Continuous pyrolysis of rice husk for sustainable biochar production and carbon sequestration: Recent advances and techno-economic perspectives

• Comprehensive review of RH-specific continuous pyrolysis technologies and performance • Achieves up to 45% biochar yield and >70% thermal efficiency under optimal conditions • Analyzes AI-driven control and modular reactor designs for decentralized deployment • Reports 1.8–2.2 kg CO₂-eq/kg biochar sequestration with ROI under 3.5 years • Proposes hybrid heating and MRV-linked carbon credits for scalable climate solutions This review consolidates recent advances in continuous pyrolysis of rice husk (RH), emphasizing reactor engineering, digital process regulation, and carbon finance opportunities within a circular bioeconomy framework. RH, produced in quantities exceeding 150 million tons annually, is characterized by high silica (15–20%), moderate lignin (∼25%), and appreciable fixed carbon, creating both design challenges and opportunities for biochar production. Unlike general biomass studies, this work focuses exclusively on continuous reactor systems, screw, rotary kiln, auger, and fluidized bed, evaluated under optimized conditions (∼500–550°C, 20 min residence time, and 50°C/min heating rate). These systems typically yield 35–43% biochar with surface areas above 300 m²/g and carbon concentrations exceeding 75%. Life cycle assessments indicate net sequestration of 1.8–2.2 kg CO₂-eq per kilogram of biochar, while techno-economic analyses estimate production costs at $120–$180 per ton with return-on-investment periods of 2.5–3.5 years. Future developments are likely to focus on hybrid heating strategies (such as microwave or solar-assisted), neural network–based predictive control for real-time optimization, and blockchain-enabled monitoring, reporting, and verification (MRV) platforms to support carbon credit trading. By linking RH pyrolysis performance with policy frameworks, market mechanisms, and advanced process regulation, this review provides actionable insights for researchers, technology developers, and policymakers pursuing scalable, climate-aligned solutions.