(a) Wood pellet

It is thought that the factors that affect on pelletizing condition are pressure, temperature, compression time, particle size of raw materials, moisture content and chemical composition of wood. As for the boundary condition on pelletizing, it is not clear yet. It is actual that pellet is produced on the basis of experience of operator. It is different with a kind of wood material, but the experience value of pelletizing pressure and temperature is 70MPa and 100-150 degrees. However, there is no doubt that lignin, glucide and pectin play as a binding agent.

(b) CCB

We use a high pressure roll type briquetting machine for production of CCB. Tablet tests are carried out to obtain the optimum blending ratio of the raw materials and indispensable as a preliminary step in briquette manufacturing. The blended material is compressed to tablet of 25 mm diameter. A steel ball with a diameter of 20 mm is placed on a tablet and the ball is forced down onto the tablet until the tablet breaks. The breaking strength is measured as the criteria of quality. Fig. 3.2.5 shows the breaking strength of the tablets prepared from coal and biomass. The breaking strength becomes increasingly higher as the content of the biomass increases. Heating the raw materials under briquetting is an effective way to increase the breaking strength. Fig. 3.2.6 shows that a higher temperature of molding increases the breaking strength of tablet. This is attributable to the enhancement of the plastic deformation of the biomass by heat. The blending ratio of coal and biomass that achieves a breaking strength of briquette of 1 kN is 20% of biomass content and molding temperature 50 degrees. Based on these results, the standard blending ratio of coal and biomass is determined. When a CCB was produced with high pressure roll press machine, the shearing stress occurs between roll tire and raw materials, and raw materials is heated in about 70-80 degrees. Therefore heating control of raw materials is not done in briquetting process.