Biomass molding is conditional, and it has certain requirements for the type, pellet size, and moisture content of the raw materials. Plant cells contain cellulose, hemicellulose, and lignin (lignin). Lignin is a structural monomer with aromatic properties and is a propane-type, three-dimensional structural polymer compound. The content of lignin in hardwood and softwood is 27% to 32% (dry basis), and the content of lignin in yarrow is 14% to 25%. Although lignin is contained in various plants, their composition and structure are not exactly the same. Lignin
It is amorphous, has no melting point, but has a softening point. When the temperature is 70 to 110°C, the adhesive strength begins to increase, and lignin softens and liquefies at an appropriate temperature (100 to 200°C). At this time, a certain pressure is applied to make it. It adheres closely to cellulose and adheres to adjacent particles, and can be solidified after cooling. Therefore, straw (or sawdust) fuel can be formed by hot pressing without any additives and adhesives, which greatly reduces the processing cost. Using the characteristics of lignin softening and liquefaction, properly increasing the temperature at the time of hot press molding is beneficial to reducing the extrusion power.
Obviously, too low a temperature is not sufficient to plasticize the lignin in the raw material, the raw material is decomposed severely at an excessively high temperature, the transportation is too fast, an effective pressure cannot be formed, and molding cannot be performed. In short, the molding temperature required for different materials is not much different, generally controlled between 100°C-200°C. However, due to the increase in yield, a large number of frictions often generate a large amount of high temperatures, which can cause serious damage to the equipment. Therefore, it is necessary to control and maintain the granulation temperature. The moisture content of the raw material The moisture content of the raw material has a great influence on the molding process and product quality of the pellet. When the moisture content of the raw material is too high, the vapor generated during the heating process cannot be smoothly discharged from the fuel center hole, causing cracking of the surface and severe explosion. Ming, but the water content is too low to form is also very difficult, this is because the trace amount of water promotes the softening and plasticizing of lignin. For sawdust, straw and other materials, suitable moisture content range of molding is 8% to 14% (Of course, the humidity in the air is also different, can control according to the actual discharge situation). Although there are great differences in the lignin content of different types of materials, the appropriate moisture content for molding is basically the same.