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Understanding ISO 17831-2:2016 – Determination of Mechanical Durability of Biomass Briquettes
A comprehensive guide to the international standard for assessing the durability of solid biofuel briquettes
Introduction
The international standard ISO 17831-2:2016 (adopted in Canada as CAN/CSA-ISO 17831-2:16) specifies a method for determining the mechanical durability of densified solid biofuels, specifically briquettes. Mechanical durability is a critical quality parameter that reflects the ability of briquettes to withstand handling, transportation, and storage without excessive breakage or dust formation. This article provides a detailed technical overview of the standard, including its scope, test requirements, implementation guidance, and compliance considerations.
Scope
ISO 17831-2:2016 is part of a series of standards addressing solid biofuels (ISO 17831 series). Part 2 focuses exclusively on briquettes, while Part 1 covers pellets. The standard defines a reproducible laboratory method to measure the mechanical durability of briquettes by simulating mechanical stress through tumbling. It applies to all types of briquettes derived from solid biofuels, such as wood, agricultural residues, and other biomass materials, regardless of their shape (cylindrical, cubical, or other forms).
The method is intended for use in quality control, product certification, and research. It does not address safety concerns associated with its use; users are responsible for establishing appropriate health and safety practices. The standard is applicable to briquettes with a maximum diameter of 100 mm and a length up to 400 mm, though larger briquettes may require adaptation of the equipment.
Technical Requirements
Principle of the Test
A sample of briquettes is tumbled inside a rotating test chamber (tumbling can) under defined conditions. After tumbling, the material is sieved to separate fines. The durability index (DU) is calculated as the ratio of the mass retained on the sieve to the initial sample mass, expressed as a percentage.
Equipment Specifications
The standard specifies the following key equipment parameters:
| Parameter | Requirement |
|---|---|
| Tumbling can internal dimensions | Length 600 mm, internal cross-section 300 mm × 300 mm (square) or diameter 300 mm (round) |
| Rotation speed | 15 ± 0.5 min⁻¹ (revolutions per minute) |
| Total number of revolutions | 500 (fixed) |
| Sample mass | approx. 2000 g (exact mass recorded) |
| Sieve aperture | According to briquette size: typically 2.0 mm or 3.15 mm |
| Balance accuracy | 0.1 g |
Tip: Ensure the tumbling can is made of steel with a smooth internal surface. Some standards allow an internal baffle to enhance mixing; however, ISO 17831-2 specifies a plain can without baffles.
When testing unusually shaped briquettes, the number of briquettes per charge may need adjustment to maintain consistent tumbling action.
When testing unusually shaped briquettes, the number of briquettes per charge may need adjustment to maintain consistent tumbling action.
Sample Preparation
Briquettes are conditioned at a specified moisture content (typically 8–12% dry basis) and temperature (20 ± 5 °C). The sample size should be representative of the batch. Briquettes are weighed individually or as a bulk sample. For the test, a total sample mass of approximately 2000 g is placed in the tumbling can. If individual briquettes are large, the number of briquettes loaded must be recorded.
Durability Index Calculation
After tumbling, the content is carefully sieved. The mass of material remaining on the sieve (including any intact briquettes or large fragments) is the retained mass m₂. The durability index DU is calculated as:
DU = (m₂ / m₁) × 100
where m₁ is the initial total mass of the sample. The result is reported to one decimal place. A higher DU indicates better mechanical durability. Typical values for good-quality briquettes exceed 90%.
Important: The sieve aperture selection significantly affects the result. The standard requires the use of a sieve with aperture of 2.0 mm for briquettes with a nominal particle size less than 25 mm, and 3.15 mm for larger briquettes. Always record the sieve size used.
Implementation Highlights
Laboratory Setup
To implement the test, a laboratory should acquire a tumbling can meeting the dimensional specifications. Many commercial test systems designed for ISO 17831-2 are available. The rotation speed must be controllable and verified periodically. A suitable test sieve shaker and analytical balance are also required.
Quality Control Measures
Regular validation of the test equipment is essential. The standard recommends:
- Calibration of the tumbling can speed at least every 6 months.
- Verification of sieve aperture size per ISO 3310-1 or ISO 3310-2.
- Participation in inter-laboratory comparison programs.
- Use of a reference material (if available) to check reproducibility.
