Page 179 - Petroleum and Gas Field Processing

This equation gives the terminal settling velocity of the water droplet. For
settling to occur, the upward average velocity of the oil must not exceed the
water settling velocity. The average oil velocity, u o , is obtained by dividing
the oil volumetric flow rate, Q o , by the flow cross-sectional area, A.
Let D be the treater inside diameter in inches and L be the effective
length of the settling/coalescing section in feet. Therefore,
3 5
Q o ðbbl=dayÞ 5:61ðft =bblÞ 1:1574 10 ðday=sÞ
u o ¼
ðD=12ÞL
Q o ft
4
u o ¼ 7:792 10 ; ð12Þ
DL s
Equating u o [Eq. (12)] to u [Eq. (3)], we obtain
Q o o
DL ¼ 436 in: ft ð13Þ
ð
Þd m

Retention Time Constraint
The retention time, t, can be obtained by dividing the volume of the settling/
coalescing section occupied by oil, V o , by the oil volumetric flow rate, Q o .
Assuming that the oil occupies only 75% of the coalescing/settling section,
2
0:75ð D L=4 144Þ
t ¼ 4 min :
5:61Q o 6:944 10 ðday= minÞ
2
Solving for D L, we get
Q o t
2 2
D L ¼ in: ft ð14Þ
1:05
Sizing Procedure
The following procedure is mostly aimed at determining the minimum size
of the coalescing/settling section of the treater and the rating of the burner.
Such information will be very useful in preparing equipment specifications
for vendors and for evaluating the quotations received from the vendors.
The vendors would provide the detailed design and dimensions of the
treater.
1. The first step is to decide on a treating temperature. This is best
determined from laboratory tests. The optimum treating tempera-
ture must provide a minimum loss of oil volume and quality along
with a practical treater size. If laboratory data are not available, the
treating temperature may be determined based on experience. In

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