Techno-Economic Analysis of Biomass Gasification for Decentralized Sustainable Aviation Fuel (SAF) Production

Introduction

The decarbonization of the aviation sector requires the deployment of renewable energy pathways capable of minimizing greenhouse-gas emissions while maintaining fuel quality and energy density. Sustainable Aviation Fuel (SAF) derived from biomass gasification and Fischer–Tropsch (FT) synthesis represents a viable route to achieve net-zero aviation. In Spain, the large availability of agricultural and forestry residues allows for decentralized production schemes located close to biomass sources.

Santamarta et al. (2025, Resources) proposed a conceptual decentralized SAF model based on residual biomass gasification but did not include detailed process validation. This study extends that framework by developing a rigorous Aspen Plus® simulation of the gasification stage and performing a techno-economic analysis to quantify the performance, syngas composition, and investment cost of a 5 MWth modular plant integrated into the decentralized SAF system.

Methods

The modeled process represents a downdraft gasifier using mixed vine-pruning and forestry residues with steam and oxygen as gasifying agents.
The process flow consists of five main Aspen Plus® blocks:

• RYIELD—biomass decomposition into elemental constituents (C, H, O, N, S, H₂O, ash)
• RGIBBS—global equilibrium for oxidation and reduction reactions
• RCSTR—reforming and Water–Gas Shift (WGS) reactor for H₂/CO adjustment
• COOLER—controlled heat recovery and gas cooling to 350 °C
• SEP—removal of solids and condensates.

To avoid full thermodynamic equilibration of the WGS reaction, the RCSTR was operated with a limited conversion, representing its kinetic limitation in real downdraft gasifiers and yielding a more realistic H₂/CO ratio close to 2.

Thermodynamic properties were calculated using the Redlich–Kwong–Soave (RKS) equation of state. Complete equilibrium was assumed in the main gasification zone, with total heat losses below 5%. Sensitivity analyses of temperature (850–1000 °C), equivalence ratio (ER = 0.25–0.35), and steam-to-biomass ratio (S/B = 1.0–2.5) were performed to optimize gas yield and composition. The target H₂/CO ratio (1.8–2.2) was selected for compatibility with FT synthesis.

Results

The optimum operating point was found at 950 °C, ER = 0.30, and S/B = 2.0, producing a clean syngas with 24.6 % H₂, 35.4 % CO, 33.7 % CO₂, and 4.9 % CH₄, resulting in an H₂/CO ratio of 1.98, cold-gas efficiency (CGE) of 49.3 %, and carbon conversion of 85 %.
The lower heating value (LHV) reached 11 MJ·Nm⁻³, consistent with high-performance O₂ + H₂O gasification systems. Limiting the WGS extent reduced CO₂ formation (≈ 29 %) and improved agreement with pilot-scale data.

The techno-economic analysis, based on cost correlations integrated in Aspen Plus®, yielded a total CAPEX of 12 million euros for the 5 MWth modular unit. The gasifier accounted for 3.5 M EUR (≈ 29 %) of the investment, followed by gas cleaning (21 %) and auxiliary systems (18 %). These results validate the assumptions used by Santamarta et al. (2025) and demonstrate the technical and economic feasibility of modular SAF production plants in Spain.

Conclusions

The Aspen Plus® model provides both technical and economic validation of the decentralized SAF concept. The combination of steam–oxygen gasification and partial WGS conversion delivers a syngas suitable for direct Fischer–Tropsch synthesis (H₂/CO ≈ 2, LHV ≈ 11 MJ·Nm⁻³) with realistic process behavior.

The derived CAPEX of 12 M EUR per 5 MWth unit supports the economic viability of a distributed network of small gasifiers capable of valorizing local biomass while minimizing transport and emissions. This integrated simulation–economic framework bridges the gap between conceptual design and industrial deployment, strengthening the basis for SAF production within the European renewable-energy transition.