🔥 Total moisture of solid biofuels — the reference method (drying at 105 °C)
In short
Drying of ≥ 300 g of sample (pellets, wood chips, sawdust) in air at (105 ± 2) °C to constant mass, weighing while hot with a correction for buoyancy (a reference tray); the result on the as-received basis, the mean of two determinations to 0. The test is performed according to PN-EN ISO 18134-1:2023-02; Temperature: (105 ± 2) °C throughout the chamber of the oven; 3–5 air changes per hour. The procedure comprises 7 steps (about 1–1 days in total); it is used for: Settlement of deliveries of energy biomass (pellets, wood chips, sawdust, straw) by dry mass, The reference method as against the simplified method (part 2) and the determinations in the analysis sample (part 3), Conversion of the net calorific value and of other parameters to the as-received basis.
At a glance
- Standard: PN-EN ISO 18134-1:2023-02
- Category: Petrochemistry
- Procedure steps: 7
- Total time of stages: 1 days–1 days
- Temperature: (105 ± 2) °C throughout the chamber of the oven; 3–5 air changes per hour
- Sample: ≥ 300 g (fine materials, for example sawdust: 100 g); particles with at least one dimension < 31.5 mm; a layer of ≤ 1 g/cm² for fine materials
- Constant mass: A change of ≤ 0.2 % of the initial mass of the test portion within 60 min; drying usually ≤ 24 h
Overview
The standard describes a method of determining the moisture of a sample of solid biofuels by drying in an oven, used when high precision is needed; it applies to all solid biofuels. The moisture of solid biofuels (as received) is always given in relation to the total mass of the sample (the as-received basis, "wet basis"). Biomass materials may contain small amounts of volatile organic compounds which evaporate during the drying; their share is small in relation to the moisture and the standard disregards it. The 2022 edition replaced ISO 18134-1:2015 — the title was changed, a warning about changes of moisture during the preparation of the sample was added and the preparation of the sample was made more precise.
Solid biofuels readily take up or give off moisture when the moisture of the sample and the humidity of the surroundings are not in equilibrium; comminution generates heat and a movement of air which cause a loss of moisture, and for that reason samples of high moisture should be pre-dried before comminution according to ISO 14780 and the moisture calculated from the two stages. Biomass, brown coal and peat show considerable variations of moisture when the humidity of the atmosphere changes — for them a distinction is drawn only between the total moisture and the moisture in the analysis sample (determined separately according to part 3 of the standard).
Because of the diversity of biofuels the standard gives neither repeatability nor reproducibility. The determination is carried out in duplicate; in the GIG laboratory the total moisture of biofuels is determined by the gravimetric method over a range of 0.50–72.80 %.
Method principle
A test portion of the biofuel is dried in an atmosphere of air at 105 °C to constant mass, and the moisture is calculated from the loss of mass with a correction for buoyancy: Mar = [(m2 − m3) − (m4 − m5)]/(m2 − m1) × 100, where m1 is the mass of the empty tray, m2 the mass of the tray with the test portion before drying (cold), m3 the mass after drying (weighed hot) and m4 and m5 the mass of an identical empty reference tray before and after drying. A hot tray weighs less than a cold one because of buoyancy, and the size of that effect depends on the size and mass of the tray — hence the reference tray. Constant mass means a change not exceeding 0.2 % of the initial mass of the test portion within 60 min. For pre-dried samples: Mar = Mp + Mr·(1 − Mp/100).
Applications
- Settlement of deliveries of energy biomass (pellets, wood chips, sawdust, straw) by dry mass
- The reference method as against the simplified method (part 2) and the determinations in the analysis sample (part 3)
- Conversion of the net calorific value and of other parameters to the as-received basis
- Proficiency testing and commercial disputes requiring high precision
- Quality control of pellets according to the specifications for solid biofuels
Key parameters
| Parameter | Value |
|---|---|
| Temperature | (105 ± 2) °C throughout the chamber of the oven; 3–5 air changes per hour |
| Sample | ≥ 300 g (fine materials, for example sawdust: 100 g); particles with at least one dimension < 31.5 mm; a layer of ≤ 1 g/cm² for fine materials |
| Constant mass | A change of ≤ 0.2 % of the initial mass of the test portion within 60 min; drying usually ≤ 24 h |
| Weighing | To 0.1 g; while hot, within 10–15 s of removal, with insulation on the pan |
| Result | The calculation to two decimal places, the mean of two determinations to 0.1 %, the as-received basis |
| Precision | The standard gives no r and R because of the diversity of biofuels |
Standard
- Standard number
- PN-EN ISO 18134-1:2023-02
- Title (PL)
- Biopaliwa stałe — Oznaczanie zawartości wilgoci — Część 1: Metoda referencyjna
- Title (EN)
- Solid biofuels — Determination of moisture content — Part 1: Reference method
Step-by-step procedure
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Sampling and preparation of the sample
Samples taken according to ISO 18135 or ISO 21945 are to be delivered to the laboratory in airtight containers; prepare the test portion according to ISO 14780 so that all the particles have at least one dimension below 31.5 mm, protecting the moisture of the sample (pre-dry very wet samples according to ISO 14780 and record Mp).
