916 PCBs AND ASSOCIATED AROMATICS
Thus, the quantity of PCBs adsorbed on the paper
is extremely small relative to the total quantity of PCBs
adsorbed by the paper.
Figure 45 illustrates the effect which processing can have
on mitigating the leaching problem. The data were obtained
using chlorobenzenes as a non-viscous surrogate for PCBs
in order to more easily quantitate any observed leaching.
The completed process allowed permanent reclassification
of the bulk retrofill fluid.
The model used virgin transformer materials impregnated
with chlorobenzenes. The bulk oil was homogenized before
samples were taken and the temperature of the tank adjusted
to 50°C. Samples of impregnated kraft paper were wound into
a coil and immersed in the oil. Several different kinetic runs
were made with different thicknesses of paper as well as dif-
ferent numbers of layers forming the overall wad of paper.
The experimental conditions shown in Figure 45 were
found convenient because a series of complete leachingcurves could be compared over a period of about 30 days
rather than the 300 days found for a 750 KVA transformer. It
is clear that sufficient time had elapsed to be able to compare
a conventional vapor cleaning retrofill system result with the
processing necessary to avoid the leaching problem.
It was found that processing beyond simple vapor
cleaning could be continued to the point where leaching
was completely stopped. In actual practice, however, such
a rigorous level need not be achieved since, if the leach-
ing rate is reduced by, say, an order of magnitude from the
measured value of 1.3 ppm PCB/day then, instead of about
one year of reclassified use, the unit would retain its clas-
sification for ten years. In this example, if the transform-
er’s life-expectancy was only for a further five years then
clearly it would remain reclassified for the remainder of its
useful life. The extent of processing can be tailored to the
level of reclassification required and the life-expectancy of
the transformer.0 100 200 300 400 500 600 700 800
Time (h)
0
200
400
600
800
1000
1200
1400
Chlorobenzene Concn.
(ppm PCBz)
Conventional Retrofill
50% process
90% process
Trichlorobenzene Leaching as a
Less Viscous Surrogate for PCBs
FIGURE 45 The completed process allowed the permanent reclassification of the bulk retrofill fluid.C016_003_r03.indd 916C016_003_r03.indd 916 11/18/2005 1:12:40 PM11/18/2005 1:12:40 PM