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The Allam Cycle or Allam-Fetvedt Cycle is a process for converting carbonaceous fuels into thermal energy, while capturing the generated carbon dioxide and water.

The inventors are English engineer Rodney John Allam, American engineer Jeremy Eron Fetvedt, American scientist Dr. Miles R Palmer, and American businessperson and innovator G. William Brown, Jr. The Allam-Fetvedt Cycle was recognized by MIT Technology Review on the 2018 list of 10 Breakthrough Technologies.

This cycle was validated at a 50 MWth natural gas fed test facility in La Porte, Texas in May 2018.

Description

The Allam-Fetvedt Cycle is a recuperated, high-pressure, Brayton cycle employing a transcritical CO₂ working fluid with an oxy-fuel combustion regime. This cycle begins by burning a gaseous fuel with oxygen and a hot, high-pressure, recycled supercritical CO₂ working fluid in a combustor. The recycled CO₂ stream serves the dual purpose of lowering the combustion flame temperature to a manageable level and diluting the combustion products such that the cycle working fluid is predominantly CO₂. The pressure in the combustor can be as high as approximately 30 MPa. The combustion feedstock consists of approximately 95% recycled CO₂ by mass.

The combustor provides high-pressure exhaust that can be supplied to a turbine expander operating at a pressure ratio between 6 and 12. The expander discharge leaves as a subcritical CO₂ mixture predominantly commingled with combustion derived water. This fluid enters an economizer heat exchanger, which cools the expander discharge to below 65 °C against the stream of CO₂ that is recycled to the combustor. Upon exiting the economizer heat exchanger, the expander exhaust is further cooled to near ambient temperature by a central cooling system, enabling liquid water to be removed from the working fluid and recycled for beneficial use.

The remaining working fluid of nearly pure CO₂ then enters a compression and pumping stage. The compression system consists of a conventional inter-cooled centrifugal compressor with an inlet pressure below the CO₂ critical pressure. The CO₂ working fluid is compressed and then cooled to near ambient temperature in the compressor after-cooler. At this point, the combination of compressing and cooling the working fluid permits it to achieve a density in excess of 500 kg/m3. In this condition, the CO₂ stream can be pumped to the high combustion pressure required using a multi-stage centrifugal pump.  Finally, the high-pressure working fluid is sent back through the economizer heat exchanger to be reheated and returned to the combustor.

The net CO₂ product derived from the addition of fuel and oxygen in the combustor is removed from the high-pressure stream; at this point, the CO₂ product is high-pressure and high purity, ready for sequestration or utilization without requiring further compression.

In order for the system to achieve high thermal efficiency, a close temperature approach is needed on the high-temperature side of the primary heat exchanger. Due to the cooling process employed at the compression and pumping stage, a large energy imbalance would typically exist in the cycle between the cooling expander exhaust flow and the reheating CO₂ recycle flow.

The Allam-Fetvedt Cycle corrects this imbalance through the incorporation of low-grade heat at the low-temperature end of the recuperative heat exchanger. Due to the low temperatures at the cool end of the cycle, this low-grade heat only needs to be in the range of 100 °C to 400 °C. A convenient source of this heat is the Air Separation Unit (ASU) required for the oxy-fuel combustion regime.

When burning natural gas as a fuel, this basic configuration has been modeled to achieve an efficiency up to 60% (LHV) as a power cycle net of all parasitic loads, including the energy-intensive ASU. Despite its novelty, the components required by this cycle are commercially available, with the exception of the combustion turbine package. The turbine relies on proven technologies and approaches used by existing gas and steam turbine design tools.

Applications

Construction began in March 2016 in La Porte, Texas on a 50 MWth industrial test facility to showcase the Allam-Fetvedt Cycle, finishing in 2017. In 2018, the Allam-Fetvedt Cycle and supporting technologies were validated, allowing OEMs to certify components for use with future production plants.

On November 15, 2021, at approximately 7:40 pm EST the test facility successfully synchronized to the ERCOT grid proving that the Allam Fetvedt Cycle was capable of generating power at 60 Hz.

This test facility is owned and operated by NET Power, which is owned by Constellation Energy Corporation, Occidental Petroleum (Oxy) Low Carbon Ventures, Baker Hughes and 8 Rivers Capital (the inventor of the technology).

NET Power was awarded the 2018 International Excellence in Energy Breakthrough Technological Project of the Year at the Abu Dhabi International Petroleum Exhibition and Conference (ADIPEC).

