Biochar engineering and life-cycle performance of biochar–BECCS systems for carbon dioxide removal - Thesis

[Geoengineering News]

https://open.metu.edu.tr/handle/11511/118491

Authors: Ali Bertan Kır

Middle East Technical University, 2026

Abstract 

Climate change is driven by the accumulation of greenhouse gases, so alongside rapid CO2 emission reductions, carbon dioxide removal (CDR) is increasingly needed, and biomass offers a strategic pathway by converting photosynthetically fixed carbon into useful products and energy while enabling net CO2 removal. Building on this biomass utilization perspective, this thesis bridges sustainable materials science and system-level CDR assessment by first producing and engineering advanced biomass-derived carbon materials (biochar) through one-step impregnation and pyrolysis, and then evaluating biochar as a standardized carbon product within a high-level, integrated biochar (BC) – BECCS (bioenergy with carbon capture and storage) framework (BC+CCS), leveraging the fact that both technologies rely on the same biomass feedstock supply chains. In the first part, poplar wood (PW) and hazelnut shell (HS) are used as biomass feedstocks. These feedstocks are impregnated with either KOH or NaOH, with optional melamine addition as a nitrogen source, and then pyrolyzed at 500°C and 700°C under CO2 and N2 atmospheres to produce engineered biochars. The biochars were characterized using N2 adsorption, XPS, and Raman spectroscopy to evaluate their textural, chemical, and structural properties. The results show that activation outcomes are strongly condition-dependent: under 500°C (N2), NaOH produced higher surface areas than KOH in the corresponding undoped samples, whereas at 700°C KOH produced highly microporous carbons with the highest surface areas, reaching 986 m2 g-1. Melamine exhibited an alkali-dependent influence, including a strong synergy at 500°C with KOH, while at 700°C melamine reduced surface area in KOH systems but improved performance in NaOH systems. Overall, these trends establish practical design rules for tuning porosity and functional surface groups for adsorption and electrochemical applications. In the second part, a hybrid CDR concept is proposed by integrating biochar production with BECCS. Carbon balances and permanence were evaluated using climate-effect-based metrics across 30, 100, and 1000-year timeframes under leakage scenarios, and environmental performance was quantified via LCA. Results show that BC delivers strong short-term performance but declines over longer horizons due to biochar decay, whereas BECCS remains highly permanent. BC+CCS provides intermediate long-term permanence while maintaining high near-term sequestration. Heat-output variants of BECCS and BC+CCS generally reduce non-climate impacts but achieve smaller CO2 reductions than electricity-focused cases in the EU context. Overall, this thesis highlights biomass conversion as a complete strategy for achieving CO2 removal and sustainable advanced material production.

Source: METU