99 - 99.999%, with oxidizer residence times of 1 minute or less.
Reference: (Oppelt, 1981).
Figure 13 Schematic Diagram Of The Modar Supercritical Water Process (Oppelt, 1981)
Click image to view a full size version.
4.4.3.2 Wet Oxidation, WETOX®, Process
WetCom Engineering Limited
222 Midwest Road
Scarborough, Ontario
M1P 3A9
Contact: Paul Gooderham
(416) 759-8595
The WETOX® process employs air oxidation in water at moderate temperatures in the range of 150 to 250°C, so-called wet oxidation. Wastes are oxidized to water, CO2 and short chain organic acids and alcohols. The process features a horizontal multi-compartmented agitated cascading reactor. Heat is recovered from the waste oxidation and is recycled for reuse.
This technology is very well developed and has been used in various modifications (e.g. Zimpro Process) for a number of years. The wastes treated include most complex organic compounds including difficult to treat chlorinated hydrocarbons. The process was developed at Michigan Technological University in Hougton, Michigan and at Ontario Research Foundation who have produced a mobile WETOX® process in a single van-truck. WETOX® was being evaluated for PCB destruction by the Ontario Research Foundation. The results obtained were not encouraging; destruction efficiency was in the 50-70% range. Long batch times and high temperatures over 250°C that taxed the ORF test equipment. The work was abandoned as a result of unrelated local political problems. Michigan Technological University on the other hand has tested the process on PCB's at higher test temperatures with some encouraging results.
Reference: (Johnston and WetCom Engineering).
4.4.3.3 IT Enviroscience, Catalyzed Wet Oxidation
Head Office: IT Enviroscience
9041 Executive Park Drive
Knoxville, TN 37919
Contact: J. Exner
(615) 690-3211
IT Enviroscience has developed a catalyzed wet oxidation process utilizing lower temperatures in a different reactor configuration than the WETOX® process. The process has been developed on the mini-plant scale and uses batch processing or a combination of continuous and batch processing. Destruction efficiencies are higher than WETOX® and >99% PCB destruction has been achieved in the mini-plant.
An adequate destruction rate was demonstrated such that a total waste processing cost of $4-5/kg (US, 1979, capital plus operating) was suggested in a brief study commissioned by Ontario Hydro. |
