Utilization of rice husk and de-oiled cashew nut shell cake agro-wastes to produce ISO standard pellets and its synergistic behavior

Abstract

The biomass pellet market is experiencing rapid growth, playing a critical role in addressing the escalating energy demand and environmental challenges. In India, pellets are predominantly produced from agricultural residues like rice husk, sawdust, straw, corn stalk, sugarcane bagasse, and groundnut shells. Among these, rice husk (RH) pellets are limited by their high ash content, low calorific value, and high moisture requirements during the pelletization process. These limitations can be effectively mitigated through rice husk co-pelletization with deoiled cashew nut shell cake (CC) that remains unexplored in the literature. This study aims to develop rice husk–cashew nut shell (RH-CC) blend pellets by identifying the optimal blend ratio and pelletizing parameters based on their physical and mechanical properties. RH-CC pellets showed that increasing CC addition to RH improved the bulk density, durability and calorific value. The optimization was performed using the desirability functional approach, based on ISO standards. The optimized conditions for 6, 8 and 10 mm pellets were identified as 84, 88, and 81 °C respectively, at a pressure of 180 MPa and 57 % CC blend for which the results are bulk densities of 684, 693, and 652 kg/m3 respectively, pellet durability of 97.1 %, moisture content ranging from 5.4 to 6.3 wt%, and calorific value of 16.7 MJ/kg belonging to I2 category. Additionally, TGA studies were performed to investigate the synergy of the pellets. Utilizing untreated rice husk in RH-CC pellets provides a sustainable alternative to fossil fuels, helping to reduce stubble burning and offering farmers additional income while supporting a cleaner energy future. © 2025 Elsevier Ltd