Overview
ISO 29541:2025 - "Coal and coke - Determination of total carbon, hydrogen and nitrogen - Instrumental method" specifies an instrumental combustion procedure for the concurrent determination of total carbon (C), hydrogen (H) and nitrogen (N) in coal and coke. The method converts sample C, H and N to gaseous products (CO2, H2O, N/NOx) by combustion in oxygen, removes interfering species, reduces NOx to N2 and quantifies the gases by instrumental gas analysis. Note: the method and its precision data were validated for coal only; precision limits for coke are not established due to insufficient interlaboratory data.
Key topics and requirements
- Principle: Single-run combustion with gas analysis for CO2, H2O and N (after NOx reduction).
- Instrument and sample: Analytical instrument with furnace, gas-handling and detectors capable of analysing test portions of 6 mg or greater; balance resolution appropriate to test mass.
- Sample preparation: General analysis test sample ground to a nominal top size of 212 µm, moisture equilibrated with laboratory atmosphere and thoroughly mixed.
- Reagents and calibration materials: Carrier gas (e.g., helium), oxygen and certified calibration materials (examples include EDTA, phenylalanine, acetanilide, BBOT). Coal must not be used for calibration because composition can change with storage.
- Procedure essentials:
- Instrument set-up and leak checks
- Daily blank analyses to monitor background C/H/N
- Conditioning and stability checks (discarding initial runs)
- Calibration and verification using independent calibration material
- Regular verification during batches (preferably every ten samples); samples analysed in duplicate
- Acceptance limits for calibration verification:
- Carbon: ±0.2% (relative)
- Hydrogen: ±0.5% (relative)
- Nitrogen: ±1% (relative)
- Quality/precision: Repeatability and reproducibility limits are provided in Clause 10 (updated in this edition); the validation follows ISO 5725-1 principles.
- Safety: Method involves hazardous operations and materials - users must follow appropriate safety practices.
Applications and users
ISO 29541:2025 is used where reliable total C, H and N measurements are required:
- Coal and coke quality control laboratories
- Power generation and utilities (combustion calculations, fuel characterization)
- Mining companies and coke producers (product specification)
- Environmental and emissions modelling (fuel carbon accounting)
- Research institutions and instrument manufacturers (method development, calibration)
The standard supports accurate carbon accounting, combustion performance assessment and compliance with fuel specification requirements.
Related standards
Keywords: ISO 29541:2025, coal and coke analysis, total carbon hydrogen nitrogen, instrumental combustion method, calibration, sample preparation, coal analysis, coke analysis, precision limits.
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