Overview
ISO 5068-1:2007 - "Brown coals and lignites - Determination of moisture content - Part 1: Indirect gravimetric method for total moisture" specifies two indirect gravimetric procedures for measuring total moisture in brown coals and lignites: a single‑stage nitrogen‑flushed oven drying method and a two‑stage method combining air (or cabinet) drying and subsequent nitrogen oven drying. The standard defines the test principle, required apparatus and reagents, sampling and sample preparation, calculation of moisture content, precision limits and reporting requirements.
Key topics and technical requirements
- Principle
- Single‑stage: loss in mass after drying at 105 °C to 110 °C in a nitrogen atmosphere.
- Two‑stage: coarse air drying (ambient or 30–40 °C) to equilibrium, then residual drying at 105–110 °C in nitrogen; total moisture is calculated from both mass losses.
- Reagents
- Desiccant (magnesium perchlorate or silica gel) and high‑purity dry nitrogen (max oxygen 30 µl/L).
- Apparatus
- Nitrogen‑flushed oven with controlled temperature and a nitrogen flow of about 15 oven volume changes per hour.
- Drying cabinet (30–40 °C) for two‑stage method, trays, weighing dishes with lids, precision balances (sensitivity 0.01 g and 0.001 g), flow meter, drying tower and cooling vessel.
- Sampling and sample size
- Single‑stage: sample crushed to pass 3.15 mm and divided to ~500 g; test portions ~10 g in weighing dish.
- Two‑stage: initial crush to 20 mm, divide to 2 kg for air drying, then crush to 3.15 mm for residual drying.
- Calculations and precision
- Moisture expressed as mass percent from loss in mass (equations provided).
- Precision limits: repeatability for total moisture 0.5% and reproducibility critical difference 1.2%.
- Annex A
- Guidance on nitrogen purification (e.g., reduced copper train) and passing nitrogen through desiccant to remove residual moisture.
Practical applications and users
ISO 5068-1:2007 is used by:
- Coal testing laboratories and quality control units in mining and power generation
- Fuel traders and shipping/receiving laboratories for contract verification
- Research institutions studying brown coal and lignite properties
- Certification bodies and regulatory laboratories assessing coal moisture for combustion, handling, and calorific calculations
The standard supports accurate, repeatable moisture determination critical for energy content calculation, combustion performance, transport fees and compliance reporting.
Related standards
- ISO 5068-2 - Indirect gravimetric method for moisture in the analysis sample (companion part)
- ISO 5069-2 - Sample preparation for determination of moisture content and general analysis
- ISO 1213-2 - Vocabulary: terms relating to sampling, testing and analysis
Keywords: ISO 5068-1:2007, brown coals, lignites, moisture content, indirect gravimetric method, total moisture, nitrogen‑flushed oven, two‑stage drying, coal testing.