What do we do about carbon dioxide?
The problem: Global warming is happening because of carbon dioxide emissions and renewable energy technology is not ready to provide for the full energy demand humans create. So, how do we mitigate global warming pollution if we have to burn fossil fuels in our power plants for the next few decades until renewables are ready for mass implementation?
The answer: Carbon capture and storage (CCS). Well, that seems pretty simple and intuitive, right? Let’s just put all of the carbon dioxide back where if came from, below the ground where it doesn’t affect our atmospheric environment. Well, it’s not exactly easy, but believe it or not, carbon sequestering technologies are catching the attention of large energy companies and government agencies around the world. But before we discuss when we can see this new technology coupled with every power plant, let’s take a look at a few of the CCS technologies that are gaining momentum today.
Carbon dioxide can be captured at any large point source such as coal fired power plants, natural gas production facilities and coal gasification plants. Currently, three methods exist to capture carbon dioxide: post-combustion, pre-combustion and oxy-fuel combustion. Post-combustion is the oldest and most costly technique to sequester harmful emissions. Carbon dioxide can be separated from flue gases using either absorbing solvents and membranes or cryogenic freezing to secure carbon dioxide. These processes have been developed for many years, but unfortunately require the power plant to produce up to 40 percent more power to operate.
In the pre-combustion method, carbon dioxide is harnessed from a relatively pure exhaust stream during the gasification of various fossil fuels, such as coal. This procedure is the cheapest and most efficient method of carbon capturing, but must be in conjunction with a power plant already using gasification processes.
Lastly, one of the most promising means still in research to alleviating greenhouse gases is oxy-fuel combustion. The basic idea of this process is to burn coal with pure oxygen yielding exhaust almost purely made of carbon dioxide and water vapor. Because the flue gas is not inundated with other gases (primary nitrogen), securing the carbon dioxide is much easier and cheaper.
Storage of captured carbon dioxide is the second hurdle to overcome in making carbon sequestration a practical solution to lessen global warming pollution. Presently, a great deal of research is being conducted in this area and many ideas are forming into feasible solutions. One practice currently in use in a handful of locations around the world is geological storage, commonly referred to as geo-sequestering. This practice involves pumping captured carbon dioxide into existing oil and gas fields and unminable coal seams. This method is very appealing due to the fact that un-attainable oil and gas can be recovered, offsetting the storage costs with additional sales.
Saline formations also represent another abundant geological storage medium. These formations exist deep below the earth’s crust and to date appear to have no benefit to humans. Injected carbon dioxide is trapped within briny porous rock where eventually it will dissolve and form minerals such as iron and magnesium carbonate.
Ocean storage of carbon dioxide is another concept with a lot of buzz currently surrounding it. One concept involves pumping carbon dioxide into the ocean at depths of 1,000 meters or more through pipelines or ships. At this depth carbon dioxide would subsequently dissolve. Another similar idea requires carbon dioxide be pumped to deep ocean floors of at least 3,000 meters, where it becomes denser than water and is expected to form a “lake” of carbon dioxide. Both of these solutions have the potential to relieve environmental effects in the atmosphere, but could potentially carry a large burden to the ocean ecosystem. Large amounts of carbon dioxide could kill many ocean organisms. Increased amounts of carbon dioxide will react with water to form carbonic acid and increase the pH of the ocean, which has various effects on organisms and plant life.
Leakage of stored carbon dioxide is another concern scientists are exploring. According to the Intergovernmental Panel on Climate Change (IPCC), well selected and designed geological locations could store carbon dioxide for millions of years with 99 percent retained over 1,000 years. Ocean storage retention varies with depth and the IPCC predicts between 30 to 85 percent of carbon dioxide would be retained after 500 years for depths of 1,000 to 3,000 meters.
Implementing carbon capture and storage worldwide presents a huge opportunity to curb global warming. Today, most CCS technologies are visible in Europe mainly because the Kyoto Protocol allows carbon sequestering as a form of carbon offsets. Applying carbon sequestering to a modern conventional power plant is expected to reduce carbon dioxide emissions by 80 to 90 percent compared to a plant without CCS. With carbon sequestering processes becoming more technologically and economically viable, it is only a matter of time and political will before real change is notable among today’s energy production methods.
Chad Worth is a fourth year industrial engineer, president of the Hydrogen Energy Club and a member of the EMPOWER Poly Coalition.