Hydrocarbon Processing - June 2021 - GP-34

TREATING AND NGL
To run the system, power of 30.31
MMBtu/hr is supplied to the compressor
by the steam turbine, which intakes
high-pressure steam and exhausts medium-pressure
steam. In this system, the
required steam flowrate is 295,900 lb/hr.
To represent the system, modelinga
was carried out as shown in FIG. 2, generating
a good match to the design. The adiabatic
efficiency of the compressor and
the isentropic efficiency of the turbine
were 75% and 70%, respectively.
Compressor design proposal. As shown
in FIG. 3, the existing compressor has only a
single suction on the left side. In the existDischarge
Compressor
Low-pressure
suction
Turbine
Medium-pressure
steam
High-pressure
steam
FIG.
3. Proposed compressor schematic.
177°F
322 psia
28.15
42°F
390 psia
61 psia
25°F
HPS MPS
83 psia
43°F
210,500 lb/hr
C2+ feed:
155,000 bpd
25°F
Deethanizer
41°F
466,500
lb/hr
C3+
from others
157,600 bpd
Depropanizer
FIG. 4. Proposed deethanizer overhead cooling system and required steam flowrate with
reduction to the turbine.
Comp Dish-2
Temperature
Pressure
Comp Suct-2
Comp Suct-2
Temperature
Pressure
Mass Flow
25.12
61.00
466.5
F
psia
Mlb/hr
Comp
2nd Suct
R
RCY-3
9-2
Heat Absorbed-2
Heat Flow 71.47 MMBtu/hr
7-2
Evaporator-2
Heat Absorbed-2
VLV-102-2
6-2
C2 Vapor-2
FIG. 5. Mass and energy balance for the proposed design, using simulation.a
34 MAY/JUNE 2021 | GasProcessingNews.com
Comp
1st Suct
Comp
Out
Comp Work-4
MIX-101
Comp Work-2
Comp
Out-2
Comp
Work-3
B
BAL-1
Temperature
Pressure
Mass Flow
Comp
Work-4 Turbine-2
MPS-2
Comp Suct-3
Comp Suct-3
43.42
83.00
210.5
F
psia
Mlb/hr
3-3
RCY-2
Flash
Drum-2
R
3-2
VLV-100-2
2-2
Heat Flow 28.15 MMBtu/hr
MPS-2
HPS-2
Mass Flow 274.8 Mlb/hr
172.1 F
322.0 psia
Comp Disch-2
Air Cooler-2
3-2
Temperature
Pressure
Mass Flow
43.42
83.00
677.0
F
psia
Mlb/hr
C2-2
Economizer-2
2-2
Temperature
Pressure
116.0 F
309.0 psia
Heat
Released-2
Heat Released-2
Heat Flow 85.38 MMBtu/hr
1-2
1-2
Temperature
Pressure
Vapour Fraction
141.5
314.0
0.0000
Temperature
Pressure
VLV-101-2
F
psia
a Simulation and modeling performed using HYSYS
Ethane-2
122.6
360.0
F
psia
Ethane-2
HAE YONG NOH is a Process
Engineer at the Yanbu NGL
Fractionation Department of
Saudi Aramco. He has 12 yr of
experience in the oil and gas industry
and is a licensed professional
engineer in chemical and mechanical
engineering. Mr. Noh earned a BS degree in chemical
engineering from Chung Ang University in Seoul, South
Korea and an MS degree in interdisciplinary engineering
from Purdue University in West Lafayette, Indiana, U.S.
Proposal
83 psia
43°F
677,000
lb/hr
116°F
41°F
122°F
360 psia
C2
product
0.5 mol% C3
Recommendations. The study reveals
that a high-pressure steam savings of
21,100 lb/hr per module can be achieved,
which is equivalent to an energy savings
of 7.1%. This initiative can be applied to
the closed recycle loop.
The air cooler duty also can be reduced
by 2.5%, since the compressor discharge
temperature drops by 5°F, from 177°F
(FIG. 1) to 172°F (FIG. 4). Reduction of air
cooler duty is helpful for plant operation
during very hot weather, especially in the
Middle East. GP
NOTE
MMBtu/hr
Air
274,800 lb/hr
Air
141°F
Low-pressure
suction
Medium-pressure
suction
Compressor
Turbine
Medium-pressure
steam
High-pressure
steam
ing system, the single suction comes from
the combined line-one for low-pressure
(61-psia) vapor from the evaporator, and
the other for a low-pressure (61-psia),
cloud-marked vapor stream from the flash
drum (83 psia), as shown in FIG. 1.
As stated, the newest module of the
deethanizer propane refrigerant compressor
has two different suctions on the
right side. The low-pressure compressor
suction line receives low-pressure vapor
from the evaporator, but the compressor
is designed to receive medium-pressure
vapor propane directly from the flash
drum without any letdown. Since there
is no letdown after the refrigerant flash
Discharge
drum, some energy conservation in the
compressor is anticipated.
Based on the configuration of the newest
module, a simulationa
was conducted
to check for improvement to the compressor
energy.
Proposed design result. To follow the
proposed design modification, the line in
the cloud-marked vapor stream shown in
FIG. 1 needs modification. As the compressor
requires medium-pressure (83-psia)
C3
was made to the schematic (FIG. 4). Since
the compressor does not accept entrained
liquid with C3
vapor to the second suction, a change
vapor, a knockout drum
was added between the flash drum and
the compressor.
Without letdown and at medium pressure
for the recycle loop compressor,
the required power to the compressor
was reduced from 30.31 MMBtu/hr to
28.15 MMBtu/hr. Accordingly, the highpressure
steam intake and medium-pressure
steam exhausts were reduced from
295,900 lb/hr to 274,800 lb/hr.
The same efficiencies for the compressor
and turbine (75% adiabatic and 70%
isentropic) were taken as in the existing
system. FIG. 5 shows the modeling result
for steam savings in the refrigeration system
when the medium-pressure C3
into the compressor without letdown.
flows
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