Environmental effects of supercritical water oxidation (SCWO) process for treating transformer oil contaminated with polychlorinated biphenyls (PCBs)

Our research was carried out with an aim of the design of a commercial plant to treat “Transformer oil contaminated with polychlorinated biphenyls (PCBs)” by a supercritical water oxidation (SCWO) process. The optimal destroying conditions were determined with a lab-scale facility, then designed and manufactured a pilot plant facility of 30 kg/h capacity. After finishing pilot plant tests, dioxin, NO, NO2 and N2O were analyzed to estimate environmental effects of SCWO process treating transformer oil contaminated with PCBs in and around the pilot plant. As the concentration of dioxin was ∼0.09 pq TEQ/m3 at four different measuring points, we concluded that our SCWO process could be utilized to treat the transformer oil contaminated with PCBs. In addition, as we have a plan to use the oxygen made from air instead of pure oxygen as an oxidant in commercial plants, a mixed gas with 92% oxygen and 8% nitrogen was tested. The sample was collected from the exhaust system, and estimated the effects of the mixed gas on the SCWO process. The total concentrations of NO, NO2 and NOx that were measured were less than 5 ppm and N2O was not detected. As a result, we could ascertain the possibility of the mixed gas prepared from air as an oxidant.