Optimization of biomass torrefaction densification process parameters: Impact on hydrogen-rich syngas generation in the gasification process

Abstract

The objective of this study was to optimize the biomass torrefaction densification process to improve the quality of solid fuel pellets for synthesis gas (syngas) energy production. We systematically investigated the effects of different pelletizing conditions on the bulk density and compressive strength of torrefied spent coffee grounds (SCGs), corn stalks (CSs), and agaric fungus bran (AFB) using response surface methodology (RSM) for multi-objective optimization. We focused on the impact of two critical parameters, mold temperature and pressure, on pellet quality. The gasification performance of the resulting pellets was further evaluated under optimal pelletizing conditions. The experimental results revealed significant effects of mold temperature and pressure on the bulk density and compressive strength of the pellets, with pressure being the decisive factor for pellet quality. Under the optimized pelletizing conditions, the bulk density and compressive strength of CSs were 1409.28 kg/m³ and 49.66 MPa, respectively, while those of AFB were 1342.3 kg/m³ and 43.27 MPa, both meeting industrial application requirements. The pelletizing performances of CSs and AFB were superior to that of SCGs. The results of our gasification tests indicated that the yield of major combustible gases, such as methane (CH₄), carbon monoxide (CO), and hydrogen (H₂), significantly increased at higher gasification temperatures, along with an increase in the H₂/CO ratio. Particularly, at a gasification temperature of 900 °C, the hydrogen intensity of SCGs was 1.28 × 10⁻⁷ kg/s, with a lower heating value of 17.36 MJ/Nm³. Thus, integrating biomass torrefaction densification with gasification technology may serve as a feasible approach for effectively extracting hydrogen-rich gas from biomass.