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Chapter 4 - Geothermal Energy
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- By Barry Goldstein, Gerardo Hiriart, Ruggero Bertani, Christopher Bromley, Luis Gutiérrez-Negrín, Ernst Huenges, Hirofumi Muraoka, Arni Ragnarsson, Jefferson Tester, Vladimir Zui, David Blackwell, Trevor Demayo, Garvin Heath, Arthur Lee, John W. Lund, Mike Mongillo, David Newell, Subir Sanyal, Kenneth H. Williamson, Doone Wyborne, Meseret Teklemariam Zemedkun, David Wratt
- Edited by Ottmar Edenhofer, Ramón Pichs-Madruga, Youba Sokona, Kristin Seyboth, Susanne Kadner, Timm Zwickel, Patrick Eickemeier, Gerrit Hansen, Steffen Schlömer, Christoph von Stechow, Patrick Matschoss
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- Book:
- Renewable Energy Sources and Climate Change Mitigation
- Published online:
- 05 December 2011
- Print publication:
- 21 November 2011, pp 401-436
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- Chapter
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Summary
Executive Summary
Geothermal energy has the potential to provide long-term, secure base-load energy and greenhouse gas (GHG) emissions reductions. Accessible geothermal energy from the Earth's interior supplies heat for direct use and to generate electric energy. Climate change is not expected to have any major impacts on the effectiveness of geothermal energy utilization, but the widespread deployment of geothermal energy could play a meaningful role in mitigating climate change. In electricity applications, the commercialization and use of engineered (or enhanced) geothermal systems (EGS) may play a central role in establishing the size of the contribution of geothermal energy to long-term GHG emissions reductions.
The natural replenishment of heat from earth processes and modern reservoir management techniques enable the sustainable use of geothermal energy as a low-emission, renewable resource. With appropriate resource management, the tapped heat from an active reservoir is continuously restored by natural heat production, conduction and convection from surrounding hotter regions, and the extracted geothermal fluids are replenished by natural recharge and by injection of the depleted (cooled) fluids.
Global geothermal technical potential is comparable to global primary energy supply in 2008. For electricity generation, the technical potential of geothermal energy is estimated to be between 118 EJ/yr (to 3 km depth) and 1,109 EJ/yr (to 10 km depth). For direct thermal uses, the technical potential is estimated to range from 10 to 312 EJ/yr. The heat extracted to achieve these technical potentials can be fully or partially replenished over the long term by the continental terrestrial heat flow of 315 EJ/yr at an average flux of 65 mW/m2.
Flame Synthesis of Carbon Nanotubes
- Murray J. Height, Jack B. Howard, Jefferson W. Tester
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- Journal:
- MRS Online Proceedings Library Archive / Volume 772 / 2003
- Published online by Cambridge University Press:
- 15 February 2011, M1.8
- Print publication:
- 2003
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- Article
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Flames offer a potential for the synthesis of carbon nanotubes in large quantities at modest costs. This study aims to examine the conditions for carbon nanotube formation in premixed flames and to characterize the morphology of solid carbon deposits and their primary formation mechanisms in the combustion environment. Single walled nanotubes have been observed in the post-flame region of a premixed acetylene/oxygen/argon flame operated at 50 Torr (6.7 kPa) with iron pentacarbonyl vapor used as a source of metallic catalyst. A thermophoretic sampling method and transmission electron microscopy were used to characterize the solid material present in the flame at various heights above burner (HAB), giving resolution of formation dynamics within the flame system. Catalyst particle formation and growth are observed in the immediate post-flame region, 10 to 40 mm HAB, with coagulation leading to typical particle sizes on the order of 5 to 10 nm. Nanotubes were observed to be present after 40 mm HAB (∼34 milliseconds) with nanotube inception occurring as early as 30mm HAB (∼25 ms). Between 40 and 70 mm HAB (∼30 ms), nanotubes are observed to form and coalesce into clusters. Based on the rapid appearance of nanotubes in this region, it appears that once initiated, the nanotube growth occurs quite rapidly, on the order of 10 νm/s. A nanotube formation ‘envelope’ is evident with a formation limited to fuel equivalence ratios between a lower limit of 1.5 and an upper limit of 1.9. A continuum of morphologies ranging from relatively clean clusters of nanotubes to amorphous material is observed between the lower and upper limits. We suggest that the diversity of morphologies is due to competition between carbon precipitation pathways. High resolution TEM revealed the nanotubes to be primarily single walled. Raman spectroscopy confirmed the presence of single wall nanotubes and indicated a broad range of diameters and differences in chirality to plasma-arc generated material.