ISO/TR 23437:2020 PDF

Overview

ISO/TR 23437:2020 - Solid biofuels - Bridging behaviour of bulk biofuels is a technical report that compiles current knowledge and a practical test method for assessing the bridging behaviour of particulate biofuels. The report is organized in three parts:

• Part I: a research method for direct determination of bridging behaviour;
• Part II: guidance for implementing the measurement principle and building test apparatus;
• Part III: experience, test performance data and typical results for a wide range of biofuels.

The core principle is simple: a sample is placed above an expandable, frictionless slot and the slot opening width at which a stable bridge forms (and ultimately collapses) is recorded as an indicator of bridging propensity.

Key Topics

• Bridging definition and mechanisms: tendency of particles to form stable arches across an opening, causing flow interruption (ratholing, channel flow).
• Test principle: expandable bottom slot in a low-friction box; measure slot opening width at bridge formation/collapse.
• Apparatus and dimensions: example device uses a box with inside dimensions 1.1 m × 2.0 m, minimum filling height 0.75 m (±0.01 m) and sample volume 1.65 m³; flexible low-friction mats form a quarter‑circular slot edge with effective radius (32 ± 5) mm.
• Sampling & preparation: standardized sample filling and conditioning to control variables such as moisture and bed depth.
• Measurement parameters & definitions: particle size (mean particle size, Feret diameter), particle shape factor (PSF), length–diameter ratio (LD), and angle of repose.
• Performance and uncertainty: sensitivity analysis, repeatability and reproducibility data from interlaboratory studies; influencing factors and limitations are discussed.

Applications

ISO/TR 23437 is aimed at professionals concerned with reliable handling, storage and transport of solid biofuels:

• R&D laboratories developing new biofuel products and grading feedstock for flowability.
• Plant and silo designers to reduce clogging, ratholing and interruptions in feeding systems (hoppers, conveyors, screw feeders).
• Fuel suppliers and quality control teams seeking to characterise material handling risks tied to particle size distribution, moisture content and overlong particles.
• Standards developers and researchers using the method to compare bridging behaviour across materials.

Practical outcomes include improved equipment design, better storage strategies, and reduced operational downtime due to bridging.

Related standards

ISO/TR 23437 complements other standards and guidance on solid biofuels, fuel specifications and material characterization used by laboratories, manufacturers and plant operators. Users are encouraged to consult national and international standards for sampling, particle sizing and fuel quality when applying the bridging test.