Microwave torrefaction integrated with gasification: Energy and exergy analyses based on Aspen Plus modeling

The serious environmental issues are risen by the high-moisture herb residue (HR). Thermochemical conversion of HR shows the potential for not only clean treatment, but also utilizing its energy. In this study, microwave torrefaction (MT) and conventional torrefaction (CT) were integrated with gasification respectively, for the HR treatment. The systems were simulated and comparatively investigated by Aspen Plus. The modeling of MT was achieved for the first time, and it was validated by the experimental data. The effects of torrefaction on gasification performance were evaluated by exergy and energy analyses. The results showed that the exergy of MT-HR was 17.68 MJ/kg, which was higher than the raw HR and CT-HR, indicating the significant improvement for HR by MT. Meanwhile, the exergy of gasification syngas reached the highest as 7.93 MJ/h with MT, while and the exergy of tar was the lowest as 3.13 MJ/h. It was proved by energy analysis that MT could achieve self-powered in the integrated process, although MT consumed some energy. MT-gasification showed the best performance for electricity yield, due to MT could not only improved the gasification and combustion efficiency, but also reduce the negative influence of tar. This study provides a comprehensive evaluation for the application of MT, and it demonstrates the potential of MT as a promising pretreatment for thermal conversion of biomass waste.

Automated summary

This study integrates microwave torrefaction and conventional torrefaction with gasification for the treatment of herb residue. The results show that microwave torrefaction significantly improves the gasification performance and achieves self-power in the integrated process, enhancing electricity yield.