Overview
ISO 5068-2:2007 specifies an indirect gravimetric method for determining the moisture content of the analysis sample of brown coals and lignites. The method measures mass loss of a weighed test portion dried under controlled conditions (105 °C to 110 °C) in a nitrogen atmosphere and is intended for routine laboratory moisture analysis of hygroscopic brown coal and lignite samples.
Key topics and technical requirements
- Principle: Moisture is calculated from the loss in mass of an analysis sample dried to constant mass in a nitrogen‑purged oven.
- Temperature and atmosphere: Oven control between 105 °C and 110 °C with a dry, high‑purity nitrogen atmosphere (oxygen ≤ 30 µl/l).
- Nitrogen flow: Recommended flow to provide approximately 15 oven‑volume changes per hour; Annex A describes a nitrogen purification train (reduced copper at ≈ 500 °C) or the use of commercial nitrogen meeting the oxygen limit.
- Sample and sample prep: Analysis sample prepared per ISO 5069-2; typically ground to pass a 0.212 mm sieve. Test portion: 1–2 g spread so layer mass does not exceed specified limits.
- Apparatus: Sensitive balance (0.001 g resolution), shallow silica/glass weighing dish with well‑fitting lid, flow meter, drying tower with desiccant and a cooling vessel/desiccator.
- Reagents and safety: Desiccants such as magnesium perchlorate or silica gel are recommended; note hazard warning for magnesium perchlorate (strong oxidizer).
- Procedure and timing: Weigh before and after drying; dry for 3 h or until constant mass. Cool covered dish on a metal plate (≤ 5 min), then to room temperature (≈ 20 min) before final weighing.
- Expression and precision: Moisture (%) calculated from mass differences; report mean of duplicate determinations to 0.1%. Repeatability: duplicate results in same lab/operator should not differ by more than 0.3%.
- Reporting: Include sample identification, standard reference, result and expression method, and test date.
Applications and users
ISO 5068-2 is used where accurate moisture determination of brown coal and lignite analysis samples is required:
- Analytical laboratories performing proximate and ultimate coal analyses (moisture, volatile matter, calorific value, C/H).
- Power generation and coal handling facilities for quality control and fuel accounting.
- Coal producers and trading operations needing standardized moisture reporting.
- Research laboratories and regulatory bodies assessing fuel properties.
Keywords: brown coal moisture determination, lignite moisture analysis, ISO 5068-2, indirect gravimetric method, nitrogen oven, coal testing laboratories.
Related standards
- ISO 5068-1 - Indirect gravimetric method for total moisture (companion part).
- ISO 5069-2 - Sample preparation for moisture determination and general analysis.
- ISO 1213-2 - Vocabulary for sampling, testing and analysis (definitions).
Open preview (PDF)Brown coals and lignites — Determination of moisture content — Part 2: Indirect gravimetric method for moisture in the analysis sample
