CO₂ transported by a container truck as part of a demonstration chain in the DemoUpCARMA project. Photo: ETH Zurich

What are the environmental impacts of CO₂ capture, transport and storage?

In order for CCTS to contribute to our net-zero goals, its value chain must store more CO2 emissions than it creates. To investigate this, PhD candidate Johannes Burger has conducted a life cycle assessment on four European CCTS value chains that are being focused on in ACCSESS: two cement plants, a pulp-and-paper plant, and a waste-to-energy plant.

Author: Johannes Burger (ETH Zürich)

Pioneering CO2 transport technologies

Carbon capture, transport, and storage (CCTS) is one of the few ways to decarbonize CO2-intensive industries (e.g., cement or paper production) and reach net zero emissions across the whole economy. However, to do this, the CCTS infrastructure must be scaled up quickly.

CCTS consists of installing capture units at industrial plants that capture CO2, which is then liquefied and transported to a storage site. In Europe, sites in the North Sea have the best conditions for permanent storage. However, it is challenging for emitters to send CO2 to storage sites in the North Sea, as there is currently no infrastructure for transporting CO2 in Europe. Pipelines would be the cheapest and most efficient mode of transport, but they are not available due to long lead times for planning and construction. Using transport modes that are already available, such as container ships or tanker trucks, can help to overcome this hurdle and start the scale-up of the CCTS industry. So-called “pioneering” CCTS technologies are already available on the market, although not widely used for CCTS.

Investigating the CO2 emissions of the CCTS supply chain

To avoid greenhouse gas emissions, CCTS chains must result in more CO2 being stored than emitted. Greenhouse gasses are emitted throughout the whole process, from capturing the CO2 to transporting and storing it safely. For a CCTS supply chain consisting of the currently available technologies, the question therefore remains whether the supply chain avoids more emissions than it creates. For any given process, a life cycle assessment (LCA) can quantify the emissions produced by the process.

In the ACCSESS project, we applied a LCA to four CCTS supply chains from mainland and northern Europe that are being examined in the project. We then analyzed the net benefits of CCTS using currently available technologies, and quantified the environmental impacts of their construction, operation and deconstruction.

The setup of the four CCTS chains considered in the LCA is shown in Figure 1. The CCTS chain starts with a CO2 capture unit (1) together with conditioning (2) and temporary storage (3) at the emitter site. From there, the CO2 is loaded onto a container, which is transported (4) to the Northern Lights storage site in the North Sea, where the CO2 is permanently stored (5).

Scientific figure
Figure 1: System boundary for pioneering CCTS chains with permanent storage in offshore aquifers.

The setup was applied to CCTS chains from two cement plants in Hannover (Germany) and Górażdże (Poland), a pulp and paper plant in Skutskär (Sweden), and a waste-to-energy plant in Linth (Switzerland). The details of the chains were modeled distinctly for each location. However, the main difference between the chains is in the transport parts.

Pioneering technologies can reduce greenhouse gas emissions from point sources

The results of our LCA show that each of the pioneering chains can reduce greenhouse gas emissions from the point sources, even when using technologies that are readily available today.

Figure 2 shows the global warming impact caused by each chain for capturing, transporting, and safely storing 1 ton of CO2. Only chains that emit less than 1000 kgCO2 per ton of CO2 stored effectively avoid greenhouse gas emissions. If the chain causes more emissions, the industrial plant could simply continue to emit. However, all chains in this LCA avoided at least 50% of the emissions of the industrial plant, thereby effectively reducing its climate impact.

Scientific illustration
Figure 2: Global warming impact of permanently storing 1 ton of CO₂. The impact is split along the parts of the CCTS supply chain.

Emissions associated with CO2 capture and transport can be further reduced

In general, two factors have a large influence on the global warming impact of the chains: the transport distance and the greenhouse gas intensity of the local electricity grid.

For chains with long distances between the emitter and storage site, the majority of greenhouse gas emissions are caused by fossil fuel-powered ships and trucks, as these are the currently available transport modes. In the near future, transport may be realized with decarbonized vehicles, such as ammonia-driven ships or electrified trucks. In the long term, however, CO2 will likely be transported via pipelines. Pipelines are the most cost-effective way of transporting large amounts of CO2 and emit the least greenhouse gases.

The greenhouse gas intensity of local electricity plays a big role in the total emissions. This effect can be observed in the chains starting in Górażdże and Hannover. The Polish and German electricity mixes rely heavily on coal and gas power plants. Thus, the electricity-intensive conditioning step indirectly causes many emissions (cf. Figure 2).

Furthermore, the capture unit requires significant amounts of heat which is subject to high emissions. With a low-carbon heat source, such as heat pumps or biomass boilers, the impact of the capture unit can be reduced drastically.

Potential improvements to and future developments of CCTS supply chains

Our study shows that implementing a CCTS chain based on currently available equipment and transport modes already avoids CO2 emissions from point sources across Europe. However, the chains’ climate impact can be further reduced through three main improvements:

  1. Decarbonizing heat for the capture process will replace the emissions from natural gas but will require another source of energy. Heat pumps, heat from biomass, or heat integration into the existing industrial plant are potential alternatives, and should be evaluated for each site individually.
  2. Deploying a shared pipeline infrastructure to transport CO2 from all over Europe to the respective storage sites is the transport option with the least environmental impact. In addition, the transport becomes much cheaper due to economies of scale.
  3. Reducing emissions from electricity generation will lead to lower indirect emissions in all supply chains. The electricity required for liquefying the CO2 will cause less indirect emissions. Especially in regions with an energy system relying primarily on fossil fuels, the climate impact of the CCTS chains can be reduced significantly.

Nonetheless, Europe can kick-off its deployment of CCTS chains and pave the way for a ramp up towards large-scale CO2 capture, transport, and storage. A functioning CCTS industry and infrastructure are crucial for reaching national and international climate goals. Our findings enable the immediate ramp-up of the CCTS infrastructure without waiting until a pipeline network is built.

Johannes Burger is a PhD student in the Reliability and Risk Engineering Laboratory and the Energy and Process Systems Engineering group at ETH Zürich. This blog post is based on the paper “Environmental impacts of carbon capture, transport, and storage supply chains: Status and the way forward”, published online in January 2024, written in connection with work done in the ACCSESS project.

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