Environmental Engineering Reference
In-Depth Information
After capture, CO 2 is generally transported in gaseous phase. Transport
in a supercritical state 1 avoids any risk of a phase change. Carbon dioxide
transport by tankers (road, rail or sea) is possible, but due to the large
flow rates which are generally required, pipe transport is considered to
be the most realistic option in the future. In the USA an extensive pipe
network already exists for transporting CO 2 used for enhanced oil
recovery (EOR).
Thus, CO 2 produced from natural underground reservoirs located in
New Mexico and Colorado is transported to West Texas. Around 22
million tons of CO 2 per year are transported through a 3980 km long
network of pipes to be used for EOR.
Transporting CO 2 by pipeline is therefore awell established technology
and the deployment of CO 2 pipe networks does not raise any specific
technical difficulty.
Furthermore, CO 2 is a stable gas, weakly toxic at least when diluted in
the atmosphere, and nonexplosive. It is less dangerous to transport and to
store than natural gas, for which the logistics of transport and distribution
have been quite well mastered. Nevertheless, installing a pipe in a densely
populated area often remains a difficult and expensive task.
Geological storage
The minimum period of time during which CO 2 needs to be stored is
long but not unlimited. It has to last over one to two centuries, in order
to cover the period during which the issue of CO 2 emission is likely to
remain critical. Beyond such a period of time, CO 2 stored underground
might be used as a source of carbon, and could be recycled by using a
low carbon energy which should become widely available by that time.
In order to keep the option fully safe, storage time durations which
are presently considered amount generally to one or several thousand years.
Storage in deep oceans has also been considered as a potential option,
but suffers two major drawbacks: firstly, the long term behaviour of
such storage is difficult tomodel; secondly, the impact of an increase of the
CO 2 concentration on marine ecosystems is difficult to assess
and potentially dangerous. An accumulation of CO 2 might lead to an
excessive acidification of the ocean. An increase of the temperature might
1 Above a certain pressure, called the 'critical pressure' in the case of a pure component, it is no
longer possible to obtain two phases, one liquid and one vapour, by lowering the temperature.
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