🔥 Moisture in the general analysis test sample of coke — gravimetric method, drying 1 g in air at 120–200 °C to constant mass; PN-ISO 687

Petrochemistry PN-ISO 687:

Overview

WHAT THE STANDARD COVERS. ISO 687:2010 (clause 1): a method for determining the moisture in the general analysis test sample of coke; it is applicable to blast-furnace coke, foundry coke and other products of high-temperature carbonization. According to the introduction, the determination is needed to correct the results of some determinations (e.g. volatile matter and hydrogen) for the effect of water and to convert all results to the dry basis. Coke is hygroscopic — its moisture varies with the humidity of the air — therefore the moisture is determined whenever samples are weighed for other analyses; if they are weighed at the same time, a single simultaneous moisture determination is sufficient. The "Scope" field of the PKN card of PN-ISO 687:2005, in full (our translation): "A method is specified for determining the moisture content in the analysis sample of coke. It is applicable to the determination of the moisture content of blast-furnace coke, foundry coke and other products of high-temperature carbonization" (without a full stop on the card).

WHICH TEXT WE READ. PN-ISO 687:2005 introduces ISO 687:2004 (second edition). We did not have the text of the 2004 edition; we read in full the third edition, ISO 687:2010, which according to its foreword is a MINOR revision of the 2004 edition — the description of the procedure below comes from the 2010 edition, and we do not know the differences between 2004 and 2010. The earlier Polish standard, PN-ISO 687:2002 (introduced ISO 687:1974, withdrawn on 22-09-2005), according to the "Scope" field of its card, dried coke in air at 190–210 °C.

PROCEDURE (ISO 687:2010, clauses 4–9 — full text of the standard read). Principle: a known mass of coke is heated in air at 120–200 °C to constant mass; the moisture is calculated from the loss in mass; under these conditions coke does not oxidize. Apparatus: analytical balance with a reading accuracy of 0.1 mg; oven adjustable in the range 120–200 °C with the possibility of a flow of air or nitrogen; flat weighing vessel of glass or corrosion-resistant metal with a well-fitting lid, large enough for the coke layer not to exceed 0.20 g/cm²; cooling vessel, e.g. a desiccator WITHOUT desiccant, with a porcelain or metal plate (preferably aluminium or copper). Sample: general analysis test sample of coke (ISO 1213-2) in moisture equilibrium with the laboratory atmosphere (if necessary spread in a thin layer for the minimum time required), mixed for at least 1 min, preferably mechanically. Determination: weigh the clean, dry vessel with its lid to the nearest 0.1 mg, add 1 g ± 0.1 g of coke in an even layer, weigh; dry uncovered at 120–200 °C; after drying cover immediately (if possible while still in the oven), cool for 10 min on a thick metal plate, then in the cooling vessel to room temperature and weigh. If there is doubt as to whether drying is complete — further periods of 30 min until the change in mass between weighings does not exceed 1 mg. The drying time needed to reach constant mass in a given oven shall be checked experimentally; note 2: 4 h is usually sufficient. The determination can be shortened considerably by drying at 320 °C in a nitrogen atmosphere (1 h is usually sufficient; a minimum-free-space oven may be used); if necessary, drying can be carried out at a lower temperature, e.g. at 105–110 °C as for hard coal — the time to constant mass shall then be checked experimentally. Result: moisture in the general analysis test sample in percent by mass = (m2 − m3) / (m2 − m1) × 100, where m1 — mass of the vessel with lid, m2 — with coke before drying, m3 — after drying; the mean of two determinations is reported to the nearest 0.1 %. Repeatability limit: 0.2 % (absolute value); the standard does not give a reproducibility limit, because humidity conditions differ between laboratories.

EDITION 2024 (ISO 687:2024, foreword and table of contents). The fourth edition (15.03.2024) replaced ISO 687:2010 as a technical revision; the main change: addition of the optional use of nitrogen and of a minimum-free-space oven (in the 2010 edition drying at 320 °C in nitrogen, also in such an oven, was already described in clause 7 as a way of shortening the determination). The table of contents has a new clause "Reagents" and an informative Annex A with an example of an oven for drying in nitrogen. The title reads "Coke — Determination of moisture in the general analysis test sample" (without "Solid mineral fuels"), and committee ISO/TC 27 is now called "Coal and coke". The scope of the 2024 edition according to the iTeh catalogue card (read on 10.10.2026) is worded the same as in the 2010 edition. We did not have the content of clauses 2–11 of the 2024 edition.

STATUS (state of the PKN cards on 10.10.2026). The card of PN-ISO 687:2005 (Polish version) carries no withdrawal label: title "Paliwa stałe -- Koks -- Oznaczanie wilgoci w próbce do badań do analizy ogólnej" (Solid mineral fuels — Coke — Determination of moisture in the general analysis test sample; our translation), publication 22-09-2005, 8 pages, Mining Sector, KT 144 Coke and Processed Solid Fuels, "Replaces: PN-ISO 687:2002 - Polish version", "Introduces: ISO 687:2004 [IDT]", ICS 75.160.10. The card of PN-ISO 687:2002 ("Koks z węgla kamiennego -- Oznaczanie zawartości wilgoci w próbce analitycznej", Hard-coal coke — Determination of moisture content in the analysis sample; our translation): withdrawn on 22-09-2005, replaced by PN-ISO 687:2005, introduced ISO 687:1974. PKN has not adopted the editions ISO 687:2010 and ISO 687:2024 (PKN search engine, query "ISO 687", 10.10.2026: only these two cards with the number 687).

