Biocoke (BIC), made from all types of biomass is a solid fuel. Hemicellulose and lignin, essential chemical components of biomass, work as bonding agents of BIC solidification because they have softening and fluidity characteristics. Their characteristics make bonding structure inside of BIC during the formation process. Previous studies suggested that physical and mechanical characteristics of BIC are different if raw materials (kinds of biomass) are different even if forming conditions are the same. It was inferred that the reason was different of content rate of main components. Among various biomass, green tea has excellent formability. In this paper, we focus on the potential of green tea as a raw material of BIC. Firstly, we compared the fluidity of green tea with other biomass. Then, compressive strength tests of BIC made from green tea and other biomass were conducted. We used the trunk of conifers, the bark of conifers, bagasse, and rice straw other than green tea. The result of fluidity test indicated that green tea is easiest-to-flow biomass among the five biomasses. Moreover, the flow starting temperature was able to estimate from a content percentage and moisture content with ±30% accuracy by using our estimated equation. As results of compressive strength test, each BIC which was made from five biomasses have two peak points of compressive strength and apparent density. Green tea BIC made under all the test conditions has high apparent density 1.3-1.4 g/cm 3. On the other hand, green tea BIC has the lowest compressive strength among the five biomasses tested. We found out that the raw material which it is easy to fluidize by heating has low compressive strength from these results.
Various sizes of high-density biomass briquette, named 'Bio-coke,' were produced from spent green tea grounds. The mechanical properties at room temperature of the Bio-coke samples were investigated using a compression testing machine. From the results, the relationship between the specimen size of Bio-coke and the ultimate compressive strength at room temperature showed that the ultimate compressive strength depends on the specimen size of Bio-coke. The maximum value of the ultimate compressive strength among the different specimen sizes of Bio-coke was at 67 MPa, obtained from the 12-mm diameter sample. In addition, at 12 mm diameter or smaller, there is hardly any difference in the ultimate compressive strengths measured. Hence, the cold compressive strength properties are divided into two groups based on the uniformity of the structure of the main components along the horizontal cross section of a Bio-coke. Results indicate that the state of the structure, composed of cellulose, hemi-cellulose, and lignin, appears to be consistent resulting from uniform permeation conditions at the 12-mm diameter or smaller samples. Meanwhile, at diameters of 20 mm or larger, the condition of the periphery of the samples were not consistent with that of the middle region because of the temperature, stress gradient and number of void occurring inside the Bio-coke caused by specimen size effect.
Noticing the color variation of torrefied woody biomass with pyrolysis process, a non-invasive method to estimate energy properties such as elemental contents, higher heating value and energy yield is investigated. When the torrefied biofuel is produced and utilized, the quality control concerning energy properties is indispensable. The energy properties of torrefied woody biomass are correlated with its mass yield, and the relationship between mass yields and colorimetric values defined by CIELAB is experimentally examined. The results obtained for torrefied Japanese cedar are as follows. (1) The energy properties of torrefied Japanese cedar are expressed by simple relations of mass yield. The optimum torrefaction condition to produce torrefied biofuel can be evaluated by the mass yield. (2) To estimate the mass yield of torrefied Japanese cedar, the experimental correlations with colorimetric values are proposed. In the case of the sap-wood and heart-wood samples for brightness, L* above 45, the mass yield is correlated with L*, and in the case of the sap-wood, heart-wood and bark samples for L* below 45, the mass yield is correlated with color coordinate, a*. From the comparison between predicted mass yields and experimental data, it is found that the proposed experimental correlations can estimate the mass yield within an accuracy of ±10%. Therefore, the energy properties of torrefied Japanese cedar is easy to be checked by using the present non-invasive estimation method with colorimetric values.
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