Evaluation of energy properties for wet torrefied woody biomass based on solid mass yield properties of primary constituent polymers

One of the effective pathways toward a sustainable society is to rapidly phase out coal. To replace coal and coal coke used in both power and industrial sectors, torrefied solid biofuels are expected to serve as an alternative fuel. This study focuses on the wet torrefaction (WT) process as a biomass reforming treatment, and investigates universal evaluation method of energy properties for wet torrefied woody biomass (WT-WB). The solid mass yield (SMY) of WT cedar and castanopsis decreases with increasing WT residence time and WT temperature, which results from the mass reduction due to WT reaction such as pyrolysis and hydrolysis. The higher heating value (HHV) property of WT cedar and castanopsis can be expressed as a single experimental correlation as a function of SMY by using the enhancement factor of HHV (EFH). From experimental results on three constituent polymers in WT cedar and castanopsis, it is found that the solid mass yields of cellulose and hemicellulose decrease and the solid mass yield of lignin remains nearly constant or increases as WT reaction proceeds. The mass gain of lignin is correlated with the total mass reduction of cellulose and hemicellulose. Assuming that the solid mass yield properties of three constituent polymers derived from the average data for both softwood cedar and hardwood castanopsis can be applied to any WT-WB, experimental correlations of solid mass yield for cellulose, hemicellulose and lignin are obtained using multiple regression analysis. The evaluation method of energy properties of WT-WB for given WT conditions is constructed by combining both experimental correlations of solid mass yields of three constituent polymers and EFH. From the comparison between experimental data and estimated SMY and HHV, it can be stated that the method constructed here is useful for evaluating energy properties of WT-WB.