Best practice: Maintain a detailed log of test conditions (temperature, humidity, sample history). Store briquettes in sealed containers before testing to avoid moisture changes that could alter durability.
Expression of Results
Report the following for each test:
- Sample identification and source,
- Moisture content at time of test,
- Nominal particle size and sieve aperture used,
- Number of revolutions (500),
- Mass retained on sieve, initial mass, and DU value,
- Any deviation from standard procedure.
Compliance Notes
Conformity Assessment
Meeting the requirements of ISO 17831-2:2016 is often a prerequisite for biofuel certification schemes (e.g., ENplus for pellets, but note that briquettes are covered by other schemes). The standard can be referenced in contractual agreements between producers and buyers. To claim compliance, the testing laboratory must follow the method exactly as written, including sample preparation, conditioning, and calculation.
Common Deviations and Pitfalls
| Deviation | Effect on Result |
|---|---|
| Non-conditioned samples (drier or wetter) | May artificially increase or decrease DU |
| Oversized sample mass (>2000 g) | Insufficient tumbling action, overestimated durability |
| Rotation speed outside tolerance | Higher speed may cause more breakage, lower DU |
| Using wrong sieve aperture | Directly alters the fines fraction measured |
Warning: Non-compliance with the specified rotation speed or number of revolutions invalidates the test. Even minor deviations can significantly change the durability index. Always use a tachometer to verify speed before each test run.
Regional Adaptations
In Canada, the standard is issued as CAN/CSA-ISO 17831-2:2016, which is identical to the international version. Some countries may adopt modifications; users should always check the locally adopted version. For briquettes intended for residential stoves, national regulations may require additional performance tests (e.g., ash content, calorific value) alongside durability.
Conclusion
ISO 17831-2:2016 provides a robust, repeatable method for evaluating the mechanical durability of solid biofuel briquettes. Adherence to this standard ensures that briquettes can withstand handling and transport without generating excessive dust or breaking apart. For producers, regulators, and consumers, the durability index derived from this test is a key indicator of product quality. Proper implementation, including equipment calibration and sample conditioning, is essential for reliable results.
Q: Why is mechanical durability important for briquettes?
A: Mechanical durability measures a briquette’s resistance to breakage and dust formation during handling, transport, and storage. Low durability can lead to fuel loss, increased dust emissions, and operational problems in combustion equipment.
A: Mechanical durability measures a briquette’s resistance to breakage and dust formation during handling, transport, and storage. Low durability can lead to fuel loss, increased dust emissions, and operational problems in combustion equipment.
Q: How does ISO 17831-2 differ from the pellet durability test (ISO 17831-1)?
A: Part 1 for pellets uses a different tumbling can (smaller, 300 mm internal diameter, longer dwell time) and applies 500 revolutions at 50 min⁻¹. The briquette method uses a larger can and slower speed to accommodate larger particles, with the same number of revolutions but different sample mass and sieve sizes.
A: Part 1 for pellets uses a different tumbling can (smaller, 300 mm internal diameter, longer dwell time) and applies 500 revolutions at 50 min⁻¹. The briquette method uses a larger can and slower speed to accommodate larger particles, with the same number of revolutions but different sample mass and sieve sizes.
Q: What is the target durability index for good-quality briquettes?
A: While no universal limit is set in ISO 17831-2 itself, many quality specifications require a DU of at least 90% for premium briquettes, and above 95% for industrial-grade briquettes. The acceptable threshold depends on the application and end-user requirements.
A: While no universal limit is set in ISO 17831-2 itself, many quality specifications require a DU of at least 90% for premium briquettes, and above 95% for industrial-grade briquettes. The acceptable threshold depends on the application and end-user requirements.
Q: Can the test be applied to irregularly shaped briquettes?
A: Yes, the standard is adaptable. However, for very large or unusually shaped briquettes, the sample mass may need adjustment, and the results should be reported with a note. The method is primarily designed for cylindrical or cubical briquettes with a maximum dimension of 100 mm.
A: Yes, the standard is adaptable. However, for very large or unusually shaped briquettes, the sample mass may need adjustment, and the results should be reported with a note. The method is primarily designed for cylindrical or cubical briquettes with a maximum dimension of 100 mm.
Published: 2026. This technical article is for informational purposes. For official requirements, refer to the latest version of ISO 17831-2:2016 or CAN/CSA-ISO 17831-2:16.