Correspondence/Rebuttal pubs.acs.org/est
Comment on “Review of Methane Mitigation Technologies with Application to Rapid Release of Methane from the Arctic”
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4. Clathrate Extraction. Established proposals exist for the commercial extraction of methane by controlled clathrate dissociation.8,9 This may be extended to unstable but uneconomic deposits. Extraction operations may risk inadvertent destabilization of surrounding deposits, necessitating caution. 5. Radical Chemistry. Zhou10 considered manipulation of atmospheric NOx, and found significant reductions to methane residency times. This technique could address a substantial fraction of the global methane budget by enhancing the principal sink. Ozone impacts are likely unacceptable in an unmodified Zhou scheme.
BACKGROUND Stolaroff discusses Global Warming Potential (GWP) and notes (with appropriate citations) methane’s short atmospheric lifetime and consequential high short-term GWP. Stolaroff also mentions the importance of possible changes to the OH radical sink upon major releaseincreasing GWP, and constituting a positive feedback to AGW. Kurtén 4 supports this argument, which is consistent with the paleoclimatic record. Stolaroff notes that two-thirds of current releases are anthropogenic, but that releases from feedbacks to AGW may alter this. Paleoclimatic records indicate a potentially significant role for natural methane releases in major climatic transitions, for example, the Palaeocene-Eocene Thermal Maximum1 (noted by Stolaroff) and the Permian-Triassic mass extinction.2 Feedback mechanisms discussed by Stolaroff, and by Lenton3 may play a role in future transitions. Therefore, possible societal and technical responses to any potential rapid releases of methane from natural sources are an important subject for research.
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EXPANDED TECHNIQUES 6. Drainage Management. Soil moisture influences methane budgets.11 A substantial fraction of the World’s land surface is artificially drained,12 and this may be extended to other wetlands. Pumped drainage, as in The Netherlands and New Orleans, allows water tables to be set below sea level. 7. Lake Sealing. Stolaroff et al. consider adding surfactants to lakes. Nonbiodegradable foaming agents may be suitable, for example, branched-chain isomers of sodium dodecylbenzene sulfonate. Biodegradability of these agents is well studied.13 Foam mechanics have been previously studied, partly due to industrial applications, such as brewing.14 Accompanying artificial aeration may be used to control anoxia and inhibit methanogenesis (where commercial recovery is not sought). However, added air can dilute the methane stream, complicating treatment. Alternatively, impermeable covers, for example, polymer sheeting, could be used to trap methane for treatment or use. 8. Bubble Management. Significant bubble streams from enduring point sources can be directed into ducting, then to the surface for flaring or use. Subject to seabed conditions, seeps may be plugged; sealed and ducted; or actively pumped. Relief wells may be drilled to intercept and depressurise source reservoirs. Engineering techniques can be adapted from the oil and gas industry.15,16 Salter17 proposed the use of pipe-laying ships to deploy impermeable sea floor sheeting, with ducting for gas recovery. This technique can be used for area sources, and grouped point sources. 9. Ignition. Small, inexpensive spark devices can ignite combustible methane/air mixtures at source. Technologies include piezo-electrics, or induction coils and spark plugs. Microrenewables can provide off-grid power. Ignition units can be designed for use on soil or water surfaces. Device distribution could be by air, vehicle or animal transport. 10. Compression-Heated Oxidation. Stolaroff et al. consider catalytically assisted compression heating and oxidation of rarefied methane, but not in reciprocating engines. Comparison of efficiency between engines types requires
ADDITIONAL TECHNIQUES
1. Water Depressurisation. Deep water in lakes exposed to local methane sources may have a partial pressure of methane greater than atmospheric. When depressurised (lifted), it becomes supersaturated and effervesces methanerich gas, permitting recovery. This ebullition changes buoyancy, therefore flow in continuous pipes can be self-sustaining, creating fountains. Installations using this principle manage CO2 concentrations in lakes, for example, Nyos, Cameroon.5 Kivu in DRC is undergoing comparable methane projects, for fuel extraction.6 This technique is potentially profitable for near-term scaling. Availability of suitable sites requires research. 2. Polytunnels. Agricultural polytunnels (hoop houses) are greenhouse-like linear structures. These are typically approximately semicircular in section; 1−5 m height; supported by metal/polymer tubes or rods; and covered with transparent polymer sheeting. They permit plant growth beneath, and infiltration of precipitation into adjacent soil. Due to gasimpermeable covers, they tend to concentrate methane seeps from covered soils, permitting treatment of methane-rich interior air. Seep distribution surveys are required, as biomescale ground coverage is likely impractical, due to costs and environmental impact. 3. Aquatic Strata Mixing. Geoengineering techniques for mixing strata have been proposed.7 Mixing may promote bubble dissolution by extending mean bubble path and altering methane partial pressure of surrounding water. Mixing may allow management of methanogenesis and methanotrophy by means of temperature adjustment, aeration, and nutrient transport. For point sources, targeted downwelling may raise water velocities at vents, thus reducing mean bubble radius, or aiding dissolution. © 2012 American Chemical Society
