Moisture content of raw materials plays a vital role in wood pellet production. It has the most considerable effect on both the output of wood pellet machine and wood pellet shaping. Therefore, controlling the moisture content of raw materials within a specified range can ensue the continuous operation of wood pellet mill.
Wood pellet mill
can be classified into two classes: extruding type wood pellet mill and rolling type wood pellet mill. For the extruding type wood pellet mill, the moisture content of raw materials should keep in the range of 15%-25%, and the moisture content of wood pellets is about 15%-23%. After the airing or cooling, the moisture content of wood pellet surface drops to 14%-18%. Therefore, it is required that the moisture content of raw materials must be controlled within a suitable range.
Generally, we can judge the moisture content of raw materials through the hand feeling or the conditions happened in pelletizing process. If the raw materials feel wet, rough, cool, and they can be squeezed into balls, loosing naturally when you open the hands, the moisture content is in a appropriate range.
Additionally, we can get the result through the extrusion conditions of wood pellet mill. The high output, low temperature, unshaped pellets, high content of powders or fines and white smoke in pelletizing show that the moisture content of raw materials is high. And the low moisture content may lead to high temperature, low output, difficult discharge and poor quality of wood pellets. Besides, the abnormal noises and blockage may happen in the wood pellet mill.
For the rolling type wood pellet mill, besides the water of raw material itself, we can add water in the production process. The requirements of moisture content of raw material itself is not so strict. With different raw materials, the requirements of their moisture content are also different. Therefore, the amount of water we need to add depends on the requirements of raw materials.