生物CCUS供应链中的碳核算—确定科学和政策的关键问题(英)-IEA.pdf-solarbe文库

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Carbon acounting in Bio-CCUS supply chains – identifying key isues for science and policy IEA Bioenergy Task 45 IEA Bioenergy Task 40 February 202 xxxx xx IEA Bioenergy Task XX Month Year xxxx xx Copyright © 202 IEA Bioenergy. All rights Reserved ISBN 979-12-80907-05-9 Published by IEA Bioenergy The IEA Bioenergy Technology Colaboration Programe TCP is organised under the auspices of the International Energy Agency IEA but is functionaly and legaly autonomous. Views, findings and publications of the IEA Bioenergy TCP do not necessarily represent the views or policies of the IEA Secretariat or its individual member countries The IEA Bioenergy Technology Colaboration Programe TCP is organised under the auspices of the International Energy Agency IEA but is functionaly and legaly autonomous. Carbon acounting acros Bio-CCUS supply chains – identifying key issues for science and policy By Olle Olsson 1 , Nabil Abdalla 2 , Silvana Bürck 2 van Vuren et al. 2017; Heck et al. 2018. Much of the discussion in the literature has taken a very long-term perspective on the isue and has been dedicated to addressing the potential broader sustainability impacts from broad deployment of Bio-CCS IPC 2018; Hanson et al. 2021. However, in the light of the increasing interest in CDR from policy makers, it is high time to also investigate aspects pertaining to the practicalities of actual near-term deployment of Bio-CCS systems and value chains. In paralel with the growing political and research interest in Bio-CCS, there has ben a similar rise of interest in capture and utilization of biogenic CO2 for diferent purposes, including as feedstock for production of materials, chemicals or fuels. This is commonly refered to as Bio- CCU or BECCU and the two are often jointly referred to as Bio-CCUS or BECCUS Text box 1. Bio-CCUS systems can be implemented in a broad range of contexts, including but not limited to sectors that already use substantial amounts of biomas as fuel or feedstock, such as heat Berndes et al. 2013; Lamers and Junginger 2013 . To this already intricate analysis shal now also be incorporated an analysis of the climate impacts related to capture, utilization and/or storage of CO2. Secondly, even with comprehensive and transparent methods by which Bio-CCUS life cycle GHG balances can be developed, a key remaining question is how to implement these methods in policy frameworks. There wil be a need to find a balance between a acknowledging the heterogeneity acros diferent value chains, and b avoiding overly complicated legal specifications that are costly to administer. In adition, it will be crucial to find ways to alocate burdens and benefits appropriately in cases where captured carbon is transfered across Bio- CCUS suply chains, not only betwen sectors e.g., agriculture/forestryindustry-air transport as might be the case with a Bio-CCU aviation fuel but between jurisdictions as well. In this report, we review the challenges around accounting for the climate effects of Bio-CCS and Bio-CCU suply chains and discuss key issues that ned to be adresed to prepare a sound scientific and legally functional foundation for political governance of Bio-CCUS. It is important to emphasize that Bio-CCUS can be implemented in many diferent contexts and sectors. This means that there can be substantial variations in terms of the actual details of carbon accounting and climate impact, and we do not strive to provide detail analysis for each context. Rather, our ambition is to give a more principal overview of some particularly important general issues. The report is structured as follows. In section 2, we provide an overview of key isues that ned to be considered when quantifying GHG emisions acros Bio-CCUS suply chains. In section 3, we discus how to apply these scientific findings within a governance context. Section 4, finally, concludes with a discussion, some recomendations for policy makers and researchers, and sugestions for further research. 2 CO 2 flows in Bio-CCUS systems – an overview This report takes as its starting point Bio-CCUS/BECCUS as a joint concept, acknowledging that the Bio-CCS and Bio-CCU value chains have many joint components and that innovation processes wil likely cross- fertilize betwen them Olsson et al. 2020. At the same time, Bio-CCS and Bio-CCU are quite distinct when it comes to their CO2 flows see Figure 1, their climate change mitigation potential and how this should be governed. For this reason, this section reviews the Bio-CCS and Bio-CCU perspectives in turn. Figure 1. Conceptual illustration of the carbon flows related to Bio-CCS and Bio-CCU. BCBiomas combustion Cowie et al. 2021; IEA Bioenergy 2021, we will focus on the later stages of Bio-CCUS suply chain. In other words, one could frame our focus herein as a “gate-to-grave” Bio-CCS or possibly “gate-to-cradle” Bio- CCU analysis, as we