Page 188 - Environmental Control in Petroleum Engineering

174 Environmental Control in Petroleum Engineering

Plate separators can be used to improve the separation of oil and
water. These separators consist of a series of closely spaced parallel
plates that allow oil droplets to adhere to the plates, coalesce, and
migrate along them. The closely spaced plates reduce the settling
distance required to separate the oil droplets from the water, Plate
separators are mechanically simple and require little maintenance. They
are relatively large and are not effective for very small oil droplets.
Plate separators can reduce oil concentrations to 2-25 mg/1, with an
average of 15 mg/1 (Simms et al., 1990), and can remove oil droplets
down to about 20-30 micrometers in diameter (Van Den Broek and
Plat, 1991). As summarized in Table 6-1, plate separators can have
operational difficulties under some conditions.
Hydrocyclones can be used to further separate oil and water. A high-
velocity stream is injected tangentially into the conically-shaped
hydrocyclones, creating a vortex. The radial acceleration created in the
hydrocyclone can be several orders of magnitude greater than that of
gravity, and forces the more dense water to the outer edge of the
hydrocyclone and the less dense oil to the center. The oil is then
produced out of one end of the hydrocyclone and the water out of the

Table 6-1
Operational Problems with Oil Separation Equipment
Plate Separators Hydrocyclones Gas Flotation
Plugging of plates Erosion Unable to handle emulsions

Unable to handle
emulsions Corrosion Level control problems
Platform motion Sand buildup Platform motion

Oil slugs Oil slugs
Surge loads Poor froth formation
Interference by treatment chemicals
Poor mechanical durability
Scale/sludge buildup

Operator/maintenance intensive
Source: Simms et al., 1990.