Carbon Capture and Storage

President Obama recently gave a speech at Georgetown University addressing global warming. He has recognized that limiting carbon emissions from power plants is an important step in reducing our contribution to the release of green house gases. One approach is the process where the Carbon Dioxide produced by burning fossil fuels such as coal is captured and stored, rather than released to the atmosphere.
 
If Carbon Capture and Storage (CCS) can be made to work, we could have our cake and eat it too.  That is, we could have the benefits of cheap energy without the negative consequences.   Basically CCS is a process of capturing the Carbon Dioxide waste stream from a power plant and then putting it somewhere other than the atmosphere.

The problem is that it is neither cheap nor easy. CCS technology could double the construction and operating costs of a power plant.   A further limitation is the need for storage sites such as airtight underground caverns or the ocean depths, where the carbon dioxide would stay for a long, long time. Like forever.
 
The best site would be a geologic formation where subsurface rock naturally reacts with carbon dioxide via a process which chemically mineralizes it. These formations exist but are few and far between. We need enough storage space for about thirty billion tonnes of carbon dioxide for this year and even more in future years due to growth.
 
Without mineralization, storage becomes much more difficult. Carbon dioxide, a gas at normal pressure, would need to be pumped into storage wells and the wells then capped to prevent release.  At atmospheric pressure it would require over six thousand cubic miles of underground open space per year. This kind of space doesn’t realistically exist, hence pressurization is necessary to reduce the volume.   The higher the pressure the more difficult it will be to contain the stored gas. Any leakage will increase the cost both economically and energetically- all that capture, transportation, and pressurization uses energy.
 
Another storage site to consider is the ocean depths.  The advantage of ocean storage is that the conditions of the abyssal plain are high pressure and low temperature.  Under these conditions carbon dioxide exists as a liquid with a volume only a fraction of that as a gas.   Slowly, the dissolved carbon dioxide would react with seawater forming carbonic acid. We would slowly turn the oceans of the world into salty soda water.  Rather than just sounding silly, it’s actually deadly.  The acidity created by the higher carbonic acid concentration would essentially sterilize the oceans.
 
The only way to store the thirty billion tonnes of carbon dioxide produced every year seems to be by pumping it at high pressure into every hole in the ground that we can find, plugging the hole and then hoping that the cap doesn’t come off, forever.  But what if a storage site does burp?
 
Lake Nyos is a crater lake in Africa.  Local conditions cause the lake to be supersaturated with carbon dioxide.  A limnic eruption occurred in 1986 for causes not entirely clear.240px-Nyos_Lake This event caused the near instantaneous release of close to 2 million tonnes of carbon dioxide. This is just like the classic mentos and diet coke eruptions, except deadly. The heavier-than-air gas killed about 1700 people and all their livestock.  This area was thinly populated or the death toll would have been much higher.
 
Carbon capture and storage, in the last analysis, is expensive, uses a lot of energy, and is quite risky to all life in the area of the storage wells.  Additionally Carbon Dioxide is only about half of the problem associated with global warming. The only real solution is abandon the use of fossil fuels and get all our energy from wind, solar and geothermal.

Leave a Reply

Your email address will not be published. Required fields are marked *