center our discusion on flows of biogenic CO2 either in diferent forms of products Bio-CCU or on the way to long-term storage Bio-CCS. 2.1 CAPTURING BIOGENIC CO 2 A general aspect to kep in mind when discusing technological aspects of Bio-CCS and Bio-CCU is to se them as sub-categories of CS and CU in general. The CO2 capture stage influences the overall climate impact of the Bio-CCUS suply chain predominantly through the capture rates and the energy neded for the proces. The capture rates can vary substantialy betwen proceses and context, depending on e.g., the number of point sources at a specific facility. If most of the CO2 emisions from a facility are concentrated at one source, this makes for lower costs of capture whereas if emisions are distributed acros several different point sources, high capture rates can become prohibitively expensive Olsson et al. 2020. As for the energy neded for capture, the higher the energy eficiency – i.e., the lower the energy penalty of the proces - and the lower the GHG fotprint of the energy used for capture, the better the overall CO2 balance of the capture stage. As is ilustrated in Figure 2, there is great heterogeneity betwen diferent sectors and processes when it comes to the energy demands of CO2 capture. An important aspect to emphasize here is that whether the CO2 to be captured is biogenic or fosil is in itself typically not a primary factor in determining the energy demand. Figure 2. Overview of energy neds for CO2 capture in diferent proceses. Data from von der Asen et al 2016. Some key aspects to be mentioned when it comes to things that determine the climate impact of the capture stage include CO2 concentration in the gas stream in question, the availability of proces heat on-site e.g, Olson et al. 2020 and if the heat used for the capture process can be recovered afterwards Bisinella et al. 2021. For example, bioethanol production facilities typically have very highly concentrated CO2 streams resulting from fermentation processes, and these can be captured at low energy expense. The same goes for biogas upgrading proceses that already have CO2 separation as one of its process stages. Pulp Autenrieth et al. 2021. Electrolysis is a very energy-intense procedure, although there are ongoing R Zimermann et al. 2018. Benet et al. 2014 distinguish between utilizations with permanent storage and utilizations with subsequent emissions of CO2. The former comprises EOR and consequently any related utilization such as EGR, as wel as the deployment of mineralization. These utilizations are considered to store carbon “permanently”. Storage in cement can last from decades to centuries Bruhn et al. 2016, whereas 7 For example, much road transportation could be electrified directly without having to use synthetic fuels. utilizations with subsequent near term emisions are products which are rather short lived, such as fuels or plastics Benett et al. 2014 that store carbon from days/weks fuels to years plastics Bruhn et al. 2016. However, to this day, there does not exist a general definition of permanence in the context of carbon storage. For example, when procuring carbon dioxide removal solutions, the software company Stripe defines permanent carbon storage to be 100 years Orbuch 2020. In the context of CCU and delayed emisions, Ramirez Ramirez et al. 2020 propose a 50-year horizon, meaning emisions within this time window should be accounted for, whereas emisions outside of this period should be ignored, under the assumption that climate change by this point in time either has been managed or has gone out of control completely. At the same time, the authors sugest that GWP20 and GWP10 should be used. In this light, intermediate storage can help mitigate climate change and could as such be considered, when discusing mid-term climate change mitigation policies. This could either entail a de-facto sink with view to the time frames 2050 and 2100, respectively, if carbon retention times exced the aforementioned, or, on the other hand, be included with a proportionated share of its GWP, coresponding to the amount of radiative forcing carried out by the year 2050 / 2100. Whereas Ramirez Ramirez et al. 2020 present among others the 500- year horizon for delayed emissions, the IPC uses 2100 as the timeframe for the reporting under the Paris Agrements IPC 2021. Consequently, further discusion is required in order to define permanence i and in order to decide how to handle utilizations with a storage time of e.g. 40 years and subsequent crediting ii. Besides this, the question of substitution and alocation between sectors and across borders ii remains, which wil be further discussed in chapter 3.2.1. In principle, as long as CCU products do not store carbon physicaly on a very long time scale, these options cannot be considered to be negative emission technologies. Only CU products with permanent storage can be considered as direct climate change mitigation measures in