Hydrocarbon Processing - March 2021 - 70

Valves, Pumps and Turbomachinery

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type of trimming device (such as an
orifice plate or a butterfly valve) in
one or both legs of the double-flow
compressors to equalize flow. The
most economical method may be
to install a valve upstream of a Y
splitter to control flow.
Case study. During commissioning,

FIG. 4. Y-type splitter arrangement for a
propylene gas compressor.

FIG. 5. Y-type splitter arrangement for a
double-suction compressor.

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70

MARCH 2021 | HydrocarbonProcessing.com

a double-flow propylene compressor
(FIG. 4) was found to have icing on one
suction nozzle and no icing on the other
prior to compressor startup. After compressor startup, the compressor had low
head pressure and it surged prematurely.
The investigation showed that the inlet
piping caused unequal flow distribution
to the compressor inlet. This resulted in
one section running near surge, while
the other section was operating near the
overload region. The inlet piping to the
compressor was modified to have the
same and symmetrical dimension and elevation. In addition, the Y splitter (FIG. 5)
was installed closer to the compressor
and was modified to have symmetrical
legs and a larger radius at the dividing
point B leg angle (FIG. 3), as well as an
internal coating and identical dimension.
All temperature instruments were relocated upstream of the strainer.

location of the strainer and of the
valve at the suction piping. Using
an individual valve for each leg
is not common practice and will
increase costs. However, to isolate
the compressor immediately after
a seal failure, the proper number
and location of the isolating valves
should be studied and confirmed
by the vendor.
* The minimum instruments at
the suction pipe should be a
temperature gauge/transmitter, a
pressure gauge/transmitter, and
a pressure differential gauge and
transmitter across the strainer. In
addition, a pressure differential
transmitter should be included
to measure the pressure at the
impeller inlet to the pipe upstream
of the compressor flange.
* The need for level transmitters at
each leg close to the compressor
should be studied. If necessary,
add a trap for the strainer bottom.
* It may be required to add some

are imperative when designing the inlet
piping of double-suction compressors.
A Y-splitter design should not be considered as a piping miter, which can be
manufactured onsite during construction.
It is recommended to ask the compressor
vendor to supply and design the Y splitter
and the associated downstream piping,
or to at least review the associated piping
design drawings. The need for an internal
coating of the inlet piping to the compressor should also be studied.
SHAHAB ZARDYNEZHAD is a
registered Senior Mechanical
Engineer, and a certified API
inspector for rotating equipment,
with more than 29 yr of experience
working on many oil, gas and
petrochemical projects. He has
experience in engineering; procurement services;
manufacturing; shop/field inspection; installation;
commissioning; startup; reliability; and the maintenance
and operation of pumps, compressors and turbines.
Mr. Zardynezhad earned a BS degree in mechanical
engineering from the University of Petroleum of Iran,
along with MS degrees in industrial engineering
from the Iran University of Science & Technology, and
in project management and mechanical engineering
from the University of Calgary.
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Hydrocarbon Processing - March 2021

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