Improvement of fuel ratio and mechanical strength of densified solid biofuels with two-step torrefaction densification molding method

In this study, to produce a densified biofuel with a high fuel ratio and high strength, two molding methods are investigated, one is the direct-densification molding method where raw biomass is directly molded, and the other is the two-step torrefaction densification molding method where raw biomass is torrefied and then molded at temperatures close to torrefaction. The fuel ratio and hot compressive strength are important properties as an alternative fuel to coke used in industrial furnaces. From the experimental results by the direct-densification molding method, it was found that the increase in pressure during molding did not have a significant effect on improving the fuel ratio, and there was a limit to the rate of substitution. On the other hand, it was confirmed that the two-step torrefaction densification molding method provided a greater improvement in both fuel ratio and hot compressive strength compared to the direct-densification molding method. This is because the lignin binder effect becomes higher because the torrefied biomass sample is molded at a torrefaction temperature. From the above, it is expected that the densified biofuel produced using the proposed two-step torrefaction densification molding method can make a significant contribution to the coke replacement rate in industrial furnaces.

Graphical abstract