🔥 Determination of gross calorific value and calculation of net calorific value of solid fuels — PN-ISO 1928

Petrochemistry PN-ISO 1928

Overview

THIS IS AN ENTRY ABOUT A PAIR OF QUANTITIES THAT MUST NOT BE CONFUSED: THE GROSS CALORIFIC VALUE IS MEASURED, THE NET CALORIFIC VALUE IS CALCULATED. The regulation on methods of testing the quality of solid fuels says this directly in item 5.2 of the annex: "Wartość opałową wylicza się w oparciu o oznaczone ciepło spalania pomniejszone o ciepło parowania wody wydzielonej podczas spalania paliwa i powstałej z wodoru zawartego w paliwie." [The net calorific value is calculated on the basis of the determined gross calorific value reduced by the heat of vaporisation of the water released during the combustion of the fuel and formed from the hydrogen contained in the fuel.] The difference between these two numbers is the heat carried away by water vapour. In the bomb calorimeter the water condenses and its heat of vaporisation remains in the result — hence the gross calorific value. In a furnace the water escapes with the gases as vapour and does not give up this heat — hence the net calorific value, which is always lower. A report giving one number without naming which of the two it is, is unusable.

THE THING THAT MAKES THIS ENTRY UNUSUAL: A LEGAL ACT KEEPS IN USE A STANDARD WITHDRAWN BY PKN — AND KNOWS IT. Finding checked on 22-09-2026 against the source texts: • PN-G-04513:1981 "Paliwa stałe — Oznaczanie ciepła spalania i obliczanie wartości opałowej" [Solid fuels — Determination of gross calorific value and calculation of net calorific value] was WITHDRAWN on 17-12-2012. Its catalogue card does NOT indicate a replacing standard — it is a standard withdrawn without a successor. • The Regulation of the Minister of Energy on methods of testing the quality of solid fuels (consolidated text: Journal of Laws 2021 item 1366) indicated in item 5.3 of the annex: "Sposób wykonania oznaczenia, sposób przygotowania próbki analitycznej, stosowane odczynniki, rodzaj stosowanej aparatury, kalibrację aparatury, sposób obliczenia i podawania wyników, a także precyzję metody określa norma PN-ISO 1928:2002 albo PN-G-04513:1981." [The method of performing the determination, the method of preparing the analysis sample, the reagents used, the type of apparatus used, the calibration of the apparatus, the method of calculating and reporting the results, as well as the precision of the method, are specified by the standard … or ….] • The amending regulation of 7 December 2023 (Journal of Laws 2023 item 2661), in force since 9 December 2023, gave this item a new wording: "w pkt 5.3 wyrazy »PN-ISO 1928:2002 albo PN-G-04513:1981« zastępuje się wyrazami »PN-ISO 1928:2002, PN-G-04513:1981 albo PN-ISO 1928:2020-05«" [w pkt = in item; wyrazy … zastępuje się wyrazami … = the words … are replaced by the words …; albo = or]. WHAT FOLLOWS FROM THIS AND WHY IT IS NOT AN OVERSIGHT: the legislator OPENED this item in December 2023 to add a newer standard to it — and in the same act LEFT both older standards in it, including one withdrawn eleven years earlier. If it were an oversight, the item would have remained untouched; here it was amended, and there was no deletion. FOR A READER WITH AN ACCREDITATION SCOPE THIS MEANS: a line citing PN-G-04513:1981 is not an error. The standard has been withdrawn from the collection of Polish Standards, but it is indicated in a legal act in force as one of three permissible bases for testing the quality of solid fuels. This is the reverse of the situation we usually describe — where a standard falls out of use and the legal act describes only the activity.

