🔩 Moisture in the analysis sample of solid recovered fuels (SRF) — oven dry method at 105 °C
In short
Drying of at least 1 g of the general analysis sample (≤ 1 mm) in a dish with a lid in a drying oven at (105 ± 2) °C in an atmosphere of air or of nitrogen to constant mass (a change of ≤ 1 mg in 60 min), weighing to a resolution of 0. The test is performed according to PN-EN ISO 21660-3:2021-08 (ISO 21660-3:2021); Temperature: (105 ± 2) °C; air or nitrogen (oxidising materials); alternatively 50 ± 10 °C for longer. The procedure comprises 6 steps; it is used for: Conversion of the results of analyses of SRF (calorific value, ash, C, N, S, Cl, metals) to the dry state — settlements in cement works, combined heat and power plants and incineration plants, Characterisation of waste-derived fuels (RDF/SRF) for classification in accordance with ISO 21640 and for the purposes of the EU ETS and of KZR, Quality control of the production of SRF in waste treatment plants.
At a glance
- Standard: PN-EN ISO 21660-3:2021-08 (ISO 21660-3:2021)
- Category: Materials and NDT
- Procedure steps: 6
- Temperature: (105 ± 2) °C; air or nitrogen (oxidising materials); alternatively 50 ± 10 °C for longer
- Sample: ≥ 1 g of the general analysis sample ≤ 1 mm (ISO 21646), layer ≤ 0.2 g/cm²; a minimum of 2 determinations
- Constant mass: a change of ≤ 1 mg over a further 60 min; usually 2–3 h of drying
Overview
ISO 21660-3:2021 specifies a method for the determination of the moisture in the general analysis sample by drying in a drying oven; it is applied to general analysis samples in accordance with CEN/TS 15414-1 and to all solid recovered fuels (SRF). If the fuel contains large amounts of oil fractions, the Karl Fischer method is recommended (e.g. ISO 760); in other cases — a lower temperature (e.g. 50 ± 10 °C) and a longer drying to constant mass. The term "moisture content" may be misleading, because recovered materials (e.g. biomass) contain variable amounts of volatile (extractive) substances, which may evaporate during the drying. The standard was drawn up by ISO/TC 300 in cooperation with CEN/TC 343; the taking over of the EN 15414 series as ISO 21660 is planned, and part 3 has been published in parallel as EN 21660-3; in Poland PN-EN ISO 21660-3:2021-08 is in force. The precision data come from a European interlaboratory study of 2008 (13–16 laboratories; samples: shredded tyres, demolition wood, dried sludge, municipal waste, a plastics/paper fraction): means 2.13–11.79 %, repeatability limit 0.22–0.81 %, reproducibility limit 0.62–1.32 % (mass fraction). A similar oven dry method (105–110 °C, about 1 g of the analysis sample < 0.2 mm, drying to constant mass in a dish with a lid, cooling in a desiccator) is applied for coal in accordance with PN-80/G-04511; the method of drying in air is not suitable for readily oxidising fuels, because the change of mass due to oxidation distorts the result.
Method principle
The analysis sample of solid recovered fuels is dried at a temperature of 105 °C in an atmosphere of air or of nitrogen; the moisture content is calculated from the loss of mass of the sample. If the material is liable to oxidation at 105 °C, it is dried in an atmosphere of nitrogen (the atmosphere used is stated in the test report). Automatic devices (e.g. gravimetric analysers) are permitted, provided that they have been validated by parallel measurements against the reference method and that they meet the requirements as to the size of the sample, the heating procedure, the temperature, the atmosphere and the accuracy of weighing. Apparatus: a drying oven controlled at (105 ± 2) °C with an air change of 3–5 times an hour and an air velocity which does not carry particles out of the dish; a dish of glass or of a material resistant to corrosion and to temperature, with a well fitting lid, of a size ensuring a layer of sample of ≤ 0.2 g/cm²; a balance with a resolution of 0.1 mg; a desiccator with a drying agent. The sample: a test sample for general analysis with a particle size of ≤ 1 mm prepared in accordance with ISO 21646, mixed (preferably mechanically) before the determination. The moisture in the analysis state Mad = (m2 − m3)/(m2 − m1)·100 %, where m1 — the mass of the empty dish with the lid, m2 — with the sample before drying, m3 — after drying; a single result to two decimal places, for the test report — the mean rounded to 0.1 %. Since finely comminuted SRF are very hygroscopic, the moisture of the analysis sample is always determined simultaneously with the weighing out of the portions for the other determinations (calorific value, carbon, nitrogen) and weighed quickly after cooling.
