H2Tech - Q2 2022 - 19

HYDROGEN INFRASTRUCTURE DEVELOPMENT
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 7-8
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 represent the most promising
options, not the only ones. Several other
machinery solutions for compression
and pumping of CO2
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 overheating
SPECIAL FOCUS
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
it can be fed directly into 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.
are commercially
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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H2Tech - Q2 2022

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