Sunday, 10 April 2011

Could Carbon Capture be the technology to save the planet?

Although nobody knows excatly how much carbon dioxide is too much, it is widely recognised that carbon dioxide does cause the planet to heat up.  It has been calculated that the release of  450 parts per million of carbon dioxide would provoke a 2 degrees celcuis rise in global temperatures and amognst some, of the many, consequences associated with this rise include a higher number of agricultural failures, ocean acidification and the possibilty of a higher frequency of natural disasters. Despite the fact that no one knows for certain how much carbon dioxide is too much, some scientists have been working on calculating the world's carbon budget and how much of it has already been used up. It is believed that the world is already over halfway through its carbon emissions budget and, to satisfy current demand, the trillionth tonne of carbon will be burned within the next 20 - 30 years, which suggests that by 2050, 57 gigatonnes/year will be emitted - unless something is done to reduce this!

These slightly worrying trends have called for the need for a rapid way to reduce carbon dioxide emissions and many countries, both developed and industralizing, are now starting to look at carbon capture and sequestration technology as a cost-effective way to provide 1/5 of the reductions required by 2050. There are currently three different methods to capture carbon dioxide, although some development is required to make them more energy efficient in the future - especially if they are to provide a sustainable option for allowing carbon dioxide reductions.

1) POST COMBUSTION - involves the capturing of carbon dioxide from exhaust gas and then the reaction between chemicals known as amines and the exhaust gas which is bubbled through it. The heating of the solvent releases the concentrated carbon dioxide thereby allowing the solvent to be reused. This process is presently used in the natural gas processing industry, as it can be fitted to existing power plants, and is being piloted at carbon capture plants. In the future it is likely that the amines used will be replaced by similar chemicals that require less heat to release the carbon dioxide and are more resistant to degradation by other chemicals present in the exhaust gas.
2) PRE-COMBUSTION - this method is the stripping of the carbon dioxide, from the fuel, before it is burned by a series of interlinked chemical reactions. Firstly, the fossil fuel is converted to carbon monoxide and hydrogen, which is reacted with water vapour to form hydrogen and carbon dioxide, a mixture that can be seperated with ease. The hydrogen can then be burned and used to generate energy and because of this, many of the proposed CCS projects are likely to utilise this method.
3) OXYFUEL COMBUSTION - this method comprimises of burning the fuel in pure oxygen instead of air as it means that the exhaust gas consists, mainly, of carbon dioxide and water which can be easily seperated. Currently, only a handful of pilot plants exploit this method as producing the pure oxygen required is both costly and energy-intensive.

These three methods are currently the most developed ways of capturing carbon dioxide but there are some others. Another technology that is currently being developed is the use of crystalline compounds called metal organic frameworks. Changes in pressure provoke these materials to selectively soak up carbon dioxide or release it. Due to the fact that minimal equipment is needed and energy consumption, compared to current methods, is relatively low, it is believed that this could be implemented on a industrial scale in the not too distant future. Another, very different method, is to use algae as, as they photosynthesise they take in carbon dioxide. This method would also produce biomass which could be reused as biofuel. However, a very large area would be required to make this method viable.

