Hydrocarbon Processing - March 2022 - 90

Valves, Pumps and Turbomachinery
be lowered to any required value based
on the coupling separation gap set at installation.
The magnetic coupling takes
up a large amount of space compared
to other traditional rigid or flexible
couplings. This challenges vertical submerged
lube oil pumps where space at
the coupling section is restricted.
Resizing pressure control/adding
recycle line. This option is applicable
to systems that require a similar flow
but at a lower pressure requirement
(e.g., removal of seal oil). Resizing the
backpressure control valve to reduce the
oil header pressure will result in lower
power demand from the pump. This
option solves some obsolescence issues
for high-pressure wet seal compressors,
as high-pressure oil controllers are no
longer manufactured and almost all new
compressors are equipped with dry gas
seals. In some cases, an additional recycle
line with an orifice can be a more
economical solution to avoid replacing
the backpressure controller while maintaining
the controllability range of the
existing valve.
Pump resize. This option is the last
resort since it requires the largest investment,
but it can be economically
justified based on the size of the pump,
energy cost, pump reliability and maintenance
cost history.
FIG. 2. Rotary oil pump. Courtesy of
Magnadrive.
Case study. A 28,000-hp steam turbine
driving a gas compressor in a gas
plant was upgraded from hydraulic to
electronic governor, while the compressor
was upgraded from oil seal to dry gas
seal. The machine was equipped with
a combined lube-control-seal oil system.
The combined system's rotary oil
pump rated capacity is 229 gpm (gal/
min) and is driven by a 100-hp motor
at 1,800 rpm, while the combined oil
system header is controlled at 300 psig.
Without the governor and seal oil, the
current system only requires lubricating
oil to the bearings, which need only 118
gpm of oil at 20 psig.
Replacing the existing motor with
one of the same frame size but with
two-thirds of the speed (1,200 rpm)
would yield two-thirds of the rated flow
(152 gpm), which is the required flow
to the bearings plus a 25% margin. The
header pressure could be lowered to approximately
100 psig, which will be controlled
further to 20 psig at the bearings.
These changes would reduce the power
requirement on the motor from 100 hp
to 25 hp. This optimization solution
results in 75% yearly power savings by
replacing the motor with a lower-speed
model and reducing the discharge pressure
on the pump.
LITERATURE CITED
NEW VERSION
InstruCalc
CONTROL VALVES * FLOW ELEMENTS * RELIEF DEVICES * PROCESS DATA
InstruCalc 9.0 calculates the size of control valves, fl ow elements
and relief devices and calculates fl uid properties, pipe pressure loss
and liquid waterhammer fl ow. Easy to use and accurate, it is the only
sizing program you need, enabling you to: size more than 50 diff erent
instruments; calculate process data at fl ow conditions for 54 fl uids, in
either mixtures or single components, and 66 gases; and calculate the
orifi ce size, fl owrate or diff erential range, which enables the user to
select the fl owrate with optimum accuracy.
Updates include Engineering Standard Upgrades and
Operational Improvements in InstruCalc Version 9.0
Please contact J'Nette Davis-Nichols
for more information at
Jnette.Davis-Nichols@GulfEnergyInfo.com
1
Forsthoffer, M., Forsthoffer's component condition
monitoring, Butterworth-Heinemann, Elsevier, 2019.
ABDULAZIZ AL-HAMOUD is a
Compressors and Steam Turbines
Engineer for Saudi Aramco's
Consulting Services. He joined
Saudi Aramco in 2011 and has since
worked on multiple field issues
associated with turbomachinery
and provided consultations on several Saudi Aramco
mega projects. Mr. Al-Hamoud holds an MS degree in
mechanical engineering from Texas A&M University,
U.S. He also teaches short courses on compressors
and steam turbines to engineers.
ABDULAZIZ AL-GOFILI works as an
Engineering Consultant for Saudi
Aramco, specializing in rotating
equipment. He has more than 5 yr
of experience in rotating equipment
operation, maintenance, reliability
and selection. Mr. Al-Gofili holds
a BE degree in mechanical engineering from
King Fahd University for Petroleum and Minerals.
MOHAMMED ALMOUSA works as a
Turbomachinery Engineer for Saudi
Aramco's Consulting Services. He
has experience working on different
types of rotating equipment in gas
plants and refineries, and holds a
BE degree in mechanical
engineering from the Colorado School of Mines.
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