Applications
- Conversion of the results of analyses of SRF (calorific value, ash, C, N, S, Cl, metals) to the dry state — settlements in cement works, combined heat and power plants and incineration plants
- Characterisation of waste-derived fuels (RDF/SRF) for classification in accordance with ISO 21640 and for the purposes of the EU ETS and of KZR
- Quality control of the production of SRF in waste treatment plants
- Testing of biomass and of waste-derived fuels in accredited laboratories (the reference method for the validation of automatic analysers)
Key parameters
| Parameter | Value |
|---|---|
| Temperature | (105 ± 2) °C; air or nitrogen (oxidising materials); alternatively 50 ± 10 °C for longer |
| Sample | ≥ 1 g of the general analysis sample ≤ 1 mm (ISO 21646), layer ≤ 0.2 g/cm²; a minimum of 2 determinations |
| Constant mass | a change of ≤ 1 mg over a further 60 min; usually 2–3 h of drying |
| Balance | resolution 0.1 mg |
| Drying oven | air change 3–5 times/h |
| Result | Mad [%] = (m2 − m3)/(m2 − m1)·100; the mean to 0.1 % |
| Precision (2008) | r = 0.22–0.81 %; R = 0.62–1.32 % (mass fraction) |
| Presence in accreditation scopes (measured 22.09.2026) | the „Laboratories” tab shows 39 entries at 21 laboratories (matching by the BEGINNING of the string); of these 32 entries at 19 laboratories carry the full designation „PN-EN ISO 21660-3:2021-08”, 6 entries at 2 laboratories give the number without the year, and one entry appends the laboratory’s own procedure to the standard number. The figures 13–16 above refer to the samples of the interlaboratory trial, not to citations |
Standard
- Standard number
- PN-EN ISO 21660-3:2021-08 (ISO 21660-3:2021)
- Title (PL)
- Stałe paliwa wtórne — Oznaczanie zawartości wilgoci metodą suszarkową — Część 3: Wilgoć w próbce do analizy ogólnej
- Title (EN)
- Solid recovered fuels — Determination of moisture content using the oven dry method — Part 3: Moisture in general analysis sample
Step-by-step procedure
-
Preparation of the dish
Dry the empty dish with its lid at (105 ± 2) °C to constant mass, cool it to room temperature in a desiccator and weigh it to an accuracy of 0.1 mg (m1).
-
Weighing out of the sample
Mix the general analysis sample (≤ 1 mm), weigh out at least 1 g in an even layer (≤ 0.2 g/cm²) and weigh the dish with the lid and the sample (m2); carry out at least two determinations.
-
Drying
Dry the uncovered dish together with its lid at (105 ± 2) °C — in air, and for materials liable to oxidation in nitrogen — to constant mass (a change of ≤ 1 mg over a further 60 min; usually 2–3 h). Note: some components of SRF are liable to spontaneous ignition at 105 °C.
-
Cooling and weighing
Put the lid on while still in the drying oven, transfer the dish to a desiccator, cool it to room temperature and weigh it quickly (m3).
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Calculations
Calculate Mad = (m2 − m3)/(m2 − m1)·100 % for each determination (to two decimal places) and give the mean rounded to 0.1 %.
-
Test report
State the laboratory and the date, the identification of the sample, the reference to ISO 21660-3:2021, the deviations, the drying atmosphere used, the results in the analysis state and any unusual observations.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Laboratory drying oven with control at (105 ± 2) °C | air change 3–5 times/h; optionally a flow of nitrogen | — |
| Weighing dish with a lid | of glass or of a material resistant to corrosion and to temperature | — |
| Analytical balance 0.1 mg | quick weighing after cooling (hygroscopic samples) | — |
| Desiccator with a drying agent | e.g. silica gel | — |
| Mechanical mixer for the analysis sample | mixing of the sample before the determination | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Nitrogen (optional) | — | drying atmosphere for materials which oxidise at 105 °C |
| Drying agent for the desiccator (e.g. silica gel) | — | protection of the sample against moisture from the air |
Health and safety (OHS)
- A risk of spontaneous ignition of some SRF materials during drying at 105 °C — do not leave the drying oven unattended, use nitrogen for materials which oxidise
- Flammable or irritating gases from the waste may be evolved during the drying — the drying oven in a ventilated room
- Hot dishes — tongs and heat-resistant gloves
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 21660-3:2021-08 (ISO 21660-3:2021) — “Solid recovered fuels — Determination of moisture content using the oven dry method — Part 3: Moisture in general analysis sample”.
How does this method work?
The analysis sample of solid recovered fuels is dried at a temperature of 105 °C in an atmosphere of air or of nitrogen; the moisture content is calculated from the loss of mass of the sample. If the material is liable to oxidation at 105 °C, it is dried in an atmosphere of nitrogen (the atmosphere used is stated in the test report).
What is the measuring range and accuracy?
Temperature: (105 ± 2) °C; air or nitrogen (oxidising materials); alternatively 50 ± 10 °C for longer; Sample: ≥ 1 g of the general analysis sample ≤ 1 mm (ISO 21646), layer ≤ 0.2 g/cm²; a minimum of 2 determinations; Constant mass: a change of ≤ 1 mg over a further 60 min; usually 2–3 h of drying; Balance: resolution 0.1 mg.
How long does the test take?
The procedure comprises 6 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Laboratory drying oven with control at (105 ± 2) °C, Weighing dish with a lid, Analytical balance 0.1 mg, Desiccator with a drying agent, Mechanical mixer for the analysis sample.
Where is this test used?
Conversion of the results of analyses of SRF (calorific value, ash, C, N, S, Cl, metals) to the dry state — settlements in cement works, combined heat and power plants and incineration plants; Characterisation of waste-derived fuels (RDF/SRF) for classification in accordance with ISO 21640 and for the purposes of the EU ETS and of KZR; Quality control of the production of SRF in waste treatment plants; Testing of biomass and of waste-derived fuels in accredited laboratories (the reference method for the validation of automatic analysers).
What safety precautions apply?
A risk of spontaneous ignition of some SRF materials during drying at 105 °C — do not leave the drying oven unattended, use nitrogen for materials which oxidise; Flammable or irritating gases from the waste may be evolved during the drying — the drying oven in a ventilated room; Hot dishes — tongs and heat-resistant gloves.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 21660-3.