ISO 5068-1:2025

Overview

ISO 5068-1:2025 - "Brown coals and lignites - Determination of moisture - Part 1: Indirect gravimetric method for total moisture" specifies laboratory procedures to measure the total moisture of brown coals and lignites. The document defines two indirect gravimetric procedures: a single-stage nitrogen‑flushed drying method and a two-stage method (air‑dry stage followed by nitrogen drying). This second edition updates terms, references and the test report and replaces ISO 5068-1:2007.

Key Topics and technical requirements

• Methods covered:
  • Single-stage method: finely prepared sample dried to constant mass at 105 °C to 110 °C in a nitrogen atmosphere.
  • Two-stage method: coarse sample air‑dried (ambient or 30–40 °C), then crushed and dried at 105–110 °C under nitrogen to determine residual moisture; total moisture is the sum of both losses.
• Atmosphere & gases: use high‑purity dry nitrogen with maximum oxygen ≤ 30 µl/l; nitrogen flow through the oven ≈ 15 oven volumes per hour.
• Apparatus & materials: nitrogen‑flushed oven, drying cabinet (30–40 °C), non‑corrodible trays/dishes, balances sensitive to 0.01 g and 0.001 g, and drying tower packed with magnesium perchlorate or silica gel (magnesium perchlorate is a strong oxidizer - safety warning included).
• Sample preparation & sizes: single‑stage sample crushed to pass 3.15 mm sieve and divided to 500 g; two‑stage coarse crush to pass 20 mm and divided to 2 kg (or as specified by particle-size rules).
• End‑point criteria: constant mass defined by successive mass changes < 0.01 g (single‑stage) or air‑dry change < 0.3 % of original mass over 2 h (two‑stage).
• Precision & reporting: the standard includes precision data (repeatability, reproducibility) and required test report details.

Applications

• Quality control and specification testing for coal producers and suppliers.
• Fuel characterization for power plants, boiler operators and gasification facilities.
• Regulatory compliance, trade, and contract verification where moisture affects energy content and pricing.
• Research and laboratory method validation in coal analysis laboratories.

Who should use this standard

• Coal testing laboratories and technicians
• Power generation and utility fuel analysts
• Coal mining and processing quality engineers
• Standards and compliance officers, and researchers in fuel characterization

Related standards

• ISO 1213‑2 - Coal and coke - Vocabulary (terms relating to sampling, testing and analysis)
• ISO 13909‑4 - Coal and coke - Mechanical sampling - Preparation of test samples
• ISO 18283 - Coal and coke - Manual sampling

Keywords: ISO 5068-1:2025, brown coals, lignites, moisture determination, indirect gravimetric method, nitrogen‑flushed oven, single‑stage, two‑stage, laboratory testing, coal moisture.