Page 255 - Petroleum and Gas Field Processing

Taking a diameter of 108 in. and substituting in Eq. (18) (the
retention-time constraint), the height of the water is determined:

ð0:7Þð8000Þð10Þ
H ¼ 2 ¼ 4:8ft
ð108Þ
The height of the skimmer (seam-to-seam length), L s , is given by
L s ¼ H þ 3 ¼ 4:8 þ 3 ¼ 7:8ft

Therefore, the skimmer is 108 in. in diameter and 8 ft high.
Any of the three skimmers will provide the required water treatment.
The final selection depends on cost, availability, and space limitation.

9.6.4 Sizing of Skimmers with PPI

In this case, the oil droplets need only to rise to the underside of plates in
a time t o that is equal to the time it takes the water to travel through the
effective length of the skimmer, t w . We shall assume that the effective
length in the settling process is 70% of the actual length of the PPI pack
and that the plates occupy 10% of the flow area (HW).
ðh=12 cos Þ
t o ¼ ð20Þ
u o
where h is defined as in the notation on page 234. Substituting for u o from
Eq. (1)

h pw
t o ¼ 4:681 s ð21Þ
ð
w
o Þd m cos
The retention time of water is given by

L L s
t w ¼ ¼ 0:7 ð22Þ
u w u w
where
5:61Q pw =ð24 3600Þ ft
u w ¼ ð23Þ
0:9HW s
Therefore,

LHW
3
t w ¼ 9:703 10 s ð24Þ
Q pw

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