Influence of wood and sawdust moisture content to the pellet

Influence of wood and sawdust moisture content to the pellet mill. Moisture content of wood or sawdust is an important factor which needs to be controlled seriously during the pellet making process. Degrees of the moisture content affect the density of the pellets.

 

1. Biomass pellet fuels which produce from low moisture content materials are easy to absorb water content in the damp air condition. So the pellet are easy to crack without pellet making and has small density; in addition, dry materials entered into the chamber, it rotate with the compression roller and ring die, the dust in the materials also enter into the chamber, so the quality of working condition is bad and it affect the workers healthy. In addition, when the material is dry with low density, the compress roller can not extrude them into the die holes, which affect the process of making pellet

 

2. If the moisture content of material is high, that increase thermal coefficient, decreasing the intermolecular force, increasing the gap, reducing the adhesive ability and lowering the density. Also, high pressure steam inside the pellet fuel causes the biomass pellet fuel extruded from the compress sleeve are easy to expand and crack, which affect the successive package, transport and affect the features of the biomass pellet fuel. The pellets are even easy to break immediately without pellet making. The higher the moisture content, the bigger the distance of molecules in the steam, which affects the heat conduction and reduce the temperature of pellet making. The lignin contents are difficult to melt and the crude fiber in the material is not softened easily, which results in decreased adhesive force. So when the moisture content is high, the temperature of heat should be improved during the pellet making. During the biomass compression process, the fuel suffers from radial force from the taped sleeves and conservation cylinder, which produce the friction forth and consume energy. High moisture content increase the radical forces of molding cylinder and increases the power consumptionResearchers found that part of the energy of preheat material consume on the redundant moisture content when material moisture content is high. At the same time, the evaporate steam is gasifying quickly and steam can not be discharged from the sleeve, which result in volume expansion and increase of occupy space and blockage. There is large vertical stream pressure in the sleeve. Sometimes it causes the cracking of the pellet fuel with rough surface. Sometimes feedstock eject from the sleeve quickly, which result in blasting. It not only damages the environment but also affect the personal safety. Low moisture content of straw is not easy to make pellet, because it lack of an essential free radicals in the biomass, which flow between the biomass pellets. It act as a binder which mixed with sugar or pectin gel under pressure. The trace water content vaporized at high temperature, which is conductive to rapid heat conduction and uniform distribution. Thereby the softening point of lignin is reducing. 

 

In summary, moisture content of wood or sawdust plays a key role for the normal operation of pellet machine, and we must pay attention to the moisture content of raw materials 

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