14.2. CARBON SEQUESTRATION or CARBON CAPTURE AND STORAGE or SCRUBBING OF CO₂

Carbon sequestration is the capture of carbon dioxide (CO₂) and may refer specifically to:

• "The process of removing carbon from the atmosphere and depositing it in a reservoir."
• When carried out deliberately, this may also be referred to as carbon dioxide removal, which is a form of geoengineering.

Carbon sequestration refers to the methods used to capture carbon dioxide from the atmosphere. This can involve various techniques that aim to either remove CO₂ from the air and store it in different forms or facilitate its natural storage in existing sinks. One key method involves capturing CO₂ and deliberately depositing it into designated reservoirs, which helps reduce the amount of greenhouse gases present in the atmosphere. This process is a critical component in efforts to combat climate change.

Think of carbon sequestration like a sponge soaking up water. Just as a sponge collects moisture from a surface, carbon sequestration techniques collect carbon dioxide from the atmosphere and store it in various places to prevent it from contributing to global warming.

Carbon sequestration includes:

• The process of carbon capture and storage, where carbon dioxide is removed from flue gases, such as on power stations, before being stored in underground reservoirs.
• Natural biogeochemical cycling of carbon between the atmosphere and reservoirs, such as by chemical weathering of rocks.

There are multiple methods for achieving carbon sequestration, primarily through carbon capture and storage (CCS) processes. In CCS, CO₂ is captured directly from emissions sources like power plants before it can escape into the atmosphere, then transported and stored underground in geological formations. Moreover, natural processes also contribute to carbon sequestration, where the carbon cycles through different forms and locations in nature, such as how rocks weather and absorb CO₂.

Imagine a factory that emits a lot of smoke. If you put a large vacuum cleaner at the exit, it can suck up the smoke before it gets into the air. This is similar to how carbon capture works at power stations, where they 'vacuum' the CO₂ from emissions to prevent it from contributing to climate change.

The process of carbon sequestration can be broken down into three main steps: A) Capturing or Scrubbing B) Transportation C) Sequestration or Storage

Carbon sequestration involves three important steps: First, capturing or scrubbing CO₂ from the air or emissions. This can use various technologies to isolate carbon dioxide. Next, the captured CO₂ must be transported to a storage site, often via pipelines. Lastly, the CO₂ is stored, which could mean injecting it deep underground or utilizing other methods of long-term storage.

Think of carbon sequestration like a recycling process. First, you collect your plastic bottles (capturing), then you take them to a recycling center (transportation), and finally, they are processed into new materials (storage). Each step is essential to ensure that plastic is removed from the environment and reused effectively.

Broadly, three different types of technologies for scrubbing of CO₂ exist:

1. Post-combustion
2. Pre-combustion
3. Oxy-fuel combustion
4. Chemical looping
5. Calcium looping

There are various technologies designed to capture CO₂, each with its specific approach. Post-combustion captures CO₂ after fossil fuels are burnt. Pre-combustion works before combustion, capturing CO₂ from a gasified fossil fuel stream. Oxy-fuel combustion uses oxygen instead of air to burn fuels, resulting in a more concentrated CO₂ emission, which is easier to capture. Chemical looping uses metal oxides to capture emissions during combustion. Finally, calcium looping involves capturing CO₂ through the reaction of calcium oxide with CO₂.

Imagine different kinds of filters used in a kitchen sink. Some filters clean water after it has already been used (post-combustion), others catch impurities before they mix (pre-combustion), while some only allow certain things to pass through (oxy-fuel combustion). Each filter serves a unique purpose, just like each CO₂ capture technology has its own method and effectiveness.

After capture, the CO₂ would have to be transported to suitable storage sites. This is done by pipeline, which is generally the cheapest form of transport. In 2008, there were approximately 5,800 km of CO₂ pipelines in the United States.

Once carbon dioxide is captured, it must be moved to a storage location. The most cost-effective way to transport CO₂ is through pipelines. As an example, in recent years, significant lengths of pipelines have been built to facilitate this transportation, connecting carbon capture facilities with places where the gas can be safely stored or used.

Consider how water is delivered in a city. Water treatment plants clean and process the water, how pipelines transport it to homes and businesses. Similarly, after CO₂ is captured from industrial processes, pipelines move it to where it can be safely stored underground or used in other applications.

Various forms have been conceived for permanent storage of CO₂. These forms include:

• Geological storage (geo-sequestration)
• Ocean storage
• Mineral storage

Once transported, CO₂ can be stored in several different forms. Geological storage involves injecting CO₂ into underground formations, which may involve natural features like oil fields or saline aquifers. Ocean storage includes potentially pumping CO₂ into the oceans at great depths. Finally, mineral storage refers to reacting CO₂ with minerals to form stable carbonates, a more permanent solution that utilizes naturally occurring processes.

Think about how we store different types of food. You might keep fresh vegetables in the fridge (geological storage), some canned food in the pantry (ocean storage), and certain dry grains in a basement (mineral storage). Each storage method has its own purpose and effectiveness, just like how CO₂ can be stored in different ways depending on the conditions and goals.

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