New technology could cut the cost of carbon capture and storage
Cooperation and collaboration are key to deploying the next generation of carbon capture technology
The unique ability of carbon capture and storage (CCS) to reduce carbon dioxide (CO2) emissions while keeping fossil fuels in the energy supply mix has an increasingly vital role to play in the transition to a low-carbon economy, though high costs have previously been a prohibiting factor in its mainstream deployment.
A wave of new CCS technologies have the potential to dramatically cut these costs for the industry, helping to accelerate the commercialisation of energy generation with CCS.
This potential is evidenced in a new TCM-commissioned SINTEF report, which provides an independent assessment of the maturity of a raft of next-generation CO2 capture technologies. The report analysed 23 types of CO2 capture, 12 of which were post-combustion technologies, three oxy-combustion technologies and eight pre-combustion technologies.
Importantly, the report highlights the ability of these next-generation methods to cut current costs by up to 50% and, given that up to 80% of the costs of CCS are related to CO2 capture, this is a real watershed in the global mission to decarbonise the energy sector.
The breadth of companies and technologies covered in the report, as well as the level of maturity that many of these technologies been advanced to - with many having moved beyond laboratory testing to pilot-stage assessments - is testimony to how seriously CCS is being taken by technologists. The movement to commercialise CCS is unsurprising given the UK Energy Technologies Institute (ETI) estimate that for the UK alone, the additional cost of decarbonising the economy without CCS will be £32 billion ($54.4bn).
While the maturity of CO2 capture technologies undoubtedly relates to their timeline to commercialisation, the report also highlights a number of promising laboratory-level technologies which have great potential to be scaled up; if their core challenges are overcome with adequate laboratory tests and simulations across the post-combustion, oxy-combustion and pre-combustion processes.
Post-combustion capture involves fuels being burnt in the traditional way with air, producing a flue gas consisting primarily of nitrogen, water vapour, CO2 and excess oxygen. CO2 is then separated from this flue gas. Many possible CO2 separation technologies exist, with the most mature based on absorption using liquid solvents and others being based on adsorption by sold sorbents, membranes, or cryogenic separation.
The 12 post-combustion technologies assessed by SINTEF include:
Two liquid phase solvents;
Enzyme catalysed CO2 absorption/desorption;
Novel solvent systems;
Calcium looping systems;
Sorbent looping systems using more novel solvents;
Vacuum pressure swing absorption (VPSA);
Temperature swing absorption (TSA);
Polymeric and hybrid membranes;
Low temperature (cryogenic) separationn of CO2 from flue gas; and
Polymeric membranes + low temperature separation - don't use chemicals and represent significant potential for environmental impact improvement compared to amine-based processes.
By comparison, oxy-combustion processes entail fuels being burnt in oxygen rather than air to provide a flue gas that will consist mainly of CO2 and water vapour, while avoiding the large amount of nitrogen normally present. The need for large amounts of oxygen presents a major challenge in oxy-combustion, so improvements in air separation are vital for this category to be a leader in the commercialisation race.
Oxy-combustion technologies assessed include:
Chemical looping combustion (CLC);
Oxy-combustion gas turbine; and
Pre-combustion capture processes see fuel undergoing partial oxidation at high pressure in a gasification or a reforming process, after which follows a water-gas shift reaction, to produce a syngas consisting mainly of hydrogen (H2), water (H2O) and CO2. Partial oxidation is usually carried out with oxygen that has been separated from air. The operating pressure and CO2 concentration will be much higher in shifted syngas than in post-combustion flue gas, meaning that the CO2 separation process is less energy-demanding, though this is countered by the high energy demands for air separation and reforming/gasification, as well as losses in energy recovery.
Pre-combustion technologies assessed include:
Sorption-enhanced water-gas shift (SEWGS);
Sorption-enhanced steam-methane reforming (SE-SMR);
Zero Emission Gas;
Palladium (Pd) membranes for H2 separation from syngas;
Ceramic-based Hydrogen transport membranes (HTMs);
O2 separation membranes;
Low temperature (cryogenic) separation of CO2 from shifted syngas; and
Advanced hydrogen gas turbines.
Research and development efforts for post-combustion are largely focused on CO2 separation, while for oxy-combustion and pre-combustion, research and development applies across all major elements of the capture process. Air separation and oxygen production carry high operational and capital costs, as well as high energy consumption. Oxygen production is fundamental to oxy-combustion and pre-combustion processes so new separation methods are being explored to address these issues, including advancing traditional cryogenic forms and investigating sorbent-based processes and membranes.
Oxy-combustion gas turbines and low temperature separation of CO2 from shifted syngas offer the highest rates of CO2 capture of all the new technologies analysed by SINTEF, with the latter capturing up to 9,000kg/hour. Methods such as chemical looping combustion (CLC), which could offer a near 100% CO2 capture rate without the need for energy inefficient air separation, will be available at utility scale from next year.
The level of political interest in CCS is inevitably leading to companies developing new and more efficient technologies. The International Energy Agency (IEA) last year released its Roadmap for CCS, which set out plans to use CCS in 30% of global energy production in order to stay below two degrees of global warming. In early June this year, US president Barack Obama and the country's Environmental Protection Agency (EPA) unveiled draft regulations for reducing greenhouse gas emissions in the US. The regulations will apply to coal-burning power plants and require a 30% reduction in greenhouse gases by 2030. Each state will be allowed to create their own plans for complying with the new rules and it is likely CCS will have a key part to play in enabling them to cut emissions from their coal-fired plants.
The next step in translating this political will into viable projects is to progress testing of cost-cutting CO2 capture technologies, and TCM provides the crucial infrastructure to do this. Many of the processes detailed in the SINTEF report have been confined to lab and pilot tests - including those using precipitating solvents, polymeric membranes and low temperature separation. Taking those technologies out of the lab and onto a commercial scale is exactly the reason that SINTEF's demonstration facility CO2 Technology Centre Mongstad (TCM) exists. Given that finding ongoing investment can be challenging, testing new technologies prior to construction in a full-scale environment, is also useful to demonstrate the commercial realities of CCS to investors.
There is clear potential for CCS to become cost competitive with other forms of low-carbon generation and testing of this significant pipeline of CO2 capture technologies is minimising costs and investment risk for the industry. Already by the 2020s the price of CCS is expected to have dropped to £100 per megawatt hour.
By focusing on international collaboration and learning from other testing projects, we are getting ever closer to CCS commercialisation. Key players in the industry are collectively creating the momentum for a standardised group of CCS technologies, which will provide investors and policy makers with the security they need. By working together the industry can also address other key issues, including developing skills, the supply chain, storage and CCS infrastructure.
The most important thing, however, is to ensure information sharing on a global scale to advance the industry and create a legacy of technology and infrastructure that will enable the market to take off once policy and a firm regulatory regime are in place. The range of the next-generation technologies being advanced will encourage competition and, while not every technology will succeed, by standing on the shoulders of previous technologies to reduce cost and risk, full-scale and cost-effective deployment of fossil fuel generation with CCS can become a market reality.
Frank Ellingsen, is the managing director of CO2 Technology Centre Mongstad