Supercritical carbon dioxide
Supercritical carbon dioxide (sCO
2) is a fluid state of
Carbon dioxide usually behaves as a
Supercritical CO
2 is becoming an important commercial and industrial solvent due to its role in chemical extraction, in addition to its relatively low toxicity and environmental impact. The relatively low temperature of the process and the stability of CO
2 also allows compounds to be extracted with little damage or denaturing. In addition, the solubility of many extracted compounds in CO
2 varies with pressure,[2] permitting selective extractions.
Applications
Solvent
Carbon dioxide is gaining popularity among
Supercritical carbon dioxide can be used as a more environmentally friendly solvent for
Supercritical carbon dioxide is used as the extraction solvent for creation of
In
Processes that use sCO
2 to produce micro and
Due to its ability to selectively dissolve organic compounds and assist enzyme functioning, sCO
2 has been suggested as a potential solvent to support biological activity on Venus- or super-Earth-type planets.[11]
Manufactured products
Environmentally beneficial, low-cost substitutes for rigid
The primary byproduct is water.sCO
2 is used in the foaming of
An
Working fluid
sCO
2 is chemically stable, reliable, low-cost, non-flammable and readily available, making it a desirable candidate working fluid for transcritical cycles.[14]
Supercritical CO2 is used as the working fluid in domestic water heat pumps. Manufactured and widely used, heat pumps are available for domestic and business heating and cooling.[14] While some of the more common domestic water heat pumps remove heat from the space in which they are located, such as a basement or garage, CO2 heat pump water heaters are typically located outside, where they remove heat from the outside air.[14]
Power generation
The unique properties of sCO
2 present advantages for closed-loop power generation and can be applied to power generation applications. Power generation systems that use traditional air Brayton and steam Rankine cycles can use sCO
2 to increase efficiency and power output.
The relatively new Allam power cycle uses sCO2 as the working fluid in combination with fuel and pure oxygen. The CO2 produced by combustion mixes with the sCO2 working fluid. A corresponding amount of pure CO2 must be removed from the process (for industrial use or sequestration). This process reduces atmospheric emissions to zero.
sCO2 promises substantial efficiency improvements. Due to its high fluid density, sCO2 enables compact and efficient turbomachinery. It can use simpler, single casing body designs while steam turbines require multiple turbine stages and associated casings, as well as additional inlet and outlet piping. The high density allows more compact, microchannel-based heat exchanger technology.[15]
For concentrated solar power, carbon dioxide critical temperature is not high enough to obtain the maximum energy conversion efficiency. Solar thermal plants are usually located in arid areas, so it is impossible to cool down the heat sink to sub-critical temperatures. Therefore, supercritical carbon dioxide blends, with higher critical temperatures, are in development to improve concentrated solar power electricity production.
Further, due to its superior thermal stability and non-flammability, direct heat exchange from high temperature sources is possible, permitting higher working fluid temperatures and therefore higher cycle efficiency. Unlike two-phase flow, the single-phase nature of sCO
2 eliminates the necessity of a heat input for phase change that is required for the water to steam conversion, thereby also eliminating associated thermal fatigue and corrosion.[16]
The use of sCO
2 presents
2 Brayton loops suffer from corrosion and erosion, specifically erosion in turbomachinery and recuperative heat exchanger components and intergranular corrosion and pitting in the piping.[17]
Testing has been conducted on candidate Ni-based alloys, austenitic steels, ferritic steels and ceramics for corrosion resistance in sCO
2 cycles. The interest in these materials derive from their formation of protective surface oxide layers in the presence of carbon dioxide, however in most cases further evaluation of the reaction mechanics and corrosion/erosion kinetics and mechanisms is required, as none of the materials meet the necessary goals.[18][19]
In 2016, General Electric announced a sCO2-based turbine that enabled a 50% efficiency of converting heat energy to electrical energy. In it the CO2 is heated to 700 °C. It requires less compression and allows heat transfer. It reaches full power in 2 minutes, whereas steam turbines need at least 30 minutes. The prototype generated 10 MW and is approximately 10% the size of a comparable steam turbine.[20] The 10 MW US$155-million Supercritical Transformational Electric Power (STEP) pilot plant was completed in 2023 in San Antonio. It is the size of a desk and can power around 10,000 homes.[21]
Other
Work is underway to develop a sCO
2 closed-cycle gas turbine to operate at temperatures near 550 °C. This would have implications for bulk thermal and nuclear generation of electricity, because the supercritical properties of carbon dioxide at above 500 °C and 20 MPa enable thermal efficiencies approaching 45 percent. This could increase the electrical power produced per unit of fuel required by 40 percent or more. Given the volume of carbon fuels used in producing electricity, the environmental impact of cycle efficiency increases would be significant.[22]
Supercritical CO
2 is an emerging natural refrigerant, used in new, low carbon solutions for domestic
Supercritical CO
2 has been used since the 1980s to enhance recovery in mature oil fields.
