CO2 mitigation options have been overviewed from an engineering point of view. There have been proposed a number of mitigation options, which can be divided into three categories; 1. reduction of energy intensity; 2. reduction of carbon intensity; 3. carbon sequestration. In this review paper, various mitigation options are reviewed focusing on the carbon sequestration options.A reduction in energy intensity is essentially an energy saving. A reduction in carbon intensity could be achieved by switching to energy resources with lower carbon contents. Based on the 2001 IPCC report, the mitigation potential related to energy intensity is estimated at 1, 900–2, 600 Mt-C/year in 2010, and 3, 600–5, 050 Mt-C/year in 2020, including other greenhouse gas equivalents. There are additional benefits in implementing these options; they are economically beneficial, and have no associated harmful effects. The carbon sequestration options can be divided into two categories; the enhancement of the natural sinking rates of CO2, and a direct discharge of anthropogenic CO2. The relevant sequestration options in the first category include terrestrial sequestration by vegetation, ocean sequestration by fertilization, and an enhancement of the rock weathering process. In the direct discharge options, the CO2 produced from large point sources, such as thermal power stations, would be captured and separated, then transported and injected either into the ocean or underground. Although the sequestration options are less beneficial in terms of cost per unit CO2 reduction compared to other options, technical developments in sequestration options are necessary for the following reasons; 1. A huge potential capacity for carbon sequestration, 2. carbon sequestration enables a continuous use of fossil fuels, which is unavoidable at the moment, before switching to renewable energy sources. Each sequestration option has advantages and disadvantages in terms of capacity, cost, the time scale of the sequestration, the stability of sequestered CO2, and additional environmental impacts, which depend on the location, time, and amount of sequestration. Thus, reliable evaluations of the mitigation efficiency are essential for each sequestration option upon implementation.

An overview of CO2 mitigation options for global warming -Emphasizing CO2 sequestration options

▪ Abstract Fossil fuels play a crucial role in satisfying growing world energy demands, but their continued use could cause irreparable harm to the environment. Unless virtually all anthropogenic carbon dioxide is captured, either at the source or subsequently from the air, and disposed of safely and permanently, fossil fuels may have to be phased out over the next few decades. Sequestration of waste carbon dioxide will require methods that can safely store several trillion tons of carbon dioxide. Long-term storage of a gaseous substance is fraught with uncertainty and hazards, but carbonate chemistry offers permanent solutions to the disposal problem. Carbonates can be formed from carbon dioxide and metal oxides in reactions that are thermodynamically favored and exothermic, which result in materials that can be safely and permanently kept out of the active carbon stocks in the environment. Carbonate sequestration methods require the development of an extractive minerals industry that provides the base i...

Carbonate chemistry for sequestering fossil carbon

http://web.mit.edu/wbdurham/www1/papers/79-Rehder-2004-GCA.pdf

Dissolution rates of pure methane hydrate and carbon-dioxide hydrate in undersaturated seawater at 1000-m depth

Direct oceanic disposal of fossil fuel CO2 is being considered as a possible means to moderate the growth rate of CO2 in the atmosphere. We have measured the rise rate and dissolution rate of freely released CO2 droplets in the open ocean to provide fundamental data for carbon sequestration options. A small amount of liquid CO2 was released at 800 m, at 4.4 degrees C, and the rising droplet stream was imaged with a HDTV camera carried on a remotely operated vehicle. The initial rise rate for 0.9-cm diameter droplets was 10 cm/s at 800 m, and the dissolution rate was 3.0 micromol cm(-2) s(-1). While visual contact was maintained for 1 h and over a 400 m ascent, 90% of the mass loss occurred within 30 min over a 200 m ascent above the release point. Images of droplets crossing the liquid-gas-phase boundary showed formation of a gas head, pinching off of a liquid tail, and rapid gas bubble separation and dissolution.

Experimental determination of the fate of rising CO2 droplets in seawater.

From the interfacial tension (γ) measurement, we have analyzed the interfacial organization that occurs between pure H2O and pure CO2 from a kinetical and rheological point of view. This article is the followup to a previous one, where we showed that this equilibrated interface is composed of small H2O−CO2 cluster blocks [Tewes, F.; Boury, F. J. Phys. Chem. B 2004, 108, 2405].1 By analyzing the variation of γ with the square root of time, we found that the organization of the H2O−CO2 interface is, in the initial times, controlled by the diffusion of the CO2 molecules into the water. We compared the frictional coefficient determined from the measured CO2 diffusion coefficient with the frictional coefficient calculated from the Stokes equation (frictional ratio). From that, we concluded that it is a hydrated form of CO2 that diffuses and that the degree of hydration decreases with pressure. Rheological properties of the equilibrated interface vary with CO2 pressure, in the range of 50−90 bar, from a viscoel...

Y. Mori

Papers

Dissolution rate of liquid CO2 in pressurized water flows and the effect of clathrate films