Encyclopedia of Environmental Science and Engineering, Volume I and II

PCBs AND ASSOCIATED AROMATICS 915

to be reclassified and also at 110°C representative of the top

oil temperature. The following table shows results obtained

for two different types of dielectric papers (Table 41).

X/M  1.32.C0.784 for diamond paper at 50°C

X  200 g.

1.2e-8

1.0e-8

8.0e-9

6.0e-9

4.0e-9

2.0e-9

0.0e+0

–2.0e-9

0 2 4 6 8 10

PCB Contaminated

Non-PCB

Diffusion Coefficient

(cm

2 /sec)

Depth of Cleaned Layer (cm)

Depth of Cleaned Layer to Obtain

Reclassification in 90 days

FIGURE 44 For diffusion coefficients  10 ^8 cm^2 /sec the depth of the cleaned layer to prevent bulk oil

contamination becomes impossibly large.

TABLE 41

Freundlich Adsorption Coefficients

Freundlich coefficients

Paper Temperature (°C) kn

Dicy 50 0.49 1.05

110 2.75 0.77

Diamond 50 1.32 0.78

110 0.04 1.22

In other words, even if the transformer can be reclassified as

non-PCB at the end of 90 days operation, it is likely that it

will have to be considered as PCB contaminated very soon

afterwards and that it will become a PCB transformer again

in less than one year.

The relative importance of the adsorption of PCBs to

their absorption can be assessed as follows.

The Freundlich adsorption isotherm is represented by

the equation,

X

M

=⋅kCn

(17)

where X and M are the masses of adsorbate and adsorbent,

respectively and ‘ k ’ and ‘ n ’ are Freundlich coefficients. C is

the equilibrium value of the PCB in the bulk oil.

Experiments were conducted at 50°C since this is the tem-

perature required by the EPA when a retrofilled transformer is

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