ISO 17827-2:2017 — Determination of Particle Size Distribution for Uncompressed Solid Biofuels (Vibrating Screen Method for Sieve Apertures ≤3.15 mm)

Scope and Introduction

ISO 17827-2:2017, adopted in Canada as CAN/CSA-ISO 17827-2:17, specifies a method for determining the particle size distribution (PSD) of uncompressed solid biofuels using a vibrating screen with sieve apertures of 3.15 mm and below. This standard is part of the ISO 17827 series, which addresses PSD for uncompressed fuels under different size ranges. Part 2 focuses on finer particles (≤3.15 mm), complementing Part 1 which covers larger fractions (≥3.15 mm). The method applies to materials such as crushed wood pellets, sawdust, hog fuel, olive residues, and other particulate biomass that have a significant proportion of particles smaller than 3.15 mm.

The vibrating screen method described in ISO 17827-2 employs a set of sieves placed in a stack, subjected to controlled vibration to separate particles by size. The standard is essential for quality control in biofuel production, combustion efficiency optimization, and compliance with fuel classification systems (e.g., ISO 17225 series). By harmonizing test procedures internationally, ISO 17827-2 enables reliable comparison of PSD results across laboratories and supply chains, directly supporting trade and utilization of solid biofuels.

Technical Requirements

Apparatus and Sieves

The standard mandates the use of test sieves conforming to ISO 3310-1 (woven wire cloth) or ISO 3310-2 (perforated metal plate). Sieve aperture sizes shall be selected to cover the expected particle size range, typically including 3.15 mm, 2.00 mm, 1.00 mm, 0.500 mm, 0.250 mm, and a bottom pan. Each sieve must have a nominal diameter of 200 mm (or 300 mm for larger samples) and comply with the tolerances specified in ISO 3310. The recommended aperture increments follow a ratio of √2 from the 3.15 mm reference. Table 1 lists suggested sieve apertures and corresponding tolerances.

A vibrating sieve shaker capable of delivering a vertical vibration amplitude of 0.5 mm to 3 mm (at 50 Hz) or equivalent shall be used. The vibration parameters must be adjustable to achieve optimal sieving efficiency without damaging the sieves or altering the sample. Additional equipment includes a balance with a precision of 0.1 g, drying oven (set at 105 °C for moisture determination), and sample dividers (e.g., riffle boxes) to obtain representative subsamples.

Sample Preparation

The test sample must be taken from a larger lot following the principles of ISO 18135 (Sampling of solid biofuels) and ISO 14780 (Sample preparation). The sample shall be air-dried to a moisture content of ≤15 % by mass (wet basis) to avoid clogging of sieves and to ensure free-flowing behavior. If the as-received moisture exceeds this threshold, the sample must be dried in an oven at 50 °C until the desired moisture level is reached, taking care not to devolatilize the fuel. The mass of the test portion (Mr) depends on the estimated nominal top size of the material (as defined in ISO 17827-1):

• For materials where ≥90 % passes the 3.15 mm sieve, a minimum sample mass of 100 g is required.
• If the material is coarser (retained fraction on 3.15 mm >10 %), the test portion must be at least 200 g to ensure representativeness.

The sample shall be divided into two replicates for duplicate determinations; the mean of both results is reported as the final PSD.

Procedure

1. Assemble the sieve stack in ascending order of aperture (largest at top, pan at bottom).
2. Weigh the empty sieves and pan. Place the test portion on the top sieve.
3. Install the lid and secure the stack on the vibrating shaker.
4. Set the vibration amplitude and frequency to achieve a vertical motion of 1.5 mm–2.5 mm at 50 Hz (typical). The duration of sieving is initially 10 min for most materials; longer times (up to 20 min) may be required for high‑fines content.
5. After sieving, carefully disassemble the stack. Weigh each sieve and the pan with the retained material. Calculate the mass retained on each sieve by subtracting the initial tape weight.
6. Optionally perform a hand-sieving check (as per Annex A of the standard) to verify the end point: further sieving for 2 min should result in less than 0.5 % by mass passing the finest sieve.
7. Repeat with the second replicate.

Calculation and Reporting

For each sieve size i, compute the mass fraction R_i (mass retained on sieve i) as a percentage of the total test mass:

R_i = (m_i / M_r) × 100

where m_i is the mass retained on sieve i (in grams) and M_r is the total mass of the test portion (in grams). The cumulative undersize (P_i) is then derived: P_i = 100 − Σ_iR_i. Results are reported as the average of the two replicate determinations, rounded to the nearest 0.1 % for each fraction. The report must include: the moisture content of the sample, the sieve apertures used, the sieving time and amplitude, and any deviations from the standard procedure.

Implementation Highlights

ISO 17827-2:2017 provides a critical tool for biofuel producers and users to characterize the fine fraction of their fuels. The standard is often referenced in fuel quality specifications (e.g., for ISO 17225‑2 for wood pellets, and ISO 17225‑4 for wood chips) to ensure that the amount of fines (material passing a 1 mm or 0.5 mm sieve) is within acceptable limits for the intended combustion technology.

Key differences from ISO 17827‑1 (which covers coarse particles ≥3.15 mm) include:

• The use of a vibrating screen rather than a horizontal or horizontal‑rotational sieve motion, because fine particles are more effectively separated by vertical vibration.
• Sieve sizes are limited to ≤3.15 mm, but the method may be extended to include a 4 mm or 5.6 mm sieve at the top if a small fraction of oversize is present (per the scope extension in Annex C).
• Greater emphasis on avoiding electrostatic charging and moisture effects.

The method is suitable for materials with a nominal top size (after cutting or crushing) of up to 3.15 mm, such as hog fuel, sawdust, and certain agricultural residues. In cases where the sample contains an appreciable amount of wood bark or fibrous material, a 1‑minute hand‑sieving step after the mechanical sieving is permitted to free trapped particles. The flexibility of the standard allows laboratories to adjust sieving parameters (within defined limits) to suit the specific fuel type, as long as the chosen conditions are documented and validated.

Compliance Notes

ISO 17827-2:2017 is a Tier 1 test method for the determination of particle size distribution of solid biofuels under the ISO 17225 series. Compliance with the standard is required for certification to the quality classes defined in ISO 17225 (e.g., A1, A2, B for pellets). Laboratories that carry out PSD testing should operate under a quality management system such as ISO 17025, and use verified reference sieves that are calibrated at regular intervals.

In Canada, the standard has been adopted as CAN/CSA‑ISO 17827‑2:17 by the Canadian Standards Association. This adoption is identical to the international version, with no deviations. Compliance with CAN/CSA‑ISO 17827‑2:17 may be required by regulatory bodies or by contractual agreements for biomass supply to Canadian power plants and district heating systems. Similarly, other countries may adopt the standard regionally, often with the same technical content.

When reporting test results for compliance purposes, the laboratory must include the complete standard reference (e.g., “CAN/CSA‑ISO 17827‑2:17”) and state the moisture content of the sample at the time of testing. Any method modifications (e.g., extended sieving time, use of wet‑sieving for sticky materials) must be clearly noted and justified. Inter‑laboratory comparisons are recommended to ensure reproducibility, especially when the PSD is used to verify fuel quality guarantees.

Frequently Asked Questions

Last updated 2026 — This article provides general technical guidance; always refer to the official ISO or CSA publication for complete requirements.