PWEAITCSE: An integrated thermodynamic framework for assessing long-term biochar carbon sequestration

Biochar-based carbon sequestration supports long-term atmospheric carbon stabilization and soil-quality improvement. However, conventional mass-accounting and life-cycle assessment methods provide limited consideration of thermodynamic inefficiencies, carbon permanence, and dynamic soil stability. To address these limitations, this study proposes a Permanence-Weighted Exergy Analysis-based Integrated Thermodynamic Carbon Sequestration Evaluation (PWEAITCSE) framework. Permanence-Weighted Exergy Analysis (PWEA) integrates retained chemical exergy with carbon-stability horizons, while the Irreversibility-Adjusted Carbon Retention Index (IACRI) accounts for exergy destruction during transportation, preprocessing, and pyrolysis. The Soil-System Coupled Exergo-Dynamic Stability Model (SC-EDSM) represents time-dependent carbon degradation influenced by feedstock composition, pyrolysis temperature, and microbial biomass. The integrated framework evaluates thermodynamic performance, carbon permanence, and soil-system stability. Shells and kernels exhibit the highest performance, with an estimated carbon-stability horizon of 95 years, 14,406 MJ-equivalent PWEA, an IACRI of 0.779, and a normalized Sequestration Performance Index (SPI) of 1.000. Sewage sludge demonstrates the lowest performance, with 48 years of stability and a normalized SPI of 0.000. Sensitivity analysis identifies stability horizon, permanence parameters, feedstock composition, and pyrolysis temperature as influential factors. Validation yields relative errors below 2.5% across the principal indicators.