contrast to indirect effects, e.g. the displacement of fossil-based products via CCU, taking into acount that the carbon storage wil be monitored regularly, as it is the case for CS Bruhn et al. 2016. This implies that only Bio-CCS can be considered an option if negative emissions is the objective Philibert 2018. However, in terms of carbon content of a product, Bio-CCU can be considered as a net-zero-CO2 compatible option Gabrielli et al. 2020 and could help face out fosil primary energy carriers or products. Provided these CCU routes achieve a reduction in GHG emisions, they could very wel help bridge the gap to a fundamentaly decarbonized economy. Comparison of two products Cumulative CO2-Storage Mio. t CO2 Annual storage rate in Mio. t CO2 Expected life-time 1 Scenario/year until 2030 until 2040 until 2050 On average, consideration of the entire observation period CCU – plastics long-lived 158 316,80 473 16 Years CCU - mineralization 26 51 77,8 2,6 Decades to centuries Source Fehrenbach et al. 2021; 1 Bruhn et al. 2016 Table 1 Potential cumulative CO2 Storage in CU of two exemplary cases in Germany The comparison of two diferent CCU products demonstrates the importance of the consideration of the CO2 storage permanence 8 . Taking an anual carbon storage rate of each CU aplication plastics and 8 These storage rates originate from calculations of the Bio-CCU potential in Germany, unpublished. mineralization into acount and modeling the storage potential for the next decades, the plastics CU deployment appears to store more carbon than the CCU mineralization. Besides the fact that both CU- products cannot be produced at the same quantity due to limited additional calcium/magnesium-rich feedstock for mineralization, the storage permanence is not considered here, which brings the carbon storage of these products into a diferent light. Even long-lived plastics have a life-time shorter than mineralized building materials, whereas most of the theoreticaly stored carbon wil practicaly be re- emited subsequently. Folowing Benet et al. 2014, such a mineralized building material can be considered a permanent storage, contrary to plastics. This example demonstrated that the factor storage permanence needs to be considered thoroughly in adition to production quantities of diferent CCU derived products. Furthermore, the substitution effects of fossil reference products ned to be considered for both applications in order to derive a holistic estimation of the climate impact of CCU plastics and CCU mineralization. 2.4.4 Key determinants of overall climate impact In sumary, the key aspects that need to be taken into consideration and that contribute most significantly to the overall climate impact of Bio-CCU products are thus i. the concentration and purity of CO2 to be further utilized, ii. the nature of utilization, e.g., PtX with high energy demands vs. mineralization and respective low energy demands, iii. the origin of hydrogen and energy, or – in other terms – the background energy system, and iv. the storage permanence. Additionaly, the demand now and in the future for such CO2-based products as well as the availability of CO2 sources in a hypothetical decarbonized economy need to be taken into account. Benet et al.2014 analyze CU options regarding their climate impact, compared to conventional product systems. Based on this, they propose thre criteria that are crucial in determining the potential impact on limiting or reducing greenhouse gas emisions. These criteria extend the previously mentioned aspects and comprise The extent of CO2 emision reduction in comparison to conventional options in order to fully assess the reduction potential, all emisions in the upstream, utilization and downstream system ned to be considered and compared to an alternative scenario. Regarding the alternative scenario, particular atention should be driven to the fact that in a “Post-Paris-2015-World” a fosil reference scenario does not correspond to the current and future state anymore. Consequently, the comparison should be driven towards a scenario that – for example - includes curent mitigation measures as wel. Cover of costs by potential revenue Idealy, the CCU product has a specific market price that entirely covers all costs during the production line. In order to lower costs, as well as energy requirements, especially utilization routes that do not require CO2 purification should need to be considered. Scalability of the utilization path The CU product can only have significant positive climate impacts, when the production is scalable and thus the demand for CO2 is high enough to be meaningful to mitigation overal. This aspect includes the demand from consumer side, as well as the suply of CO2 for the production phase. Finaly, with regard to i, Schwan et al. 2018 conclude that CU can only be considered as an option, when a lot of renewable energy is available and when les energy is consumed than available. These circumstances