🔥 Ash in solid biofuels — ashing at 550 °C
In short
Ashing of ≥ 1 g of the analysis sample (< 1 mm) with the programme: to 250 °C in 30–50 min, held for 60 min, to (550 ± 10) °C in 30 min and ≥ 120 min; the result on the dry basis to 0. The test is performed according to PN-EN ISO 18122:2023-05; Final temperature: (550 ± 10) °C, at least 120 min; the alternatives 710 °C and 815 °C (outside the precision of the standard). The procedure comprises 7 steps (about 2 h 5 min–2 h 10 min in total); it is used for: Classification of pellets and wood chips according to the specifications for solid biofuels (ash classes), Settlement of deliveries of energy biomass and assessment of the costs of the management of the ash, Assessment of the tendency of a fuel to slagging and corrosion (the amount of ash; the composition according to other standards).
At a glance
- Standard: PN-EN ISO 18122:2023-05
- Category: Petrochemistry
- Procedure steps: 7
- Total time of stages: 2 h 5 min–2 h 10 min
- Final temperature: (550 ± 10) °C, at least 120 min; the alternatives 710 °C and 815 °C (outside the precision of the standard)
- Programme: Cold furnace → 250 °C in 30–50 min (4.5–7.5 °C/min), held for 60 min → (550 ± 10) °C in 30 min (10 °C/min)
- Sample: ≥ 1 g of the analysis sample with a nominal particle size of ≤ 1 mm (sometimes 0.25 mm); loading ≤ 0.1 g/cm²
Overview
The standard specifies a method of determining the ash content in all solid biofuels. Ash is a by-product of combustion which has to be removed as bottom ash or fly ash, and its chemical composition affects the slagging and corrosion of the equipment — for that reason the amount of ash in a fuel is of technical and economic importance. The 2022 edition (PN-EN ISO 18122:2023-05) replaced ISO 18122:2015: a more detailed description of the furnace and of the ashing procedure was added and the data on repeatability and reproducibility were updated.
The standard final temperature is (550 ± 10) °C; other final temperatures may be used (other methods give 710 °C and 815 °C), provided that the remaining conditions of the furnace are kept and the temperature is clearly stated in the test report, but the precision data then do not apply. The difference from ash determined at 815 °C (as for coal according to ISO 1171) arises from the decomposition of carbonates with the evolution of CO2, from losses of volatile inorganic compounds and from the further oxidation of inorganic constituents. Automatic apparatus is permitted (for example gravimetric analysers) if the method has been validated on reference samples of the appropriate type of biomass and if it meets the requirements of clause 7 as to the mass of the sample, the heating programme, the atmosphere, the temperature and the accuracy of weighing.
Ash from biofuels is very hygroscopic — the desiccant in the desiccator has to be checked and dried often, and the dishes have to be covered. In the scope of accreditation of GIG the ash in biofuels is determined according to PN-EN ISO 18122:2023-05 by the gravimetric method (slow ashing) and by the thermogravimetric method over a range of 0.10–34.50 %.
SCALE OF CITATIONS — A MEASUREMENT ON THE DATABASE OF ACCREDITATION SCOPES (read on 23-09-2026, matching on the BEGINNING of the notation "PN-EN ISO 18122", i.e. the way the "Laboratories" tab of this entry searches): 46 entries at 26 laboratories.
Method principle
The ash content is calculated from the mass of the residue after the sample has been heated in air under strictly controlled conditions of time, of mass of sample and of apparatus to a controlled final temperature of (550 ± 10) °C: Ad = (m3 − m1)/(m2 − m1) × 100 × 100/(100 − Mad), where m1 is the mass of the empty dish, m2 that of the dish with the sample, m3 that of the dish with the ash and Mad the moisture of the analysis sample determined in parallel according to ISO 18134-3. The loading of the dish must not exceed 0.1 g/cm² of its bottom (otherwise there is a risk of incomplete combustion of the bottom layer or of the uptake of CO2 by ash rich in calcium, for example from clean wood). The air change in the furnace is to remove the SO2 and CO2 from the decomposition of the fuel before they react with the constituents of the ash.
Applications
- Classification of pellets and wood chips according to the specifications for solid biofuels (ash classes)
- Settlement of deliveries of energy biomass and assessment of the costs of the management of the ash
- Assessment of the tendency of a fuel to slagging and corrosion (the amount of ash; the composition according to other standards)
- Preparation of ash for the analysis of its composition (major and trace elements)
- Validation of thermogravimetric analysers (TGA) against the gravimetric method
Key parameters
| Parameter | Value |
|---|---|
| Final temperature | (550 ± 10) °C, at least 120 min; the alternatives 710 °C and 815 °C (outside the precision of the standard) |
| Programme | Cold furnace → 250 °C in 30–50 min (4.5–7.5 °C/min), held for 60 min → (550 ± 10) °C in 30 min (10 °C/min) |
| Sample | ≥ 1 g of the analysis sample with a nominal particle size of ≤ 1 mm (sometimes 0.25 mm); loading ≤ 0.1 g/cm² |
| Balance | Accuracy 0.1 mg |
| Criterion for the end of ashing | Further heating in 30 min periods at 550 °C until the change of mass is < 0.05 % of the initial mass |
| Result | The dry basis, the calculation to two decimal places, the mean of ≥ 2 determinations to 0.1 % |
Standard
- Standard number
- PN-EN ISO 18122:2023-05
- Title (PL)
- Biopaliwa stałe — Oznaczanie zawartości popiołu
- Title (EN)
- Solid biofuels — Determination of ash content
Step-by-step procedure
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Preparation of the sample
From the laboratory sample (ISO 18135 or ISO 21945) prepare according to ISO 14780 a general analysis sample with a nominal particle size of ≤ 1 mm, in an amount sufficient for the ash and the moisture. Carry out the determination directly with a simultaneous determination of the moisture according to ISO 18134-3, or on a portion dried by the same procedure and kept in a closed vessel in a desiccator.
