Page 96 - Petroleum and Gas Field Processing

Solving for the gas velocity, u, gives
TZ 1 ft

u ¼ 0:327Q g ð6Þ
P A g s
where, Z is the gas compressibility at the operating pressure (P) and
2
temperature (T) and A g is the available area for gas flow (ft ).

3.6.5 Liquid Capacity of Separators
The basic relationship that combines the oil flow rate or oil capacity of a
separator, Q o , the volume of separator occupied by oil, V o , and the
retention time or residence time, t,is
3 ! 3
ft V o ðft Þ
Q o ¼ ð7Þ
min tðminÞ
Equation (7) is rewritten in terms of barrels per day instead of cubic feet
per minute:
bbl V o

Q o ¼ 257 ð8Þ
day t
3
where 1 ft /min ¼ 257 bbl/day.

3.6.6 Sizing Vertical Gas–Oil Separators
The size (diameter and height or length) of a separator is normally
determined by consideration of its required capacity for gas and oil as
discussed in the following subsections.

Gas Capacity Constraint
For vertical separators, the upward average gas velocity should not exceed
the downward terminal velocity of the smallest oil droplet to be separated.
This condition is expressed mathematically by equating Eqs. (2) and (6):

1=2

TZ 1 o g d m
0:327Q g ¼ 0:01186
P A g g C d
Substituting for A g from
2
D

A g ¼
4 12

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