Enhancing the strength of formed coke from rice husk via sequential hydrothermal treatment, hot briquetting, and carbonization

The growing severity of energy shortages and environmental challenges underscores the necessity of developing sustainable biomass energy. Rice husk (RH) biomass is abundantly available but often incinerated or discarded, causing environmental issues and resource underutilization. Converting RH into solid fuels in the form of formed coke offers a promising pathway for valorization. However, the inherently weak mechanical strength of formed coke hinders its transportation and applications. This study proposes a comprehensive strategy to produce high-strength formed coke, involving hydrothermal treatment (HT) of RH followed by sequential hot briquetting and carbonization. The effects of HT temperature (160–300 °C) on the structure, yield, and strength of the formed coke were systematically investigated. As a green pretreatment method, HT effectively disrupts RH structure, improves its heating value, and enhances the compactness and strength of the final product. The hydrothermally treated RH at 250 °C exhibited a 27% increase in heating value compared to raw RH, and achieved a high coke yield of 69% from the briquette. At the HT temperature of 230 °C, the formed coke achieved a maximum tensile strength of 32 MPa and a density of 1.4 g/cm 3 , which are 2.8 and 1.2 times higher than those of coke produced from non-treated RH, respectively. In addition, the strength mechanisms of the formed coke and briquette are discussed based on the characterization results of the products under various treatment conditions. This study provides valuable insights for the valorization of agricultural and forestry waste as high-quality fuels.