Page 253 - Petroleum and Gas Field Processing

respectively, and the oil specific gravity is 0.87. It is required to treat the
produced water to reduce it oil content to 800 mg/L.
Taking the retention time as 10 min, determine the dimensions of (1)
horizontal cylindrical skimmer, (2) horizontal, rectangular cross-section
skimmer, and (3) vertical cylindrical skimmer to provide the required
treatment.

Solution
The first step is to determine the size of the oil droplet that must be
removed to achieve the required treated water quality. Because the
relationship between the oil droplet size and concentration is approxi-
mately linear, the droplet diameter, d m , that must be removed is obtained
from

800
d m ¼ 500 ¼ 200 mm
2000
1. Horizontal Cylindrical Skimmer. The dimensions of the skimmer
must satisfy both settling and retention time constraints, Eqs. (5)
and (7), respectively. Using Eq. (5),
ð1000Þð8000Þð1:1Þ
DL ¼ 2
ð1:07 0:87Þð200Þ
DL ¼ 1100 ðE1Þ
Using Eq. (7),

2
D L ¼ð1:43Þð8000Þð10Þ¼ 114,400 ðE2Þ
Assuming various values for D and determining the correspond-
ing values of L from Eqs. (E1) and (E2) the following table is
constructed:

Settling Eq. (E1) Retention time [Eq.(E2)]
D (in.) L(ft) L s (ft) L(ft) L s (ft)
60 18.33 24.44 31.78 42.26
72 15.28 20.36 22.07 29.35
84 13.10 17.46 16.21 21.56
96 11.46 15.27 12.41 16.51
108 10.19 13.58 9.81 13.05
120 9.17 12.22 7.94 10.57

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