Overview
CEN ISO/TS 21596:2021 - "Solid biofuels - Determination of grindability - Hardgrove type method for thermally treated biomass fuels" specifies a laboratory procedure to determine the grindability of thermally treated and densified biomass (e.g., torrefied pellets, steam-treated or hydro-thermal carbonized fuels). The method adapts the traditional Hardgrove/Hardgrove Grindability Index (HGI) approach to biomass so suppliers, fuel preparers and boiler operators can predict pulverizing mill performance and achieve a defined particle size distribution for effective combustion in pulverized fuel boilers.
Key topics and technical requirements
- Scope and materials: Applies to thermally treated and densified biomass classified under ISO/TS 17225-8 and to certain non-densified treated biomass (see ISO 17225-1:2021, Tables 14 & 15). Not suitable for large wood chips or materials outside typical coal-mill limitations.
- Adaptations from coal HGI:
- Sample quantity adapted to a fixed bulk volume (to account for wide density variation in biomass).
- Particle-size criterion changed: 500 µm sieve aperture is used (instead of 75 µm for coal) to reflect reactivity and fineness needs of high‑volatile biomass.
- Dedicated reference materials and a calibration curve produce a Thermally Treated Biomass Grindability Index (TTBGI) for inter-laboratory consistency.
- Apparatus and procedure: Uses a standard HGI-type mill, sieves, glass measuring cylinder, sieving machine, balance and cutting mill. The document covers sampling, moisture conditioning, pre‑grinding, test execution, calculation and reproducibility.
- Deliverables: Test report format, calibration data (Annex A), and TTBGI reference values.
Practical applications and users
- Who benefits:
- Fuel producers (torrefaction/HTC/steam-treatment plants) - to specify downstream pulverization behavior.
- Power plant operators & boiler engineers - to predict mill throughput, fuel feeding and combustion performance for co‑firing in pulverized coal boilers.
- Mill manufacturers - to correlate TTBGI with mill capacity and power curves.
- Testing laboratories & certification bodies - for routine grindability testing and quality control.
- Practical uses:
- Selecting or conditioning biomass fuels to meet combustion fineness requirements.
- Estimating pulverizer capacity changes when switching from coal to thermally treated biomass.
- Supporting fuel specifications and contractual guarantees for co‑firing projects.
Related standards
- ISO/TS 17225-8 (classification of torrefied/densified biofuels)
- ISO 17225-1:2021 (solid biofuel fuel classes and tables)
- Original Hardgrove/HGI references (e.g., ASTM D409) for context
Keywords: CEN ISO/TS 21596:2021, grindability, Hardgrove, TTBGI, thermally treated biomass, torrefaction, pulverized fuel boilers, particle size distribution, biomass pellets.