⛽ Total moisture in hard coal — drying in nitrogen or in air — PN-ISO 589

Petrochemistry PN-ISO 589

Overview

SCOPE FROM THE PKN CATALOGUE CARD, QUOTED VERBATIM (our translation): "Two methods for the determination of total moisture in hard coal are given. The methods using a nitrogen atmosphere are suitable for all types of hard coal; the methods involving drying in air are suitable only for hard coal not susceptible to oxidation."

WHY THE CHOICE OF ATMOSPHERE IS NOT A TECHNICAL DETAIL. Coal dried in air at elevated temperature can oxidise. Oxidation changes the mass of the sample in the same measurement in which the loss of mass is interpreted as evaporated water — and the result stops measuring what it was meant to measure. The standard solves this not by a correction but by separating the fields of application: nitrogen for all coals, air only for those that do not oxidise. A laboratory accepting an order must therefore first establish what coal it is dealing with, and only then choose the way of determination.

TOTAL MOISTURE VERSUS MOISTURE IN THE ANALYSIS SAMPLE. These are two different quantities and two different documents. Total moisture, the subject of this standard, refers to the coal in the as-received state and is the basis for converting results to reference states and for commercial settlements. Moisture in the analysis sample is determined separately — in the knowledge base it is described by the entry on the determination of moisture, volatile matter and ash with an automatic analyser according to PN-G-04560. Confusing these two quantities is one of the more frequent errors in reports.

WHAT FOLLOWS FOR SETTLEMENTS. Total moisture enters the conversion of the calorific value to the as-received (working) state. Understated moisture raises the calculated calorific value of the fuel in the as-received state, overstated moisture lowers it. With deliveries counted in thousands of tonnes, a difference of the order of one percentage point translates into tangible money, which is why this standard is sometimes cited in contracts and not only in accreditation scopes.

RELATION TO THE INTERNATIONAL STANDARD. The Polish Standard adopts ISO 589:2003 as identical (IDT), which means that a result obtained according to PN-ISO 589 is a result according to ISO 589 — important for foreign deliveries and when comparing results between laboratories in different countries.

WHAT THIS LOOKS LIKE IN THE PRACTICE OF A LARGE COAL LABORATORY. The Department of Solid Fuels Quality Assessment of the Central Mining Institute (Główny Instytut Górnictwa) describes its proximate analysis in a way worth knowing before accepting an order: it determines FREE MOISTURE and MOISTURE IN THE ANALYSIS SAMPLE, and CALCULATES TOTAL moisture from these two quantities. The way to total moisture is therefore not always a direct measurement — it is sometimes a calculation from two separate determinations. For the client this means that the question "by what method was total moisture determined" is justified, and the answer is not always "by drying the sample in the as-received state". The same department analyses not only hard coal but also lignite, coke, semi-coke, briquettes, solid biofuels, solid recovered fuels and their mixtures with coal — whereas the scope of this standard covers HARD COAL only.

WHAT WE DO NOT GIVE. We did not have the text of the standard — PKN sells it (12 pages, ICS 73.040). That is why WE DO NOT GIVE: drying temperatures, drying times, sample masses, sample particle size, nitrogen flow, constant mass criteria or precision values. The catalogue card gives only the distinction between the two methods quoted above, and this distinction is the content of this entry.

SCALE OF CITATIONS — MEASUREMENT IN THE ACCREDITATION SCOPE DATABASE (read on 23-09-2026, matching by the BEGINNING of the notation "PN-ISO 589", i.e. the way the "Laboratories" tab of this entry searches): 120 entries at 45 laboratories.

Method principle

The determination consists in drying a weighed sample of coal at elevated temperature and determining the loss of mass, which is attributed to evaporated water. The standard provides two ways differing in the drying atmosphere: in nitrogen — for any hard coal, and in air — only for coal not susceptible to oxidation, in which drying does not change the mass of the sample in any way other than by evaporation of water. The standard does not make the drying conditions available in the catalogue card, and we do not give them in this entry.

Applications

• Commercial settlements of hard coal deliveries — total moisture as the basis for conversions
• Conversion of the calorific value to the as-received (working) state of the fuel
• Quality control of coal in utility and industrial power generation
• Testing of coal before processing and beneficiation
• Assessment of the conformity of deliveries with the terms of the contract or specification

Key parameters

Standard

Standard number

PN-ISO 589:2006 (wersja polska; wprowadza ISO 589:2003 [IDT])

Title (PL)

Węgiel kamienny — Oznaczanie wilgoci całkowitej

Title (EN)

Hard coal — Determination of total moisture

Step-by-step procedure

1. Establishing whether the coal is susceptible to oxidation

   This decides the choice of method: for coal susceptible to oxidation only the variant in a nitrogen atmosphere may be used. The chosen variant should be recorded.

2. Distinguishing the measured quantity

   Check whether the order concerns TOTAL moisture (this standard) or moisture in the analysis sample (a different document). Confusing these quantities changes the result and its use.

3. Sample preparation

   The sample is prepared in accordance with the requirements of the standards on sampling and sample preparation of coal. WE DO NOT GIVE THE PARTICLE SIZE OR SAMPLE MASS — they are in the text of the standard.

4. Drying

   Drying in the chosen atmosphere. WE DO NOT GIVE THE TEMPERATURE, TIME OR CONSTANT MASS CRITERION.

5. Cooling and weighing

   Cooling in a desiccator and weighing; the loss of mass is attributed to evaporated water.

6. Entry in the report

   State the total moisture and the variant of the method (nitrogen or air). Without stating the variant, the customer does not know whether the result is reliable for coal susceptible to oxidation.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Nitrogen is an asphyxiant gas — it displaces oxygen; a room with a cylinder requires ventilation and, for larger quantities, an oxygen sensor
• Secure pressurised cylinders against tipping over, keep pressure regulators in working order
• Coal dust is combustible and explosive when suspended in air — avoid dust formation, do not use open flames during crushing
• Hot dishes and oven — risk of burns, tongs and heat-resistant gloves are mandatory
• Fine coal dust irritates the respiratory tract — crushing under extraction

Frequently asked questions