ISO 21637:2020

Overview - ISO 21637:2020 (Solid recovered fuels - Vocabulary)

ISO 21637:2020 is an international vocabulary standard published by ISO to establish clear, harmonized terms and definitions for solid recovered fuels (SRF). Its primary purpose is to enable consistent understanding across the work of ISO/TC 300 (Solid recovered fuels) and to provide referenced terminology for other SRF standards. The document clarifies vocabulary boundaries (e.g., distinction from solid biofuels covered by ISO/TC 238) and groups terms for easy use (see Annex A).

Key topics and technical terms

This vocabulary standard defines core terminology used throughout SRF standards, including (but not limited to):

• Sampling and sample types: analysis sample, duplicate sample, increment, lot, minimum sample size, effective sample size
• Material condition and bases: as received (ar), dry, dry matter, dry ash free (daf)
• Physical and compositional properties: bulk density, energy density, composition, fines, fluff, bale, chips
• Combustion and ash properties: calorific value (GCV and net), ash, ash fusibility, ash sphere temperature
• Fuel forms and processing: densified solid recovered fuel (pellets, briquettes), crushing, milling, drying, homogenization
• Quality, classification and sampling errors: classification of solid recovered fuels (by key properties such as calorific value, chlorine, mercury), heterogeneity, homogeneity, fundamental error, distribution factor
• Applications and risk categories: energy conversion, energy purposes, hazardous waste (definitions relevant to SRF supply chain)
• Cross-references to source standards (e.g., ISO 16559, ISO 540) are used where applicable.

Practical applications - who uses ISO 21637:2020

ISO 21637 is intended for stakeholders across the SRF value chain who require consistent terminology:

• Standards developers and ISO/TC 300 working groups - to harmonize definitions across SRF standards
• SRF producers and processors - for product specifications, sampling and quality control
• Testing laboratories - to ensure consistent interpretation of sample types and calculation bases (ar, dry, daf)
• Waste-to-energy and cement plants - for procurement, fuel classification and combustion/ash analyses
• Regulators, procurers and consultants - for contracts, regulatory compliance and reporting involving SRF Consistent vocabulary reduces ambiguity in testing, sampling protocols, classification and energy conversion processes.

Related standards

• ISO/TC 300 suite of SRF standards (vocabulary supports these documents)
• ISO/TC 238 standards for solid biofuels (distinct scope)
• Referenced sources include ISO 16559 and ISO 540 where specific definitions were adapted

Using ISO 21637:2020 ensures clear communication, improves comparability of SRF data, and supports reliable fuel classification, sampling and laboratory analysis across international markets.