Hydrocarbon Processing - March 2022 - 31

Petrochemical Technology
Proprietary heat transfer solutions.
For the past 20 yr, the co-authors' companiesc
have
jointly developed technologies
to serve the energy industry. These technologies
primarily target the light hydrocarbon
boiling and condensing services.
Propane chilling trains on propane/
mixed-refrigerant LNG trains or C2
/C3
fractionations and splitting services and
C3
to benefit from the proprietary enhanced
nucleate boiling tube technologya
technologya
refrigeration units are good candidates
. This
is a dual enhanced tube promoting
nucleate boiling on the shell side,
while inner microfin grooves increase
surface area and promote turbulence, increasing
the heat transfer on the tube side
(FIG. 2). Typical fluids are light hydrocarbons
such as ethylene, ethane, propane,
propylene and butane.
Case study: C3 splitter reboiler/condenser-Open
heat pump loop. A C3
splitter unit-more accurately referred to
as a propylene/propane splitter unit-is
used in the separation of propane and propylene.
The difference in the molecular
weights of propylene and propane is small
(42.08 g/mol vs. 44.1 g/mol), as is the difference
in their liquid-vapor equilibrium
temperatures. For example, at 12 bara, the
boiling point of propane is 34.3°C, while
the boiling point of propylene is 26.2°C.
The difference of 8.1°C is well below 45°C,
and the boiling points are also lower than
100°C. The fractionation column of such
a unit will receive a feed stream where the
two molecules are mixed with potential
traces of heavies. The propylene will be
separated from the propane and will exit
in the gas phase at the top of the column,
while the propane-concentrated liquid
stream will leave at the bottom of the column.
A reboiler will partially vaporize the
stream, starting the propylene/propane
separation and heating the column. Because
of the very close volatility of the two
components, the separation is difficult
and will require many trays in the column
and even several columns in series.
The propylene gas phase will generally
be condensed with cooling water, and
a part of the condensate will come back
to the column as reflux stream. The main
part of condensate will leave the unit as
propylene product. The heat available in
the vapor is lost to the environment. By
directing the vapor to the reboiler, some
heat can be saved. Nevertheless, the temperature
level of the exhausting vapor is
too low to ensure the heat transfer in the
reboiler. It is necessary to increase the
pressure of the pure propylene stream to
increase its dewpoint.
Application of a heat pump to
Borealis' C3
splitter
unit
at
its
Porvoo facility. As presented at Hydrocarbon
Processing's International Refining
and Petrochemical Conference (IRPC)
EurAsia in June 2019 in Helsinki, Finland,
Borealis evaluated several process
schemes to upgrade the C3
splitter unit
for additional propylene production
capacity at the Porvoo facility (FIG. 3),
along with changing from chemical grade
propylene (98 wt%) to polymer grade
(99.5 wt%). The upgrade had to be performed
within a given setup and within
a limited plot space. As the reboiler and
condenser duties will increase signifiON
DEMAND WEBCAST
Mike Brooks
Sr. Director, APM Business Solutions
Aspen Technology, Inc.
Managing Asset Health by Combining Behavior Patterns
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John Campbell
Sr. Director of Product Management
Aspen Mtell
Join AspenTech's Mike Brooks and John Campbell to understand how 'Smart' FMEA combined
with Aspen Mtell® predictive maintenance can help you:
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Lee Nichols
Editor-in-Chief/Associate Publisher
Hydrocarbon Processing
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Hydrocarbon Processing - March 2022

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