POWER October 2021 - 11

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provide opportunities both from a pure
thermodynamic point of view and from a
system integration perspective. " However,
challenges here, too, are hefty: " Most
advanced cycles gas turbines (GTs) are
interconnected to other systems and
components, or even processes such as
high-temperature fuel cells or solar air
heaters. Their integration often requires
a change in mass flow rates of compressor
or turbine as well as different working
fluids. Most GTs currently on the market
are not designed for this type of process
integration, " it notes. It suggests future
R&D activities should target the development
of concepts for " easy-to-integrate "
and flexible gas turbines, " since otherwise
each cycle would need its specific
gas turbine adaptation. " Attention should
especially be devoted to upgrade and
conversion applicability, it says, considering
that most of the current installed
capacity, mainly composed of traditional
power plants, will continue to serve in a
2030 energy landscape and beyond.
Getting that accomplished, however,
will require deep study, and testing of materials
and coatings. It will also need reliable
numerical simulation tools, including
a system of tools that allows the analysis
of advanced integrated cycles without
needing
to
manually
iterate
between
power plant simulation and process modeling
tools. Tools must also be developed
for transient analysis of the process because
gas turbines are increasingly used
for energy balancing, it says.
Among several promising advanced
cycles the report highlights are supercritical
CO2
cycles (Figure 2). " Commercial
systems are currently available for waste
heat recovery at the 5 to 10 MW scale
[on a technological readiness level (TRL)
of 9] whilst the technology is in the precommercial
phase (TRL7-8) for natural
gas applications. " Yet, these systems still
need development of compact, highly efficient,
cost-effective heat exchanger designs,
high-temperature oxycombustion
systems, and improved turbomachinery
designs. " System integration as a function
of scale must also be better understood,
insofar as this turns out critical to
optimise the type of drive of compressors
and pumps and the operation of the
system in off-design conditions, " it says.
Though it still needs research at the
fundamental and applied levels, pressure
gain combustion, another advanced
cycle, has the potential to achieve the
same time-averaged combustor exit
temperature as conventional
Brayton
cycles but at a higher pressure level. Wet
October 2021 | POWER
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11
cycles-which use a working fluid with
a high water content-present different
options with TRLs between 2 and 9 (the
most mature being the Cheng Cycle),
but R&D is needed here, too, on different
components and at a system level.
Organic Rankine cycles (ORCs) for stationary
power generation are already currently
commercial (for use in small- and
medium-scale applications), but further
research could enhance performance
and cost-effectiveness. " New cycle concepts
enabling higher thermal efficiency
are needed through the exploitation of
features such as supercritical vapour
generation, cascade layouts or cycles
including wet expansion, tailored to the
singularities of certain applications like
waste heat recovery, " the report notes.
Systems Integration and Energy
Storage. The integration of gas turbine
technology in other systems can offer
innovative solutions, but several technical
challenges need to be tackled. While
commercial pilots are in the works for
compressed air and liquid air energy
storage, challenges involve areas of fluid
storage and heat/cold storage.
Thermal storage, meanwhile, could be
used in several different power cycles.
2. Several 280-MW NET Power plants that
will use the Allam-Fetvedt Cycle, a novel
power cycle that uses supercritical carbon dioxide,
are under development in the U.S. and
UK. This image shows NET Power's test facility
in La Porte, Texas, which achieved first-fire
of a commercial-scale 50-MWth combustor in
May 2018. Courtesy: NET Power
" The current state of the art of high
temperature storage includes phase
change (molten salts) technology; while
different salt combinations (binary and
ternary) are being looked at to go above
520C and other media are being investigated
(like the promising silicon-based
technology or calcium/carbon looping
salts based technology). Stability, maintenance
requirements and material compatibility
are all issues to be addressed in
this field, " the report says.
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POWER October 2021

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