Carbon+Sequestration

Carbon Sequestration

 Table of Contents What is Carbon Sequestration? What are the Problems with Carbon Sequestration? What is the chemistry involved with Carbon Sequestration? Carbon Sequestration's relation to the Carbon Cycle and Coral Reefs Carbon Storage What is the Importance of Carbon Sequestration?  What is Carbon Sequestration? Carbon Sequestration is the process of separating carbon dioxide from the air and then storing it where it will not enhance the effects of global warming. There are two steps to carbon sequestration, capturing the carbon dioxide from the atmosphere and then storing it in a safe location. The two ways of doing this are geologic and terrestrial sequestration. Geologic Sequestration captures the carbon dioxide directly from industrial sources and then stores it underground in porous rock formations. The process is relatively simple; the CO2 is captured by filtering it from amongst the other gases emitted by the factory. It is then pumped deep underground to a layer of porous rock with thick bedrock above it which the carbon dioxide cannot escape through. Indeed, this process is being used today to great effect and has very little or no effects on the environment. The film below explains more of how geologic sequestration works. media type="youtube" key="zqKHsY-swgk" height="344" width="425"

Terrestrial Sequestration involves the removal of carbon dioxide from the atmosphere by plants that use CO2 in their natural cycles. By replanting areas that have been destroyed by industrial development, more CO2 can be absorbed out of the atmosphere. Terrestrial sequestration simply requires for more plants to be planted. 

What are some of the Problems with Carbon Sequestration? One of the largest barriers facing Carbon Sequestration is its cost. Industries that use carbon capture technologies increase their cost of electricity by as much as 30%, from 7.8 cents per kilowatt hour to 10.2 cents per kilowatt hour! Carbon Sequestration technology is still in its infancy and is not as efficient as it could be. Storing carbon dioxide underground and in plants is relatively simple. The process of separating the CO2 from the air however is a highly complex chemical process. media type="custom" key="3017964"

The Chemistry These are the two main ways of mechanically capturing CO2 from power plants. Pre-combustion capture is more cost efficient but can only be applied to new plants. Post-combustion capture is less cost efficient, but can be applied to existing plants. Capture is necessary for sequestration because the CO2 used in generating power must be converted to a substance suitable for being stored.

__Pre-Combustion Capture__ This process is for separating CO2 from coal before it is burned or combusted. To do this the coal is first gasified so it is put into a pressurized chamber with heat and steam in a controlled oxygen environment. This creates syngas which is primarily made up of hydrogen (H2) and carbon monoxide (CO). The CO is then reacted with water (H2O), this creates carbon dioxide (CO2) as well as additional H2 molecules. Simplified, this is the reaction that occurs, **CO + H2O ~ CO2 + H2.** The CO2 from this process is ready to be stored. The H2 is then sent on to be combusted in fuel cells to generate power in the factory. The problem with this process is that factories will have to be modified at a great expense in order to make use of this highly efficient technology. The process of pre-combustion sequestration is shown in the diagram below. H2 gas sent up to the fuel cell plant to be converted into energy, while the CO2 captured from the reaction is ready to be stored after it is compressed on the right side of the diagram. In this diagram we also see how heat from the reaction is also used for power.

__Post__ __Combustion Capture__ This process can be used to capture CO2 after the coal has been burned, and so it can be applied more easily to existing coal plants, the problem is however, it is less efficient then pre-combustion technologies. Because of this, the option of post-combustion carbon capture has largely been disregarded. In this process, the flue gas which comes out as exhaust from a factory, is separated into CO2 and nitrogen gas. This is done by utilizing solvents such as amines, or nitrogen based organic compounds.

**Carbon Storage** After the Carbon has been taken from the plant and converted into a form suitable for storage, the problem still remains as of where to put all of it. The three major modes of storage can be summarized as geologic storage, oceanic storage, and mineral storage. Geologic storage involves injecting the converted carbon directly into geologic formations. Areas of earth would be used that have a large amount of cap rock, which would lock in the carbon and prevent it from reaching back up to the surface. Another option of geological storage is in saline formations, which are underground aquifers that are so full of minerals they have no use to humans. The problem here is that very little is known of these formations and the affect of massive amounts of carbon waste on them. Oceanic storage would not be a temporary solution because as it is in oceanic storage, carbon is essentially dumped into the ocean at very great depths. Also, large amounts of CO2 in one place is very dangerous to wildlife. Mineral storage of carbon is when carbon is reacted with other minerals such as magnesium and calcium, to form carbonates. These carbonates have a lower chemical energy state, so reactions occur naturally. The carbon in these carbonates would be very unlikely to escape to the atmosphere because the carbon would have undergone a chemical change.  **Carbon Sequestration’s relation to the Carbon Cy****cle** The carbon cycle is the natural process through which carbon circulates from the Earth to its atmosphere and back. Before humans began extracting and burning fossil fuels at the extreme rate they are now, the carbon cycle was in a state of equilibrium; meaning that the amount of carbon released into the atmosphere by animals and natural occurrences such as volcanic eruptions were was being brought back out by plants and the ocean. This balanced cycle kept the global climate relatively constant. However, now humans have disrupted that balance by taking the stored carbon out of the earth and releasing it back into the atmosphere faster than it can be taken out. If humans were to use carbon sequestration to counteract this, then the carbon cycle would much closer to its previous state of equilibrium.

**Carbon Sequestration’s relation to Coral Reefs** Coral reefs are being severely affected by global warming. As the level of carbon dioxide rises in the atmosphere, the level also increases in the oceans. As the oceans levels of carbon dioxide rise, the water naturally becomes more acidic as the carbon bonds with the oxygen and hydrogen atoms in water to form carbonic acid. The more acidic water creates a harsher environment for the coral to grow in. However, this process can be slowed or even reversed if geologic sequestration and terrestrial sequestration are used to control the amount of carbon dioxide released into the atmosphere and ultimately the oceans.

 Importan ce of Carbon Sequestration If practiced properly, the process of geologic carbon sequestration could prove to be a key element in the fight against global warming. New power plants that open up may be able to utilize pre-combustion carbon recovery techniques which is the most efficient known way of going about carbon recovery. Scientists speculate that it could reduce CO2 emissions in a given plant from between 90 and 95 percent. This would be a significant amount of CO2 that would be essentially taken out of the air and away from enhancing the greenhouse effect. Terrestrial carbon sequestration however is a much more practical way to go about the process of carbon sequestration. This requires no new technology to be developed because the process is completely natural. All it requires is for the planting of trees.



__Sources__ http://www.nma.org/ccs/carboncapture.asp