Amine scrubbing

Amine scrubbing is a solvent-based carbon capture method that is suitable for industries with large flow rates, such as power stations, chemical processing plants or steel mills. Where multiple high-emitting industries are clustered together, amine scrubbing systems can even be centralized, with one installation used by multiple factories.

First, the flue gas, also known as exhaust gas, is cooled to just above room temperature in a cooling tower. Then, the cooled flue gas enters the absorption tower where amine, a liquid alkaline adsorbent, is introduced. The CO₂ from the flue gas dissolves in the amine and is trapped. All other gases continue rising through the tower and are discharged.

The amine now contains a high concentration of CO₂. To separate it, the amine is transferred to the regeneration tower, where it is heated under vacuum with steam. By applying vacuum, the boiling point of the amine can be lowered. The steam releases the captured carbon dioxide, now at a very high level of purity. Amine degrades at high temperatures. Thus, by lowering its boiling point, the amine is preserved and can be reused – for many years, when treated correctly. Amine regeneration therefore results in a process that is both more sustainable and more cost-efficient: New amine is expensive to purchase and difficult to dispose of.

The final stage is transferring the CO₂ to a collection vessel. A vacuum pump suctions the captured gas from the regeneration tower to the collection vessel. The carbon dioxide can then be transported for reuse or storage, and the amine liquid returns to the absorption tower.

Moving bed process

The moving bed process of carbon capture consists of three stages: the adsorption reactor, the desorption reactor, and the adsorbent dryer. In this process, the CO₂ is collected by solid sorbents. These are balls made of a porous material and saturated in amine solvent, which circulate through the three areas of the system.

Adsorption reactor
The process begins in the adsorption reactor. Here, the flue gas from the industrial process is introduced, and the CO₂ is adsorbed by the sorbent. Although the method is different, this step works exactly the same as in the amine scrubbing process: The carbon dioxide dissolves in the amine solvent and is trapped.

Desorption reactor
The CO₂-laden solid sorbent then moves to the desorption reactor. Steam is blown into the reactor and condenses on to the solid sorbent, releasing the CO₂, which can then be extracted.

A vacuum pump connected to the outlet of the desorption reactor suctions the CO₂. The gas travels through the vacuum pump and enters the collection vessel at the outlet. From there, it can be transported for reuse or storage.

Adsorbent dryer
Next, the solid sorbent, now saturated with moisture, moves to the adsorbent dryer. A blower pushes warm air into the dryer, reducing its moisture content. The solid sorbent is then discharged from the adsorbent dryer, ready to be reused.

Vacuum swing adsorption (VSA)

Vacuum swing adsorption (VSA), also known as pressure swing adsorption (PSA) or vacuum pressure swing adsorption (VPSA), is a CO₂ separation process that follows the same general steps as the moving bed process: adsorption, desorption and regeneration.

Adsorption
First, the flue gas is passed at high pressure through what is known as an adsorption bed. This is kind of filter made of a solid sorbent: a porous material that can either be amine-based, just like the other capture methods, or can be another compound such as activated carbon or zeolite. It selectively captures the CO₂ molecules while allowing other gases to pass through.

Desorption
After the CO₂ has been separated from the rest of the flue gas and the adsorbent bed is saturated, vacuum is applied in the chamber. As a result, the pressure on the captured carbon dioxide molecules is lowered, allowing them to detach, or desorb, from the adsorbent bed and return to a gas state. When the temperature is increased at the same time, the desorption process is even more efficient.

Regeneration
Just like in the amine scrubbing process, this process to release the carbon dioxide also regenerates the amine-based adsorbent bed, allowing it to be reused.

The molecules can subsequently be recaptured, now at a high purity, for transportation or storage.

Carbon capture using membranes is an easily scalable method suitable for small to medium emitters of carbon dioxide, such as biogas upgrading or petrochemical refining processes. The membrane capture process consists of multiple different membranes. These act as filters: The membrane material allows CO₂ to easily permeate it, but other gases are left behind.

By applying vacuum and overpressure to these membranes, the overall efficiency of the process increases. Vacuum and overpressure help maintain a pressure differential across each membrane. Pressure is reduced on one side of the membrane using a vacuum pump and increased on the other using a blower. This increases the permeation rate of CO₂ through the membrane.

Membrane capture is typically divided into two separate stages, each consisting of multiple membrane modules that operate in parallel. By filtering twice, the maximum amount of flue gases is separated and removed, which allows for higher purity of the recovered CO₂.

