Overview
EN ISO 21656:2021 / ISO 21656:2021 - "Solid recovered fuels - Determination of ash content" specifies laboratory methods for measuring the ash content of all solid recovered fuels (SRF). Adopted by CEN in 2021 and superseding EN 15403:2011, the standard is intended for laboratories, producers, suppliers, purchasers and regulatory or inspection bodies involved in SRF quality control and trade.
Key topics and technical requirements
- Scope: Methods for determination of ash content of SRFs, including treatment of coarse inert materials (removed ash contributors - rac) in total ash calculations.
- Principle: Heating a prepared sample in air to controlled temperatures and times and calculating ash from the mass of inorganic residue.
- Two temperature methods:
- Method A: Ash content determined at (550 ± 10) °C (commonly used for biomass-rich SRFs and for many elemental determinations).
- Method B: Ash content determined at (815 ± 10) °C (captures effects from carbonate decomposition and volatile inorganic losses).
- Apparatus & limits: Examples given in the standard include inert ash dishes (depth 10–20 mm, sample load ≤ 0.1 g/cm²), furnaces with uniform temperature and 5–10 air changes/min ventilation, and balances with 0.1 mg readability.
- Sample handling: Requirements for sampling, pre-drying, removed ash contributors (rac), and sample preparation are referenced (ISO 21645, ISO 21646 and ISO 21660-3).
- Calculation, precision & reporting: Procedures for calculating ash on as-received and dry bases, inclusion of rac in total ash, precision data (repeatability/reproducibility limits), and mandatory test report contents.
- Validation: Use of automatic thermogravimetric equipment is permitted if validated against the reference method.
- Environmental considerations: Annex B addresses environmental aspects related to ash determination.
Applications and users
- Who uses it: Analytical laboratories, SRF producers/suppliers, fuel purchasers, waste-to-energy plants, environmental regulators, and certification/inspection bodies.
- Practical uses:
- Quality control and specification compliance for SRF batches.
- Determining inorganic fraction for combustion performance, emissions forecasting and ash handling logistics.
- Basis for further elemental/trace analysis (references to EN 15410 / EN 15411 for elemental determinations).
- Contractual testing and regulatory reporting.
Related standards
- ISO 21637 - SRF vocabulary
- ISO 21645 - SRF sampling methods
- ISO 21646 - SRF sample preparation
- ISO 21660-3 - Moisture determination (oven dry method)
- EN 15403:2011 - superseded by EN ISO 21656:2021
- EN 15410 / EN 15411 - referenced for major and trace elemental determinations
This standard is essential for consistent, repeatable ash-content measurement of solid recovered fuels and supports reliable fuel specification, combustion planning and regulatory compliance.