Page 98 - Petroleum and Gas Field Processing

The velocity, u, is given by Eq. (2) and is a function of C d . Therefore,
C d could only be determined by an iterative procedure as follows:
1. Assume a value for C d (a value of 0.34 could be used as a first
assumption).
2. Calculate the velocity, u, from Eq. (2).
3. Calculate Re from Eq. (11).
4. Calculate C d from Eq. (10) and compare to the assumed value.
5. If no match is obtained, use the calculated value of C d and repeat
steps 2–4 until convergence is obtained.

Oil Capacity Constraint
The oil has to be retained within the separator for a specific retention
time, t. The volume of separator occupied by oil, V o , is obtained by
multiplying the cross-sectional area by the height of the oil column, H
(in.). Equation (8) could, therefore, be rewritten as
2

1
D H bbl
Q ¼ 257 ð12Þ
o
4 12 12 t day
or
2
D H ¼ 8:565Q o t in: 3 ð13Þ
Sizing Procedure
In summary then, the size (diameter and seam-to-seam length or height) of
a vertical separator is determined as follows:
1. Equation (9) is used to determine the minimum allowable vessel
diameter.
2. For diameters larger than the minimum, Eq. (13) is used to
determine combinations of D and H.
3. The seam-to-seam length, L s , for each combination of D and H is
determined using one of the following expressions as appropriate:
D < 36 in.
H þ 76
L s ¼ ft ð14Þ
12
D >36 in.
H þ D þ 40
L s ¼ ft ð15Þ
12

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