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Carbon Capture and Storage

There’s no getting away from it; making cement is an energy intensive process.  First you need to dig large amounts of limestone out of the ground.  Then you need to crush it to a fine powder.  Then you need to heat it to volcanic temperatures until it forms nodules of cement ‘clinker’.  Finally, you need to grind the cement clinker back to a fine powder, add a bit of gypsum to control setting times, and hey presto you have that well known grey powder called cement!

So why go to all that trouble, use all that energy and emit greenhouse gases for something as basic as cement?  The answer is simple: cement is essential for economic and social development.  Cement is the critical ingredient in concrete, said to be the second most consumed substance on the planet after water.  The very foundations of our modern lives depend on it.  The homes we live in, the schools our children go to, the hospitals we go to when we need medical help, the roads and bridges we drive on and much, much, more all depend on concrete.  Look around you and you will hardly notice it.  Look again and it is everywhere.

The UK cement industry has made impressive progress to address the carbon issue.  Since 1990, the Kyoto Protocol baseline year, the UK cement industry has reduced its absolute carbon footprint by 58%.  Some of this is through reduced production, but a large part is down to major investment in energy efficiency and the use of waste derived fuels to replace fossil fuels.

This is an essential part of the industry’s carbon reduction strategy, but it can only go so far.  In the UK 39% of the cement industry’s carbon emissions come from fuels and other sources, 61% comes from the calcination (driving off carbon) from the limestone raw materials.  These emissions are irreducible because it is part of the essential chemistry of making cement.  The big questions is “is there anything we can do about these emissions either now or in the future”?  The answer is “yes, a little now and a lot, possibly, in the future”. 

In the short term, the industry is doing all it can to reduce the amount of natural raw material it needs to calcine and new ‘novel’ low carbon cements are beginning to emerge but are still some way off production.  The long term possibility is to capture CO2 emissions and lock them away in geological formations forever.  This process is more commonly known as Carbon Capture and Storage (CCS).

So why don’t we just get on with it?  The truth is it is not that simple.  CCS is a new technology, not yet proven at an industrial scale in cement manufacture.  The electricity generation industry is pioneering the development of CCS because of the scale of their emissions in comparison to other industrial processes such as cement and steel. 

Nevertheless, the cement industry does consider CCS to be a long term possibility and is investing in research and development to see if, how and when the technology can be applied to clinker production.  It is important to note, however, that capture technologies can only be useful when the full chain of CCS is available, including transport infrastructure, access to suitable storage sites and a legal framework for CO2 transport and storage, monitoring and verification, and licensing procedures.

There are two principle capture technology candidates that are worthy of further investigation with regard to cement manufacture: post-combustion capture; and oxyfuel combustion.

Source: European Cement Research Academy (ECRA)

Post-combustion capture technologies

Post-combustion CO2 capture is an end-of-pipe mechanism that would not require fundamental changes to the kiln burning process and so could be available for new kilns and, in particular, for retrofits.  The most promising post-combustion technology is chemical absorption.  High capture rates in other industries have been achieved using amines, potassium and other chemical solutions.  Membrane technologies may also be an answer if suitable materials and cleaning technologies can be developed.  Both of these technologies are still at research & development stages and have not been tested at an industrial scale.  Initial research by the International Energy Agency GHG Programme suggest that post-combustion technology could capture up to 77% of CO2 exhaust gases, but the capital cost of constructing a new plant would be approximate double the cost of a non-CCS plant.  Operational costs for this type of plant would also be double conventional cement plants.  Post combustion technology requires a considerable energy to capture and compress the CO2, and would probably require a cement plant to generate additional power as well as produce steam to replenish the capture medium.

 

Source: European Cement Research Academy (ECRA)

Oxyfuel combustion

Using oxygen instead of air in cement kilns would result in a comparatively pure CO2 stream.  This technology is in its infancy and still requires extensive research.  Initial studies show that while oxyfuel combustion could have a lower capital cost than post-combustion technology, it would still be 25% more expensive than a conventional cement plant and would have 25% higher operating costs.  Oxyfuel combustion can only be used for new build and is not appropriate for retrofit. Oxyfuel combustion would change the atmosphere in the kiln and potentially influence how the clinker is produced. Consequently, an oxyfuel kiln would represent a significant shift in the production of clinker and this requires a great deal of research to establish that the product and process are unaffected by the change.

CO2 Transport

Captured CO2 is compressed to a liquid and then transported by pipeline or road tanker and ship to be stored deep underground.  CO2 is already transported in this way for commercial purposes.

 Storage

CO2 can be stored in depleted gas and oil fields, in deep saline aquifer formations, or injected into declining oil fields to increase the amount of oil recovered – a process known as Enhanced Oil Recovery (EOR). Storage sites are typically several kilometres under the Earth’s surface.

 

Source: Shell

 

CO2 is injected into microscopic spaces in the porous rock that makes up the storage site and over time it gradually binds chemically to the rock. It is the same process that has kept oil and natural gas secure under the ground for millions of years.

Clearly the ability of storage sites to retain injected CO2 is essential to the success of anyCCS project but the UK is well placed to access a number of these. Storage sites will therefore be very carefully selected and monitored to ensure the highest confidence in permanent storage.

The future

It is unlikely that CCS technologies in the cement industry will be deployed before 2025.  However, the International Energy Association’s vision for 2050 is to have 50% of all cement kilns in the OECD (Organisation for Economic Cooperation and Development) countries, and not less than 20% in India and China, equipped with CCS technology.  The UK cement industry looks forward to playing its part in this long term vision.

Further information on CCS can be found at:

www.iea.org

www.wbcsd.org

www.ecra-online.org

www.ccsassociation.org.uk

 
 
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