How is wood pellets made?


There are many raw materials for the granules, such as wood, paper, cardboard, grain, alfalfa, corn husks and straw, grass clippings, garden waste, forest and agricultural waste. In this article, we will focus on introducing wood into granules, but the process of making it with other ingredients is basically the same.

The wood or other raw materials to be used in the process are pulverized into wood chips. The material is then forced through a funnel-shaped mold and forced out of the mold hole to a fixed diameter, which is finally compressed into dense particles.

The heat generated by compression and friction from this process can melt the lignin in the wood. As the particles pass the other end of the mold, it slowly cools. Due to the cooling of the lignin, all the raw materials can be cemented to produce hard and strong particles.

Most of the pellets are produced in large pellet plants, but in recent years small-scale pellet mills have become increasingly popular with households and small-scale pellet companies. If you are thinking about making pellets yourself, here’s how to make wood pellets and better teach you how to choose a pelletizer.

Steps for making wood pellets:

First, broken

The raw materials used in the production process must be broken up to a small extent. It should be small enough to fit into the mold. If the raw material exceeds one inch, it must first be broken. If the material is like wood chips, you can skip this step.

Wood chips or other small pieces can be further reduced with a hammer mill.

Second, the transportation of raw materials

Once the material is broken, it must be transported to the dryer. There are several ways to transport these materials, namely screw conveyors, conveyor belts and vacuum systems. Among them, the screw conveyor is the most common mode of transportation.

Third, dry

Before making the granules, it must be ensured that the ingredients are dry. The water content should be between 10% and 20%, depending on the raw materials used. In order for the granulation process to be normal, the raw material should have an appropriate amount of moisture. Drying the material to the right amount of moisture is critical to the manufacture of high quality granules.

Heating and drying is a very expensive part of the granulation process. It is usually more cost effective to burn the particles to generate heat. The dryer is also used to heat the material, which makes it more mellow.

Fourth, mixing

To make homogenous particles, a batch of homogeneous raw materials is important. Raw materials with the same humidity and density do not need to be mixed. Other raw materials coming out of the dryer may have different humidity or density. If there are inconsistent materials, they should pass through a batch mixer, usually a roller and a stirrer.

V. Adjustment

Raw materials must have the correct properties before they are produced. Many raw materials contain enough natural lignin to be glued together. Other materials may require the addition of additional additives such as vegetable oils.

If the water content is too low when the raw material is discharged from the dryer, water may be added, or the mixed water may contain a high amount of raw materials.

Some materials require more heat and pressure to make the pellets, so they must be heated in advance. In general, it is sufficient to use a dryer to heat the raw materials. But in some large pellet plants, the raw materials are heated with dry steam.

Six, pellet production

There are two basic types of pellet machines, flat and ring molds.

Using a flat die granule machine, the press roll and the die are moved relative to each other to clamp, compress, and compact the material into the die hole, and then cut through the die cavity to form a granule or a block.

The ring die machine has a ring die. It is extruded through a ring die and a press roll, extruded into a ring die hole, and continuously extruded toward the outer end.

Seven, screening

Not all particles are available. Some will break into small pieces. These small pieces must pass through the screening. Depending on the quality and consistency of the particles produced, it may also be screened by particle size.

Eight, cooling

When the finished granules leave the granule machine, they are very hot and will also release water vapor. Therefore it must be cooled and dried. The most common methods are naturally air dried, sometimes through their blowers or fans. Care must be taken to dry too quickly to prevent cracking.

Nine, particle transport

Once the particles have cooled, they will be delivered to the packaging equipment. Screw conveyors are not used in this process as they can damage the particles. Usually a bucket elevator is used.

Ten, bagging, storage particles

At this point, the granules are complete and ready for use. But in most cases, they need to be stored and transported to consumers. The granules must be stored away from moisture. If the particles absorb moisture, they will expand and become useless.

The granules are usually sealed in a plastic bag. For most consumers, the bag is an easy to carry size. Large bags weighing up to one ton can also be used for large equipment. Store directly in large silos and ship them in bulk.

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