⚖️ Moisture, volatile matter and ash in solid fuels — thermogravimetric analyser — PN-G-04560

Petrochemistry PN-G-04560

Overview

SCOPE FROM THE PKN CATALOGUE CARD, QUOTED VERBATIM (our translation): "A method is specified for the determination of the content of moisture, volatile matter and ash in solid fuels with an automatic thermogravimetric analyser. The principle, reagents and materials used, apparatus, preparation of the test sample and preparation of the analyser, the procedure of determination, the precision of the method and the final result are given."

THREE QUANTITIES IN ONE RUN — THIS IS THE POINT OF THIS STANDARD. Classically, each of these determinations is carried out separately: moisture by drying, volatile matter by heating in a covered crucible without access of air, ash by incineration in a muffle furnace. The thermogravimetric analyser carries out these three stages one after another on the same test portion, weighing it during the process and changing the furnace atmosphere. For the laboratory this means a shorter time and less sample consumption, and for the accreditation scope — one citation of the standard covering three determinations.

VOLATILE MATTER IS A CONVENTIONAL QUANTITY, NOT A CONSTITUENT OF THE FUEL. This distinction decides whether the result is correct. There is no substance in coal called "volatile matter" — there is an agreed loss of mass on heating under strictly defined conditions: temperature, time and without access of air. Changing any of these conditions changes the result, and results obtained under different conditions are not comparable. That is why, for this quantity, compliance with the conditions of the standard is not a formality.

WHY THE ATMOSPHERE MUST CHANGE DURING THE CYCLE. Drying and the determination of volatile matter must proceed without access of air, so that the sample does not oxidise or burn; incineration, on the contrary, requires oxygen, because it is precisely the combustion of the combustible matter that leaves the ash. The analyser achieves this by switching the gas in the chamber. We do not give the requirements for gases, temperatures and times, because we did not have the text of the standard.

THE MOISTURE OF THIS STANDARD IS NOT TOTAL MOISTURE. The determination is carried out on the analysis sample, not on the coal in the as-received state. Total moisture — the quantity used in commercial settlements and in conversions to the as-received (working) state — is determined according to a separate document, described in this database under PN-ISO 589. Entering the analyser result in the "total moisture" field is a substantive error, not a rounding.

THE DOCUMENT IS STILL IN THE COLLECTION, DESPITE ITS AGE. The standard dates from 1998 and replaced the 1992 edition. The PKN catalogue card has no "Withdrawn" heading and no "Withdrawal date" line — the document therefore remains in the collection of Polish Standards and citing it in an accreditation scope is correct.

WHAT IT IS MEASURED WITH IN PRACTICE. The Department of Solid Fuels Quality Assessment of the Central Mining Institute (Główny Instytut Górnictwa) lists the same apparatus for the determination of moisture in the analysis sample, ash and volatile matter: TGA and MAC 500 thermogravimetric analysers. This confirms that in Polish practice these three quantities are indeed obtained from one instrument and one cycle, not from three separate determinations. The same department CALCULATES total moisture from free moisture and moisture in the analysis sample — i.e. the result from the analyser described in this standard is sometimes a component of a calculation, not a separate final result. WHAT WE DO NOT GIVE. We did not have the text of the standard. WE DO NOT GIVE: the temperatures or times of any of the three stages, the particle size and mass of the test portion, the type and flow of gases, the requirements for crucibles, the method of preparing the analyser or precision values. The card states that the standard contains this information — but does not quote it, and we do not guess.

SCALE OF CITATIONS — MEASUREMENT IN THE ACCREDITATION SCOPE DATABASE (read on 23-09-2026, matching by the BEGINNING of the notation "PN-G-04560", i.e. the way the "Laboratories" tab of this entry searches): 96 entries at 36 laboratories.

Method principle

A weighed sample of fuel is placed in a thermogravimetric analyser, which heats it according to a programmed course while weighing it. In the first stage, in an oxygen-free atmosphere and at a lower temperature, water evaporates — the loss of mass gives the moisture. In the second, at a higher temperature and still without access of air, products of thermal decomposition are released — the loss of mass gives the volatile matter. In the third, after air has been introduced, the combustible matter burns and the residue is the ash. We do not give the conditions of each stage — they are in the text of the standard.

Applications

• Proximate analysis of hard coal and lignite in power generation
• Quality control of solid fuels in deliveries and trade
• Testing of coke and secondary fuels, if the documentation cites this standard
• Obtaining data for converting results to reference states
• Rapid in-process control in coal preparation plants

Key parameters

Standard

Standard number

PN-G-04560:1998 (wersja polska)

Title (PL)

Paliwa stałe — Oznaczanie zawartości wilgoci, części lotnych oraz popiołu analizatorem automatycznym

Title (EN)

Solid fuels — Determination of moisture, volatile matter and ash content by automatic analyser

Step-by-step procedure

1. Establishing which moisture is meant

   This standard gives moisture in the analysis sample. If the order concerns TOTAL moisture, the appropriate document is PN-ISO 589, not this standard.

2. Preparation of the analysis sample

   Crushing and dividing the sample in accordance with the standards on the preparation of solid fuel samples. WE DO NOT GIVE THE PARTICLE SIZE OR TEST PORTION.

3. Preparation of the analyser

   Checking the internal balance, the tightness of the chamber and the gas supply. The card lists this step as a separate clause of the standard; we do not give its content.

4. Running the cycle

   Three stages on the same test portion: drying, volatile matter, incineration, with switching of the atmosphere. WE DO NOT GIVE THE TEMPERATURES OR TIMES.

5. Quality control of the series

   Reference material in the series and repetition of the determination; permissible differences are given by the standard in the clause on precision.

6. Recording the result

   State the three quantities together with an indication of the reference state. A result without a reference state is unclear to the customer.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The analyser operates at high temperature — crucibles and the chamber remain hot long after the end of the cycle
• During the determination of volatile matter, products of thermal decomposition are released, including carbon monoxide and hydrocarbons — an efficient extraction system is required
• Coal dust is combustible and explosive in suspension — avoid dust formation when crushing and filling crucibles
• Secure pressurised gas cylinders against tipping over; inert gas displaces oxygen in the room
• Ash after incineration is often fine and easily raised as dust — remove carefully, after cooling

Frequently asked questions