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a theoretical conversion efficiency of more than 50%. The RCBC has the potential to be significantly more efficient than the traditional steam-based Rankine cycle because sCO2
can
operate between low and high temperatures and low and high pressures without a phase change.
Unlike the Allam–Fetvedt cycle, fuel combustion takes place outside the RCBC since it is an indirectly heated process. The RCBC therefore has the flexibility of being fuel agnostic, but if CO2
the resultant CO2
is generated by fossil fuel combustion, would need to be captured to
yield climate-neutral power generation. Supercritical CO2
as a working fluid offers
high power density and simplicity of operation compared to a steam-based power cycle and can use more compact turbomachinery. This makes the cycle relevant to a wide range of applications in addition to power generation from nuclear, fossil, geothermal and concentrated solar heat sources. For example, the sCO2
power cycle can be used
for maritime propulsion and waste heat recovery. Supercritical CO2
as a working fluid is also
has the advantage of lower temperature operation. To achieve a similar heat to power conversion efficiency, helium would need to be heated to circa 850°C, whereas sCO2 required to be heated to around 550°C. sCO2
is can
being considered for advanced nuclear reactors. When compared to the helium Brayton cycle, sCO2
therefore be applied to nuclear reactors with a core outlet temperature above 500°C.
Gaseous CO2 grid balancing
cycle for LDES and
The Italian startup Energy Dome uses subcritical gaseous CO2
in a closed cycle in its CO2
(see also page 25). The technology is a form of long duration energy storage (LDES) that avoids the use of conventional batteries. The Energy Dome cycle expands vaporised liquid CO2
Battery™ The expanded CO2 is stored in a large dome at atmospheric pressure.
When there is abundant renewable power generation from solar PV sources during the peak daylight hours, CO2
gas is withdrawn from
across a turbine to generate power during periods of peak demand, typically overnight and in the early morning when power is drawn from the grid before solar generation has begun.
NET Power focuses on Project Permian
Lummus Technology has signed a strategic supply agreement with NET Power to design and supply recuperative heat exchangers (HXR) for utility scale power plants employing the Allam–Fetvedt cycle (also now sometimes referred to as the NET Power Cycle). The first planned utility scale plant is Project Permian (300 MWe), located near Midland- Odessa in Texas, with initial power generation envisaged in the second half of 2027/ first half of 2028. NET Power says it is “engaging its strategic shareholders to support the
project”: Baker Hughes (key integrated process equipment and technologies); Oxy (CO2 transport & sequestration and power off-take); Constellation (expertise in plant operations and power off-take); and 8 Rivers (project development support). Front-end engineering and design (FEED) for Project Permian is underway in
reheat recirculated CO2 NET Power Cycle.
partnership with Zachry Group. It is expected to conclude in 2024 and will form the basis for NET Power’s standardised utility-scale plant design. Site related permitting is also progressing for Project Permian. The HXR recovers energy from the turboexpander exhaust and air separation unit to , making it one of the most important pieces of equipment in the
Upon completing the FEED for Project Permian, NET Power says intends to issue a
purchase order to Lummus for that plant. Under the terms of the strategic supply agreement, Lummus, in its role as the licensed NET Power HXR supplier, intends “to leverage its global supply chain network to increase global HXR manufacturing capacity, enabling NET Power deployments at scale to help countries and communities around the world rapidly achieve their energy and environmental goals.“ Heatric, part of Meggitt, now a division of the Parker Hannifin Filtration Group, supplied printed circuit heat exchangers for NET Power‘s La Porte Allam–Fetvedt demo facility. The La Porte test facility site is currently being prepared for combustor and
turboexpander demonstrations to be carried out in conjunction with Baker Hughes, with the aim of de-risking the first utility-scale project and further refining NET Power’s proprietary plant controls architecture. Looking beyond Project Permian, NET Power also reports progress on what it calls its “first originated project“ (OP1), which will be “located in North America.“ A technical feasibility study has been completed and NET Power says it is preparing to submit permits for grid interconnection and carbon sequestration, in 2024.
to ensure maximum cycle efficiency. The whole cycle operates below the triple point of CO2
the dome. It is compressed and liquefied using excess power from the grid which may otherwise be curtailed. Heat energy from the compression is stored in a thermal energy storage system. This heat is subsequently used to revaporise the liquid CO2
, avoiding supercritical operation. Energy Dome has developed a standard design that produces 20 MW of power over a 10 hour discharge period. The charging time is 10 hours, which can match well with the solar excess period in many renewables-led grids. The duration of discharge is longer than most battery systems can offer and is a complementary fit to solar-heavy grids. Excess solar generation is increasingly common in areas with a high percentage of rooftop solar generation, such as South Australia. Furthermore, green hydrogen systems based on solar power without overnight wind power integration may benefit from the Energy Dome for overnight power to the electrolysers to ensure high utilisation and avoid periods of shutdown. The daily cycling of the Energy Dome system is also a good fit to the LDES business model, which relies on high utilisation of the capital asset to ensure maximum revenue generation with frequent charging and discharge cycles. Revenue can also be generated through grid management services and excess power withdrawal to avoid power surges on the grid. Low-pressure CO2
storage is an integral
aspect of the Energy Dome concept. The amount of CO2
the amount of power that the CO2
gas that is stored determines Battery™
can release on demand. To enable low-cost storage of a large volume of CO2
gas at close to
atmospheric pressure, Energy Dome can use the concept developed by another Italian company, Ecomembrane.
The Ecomembrane technology relies on a PVC-coated polyester fabric membrane. This material has been used for decades as a low-cost means to contain biogas in wastewater treatment plants and store recovered landfill gas. The Ecomembrane has been used on more than 1000 installations around the world for these purposes.
18 | January/February 2024|
www.modernpowersystems.com
Above: Ecomembrane
Left: Air Separation Unit for oxygen production for oxyfuel combustion
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