The process of producing fuel pellets

According to data collected by the Central Emission Register of Buildings, there are over 400,000 pellet boilers registered in Poland. We can assume that the demand for this fuel coincides with the annual production, estimated at approximately 2 million tons. Due to last year's turbulence related to the supply and price of pellets, many potential producers and distributors

and users refrain from purchasing a pellet production line as well as the pellet itself, explaining that

that pellets are too expensive.

What is pellet and what is it made of?

Pellet is a heating fuel made from chemical-free by-products from sawmills

and carpentry shop. These are sawdust, shavings and chips from both softwood and hardwood processing. Pellet is a granulate whose diameter is usually 6 or 8 millimeters. This pellet size is optimal for automatic filling of the heating boiler and ensures clean combustion and operation.

Advantages and disadvantages of pellets

There is no doubt that for the end user, pellets are an energetically beneficial fuel, the energy value of which (19MJ/kg) is slightly lower than the energy value of coal (23MJ/kg). From an ecological point of view, it is a renewable fuel that contributes to sustainable development, and for the consumer it means convenience resulting from less involvement in the maintenance and servicing of the heating boiler.

In terms of ecological balance and sustainable development, pellet production is justified if the raw material is wood waste and not a raw material obtained as a result of deforestation. Therefore, ecologists emphasize that whole logs should not be used to produce pellets.

Another important aspect perceived by consumers as a disadvantage is the instability of pellet prices in recent years. However, prices should always be looked at in the long term.

Pellet production process

The production of this fuel is based on the compression of raw materials such as shavings or sawdust.

To produce one ton of pellets, you usually need 6-8 m3 of raw material. The final result depends on physical properties such as humidity and density.

The first stage in the production process is to clean the raw material from unwanted impurities. These may be particles of pink metals or stones. This is what separators of metals and heavy materials are used for. In the case of pure raw material, this step can be omitted. Then, due to the diversity of the raw material in terms of size, it is sent to a hammer mill, where we obtain a homogeneous fraction.

In the second stage, the raw material undergoes a drying process. As a rule, sawdust, shavings and wood chips have a much higher moisture content than required. It even reaches the level of approximately 40%-50%. After drying, the moisture of the raw material drops by up to 10% and this is a parameter that determines the quality of the pellet

and its subsequent clean combustion in the boiler.

The next stage is the conditioning of the raw material. This is usually done by adding a small amount of water during the pelletizing process itself, however, some manufacturers add various types of agents supporting the production of pellets, such as starch or flour.

The next stage takes place in the pelletizing machine matrix itself. The soft raw material is pressed under high pressure into the die holes using rollers, and the finished pellet emerging from them is cut to a given length using knives. During the pelletization process, the temperature at the junction of the matrix and rollers is between 60°C and 80°C. This causes the lignin contained in the raw material, which is a natural binder, to form and bind the pellet.

The fifth stage is cooling the final product. The pellet granules cool in the open air. Cooling can be intensified with additional fans mounted on the conveyor belt. During the cooling process, the bonds solidify and become stable. Thanks to this, the pellet retains its shape until it is burned in a boiler, stove or fireplace.

The final step is sifting. Dust and improperly compressed pellets are separated

and sent back to the production process, while good pellets are packed in bags or transported to a container/silo as loose goods.

The final product can be certified. Depending on the content of ash and nitrogen compounds

and calorific value and humidity, fuel pellets are divided into 3 quality classes.

A1 class pellet guarantees the highest quality and is offered mainly to individual customers. Class A2 pellets are medium quality pellets and are mainly used in large heating installations. Class B pellets are mainly used in boilers equipped with a self-cleaning burner.