A MEASUREMENT ON ACCREDITATION SCOPES CONFIRMS THAT THIS IS NOT A PAPER CASE (state on 22-09-2026). The standard withdrawn in 2012 is cited by 27 entries ON ITS OWN and by 29 further entries together with PN-ISO 1928:2020-05; the current standard alone — by 54 entries. A laboratory that has "PN-81/G-04513" in its scope is therefore neither an exception nor a mistake: it is one of several dozen. A NOTE ON THE FORM OF THE NUMBER, BECAUSE IT MAKES SEARCHING HARDER: accreditation scopes write this standard as PN-81/G-04513 — in the old scheme, with the abbreviated year at the front — and the PKN catalogue card as PN-G-04513:1981. It is the same document; anyone searching for the form on the card will not find a single entry in the scopes. WHAT JOINT CITATION MEANS HERE — AND WHY NOT THE SAME AS ELSEWHERE. The distribution of methodologies when both standards are cited at once is EXACTLY THE SAME as when one is cited: "Ciepło spalania" [gross calorific value] and "Wartość opałowa (z obliczeń)" [net calorific value (calculated)]. There is thus no division of activities between the documents here — there is an indication of two EQUIVALENT bases for the same test. This distinguishes this case from joint citation in the determination of hydrogen fluoride (ISO 15713 with CEN/TS 17340), where DIFFERENT methodologies appear with two documents than with one, because each of them is responsible for a different activity. **The mere juxtaposition of two numbers in a scope line therefore does not say whether it is a division of work or an alternative — only a comparison of the methodologies decides.**

WHAT APPLIES TODAY — THREE DOCUMENTS, EACH IN A DIFFERENT STATE: • PN-ISO 1928:2020-05 (English-language version), implements ISO 1928:2009 [IDT], 68 pages, published 28-05-2020 — a CURRENT standard, not withdrawn; • PN-ISO 1928:2002 (Polish-language version), implemented ISO 1928:1995 [IDT] — WITHDRAWN 28-05-2020, replaced by the 2020-05 edition, but still indicated in item 5.3 of the regulation; • PN-G-04513:1981 — WITHDRAWN 17-12-2012, without a successor on the card, still indicated in item 5.3 of the regulation. A laboratory therefore has a choice among three documents, of which only one is a current Polish Standard — and all three comply with the provision.

PRINCIPLE OF MEASUREMENT, QUOTED FROM THE SCOPE OF THE CURRENT STANDARD: the method is defined as the determination of the gross calorific value of a solid fuel "w stałej objętości i w temperaturze odniesienia 25 °C, w bombie kalorymetrycznej wykalibrowanej przez spalenie certyfikowanego kwasu benzoesowego" [at constant volume and at a reference temperature of 25 °C, in a bomb calorimeter calibrated by the combustion of certified benzoic acid]. The result obtained is the gross calorific value of the analysis sample at constant volume, INCLUDING the water in liquid form contained in the combustion products. The standard goes on to explain why one passes from this result to another quantity: "W praktyce paliwo spala się przy stałym (atmosferycznym) ciśnieniu, a wody nie skrapla się, lecz usuwa jako parę wraz z gazami spalinowymi. W tych warunkach wytworzone ciepło spalania jest wartością opałową paliwa przy stałym ciśnieniu." [In practice, fuel is burned at constant (atmospheric) pressure, and the water is not condensed but removed as vapour together with the flue gases. Under these conditions, the heat of combustion released is the net calorific value of the fuel at constant pressure.] The standard gives formulas for calculating the net calorific value both at constant pressure and at constant volume.

TWO REQUIREMENTS THAT DECIDE THE RELIABILITY OF THE RESULT. The first: calibration of the calorimeter by burning CERTIFIED benzoic acid — a requirement repeated both in the standard and in the regulation (item 5.1: a bomb "skalibrowana w oparciu o testy spalania wzorcowego kwasu benzoesowego" [calibrated on the basis of combustion tests of reference benzoic acid]). The second: the distinction between types of calorimeters — the standard describes the general principles and calibration procedures in the main text, and the arrangements specific to particular types of calorimeters in Annexes A–C, with checklists in Annex D.

WHAT WE DO NOT GIVE IN THIS ENTRY. We do not give any of the calculation formulas, the precision values of the method or the details of the procedures for particular types of calorimeters. We did not have the text of any of the three standards — the description of the method comes from the scopes given in the PKN catalogue cards and from items 5.1–5.3 of the annex to the regulation, that is, from sources that describe the method but do not contain it. Nor do we state how PN-G-04513:1981 differs in execution from PN-ISO 1928 — we have not checked this, and the provision places them side by side as equivalent.

