Page 187 - Environmental Control in Petroleum Engineering

Waste Treatment Methods 173

6.1.1 Removal of Suspended Hydrocarbons

Suspensions of oil droplets in water (emulsions) can be difficult to
separate because they can be stabilized by the interfacial energy
between the oil droplets and the continuous water phase. A variety of
methods are available to remove suspended droplets from water. These
methods consist primarily of variations of gravitational separation,
filtration, or biological degradation.

Gravity Separation

The first step in the removal of hydrocarbons from water is norm-
ally gravity separation. Through properly selected separator tanks with
skimmers, most free oil and unstable oil emulsions can be separated
from the water. Gravity separation is usually the simplest and most
economical way to remove large quantities of free oil from water.
However, more advanced methods are normally required to separate
stable emulsions.
The first stage of gravity separation is to pass the water through
large tanks to allow the phases to separate. These tanks are commonly
called free water knockouts, wash tanks, settling tanks, or gun barrels.
The effectiveness of these tanks depends on the droplet size and how
long the water is in the tank (Arnold and Koszela, 1990; Arnold, 1983;
Powers, 1990 and 1993). A schematic of a horizontal separator is
shown in Figure 6-1.

Mist Eliminajtor __. _ ^
Gas Out

Inlet

Oil
V Water
u

Water Out
Figure 6-1. Schematic of a horizontal separator.