"
2 is captured, compressed to the supercritical state and injected into geological storage, possibly into existing oil fields to improve yields.[24][25][26]
Supercritical CO
2 can be used as a working fluid for geothermal electricity generation in both
2 Plume Geothermal).[31][32] EGS systems utilize an artificially fractured reservoir in basement rock while CPG systems utilize shallower naturally-permeable sedimentary reservoirs. Possible advantages of using CO
2 in a geologic reservoir, compared to water, include higher energy yield resulting from its lower viscosity, better chemical interaction, and permanent CO
2 storage as the reservoir must be filled with large masses of CO
2. As of 2011, the concept had not been tested in the field.[33]
Aerogel production
Supercritical carbon dioxide is used in the production of silica, carbon and metal based
2. When the CO
2 goes supercritical, all surface tension is removed, allowing the liquid to leave the aerogel and produce nanometer sized pores.[34]
Sterilization of biomedical materials
Supercritical CO
2 is an alternative for thermal sterilization of biological materials and medical devices with combination of the additive peracetic acid (PAA). Supercritical CO
2 does not sterilize the media, because it does not kill the spores of microorganisms. Moreover, this process is gentle, as the morphology, ultrastructure and protein profiles of inactivated microbes are preserved.[35]
Cleaning
Supercritical CO
2 is used in certain industrial cleaning processes.
See also
- Caffeine
- Dry cleaning
- Perfume
- Supercritical fluid
- Atmosphere of Venus, nearly all carbon dioxide, supercritical at the surface
References
- ^ doi:10.1063/1.555991.
- ^ Discovery - Can Chemistry Save The World? - BBC World Service
- ^ Department of Pharmaceutical Analysis, Shenyang Pharmaceutical University, Shenyang 110016, China
- ^ Stewart, Gina (2003), Joseph M. DeSimone; William Tumas (eds.), "Dry Cleaning with Liquid Carbon Dioxide", Green Chemistry Using Liquid and SCO
2: 215–227 - PMID 25471637.
- PMID 17353022.
- ^ "Test Methods | Wastes - Hazardous Waste | US EPA". wayback.archive-it.org. Archived from the original on 17 December 2008. Retrieved 5 February 2018.
{{cite web}}
: CS1 maint: bot: original URL status unknown (link) - ^ U.S.EPA Method 3561 Supercritical Fluid Extraction of Polycyclic Aromatic Hydrocarbons.
- ^ Use of Ozone Depleting Substances in Laboratories. TemaNord 2003:516.
- .
- PMID 25370376.
- ^ Rubin, James B.; Taylor, Craig M. V.; Hartmann, Thomas; Paviet-Hartmann, Patricia (2003), Joseph M. DeSimone; William Tumas (eds.), "Enhancing the Properties of Portland Cements Using Supercritical Carbon Dioxide", Green Chemistry Using Liquid and Supercritical Carbon Dioxide: 241–255
- PMID 17564481.
- ^ ISSN 0360-5442.
- ^ "Supercritical CO2 Power Cycle Developments and Commercialization: Why sCO2 can Displace Steam" (PDF).
- ^ "Supercritical Carbon Dioxide Power Cycles Starting to Hit the Market". Breaking Energy.
- ^ "Corrosion and Erosion Behavior in sCO
2 Power Cycles" (PDF). Sandia National Laboratories. - ^ "THE EFFECT OF TEMPERATURE ON THE sCO2 COMPATIBILITY OF CONVENTIONAL STRUCTURAL ALLOYS" (PDF). The 4th International Symposium - Supercritical CO2 Power Cycles. Archived from the original (PDF) on 23 April 2016.
- ^ J. Parks, Curtis. "Corrosion of Candidate High Temperature Alloys in Supercritical Carbon Dioxide" (PDF). Ottawa-Carleton Institute for Mechanical and Aerospace Engineering.
- ^ Talbot, David (11 April 2016). "Desk-Size Turbine Could Power a Town". MIT Technology Review. Retrieved 13 April 2016.
- ^ Blain, Loz (1 November 2023). "Supercritical CO2 pilot aims to make steam turbines obsolete". New Atlas. Retrieved 4 November 2023.
- ^ V. Dostal, M.J. Driscoll, P. Hejzlar, "A Supercritical Carbon Dioxide Cycle for Next Generation Nuclear Reactors" (PDF). Retrieved 20 November 2007. MIT-ANP-Series, MIT-ANP-TR-100 (2004)
- ^ "Heat Pumps". Mayekawa Manufacturing Company (Mycom). Retrieved 7 February 2015.
- ^ "The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs", p. 84 (2004)
- ^ "FutureGen 2.0 Project". FutureGen Alliance. Archived from the original on 10 February 2015. Retrieved 7 February 2015.
- ^ "Øyvind Vessia: "Fischer- Tropsch reactor fed by syngas"". Archived from the original on 29 September 2007.
- ^ K Pruess(2006), "A hot dry rock geothermal energy concept utilizing sCO
2 instead of water" Archived 2011-10-08 at the Wayback Machine - ^ Donald W. Brown(2000), "On the feasibility of using sCO
2 as heat transmission fluid in an engineered hot dry rock geothermal system" Archived 2006-09-04 at the Wayback Machine - ^ K Pruess(2007)Enhanced Geothermal Systems (EGS) comparing water with CO
2 as heat transmission fluids" - ^ J Apps(2011), "Modeling geochemical processes in enhanced geothermal systems with CO
2 as heat transfert fluid" - .
- .
- ^ http://earthsciences.typepad.com/blog/2011/06/achieving-carbon-sequestration-and-geothermal-energy-production-a-win-win.html ESD News and Events "Achieving Carbon Sequestration and Geothermal Energy Production: A Win-Win!"
- ^ "Aerogel.org » Supercritical Drying".
- PMID 16497403.
Further reading
- Mukhopadhyay M. (2000). Natural extracts using supercritical carbon dioxide. United States: CRC Press, LLC. Free preview at Google Books.