5 Jan 91
Backfilling Packaged Anodes With Coke Breeze.
Although the calculations shown in Sections 2-2 and 2-3 assume
that the packaged ceramic anodes will be buried directly in
the earth, the accepted fail-safe design practice is to bury
the packaged anode canister in a coke breeze backfill.
Backfilling the packaged anodes in coke breeze offers three
advantages. First, it reduces anode-to-ground resistance. A
typical example would be to backfill a 3-in. by 60-in. anode
in a 8-in. diameter by 84-in. long coke breeze column. These
dimensions, d = 0.66 ft and L = 7.0 ft, are then used in
equation 2-8 or 2-10 to calculate resistance-to-earth.
The second advantage of using coke breeze backfill around
packaged anodes is that coke breeze often results in better
compaction then does soil. This also reduces anode-to-ground
resistance and improves anode performance.
The most important reason, however, for backfilling these (as
well as any other) prepackaged anode is that gas-blocking of
the anodes will not occur.
Gases (primarily oxygen) are
released at the anode package surface. These can be entrapped
by the soil at the anode package surface which can prevent
further current discharge by the anode.
The coke breeze
provides a porous media through which these gases can migrate
and dissipate preventing the possibility of gas blocking.