How are wood pellets made

Wood pellets are a type of biomass fuel produced from raw materials like forest slash and construction wastes through a process called biomass densification. This process transforms the raw biomass materials, which are typically low in density and high in moisture content, into solid bio-fuel pellets. As a result, wood pellets offer consistent quality, low moisture content, high energy density, and uniform size and shape, making them an efficient and convenient source of fuel.

Why to make wood pellets?

There are several compelling reasons for producing wood pellets. Firstly, wood pellets serve as a clean alternative to fossil fuels, offering environmental benefits over traditional fuels. Secondly, wood pellet production can make use of biomass harvested from unhealthy forests, contributing to forest restoration and reducing the risk of fires. Thirdly, urban biomass sources can also be utilized as feedstock for wood pellet production, thereby reducing landfill costs. Fourthly, the densified biomass pellet mill industry can be developed in rural and remote areas, allowing for the production of self-made pellets to meet energy needs locally. Lastly, wood pellet fuel represents a valuable commodity in the international market.

How are wood pellets made?

Wood pellets are typically produced from sawdust and planer shavings, which are dried, screened for stones and metal, hammer-milled, pressed into pellets using pellet machines, screened again for sawdust, and finally stored.

Regarding the specific process in a wood pellet machine, the method can vary based on the type of pellet maker being used, such as a flat die pellet mill or a ring die pellet mill.

In the case of a small flat die wood pellet machine, the pellets are created as follows: Once the feedstock, such as sawdust, is fed into the pelleting chamber, the rollers of the wood pellet machine exert pressure to compress the sawdust into the die holes. Subsequently, the pellets are formed and extruded out of the die holes.

How to check the quality of wood pellets?

1. Evaluate the smell of the wood pellets by sniffing the odor from a plastic bag. High-quality wood pellets should exude the fragrance of freshly cut softwood. Alternatively, lighting a sawdust pellet should produce a smoke that smells of burning wood. Any noticeable difference in odor warrants attention.
2. Inspect the appearance of the wood pellets. Those made from clean conifer sawdust should be light brown, while dark brown particles indicate the presence of bark, resulting in increased ash content. Breaking a pellet to examine the color of the layers can reveal that the friction from pellet making might darken the outer layer, which is not an issue if the inner layers remain light in color.
3. Conduct a simple test by placing a small amount of sawdust pellets into a glass of water. The pellets should dissolve into sawdust quickly. If not, it may indicate the use of a binding agent or improper feedstock. After the pellets dissolve, shaking the glass and observing for the heaviest particles at the bottom can reveal the presence of dust from a sanding machine, signaling an increased risk of sintering and higher ash content.