Info

Figure 6.13 Volume of water with a ApH less than the value shown on the horizontal axis for the simulations shown in Figure 6.12 corresponding to CO2 releases from a 500 MWe power plant. The fixed pipe simulation produces a region with ApH < -1, however, the moving ship disperses the CO2 more widely, largely avoiding pH changes of this magnitude.

injected CO2 for hypothetical examples of ocean storage (e.g., Orr, 2004). Wickett et al. (2003) estimated that injection into the deep ocean at a rate of 0.37 GtCO2 yr-1 (= 0.1 GtC yr-1) for 100 years would produce a ApH < -0.3 over a volume of sea water equivalent to 0.01% or less of total ocean volume (Figure 6.14). In this example, for each GtCO2 released to the deep ocean, less than about 0.0001%, 0.001% and 0.01% of

Figure 6.14 Estimated volume of pH perturbations at basin scale (Wickett et al., 2003). Simulated fraction of global ocean volume with a ApH less than the amount shown on the horizontal axis, after 100 years of simulated injection at a rate of 0.37 GtCO2 yr-1 (= 0.1 GtC yr-1) at each of four different points (two different depths near New York City and San Francisco). Model results indicate, for example, that injecting CO2 at this rate at a single location for 100 years could be expected to produce a volume of sea water with a ApH < -0.3 units in 0.01% or less of total ocean volume (0.01% of the ocean is roughly 105 km3). As with other simulations of direct CO2 injection in the ocean, results for the upper ocean (e.g., 800 m) tend to be more site-specific than are results for the deep ocean (e.g., 3000 m).

Figure 6.14 Estimated volume of pH perturbations at basin scale (Wickett et al., 2003). Simulated fraction of global ocean volume with a ApH less than the amount shown on the horizontal axis, after 100 years of simulated injection at a rate of 0.37 GtCO2 yr-1 (= 0.1 GtC yr-1) at each of four different points (two different depths near New York City and San Francisco). Model results indicate, for example, that injecting CO2 at this rate at a single location for 100 years could be expected to produce a volume of sea water with a ApH < -0.3 units in 0.01% or less of total ocean volume (0.01% of the ocean is roughly 105 km3). As with other simulations of direct CO2 injection in the ocean, results for the upper ocean (e.g., 800 m) tend to be more site-specific than are results for the deep ocean (e.g., 3000 m).

the ocean volume has ApH of less than -0.3, -0.2, and -0.1 pH units respectively. Caldeira and Wickett (2005) predicted volumes of water undergoing a range of pH changes for several atmospheric emission and carbon stabilization pathways, including pathways in which direct injection of CO2 into the deep ocean was assumed to provide either 10% or 100% of the total atmospheric CO2 mitigation effort needed to stabilize atmospheric CO2 according to the WRE550 pathway. This assumed a CO2 production scenario in which all known fossil-fuel resources were ultimately combusted. Simulations in which ocean injection provided 10% of the total mitigation effort, resulted in significant changes in ocean pH in year 2100 over roughly 1% of the ocean volume (Figure 6.15). By year 2300, injection rates have slowed but previously injected carbon has spread through much of the ocean resulting in an additional 0.1 pH unit reduction in ocean pH over most of the ocean volume compared to WRE550.

6.2.1.6 Behaviour of CO2 lakes on the sea floor Long-term storage of carbon dioxide might be more effective if CO2 were stored on the sea floor in liquid or hydrate form below 3000 metres, where CO2 is denser than sea water (Box 6.2; Ohsumi, 1995; Shindo et al., 1995). Liquid carbon dioxide could be introduced at depth to form a lake of CO2 on the sea floor (Ohsumi, 1993). Alternatively, CO2 hydrate could be created in an apparatus designed to produce a hydrate pile or pool on the sea floor (Saji et al., 1992). To date, the concept of CO2 lakes on the sea floor has been investigated only in the laboratory, in small-scale (tens of litres) in-situ experiments and in numerical models. Larger-scale in-situ experiments have not yet been carried out.

Liquid or hydrate deposition of CO2 on the sea floor could increase isolation, however in the absence of a physical barrier the CO2 would dissolve into the overlying water (Mori and Mochizuki, 1998; Haugan and Alendal, 2005). In this aspect, most sea floor deposition proposals can be viewed as a means of 'time-delayed release' of CO2 into the ocean. Thus, many issues relevant to sea floor options, especially the far-field behaviour, are discussed in sections relating to CO2 release into the water column (e.g., Section 6.2.1.5).

CO2 released onto the sea floor deeper than 3 km is denser than surrounding sea water and is expected to fill topographic depressions, accumulating as a lake of CO2 over which a thin hydrate layer would form. This hydrate layer would retard dissolution, but it would not insulate the lake from the overlying water. The hydrate would dissolve into the overlying water (or sink to the bottom of the CO2 lake), but the hydrate layer would be continuously renewed through the formation of new crystals (Mori, 1998). Laboratory experiments (Aya et al., 1995) and small deep ocean experiments (Brewer et al., 1999) show that deep-sea storage of CO2 would lead to CO2 hydrate formation (and subsequent dissolution).

Predictions of the fate of large-scale CO2 lakes rely on numerical simulations because no large-scale field experiments have yet been performed. For a CO2 lake with an initial depth of 50 m, the time of complete dissolution varies from 30 to 400 years depending on the local ocean and sea floor environment. The time to dissolve a CO2 lake depends on its depth, complex

Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment