The "gold standards" for processing high-quality raw materials in biomass pellet machines are the core prerequisite for ensuring pellet fuel quality (such as combustion efficiency, hardness, and stability). They cover multiple dimensions, including the raw material's physical properties, compositional indicators, and pretreatment requirements. The following are specific standards:
1. Raw material type and purity: Single, impurity-free
Prioritize single raw materials: High-quality pellets are typically made from a single biomass raw material (such as pure sawdust, pure straw, pure rice husks, etc.), avoiding the compositional fluctuations caused by mixing multiple raw materials. For example, pure pine wood pellets have a stable calorific value, while mixed straw may affect combustion due to ash content differences.
Free from impurities: The raw materials must be free of impurities such as metal, stone, plastic, and soil. Impurities can increase wear on pellet machine dies, reduce pellet density, and even produce harmful gases during combustion (for example, burning plastic releases dioxins).
2. Moisture Content: Strictly Controlled at 10%-15%
Moisture content is a key indicator affecting pellet forming and combustion performance:
Too low (<10%): The raw material fibers become more brittle, making bonding difficult during forming. The pellets are prone to breakage, and a high amount of dust is generated during processing.
Too high (>15%): The pellets are prone to mold and caking after forming, producing large amounts of black smoke and tar during combustion, reducing calorific value, and potentially causing clogging of the pellet machine mold.
The Golden Range: A moisture content of 10%-15% ensures that the raw material fibers maintain moderate flexibility. Under the high pressure of the pellet machine, they are bonded together by their own lignin (a natural binder), resulting in high pellet hardness and resistance to breakage.
3. Raw Material Particle Size: Uniform and Meets Equipment Requirements
The size of the crushed raw material particles must match the pellet machine mold aperture. General requirements:
Diameter ≤ 3mm (for small and medium-sized pellet machines, the mold aperture is 8-12mm);
Length ≤ 5mm to prevent long strips of raw material from wrapping around the equipment or causing uneven pellet density. Particle Size Uniformity: Excessive variations in raw material coarseness (e.g., a mixture of powder and coarse strands) can lead to uneven force during molding, making the pellets prone to cracking or hollowing, affecting hardness and combustion stability.
4. Ash Content: The lower the better, typically <5%.
Ash content is the inorganic impurities (such as mud, sand, and metal oxides) remaining after raw material combustion, directly affecting the cleanliness of pellet fuel and equipment life.
Quality Standard: Ash content ≤ 5% (e.g., pure hardwood ash content is approximately 1%-3%).
Excessive ash content (e.g., straw ash content often reaches 8%-10%) can easily lead to coking after combustion, clogging boiler pipes, increasing cleaning costs, and reducing combustion efficiency.
Control Method: Select raw materials free of dirt (e.g., debarked wood, cleaned straw) to prevent the incorporation of dirt and sand during the collection process.
5. Calorific Value: Meet the standard based on the type of raw material.
Calorific value is a core indicator of the energy density of pellet fuel. High-quality raw materials must meet the following requirements:
Wood (wood chips, branches): Calorific value ≥ 18MJ/kg (approximately 4300 kcal/kg);
Straw (corn stalks, wheat straw): Calorific value ≥ 15MJ/kg (approximately 3600 kcal/kg);
Mixed raw materials: Calorific value must be maintained at 16-18MJ/kg to avoid a sudden drop in calorific value due to the incorporation of low-quality raw materials (such as rotten leaves).
6. Raw Material Freshness: Free from mold and rot.
Moldy or rotten raw materials (such as wet straw that has been stored for a long time) can produce mycotoxins, emit unpleasant odors and harmful gases (such as hydrogen sulfide) when burned, and their fiber structure is damaged, making them difficult to form.
High-quality raw materials must be kept dry and fresh, and stored in well-ventilated and moisture-proof areas to prevent mold. 7. Impurity Content: Strictly Limit Harmful Substances
In addition to physical impurities, chemical contaminants in raw materials must be controlled:
Paint, preservatives (such as treated wood waste), and straw with excessive pesticide residues must not be present.
The chlorine and sulfur content in the ash must be low (chlorine <0.2%, sulfur <0.1%). Otherwise, combustion will corrode the boiler and produce acid rain pollutants.
Summary
The "golden standard" for biomass pellet machines can be summarized as: pure, single-source material, moisture content of 10%-15%, particle size ≤3mm, ash content <5%, calorific value compliance, freshness, and absence of mold and mildew, and the absence of harmful impurities. Raw materials that meet these standards not only improve pellet machine production efficiency (reducing mold blockage and wear), but also ensure the combustion performance of pellet fuel (high calorific value, low pollution, and high hardness), thereby enhancing the product's market competitiveness.