datasheet1_Carbon Allocation in Multi-Product Steel Mills That Co‐process Biogenic and Fossil Feedstocks and Adopt Carbon Capture Utilization and Storage Technologies.docx

This work investigates the effects of carbon allocation on the emission intensities of low-carbon products cogenerated in facilities that co‐process biogenic and fossil feedstocks and apply the carbon capture utilization and storage technology. Thus, these plants simultaneously sequester CO2 and synthesize fuels or chemicals. We consider an integrated steel mill that injects biomass into the blast furnace, captures CO2 for storage, and ferments CO into ethanol from the blast furnace gas. We examine two schemes to allocate the CO2 emissions avoided [due to the renewable feedstock share (biomass) and CO2 capture and storage (CCS)] to the products of steel, ethanol, and electricity (generated through the combustion of steel mill waste gases): 1) allocation by (carbon) mass, which represents actual carbon flows, and 2) a free-choice attribution that maximizes the renewable content allocated to electricity and ethanol. With respect to the chosen assumptions on process performance and heat integration, we find that allocation by mass favors steel and is unlikely to yield an ethanol product that fulfills the Renewable Energy Directive (RED) biofuel criterion (65% emission reduction relative to a fossil comparator), even when using renewable electricity and applying CCS to the blast furnace gas prior to CO conversion into ethanol and electricity. In contrast, attribution fulfills the criterion and yields bioethanol for electricity grid intensities <180 gCO2/kWhel without CCS and yields bioethanol for grid intensities up to 800 gCO2/kWhel with CCS. The overall emissions savings are up to 27 and 47% in the near-term and long-term future, respectively. The choice of the allocation scheme greatly affects the emissions intensities of cogenerated products. Thus, the set of valid allocation schemes determines the extent of flexibility that manufacturers have in producing low-carbon products, which is relevant for industries whose product target sectors that value emissions differently. We recommend that policymakers consider the emerging relevance of co‐processing in nonrefining facilities. Provided there is no double-accounting of emissions, policies should contain a reasonable degree of freedom in the allocation of emissions savings to low-carbon products, so as to promote the sale of these savings, thereby making investments in mitigation technologies more attractive to stakeholders.

本研究探究了碳分配对协同处理生物质与化石原料、并应用碳捕集利用与封存（Carbon Capture Utilization and Storage, CCS）技术的联产设施所产出低碳产品排放强度的影响。此类工厂可同时实现二氧化碳封存与燃料或化学品的合成。
我们以向高炉注入生物质、捕集二氧化碳用于封存，且可将高炉煤气中的一氧化碳发酵制备乙醇的一体化钢厂为研究对象。针对钢铁、乙醇以及通过钢厂废气燃烧发电这三类联产产品，我们考量了两种将因可再生原料占比（生物质）与碳捕集利用与封存（CCS）所避免的二氧化碳排放进行分配的方案：其一为按（碳）质量分配，该方案可反映实际碳流；其二为自由选择归因法，该方法可最大化分配至电力与乙醇的可再生占比。
基于选定的工艺性能与热集成假设，我们发现按质量分配的方案更有利于钢铁产品，且即便使用可再生电力，并在将高炉煤气中的一氧化碳转化为乙醇与电力前应用CCS技术，也难以产出满足《可再生能源指令》（Renewable Energy Directive, RED）生物燃料标准（相较于化石基准品减排65%）的乙醇产品。
与之相反，自由选择归因法可满足该标准：在未应用CCS的情况下，当电网排放强度低于180 gCO₂/kWhel时即可产出符合要求的生物乙醇；而应用CCS时，电网排放强度最高可达800 gCO₂/kWhel时仍可产出合格生物乙醇。
短期与长期未来场景下，总减排量分别可达27%与47%。碳分配方案的选择对联产产品的排放强度影响显著。因此，有效碳分配方案的集合决定了制造商生产低碳产品的灵活度，这对于产品目标行业对排放价值判定存在差异的产业而言尤为关键。
我们建议政策制定者关注非炼油设施中协同处理工艺的新兴相关性。若不存在碳排放重复核算问题，政策应在向低碳产品分配减排量时保留合理的自由度，以推动此类减排量的交易，进而提升减排技术投资对利益相关方的吸引力。