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Weighing of the trays
Weigh the empty, clean drying tray (m1) and an identical empty reference tray (m4) to 0.1 g.
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Transfer of the test portion
If condensate is visible on the inner walls of the packaging, shake the packaging so that the material takes the moisture up. Transfer the test portion (≥ 300 g; fine materials 100 g) onto the tray and spread it in an even, thin layer (fine materials ≤ 1 g/cm²). Weigh the tray with the test portion (m2).
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Drying
Put the tray with the test portion together with the reference tray into the oven at (105 ± 2) °C and dry to constant mass (a change of ≤ 0.2 % of the initial mass within 60 min). Do not overload the oven — provide a free flow of air above and between the trays; the drying time should usually not exceed 24 h.
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Weighing while hot
Take both trays out and weigh each one while still hot, within 10–15 s, to 0.1 g (m3, m5), with insulation on the pan, so as to avoid the uptake of moisture.
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Calculation
Mar = [(m2 − m3) − (m4 − m5)]/(m2 − m1) × 100 to two decimal places; for a pre-dried sample Mar = Mp + Mr·(1 − Mp/100). Carry out the determination in duplicate; round the mean to 0.1 %.
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Test report
Give the laboratory, the date, the identification of the product, a reference to ISO 18134-1:2022, the result on the as-received basis, any unusual observations and any departures.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Laboratory oven | Control at (105 ± 2) °C, 3–5 air changes/h, an air velocity which does not blow the particles off the tray | — |
| Trays and vessels | Of a material resistant to corrosion and to temperature, with a clean, smooth surface, holding the test portion in a thin even layer; an identical reference tray | — |
| Balance | Readable to 0.1 g | — |
| Insulating pad for the pan of the balance | A heat-insulating material for weighing hot trays | — |
| Airtight containers or bags | For the delivery and storage of samples without exchange of moisture | — |
Health and safety (OHS)
- Trays weighed hot straight after removal — heat-resistant gloves and an insulating pad on the balance
- Dry biomass dusts are flammable — do not allow dust to accumulate in the oven, keep the trays clean
- Mouldy materials (wet wood chips) — a dust mask when spreading the sample out
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 18134-1:2023-02 — “Solid biofuels — Determination of moisture content — Part 1: Reference method”.
How does this method work?
A test portion of the biofuel is dried in an atmosphere of air at 105 °C to constant mass, and the moisture is calculated from the loss of mass with a correction for buoyancy: Mar = [(m2 − m3) − (m4 − m5)]/(m2 − m1) × 100, where m1 is the mass of the empty tray, m2 the mass of the tray with the test portion before drying (cold), m3 the mass after drying (weighed hot) and m4 and m5 the mass of an identical empty reference tray before and after drying. A hot tray weighs less than a cold one because of buoyancy, and the size of that effect depends on the size and mass of the tray — hence the reference tray.
What is the measuring range and accuracy?
Temperature: (105 ± 2) °C throughout the chamber of the oven; 3–5 air changes per hour; Sample: ≥ 300 g (fine materials, for example sawdust: 100 g); particles with at least one dimension < 31.5 mm; a layer of ≤ 1 g/cm² for fine materials; Constant mass: A change of ≤ 0.2 % of the initial mass of the test portion within 60 min; drying usually ≤ 24 h; Weighing: To 0.1 g; while hot, within 10–15 s of removal, with insulation on the pan.
How long does the test take?
The times given for the individual stages add up to approximately 1 days–1 days. The procedure comprises 7 steps.
What equipment is required?
Laboratory oven, Trays and vessels, Balance, Insulating pad for the pan of the balance, Airtight containers or bags.
Where is this test used?
Settlement of deliveries of energy biomass (pellets, wood chips, sawdust, straw) by dry mass; The reference method as against the simplified method (part 2) and the determinations in the analysis sample (part 3); Conversion of the net calorific value and of other parameters to the as-received basis; Proficiency testing and commercial disputes requiring high precision; Quality control of pellets according to the specifications for solid biofuels.
What safety precautions apply?
Trays weighed hot straight after removal — heat-resistant gloves and an insulating pad on the balance; Dry biomass dusts are flammable — do not allow dust to accumulate in the oven, keep the trays clean; Mouldy materials (wet wood chips) — a dust mask when spreading the sample out.
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 18134-1.