Carbon Capture and Storage

Introduction

Fig. 1: Post-combustion carbon capture and storage technology. (Source: Wikimedia Commons)

Climate change is a global crisis that policy makers and scientist must prioritize. The Earth's temperatures are rising at alarming rates due to increased CO₂ emissions. Fossil Fuels account for almost all of the 6.5 billion tons of carbon that is released into the atmosphere. [1] Thus, engineers, policy makers, and corporations are engineering new ways to reduce these emissions. One promising way to do this is through the mechanism of carbon capture and storage (CCS). In this process, CO₂ is taken from the electric plants and chemical factories that usually emit large amounts into the air and then pumped deep underground where it remains without side effects. Oil companies have been unintentionally utilizing these methods for years by tapping into deep oil reserves underground and using CO₂ to lessen the viscosity of the oil. [1] However, this concept has evolved and gained popularity among climate change advocates as a way to seqeuester CO₂. According to Professor Sally Benson, the hope is to reduce CO₂ emissions by 20% in the next 100 years. [2]

Capture

The Basic mechanism of CCS, illustrated in Fig. 1, is to capture the CO₂ released at the site of release, and then compress the CO₂, transport it by pipeline, and inject it into a site in the ground. [2] There will be an injecting well that is located close to the capture site. The timing of capture differs for industrial CO₂ sources verses fossil fuels and biomass. In Industrial sources, the products and the CO₂ are separated. In the cases of biomass and fossil fuel energy sources, there are three options of capture and combustion:

• Post Combustion: Air is put in and then those consequential products are separated. The CO₂ is captured, and everything else is used for heat and power.

• Pre Combustion: This inputs air/O₂ and steam to gasification/reforming. This produces products of H₂, which is used for heat and power, and the CO₂, which is captured.

• Oxyfuel: This is where O₂ is pumped into combustion and CO₂ and heat and power are the outcomes.

Storage

The CO₂ needs to be injected into the microscopic pores of sedimentary rocks in the correct place and at the right time. [3] According to Professor Benson, there are two levels of trapping: primary and secondary. Primary trapping is beneath rocks that will trap the CO₂ beneath them such as shale, carbonates, and clay. Secondary trapping will include natural molecular trapping such as water, coal, and solid minerals. Then precautious will be taken to increase security and monitoring in order to make sure the CO₂ stays in the capillary spaces.

Conclusion

There has been promising research so far in understanding what happens to the CO₂ when in these deep reserves. Previously, a major concern was that the CO₂ would eventually make its way back up through natural processes and into the atmosphere, but recent research has shown that there is no sign of movement after the CO₂ is deep in the Earth. However, researchers must be cautious when implementing this practice on a larger scale due to the unknown of how large amounts of CO₂ in the Earth's core will react. These environmental risks are very high that tampering with the boundary of how much CO₂ to pump into the Earth is risky. [2] In addition, currently these technologies are relatively expensive. In places such as the United Kingdom, using this technology in a household could raise their electricity by 10% per year. [3] As technology develops and research continues, there will be solutions to these current limitations.

© Gracia Mahoney. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] R. F. Service, "The Carbon Conundrum," Science 305, 962 (2004).

[2] S. M. Benson and T. Surles, "Carbon Dioxide Capture and Storage: An Overview With Emphasis on Capture and Storage in Deep Geological Formations," Proc. IEEE 94, 1795 (2006).

[3] R. S. Haszeldine, "Carbon Capture and Storage: How Green Can Black Be?" Science 325, 1647 (2009).