From power generation to food production, there is a need to reduce the amount of carbon dioxide entering the atmosphere. Techniques for separating CO₂ from gas streams are evolving rapidly, but the sustainability imperative is raising new challenges for everyone involved.
Decarbonisation at scale is a big challenge. The 2015 Paris Agreement committed signatories to limit global temperature rise to well below 2°C above pre-industrial levels (https://unfccc.int/about-us/unfccc-archives/the-unfccc-archival-exhibition/the-paris-agreement-exhibit). Estimates suggest that between 350 and 1,200 gigatonnes (Gt) of CO₂ must be captured and stored this century to achieve this target. Currently, around 40 megatonnes (Mt) of CO₂ are captured and stored annually, so capacity must increase at least 100-fold by 2050 ( https://www.weforum.org/agenda/2020/12/carbon-capture-and-storage-can-help-us-beat-climate-change/). Development and deployment of carbon capture, utilisation and storage (CCUS) technologies at scale is essential.
CCUS encompasses a suite of technologies designed to capture CO₂ including emissions from point sources such as power plants and industrial facilities, preventing their release into the atmosphere. The captured CO₂ can then be processed for storage underground or repurposed for industrial use. Filtration plays a critical role at every stage: from decontaminating the source gas, through CO₂ capture & onwards to compression, transportation, and storage or reuse.
The cost of carbon capture
Industrial-scale decarbonisation poses the question of what to do with all that captured carbon. Essentially, the choice is permanent storage or reuse.
Permanent CO₂ storage raises several challenges. Identifying and assessing potential storage sites can be time-consuming and expensive. Where appropriate geological sites are identified, they may need to be adapted and monitored continuously. Transportation to suitable sequestration locations is arguably the biggest barrier to CO₂ storage. Transportation distances can be considerable, or downright impractical. Building, monitoring and maintaining the necessary infrastructure adds significant costs (https://www.solartronisa.com/industries/clean-energy/carbon-capture/challenges-of-ccs). For carbon capture to become viable at the scales required to achieve industrial decarbonisation targets, storage is unlikely to present the most economical or practical long-term solution.
Utilisation can be a simpler and less costly option. Reusing captured CO₂ in other industrial processes supports the spirit and intent of the Paris Agreement by making the process more sustainable. There are already established markets for CO₂, such as carbonated drinks, food packaging, fire suppression & enhanced plant growth plus emerging markets that include the production of eFuels. Using circular economy principles means that captured CO₂ becomes a value stream rather than a financial burden for carbon-intensive industries ( www.sciencedirect.com/science/article/pii/S1674987123001494).
Filtration and carbon quality
Whether you are designing a carbon capture system for storage or utilisation, the quality of the captured CO₂ is critical for success – and this is where filtration comes into its own. Filtration not only removes contaminants to deliver the desired final product quality, it also protects processing equipment and improves operational efficiency.
CCUS projects primarily focus on capturing CO₂ emissions from point sources. It is currently far more cost-effective to capture the gas directly from concentrated exhaust streams rather than from the ambient air. Correctly applied, filtration maintains carbon capture system efficiency and delivers the CO2 to downstream processes with minimal contamination.
1. Post-combustion filtration
Chemical absorption is the most mature technology for post-combustion capture. It uses solvents such as amines to selectively absorb CO₂ from the flue gas and is commonly deployed in power plants, cement production, and other industries that burn hydrocarbons to produce energy. Closed loop heat regeneration cycles are then employed to the captured CO₂ from the solvents, thus allowing the concentrated CO2 to be compressed for transportation or storage. Figure 1 illustrates the primary points where filtration should be applied in a solvent absorption system.
An effective filtration system will utilise a combination of gas filters to reduce flue gas contaminant allied with liquid particulate filters to maintain solvent quality & reduce absorber fouling, foaming, and solvent degradation, which result in a lower per unit CO₂ capture rate and exhausted CO₂ escaping into the atmosphere. Residual organics and hydrocarbon removal via activated carbon filtration is equally important. Any contamination reaching the top of the absorber column will directly impact the quality of the CO₂ and may lead to inefficient CO₂ capture.
