Page 258 - Petroleum and Gas Field Processing

SP packs is approximately 1000 mm). The efficiency of the SP pack could
then be determined from

d m
E SP ¼ 1 ð31Þ
d max
Therefore, for n SP packs staged in series, the overall efficiency could be
expressed in terms of the efficiency of the SP pack by
n
E ¼ 1 ð1 E SP Þ ð32Þ

9.6.8 Sizing of Flotation Units
Flotation units manufacturers have various standard units with specific
dimensions and flow rate limitations. The role of the facilities engineer is,
therefore, limited to determining whether flotation units are needed for
the treatment process and the number of units needed. The need for
flotation units depends on the required quality of the treated (effluent)
water. Normally, if the maximum allowable oil droplet size in the effluent
water is about 30 mm or less, flotation units should be considered.
The efficiency of the flotation unit, which is typically between 87% and
94% depending on the number of cells, is then used to determine the
quality (oil concentration, or maximum oil droplet size) of the influent
water that could be treated by the flotation unit from Eq. (29) or (30).
The quality of the influent water is then compared to the quality of the
produced water to determine whether a primary treatment stage is
needed.

Example 2
For the same conditions of Example 1, design the required treatment
facilities such that the treated water does not contain more than 80 mg of oil
per liter of water.

Solution
The maximum oil droplet size that can exist in the treated water is
determined from

ð80Þð500Þ
d m ¼ ¼ 20 m
2000
This size is too small to be separated by skimmers of any reasonable size.

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