Carbon Capture and Storage Technology (Individual Project)

It has been already established that Global Warming is currently changing our world a degree higher than its regular atmospheric temperatures. This could eventually lead the bio system into chaos, rather, a shift to a massive change that may result to extinction and biosphere behavioural and survival alterations. This is due to the Greenhouse Effect which utilizes the "trapping" action of the atmosphere to the greenhouse gases.

These gases are essential in balancing out the system such as supplying the needed heat of the earth to survive. Though at larger volumes, more gases accumulate and becomes trapped which cause more heat to be trapped as well inside our atmosphere. This phenomenon results to a more varied climate change and increased water volume through the melting of the ice caps and frozen regions. These are catalysed by the increased heat absorption of the darker coloured oceans, which simultaneously releases captured methane, and in effect adds to the greenhouse gas volume. 

The urgency of developing a process in reducing, if not to completely eliminate, the greenhouse gases becomes a major challenge in the continuous use of fossil fuels as one of the primary resource in energy consumption.

Figure 1.  Global Greenhouse Gas Emission

Figure 2. Total U.S. Greenhouse Gas Emissions by Economic Sector in 2011

The amount of Carbon dioxide (CO₂), the main component of the greenhouse gases, has alarmingly grown to 80% from 1970 to 2004. Due to the excessive emission of CO₂, scientists have developed carbon capture facilities which primarily and directly utilize the reduction of CO₂ emission in the atmosphere. Three stages defines the process: (1) Capture and Separation of CO₂ from other gases; (2) Transportation of the Captured Gas to Storage Location; and (3) Underground Storage.

            Processes involving the capture and separation of CO₂ are mainly classified according to which stage of combustion they were performed, or the type of oxygen enrichment process used.

            Post-Combustion Carbon Capture involves recovery of CO₂ from the resulting flue gases after fuel combustion. The flue gases usually include water vapour, sulphur dioxides, nitrogen oxides, and CO₂. To separate the CO₂, filters made out of solvents are attached to the smokestacks, which then preferentially absorb CO₂. This prevents 80% to 90% of a plant’s carbon emissions.

            Pre-Combustion Carbon capture on the other hand recovers CO₂ before fuel combustion. The process mainly involves the oxidation of fuel, and transformation of the resulting synthesis gas comprising of H₂ and CO, into H₂ and CO₂. The CO₂ can therefore be separated from this relatively pure stream, while the remaining H₂ can be used as fuel for combustion.

            Oxy-fuel Combustion is done when the fuel is burned in oxygen instead of air. The resulting flue gas is relatively pure comprising of mainly CO₂ and water vapour. The water vapour is condensed via cooling which leaves a pure stream of CO₂.

            Captured CO₂ are transported to suitable storage locations. Currently, utilization of pipelines is the cheapest form of transport. Pipelines start from the carbon capture sites extending towards the storage sites. They may be installed underground or underwater. Pipelines can also handle transportation of CO₂ in solid (dry ice form), liquid, or gaseous state. Proper CO₂ quality is maintained to avoid the corrosion of the pipelines.

            The captured CO₂ may be stored in either underground or under water storage sites.

            The higher pressure underground causes CO₂ to behave like a liquid causing it to seep inside the porous rocks. In the process called Geological Sequestration, CO₂ is injected into these underground porous rocks, which then uses the overlying rocks as a “sea” to contain the gas. In some applications, CO₂ is injected into Basaltic formations, turning them into limestone, essentially storing the CO₂ permanently.

            Studies are being done for underwater storage of captured CO₂. It is claimed that at great depths (greater than 3500 m), the high water pressure will compress the CO₂, making it fall towards the ocean floor. However, there are still concerns about its effect on marine life and possibility of the resurfacing of CO₂.

            Currently, Carbon Capture and Storage technology is still facing various concerns regarding its efficiency. It also requires higher energies to implement based on our current technological capacities. Still, it is a promising solution to effectively reduce CO₂ emission into the atmosphere. Thus, it is of the utmost importance that we continue research in this field.

References:

[1] 2014. How Carbon Capture Works. How Stuff Works. http://science.howstuffworks.com/environmental/green-science/carbon-capture.htm. March 7, 2014.

[2]   2014. Sources of Greenhouse Gas Emissions. United States Environmental Protection Agency. http://www.epa.gov/climatechange/ghgemissions/sources/agriculture.html. March 7, 2014.

[3]   2014. Global Greenhouse Gas Emissions Data. United States Environmental Protection Agency. http://www.epa.gov/climatechange/ghgemissions/sources/agriculture.html. March 7, 2014.