CCUS: status and priorities for research and development
An update on CCUS R&D that could significantly reduce net CO2 emissions by way of identifying research gaps, opportunities, and priorities in CCUS.
Dr Himmat Singh
Scientist ‘G’ & Prof (Retd)
Viewed : 1827
With the rise in demand for energy globally, CO2 levels have risen sharply, from preindustrial levels of 280 ppm a century ago to over 380 ppm in 2009. These levels are projected to increase even more dramatically over the next 50 years as global energy demand is anticipated to double (Alivisatos & Buchanan, 2010). Carbon capture, utilisation and storage (CCUS) is considered a critical carbon dioxide (CO2) mitigation technology. The CCUS process can be used to capture CO2 emissions from power plants (fuelled by coal, natural gas, and biomass), oil and gas production, oil refineries, industrial applications such as cement, iron and steel production, and fertiliser manufacturing. The captured CO2 can then be used (CCU) or permanently stored (CCS).
Achieving Paris Agreement (PA) targets will require a significant acceleration of the development and deployment of technologies that dramatically reduce CO2 emissions. McKinsey’s analysis of the net-zero pathways for Europe indicates that some 40% of the necessary emissions abatement could come from technologies that are either still in R&D or demonstrated but not yet mature. The remaining 60% could be achieved by widely deploying proven, mature technologies (McKinsey & Co, 2020).
CCUS developments to date are noteworthy, but additional extensive and far-reaching efforts are required to combat climate change. The IEA’s Energy Technology Perspectives 2016 report estimated that CCUS could provide 12% of the GHG emission reductions in the power sector alone. The IPCCC 2°C by 2050 scenario requires the capture of 6.4 Gt/a of CO2 from the power and industrial sectors combined (IEA, 2016).
Carbon capture combined with sequestration is the main means of reducing net CO2 emissions in the near term and could serve as a bridging strategy to a time when non-carbon energy technologies are broadly deployed. Conversion of CO2 (such as reduction to methane or methanol) could help reduce the amount needing to be sequestered. However, the magnitude of the problem of unfettered carbon emissions to the environment is daunting. Continued use of fossil fuel while capping the atmospheric concentration of CO2 at levels of less than 500 ppm is projected to require the capture of ~10 Gt of CO2 per year globally — over a quarter of the CO2 that is generated globally today — and the problem continues to grow as energy use grows (Alivisatos & Buchanan, 2010), (IEA, 2020).
The CO2 capture options can be classified as post, pre-, and oxy-fuel combustion (Cuellar-Franca & Azapagic, 2015). Post-combustion carbon capture is most effective at sites where large quantities of CO2 are generated, including: large electrical power plants fuelled by fossil fuels or biomass; major industrial sites (e.g., for cement, steel or aluminum production or ethanol fermentation); or facilities in which natural gas, petroleum, synthetic fuels, or fossil-based hydrogen is produced. A typical 550 MW coal-fired power plant produces about 2 million ft3 of flue gas per minute at atmospheric pressure. This large volume of flue gas contains CO2 at concentrations of about 12—14% along with water, nitrogen, oxygen, and traces of sulphur oxides, nitrogen oxides, and other materials originating from the fuel and the air used for combustion. Thus, capturing CO2 from this complex mixture at high levels of purity requires highly efficient separation techniques.
Pre-combustion capture is primarily applicable to gasification plants in which the fuel (e.g., coal, biomass) is converted to gaseous components prior to combustion; it concentrates the levels of CO2 to greater than 40%. In oxy-combustion, relatively pure oxygen is used and produces CO2 at levels of about 60%. The advantage of both of these processes is that CO2 is produced in significantly higher concentrations than with post-combustion capture processes, making capture much more efficient. In all three strategies, CO2 must be efficiently separated from other gaseous components and water vapour for subsequent sequestration or conversion. While CO2 capture is relatively easy with oxy-combustion, the process requires the ability to separate oxygen from air at low cost (Jiang & Ashworth, 2021).
The science and technologies supporting CCUS has advanced over the last decade, yet opportunities remain for reducing costs, improving performance, creating better business and regulatory models, and discovering new uses for CO2. This article screens recent unique scientific publications/articles related to CCUS and presents an assessment of the ongoing innovative researches and their translation into low cost efficient technological solution towards reduction in carbon emissions.
CCUS is the combined term covering two alternatives, both of which start with the process of capturing the CO2. In CCU, the captured CO2 is recycled for further use, whereas with CCS the captured CO2 is compressed as pressurised gas for long-term storage or sequestration at geological sites. The two alternatives are considered to be one of the solutions critical in mitigating climate change (Cuellar-Franca & Azapagic, 2015), (IEA, 2020). While CCU has a lower capacity level than CCS for reducing CO2 levels in the short term, it does nevertheless offer a route to reduce CO2 emissions, as well as providing a process to develop value-added materials for further use as part of the circular economy paradigm.
CCU value chain and supporting themes
Hasan et al. developed a multi-scale framework for CCUS and CCU through a process of inductive reasoning and by a series of cross-cutting supporting basic themes. These represent different perspectives of CCU, namely: industrial, governmental and societal, as well as the ultimate objective to reduce CO2 emissions and mitigate climate change. This multi-scale framework enables generalisation of findings from analysis of specific installations and it is possible to synthesise a value chain for development of CCU technologies (see Figure 1).
The four main stages of the CCU value chain are the source, capture, transport, and utilisation stages, where each stage identifies key areas that require further R&D. It is envisaged that the value chain can guide future research trajectories on CCU and assist industry to evaluate CCU as part of the technology development and commercialisation process.
Currently practiced carbon capture technologies — their limitations
The workshop Carbon Capture: Beyond 2020 (Alivisatos & Buchanan, 2010) identified the following limitations: three main types of separation strategies are used — liquid absorbents, solid adsorbents, and membranes — which all depend upon materials and chemicals and physical processes to separate a targeted gas from a mixture. Although some of today’s technologies for capturing CO2 may be relatively efficient, all require considerable energy for isolation of the CO2 due to changes in temperature and/or pressure to drive the separation process. In addition, because of the massive volumes of CO2 involved, regeneration and reuse of the materials used to capture the CO2 is required. Carbon capture materials, including aqueous amines, require a large amount of energy to release the captured CO2. The additional energy required lowers the overall efficiency of a power plant, resulting in substantially higher overall costs for electricity (50-80% higher) compared with facilities without carbon capture. There is a critical need for next-generation separation concepts that will provide efficient, cost-effective technologies for carbon capture in the future.
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