直接空气捕获：实现净零排放的关键技术（英）-IEA.pdf

Direct Air Capture A key technology for net zero The IEA examines the full spectrum of energy issues including oil, gas and coal supply and demand, renewable energy technologies, electricity markets, energy efficiency, access to energy, demand side management and much more. Through its work, the IEA advocates policies that will enhance the reliability, affordability and sustainability of energy in its 31 member countries, 8 association countries and beyond. Please note that this publication is subject to specific restrictions that limit its use and distribution. The terms and conditions are available online at www.iea.org/t Copernicus for hourly wind speed datal. Innovation is needed across the direct air capture value chain DAC technologies require significant amounts of energy. The two leading DAC technologies – solid DAC (S-DAC) and liquid DAC (L-DAC) – were initially designed to operate using both heat and electricity. The lower temperature heat needs of S-DAC mean it can be fuelled by renewable energy sources (including heat pumps and geothermal). The high temperature heat needs of L-DAC (up to 900nullC) underpin current plant designs that rely on natural gas for heat, although the CO 2 from the use of this gas is inherently captured within the process and not emitted. Innovation to support renewable energy options for high-temperature industrial heat would maximise the carbon removal potential of L-DAC plants. DAC still needs to be demonstrated in different conditions. A major advantage of DAC is its flexibility in siting: in theory, a DAC plant can be situated in any location that has low-carbon energy and a CO 2 storage resource or CO 2 use opportunity. It can also be located near existing or planned CO 2 transport and storage infrastructure. Yet there may be limits to this siting flexibility. To date, DAC plants have been successfully operated in a range of climatic conditions in Europe Direct Air Capture Executive summary A key technology for net zero PAGE | 11 I E A . A ll r ight s r es er v ed. and North America, but further testing is still needed in locations characterised, for instance, by extremely dry or humid climates, or polluted air. Innovation in CO 2 use opportunities, including synthetic fuels, could drive down costs and provide a market for DAC. Early commercial efforts to develop synthetic aviation fuels using air-captured CO 2 and hydrogen have started, reflecting the important role that these fuels could play – alongside biofuels – in the sector. In the Net Zero Emissions by 2050 Scenario, around one-third of aviation fuel demand in 2050 is met by these synthetic fuels, but currently their cost can be more than five times conventional fossil-based options. Further innovation is needed to support cost reductions and faster commercialisation, and build a potentially large market for air-captured CO 2 . Robust certification of direct air capture can support future investment Business models for DAC are linked to high-quality carbon removal services and CO 2 use opportunities. DAC companies are offering commercial CO 2 removal services to individuals and companies. Although DAC with CO 2 storage is among the most expensive options to balance emissions, it is attracting interest from companies seeking high-quality CDR that offers additionality, durability and measurability. The purchase of DAC-based carbon removal is currently limited to voluntary carbon markets. Internationally agreed approaches to the certification and accounting of DAC are needed. The development of agreed methodologies and accounting frameworks based on life cycle assessment (LCA) for DAC – alongside other CDR approaches – will be important to support its inclusion in regulated carbon markets and national inventories. Notably, the latest IPCC Guidelines for National Greenhouse Gas Inventories do not include an accounting methodology for DAC, meaning that CDR associated with DAC cannot be counted towards meeting international mitigation targets under the United Nations Framework Convention on Climate Change (UNFCCC). Efforts to develop carbon removal certification, including for DAC-based CDR, have commenced in Europe and the United States, as well as through initiatives such as the Mission Innovation CDR Mission. These efforts should be co-ordinated with the aim of establishing internationally consistent approaches. Six priorities for direct air capture deployment DAC deployment must be accelerated for net zero. The Net Zero Scenario requires the immediate and accelerated scale-up of DAC, calling for an average of 32 large-scale plants (1 MtCO 2 /year each) to be built each year between now and 2050. This will require increased public and private support to reduce costs, Direct Air Capture Executive summary A key technology for net zero PAGE | 12 I E A . A ll r ight s r es er v ed. improve technologies and build the market for DAC technologies. The IEA has identified six near-term priorities for DAC deployment aligned with net zero goals: 1. Demonstrate DAC at scale as a priority. Targeted policies and programmes are needed for near-term demonstration and deployment. Governments should ensure that planned projects are able to progress to operation and provide essential learnings for DAC technologies and supply chains. 