As we collectively address climate change and undertake an energy transition, the need to provide clean, affordable and reliable energy for all requires a blend of solutions, which includes hydrocarbons together with Carbon Capture Utilisation and Storage (CCUS). This requirement is why the International; Energy Agency (IEA), International Renewable Energy Agency (IRENA) and Intergovernmental Panel on Climate Change (IPCC) all identify a rapid expansion of CCUS projects will be required to meet the Paris Agreement .
When the United States introduced the Inflation Reduction Act (IRA) in October last year, one of the most eye catching incentivisation schemes was the change to the 45Q tax credit scheme for US domestic CCUS projects. The IRA looked to better incentivise projects through a variety of changes including:
An increase to the tax credit amounts.
A wider definition of what project qualify for the credits.
Extension of the construction deadline for eligible projects.
Allowing developers to take direct payment, as opposed to credits, for the first 5 years .
It was generally accepted that the act would serve to unlock CCUS projects in the US and kick start the required expansion, and that is certainly what we have experienced at io as we bring our expertise to an increasing number of US clients, including techno-economic consultancy for a project in California and Owner’s Agent advisory services to a major development in Texas.
With the UK Government having a target of capturing and storing 20-30MtCO2/yr and there being no active CCUS project, Government followed the US lead and made financial commitments to unlock CCUS. The UK spring budget on 15 March 2023 included an allocation of £20bn investment in low carbon energy projects with a focus on CCS , including the identification of eight projects to progress to negotiation to form carbon clusters . Subsequently, the North Sea Transition Authority (NTSA) announced that 20 licences had been offered for award for storage of CO2 in the reservoirs .
This is matched by the EU’s proposed Net Zero Industry Act, published on 16 March 2023, which includes:
Prioritisation of Net-Zero Strategic Projects, that are deemed essential for reinforcing the resilience and competitiveness of the EU industry, including sites to safely store captured CO2 emissions.
an EU objective to reach an annual 50Mt injection capacity in strategic CO2 storage sites by 2030, with “proportional contributions from EU oil and gas producers. ”
It is clear that legislative bodies are moving to unlock and accelerate CCUS. However, while this show of legislative support for CCUS is a positive move in terms of providing an enabling economic framework for the short term, CCUS projects are not without technical and, even given the schemes described above, longer term economic challenges. Here we will consider some of the technical challenges of capturing carbon, in subsequent insights pieces, we will look as some of the challenges associated with transportation, utilisation, sequestration and the long-term economic viability of such projects.
There are three broad categories of capture methods  :
Post-combustion, where CO2 is separated from the flue gas after the fuel has been burnt.
Pre-combustion, which involves the removal of CO2 prior to combustion
Oxy combustion, where fuel is combusted in nearly pure oxygen, producing a flue gas of primarily CO2 and water.
Post-combustion, particularly amine based chemical absorption processes, are the most mature and have been successfully deployed in industrial settings for decades. However, despite the commercial scale deployments, expansion still has a number of hurdles to overcome, including:
CO2 capture efficiency is dependent on the circulation of the amine solvent, which has energy impacts thus there is a trade-off between capture efficiency and energy requirements.
Amine degradation due to impurities.
Volumes of CO2 captured from large industrial facilities (500-800MW) using liquid amine will require multiple trains, which comes at a cost. There will also need to be advances in manufacturing techniques for columns at this scale to ensure integrity.
Other absorbent processes, such as chilled ammonia processes, face the same construction constraints as the other processes. However, it is just more expensive to run in terms of energy.
As part of the efforts to mitigate these challenges other post combustion capture techniques are in development such as using adsorption processes (molecular sieves), potassium carbonate or cryogenic refrigeration. These processes remain some time away from deployment at scale but are expected to reach TRL 8 and 9 by 2025, once the pilot plants are operational the processes will prove their efficiencies.
One means that offers an alternative to the complexities of integrating a post combustion capture system with wider processes is to utilise Oxy combustion as a means to produce a high purity stream of CO2 that can be readied for transportation without the need for a capture facility. Oxy combustion can also mitigate the challenge of high heat requirements for carbonate looping processes for CO2 capture. Oxy combustion, in particular the NET Power application of the Allam-Fedvet cycle, is advancing at pace but remains at TRL 7. Additionally, which is significant for retrofit to existing facilities, it will require a supply of oxygen, which is most likely to come from an additional air separation facility.
Pre-combustion capture technologies can generally be grouped as adsorbents, cryogenic separation, liquid absorbents and gas-separation membranes.
Large-scale demonstration of post combustion capture of CO2 using sorbents has been achieved by Air Products at the Valero Refinery, Port Arthur, Texas . This process is based on a Pressure Swing Adsorption (PSA). However, the focus of applications of the PSA processes has been on the production of Hydrogen. For carbon capture, the cycle design will need to be modified, if it is to be used without cryogenic separation. An advantage of adsorption which lends itself to pre combustion capture is the potential for CO2 production at higher pressures: the higher partial pressures of CO2 in pre-combustion capture cause an increase in the effectiveness of the sorbents, when compared to post combustion .
Air Liquide has deployed a cryogenic capture process at the Port-Jerome SMR facility. The technology uses cryogenic purification to separate CO2 from PSA off-gas . However, this is considered TRL-5 . Linde’s HISORP® process combines adsorption with cryogenic separation . The cost of refrigeration is high, and it is most likely this capture method will be integrated with LNG where the cold duty already exists.
Physical absorbents are well established and have been deployed in pre-combustion projects. Processes tend to be operated at low temperatures. There is also ongoing research into identifying new physical absorbents and improving current processes. Chemical absorbents have been considered for pre-combustion applications, but they currently have higher energy requirements than physical sorbents due to the energy required for regeneration. Ionic liquid and clathrate absorbents are in development and require further work to be commercially deployed. As development progresses, scale should be achievable, albeit the time to achieve scale will be dependent on whether novel reactors are required.
Membranes remain in development, the most significant area that will dictate their deployment at scale being their operational life.
Each of the methods, whether pre or post combustion, described come with their own advantages and disadvantages, no one solution is best suited to all applications. There are trade-offs that are required to identify the optimal technical solution; these trade-offs are compounded when economic factors are layered into the consideration. To resolve this multi-faceted problem, the application of capture technology must be considered as part of the wider project system and often part of a wider network of carbon capture projects.
At io, our deep domain expertise in process modelling and simulation, coupled with our system modelling capability is unique in its ability to rapidly assess and optimise these projects. Moreover, our energy innovation capability sees us work with developers of new technologies to help them optimise, commercialise and scale their technology from the lab to industrial deployment. This is demonstrated by our extensive track record in enabling CCUS projects in the US, Europe and Asia Pacific, and we stand ready to support these projects and accelerate this key element of the energy trilemma solution.
notes and references:
Note: Carbon Dioxide Removal (CDR) methods have been excluded from this report
Note: mineralisation shall be considered in a subsequent utilisation & sequestration report
Further assessment of emerging CO2 capture technologies for the power sector and their potential to reduce cost, CSIRO