A multi-parameter optimization of the bio-pellet manufacturing process: Effect of different parameters and different feedstocks on pellet characteristics

Highlights: • Microalgae, seed husks, wood chips and corn cobs can be used to make pellets. • The correlation between pellet quality and manufacturing parameters was investigated. • Microalgae is one of the most preferred feedstock for biomass pellet fuel. • A low energy consumption can be used to obtain high quality microalgae pellets. Biomass pellet fuel is one of the important forms of biomass energy utilization. How to get high quality pellet fuel in the production process is a hot topic of discussion nowadays. Since the quality of biomass pellets is sensitive to the pelletizing conditions, the aim of this research is to investigate the complex relationship between pelletizing conditions, physical quality, and pelletizing energy consumption. In this study, Microalgae, apple tree wood chips, corn cobs and sunflower seed husks were selected for pelletizing in a single pelletization system, with several controlled operating parameters. Subsequently, pellet sample density, durability, and pelletizing energy consumption were tested. A response surface methodology (RSM) multi-objective optimization method was used to develop models for predicting and describing the physical properties of the pellets and the pelletizing energy consumption, and to optimize the operating parameters. The results showed that the optimization results of the four pellet RSM methods corresponded well with the values of the high-quality pellets produced (all ≤5%). Compared to other materials, microalgae can generate high density pellets at lower pressures and thus reduce energy consumption and cost. The microalgal pellet optimal preparation parameters were also obtained via RSM (temperature 108 °C, pressure 76.2 MPa and moisture content 11%). Under the optimal parameters, the pellet durability, density, and pelletizing energy consumption were 96.5%, 1658.4 kg/m³ and 9.19 kJ/kg, respectively. It is clear that raw materials such as microalgae are potential and valuable feedstocks for the production of biomass pellets.