Hydrocarbon Processing - April 2021 - GP-16

SPECIAL FOCUS: GREEN TECHNOLOGIES
psig. The simulation results also validate
the pressure drop calculation performed
by a third party.

FIG. 3. Flow scheme of ejector-based FGRS at the Yanbu facility.

FIG. 4. Ethane recovery system simulation.

only the means to transport the gas
from the ethane tank flare system site to
the boiler utility area at the gas plant (a
total distance of approximately 1.7 km)
within the limited differential pressure.
Appropriate pipe sizes within the available differential pressures were determined by careful analysis of the hydraulic simulation results. The results show
that 2.05 MMsft3d of mixed high-pressure fuel gas and ethane at 17.5 psig will
arrive at 8 psig at the utility area, using
6-in. piping.
In the proposed recovery system,
the pressure control valve already exists
between the flare gas offtake points and
the flare knockout drum. This design
maintains a slight positive pressure in
the flare header and prevents both an
undesirable opening condition for the
control valve and the release of ethane to the flare system. Whenever the
amount of gas released into the flare
system exceeds the capacity of the recovery system (1.1 MMsft3d), a pressure control valve on the flare recovery line will act to maintain the flow at
1.1 MMsft3d. The proposed recovery
scheme is illustrated by the flow scheme
shown in FIG. 3.
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MARCH/APRIL 2021 | GasProcessingNews.com

Simulation results. The ethane recovery system is designed to take ethane
from the ethane storage tanks and compress it for firing at 1.5 psig-2 psig and
for delivery at approximately 3.7 psig to
the two boiler skids.
The ethane recovery system was
simulated, using proprietary softwarea
to perform the hydraulic analysis and
predict the process conditions (FIG. 4).
Actual pipe lengths for the existing and
new pipes are taken from an isometric drawing, to account for the pressure losses from the ethane tank to the
boilers at the utility unit. The design
flow used to size the recovery system is
0.4 MMsft3d-1.1 MMsft3d, with an ethane composition of 98%.
The results of the hydraulic analysis
indicated that new and existing pipes are
of adequate size to avoid backpressure on
the ethane tank under normal operation,
and they are able to deliver the mixed
gas stream at a pressure of 3.7 psig to the
boiler skids. A sensitivity analysis, including summer and winter conditions,
was also run to calculate the system pressure drop. The calculated pressure drop
for the 8-in. ethane line from the tank
vapor line to the ejector skid inlet is 0.1

Takeaway. The established FGRS
scheme has multiple economic benefits. First, it will recover approximately
1.1 MMsft3d of valuable C2+, which is
equivalent to 1,961 MMBtu/d in fuel
energy savings.
Second, the system will operate without any energy consumption or rotating
equipment (all installations are static
equipment-i.e., no moving parts). The
system will utilize energy that would
otherwise have been wasted or flared
since plant startup.
Third, the flare gas recovery system
will improve the reliability and life span
of the flare tip, thereby reducing the recurring cost of flare tip replacements.
The proposed system will minimize
greenhouse gas emissions and provide a
positive environmental impact.
Finally, operation of the established
FGRS at the Yanbu NGL fractionation
plant will provide an operating experience base within Saudi Aramco for other facilities to adopt. GP
NOTE
a

HYSYS

ABDULAZIZ H. AL-TIJANI is
an Engineering Specialist at
Saudi Aramco's Process and
Control Systems Department in
Dhahran, Saudi Arabia. He holds a
BS degree in chemical engineering
from King Fahd University of
Petroleum and Minerals (KFUPM) and a MS degree
in oil and gas surface facilities from KFUPM
(in partnership with IFP). Mr. Al-Tijani supports
company operations and project design, mainly in
flare and relief systems and flare gas recovery
applications. He supports Saudi Aramco and jointventure oil and gas operational facilities, pipelines,
process simulations and various phases of projects.
IRFAN ASHIQ is a Senior
Operations Engineer for Saudi
Aramco at the Yanbu NGL
fractionation plant. He has more
than 22 yr of professional
experience in process design,
operation and commissioning
for upstream oil and gas, heavy oil and
petrochemicals. Prior to joining Saudi Aramco,
he was the Lead Process Engineer at SNC Lavalin
in Canada and a Senior Process Engineer at
Propak Systems Ltd. in Canada. He holds an
MS degree in chemical engineering from the
University of Calgary in Canada and a professional
certification from the Association of Professional
Engineers and Geoscientists of Alberta (APEGA).

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Hydrocarbon Processing - April 2021

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