ISO 18134-3:2023

Overview

ISO 18134-3:2023 specifies the oven-drying method to determine moisture content in the general analysis sample of solid biofuels. The method applies to all solid biofuels and requires reporting moisture on a wet basis (percentage of the total test sample mass). The standard highlights that fine particles are highly hygroscopic, so moisture determination is carried out simultaneously with other analyses (e.g., calorific value, volatile matter, metals) to avoid moisture change during handling.

Key Topics

• Principle: Dry a representative test portion of the general analysis sample at (105 ± 2) °C in air until constant mass and calculate moisture from the mass loss.
• Sample preparation: General analysis sample prepared per ISO 14780; nominal top size reduced to below 1 mm. Mix thoroughly and minimize exposure to ambient humidity. Test portion minimum mass: 1 g.
• Apparatus and conditions:
  • Drying oven controlled to (105 ± 2) °C with air exchange 3–5 times per hour.
  • Dishes of non-corrodible, heat-resistant material; layer thickness limited to minimize uneven drying.
  • Balance capable of 0.1 mg readability and a desiccator for cooling and weighing.
• Procedure highlights:
  • Dry empty dish to constant mass, cool in desiccator and weigh.
  • Add test portion in an even layer, weigh, dry uncovered at (105 ± 2) °C until constant mass (change ≤ 1 mg in 60 min), allow up to 3 h depending on material.
  • Replace lid immediately on removal, cool in desiccator and weigh promptly.
  • Perform duplicate determinations and report the mean (results calculated to two decimal places and rounded to 0.1%).
• Atmosphere: Air atmosphere is standard; if sample is susceptible to oxidation at 105 °C, drying in nitrogen is allowed in accordance with ISO 11722 and must be reported.
• Considerations: Small amounts of VOCs can be released during oven drying; ISO notes this release is negligible for overall moisture determination.

Applications

• Ensures consistent, standards-based moisture measurement for quality control of pellets, briquettes, chips and other solid biofuels.
• Supports accurate calorific value, volatile matter and metal content analyses by providing moisture values on the correct (wet) basis used in reporting and conversion (see ISO 16993 for conversions).
• Useful for laboratories requiring repeatable moisture data for fuel specification, energy content reporting and regulatory compliance.

Related Standards

• ISO 14780 - Sample preparation for solid biofuels (preparation of general analysis sample).
• ISO 11722 - Moisture determination in general analysis sample by drying in nitrogen (for oxidation-prone samples).
• ISO 18135 and ISO 21945 - Sampling methods for solid biofuels.
• ISO 16993 - Conversion of analytical results between bases.

Practical value: ISO 18134-3:2023 provides a validated, repeatable oven-drying procedure and reporting requirements to ensure moisture results are reliable and directly usable in energy and composition analyses of solid biofuels.