What are the effects of too dry raw materials for biomass pellet machine on pellet forming?

Pellet machines are widely used in the fields of biomass energy utilization and feed production. The raw materials for pelleting are diverse, covering plant raw materials, agricultural waste, wood waste and other combustible materials:

Common raw materials for making feed pellet machines: corn, soybean meal, straw, grass, rice husk, wheat, bran, rice bran, oats, soybeans, cottonseed meal, peanut shells, straw, wheat straw, corn straw, weeds, grass, leaves, etc.

Common raw materials for biomass fuel pellet machines: including straw, wood, branches, boards, corn cobs, peanut shells, straw, bark, wheat bran, distiller's grains, sawdust, wood boards, furniture factory scraps, waste templates, wooden pallets, wooden strips, wood, tree roots, bamboo, board skin, waste mushroom bags, round wood, packaging boxes, etc. are also processable raw materials.

In addition, various wood scraps, crop straw, bamboo chips, palm, caragana, medicinal residues, mushroom residues, waste cloth and other combustible materials can also be used as raw materials for biomass pellet machines.

Requirements for raw materials in pellet making

In order to produce high-quality pellets, in addition to selecting a high-quality pellet machine and a mold compression ratio that matches the raw materials, there are also certain requirements for the raw materials it processes:

Moisture content of raw materials

The pellet machine has strict requirements for the moisture content of raw materials. Too dry or too wet will affect the pellet forming. Raw materials that are too dry will not form and are prone to powder; if the moisture content is high, they will be loose and cracked, and there will be coking after burning. The moisture content of wood in the south is higher than that in the north.

Raw material particle size

The raw material particle size is too fine or too coarse. Too fine particles have a low forming rate; too coarse particles will cause great wear on the mold roller, affecting production efficiency and power consumption. The pellet making of the pellet machine requires that the larger size of the raw material shall not exceed the die hole diameter.

Types of raw materials

Different raw materials, such as pine, poplar, miscellaneous wood, straw, etc., have different properties, different fiber structures, and different forming difficulties. Different raw materials have different compression ratios of the mold.

The harder the raw material, the smaller the compression ratio, and the fluffier the raw material, the larger the compression ratio. In other words, the fluffier the raw material, the easier it is to press and form. The fluffier the raw material, the more fiber it contains, and the more fiber-containing raw material is easy to form. In addition, the ratio between the mixed materials will also affect the forming rate.

Raw material impurities

The raw materials must not be mixed with hard objects such as iron blocks and stones. Iron and impurity removal must be done well, and the iron removal device must be cleaned once per shift, otherwise it will cause abnormal wear of the mold roller and even damage the equipment.

The impact of low raw material moisture on pellet forming

In the production process of the pellet machine, the moisture content of the raw material plays a key role in the quality of pellet forming. When the raw material is too dry, it will have a significant negative impact on pellet forming in many aspects.

Influence on the cohesiveness of the raw material

The wood chip pellet forming requires a certain humidity to promote the bonding between the wood chips. When the raw material is too dry, natural binders such as lignin in the wood chips are difficult to play a role.

Lignin will soften and have a bonding effect under appropriate temperature and humidity conditions, but dry raw materials will keep lignin in a solidified state, which cannot effectively bond the wood chip particles together, resulting in difficulty in molding, and the particles are easy to loosen and break, making it difficult to form complete and solid particles.

Increased equipment wear and energy consumption

Dry materials are hard in texture, and during the pressing process, they will produce greater friction with key components such as the mold and roller of the pellet machine.

This greater friction will not only cause the mold and roller to wear quickly, greatly shortening the service life of the equipment, but also cause the equipment to consume more energy to overcome friction resistance during operation, thereby causing a sharp increase in energy consumption.

At the same time, greater friction may also cause unstable equipment operation, affecting the quality and production efficiency of pellet molding.

Poor surface quality of pellets

Due to the excessive dryness of the raw materials, it is difficult for the wood chip particles to be tightly bonded during the pressing process, making it easy for the surface of the pellets to have problems such as cracks and roughness.

These surface defects will reduce the appearance quality of the pellets, and during storage and transportation, they are more susceptible to external factors and breakage and pulverization, reducing the overall quality and use value of the pellets.

Impact on particle density and strength

Appropriate raw material humidity helps to make the wood chip particles more densely stacked and formed during the pressing process, thereby obtaining higher density and strength.

When the raw material is too dry, the wood chip particles cannot be fully filled and compacted, and the particles produced have low density and insufficient strength. Such particles may have problems such as incomplete combustion and easy breakage during the combustion process, affecting their performance as fuel or other uses.

What should I do if the raw material is too dry?

In general, it is more appropriate to keep the moisture content of the raw material in the range of 13%-18%, and the optimal moisture content is 15%. If the moisture content of the raw material is too dry and affects the pelletizing and forming, it can be improved by the following methods.

Adjust the moisture content of the raw material

Use professional moisture measurement equipment to accurately detect the initial moisture content of the raw material, use a spray device or stirring and watering equipment to evenly add an appropriate amount of moisture to the dry raw material, or add other raw materials with high moisture. After adding moisture, it is necessary to fully stir and mix to ensure that the moisture is evenly distributed in the raw material.

Place the dry raw material in an environment with relatively high humidity, let it naturally absorb moisture from the air, and naturally rehydrate to reach an appropriate moisture content. However, this method takes a long time, and the degree of moisture absorption is difficult to accurately control.

Optimize the process parameters of the pellet machine

Appropriately reduce the compression ratio of the ring die, reduce the pressure of the roller, and avoid excessive crushing of the dried raw materials due to excessive pressure. At the same time, regularly check and maintain the mold and roller to ensure that their surface is smooth and reduce friction.

Control the feed speed

Reduce the feed speed so that the dried raw materials have more time to form in the biomass pellet mill machine to avoid inadequate forming due to too fast feeding.

Optimize the drying and cooling process

If there is a drying step in the production process, the drying temperature and drying time can be appropriately reduced to avoid excessive drying of the raw materials. After the pellets are formed, a reasonable cooling method, such as natural cooling or forced air cooling, is adopted to avoid cracks in the pellets due to too fast cooling speed.