Biomass pellets are a type of clean energy that play a crucial role in energy conversion and environmental protection. The hardness of pellets is an important quality indicator that directly affects their combustion efficiency, storage stability, and transportation convenience. This article will thoroughly analyze the various factors that influence the hardness of biomass pellets produced by pellet machines and provide optimization suggestions to help wood pellet plant companies improve product quality.

1. Raw Material Particle Size
1.1 Impact of Particle Size on Pellet Hardness
The particle size of raw materials is one of the key factors affecting pellet hardness. Finer particle sizes allow the raw materials to gelatinize more easily during the pelletizing process, enhancing the internal bonding of the pellets and thereby increasing their hardness. Fine particles can combine more tightly during compression, reducing internal gaps and making the finished pellets less prone to breakage and harder.

1.2 Optimization of Particle Size Distribution
To improve pellet hardness, the particle size distribution ratio of the raw materials can be adjusted as follows:

Coarse Particles (particle size above 900μm): No more than 15%. Excessive coarse particles can lead to a loose internal structure, reducing hardness.
Medium Particles (particle size around 700μm): Approximately 35%. Medium-sized particles help enhance the structural stability of the pellets.
Fine Particles (particle size below 500μm): Over 50%. Fine particles provide a good bonding foundation, increasing pellet hardness.
Ultra-Fine Particles (particle size below 250μm): At least 25%. Ultra-fine particles further strengthen the bonding force, enhancing overall hardness.
This particle size distribution not only facilitates pellet formation and improves appearance quality but also ensures appropriate hardness while reducing pellet friability, thereby enhancing overall product quality by wood pellet machine.

2. Type of Raw Material
2.1 Impact of Different Raw Materials on Pellet Hardness
raw material for pellet making
Different types of biomass raw materials exhibit varying hardness characteristics during the pelletizing process. For example:
Woody Materials: Such as sawdust and wood chips, have high cellulose and hemicellulose content, providing good bonding properties and resulting in harder pellets.
Herbaceous Materials: Such as straw and grass, have high fiber content but relatively lower bonding properties, leading to softer pellets.
Other Biomass: Such as agricultural waste and energy crops, have hardness influenced by their specific composition and fiber structure.
2.2 Importance of Formula Adjustment
Proper adjustment of the proportions of different raw materials is an effective way to regulate pellet hardness. By scientifically balancing different materials, it is possible to ensure both the hardness of the pellets and the cost-effectiveness and utilization rate of the raw materials. For instance, increasing the proportion of woody materials can enhance pellet hardness, while adding herbaceous materials can reduce production costs and improve raw material utilization.

3. Moisture Content of Raw Materials
biomass raw materials moisture content

3.1 Impact of Moisture Content on Pellet Hardness
The moisture content of raw materials is a critical factor influencing pellet hardness. Generally, raw materials should have a moisture content controlled between 13% and 18%. Specific requirements may vary depending on the type and nature of the raw material. For example, woody materials can tolerate a wider range of moisture content, whereas herbaceous materials require more stringent moisture control.

3.2 Negative Effects of Excessive Moisture
Excessive moisture in raw materials can increase the air content within the pellets, affecting their compactness and reducing hardness. Additionally, high moisture levels may lead to mold growth and deterioration during storage, compromising product quality. Therefore, it is essential to adequately dry raw materials before pelletizing to ensure the moisture content meets the required standards.

3.3 Impact of Environmental Humidity
Environmental humidity also plays a significant role in affecting pellet hardness. In high-humidity environments, raw materials are more prone to moisture absorption, increasing their moisture content. Therefore, controlling the production environment is crucial to maintaining pellet hardness.