Gasification performance of switchgrass pretreated with torrefaction and densification

• We evaluated effects of switchgrass torrefaction and densification on the syngas.
• The pretreatment and gasification temperature significantly effected performance.
• Combined torrefaction and densification had the highest gas yield and efficiencies.
• Increase in gasification temperature increased the gas yield and efficiencies.

The purpose of this study was to investigate gasification performance of four switchgrass pretreatments (torrefaction at 230 and 270 °C, densification, and combined torrefaction and densification) and three gasification temperatures (700, 800 and 900 °C). Gasification was performed in a fixed-bed externally heated reactor with air as an oxidizing agent. Switchgrass pretreatment and gasification temperature had significant effects on gasification performance such as gas yields, syngas lower heating value (LHV), and carbon conversion and cold gas efficiencies. With an increase in the gasification temperature, yields of H2 and CO, syngas LHV, and gasifier efficiencies increased whereas CH4, CO2 and N2 yields decreased. Among all switchgrass pretreatments, gasification performance of switchgrass with combined torrefaction and densification was the best followed by that of densified, raw and torrefied switchgrass. Gasification of combined torrefied and densified switchgrass resulted in the highest yields of H2 (0.03 kg/kg biomass) and CO (0.72 kg/kg biomass), highest syngas LHV (5.08 MJ m−3), CCE (92.53%), and CGE (68.40%) at the gasification temperature of 900 °C.