Page 239 - Petroleum and Gas Field Processing

the height of the oil pad may be controlled by an interface level controller
or by an external water leg. The treated water is withdrawn from the
skimmer at the bottom of the vessel. The liberated gas leaves the vessel at
the top through a mist extractor.
Figure 2 shows a schematic of a vertical skimmer that is equipped
with an inlet spreader and a water outlet collector, which work to even the
distribution of the incoming and outgoing flow, respectively. As with the
horizontal skimmers, the produced water enters the vessel below the oil–
water interface. Water flows downward while the oil droplets rise upward
to the oil pad. Because of this countercurrent flow of the water and oil,
vertical vessels are generally less efficient than horizonal vessels. The oil is
skimmed over the weir into the oil collection section, where it is withdrawn
from the vessel. The water outlet is at the bottom of the vessel through the
water collector. The liberated gas leaves at the top of the vessel through a
mist extractor.
Vertical vessels are preferred over horizontal vessels when treating
water containing sand or other solids. A sand drain at the bottom of the
vertical vessel always provide a simpler and more effective means for

Figure 2 Vertical skimmer schematic.

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.