2. Foster innovation across the DAC value chain. Innovation will be critical to: reducing manufacturing and operational costs, as well as the energy needs for DAC plants; supporting the availability of low-emission energy sources for high-temperature heat; and developing and reducing the cost of CO 2 use applications including synthetic aviation fuels. 3. Identify and develop CO 2 storage. The potential for DAC to remove CO 2 from the atmosphere in large quantities rests on the development of suitable geological CO 2 storage. Although the storage potential is vast, the time to develop these resources can be as long as ten years and could act as a brake on the scale-up of DAC in some regions. 4. Develop internationally agreed approaches to DAC certification and accounting. Robust, transparent and standardised international certification and accounting methodologies for DAC are needed to facilitate its recognition in carbon markets and IPCC greenhouse gas inventory reporting. 5. Assess the role of DAC and other CDR approaches in net zero strategies. Improved understanding and communication of the anticipated role of DAC and other CDR approaches in net zero strategies will help identify the technology, policy and market needs within countries and regions. For example, the United Kingdom’s Net Zero Strategy identifies a need for around 80 MtCO 2 of technology-based carbon removals by 2050. 6. Build international co-operation for accelerated deployment. Collaboration through international organisations and initiatives such as the IEA, Clean Energy Ministerial, Mission Innovation, and Technology Collaboration Programme on Greenhouse Gas R Climeworks (2021), Direct air capture and storage and carbon dioxide removal; Keith et al. (2018), A Process for Capturing CO 2 from the Atmosphere; McQueen et al. (2021), A review of direct air capture (DAC): scaling up commercial technologies and innovating for the future; Fasihi et al. (2019), Techno-economic assessment of CO 2 direct air capture plants; Beuttler et al. (2019), The Role of Direct Air Capture in Mitigation of Anthropogenic Greenhouse Gas Emissions; WRI (2021), Direct Air Capture: Resource Considerations and Costs for Carbon Removal; IEAGHG (2021), IEA Greenhouse Gas R however, it is still in its infancy and major challenges are yet to be overcome. Generally speaking, membrane-based approaches are technically challenged by the low concentration of CO 2 in the air, and show low CO 2 selectivity at ambient pressure, requiring the expensive compression of a very large amount of ambient air to separate CO 2 efficiently. In the literature it has also been argued that better gas permeance (i.e. the ratio between the gas permeability of the membrane and its thickness) could play a larger role than CO 2 selectivity in membrane cost reduction. If true, polymeric materials with high CO 2 permeance could represent a suitable option for DAC. In more traditional CCUS applications, membrane-based separation technologies are currently at TRL 4 for the cement industry and at TRL 6 for natural gas processing. 10 Fundamental research into alternative DAC approaches is currently taking place at a number of institutes. For instance, the Oak Ridge National Laboratory is separating CO 2 from the air at lab scale and regenerating the solvent at relatively mild temperatures (15-120°C) (Brethomé et al., 2018) (Custelcean et al., 2021), while the Center for Negative Carbon Emissions at Arizona State University is prototyping “mechanical trees” that rely on wind instead of fans for air recirculation. The TRL scale One way to assess where a technology is on its journey from initial idea to market is to use the TRL scale. Originally developed by the National Aeronautics and Space Administration (NASA) in the United States in the 1970s, the TRL provides a snapshot in time of the level of maturity of a given technology within a defined scale. The scale provides a common framework that can be applied consistently to any technology, to assess and compare the maturity of technologies across sectors. 