Effect of wet torrefaction conditions (B/W) on the energy properties of densified solid biofuels made from cedar

Abstract

To build a sustainable society, the utilization of solid biofuels is expected to replace coal and coal coke. In this study, we focused on wet torrefaction (WT) treatment and densification forming to produce solid biofuels with fuel properties comparable to coal. WT is advantageous for reforming high moisture biomass feedstock, and Japanese cedar powder with 83% and 95% moisture content is used as the WT experimental sample. The aim of the study is to clarify the effects of WT conditions (WT temperature, holding time, water/biomass mass ratio) and densification on the char yield of four types of solid biofuels, Fuel-R (raw powder), Fuel-WT (wet torrefied powder), Fuel-RB (raw densified biocoke) and Fuel-WTB (wet torrefied densified biocoke). The obtained results are as follows. Char yield is enhanced by densification forming due to suppression of volatile matter evaporation. Char yield of WTB at B/W=1/5 is higher than that at B/W=1/20. The optimal WT conditions for producing fuel with high char yield is found to be B/W=1/5, WT temperature 240°C and WT residence time 120min. The Enhancement factor of char for RB and WTB is correlated with particle density.