Milling Characteristics of Coal and Torrefied Biomass Blends in a Roller Mill.

CO2 emissions from coal power generation could be reduced by maximizing the amount of torrefied biomass that can be used in pulverized-coal-fired power plants. In this study, to evaluate the milling performance of coal and torrefied wood pellets (TPs), various blend ratios were tested using a bench-scale roller mill. Neutral sugar analysis was performed to evaluate the biomass-derived part of the milled products. Under the test conditions, mill power consumption and differential pressure increased with the TP content. As the TP content increased, the particle size of the milled products also increased. Furthermore, the biomass-derived neutral sugar content and the xylose/glucose (X/G) ratio were higher in the larger particles of the milled product and in the samples collected inside the roller mill than those in the input feedstock. The biomass-derived part with the highest X/G ratio accumulated inside the roller mill, which is probably why the mill power and differential pressure increased with the TP content. The TP, with poor grindability, was discharged from the mill with a larger particle size than that of coal. Although torrefaction treatment pyrolyzed the biomass, the degree of torrefaction can vary within the pellets depending on the torrefaction conditions. To ensure stable operation of the roller mill and an effective reduction in the size of the coal-TP blend, the selection and use of uniformly and sufficiently torrefied wood pellets are important.

Effect of Biomass Carbonization on the Grinding of Coal/Biomass Mixtures.

To increase the co-firing ratio of biomass in existing pulverized coal-fired power plants, biomass should be pulverized to obtain a particle size suitable for combustion. However, evaluation of the particle size distribution of each coal and biomass mixture via traditional fuel analysis is difficult. Because coal does not contain neutral sugars, the particle size distribution of biomass in the mixture can be estimated based on its neutral sugar content. The current study was conducted to evaluate the effect of biomass carbonization on the grinding process via neutral sugar analysis. Mixtures of coal and carbonized pine chips with three different degrees of carbonization were prepared and ground using a Hardgrove grindability index mill. In the pulverized mixtures of low carbonized biomass and coal, the biomass content at all particle size ranges was nearly the same as that of the input feedstock. As the degree of biomass carbonization increased, the biomass content in the mixture of large particle sizes was decreased, whereas it was increased in the mixture of small particle sizes. The current study indicated that particle size distribution of coal and biomass in the pulverized mixture depends on the degree of carbonization of biomass.

Evaluation of Ammonia Pretreatment for Enzymatic Hydrolysis of Sugarcane Bagasse to Recover Xylooligosaccharides.

Sugarcane bagasse is a useful biomass resource. In the present study, we examined the efficacy of ammonia pretreatment for selective release of hemicellulose from bagasse. Pretreatment of bagasse with aqueous ammonia resulted in significant loss of xylan. In contrast, pretreatment of bagasse with anhydrous ammonia resulted in almost no xylan loss. Aqueous ammonia or anhydrous ammonia-pretreated bagasse was then subjected to enzymatic digestion with a xylanase from the glycoside hydrolase (GH) family 10 or a xylanase from the GH family 11. The hydrolysis rate of xylan in bagasse pretreated with aqueous ammonia was approximately 50 %. In contrast, in the anhydrous ammonia-treated bagasse, xylan hydrolysis was > 80 %. These results suggested that anhydrous ammonia pretreatment would be an effective method for preparation of sugarcane bagasse for enzymatic hydrolysis to recover xylooligosaccharides.