Page 261 - Petroleum and Gas Field Processing

Skim Piles
Due to the complexity of the flow regime in skim piles, no analytical
equation exists for sizing such piles. However, an adequate and simple
equation that is based on field experience, developed in this subsection,
may be used for determining the size of skim pile.
Let L be the length of the submerged section of the pile as
determined from Eq. (35). The length of the baffle section, L b , is then
determined from
L b ¼ L 15 ft ð36Þ

If d is the diameter of the pile (in in.) and assuming that the baffles and oil
collection risers occupy 25% of the volume, the volume occupied by water,
v, is then given by
!
2
D 3
V ¼ 0:75 L ft ð37Þ
b
4 1144
The retention time in the baffle section, t r , is obtained by dividing the
volume, V, by the water flow rate, Q w , which is determined from Eq. (34);
therefore,
V
t r ¼ min ð38Þ
5:61Q w =ð24 60Þ
Experience has shown that a retention time of 20 min is sufficient in
meeting disposal requirements. Therefore, combining Eqs. (37) and (38)
2
assigning a value of 20 to t r , and solving for D L b , we get
2
2
D L ¼ 19:1Q in: ft ð39Þ
b w
SP Piles
The procedure for determining the number of SP packs needed is the
similar to that used for skimmers. A pile diameter is first selected and
the efficiency per SP stage is determined. The number of stages is then
determined from Eq. (32) for an overall efficiency of 90%.

Example 3
2
An offshore production platform having a deck area of 3000 ft produces
4500 BPD of water. Primary and secondary treatment stages are used and
result in a final water quality of 45 mg oil per litre of water, which meets the
offshore disposal requirements. The average rainfall in the area is 1.5 in./h
and the deck is equipped with a 50-gpm washdown hose.

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