Page 101 - Petroleum and Gas Field Processing

(diameter and seam-to-seam length) of a horizontal separator is
determined as follows:
5. Assume various values for the separator diameter, D.
6. For each assumed value of D, determine the effective length, L g ,
that satisfies the gas capacity constraint from Eq. (19) and
calculate the seam-to-seam length, L s , from

D
L s ¼ L g þ ft ð21Þ
12
7. For each assumed value of D, determine the effective length, L o ,
that satisfies the liquid capacity constraint from Eq. (20) and
calculate the seam-to-seam length, L s , from

4
L s ¼ L o ft ð22Þ
3

8. For each value of D used, compare the values of L g and L o to
determine whether the gas capacity constraint or the oil capacity
constraint governs the design of the separator. Of course, the
larger required length governs the design.
9. Select reasonable combinations of D and L s such that the
slenderness ratio SR is in the range of 3–5. The cost and
availability would then determine the final selection.
The above equations and sizing procedures are very sufficient for
the determination of separator diameter and length as well as for the
performance evaluation of existing separators. The students and
practicing engineers should be familiar with such design equations and
procedures before attempting the use of commercially available software.
The retention time is an important parameter in designing gas–oil
separators. It is best obtained from laboratory tests that simulate the
field operating conditions. This, however, may not always be available. In
such cases, experience and data from offset fields, if available, will be
very valuable.
On the commercial side, computer programs for sizing gas–oil
separators have been developed by Ellis Engineering Inc. [1]. Capacity
curves based on computer programs have been introduced as well by
Smith and Ellis [1]. These curves are suitable for preliminary sizing for
estimating gas and liquid capacities.
For spherical separators, curves have been developed [5] for sizing
gas capacity as illustrated by the diagram given in Figure 18.

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