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database of 10.10.2026 and current PCA documents read on 10.10.2026). The number 687 as a standard appears in 11 records at 8 laboratories: AB 079, AB 081, AB 103, AB 300 (3 records), AB 313 (2), AB 687, AB 914 and AB 1913; the standard is present in all 8 current PCA documents, no entry is suspended. Forms: "PN-ISO 687:2005" — all laboratories; AB 313 additionally gives "ISO 687:2024" next to it (in both records), AB 103 — "ISO 687:2024-03". The "Laboratories" tab searches for "PN-ISO 687:" (with a colon) and shows the same 8 laboratories; without the colon a laboratory with the standard PN-ISO 6878 (phosphorus in water) would be added.

WHAT THE LABORATORIES TEST (copy and PCA documents). "Moisture content in the analysis sample" by the gravimetric method, subject: coke, hard-coal coke; AB 313 also applies the standard to petroleum coke. Measuring ranges are given by each of the eight laboratories — from 0.1–1.0 % (AB 300, one of its three entries) to 0.10–20.0 % (AB 687); for petroleum coke AB 313 has 0.1–2.4 %. AB 300 has the standard in one entry together with PN-80/G-04511 and PN-G-04611:2020-06, AB 313 — together with PN-G-04611:2020-06, ISO 687:2024 and ASTM D 3173-17a.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — a sample not in equilibrium with the laboratory air: moisture determined earlier (or later) than the samples for other analyses does not correct their results properly, because coke absorbs moisture from the air; the standard requires it to be determined at every weighing. Second — a desiccator with desiccant: the standard provides for a cooling vessel WITHOUT desiccant. Third — shortened drying: 4 h is a value that is usually sufficient, not a rule; constant mass (change not greater than 1 mg) has to be demonstrated for the given oven. Fourth — a subject outside the scope: the text of the standard lists blast-furnace coke, foundry coke and other products of high-temperature carbonization; petroleum coke (AB 313) is not on this list — the application should be described in the report. Fifth — a result "as analysed" is the moisture of the analysis sample, not the total moisture of coke (PN-ISO 579, a separate entry in this database).

WHAT WE DO NOT GIVE. We did not have the content of the 2024 edition beyond the foreword, introduction and table of contents — we do not give the conditions for drying in nitrogen according to that edition, the description of the oven in Annex A or any changes to the repeatability limit.

Method principle

A known mass of the general analysis test sample of coke (1 g ± 0.1 g) is dried in air at 120–200 °C to constant mass (change not greater than 1 mg after a further 30-minute drying); the moisture is the loss in mass related to the mass of the sample, in percent (ISO 687:2010, clauses 4, 7, 8). Under these conditions coke does not oxidize. Drying can be shortened at 320 °C in nitrogen (usually 1 h).

Applications

• Blast-furnace coke, foundry coke and other products of high-temperature carbonization (ISO 687:2010, clause 1)
• Conversion of the results of other determinations (e.g. volatile matter, hydrogen) to the dry basis — moisture is determined at every weighing of samples for analysis
• In the accreditation scopes: 8 laboratories; one also applies the standard to petroleum coke

Key parameters

Standard

Standard number

PN-ISO 687:2005 (wersja polska; wprowadza ISO 687:2004 [IDT])

Title (PL)

Paliwa stałe — Koks — Oznaczanie wilgoci w próbce do badań do analizy ogólnej

Title (EN)

Solid mineral fuels — Coke — Determination of moisture in the general analysis test sample (ISO 687:2010; 2024 edition: Coke — Determination of moisture in the general analysis test sample)

Step-by-step procedure

1. Sample preparation

   General analysis test sample of coke in moisture equilibrium with the laboratory atmosphere (if necessary spread in a thin layer); mix for at least 1 min, preferably mechanically.

2. Weighing

   Weigh the clean, dry vessel with its lid (0.1 mg), add 1 g ± 0.1 g of coke in an even layer and weigh again.

3. Drying

   Uncovered vessel in the oven at 120–200 °C (4 h is usually sufficient; check the time to constant mass for the given oven). Shortened variant: 320 °C in nitrogen, usually 1 h.

   🌡 Temperature: 120–200 °C (air) or 320 °C (nitrogen)

4. Cooling and weighing

   Cover immediately, cool for 10 min on a thick metal plate, then in the cooling vessel to room temperature; weigh to the nearest 0.1 mg. With a cooling vessel with a flow of air or nitrogen, the vessel can be transferred directly.

   ⏱ Time: 10 min on the plate + to room temperature

5. Constant mass

   If in doubt, continue drying in periods of 30 min until the change in mass does not exceed 1 mg.

6. Result and report

   Moisture = (m2 − m3)/(m2 − m1) × 100 %; mean of two determinations to the nearest 0.1 %; repeatability 0.2 %. Report: reference to the standard, sample identification, result, date of the determination. PN-ISO 687:2005 current (state of the PKN card on 10.10.2026).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Oven at 120–200 °C (and 320 °C in the shortened variant) — gloves and tongs for the vessels
• Working with nitrogen in a closed room — ventilation (risk of oxygen deficiency)
• NOTE ON SUBSTANCE: cooling vessel without desiccant; determine moisture at every weighing of samples for other analyses

Frequently asked questions