Lignin And Binders For Making Your Own Pellets
For the sake of better pellets quality, binding agents are used in pellet production. Pellets without binding agent may easy get decomposed during storage, forming hazardous gases such as carbon monoxide and hexanal. Therefore, sometimes it is practical to use binding agents to make your own pellets when it concerns the profitability of production and occupational problems such as wood dust exposure, fire and explosion risk, coherence, etc.
Actually, one of the best aspects of pellet production is versatility, the ability to produce pellets using nearly any sort of plant as the raw material. However, the characteristics of each plant are different, the most important difference for making pellets being the plant's lignin content. Lignin is a compound found in the cell walls of plants that functions to add rigidity and conduct water. It the key material toward the production of dense, durable pellets. Sturdier plants, such as trees, generally contain more lignin than those less sturdy, such as grass.
As for sturdy materials, such as wood, the lignin is the natural binder. The high pressure and friction produced during the compressing of pellet making machine causes the increases of wood temperature significantly, and plasticization of the lignin slightly in the temperature range around 100 to 130 centigrade ( Kaliyan and Vance 2009) and forming a natural “glue” that holds the pellet together as it cools down.
In pellets, lignin is the material that creates dense, durable pellets. In order to get the same quality from pellets produced using plants with lower lignin content, a binder must be added during the process of making your own pellets. Water, vegetable oil and starch are some of the most common binders used, although a variety of materials may be used for this purpose.
Actually, water is not a binder, binder is the natural lignin of the materials. However, adding water to materials can help to increase the bond within the pellets by spreading the natural lignin within the pellet and also can help to increase the pressure of the raw material within the die hole. What’s more, water can function as a lubricant however when the water is too much, the die holes may be blocked and the combustion efficiency will be lowered.
Vegetable oil is another materials that can be used as a binder within certain amount however it is used more as a lubricant to reduce resistance when material go through the die holes. It is good to use oil to improve the material flow through the die however too much oil will harm the pellet quality by reducing pellets density.
Starch is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. The polysaccharide is produced by all green plants as energy storage. It is contained in potatoes, corn, wheat, cassava and rice, etc. Starch contains linear, helical amylase and branched amylopectin. Varying with plant species, starch generally contains 20% – 25% anmylose and 75%-80% amylopectin. Starch can function as a thickening, stiffening or gluing agent when dissolved in warm water.
Adding a small amount of binder when making your own pellets is aimed to improve the pellet quality and avoiding decomposition and at the same time to reduce energy consumption, improve pellet making machine productivity and increase the service life of consumable spare parts like roller and die of a pellet mill. However, it would be tricky task to produce high density pellets with low moisture content while keeping pellet making machine productivity as high as possible and pellet making machine energy consumption as low as possible.