Inlet gas separation upstream of processing units and compres- sors is far more common for gas
streams as opposed to liquid streams
because of its prevalent and diversified contamination profiles. Similarly,
inlet separation is far more common
in gas processing operations as opposed to refinery activities.
Inlet gas separation is usually con-
ducted through the use of a knock-
out drum equipped with a demister
section, using a mesh pad or a vane
pack. Some plants use horizontal filter
separators with a vane, or cyclonic el-
ements or stages.
All these systems are not entirely
adequate for an effective inlet contaminant removal from sour gas feeds.
These systems are typically designed
for bulk liquids removal and large aerosol droplet sizes. In addition, none of
these devices is really designed for solids separation (usually done effectively
by a wet scrubber or a particle filter).
With the exception of cyclonic sys-
tems and some filter separators that
could remove certain solid particles
and some liquid-like solids, most con-
taminants often enter the gas process-
ing units untouched. Only a minority
number of plants have the necessary
means to adequately condition sour
gas for processing because of the di-
verse nature of its contaminants.
The most difficult and challenging
contaminants in any gas stream are
small aerosols. These are finely di-
vided liquid particles with diameters
ranging from a few hundred microns
to less than 0.1 µ.
Basically, the reason for this ineffi-
ciency is directly related to the aerosol
droplet size distribution and the flow
pattern geometry inside the separator
vessel. In other words, the separation
media is not capable of separating small
liquid droplets. Most aerosols just travel
intact across the vessel without being
separated from the main gas stream.
The vessel design is also fundamental. In some instances, the separation
media could be appropriate; however,
if the liquids removal from the vessel
or the internal flow pattern is deficient,
the vessel will experience considerable decrease in efficiency. Additionally, some defective vessel designs may
actually shatter and disperse liquids in
the gas stream manifested as much
smaller droplet sizes, adding difficulty
to the separation process.
The aerosol contaminant distribution
in a gas stream is primarily in the submicron range. Larger droplets tend to
not be as persistent in the gas stream
since the larger droplets are more likely
to gravitationally separate. Larger droplets are also more likely to shatter as
a result of the shear forces applied to
the droplet surface. When large droplets shatter, they create progressively
smaller droplets until the distribution
is stabilized by the balance between
Natural Gas Contaminants In
Compressor Feeds > Effective strategies must be based on careful evaluations
BY DAVID ENGEL AND MICHAEL SHEILAN
n Figure 1. This graph shows typical liquid aerosol size distribution at the
outlet of a compressed gas stream.
David Engel has more than 20 years of industrial experience and is the inventor in 15
U.S. patents. He recently has focused on new technologies for efficiency, reliability and
throughput increase. Engel is president of the American Filtration & Separations Society
(Southwest Region) and is managing director of Nexo Solutions. Contact him at: david.
firstname.lastname@example.org. Michael Sheilan is a chemical engineer with 32 years of experience in the gas processing industry, primarily in processes and chemicals used in
gas treating. The author of several papers, he is a senior consultant at Amine Experts,
a division of Sulfur Experts.