SCALE OF CITATIONS — A MEASUREMENT ON THE DATABASE OF ACCREDITATION SCOPES (reading of 23-09-2026, matching by the BEGINNING of the notation "PN-ISO 1928", that is, the way the "Laboratories" tab searches for this entry): 69 entries at 43 laboratories.

Method principle

A weighed analysis sample of the fuel is burned in an oxygen atmosphere in a constant-volume bomb immersed in the calorimeter. From the temperature rise and the heat capacity of the system — determined beforehand by burning certified benzoic acid — the gross calorific value at the reference temperature of 25 °C is calculated, including the water condensed in the combustion products. The net calorific value is calculated from the gross calorific value by subtracting the heat of vaporisation of the water released from the fuel and formed by the combustion of the hydrogen it contains.

Applications

• Testing the quality of solid fuels placed on the market — a test performed on the basis of the regulation on methods of testing the quality of solid fuels
• Hard coal and brown coal, including commercial size grades (cobbles, nuts, peas, eco-peas, eco-fines, anthracite)
• Solid fuels from biomass and waste — as a determination of energy value
• Commercial settlement of fuel deliveries — price related to the net calorific value
• Emission reporting and energy balance calculations, where the net calorific value is an input quantity
• Assessment of a fuel against the requirements for heating appliances

Key parameters

Standard

Standard number

PN-ISO 1928:2020-05 (wersja angielska; wprowadza ISO 1928:2009 [IDT])

Title (PL)

Paliwa stałe — Oznaczanie ciepła spalania metodą spalania w bombie kalorymetrycznej i obliczanie wartości opałowej

Title (EN)

Solid mineral fuels — Determination of gross calorific value by the bomb calorimetric method and calculation of net calorific value

Step-by-step procedure

1. Preparation of the analysis sample

   The sample is prepared in the manner specified by the chosen standard. The provision expressly leaves this activity to the standard — it does not describe it itself.

2. Calibration of the calorimeter

   The heat capacity of the system is determined by burning certified benzoic acid. This requirement is also repeated by the regulation.

3. Weighing the sample and preparing the bomb

   The weighed sample is placed in the crucible, the firing wire is attached, water is introduced into the bomb, and the bomb is filled with oxygen under pressure.

4. Combustion

   The bomb is placed in the calorimeter and ignited, and the course of the temperature is recorded.

5. Determination of the gross calorific value

   From the temperature rise and the heat capacity of the system, the gross calorific value at constant volume is calculated at the reference temperature of 25 °C, taking corrections into account — among others for the heat of combustion of the firing wire and for the acids formed.

6. Calculation of the net calorific value

   The heat of vaporisation of the water released during the combustion of the fuel and formed from the hydrogen it contains is subtracted from the gross calorific value. The standard gives formulas for the net calorific value at constant pressure and at constant volume; the choice depends on what the result is to be used for.

7. Reporting the result with the quantity and the state of the fuel named

   The report decides whether the gross or the net calorific value is given, under what conditions (constant volume or constant pressure) and to what state of the fuel the result is referred. The number in megajoules per kilogram alone does not decide any of these three things.

8. Indicating the reference document

   It is indicated according to which of the three standards permitted by item 5.3 the determination was performed. Since two of them have been withdrawn from the collection of Polish Standards, a bare "according to PN" is not enough — the number together with the year is needed.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The bomb works under high oxygen pressure — a leak or overloading with sample risks rupture; the permissible sample mass and filling pressure are specified by the standard and the manufacturer's instructions
• Pressurised oxygen in contact with organic substances, oil or grease creates an ignition hazard — keep threads and valves free of grease
• After combustion, the inside of the bomb contains gases under pressure and the nitric and sulphuric acids formed — release the pressure slowly; handle the rinsing and the washings as corrosive reagents
• Samples of pulverised fuels are flammable and make the workstation dusty — prepare samples with local exhaust ventilation
• The oxygen cylinder must be secured and is subject to separate storage rules; the pressure regulator is intended for oxygen only
• Benzoic acid used as a standard is an irritant — handle it as a reagent, despite its role as a standard

Frequently asked questions