The Role of Carbon Capture and Sequestration in Mitigating Climate Change
The growing global population and the economic growth in industrialized and developing countries give rise to a continuous increase in demand for energy. Energy production worldwide depends on the combustion of fossil fuels, which produces greenhouse gases (GHGs) and other undesired emissions. GHGs such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3) trap heat in the atmosphere by absorbing infrared radiation. The term “global warming potential” (GWP) refers to the potential that GHGs have to trap heat in the atmosphere over a certain time period and is generally based on their cumulative radiative forcing (IPCC, 2007). GWP is typically calculated for various GHGs over a span of 20, 100, or 500 years and expressed in the form of CO2-equivalent (CO2-e) (Metz, Davidson, de Coninck, Loos, & Meyer, 2005; Solomon, 2007). Discussion of GHGs is usually focused on carbon dioxide because (1) CO2 is the largest contributor to radiative forcing, and (2) human beings are adding CO2 to the atmosphere at a historically high rate (Chen, 2005).
According to the Intergovernmental Panel on Climate Change (IPCC), preventing the catastrophic impacts of climate change will require maintaining the global average temperature at 1.1 o C/2 o F below the present level (IPCC, 2007). To avoid an increase in temperature, the atmospheric concentrations of CO2 would need to be stabilized within the range of 400-450 ppm at maximum, and they could not exceed 400 ppm in the long term (IPCC, 2007). Achieving these targets requires that global CO2 emissions be reduced by approximately 60% by 2050 in comparison to 2010 levels (Kasibhatla & Chamedies, 2007). Kasibhatla and Chamedies (2007) have found that industrialized countries, including the U.S., would need to decrease their GHG emissions by 80% in the same time period. In theory, this goal could be achieved with an annual reduction of only 2%, which would be approximately 136 million metric tons of CO2-e per year. In view of making substantial CO2 reductions, the IPCC has explored various technological options for generating low-carbon energy. Among the most promising options is carbon capture and sequestration (CCS).
In brief, CCS collects and compresses CO2 from point sources, including those in the power generation industry, and then transports the CO2 by pipeline, truck, ship, or train to suitable geological formations. CCS technologies have the potential to become a widely used means of providing low carbon energy. For example, CCS could be used in the power generation industry in general, and more specifically in the coal-fired power industry, to produce low-carbon electricity (UK DECC, 2012).
Figure 1 Schematic showing geological sequestration of carbon dioxide emissions from a power station with CO2 capture system Source: (Alberta Energy, 2011)
The most applicable CCS technology for existing industrial facilities, is post-combustion capture, in which an amine-based solvent such as monoethanolamine (MEA) or methyl diethanolamine (MDEA) is used as an absorbent. Furthermore, integration of CCS with CO2-enhanced oil recovery (EOR) could allow the production of transportation fuel that is less carbon-intensive than conventional petroleum-based fuels such as gasoline and diesel (De Oliveira, Marcelo E Dias, Vaughan, & Rykiel, 2005).
In conclusion, CCS have great potential to reduce the carbon intensity of electric or transportation fuel. However, under existing carbon policies and at the current cost of CCS deployment, the strategy of the ethanol industry would be dominated by CCS deployment. By contrast, conventional power plants would not have sufficient governmental or economic incentives to deploy CCS because of the gap between the cost capturing and transporting CO2 and the price of CO2.
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