CARBON CAPTURE – How it’s done at ARC

A new ground-breaking project can remove 500.000 tons of the CO2 emitted from Amager Ressource Center (ARC) annually from late 2025. This will serve as significant support for the Municipality of Copenhagen’s visionary ambition of becoming the world’s first CO2 -neutral capital by 2025. Additionally, the project will innovate the capture process by reharvesting the residual heat from the process and turn it into district heating, thus lowering the overall costs of the process.

Scientists agree that we need to reduce the amount of CO2 in the atmosphere. This is possible when capturing and storing
CO2. The IPCC, the European Commission, and the IEA consider deploying Carbon Capture and Storage (CCS) at a large scale as a crucial and necessary means to solving the climate crisis. CCS is vital to reaching the goal of the Paris Agreement to limit global warming below 2, preferably 1,5 degrees Celsius, compared to pre-industrial levels.

Waste-to-Energy (WtE) plants

One of the many tools to handle the climate crisis is reducing the total amount of waste produced. But as a society, we need to address the residual waste which cannot be reused or recycled. This is done in a good way at Waste-to-Energy (WtE) plants, where the residual waste is being turned into electricity and district heating. At ARC, we supply electricity for 80.000 households and district heating for 90.000 apartments.

The incineration of the residual waste leads to unavoidable CO2 emissions. The WtE sector can substantially contribute to decarbonizing the European economy by implementing CCS on WtE plants while creating green jobs and green growth.

Pilot carbon capture at ARC

The flue gas cleaning process at ARC is one of the best in the world. Almost all toxic flue gas components are being removed in the cleaning process. This means that nearly only steam and CO2 are emitted into the atmosphere.

ARC is determined to take the flue gas cleaning to the next level by implementing carbon capture. The goal is to capture 500.000 tons of the CO2 emitted annually by late 2025.

On June 24th, Danish Minister for Climate, Energy, and Utilities, Dan Jørgensen and Lord Mayor of Copenhagen, Lars Weiss inaugurated a pilot unit for carbon capture at ARC. The pilot unit is the first step towards carbon capture at ARC. It provides a unique opportunity to test the technology which can bring Denmark at the global forefront of carbon capture.

During the 2nd half of 2021, ARC, DTU, Pentair, and Rambøll will be testing and maturing the technology, including the solvents used for capturing CO2. The goal is to optimize the capture technology to capture CO2 most efficiently and cost effectively.

How carbon capture works

To capture CO2, the cleaned flue gas is led into a wet filter. When removing the CO2, the flue gas is led into a high tower (an absorber). The 40 degrees Celsius hot flue gas is moving towards the top of the tower while a liquid with alkaline amines is streaming down from above and is washing the CO2 out of the flue gas. The amines are chemically binding the CO2 molecules.

The liquid with the absorbed CO2 is lead to another high tower (a desorber). Here, the liquid is heated to 105 degrees Celsius to release the CO2 molecules while the liquid with the alkaline amines goes back to the first tower and captures CO2 again.

This means that the liquid with alkaline amines can be reused. The amine absorption technology is well known and has been used for decades. But it’s always been very energy-intensive and expensive. The project at ARC aims to reduce energy consumption and overall cost level by optimizing the energy flows inside the carbon capture unit, reharvesting the residual heat from the capture process, and using it for district heating.

Carbon capture with net-zero energy consumption

ARC is producing electricity, some of which can be used for the carbon capture unit. The residual heat from the capture process is being turned into district heating.

“In terms of megawatts, the capture process is energy neutral. But in terms of economy, there is a loss since electricity has a higher economic value than district heating”, says ARC program manager Peter Blinksbjerg.

The way to reach net-zero energy consumption is to study the energy streams of the capture unit.

“We need to be certain that the amine liquid entering the absorber tower is cold enough. When it comes from the desorber, it will run through a heat exchanger, but the temperature of the amine won’t be low enough. In standard installations, you would either dry cool it or take in seawater to cool it.

But instead, we will harvest the residual heat with heat pumps and send it into the district heating network”, says Peter Blinksbjerg and continues: “The amine liquid with the absorbed CO2 will release the CO2 molecules when it is heated to 105 degrees Celsius. This heating process releases huge amounts of water vapor which holds much energy. It takes a lot of energy to evaporate it, and it releases a lot of energy when it’s being liquified by cooling. So, when liquifying the CO2 before cooling it, you gain a lot of condensation heat from the water vapor, which we can harvest and make use of”.

This is why a district heating network is of great importance when bringing down costs of carbon capture. The traditional energy loss from the capture process can be turned into a source of income.

Increased demands for flue gas cleaning

The traditional setup of a carbon capture unit is – basically speaking – an absorber and a desorber. At ARC, we’ve added two additional towers, one of which supports the goal of net zero energy consumption while the other is added to cleanse the flue gas after the carbon capture process. “When the flue gas is led through the absorber, it is mixed with the amine liquid through a large surface area. But when the amine liquid captures the CO2, we cannot avoid that there can be other chemical agents that will go from the amine liquid to the flue gas.

These chemical agents need to be cleaned in a separate cleaning process”, says Peter Blinksbjerg and adds: “When implementing carbon capture, we don’t want to introduce a potential new source of air pollution. Therefore, the fourth tower of the pilot capture unit is sort of a washing section with several possible ways of cleaning the flue gas with both water, alkaline liquid, etc.”

The steps ahead – and necessary preconditions

The pilot carbon capture unit at ARC is capturing app. 850 kg. of CO2/day. It is a stepping stone towards a scaled-up demonstration unit planned to be operational in early 2023. The demonstration unit will capture 12 tons of CO2/day.

By late 2025 the full-scale carbon capture unit will be operational, capturing 500.000 tons of CO2/year. To meet this ambitious time schedule, the right policies and economic incentives must be set up by the Danish Parliament very soon.
Furthermore, full-scale carbon capture at ARC – as well as on any other plant – is dependent on the existence of a mature value chain. This means that both transportation (by pipeline and/or ship) and storage facilities (offshore or nearshore) must be available at competitive prices.