Comparative techno-economic and life cycle analyses of synthetic “drop-in” fuel production from UK wet biomass

Renewable synthetic hydrocarbon “drop-in” fuels can help mitigate greenhouse gas emissions from transport, particularly in hard-to-abate sectors like freight and aviation. However, no study has extensively addressed the concerns over biomass availability, cost viability, and CO2 reduction feasibility that are associated with diverse production configurations and feedstocks. Here, we report detailed techno-economics and life cycle greenhouse gas emission assessments of drop-in fuel productions via hydrothermal liquefaction to assess their economic viabilities, CO2 mitigation potentials, and prospects for scale-up specifically within the UK context. Our approach integrates key production factors which include regional availability of main feedstocks (digestates, food waste, biodegradable municipal waste, and sewage sludge), plant configurations (centralised vs decentralised) and hydrogen sources (grey, blue, green). We demonstrated the economic trade-off between economy-of-scale and feedstock transport distances in the centralised/decentralised configurations, and also the economic and emissions trade-offs associated with the use of different hydrogen sources. We find that co-processing of different waste feedstocks is an important strategy to minimise fuel selling price by enabling better economy of scale and feedstock transport, resulting in a fuel selling price of £14.76 – 20.30 per GJ. The corresponding greenhouse gas emissions from the co-processing case vary from 11.4 to 24.9 kg CO2eq per GJ for 2021, based on the consequential life cycle assessment approach. Furthermore, we estimated that the utilisation of key UK wet feedstocks could only provide 4.5 % of current fuel consumptions and reduce emissions by 4.5 – 5.4 Mt CO2eq/year, which translates to 3.4 – 4.0 % reduction in the UK’s 2021 transport emissions

A review of techno-economic analyses and life cycle greenhouse gas emissions of biomass-to-hydrocarbon “drop-in” fuels

Synthetic “drop-in” fuels are compatible with existing fuel and vehicle infrastructures and, when produced sustainably, they could play an important role in mitigating the emissions of greenhouse gases (GHG) from transportation, especially in the hard-to-decarbonise sectors like freight and aviation. However, there is a need to understand the availability of biomass resources for drop-in fuel applications and the potential challenges associated with using these feedstocks including the supply chain issues. Hence, this paper offers a critical review of non-food biomass and drop-in fuel production including the biomass availability in the UK, the production of drop-in fuels from biomass feedstocks via thermochemical routes, estimated fuel production prices and volumes, and life cycle GHG impacts. The paper explores several fuel production factors, including energy and hydrogen requirements, as well as supply-chain considerations, which were used to estimate the drop-in fuel potential in the UK economy. We estimate the availability of non-food biomass resources in the UK to be in the range of 167–205 Mtpa (wet) [839–1033 PJ per year], as more than 50 % of these volumes are from high moisture content feedstocks such as biogenic municipal waste and sewage sludge. Other biomass feedstocks that are produced in significant quantities include straw and wood waste. Also, it is estimated that the total UK drop-in fuel manufacturing potential is in the range of 269–563 PJ per year. When used to displace fossil fuels in road transportation, this could lead to a total GHG reduction of 18.7–64.4 Mt. CO2eq per year which is 18.8–64.7 % relative to the UK's overall road transport emissions from all fuels in 2021