2. Pre-combustion capture
Carbon dioxide can also be separated from the fuel before combustion occurs. The pre-combustion capture method is commonly used in integrated gasification combined cycle (IGCC) plants, where fossil fuels are converted into syngas (a mixture of carbon monoxide, hydrogen, and CO₂). In a process known as a phase shift reaction, carbon monoxide reacts with steam to increase the concentration of hydrogen and CO₂ in the gas mixture. The CO₂ is then separated and the hydrogen is used as a clean fuel.
Filtration is required to remove impurities such as sulfur compounds, particulates and moisture from the syngas before CO₂ separation. Membrane technologies, pressure swing adsorption (PSA), and solid sorbents are often used for CO₂ removal in these pre-combustion systems.
3. Oxy-combustion capture
Oxy-combustion involves burning fossil fuels in an environment of pure oxygen (O₂) instead of air. This reduces the presence of nitrogen in the flue gas, leaving primarily CO₂ and water vapour as combustion byproducts. The water vapour can be easily condensed, leaving a highly concentrated stream of CO₂.
The key component of an oxy-combustion system is the air separation unit (ASU), which generates the pure oxygen required. Filters are essential for removing impurities from the incoming air to protect the ASU and ensure efficient oxygen production.
Transportation and beyond
Following capture, CO₂ is typically dehydrated and compressed to high pressure for transport and storage. CO₂ post compression is more commonly referred to as being ‘Supercritical’ or ‘Dense Phase’ state. Filtration is essential for efficiency and safety during this process.
Contaminants such as water, lube oil, oxygen and hydrogen sulphide (H₂S) present in the CO₂ can threaten pipeline integrity by causing corrosion or pipeline blockages. Solid corrosion products and pipe scale can also be carried downstream, fouling critical equipment such as control valves, metering stations, and high-pressure injection pumps. This increases maintenance costs and can involve equipment replacement or unscheduled downtime. Solid contaminants can also plug permeable storage reservoir pore structures, requiring increased energy for CO₂ injection and limiting the amount of available reservoir storage capacity.
Figure 2 illustrates where filtration should be applied during the supercritical phase. In selecting filters and separators for dense phase CO₂ applications, substantial care must be taken over which materials are used, how filter sizing is performed, and the correct filtration rating. To protect reservoirs, the filter rating must be selected based on the reservoir permeability and approximate pore diameter.
What next for CCUS?
Better filtration equipment alone will not solve the challenges of decarbonising industrial processes. No ‘standard’ design for CCUS yet exists and each application will have unique process challenges. This makes it difficult to identify the best filtration technology for the task.
Cleanova.C-CLEAN provides a solution. This innovative approach recognises that each process has unique parameters and each customer has specific needs and desired outcomes. It provides tailored filtration solutions designed for each carbon capture process, based on the chosen method, load quantities, type of contaminants, CO₂ concentration, pressure and temperature. The aim is to collaborate with industrial clients and CCUS operators from the earliest concept stages, because considering filtration requirements from the outset, and within the context of the entire system design and business model, will yield the best results.
Conclusion
The successful adaptation of existing technologies such as filtration to meet the specific requirements of CCUS operations is an ongoing process, and early collaboration is crucial to the success of our decarbonisation journey. Correctly applied, filtration can achieve a high quality end product that enables captured CO₂ to be reused in a variety of markets.
Driving down costs, optimising uptime, and delivering high quality products are common aims in any industrial application. The correct application of filtration in CCUS systems contributes at every level and is critical to achieving global decarbonisation.
This article is based on the whitepaper “Carbon capture, utilisation and storage: a filtration perspective”, which can be downloaded here: https://www.cleanova.com/ccuswhitepaper/
