Page 148 - Petroleum and Gas Field Processing

The volume is also calculated by multiplying the volumetric flow rate by
the retention time; therefore,

5:61 ft 3 3
V o ¼ Q o t o min ft
24 60 min
5:61 ft 3 3
V w ¼ Q w t w min ft
24 60 min
Then,
3
V o þ V w ¼ 3:896 10 ðQ o t o þ Q w t w Þ ð25Þ
From Eqs. (24) and (25), we obtain
2 3
ðH o þ H w ÞD ¼ 8:576ðQ o t o þ Q w t w Þ in: ð26Þ
In summary then, the diameter and seam-to-seam length of vertical three-
phase separators are determined as follows:

1. Determine the minimum diameter that satisfies the water
droplets settling constraint from Eq. (22).
2. Determine the minimum diameter that satisfies the gas capacity
constraint from Eq. (23).
3. The larger of the two minimum diameters determined in steps 1
and 2 is then considered as the minimum allowable vessel
diameter.
4. For various values of diameter larger than the minimum
allowable vessel diameter, use Eq. (26) to determine combina-
tions of diameters and liquid heights.
5. For each combination, determine the seam-to-seam length from
the following:

For D > 36 in.
1
L s ¼ ðH o þ H w þ D þ 40Þ ft ð27Þ
12
For D < 36 in.
1
L s ¼ ðH o þ H w þ 76Þ ft ð28Þ
12
Example 2
Determine the diameter and seam-to-seam length of a three-phase vertical
separator for the following operating conditions:
Oil production rate: 6000 BPD
Water production rate: 3000 BPD

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