Published: October 8, 2012 13552
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Environmental Science & Technology
Correspondence/Rebuttal
rising methane and NOx concentration levels in the troposphere. http://www.atm.helsinki.fi/FAAR/reportseries/rs-109/abstracts/ Luxi%20Zhou.pdf (accessed August 6, 2012). (11) Torn, M.; Chapiniii, F. Environmental and biotic controls over methane flux from Arctic tundra. Chemosphere 1993, 26, 357 DOI: 10.1016/0045-6535(93)90431-4. (12) Feick, S., Siebert, S. Döll, P. A digital global map of artificially drained agricultural areas. In Frankfurt Hydrology Paper; Institute of Physical Geography, Frankfurt University: Frankfurt am Main, Germany, 2005; Vol. 4. (13) Zhang, C.; Valsaraj, K. T.; Constant, W. D.; Roy, D. Aerobic biodegradation kinetics of four anionic and nonionic surfactants at suband supra-critical micelle concentrations (CMCs). Water Res. 1999, 33, 115 DOI: 10.1016/S0043-1354(98)00170-5. (14) German, J. B.; McCarthy, M. J. Stability of aqueous foams: Analysis using magnetic resonance imaging. J. Agric. Food Chem. 1989, 37 (5), 1321 DOI: 10.1021/jf00089a025. (15) Bruist, E. H.; Shell Oil, Co A New Approach in Relief Well Drilling. J. Pet. Technol. 1972, Volume 24 (Number 6), 713−722. (16) Kuckes, Arthur F., Cornell U.; Lautzenhiser, T., Amoco Production Co.; Nekut, A.G., Amoco Production Co.; Sigal, R., Amoco Production Co. An electromagnetic survey method for directionally drilling a relief well into a blown out oil or gas well. SPE J., 1984, 24 (3), 269−274 (17) Salter, S. Can we capture methane at the Arctic seabed? Presentation to Methane Hack; Geological Society: London, December. 2011; http://www.methanenet.org/files/methanenet/ Book%20of%20Abstracts%201%20Dec_0.pdf (accessed August 6, 2012).
numerical modeling. Heat transfer losses are reduced in larger reciprocating engines (due to scale effects) therefore large marine diesel engines offer a starting point for modeling.
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CONCLUSION We broaden and refine the range of strategies for intervention in the methane budget proposed by Stolaroff. We note as background: a potential risk of methane feedbacks and Earthsystem tipping points; possible future increases in the GWP of methane; and the possible role of methane in mass extinctions. We note the expected low cost of additional study, and suggest research into a possible future global methane research and emissions limitation strategy, including management of natural sources. We recommend particular focus on techniques which offer near-term economic benefits by fuel recovery (e.g., clathrate extraction [4]; water depressurisation [1]), and globalscale techniques, (e.g., radical chemistry [5]). No criticism of Stolaroff’s work is implied. Andrew Lockley* 5 Park View, Newport Pagnell, Milton Keynes, MK16 9AD, U.K.
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AUTHOR INFORMATION
Corresponding Author
*Phone: +(44)7813979322; e-mail: andrew.lockley@gmail. com. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Schmidt, G. A.; Shindell, D. T. Atmospheric composition, radiative forcing, and climate change as a consequence of a massive methane release from gas hydrates. Paleoceanography 2003, 18, 1004 DOI: 10.1029/2002PA000757. (2) Krull, E. S.; Retallack, G. J. δ13C depth profiles from paleosols across the Permian-Triassic boundary: Evidence for methane release. Geol. Soc. Am. Bull. 2000, 112, 1459 DOI: 10.1130/0016-7606(2000) 1122.0.CO;2. (3) Lenton, T. M.; Held, H.; Kriegler, E.; Hall, J. W.; Lucht, W.; Rahmstorf, S.; Schellnhuber, H. J.Tipping elements in the Earth’s climate system. Proc. Natl. Acad. Sci. 2008, 105 (6): 1786−1793. doi:10.1073/pnas.0705414105 (4) Kurtén, T.; Zhou, L.; Makkonen, R.; Merikanto, J.; Räisänen, P.; Boy, M.; Richards, N.; Rap, A.; Smolander, S.; Sogachev, A.; Guenther, A.; Mann, G. W.; Carslaw, K.; Kulmala, M. Large methane releases lead to strong aerosol forcing and reduced cloudiness. Atmos. Chem. Phys. 2011, 11, 6961−6969, DOI: 10.5194/acp-11-6961-2011. (5) Kling, G. W.; Evans, W. C.; Tanyileke, G.; Kusakabe, M.; Ohba, T.; Yoshida, Y.; Hell, J. V. Degassing Lakes Nyos and Monoun: Defusing certain disaster. Proc. Natl. Acad. Sci. 2005, 102 (40), 14185 DOI: 10.1073/pnas.0502274102. (6) Contour Global website; “KivuWatt” project information. http:// www.contourglobal.com/portfolio/?id=11 (accessed August 6, 2012). (7) Zhou, S.; Flynn, P. C. Geoengineering Downwelling Ocean Currents: A Cost Assessment. Clim. Change 2005, 71, 203 DOI: 10.1007/s10584-005-5933-0. (8) MacDonald, G. J. The future of methane as an energy resource. Ann. Rev. Energy 1990, 15, 53−52, DOI: 10.1146/annurev.eg.15.110190.000413. (9) Lee, S. Methane hydrates potential as a future energy source. Fuel Process. Technol. 2001, 71, 181−186, DOI: 10.1016/S0378-3820(01) 00145-X. (10) Zhou Luxi, S. Smolander, T. Kurtén, A. Sogachev, A. Guenther, M. B.: “Assessing a NOx mitigation technique in an extreme methane concentration scenario: The chemical and climatic consequences of 13553
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