Fossil Fuels – Co2 Capture
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Introduction
Fossil fuels account for 85% of the global energy production (US Department of Energy, n.d.), and this continued reliance on fossil energy is contributing to large amounts of carbon dioxide (CO2) in the atmosphere. Science has shown that the increased levels of CO2 have become the dominant cause of climate change. Climate change experts have called for an 85% reduction is CO2 emissions by 2050 to avoid some of the more serious effects of global warming (Bellona Foundation, 2009).
There are currently many technologies being tested and developed to reduce the amount of CO2 emitted. One such technology is Carbon Capture and Storage, or CCS. CCS is a technology primarily targeted at capturing CO¬2 from fossil power plants and then storing that CO2 underneath the ground. CCS has terrific potential: it could capture 95% of CO2 from fossil plants (Eccleston, 2008), and could reduce EU CO2 emissions by over 50% by 2050 (European Technology Platform for Zero Emission Fossil Fuel Power Plants, 2008). However, it is still a relatively new technology and as such the cost is very high.
Moreover, Carbon Capture and Storage is an excellent technology that drastically reduces humans large CO2 emissions, mainly due to a reliance on the cheap fossil energy, and must therefore be installed in all new fossil plants and retrofitted to all existing fossil plants by 2015.
2. Capture of CO2 CCS consists of three stages: capture, transportation and storage. Monitoring of CO2 levels must start before any injection and continue throughout project until after capping of the storage site has proved successful and the injected CO2 stable (Griffiths, Cobb, & Marr-Laing, 2005).
Carbon capture takes place in three general forms: post-combustion, pre-combustion or oxyfuel combustion.
2.1. Post-combustionPost-combustion removes CO2 after combustion from the resulting flue gas, the gaseous combustion product. This is a common technology because it can be retrofitted to existing plants, meaning corporations do not have to build brand new plants just for CCS. However, it is an expensive and energy intensive process.
A traditional fossil plants flue gas will typically contain 7-10% CO2, the rest of which consists of nitrogen and water vapour (Bellona Foundation, n.d.). The most common technique used to separate the CO2 from the flue gas is absorption.
An absorption carbon capture process is when the CO2 is made to chemically react with another chemical, the absorbent. Inside a scrubber column, the flue gas is exposed to the absorbent in solution. The absorbent then reacts with the CO2, isolating it from the rest of the flue gas. Common absorbents include amines and carbonates. After absorption, the CO2 is separated from the absorbent. This process occurs in the regeneration column. The two separate to yield pure CO2 and pure absorbent, which can then be recycled into the scrubber column.
CO2 is also captured post-combustion through adsorption instead of absorption. The difference is that in absorption the CO2 reacts with a solution, whereas in adsorption the CO2 attaches to the surface of a chemical, which is often a solid material (Bellona Foundation, n.d.). Most literature on the subject covers post-combustion CO2 capture as sorbents, meaning either adsorption or absorption.
A third post-combustion CO2 capture can also be performed using a membrane module. The membrane allows certain molecules to pass through while trapping others (CO2), like a sieve.
Currently absorption is a more mature technology than membranes or adsorption. The Bellona Institute therefore believes that the first large-scale CO2 capture plant will be based around absorption. However, with further research membranes may prove to be more cost-effective and therefore more popular.
Post-combustion CO2 capture is an advantages position over pre-combustion and oxyfuel combustion because it is already a mature, near-market-ready technology. It has been proved that the technology works, both in the laboratory and in pilot plants. In spite of this no large CO2 capture plants at the scale of a commercial coal power plant have been built to date. Due to recent funding of CCS from governments such as the US and Germany, there are now plans for building large-scale CCS demonstration plants worldwide.
Post combustion CO2 capture can also easily be added to fossil plants. In these cases the plants need to make only minor, often even no, changes to add the CO2 capture infrastructure.
There are several problems with post-combustion CO2 capture though. It uses a lot of energy, meaning plants would need to up to 50% bigger in order to have the same output (McKinsey & Company, 2008). The first CO2 capture plant with amine absorption is expected to be in operation around 2015, at which time it is estimate that ten percent of the energy will be consumed in the CCS process (Bellona Foundation, n.d.).
This energy loss means that plants will lose money, or, more likely, will pass on that difference to the consumer. The capturing process of CCS is the most expensive component at this time. In order for CCS to be a forerunner in the fight against global warming, costs must be reduced (Butts, 2009).
One of the pluses of post-combustion CO2 capture is that it is easily to retrofit an existing plant with the technology. However, some plants are in industrial areas with limited space, and therefore do not have the space to install a CCS plant.
2.2. Pre-combustion facilities treat the CO2 before the combustion. This is done by taking the raw fossil fuel and converting it to syngas, a mixture of CO and H2. The CO reacts with steam in the air to become CO2. The CO2 can then be removed from the syngas using similar techniques as the post-combustion, but in a smaller space and more efficiently (European Technology Platform for Zero Emission Fossil Fuel Power Plants, 2009). The remaining gas, a hydrogen-rich gas, can be used for fuel in vehicles or then be combusted for energy production, which in the case of hydrogen gas does not lead to more CO2 (Statoil Hydro, 2008).
Pre-combustion CO2 capture can remove 90% of CO2 normally emitted by a power plant (McKinsey & Company, 2008). However, the technology would require significant alteration of existing plant configurations in order to work, making it viable only for new plants and not for existing ones.
The costs of pre-combustion CO2 capture are currently very high, but it is expected that in the next 15 to 20 years, as research improves the technology, costs will come down (Green Facts, 2007). The cost is partly so high because few are willing to venture down this path since it requires whole-hearted investment with little assurance that it will