Article
THERMOCHEMICAL VALORIZATION AND ENGINEERED DENSIFICATION OF RICE HUSK BIOMASS
Rice husk (RH) is an abundant agricultural residue generated during milling, representing an important prospective alternative to wood fuels in developing nations where traditional biomass drives extensive deforestation and greenhouse gas emissions. However, raw rice husk possesses low bulk density (86–150 kg/m³), high volatile content, and an abrasive, refractory inorganic ash fraction (6.5%–22.4 wt.%) dominated by silicon dioxide (SiO₂ > 90%), which resists particle deformation and causes severe die cracking during binder less compression. This review synthesizes processing advancements across thermal pretreatments, binder formulation chemistry, densification mechanics, and combustion dynamics. Slow pyrolysis between 400–500°C successfully concentrates fixed carbon (35%–49%), producing biochar with higher heating values reaching 18–22 MJ/kg. Under low-pressure densification (≤15 MPa), binder chemistry governs briquette performance. While inorganic clay binders increase bulk density and burn duration, they introduce incombustible ash, lowering calorific value down to 9.5 MJ/kg. Edible starch adhesives deliver high drop durability (>94%) and clean combustion, yet raise serious food security concerns in developing countries. Consequently, non-edible municipal peelings (cassava, matooke, sweet potato), rice dust, and natural tree resins have emerged as high-performance substitutes, achieving shatter resistance exceeding 87% to 100% and flame temperatures up to 828.7°C. Furthermore, integrating central draft holes optimizes air-fuel contact, expediting ignition and minimizing particulate emissions. Overcoming machinery wear from abrasive silica and establishing standardized testing protocols remain vital for industrial scaling.
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