Wednesday, January 23, 2008

IS IT SAFE TO BURY CARBON DIOXIDE TO REDUCE GLOBAL WARMING?

IS IT SAFE TO BURY CARBON DIOXIDE TO REDUCE GLOBAL WARMING?
By
Dr. Nitish Priyadarshi


Each time you draw breath today, 380 molecules per million are carbon dioxide. That portion climbs about two molecules every year. Scientists know that carbon dioxide is warming the atmosphere, which in turn is causing sea level to rise, and that the carbon dioxide absorbed by the oceans is acidifying the water. But they are unsure of exactly how climate could alter across the globe, how fast sea level might rise, what a more acidic ocean could mean, which ecological systems on the land and in the sea would be most vulnerable to climate change and how these development might affect human health and well-being.

By burning fossil fuels-coal, oil, and natural gas- we are adding to the concentration of carbon dioxide, in the atmosphere. The carbon dioxide concentration is now 379 parts per million. This is significantly more than it has been at any time in the past 600,000 years. The consensus among climatologists is that the increased carbon dioxide concentration is the main cause of the increase in global temperature.

One way to reduce the amount of carbon dioxide being released into the atmosphere is to rely more on alternative energy source that do not produce CO2. These include hydroelectric, wind, solar, nuclear, geothermal, and tidal energy. Each of these has limitations, and it will be difficult to make a quick shift from fossil fuels to these other sources. But what if the CO2 produced by burning fossil fuels did not reach the atmosphere? Instead of letting CO2 go up the smokestack and into the air, can we capture it and put it somewhere? Is this possible?
Yes, it is. The process is called CO2 capture and storage. It is being done on a small scale right now. It has the potential to make a significant difference in the amount of CO2 we release into the atmosphere. As the name implies, there are two phases to the process. The first challenge is to capture the CO2 instead of letting it go up the smokestack. Then it has to be stored or “sequestered” safely and for a long time. The idea of sequestering CO2 to reduce the amount entering the atmosphere is fairly new. But the technology needed to do this has been developed for other reasons.
The best place to capture CO2 is at the major sources of emissions. Power stations that generate electricity produce about one-third of global CO2 emissions. In addition, CO2 is a by-product of iron and steel production, and cement production. CO2 is also removed from natural gas before it can be used as a fuel. These industrial processes are good candidates for CO2 capture and storage because they are large-scale sources in a fixed place. In contrast, it would be difficult to capture CO2 emissions from automobiles.

Storage in Geological Formations is currently the most promising solution for widespread, long term sequestration of CO2. The study shows that carbon dioxide could be compressed as it leaves the power plant and injected through a well deep underground into a natural sub layer consisting of porous rock, such as sandstone or limestone, saturated with saltwater. Some projects are already under the way. In order to reduce greenhouse gases and global warming, stored carbon dioxide must be kept out of atmosphere for hundreds or thousands of years. Oil and natural-gas reservoirs, deep saltwater aquifers, and coal seams have existed for millions of years with only very gradual changes. There is strong evidence that if properly managed, these formations could provide for long-term storage of carbon dioxide.

There are many underground sealed geological “traps” that have never contained oil or natural gas. Their pores are filled with water. These are called aquifers. The aquifers that are most suitable for CO2 storage are deep underground .They are filled with salt water, so they are unsuitable for supplying or storing fresh water for human use. CO2 would partially dissolve in the water in the aquifer. In some rock types, it might react with minerals to form stable carbonate deposits. This would permanently lock up the CO2. Geological studies would need to be made, as is routinely done for oil and natural-gas reservoirs, to confirm that the aquifer would not leak carbon dioxide.

Another potential storage medium is in coal deposits that are too deep to be mined. Coal is mostly carbon. It will absorb CO2 and lock it up permanently. In the process it releases methane that was previously adsorbed to the coal surface and that may be recovered. But the big problem arises here. Methane the other green house gas if not trapped properly can create more problem than CO2. After carbon dioxide, methane is the second most important greenhouse gas. Scientists believe that methane may have caused up to 20 percent of the global warming in the last 200 years. The gas is also highly flammable, which means it catches fire easily. Though methane remains in the atmosphere for only twelve years it may cause problem if not handed properly.

Storage of the carbon dioxide is envisaged either in the deep geological formations, deep oceans, or in the form of mineral carbonates. In the case of deep ocean storage, there is a risk of greatly increasing the problem of ocean acidification, a problem that also stems from the excess of carbon dioxide already in the atmosphere and oceans. Geological formations are currently considered the most promising sequestration sites, and these are estimated to have storage capacity of at least 2000 Gt C02 (currently, 30 Gt per year of carbon dioxide is emitted due to human activities). The State like Jharkhand of India which is reach in coal mines and thermal power stations, most of the areas are composed of highly weathered metamorphic rocks. Great amount of small to medium size fractures and joints are present in rocks. In the coal fields area numerous faulting has also been identified. It can allow escape of the carbon dioxide back to the atmosphere if injected here. It will multiply the problem.

Possible risks of capturing carbon dioxide:



1.Two classes of risk must be addressed for every storage reservoir: gradual and sudden leakage. Gradual release of carbon dioxide merely some of the green house gas to the air. Rapid escape of large amounts, in contrast, could have worse consequences than not storing it at all.

2. Although carbon dioxide is usually harmless, a large, rapid release of the gas is worrisome because high concentrations can kill.

3. Gradual leaks may pose little danger to life, but they could still defeat the climate goals of sequestration.

4. Geologists will have to search for faults in the caprock that could allow escape as well as determine the amounts of injection pressure that could fracture it.

5. Even if the geology is favorable, using storage formations where there are old wells may be problematic.

References:
1.Socolow, R.H. 2005. Can we bury Global Warming. Scientific American India.
2. http://web.mit.edu/newsoffice/2007/co2-0207.html
3. http://www.seed.slb.com/en/scictr/watch/climate_change/capture.htm
4.Our Warming Planet, 2004. Green alert, Times Editions, Singapore.

Dr. Nitish Priyadarshi
Geologist
Email: nitish.priyadarshi@gmail.com
rch_nitishp@sancharnet.in

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