Sequestration of carbon

A number of current coupled ocean-atmosphere climate models predict that the overturning of the North Atlantic may decrease somewhat under a future warmer climate.While this is not a feature that coupled models deal with well, its direct impact on the ocean s sequestration of carbon would be to cause a significant decline in the carbon that is stored in the deep water. This is a positive feedback, as oceanic carbon uptake would decline. Flowever, the expansion of area populated by the productive cool water plankton, and the associated decline... 

There are two main schemes proposed for sequestration of carbon dioxide. The first (referred to as a chemical absorption process), suitable for use at low pressures and temperatures, is usually adopted where the CO2 is to be removed from exhaust flue gases. The second (usually referred to as a physical absorption process), for use at higher pressures, is recommended for separation of the CO2 in syngas obtained from conversion of fuel. 

The steam reforming of natural gas process is the most economic near-term process among the conventional processes. On the other hand, the steam reforming natural gas process consists of reacting methane with steam to produce CO and H2. The CO is further reacted or shifted with steam to form additional hydrogen and CO2. The CO2 is then removed from the gas mixture to produce a clean stream of hydrogen. Normally the CO2 is vented into the atmosphere. For decarbonization, the CO2 must be sequestered[l,2]. The alternative method for hydrogen production with sequestration of carbon is the thermal decomposition of methane. 

White C. Sequestration of carbon dioxide in coal with enhanced coalbedmethan re-covery-a review. 2005 Energy Fuels 19(3) 659-724. 

The sequestration of carbon in soil has a considerable influence on the GHG balance of biofuels. Although the GHG balance of the production and utilisation of energy crops is approximately zero, except for some additional C02 equivalents mainly caused by the N fertilisation and the consumption of fossil energy (see Chapters 7 through 9), the storage or the release of carbon in soil may disturb this balance. 

Stanton, R., Flores, R., Warwick, P. D., Gluskoter, H. and Strieker, G. D. (2001). Coal bed sequestration of carbon dioxide. Proceedings of the First National Conference on Carbon Sequestration, 14-17 May 2001. Washington, DC. 

The idea here is to capture carbon dioxide from power plants and then inject it into natural gas hydrate reservoirs assumed to contain primarily methane hydrate. Thus one achieves the simultaneous sequestration of carbon dioxide with the production of natural gas. Lee et al. (2003) presented laboratory data that showed the replacement of methane molecules by C02. Yoon et al. (2004) and Ota et al. (2005) confirmed these laboratory findings. Park et al. (2006a) used a CO2/N2 mixture containing 20 mol % carbon dioxide (flue gas) instead of pure C02 and noticed that the methane recoveiy increased from 64 to 85 %. A similar idea for sequestering captured C02 is to use it as cushion gas for natural gas storage in reservoirs (Oldenburg, 2003). 

Kaszuba, J. P Janecky, D. R. Snow, M. G. 2003. Carbon dioxide reaction processes in a model brine aquifer at 200 degrees C and 200 bars implications for geologic sequestration of carbon. Applied Geochemistry, 18, 1065-1080. 

An additional step that can be added to IGCC plants is the capture or sequestration of carbon. 

Some of the technologies in the analysis are further differentiated by whether carbon dioxide resulting from hydrogen generation is separated and sequestered. In particular, the midsize and the central station production facilities at which production is based on natural gas, coal, or biomass are examined both with and without the sequestration of carbon dioxide. 

Finding 5-11. Carbon dioxide emissions could be brought down to near zero with biomass, with electrolysis depending exclusively on wind turbines or photovoltaics, with nuclear energy, or with the successful sequestration of carbon diox-... 

Following are the hydrogen production spreadsheets that are the basis for Chapter 5 in this report. As noted there, these charts are for different combinations of feedstock, status of technology (current versus possible future), and whether or not sequestration of carbon dioxide is required at facilities processing hydrocarbon feedstock. A modified version of Table 5-2, with additional pathways, is included here as Table E-l for convenience in following the charts. This table lists the code for each pathway as used for identification in the charts. 

For geo-sequestration of carbon dioxide in flue gas it may be necessary to first remove sulphur so as to protect the carbon dioxide solvent. The flow from the flue system has to be modified to include an additional plant prior to compression, carbon dioxide and geosequestration as illustrated by Figure 6.3. 

Sombroek, W. G., F. O. Nachtergaele, and A. Hebei. 1993. Amounts, dynamics and sequestration of carbon in tropical and subtropical soils. Ambio 22 417-426. 

The availability of nitrogen in the euphotic zone is an important, potentially limiting factor for productivity and the biological sequestration of carbon in the ocean. There are three principal routes by which new nitrogen makes its way into the euphotic zone of the Atlantic Ocean Physical transport of nitrate, nitrogen fixation by diazotrophic organisms, and aeolian transport and deposition. 

Michaels et al., 2001) (see Carpenter Capone, Chapter 4, this volume). In part because of its sensitivity to climate variabihty and its potential role in the marine sequestration of carbon. 

Mineral dissolution kinetics influence such phenomena as development of soil fertility, amelioration of the effects of acid rain, formation of karst, acid mine drainage, transport and sequestration of contaminants, sequestration of carbon dioxide at depth in the earth, ore deposition, and metamorphism. On a global basis, mineral weathering kinetics are also involved in the long-term sink for CO2 in the atmosphere ... 

Draper, E.L. Becker, R.A. Research and Development Needs for the Sequestration of Carbon Dioxide as Part of a Carbon Management Strategy The National Coal Council Washington, DC, 2000. 

Explain the role of increased nitrogen deposition in sequestration of carbon. Use the description of the MEL model for the discussion. 

Management of atmospheric carbon dioxide levels will require sequestration of carbon dioxide. Research and development into methods to cost effectively capture and geologically sequester carbon dioxide is required in the next 10 to 20 years.5... 

Biomass burning results in the sequestration of carbon as charcoal, constituting a significant sink for atmospheric carbon dioxide and therefore a source of atmospheric oxygen. The charcoal is not subject to microbial oxidation. On the geological time scale atmospheric oxygen levels may increase, which increases the risk of fires and thus establishes a positive feedback loop for the buildup of atmospheric oxygen. 

In summary, it is clear that vigorous basic research programmes on catalysts and on membrane separation processes should be instigated if hydrogen from fossil sources is to reach its full potential and become cost-effective. Similarly, further investigation is necessary to define the optimum conditions for the direct conversion of wet biomass to hydrogen. Sequestration of carbon dioxide, which is another important topic for research, is discussed in the following chapter. 

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