Whichever method of carbon dioxide removal is used, the CO₂ can either be utilized or permanently stored.

Utilization

Carbon dioxide is an important resource required in a variety of industries. Globally, over 230 million tons of CO₂ are needed every year. The largest consumer is the fertilizer industry, followed by the oil and gas sector, which uses the gas for enhanced oil recovery.

However, it is also an important commodity in other commercial applications. The gas is used in fire suppression systems, to stimulate plant growth in greenhouses, and in food and beverage production.

By re-using carbon dioxide that would otherwise be released into the air, a more circular and sustainable system is created.

Storage

The second option for handling captured carbon dioxide is to permanently store it. Carbon dioxide can be stored deep underground within the bedrock.

To do so, the CO₂ is first mixed with water to create carbonic acid. This is pumped down below the Earth’s surface. The acidity of the carbonated water dissolves the minerals inside the basalt bedrock, and their ions are released into the water.

Over time, these ions react with and bind to the carbon dioxide. This mineralizes it and creates a solid – meaning that the carbon dioxide essentially becomes part of the rock itself.

After two years, over 90% of the mixture will have completed this process. This ensures a safe and permanent resting place for the carbon dioxide and makes sure it doesn’t return to the atmosphere.

Turning CO2 into solid rock

Direct ocean capture is another method of removing carbon dioxide from our natural environment that is currently in development.

Our planet’s oceans are natural carbon sinks: Over a period of many decades, CO₂ from the air diffuses and dissolves in the ocean. The top layer of ocean water can be treated to remove the carbon dioxide it contains. A small amount – less than 1% – of the water that is captured is diverted and pre-processed to create an acid. The acid is then added to the rest of the captured water, where it triggers a chemical process that draws out the CO₂. The water is then restored to its original pH level and returned to the ocean.

This process would allow the ocean water to draw down the same quantity of CO₂ as was just removed, turning it into a very sustainable solution.

If put into operation, this would be an extremely environmentally friendly method of carbon dioxide capture, as it uses exclusively the ocean water, involving no absorbents or solvents and creating no by-products.

A variety of different vacuum technologies are used in carbon capture, depending on the type and the techniques employed.

Dry screw, claw, and liquid ring vacuum pumps can all be used for direct air capture (DAC), while industrial capture methods can also use rotary vane and rotary lobe vacuum pumps as well as side channel blowers.

Browse through our product finder or contact us – we will work with you to find the right solution for your application.

Direct air capture (DAC) is a method of carbon capture that extracts carbon dioxide straight from the atmosphere.

Unlike industrial carbon capture, this does not take place at the site of the emissions but can be done from anywhere.

The carbon can then be permanently stored beneath the Earth’s surface or can be reused in industries that require carbon dioxide for their processes.

Vacuum pumps from Busch are used in carbon capture processes around the world. You will find our vacuum pumps in all kinds of carbon capture technologies, both in industrial carbon capture and direct air capture.

As our vacuum pumps play a decisive role in the capture and storage of carbon, we are also contributing to a greener world. Our pumps ensure that the carbon dioxide is effectively and efficiently removed from our atmosphere and reused or stored safely.

Instead of being located at the source of the emissions, direct air capture (DAC) removes pre-existing carbon dioxide from the atmosphere.

The capturing system does not need to be attached to a factory or power station, meaning that it can be located anywhere, completely independently of other industries.

DAC is also a way of capturing carbon emitted from sources where a direct system is not possible, such as from vehicles, as well as legacy carbon – the carbon dioxide emissions that built up in our atmosphere over the many years before carbon capture technology was available.

Yes, the carbon dioxide that is captured in carbon capture processes can be reused.

CO₂ is an important resource in a variety of industries – it is used in the production of fertilizer and fire suppression systems and is introduced into greenhouses to stimulate plant growth, to name just a few.

By reusing carbon dioxide that would otherwise be released into the air, a more circular and sustainable system is created.

Carbon capture can minimize CO₂ emissions and therefore the overall effect that existing power plants have on our atmosphere.

An industrial carbon capture system can be retrofitted to an existing power plant that operates using fossil fuels.

And with a direct air capture (DAC) system, carbon capture can also remove previous emissions from the atmosphere.

Carbon capture is therefore a way of mitigating the impact of our existing technology while the world makes the change to greener power generation.