10 TRL 9 for commercial separation of CO 2 for natural gas processing. Direct Air Capture Chapter 2. Technologies to capture CO 2 from the air A key technology for net zero PAGE | 26 I E A . A ll r ight s r es er v ed. The technology journey begins from the point at which its basic principles are defined (TRL 1). As the concept and area of application develop, the technology moves into TRL 2, reaching TRL 3 when an experiment has been carried out that proves the concept. The technology now enters the phase where the concept itself needs to be validated, starting from a prototype developed in a laboratory environment (TRL 4), followed by testing of components in the conditions it will be deployed (TRL 5), through to testing the full prototype in the conditions in which it will be deployed (TRL 6). The technology then moves to the demonstration phase, where it is tested in real-world environments (TRL 7), eventually reaching a first- of-a-kind commercial demonstration (TRL 8) on its way towards full commercial operation in the relevant environment (TRL 9). Arriving at a stage where a technology can be considered commercially available (TRL 9) is not sufficient to describe its readiness to meet energy policy objectives, for which scale is often crucial. Beyond the TRL 9 stage, technologies need to be further developed to be integrated within existing systems or otherwise evolve to be able to reach scale; other supporting technologies may need to be developed, or supply chains set up, which in turn might require further development of the technology itself. For this reason, the IEA has extended the TRL scale it uses in its reports to incorporate two additional readiness levels, which focus on market (rather than technology) development: one where the technology is commercial and competitive, but needs further innovation for its integration into energy systems and value chains when deployed at scale (TRL 10), and a final one where the technology has achieved predictable growth (TRL 11). Maturity categories and TRLs along innovation cycles IEA. All rights reserved INTEGRATION NEEDED AT SCALE Solution is commercial and competitive but needs further integration efforts 7 1 INITIAL IDEA Basic principles have been defined 3 CONCEPT NEEDS VALIDATION Solution needs to be prototyped and applied 4 EARLY PROTOTYPE Prototype proven in test conditions 5 LARGE PROTOTYPE Components proven in conditions to be deployed PRE-COMMERCIAL DEMONSTRATION Solution working in expected conditions COMMERCIAL OPERATION IN RELEVANT ENVIRONMENT Solution is commercially available, needs evolutionary improvement to stay competitive FIRST OF A KIND COMMERCIAL Commercial demonstration, full scale deployment in final form 8 9 10 2 APPLICATION FORMULATED Concept and application of solution have been formulated FULL PROTOTYPE AT SCALE Prototype proven at scale in conditions to be deployed 6 PROOF OF STABILITY REACHED Predictable growth 11 SMALL PROTOTYPE or lab LARGE PROTOTYPE DEMONSTRATION MATURE Level TECHNOLOGY DEVELOPMENT MARKET DEVELOPMENT Category Sub-category SMALL PROTOTYPE LARGE PROTOTYPE EARLY ADOPTION STEADY SCALE UP CONCEPT DEMONSTRATION MATURE MARKET UPTAKE Direct Air Capture Chapter 2. Technologies to capture CO 2 from the air A key technology for net zero PAGE | 27 I E A . A ll r ight s r es er v ed. Cost of capturing CO 2 directly from the air Current capture costs via DAC are high and uncertain Capturing CO 2 from the air is more expensive than capturing it from a point source. This is because the CO 2 in the atmosphere is much more dilute than, for example, in the flue gas of a power station or a cement plant. 11 This contributes to the higher energy need and cost of DAC relative to other CO 2 capture technologies and applications. CO 2 capture cost at varying CO 2 concentrations, 2020 IEA. All rights reserved. Notes: Average values by application. H 2 = hydrogen; SMR = steam methane reforming; NG = natural gas; EO = ethylene oxide. The empirical trend line shows the correlation between capture cost and CO 2 concentration. As DAC technology has yet to be demonstrated on a large scale (1 MtCO 2 /year and over), its costs are extremely uncertain. Capture cost estimates reported in the literature are wide, typically ranging anywhere from USD 100/t to USD 1 000/t, while cost estimates from the main technology providers vary across USD 95-230/tCO 2 for L-DAC and USD 100-600/tCO 2 for S-DAC (Keith et al., 2018; European Commission Joint Research Centre, 2019; Clean Energy Solutions Center, 2020; The Catalyst Group, 2019). A recent assessment by IEAGHG estimates DAC costs for removal to be in the range of 11 CO 2 concentration: in air = 410 ppm = 0.041 mol%; in flue gas from natural gas based power generation = 4-8 mol%; in flue gas from cement production = 14-33 mol%. Direct Air Capture Chapter 2. Technologies to capture CO 2 from the air A key technology for net zero PAGE | 28 I E A . A ll r ight s r es er v ed. USD 200-700/tCO 2 . 12 For context, carbon removal via BECCS costs USD 15-80/tCO 2 , while afforestation/reforestation can cost as little as USD 10/tCO 2 . Costs and energy needs vary according to the type of technology (solid or liquid), the source of energy (fuel, electricity, or both) and whether the captured CO 2 is going to be geologically stored or used immediately at low pressure. For CO 2 storage, the CO 2 needs to be compressed at a very high pressure to be injected into geological formations. This step increases both the capital cost of the plant (due to the requirement for additional eq