3.2.1 What are Pellet and Pelletizing?

Pelletizing is to compress the materials into the shape of a pellet. A large range of different raw materials such as solid fuels, medicine, feed, ore, and more are pelletized. On the solid fuel, we call them the wood pellet, ogalite(wood briquette), coal briquette or composite fuel. The wood pellet shown in Fig. 3.2.1(a) is made of wood waste such as sawdust and grinding dust. A diameter of a pellet is 6-12 mm, a length is 10-25mm. Figure (b) and (c) show a large size pellet (wood briquette and rice husk briquette). A diameter of briquette s 50-80 mm, and a length is 300 mm. Figure (d) shows CCB that is a kind of the Composite fuel of Coal and Biomass. We call it Biobriquette.

(a)Wood pellet (b) Ogalite (c) Rice husk briquette (d) CCB

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Fig. 3.2.1. Various types of briquette.

(a) Wood pellet

Apart from a rice husk briquette, wood pellet and wood briquette are produced in the following manufacturing processes.

(1) drying process

Generally the original moisture content of wood is about 50%. It is necessary to dry the raw materials to moisture content 10-20% in order to obtain the optimum pulverizing and pelletizing conditions. Big particle size of raw material should be dried with the rotary kiln, and small particle size of raw material should be dried with the flash dryer.

(2) pulverizing process

The raw materials should be pulverized in accordance with size of the pellet. In case of whole wood or large size wastes, the raw materials should be crushed before drying process in order to prepare the moisture content uniformly. This process is needless in case of the raw material is rice husk.

(3) pelletizing process

Pelletizer consists of feeder, roller, dies as shown in Fig. 3.2.2-3.2.3. Fig. 3.2.2 shows the schematic drawing of pelletizer for wood pellet. This type of pelletizer is the most popular in the world. Fig. 3.2.3 shows the schematic drawing of briquetting machine for wood briquette and rice husk briquette.

(4) cooling process

Because the pellet of manufacture right after is high temperature and contains much moisture, it needs to cool off.

(5) screening process

Low quality pellets are removed in this process. They are utilized as energy for drying.

(b) CCB (Composite fuel of Coal and Biomass;Biobriquette)

In the second oil crisis, CCB was developed as kerosene substitute fuel in Japan. CCB is a kind of composite fuel of coal (<2 mm) and biomass (<2 mm) that is produced by the high pressure briquetting machine as shown in Fig.

3.2.4. The fundamental raw materials mixing ratio of CCB is coal 70-90%, biomass 10-30% by the weight. When coal includes sulfur content, slaked lime or lime stone of equivalence ratio 1-2 is added as a desulfurizer. Coal can be utilized from a lignite to smokeless coal, and wood waste, agricultural waste and something like that can be utilized as biomass. Because biomass is mixed with coal and the combustion efficiency of fuel is high, ignitability and flammability is good, there is a little emission of smoke, the effect of energy saving is high. In particular the reduction of the carbon dioxide is easy so that CCB includes 10-30% of biomass. The sulfurous acid gas of 50-80% can be reduced by adding a desulfurizer with fuel The technology of CCB is one of the clean coal technology and transferred to many countries as alternative fuels production technology of firewood, kerosene and charcoal In particular, the technical support requests for energy saving, reduction of carbon dioxide and prevention of acid are increasing rain from China.