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The Role of Lignin in Pelleting Process

When the crushed raw materials are fed into the pellet mill, they will be pelletized after being processed by rollers and die. You may wonder how the powdered materials could be formed into compact and glossy pellets. The magic lies in a kind of natural element named lignin.
The Introduction of Lignin
Lignin is a complex chemical compound commonly derived from wood, and it is an integral part of the secondary cell walls of plants. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood. It is one of the most abundant organic polymers on Earth, exceeded only by cellulose, employing 30% of non-fossil organic carbon and constituting from a quarter to a third of the dry mass of wood. As a biopolymer, lignin is unusual because of its heterogeneity and lack of a defined primary structure.
Lignin comes from abundant and renewable resources: trees, plants, and agricultural crops. Lignin is nontoxic and extremely versatile in performance and qualities, which have made it increasingly important in many industrial applications.

wood pellets

The Function of Lignin in Pelleting Process
During pelleting process, lignin really plays an essential role. Its type and percentage affect pellet quality, pellet mill lubrication and production. However, in some cases, there is not enough pellet mill lignin or the lignin available can not be used to produce pellets of good quality. Then the natural binders on the market are used. Besides the naturally produced pellet mill lignin, the raw materials density can also influence the amount of lignin.
Lignin makes the pellets hold together. However, it depends on how wet the materials are, so additional moisture may have to be added as you make pellets. This may be as simple as spraying the materials with a little water. Under high pressure and heat in the pellet mill, the lignin in the materials will be softened and then bind the powered materials together just like glue. As the pellets come out of the pellet press dies, the lignin will be cooled down, and then the pellets will become hard.
As we realize the importance of lignin in pelleting, there are ways we can adopt to greatly soften the lignin in the raw materials in order to increase the biomass pellet production efficiency.
i Steam Conditioning
Dry steam will not increase the water content but can provide more heat to better soften the lignin.
ii Drying
Rotary drum dryer can not only reduce the moisture content of the raw material but also can heat the lignin.
iii Adding Water
Adding water in the process of production can increase the pressure and generate more heat to soften the lignin to make the pellets denser.
The information above is all about pellet mill lignin. Study carefully and you will benefit from it. As the professional supplier of feed pellet mills, Allance always offers the latest news, the first-class equipment and after-sales service.