Effect of wet torrefaction temperature on char yield of high-density 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. The apparent density of WTB is larger than that of RB under the same forming temperature. 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. From the investigation on the effect of WT on the char absolute mass, it is found that both volatile matter releasing, and char leaching occurs in the case of WT at B/W=1/20. The optimal WT conditions for producing fuel with high char yield are found to be B/W=1/5 and WT temperature 240°C.