Carbon Capture Lab

The carbon within plants and animals is recycled when they die through a process called the carbon cycle. Carbon is recycled and reused throughout the biosphere, and is key to Earth sustaining life. Human activity introduces additional carbon dioxide into the environment, leading to a dangerous imbalance.

A rise in the global temperature of just 1 or 2 degrees can cause devastation on Earth. Melting glaciers lead to rising sea levels, which, combined with an increase in storms, would also affect cities and towns along coastlines. 

Chemical engineers have figured out that carbon dioxide can be captured and stored. But how does it work? A gas mixture containing carbon dioxide is passed through a solution of monoethanolamine (MEA) or similar compound. 

The liquid absorbs the CO₂ from the gas mixture; the CO₂ can then be extracted from the solution and isolated. The remaining gas mixture can now be emitted into the atmosphere safely while the extracted CO₂ is stored safely. 

This plant at Imperial College London has 4 levels. It’s as high as 3 double-decker buses! However, this is just a pilot scale carbon facility used to teach students – an industrial scale facility can process as much as 1 million tonnes of carbon per year.

The carbon capture main control room is the same kind of control room you would find in a large-scale oil platform or refinery. These students work in groups to do the kinds of tasks performed in a full-scale processing plant. 

Using these screens, the students can monitor how well the system is operating and make any necessary adjustments to the numerous valves and pumps in the plant to improve the performance of the process. 

Each floor of the plant is devoted to a different stage in the carbon capture process. On the first floor, a gas mixture enters the system. But instead of letting it go up into the atmosphere, the gas is fed through a vessel and saturated with water before passing through what’s called the absorber tower.

The gas mixture that enters the system contains carbon dioxide and nitrogen. This is a similar kind of gas mixture to the kind that would normally be emitted into the air from power stations.

When CO₂ gets wet, it becomes slightly acidic. Once acidic, an alkaline solution can be used to cause a reaction that will remove the CO₂ from the other gases.

A piping and instrumentation diagram is a map of the plant that shows all the key details of the process and how they fit together. 

The gas that is now saturated with water rises up the absorber tower, at the same time as a solution called monoethanolamine (MEA) flows down from the top. The pressure, temperature and pH conditions all need to be just right in order for the CO₂ to be absorbed in the solution.

Atmospheric pressure decreases with height while liquid pressure increases with depth. This is partly why it is so important to monitor pressure continually in the carbon capture plant.  

Student Qianyue “Jimmy” Zhang thinks that chemical engineering combines chemistry, physics, applied maths, economics and environmental impact into products and services. He regards engineering’s core purpose as the minimization of energy and material used to make a greener production process.

Dr Colin Hale says that carbon capture has now moved from a demonstration phase to mainstream commercial projects, opening up many opportunities for chemical engineers and other scientists to work together to meet a major global challenge.

The CO₂ is absorbed by the liquid solution because of the acid-alkaline reaction. In order for it to be used elsewhere, it now needs to be separated out. The liquid will be heated in a second column called a desorber, which shifts the equilibrium of the reaction so that the carbon dioxide will separate from the liquid. 

In the desorber column, the solution is heated to about 110–115°C, which allows the CO2  to be released from the liquid. The warmer liquid then begins to rise. This movement of fluid caused by heat energy is known as convection. 

Jannie Khoo is checking the flow rate measurements for the clean gas that no longer contains carbon dioxide. This gas can be emitted safely into the atmosphere.

When asked what inspired her to study chemical engineering Carolyn Seow said she was inspired to study chemical engineering after the 2011 Fukushima disaster. She thought that technology could be used in the future to avoid situations like that from happening again.

In the final stage of the carbon capture process, the vapor containing the CO₂  rises up the desorber column into a condenser. The vapor in this stream is condensed to separate it from the CO₂  gas. 

The condensed liquid is then returned to the desorber column, while the purified CO2 is compressed to be used elsewhere. On full-size versions of this process, the CO2 is compressed until it forms a liquid and is then pumped into the ground for safe storing. 

When vapor is cooled, the molecules move around less vigorously, meaning that it becomes denser. If the vapor is cooled enough, it can form a liquid. A condenser is used for this process. 

Once the monoethanolamine (MEA) solution in the desorber column has released the CO₂, it is cooled before being sent back to the absorber column, where it will begin the process of separating CO₂ from the gas feed again.

Ivan Taptygin is looking at the pressure and temperature inside the stripper column to ensure the levels are correct. He says that they always have to consider the safety of the plant, making sure nothing goes out of acceptable range.