Patent history

See also

• Oxy-fuel combustion process

References

1. Carbonaceous fuels include natural gas, biomass, coal, municipal solid waste, and sour gas (natural gas with a high content of sulfur dioxide).
2. ^ US patent 8959887, Allam; Rodney John (Wiltshire, GB), Brown, Jr.; Glenn William (Durham, NC), Palmer; Miles R. (Chapel Hill, NC),; Brown, Jr., Glenn William & Palmer, Miles R., "System and method for high efficiency power generation using a carbon dioxide circulating working fluid", published 2015-02-24, issued 2013-11-04, assigned to Palmer Labs, LLC and 8 Rivers Capital, LLC 
3. ^ US patent 8986002, Palmer; Miles R. (Chapel Hill, NC), Allam; Rodney John (Chippenham, GB), Brown, Jr.; Glenn William (Durham, NC), Fetvedt; Jeremy Eron (Raleigh, NC); Allam, Rodney John & Brown, Jr., Glenn William et al., "Apparatus for combusting a fuel at high pressure and high temperature, and associated system", published 2015-03-24, assigned to 8 Rivers Capital, LLC and Palmer Labs, LLC 
4. ^ US patent 9062608, Allam; Rodney John (Wiltshire, GB), Palmer; Miles R. (Chapel Hill, NC), Brown, Jr.; Glenn William (Durham, NC); Palmer, Miles R. & Brown, Jr., Glenn William, "System and method for high efficiency power generation using a carbon dioxide circulating working fluid", published 2015-06-23, issued 2013-03-13, assigned to Palmer Labs, LLC and 8 Rivers Capital, LLC 
5. ^ US patent 9068743, Palmer; Miles R. (Great Falls, VA), Allam; Rodney John (Chippenham, GB), Brown, Jr.; Glenn William (Durham, NC); Allam, Rodney John & Brown, Jr., Glenn William, "Apparatus for combusting a fuel at high pressure and high temperature, and associated system", issued 2015-03-24, assigned to 8 Rivers Capital, LLC and Palmer Labs, LLC 
6. ^ US patent 9416728, Palmer; Miles R. (Great Falls, VA), Allam; Rodney John (Chippenham, GB), Brown, Jr.; Glenn William (Durham, NC); Allam, Rodney John & Brown, Jr., Glenn William, "Apparatus and method for combusting a fuel at high pressure and high temperature, and associated system and device", issued 2016-08-16, assigned to 8 Rivers Capital, LLC and Palmer Labs, LLC 
7. ^ US patent 9869245, Allam; Rodney John (Wiltshire, GB), Palmer; Miles R. (Chapel Hill, NC), Brown, Jr.; Glenn William (Durham, NC); Palmer, Miles R. & Brown, Jr., Glenn William, "System and method for high efficiency power generation using a carbon dioxide circulating working fluid", published 2015-09-10, issued 2018-01-16, assigned to 8 Rivers Capital, LLC 
8. ^ US patent 10018115, Palmer; Miles R. (Chapel Hill, NC), Allam; Rodney John (Chippenham, GB), Brown, Jr.; Glenn William (Durham, NC), Fetvedt; Jeremy Eron (Raleigh, NC); Allam, Rodney John & Brown, Jr., Glenn William et al., "System and method for high efficiency power generation using a carbon dioxide circulating working fluid", published 2015-03-24, assigned to 8 Rivers Capital, LLC 
9. ^ US patent 10047671, Allam; Rodney John (Wiltshire, GB), Brown, Jr.; Glenn William (Durham, NC), Palmer; Miles R. (Chapel Hill, NC),; Brown, Jr., Glenn William & Palmer, Miles R., "System and method for high efficiency power generation using a carbon dioxide circulating working fluid", published 2018-08-14, issued 2015-01-23, assigned to Palmer Labs, LLC and 8 Rivers Capital, LLC 
10. "2018". MIT Technology Review. Retrieved 2020-10-01.
11. "Breaking ground for a groundbreaker: the first Allam Cycle power plant". Modern Power Systems. 15 May 2016. Retrieved 29 November 2016.
12. Isles, Junior (2014). "Gearing up for a new supercritical CO₂ power cycle system" (PDF). Gas Turbine World. Vol. 44, no. 6. Pequot Publishing. Archived from the original (PDF) on 11 August 2016. Retrieved 29 November 2016.
13. Grant, Annalee (6 March 2015). "Exelon, NET Power confident in planned carbon capture pilot project in Texas". SNL. S&P Global. Retrieved 29 November 2016.
14. Dodge, Edward (14 November 2014). "CCS Breakthrough: sCO2 Power Cycles Offer Improved Efficiency and Integrated Carbon Capture". Breaking Energy. Breaking Media. Retrieved 29 November 2016.
15. Allam, Rodney; Martin, Scott; Forrest, Brock; Fetvedt, Jeremy; Lu, Xijia; Freed, David; Brown, G. William; Sasaki, Takashi; Itoh, Masao; Manning, James (2017-07-01). "Demonstration of the Allam Cycle: An Update on the Development Status of a High Efficiency Supercritical Carbon Dioxide Power Process Employing Full Carbon Capture". Energy Procedia. 114: 5948–5966. doi:10.1016/j.egypro.2017.03.1731. ISSN 1876-6102.
16. Lu, Xijia; Forrest, Brock; Martin, Scott; Fetvedt, Jeremy; McGroddy, Michael; Freed, David (2016-09-20). "Integration and Optimization of Coal Gasification Systems With a Near-Zero Emissions Supercritical Carbon Dioxide Power Cycle". Proceedings of the ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy. American Society of Mechanical Engineers Digital Collection. doi:10.1115/GT2016-58066. ISBN 978-0-7918-4987-3.
17. Rathi, Akshat (31 May 2018). "A US startup has lit the first fire in its zero-emissions fossil-fuel power plant". Quartz. Retrieved 2020-10-01.
18. "Power Engineering International". Power Engineering International. 18 November 2021. Retrieved November 18, 2021.
19. LLC, NET Power. "NET Power Demonstration Plant Wins 2018 ADIPEC Breakthrough Technological Project of the Year". www.prnewswire.com (Press release). Retrieved 2020-10-01.

External links

• Process diagram for natural gas
• Process diagram for coal
• Mass flow diagram
• Pressure and specific enthalpy diagram

• Energy conversion
• Thermodynamic cycles
• English inventions
• Power station technology
• Carbon capture and storage