POWER April 2021 - 12

GLOBAL MONITOR
deploy the technology, with the potential
to generate 300 MW of emissionsfree
power. "
GTI's MacAdam said the prospects
for the near-term application
for sCO2
5. A schematic showing Echogen's waste recovery cycle using supercritical carbon dioxide.
Courtesy: Echogen
One benefit of using sCO2
as a working
fluid is that it " just so happens that
CO2
has some very unique thermodynamic
properties, " that, under certain
conditions-above its critical point of
87.76F at 1,070 psi (30.98C at 73.78
bar)- " make it a superior working fluid
to steam, " explained Scott MacAdam, a
chemical engineer at gas research entity
GTI. Power generation thrives on the efficient
conversion of heat into power, he
noted, and various studies have shown
that CO2
cycles that operate at 700F or
higher can enable cycle efficiencies of
more than 50%.
" That's significantly higher than what
can be attained with steam-we're
talking about up to a five percentage
point improvement in cycle efficiency,
which has significant ramifications
both on emissions, water usage, and
a variety of other parameters, " MacAdam
said. The no-water requirement
is of particular interest in modern power
systems owing to climate-related
changes, especially for facilities in arid
zones or regions subject to freezes or
sub-freezing temperatures.
Another benefit is " The high density
and volumetric heat capacity of CO2
with respect to other working fluids
makes it more energy dense, meaning
that the size of all system components
can be considerably reduced without
losing performance-including the turbine,
pump, and heat exchangers, " EPS
said. But CO2
also " more effectively
captures waste heat from sources that
have an approximately constant heat
capacity " such as turbine exhaust or
other gases, owing to the character
of its heat capacity in the " supercritical
region, " which " provides superior
matching to the heat source tempera12
ture
profile compared to the boiling
process utilized with other working fluids
such as steam or organic working
fluids used in Organic Rankine Cycle
(ORC) systems, " EPS said.
" In short, sCO2
provides better performance
and cost than both Rankine
cycles over the full range of applications
[EPS has] studied, with heat source temperatures
ranging from 300C to 1,500C, "
said EPS's Held. " Compared to ORC systems,
the working fluid in sCO2
power
cycles is low-cost, non-flammable, and
thermally stable, allowing for direct heat
exchange between a hot stack gas and
the working fluid. ORCs require an intermediate
heat transfer fluid to transport
heat from the stack to the working fluid,
which adds cost and reduces performance,
and adds a fire risk in the event
of a heat exchanger leak. "
These advantages are well-suited
to midstream oil and gas operations,
noted Siemens, which will build, own,
and operate the facility under the agreement
with TC Energy (though TC Energy
will hold option to own it at a later
date). Benefits include a 25% to 40%
smaller footprint than steam-based systems,
a 10% increase in compressor
station efficiency, and the capability to
produce clean, emissions-free electricity,
Siemens said. " Moreover, because
the working fluid is contained within a
closed-loop system, no boiler operator
is required, making the system suitable
for remote operation. "
Arja Talakar, senior vice president
of Industrial Applications Products for
Siemens Energy, suggested the pilot
project will open up new opportunities
to scale the technology. Meanwhile,
TC Energy said it is " currently evaluating
other compressor station sites to
www.powermag.com
of waste heat recovery is promising.
" Many systems around the world-
thousands of systems-release either
exhaust gas or flue gases at temperatures
up to 500C. These are prime candidates
for converting heat into power
at smaller scale, and examples include
small gas turbines, either at compressor
pipeline stations, offshore oil and
gas platforms, possibly peaking power
plants, as well as industrial sources
such as steel mills class furnaces and
cement plants, " he said. MacAdam said
initial commercial projects-including
the 10-MW design being launched in
Alberta-will " pave the way to larger
projects in the future. "
The pilot installation in Canada is
backed by $8 million in funding from
Emissions Reduction Alberta's (ERA's)
Industrial Efficiency Challenge, a program
that invests carbon price revenues
earned from large final emitters to boost
clean technology development. Held
noted that stateside the DOE is supporting
several other applications for sCO2
cycles, and Echogen is involved in several
of those initiatives.
" Echogen has led and partnered with
other groups on multiple U.S. DOE-funded
projects, furthering developments of
sCO2
power cycles in applications as varied
as concentrating solar power (CSP),
coal-fired power plants, and micronuclear
reactor systems, " he said. " These
projects have enabled us to optimize our
design methodologies, including highly
developed steady-state design modeling
tools, and high-fidelity transient simulations
that allow us to refine our system
control strategies. "
-Sonal Patel is POWER's senior
associate editor.
POWER Digest
European Commission Probing Germany
Lignite Power Compensation.
The European Commission on March
2 opened an " in-depth investigation "
to assess whether Germany's plans
to compensate its lignite-fired power
plants for early closure is in line with
the European Union's (EU's) state aid
rules. Germany, which has announced
a coal phaseout by 2038, has entered
into agreements with lignite power
generators, RWE and LEAG, for compensation
of " foregone profits, " and
POWER | April 2021
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POWER April 2021

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