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Conditioning of the dish
Ignite the empty dish at (550 ± 10) °C for ≥ 60 min, cool it for 5–10 min on the heat-resistant plate, then in the desiccator to ambient temperature; weigh to 0.1 mg (m1).
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Weighing out
Mix the sample thoroughly; spread at least 1 g in an even layer on the bottom of the dish and weigh to 0.1 mg (m2). A portion dried earlier in an oven is to be dried again together with the dish at 105 °C before weighing. When a very low ash content is expected, use a larger test portion and a larger dish.
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Ashing
Put the dish into the cold furnace; raise the temperature uniformly to 250 °C in 30–50 min and hold for 60 min, so that the volatile matter escapes before ignition; then raise it uniformly to (550 ± 10) °C in 30 min and hold for at least 120 min.
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Cooling and weighing
Take the dish out, cool it for 5–10 min on the heat-resistant plate, transfer it to the desiccator with the desiccant and, once it has cooled, weigh it at once to 0.1 mg (m3).
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Check of the completeness of combustion
In case of doubt (soot) heat further in the hot furnace at 550 °C in 30 min periods until the change of mass is < 0.05 % of the initial mass; a few drops of distilled water may be added and the heating from the cold furnace to (550 ± 10) °C repeated.
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Calculation and test report
Ad = (m3 − m1)/(m2 − m1) × 100 × 100/(100 − Mad), the calculation to two decimal places, the mean of at least two determinations to 0.1 % on the dry basis. Give the laboratory, the date, the identification of the sample, a reference to ISO 18122:2022, the final temperature if it is other than 550 °C, and any departures.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Muffle furnace with a temperature programme | A zone of uniform temperature, reaching the temperatures in the prescribed times, an air change removing SO2 and CO2 | — |
| Dishes | Of an inert material: porcelain, silica or platinum, chosen so that the loading is ≤ 0.1 g/cm² | — |
| Analytical balance | Accuracy 0.1 mg | — |
| Desiccator with a desiccant and lids for the dishes | The desiccant checked and dried often — biomass ash is very hygroscopic | — |
| Heat-resistant plate | For cooling the dishes for 5–10 min after removal from the furnace | — |
| Thermogravimetric analyser (optional) | Automatic apparatus permitted after validation on reference biomass samples | — |
Health and safety (OHS)
- A furnace at 550 °C — tongs and heat-resistant gloves, cooling on the heat-resistant plate before the desiccator
- Light biomass ash is easily blown away by a stream of air — do not open the furnace abruptly, do not blow on the dishes
- Biomass dust is flammable and irritant — weigh out in a fume hood or wearing a dust mask
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 18122:2023-05 — “Solid biofuels — Determination of ash content”.
How does this method work?
The ash content is calculated from the mass of the residue after the sample has been heated in air under strictly controlled conditions of time, of mass of sample and of apparatus to a controlled final temperature of (550 ± 10) °C: Ad = (m3 − m1)/(m2 − m1) × 100 × 100/(100 − Mad), where m1 is the mass of the empty dish, m2 that of the dish with the sample, m3 that of the dish with the ash and Mad the moisture of the analysis sample determined in parallel according to ISO 18134-3. The loading of the dish must not exceed 0.
What is the measuring range and accuracy?
Final temperature: (550 ± 10) °C, at least 120 min; the alternatives 710 °C and 815 °C (outside the precision of the standard); Programme: Cold furnace → 250 °C in 30–50 min (4.5–7.5 °C/min), held for 60 min → (550 ± 10) °C in 30 min (10 °C/min); Sample: ≥ 1 g of the analysis sample with a nominal particle size of ≤ 1 mm (sometimes 0.25 mm); loading ≤ 0.1 g/cm²; Balance: Accuracy 0.1 mg.
How long does the test take?
The times given for the individual stages add up to approximately 2 h 5 min–2 h 10 min. The procedure comprises 7 steps.
What equipment is required?
Muffle furnace with a temperature programme, Dishes, Analytical balance, Desiccator with a desiccant and lids for the dishes, Heat-resistant plate, Thermogravimetric analyser (optional).
Where is this test used?
Classification of pellets and wood chips according to the specifications for solid biofuels (ash classes); Settlement of deliveries of energy biomass and assessment of the costs of the management of the ash; Assessment of the tendency of a fuel to slagging and corrosion (the amount of ash; the composition according to other standards); Preparation of ash for the analysis of its composition (major and trace elements); Validation of thermogravimetric analysers (TGA) against the gravimetric method.
What safety precautions apply?
A furnace at 550 °C — tongs and heat-resistant gloves, cooling on the heat-resistant plate before the desiccator; Light biomass ash is easily blown away by a stream of air — do not open the furnace abruptly, do not blow on the dishes; Biomass dust is flammable and irritant — weigh out in a fume hood or wearing a dust mask.
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 18122.