Although the idea of capturing carbon dioxide may sound like an attractive option to many of you, like every method of boosting environmental credientals and every step taken to a more greener sustainable lifestyle, it is not a simple as it first seems. There are huge costs involved, at present, with constructing CCS's and unless governments commit funds to the development of this technology, it is unlikely to be developed on a commercial scale. In the UK, the government has committed £1 billion to a project that aims to develop the UK's first large-scale project and, as part of the European Economic Recovery Plan, 1 billion euros has been split between six CCS projects.  It is hoped that the EU's emissions trading scheme will also help to encourage industries to develop CCS's projects. At present, Norway is the most developed country, in terms of carbon capture. In 1991 they introduced a high tax on carbon dioxide emissions which resulted in the implementation of CCS at two of the large offshore natural gas facilities (Sleipner opened in 1996 and Snohvit in 2007). To date, these projects, combined, have mananged to capture 12 million tonnes of carbon dioxide and store deep beneath the bed of the Norwegian Sea. Although Norway have managed to store the carbon they have collected, this is the problematic issue surrounding the idea of carbon capture and, where do you store it?   Well firstly the carbon dioxide has to be compressed to a supercritical state (which is neither liquid or gas but kind of a bit of both) so it can be transported, via pipes, to suitable sites for sequesteration. The transportation stage of the process is easy enough and there is already 3,900 miles of transport pipes across the USA alone. carbon dioxide can also be transported by sea in tankers and tankers continually cross the North Sea carrying carbon dioxide for fizzy drinks and cleaning and so far, there have been no major accidents. The issue is, where do you transport the carbon dioxide to. Only certain areas have the right geology to contain carbon dioxide within the rocks and Europe seems to hold many of them. and the UK accounts for 35% of the known possible sites for geological sequestration at present. Although development into building materials that are capable of stabilizing and embodying carbon dioxide is taking place, saline aquifers, at present, remain the best locations for geological sequestration. Saline aquifers in rocks are suffieciently permeable to absorb the carbon dioxide and suffieciently stable and isolated to ensure that the carbon dioxide remains within the rocks. The pores, within the rocks, inside the saline formations trap the carbon dioxide via cappilary forces. Over a long period of time the carbon dioxide dissolves into the liquids contain within the saline formations and the minerals within the rocks. Due to the fact that carbon dioxide is buoyant and naturally migrates towards the surface it has to be injected into, not only th e correct geological area, but also to a depth of atleast 1 kilometre. The pressure and heat at this depth maintains the carbon dioxides supercritical state and thus it is less likely to migrate towards the surface. The layers of impermeable rocks,normall yshale and clays or minerals and salts left behind by the evaporation of ancient waters in an earlier geological age, also prevents the migration of the sequester carbon dioxide to the surface. Finding suitable sites for storing carbon dioxide is not the only problem -  get liscensing and public support for such projects is hard due to othe risks involved. Although not linked in any way to the sequestration of carbon dioxide the Lake Nyos tradegy has made people aware of the potential risks to human health if the stored carbon dioxide managed to migrate to the surface. This tradegy occured in 1986 in Cameroon and it furthered the public's concern about the siting of CCS repositories. The sudden release of large amounts of carbon dioxide from deep beneath the bottom of the Lake Nyos killed more than 1,700 people and 3,000 cattle. The orgin of the carbon dioxide was melted magma located 50 miles beneath the bottom of the lake and as the gas made its way through the vents in the underlying rocks it saturated the water at its bottom depths. The natural movement and churning of freshwater, from top to bottom, caused a sudden explosive geyser of carbon dioxide to powerfully spout to the surface and because carbon dioxide is heavier than air, it spilled over the banks and down the hillside. People are, understandable concerned, about the possibility of this happening due to carbon dioxide being injected into the ground, the possibilty of freshwater aquifers being contaminated and, if not checked and plugged, abandoned wells serving as chimneys for the sequestered carbon dioxide.

Despite this, it does look as if there is a future for carbon capture and sequestration. Scientists and engineers are getting more and more confident that safe transport and storage is possible as natural carbon dioxide has been stored underground, for example under large swathes of central France and the south-west of America, for millions of years. It is true that further development of the current methods and technolgy is needed but it is believed that much of this can be derived from the oil and natural gas industries. Countries like China, India and Brazil, who are all rapdily industralising, are also looking to develop this technology as it seems to hold a rapid, and attractive, way of reducing carbon dioxide emissions. Do I think that this technology can save the planet? Well, on its own, no. Data suggests that it can only provide 20% of the reductions in emissions required by 2050 and although this is quite a substantial chunk, it is not enough. The idea is quite attractive and, as urgency is required, it starts to look more and more so.  However, I worry slightly that if science continues to develop technologies, like this one, people will continue to lead our current unsustainable lifestyles and that attitudes towards energy consumption will not change due to an optmisitic belief that we will solve every problem we face. I also think that strict regulations need to be implemented along with this developing industry as storing carbon dioxide in the wrong areas could have disastrous impacts. Therefore, I think that this technology could have a future and, along with a change in attitudes and a more greener approach to energy production, it would help to reduce emissions. This is just my opinion and so what do you think? Do you think that carbon capture could be the technology to save the planet or do you think that governments would be better off investing in other technologies that could boost their countries environmental credentials?

1 comment:

  1. great :) Greener tech + carbon capture = planet saved