Ocean Storage

The following question then arises would it be sensible and acceptable to dispose of captured carbon dioxide in the oceans Such action would merely be accelerating a natural process and may not therefore fall under the international convention on the dumping of industrial wastes at sea. This is a matter for marine biologists, lawyers and politicians to debate. In terms of the technology, there are two broad approaches that might be adopted  

Both of these methods have the potential to increase significantly the rate at which carbon is absorbed by the marine environment. 

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In spite of these limitations, estimates for ocean storage capacity in excess of 100,000 billion GtC have been cited (Herzog et al., 1997). Such numbers would only be feasible if alkalinity (i.e., NaOH) is added to the ocean to neutralize the corresponding amounts of carbonic acid formed. Over thousands of years, the dissolution of calcareous oozes at the bottom of the ocean could provide such alkalinity (Archer et al., 1997 Broecker and Takahashi, 1978). 

Although ocean sequestration is promising in terms of carbon sequestration capacity, the environmental impact may limit the acceptability of ocean storage since the strategy is predicated on the notion that the impacts on the ocean will be less than the avoided impact of these emissions to the atmosphere. Environmental concerns in ocean sequestration focus... 

In the mid-term, sequestration pilot testing will develop options for direct and indirect sequestration. The direct options involve the capture of C02 at the power plant before it enters the atmosphere coupled with "value-added" sequestration, such as using COz in enhanced oil recovery (EOR) operation and in methane production from deep unmineable coal seams. "Indirect" sequestration involves research on means of integrating fossil fuel production and use with terrestrial sequestration and enhanced ocean storage of carbon. 

Herzog et al [5] compared and summarized five ocean storage options as shown in Table 1. Fujioka et al [11] reported cost evaluation results on ocean disposal (capture and storage) options as shown in Table 2. 

The high pointial for underground-storage and lower cost than that of ocean storage has led to geological storage as a major option for COj disposal. 

Figure 3.10 Schematic representation of ocean storage options. In dissolution type ocean storage, the carbon dioxide rapidly dissolves in the ocean water, whereas in lake type ocean storage, the carbon dioxide is initially a liquid on the sea floor, soon crystallizing as a hydrate. Given sufficient time, all forms of carbon dioxide - gas, liquid, hydrate - will dissolve in the water.

W.G. Ormerod, P. Freund and A. Smith (eds.), with revisions by J. Davison, Ocean Storage of Carbon Dioxide, 2nd Edition, March 2002, Report by the lEA Greenhouse Gas R D Programme, Cheltenham, 2002. 

Environmental impacts may be the most significant factor determining the acceptability of ocean storage, since the strategy is predicated on the notion that impacts to the ocean will be significantly less than the avoided impacts of continued emission to the atmosphere. Earlier, environmental impacts were discussed from the global viewpoint. Here, we examine the environmental impacts near the injection point. 

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