Sept/Oct 2007

The search for low-cost CO2 storage

By H. E. Robinson

It is impossible to mention clean coal technology without discussing the challenges of carbon capture and sequestration (CCS). While the development of new technologies in coal processing address how to reduce emissions and make the best use of by-products, CCS deals with long-term storage of carbon dioxide. Carbon dioxide (CO2) is a greenhouse gas associated with the increase in global temperatures. In an attempt to reduce the negative effects of fossil fuel burning, CO2 produced by this process can be stored to prevent emissions to the atmosphere. Coal gasification is one method of producing high-purity CO2 that can be used for applications such as enhanced oil recovery.

One of the ways to manage captured CO2 is storing it in geological formations. These may include oil fields, coal seams, or saline formations. Redistributing CO2 in soil beneath the surface traps the gas and prevents it from escaping to the atmosphere. Enhanced oil recovery is an example of this method being used by projects such as the International Energy Agency’s Weyburn project in Saskatchewan. Carbon dioxide is injected into depleted oil fields in order to improve the flow of oil, which can then be extracted. Because this method enhances oil field production, it can offset the cost of injecting CO2. Similarly, CO2 can be stored in unminable coal seams where the gas releases methane, which can be recovered and used as compensation for the cost of CO2 storage. Other methods of geo-sequestration include storage in saline formations; however, there are no economically viable by-products to offset the costs associated with carbon sequestration.

Geo-sequestration has a great deal of potential for Alberta. The Western Sedimentary Basin can provide storage for CO2 in large quantities. Paul Clark, president of Ripley Canyon Resources Ltd. and a proponent of clean coal technology, said “Alberta has unlimited storage or sequestration in aquifers.” He also noted “carbon capture and sequestration is not cheap. Examples like the Weyburn project put a value on CO2 by using it in enhanced oil recovery.”

Using old oil fields for carbon storage can present problems such as leakage. This means that all entrances and pipes leading from the surface to the oil field must be entirely sealed. For storage sites that are selected and managed well, CO2 can be retained for hundreds of years.

Another alternative for CO2 storage is deep in the oceans. Water at these depths can circulate for hundreds of years before reaching the surface. However, little is known about the effects that this would have on marine life. Also, CO2 reacts with seawater and could increase the acidity of the oceans, which would affect organisms that have calcium bicarbonate structures, such as snails, clams, and corals.

There are several different options for carbon storage that are currently being explored. The challenges any effective measure will have to overcome are primarily the cost of CSS and the potential long-term effects to the environment.

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