Page 259 - Petroleum and Gas Field Processing

Therefore, either flotation units or SP packs should be used. Let us examine
both options.
1. Using flotation units. Flotation units are normally available as
standard units for a flow rate of 5000 BPD. Because we have
8000 BPD of water to be treated, two units must be used in
parallel. Assume that a four-cell unit is being used and that the
efficiency of the unit is 90%. The quality of the water that could
be treated by the flotation unit is, therefore, determined from

d mo
E ¼ 1
d mi
20

0:9 ¼ 1
d mi
d mi ¼ 200 m
Because this is smaller than the droplet size in the produced
water, a primary treatment of the water is necessary before it can
be treated in the flotation unit. The primary treatment is
required to remove all oil droplets of 200 m and larger. This is
the same as the requirement for Example 1. Therefore, any of
the three skimmers designed in the previous example could be
used. The treatment system could, therefore, consist of a
horizontal cylindrical skimmer 96 in. 17 ft, or a vertical
skimmer of 108 in. diameter by 8 ft high, and two flotation
units in parallel.
2. Using SP packs. The overall required efficiency is first calculated
from
2000 80
E ¼ ¼ 0:96
2000
Assume that we will use the vertical skimmer designed in
Example 1. The droplet size that can be treated in such a
skimmer is 200 mm. Therefore, the efficiency of the SP pack
(assuming it grows 1000-mm droplets) is
200

E SP ¼ 1 ¼ 0:8
1000
From Eq. (32),
n
0:96 ¼ 1 ð1 0:8Þ
n ¼ 2

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