Page 204 - Environmental Control in Petroleum Engineering

190 Environmental Control in Petroleum Engineering

are present, they will not be distilled and will form a heavy residual tar
on the solids. For example, distillation may remove only about 65% of
the heavy polynuclear aromatics. Another limitation to distillation is the
high energy costs of heating the materials to a sufficiently high tempera-
ture. An operating temperature of about 800°F may be required for
effective distillation of heavy ends (Young et al, 199la). An operating
temperature of 473°F, however, has proven to be effective in lowering
the hydrocarbon level of cuttings to 10 g/kg (Van Elsen and Smits, 1991),
If the distillation temperatures are high enough, the hydrocarbon
molecules will be broken by pyrolysis, forming coke. This would
solidify the remaining hydrocarbons, preventing their migration upon
disposal of the waste.

Incineration

Another way to remove hydrocarbons from solids is to burn the
mixture in an incinerator. Incinerators are specially designed burners
that can burn the relatively small volume of combustible materials
found in oily solids. Following combustion, the resulting ash, including
any salts and heavy metals, is solidified to prevent leaching of any
hazardous residue. Incineration typically removes over 99% of the
hydrocarbons in the soil.
A significant limitation to incinerators is that they emit air pollu-
tants, particularly metal compounds like barium, cadmium, chromium,
copper, lead, mercury, nickel, vanadium, and zinc. Incineration des-
troys hydrocarbon wastes, but merely changes the chemical form of
heavy metal wastes. Because of the air pollutants emitted, all incinera-
tors require permits. Another limitation to incineration is that a second-
ary fuel is required because the heat content of the hydrocarbons in
many petroleum solid wastes is insufficient for combustion, particu-
larly when a high volume of noncombustible material is present, e.g.,
the solids. The need for secondary fuel increases the cost of operations.
Although incineration is expensive, it has low future liability (Goodwin
and Turner, 1990).

Solvent Extraction

Solvent processes can also be used to separate hydrocarbons from
solids. In these processes, a solvent with a low boiling point is mixed