The application of titanium for treatment of hazardous and toxic wastes by wet air oxidation (WAO) is discussed. Process equipment utilized in 10.9 to 54.5 m3/day (2 to 10 gal/min) WAO units is illustrated. These systems typically operate at 250 to 300°C and 10.4 to 15.2 MPa (1500 to 2200 psig). Laboratory autoclave corrosion studies used to determine compatible materials of construction for WAO applications are described and results of these tests on representative wastes are presented. Results on titanium are compared with other candidate materials of construction.
Field experience obtained with Grade 2 titanium at a California Class I landfill site that uses WAO to detoxify hazardous wastes is presented. Results of autoclave corrosion tests, run on actual waste feed samples, are compared to in-line reactor specimens. Types of wastes treated and tested were those containing cyanides, phenols, sulfides, and pesticides.
Advantages of using Grade 12 titanium over Grade 2 for WAO toxic waste treatment are discussed. Some initial fabrication and forming problems encountered with Grade 12 are presented. The effects of surface conditions on successful forming and welding of Grade 12 were found to be significant. Adequate pickling of the starting base material was the most critical variable. The first toxic WAO unit constructed of Grade 12 titanium is illustrated, and a comparison of various fittings constructed of Grade 2 and Grade 12 is made.