Energy and GHG emissions assessment for biochar-enhanced advanced biofuels value chains

[Geoengineering News]

https://www.sciencedirect.com/science/article/pii/S0196890424003911

Authors 

M. Buffi, O. Hurtig, M. Prussi, N. Scarlat, D. Chiaramonti

https://doi.org/10.1016/j.enconman.2024.118450

20 April 2024

Highlights

•Innovative integration of slow and fast pyrolysis within drop-in biofuel production.

•Biochar co-production leads to carbon sequestration and high GHG emission savings.

•Tuning biomass flows, significant reductions of fossil-based inputs are achieved.

•Improved scenarios at higher RES share to further reduce GHG emissions are proposed.

•The proposed methodology establishes a foundation for innovative BECCS solutions.

Abstract

Biochar has an enormous potential to store carbon in the long-term. Differently than BioEnergy Carbon Capture and Storage (BECCS) technologies, biochar incorporates biogenic carbon in a solid form that offers multiple benefits as carbon sink, soil improver or for advanced materials production. The present study proposes an innovative approach, where carbon sequestration through biochar is obtained through the integration of slow pyrolysis with fast pyrolysis in decentralised biorefining systems, and then converted producing drop-in fuels from pyrolysis oil hydrotreating or gasification and Fischer-Tropsch (FT) synthesis. The scope is either to achieve negative GHG emissions assigned to advanced biofuels, or to export the generated carbon credit for the carbon markets (i.e. outside the biofuels carbon intensity). The innovative concept entails process integration and optimisation for the different stages of biomass drying, conversion and upgrading into biofuels in a way to reduce fossil-based inputs, applying a full value chain approach. Methodological choices for the assumptions on life cycle emissions calculation are discussed, evaluating the environmental performances by comparing the new concept to traditional biofuels value chains. Using a tailored lifecycle accounting methodology, this paper demonstrates that high GHG emissions savings can be achieved. The improved scenario shows how the carbon sequestration with biochar further reduces the carbon intensity up to –4.2 gCO2e MJ−1 for pyrolysis oil-based fuels, and to −20.2 gCO2e MJ−1 for FT-based fuels: this demonstrated that carbon negative sustainable biofuels can be obtained. The study demonstrates that an integrated biorefinery of 100 MW capacity can deliver additional 13.3 and 6.8 ktons of CO2e of GHG savings of per year, from drop-in fuels made of hydrotreated pyrolysis oil and FT synthesis, respectively.

Source: ScienceDirect 

[Michael Hayes]

The CDR methods that can generate fuels have a market advantage over those that do not. The operational advantages of such dual functioning CDR/emissions reduction methods can lead to multiple CDR methods being mutually supportive at the technical and economic levels. However, the sustainability of the upstream biomass is still the ultimate limiting factor for biomass-based CDR methods.

To achieve a CDR scale of >10 GtC/y, a biomass-based CDR effort would be large enough to justify development cost of a new-ish form of agriculture specifically for such CDR methods. Avoiding typical land ag related CDR complications such as food crop displacements, forest conversions to crop land, downstream chemical pollution, CO² emissions etc. can likely be achieved with today's marine technology. 

Biochar, and the synthetic gas pyrolysis stoves generate, can be the pivotal tech for a largely self-replicating agricultural mCDR method. In thebpast, I've used the term 'Blue Biochar' for such operations.

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