Cutting costs of CCS – Part 1

The unique ability of CCS to reduce carbon dioxide 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. These will be explored in a two part series, with the first installment looking at the new carbon capture technologies and the second looking at what these mean for the wider industry.

The potential for cost reduction 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. A total of 23 novel forms of CO₂ capture were analysed, with 12 of these categorised as post combustion technologies, three as oxy combustion technologies and eight as precombustion technologies.

Importantly, the milestone 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. Learning by doing is vital for achieving commercialisation.

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.

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:

• Precipitating solvents.
• Two liquid phase solvents.
• Enzyme catalysed CO₂ absorption/desorption.
• Ionic liquids.
• 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) separation of CO₂ from flue gas.
• Polymeric membranes + low temperature separation – do not 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 in the report include:

• Chemical looping combustion (CLC).
• Oxy combustion gas turbine.
• High pressure oxy combustion.

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 H₂, 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.
• Advanced hydrogen gas turbines.

Research and development efforts for post combustion are largely focused on CO₂ separation, while for oxy combustion and pre combustion, R&D 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 9000 kg/hr. 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.

Part 2 coming soon.

Written by Frank Ellingsen, Managing Director, CO₂ Technology Centre Mongstad

Edited by Claira Lloyd

Read the article online at: https://www.hydrocarbonengineering.com/special-reports/26062014/ccs_cost_cutting_part_1/