Page 92 - Petroleum and Gas Field Processing

operational problems:
1. Foam will occupy a large space in the separator that otherwise
would be available for the separation process; therefore, the
separator efficiency will be reduced unless the separator is
oversized to allow for the presence of foam.
2. The foam, having a density between that of the liquid and gas,
will disrupt the operation of the level controller.
3. If the volume of the foam grows, it will be entrained in the gas
and liquid streams exiting the separator; thus, the separation
process will be ineffective. The entrainment of liquid with the
exiting gas is known as liquid carryover. Liquid carryover could
also occur as a result of a normally high liquid level, a plugged
liquid outlet, or an undersized separator with regard to liquid
capacity. The entrainment of gas in the exiting liquid is known as
gas blowby. This could also occur as a result of a normally low
liquid level, an undersized separator with regard to gas capacity,
or formation of a vortex at the liquid outlet.
Foaming problems may be effectively alleviated by the installation of
defoaming plates within the separator. Defoaming plates are basically a
series of inclined closely spaced parallel plates. The flow of the foam
through such plates results in the coalescence of bubbles and separation of
the liquid from the gas.
In some situations, special chemicals known as foam depressants
may be added to the fluid mixture to solve foaming problems. The cost of
such chemicals could, however, become prohibitive when handling high
production rates.

Vortex Breaker
A vortex breaker, similar in shape to those used in bathroom sink drains,
is normally installed on the liquid outlet to prevent formation of a vortex
when the liquid outlet valve is open. The formation of a vortex at the
liquid outlet may result in withdrawal and entrainment of gas with the
exiting liquid (gas blowby).

Sand Jets and Drains
As explained in Chapter 1, formation sand may be produced with the
fluids. Some of this sand will settle and accumulate at the bottom of the
separator. This takes up separator volume and disrupts the efficiency of
separation. In such cases, vertical separators will be preferred over
horizontal separators. However, when horizontal separators are needed,

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