Review of biochar production via crop residue pyrolysis: Development and perspectives.

• Crop residue-derived biochar production reduces global warming potential. • The feedstock composition and pyrolysis temperature strongly regulate biochar yields. • Slow pyrolysis and microwave-assisted pyrolysis suitable for biochar production. • Physical and chemical properties of biochar are critically discussed. • The concept of biochar, bio-oil, and gas nexus is important for sustainability. Worldwide surge in crop residue generation has necessitated developing strategies for their sustainable disposal. Pyrolysis has been widely adopted to convert crop residue into biochar with bio-oil and gas being two co-products. The review adopts a whole system philosophy and systematically summarises up-to-date knowledge of crop residue pyrolysis processes, influential factors, and biochar applications. Essential process design tools for biochar production e.g., cost-benefit analysis, life cycle assessment, and machine learning methods are also reviewed, which has often been overlooked in prior reviews. Important aspects include (a) correlating techno-economics of biochar production with crop residue compositions, (b) process operating conditions and management strategies, (c) biochar applications including soil amendment, fuel displacement, catalytic usage, etc., (d) data-driven modelling techniques, (e) properties of biochar, and (f) climate change mitigation. Overall, the review will support the development of application-oriented process pipelines for crop residue-based biochar. [ABSTRACT FROM AUTHOR]