Hydrocarbon Processing - May 2022 - 51

Carbon Capture/CO2
the gas temperature at reasonable levels
so as not to damage the compressor seals
and bearings. Furthermore, because of its
rapid density change with pressure, a significant
flow volume reduction requires a
wide range of aerodynamic high-to-low
flow compression stages.
The following types of compressors
are typically considered for high-pressureratio
carbon sequestration applications:
* Reciprocating
* Screw
* Centrifugal barrel
* Centrifugal horizontally split
* Integrally geared
* Hybrid centrifugal with dense
phase pump.
Since both reciprocating and screw
compressors are severely flow limited,
in practice they cannot be used for largescale
carbon sequestration applications;
the other options all rely on proven centrifugal
compressor or pump impellers
and differ primarily in their layouts and
stage arrangements. The best configuration
for the application type under discussion
is either an intercooled, barrel,
straight-through centrifugal compressor
with a dense phase pump (FIG. 2) or an
integrally geared intercooled compressor
(FIG. 3). Both arrangements require seven
to eight compression or pumping stages,
with intercoolers between them, to meet
the specified compression ratio (for simplicity's
sake, the schematics shown do
not include all stages). Industry opinions
vary as to which is the better selection:
both arrangements have pros and cons
depending on operating conditions and
range, application-specific standards,
plant type, maintenance expectations
and service cycle.
Compressor designs. The two designs
discussed above represent the most promising
options, not the only ones. Several
other machinery solutions for compression
and pumping of CO2
are commercially
available, such as the multi-stage
barrel centrifugal compressor shown in
FIG. 4 or the horizontally split centrifugal
compressor in FIG. 5. In both cases, two
casing section intercoolers and one discharge
cooler are required to avoid overMitigation
heating
and achieve efficient CO2
compression;
typical operating conditions
for these machines range from < 50 psia
(for suction pressures) to > 1,100 psia
(for discharge pressures). At 1,100 psia,
the compressor discharge gas will be in
the supercritical state, meaning that after
cooling the CO2
the dense phase pump for higher-pressure
pipeline transport or storage injection.
Although the technical challenges of CO2
compression are often application-specific
and must be individually addressed for
new carbon sequestration technologies, a
wide toolkit is available for further development,
as necessary.
KLAUS BRUN is the Director of
Research and Development at
Elliott Group, leading a group of 60+
professionals in the development of
turbomachinery and related systems
for the energy industry. He holds
nine patents, has authored more
than 350 papers, and is the editor of three textbooks
on energy systems and turbomachinery. In the past,
Dr. Brun has held positions in product development
and management, engineering and executive
management at Southwest Research Institute,
Solar Turbines, General Electric and Alstom.
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