Overview
ISO 11724:2019 specifies a laboratory method for the determination of total fluorine in solid mineral fuels - specifically coal, coke and fly ash. The method uses pyrohydrolysis (thermal treatment at about 1 200 °C in an oxygen/water vapour atmosphere) to volatilize fluorine compounds, collects the pyrohydrolysate in an absorption solution and quantifies fluorine by ion-selective electrode (ISE) or ion chromatography (IC). The standard also notes a key limitation: total fluorine alone does not predict fluorine emissions during fuel use or disposal of ash.
Key topics and requirements
- Scope and limitation: Total fluorine measurement for coal, coke and fly ash; does not estimate environmental release.
- Principle: Mixing sample with silica, pyrohydrolysis in a tube furnace and absorption of volatilized fluorine for subsequent analysis.
- Analytical routes: Measurement by fluoride ion-selective electrode (ISE) (direct-comparison or analyte-addition methods) or ion chromatography (IC).
- Apparatus and reagents: Detailed requirements for silica, absorption solutions (e.g., NaOH-based for ISE, carbonate/bicarbonate for IC), oxygen supply, tube-furnace pyrohydrolysis apparatus, ISE electrodes and IC systems.
- Sample handling: Test portions prepared from general analysis samples (per ISO sampling standards); attention to representative sampling and avoidance of contamination for fly ash.
- Procedure controls: Duplicate determinations, blank tests, apparatus conditioning, electrode conditioning and calibration, and solution processing prior to measurement.
- Safety and quality: Cautions on toxic/corrosive reagents and silica dust; use analytical-grade reagents and purified water.
- Reporting and precision: Requirements for calculations, expression of results and precision data (repeatability/reproducibility limits included in the standard).
Applications and users
- Laboratories performing fuel quality analysis and geochemical testing.
- Coal and coke producers for product quality control.
- Power plants and utilities assessing feedstock composition and ash management.
- Environmental labs and regulators monitoring fluorine content in combustion residues.
- Research institutions studying fluorine distribution in solid fuels and combustion products.
Practical uses include feedstock specification, process control, ash characterization and baseline data for environmental assessments - while keeping in mind that further testing or modelling is required to estimate fluorine emissions.
Related standards
Normative references in ISO 11724:2019 include:
