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A commercialization strategy for carbon-negative energy Daniel L. Sanchez & Daniel M. Kammen Climate change mitigation requires gigatonne-scale CO2 removal technologies, yet few examples exist beyond niche markets. The flexibility of thermochemical conversion of biomass and fossil energy, coupled with carbon capture and storage, offers a route to commercializing carbon-negative energy. The Intergovernmental Panel on Climate Change (IPCC) envisages the need for large-scale deployment of net-negative CO2 emissions technologies by mid-century to meet stringent climate mitigation goals and yield a net drawdown of atmospheric carbon. These CO2 removal technologies complement low- or zero-carbon energy technologies1,2. Industrial-scale sequestration of CO2from bioenergy production — a process known as bioenergy with carbon capture and sequestration (BECCS) — can produce fuels, chemicals and electricity while removing atmospheric CO2. Yet there are few commercial deployments of BECCS outside of niche markets, creating uncertainty about commercialization pathways and sustainability impacts at scale3. This uncertainty is exacerbated by the absence of a strong policy framework, such as high carbon prices and research coordination. Here, we propose a strategy for the potential commercial deployment of BECCS via thermochemical co-conversion of biomass and fossil fuels, particularly coal, challenging governments, industry incumbents and emerging players to research and support these technologies. Although biochemical conversion is a proven first market for BECCS, this trajectory alone is unlikely to drive commercialization of BECCS at the gigatonne scale. The early development of BECCS has been focused on biochemical facilities converting sugars to ethanol, a transportation fuel, for use in enhanced oil recovery and large-scale industrial sequestration demonstration4. Yet, biochemical conversion pathways are limited by the market size of fuel products, scale, sensitivity to biomass inputs, and throughput. For example, alcohol fuels from biochemical conversion processes face compatibility issues with existing transportation infrastructure, whereas high lignin content inhibits biochemical conversion. Reaching gigatonne-scale carbon sequestration via this pathway will require at least fourfold higher ethanol production than current levels. Although proposals for large-scale bioenergy deployment focus on the conversion of lignocellulosic feedstocks to liquid fuels, BECCS is also valuable to the electricity sector2,5. Flexibility as a virtue In contrast to biochemical conversion, thermochemical conversion of coal and biomass enables large-scale production of fuels and electricity with a wide range of carbon intensities, process efficiencies and process scales (Fig. 1). We focus on two representative thermochemical pathways: electricity production via integrated gasification combined cycle with CCS (IGCC-CCS), and long-chain hydrocarbon fuels production via gasification and the Fischer–Tropsch process with CCS (FT-CCS). Fischer–Tropsch and combined-cycle systems can be combined for polygeneration-CCS systems that produce both electricity and fuels. The energy and capital penalties of adding CCS are comparatively small for these processes, and, for FT, can reduce downstream equipment size requirements, further reducing capital costs6. Addition of biomass into coal gasification increases the ratio of H2 to CO in syngas, which is beneficial for fuels production. (inset starts) Figure 1: Flow diagrams for carbon capture and storage processes. a,b, Simplified flow diagram for IGCC-CCS (a) and polygeneration-CCS (b) processes for production of electricity and fuels from coal and biomass. Green boxes and dashed green lines indicate options to decrease the carbon intensity of resulting fuel or electricity products. Dashed lines indicate optional process enhancements. Options to decrease the carbon intensity of products in IGCC-CCS systems include (1) increasing the ratio of biomass to coal inputs, (2) increasing the shift of syngas in the water–gas shift reactor, and (3) recycling CO2 from the sulfur removal process to the acid gas removal system. For polygeneration-CCS, options include (i) increasing the ratio of biomass to coal inputs, (ii) recycling CO2 from the sulfur removal process to the acid gas removal system, and (iii) autothermal reforming and shift prior to electricity production. Panel ais based on data from ref. 11 and panel b is based on data from ref. 6. (inset ends) Other promising thermochemical pathways may complement IGCC-CCS and FT-CCS. For example, torrefaction — a mild thermal pre-treatment — improves biomass suitability for gasification7. Integration of reformed natural gas with syngas from coal and biomass presents further opportunities for electricity or fuels production, though this has been studied less extensively8. Likewise, synthetic gasoline production via the methanol-to-gasoline process is a less widely implemented alternative to FT synthesis9. Alternatively, all of the carbon in the biomass feedstock could be converted to liquid fuels using external hydrogen and low-carbon electricity inputs from nuclear, renewable energy or hydropower10. Thermochemical co-conversion creates flexibility for producers to balance product cost and carbon reduction goals. Incremental carbon reduction from these systems is cheaper when leveraging both CCS and biomass in concert6,11. IGCC-CCS producers can adjust biomass, water–gas shift, and CCS integration to produce low-carbon or carbon-negative electricity, with lower-carbon-intensity systems having smaller scale and higher costs in the absence of supportive climate policy. Similarly, polygeneration producers can adjust biomass, CCS, or autothermal reformer integration (Fig. 1). Polygeneration systems with flexible ratios of fuel inputs or product outputs can increase profitability for producers, though at additional cost8. In addition to technical advantages, the flexibility of co-conversion is also advantageous for existing industries, supply chains and workforces. Here, firms can embrace a gradual transition pathway to deep decarbonization, limiting economic dislocation and increasing transfer of knowledge between the fossil and renewable sectors. The scale of both biomass and co-utilization systems holds unique advantages. In the United States, dedicated biomass plants average half the efficiency of coal plants12. Co-utilization systems can leverage economies of scale associated with coal inputs to increase efficiency and decrease unit costs, while lessening feedstock variability issues associated with biomass-only systems. Co-utilization also requires less biomass per unit product than biomass-only systems, which further extends the impact of scarce sustainable biomass resources. Minimum capital expenditures for co-conversion systems are smaller than those for envisaged coal-to-liquid facilities, easing project finance6. In practice, many deployed biomass systems are several times smaller than coal-only systems, enabling greater experimentation at lower cost13. This strategy is likely to work best in developed economies, such as the US. The US has relatively advanced bioenergy, hydrocarbon production and CCS sectors. Its advanced engineering, construction and financial industries are capable of commercializing new, risky, capital-intensive technologies. Other regions, such as Scandinavia and British Columbia, have considerable expertise in thermochemical conversion of biomass. Following technology development, other developing countries, particularly rapidly expanding economies dependent on coal, could deploy BECCS and avoid lock-in with conventional fossil fuel infrastructure. International development finance could help promote BECCS in these locations. In contrast, certain regions with large biomass resources and advanced alcohol fuel industries, such as Brazil, may rely on biochemical conversion for BECCS in the future. Other developing countries could embrace biochar production for CO2 removal1. Spatial optimization can account for biomass supply limitations, transportation logistics, and geological CO2 storage capacity, and help balance economies- and diseconomies-of-scale inherent in bioenergy production, including gasification2,8. (continues online) -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. 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