🔥 Moisture in the analysis sample of hard coal — drying in nitrogen
In short
Drying of 1 g of coal in a stream of nitrogen at 105–110 °C for at least 60 min to constant mass; the moisture from the loss of mass, the mean of two determinations to 0. The test is performed according to PN-ISO 11722:2009; Temperature: 105–110 °C. The procedure comprises 6 steps (about 1 h 10 min in total); it is used for: Correction of the results of determinations of volatile matter, of hydrogen and of other analyses of hard coal for the water content, Conversion of the results of the analysis to the dry basis, Determination of the moisture in readily oxidising fuels, where drying in air falsifies the result.
At a glance
- Standard: PN-ISO 11722:2009
- Category: Petrochemistry
- Procedure steps: 6
- Total time of stages: 1 h 10 min
- Temperature: 105–110 °C
- Time: At least 60 min; further heating in 30 min periods until the change of mass is ≤ 1 mg
- Flow of nitrogen: About 15 oven volumes per hour; nitrogen free of moisture, O2 < 30 µl/l
Overview
The standard specifies a method of determining the moisture in the general analysis sample of hard coal by drying in nitrogen. The determination of the moisture in the analysis sample is needed in order to correct the results of other determinations (for example of volatile matter and of hydrogen) for the effect of the water and in order to convert all the results to the dry basis. Because hard coal is hygroscopic, its moisture changes with the humidity of the atmosphere, and for that reason the moisture has to be determined every time portions are weighed out for other analyses; if they are weighed out at the same time, one simultaneous determination of the moisture is enough. The description is based on the preview of ISO 11722:2013 (a minor revision of ISO 11722:1999, which is adopted by PN-ISO 11722:2009).
Drying in an atmosphere of air must not be used for readily oxidising solid fuels, because the change of mass caused by the oxidation affects the result of the moisture determination — for such fuels drying in an atmosphere of an inert gas (nitrogen or argon) or the distillation method is used. The nitrogen method eliminates that error: the nitrogen is to be free of moisture, with a volume fraction of oxygen below 30 µl/l (commercial nitrogen with a water content below 5 µl/l does not require further drying).
The result is given as the mean of two determinations to 0.1 % by mass. Because the humidity conditions in different laboratories differ, the standard does not give a reproducibility limit — only repeatability (0.10 % for moisture below 5 %, 0.15 % for moisture ≥ 5 %).
Method principle
A known mass of coal is heated in a stream of nitrogen at a temperature of 105–110 °C and kept at that temperature to constant mass; the moisture content is calculated from the loss of mass of the coal: wM = (m2 − m3)/(m2 − m1) × 100, where m1 is the mass of the empty dish with its lid, m2 the mass of the dish with the lid and the coal before heating and m3 the mass after heating. The oven must allow a flow of nitrogen of about 15 oven volumes per hour with the free space as small as possible; the weighing dish is flat, of glass or of a corrosion-resistant metal, with a well-fitting lid, such that the layer of coal does not exceed 0.20 g/cm².
Applications
- Correction of the results of determinations of volatile matter, of hydrogen and of other analyses of hard coal for the water content
- Conversion of the results of the analysis to the dry basis
- Determination of the moisture in readily oxidising fuels, where drying in air falsifies the result
- Routine proximate analysis of hard coal in the laboratories of mines, of power stations and of GIG
Key parameters
| Parameter | Value |
|---|---|
| Temperature | 105–110 °C |
| Time | At least 60 min; further heating in 30 min periods until the change of mass is ≤ 1 mg |
| Flow of nitrogen | About 15 oven volumes per hour; nitrogen free of moisture, O2 < 30 µl/l |
| Sample | 1 ± 0.1 g of the general analysis sample in an even layer of ≤ 0.20 g/cm² |
| Balance | Analytical, 0.1 mg |
| Repeatability | 0.10 % (moisture < 5 %), 0.15 % (moisture ≥ 5 %); reproducibility is not given |
Standard
- Standard number
- PN-ISO 11722:2009
- Title (PL)
- Paliwa stałe — Węgiel kamienny — Oznaczanie wilgoci w próbce do analizy ogólnej metodą suszenia w azocie
- Title (EN)
- Solid mineral fuels — Hard coal — Determination of moisture in the general analysis test sample by drying in nitrogen
Step-by-step procedure
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Preparation of the sample
Use the general analysis sample; make sure that its moisture is in equilibrium with the atmosphere of the laboratory (if need be spread it out in a thin layer for the minimum time). Before the determination mix it thoroughly for at least 1 min, preferably mechanically.
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Weighing out
Weigh the clean, dry, empty dish with its lid to 0.1 mg; add 1 ± 0.1 g of coal in an even layer and weigh again.
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Drying
Heat the uncovered dish in the oven at 105–110 °C for at least 60 min with a flow of nitrogen of about 15 oven volumes per hour. Do not open the door of the oven during the drying.
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Cooling
Take the dish out and put the lid on at once (if the oven allows it — while still in the oven). Cool it for 10 min on the thick metal plate, then in the cooling vessel to room temperature (with cooling in a flow of nitrogen the dish may be transferred directly).
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Weighing
Weigh to 0.1 mg immediately after room temperature is reached. If there is any doubt about the completeness of the drying, heat further at 105–110 °C in 30 min periods until the change of mass does not exceed 1 mg.
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Calculation and test report
wM = (m2 − m3)/(m2 − m1) × 100; give the mean of two determinations to 0.1 % with a reference to the standard, the identification of the sample and the results.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Oven with a flow of nitrogen | Control at 105–110 °C, a flow of nitrogen of about 15 volumes/h, minimal free space (an example is in Annex A of the standard) | — |
| Analytical balance | Accuracy 0.1 mg | — |
| Weighing dishes | Flat, of glass or of a corrosion-resistant metal, with well-fitting lids | — |
| Cooling vessel | For example a desiccator without a desiccant, with a metal plate (aluminium or copper); it may have a flow of nitrogen during the cooling | — |
| Thick metal plate | For cooling the dish for 10 min | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Nitrogen | — | Free of moisture, volume fraction of oxygen < 30 µl/l; commercial nitrogen with a water content < 5 µl/l does not require further drying |
Health and safety (OHS)
- Nitrogen in a closed room displaces oxygen — provide ventilation, lead the gas from the oven outside or into a fume hood
- An oven at 110 °C — heat-resistant gloves; cool the dishes on a metal plate
- Coal dust — goggles and a dust mask when mixing and weighing out
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-ISO 11722:2009 — “Solid mineral fuels — Hard coal — Determination of moisture in the general analysis test sample by drying in nitrogen”.
How does this method work?
A known mass of coal is heated in a stream of nitrogen at a temperature of 105–110 °C and kept at that temperature to constant mass; the moisture content is calculated from the loss of mass of the coal: wM = (m2 − m3)/(m2 − m1) × 100, where m1 is the mass of the empty dish with its lid, m2 the mass of the dish with the lid and the coal before heating and m3 the mass after heating. The oven must allow a flow of nitrogen of about 15 oven volumes per hour with the free space as small as possible; the weighing dish is flat, of glass or of a corrosion-resistant metal, with a well-fitting lid, such that the layer of coal does not exceed 0.
What is the measuring range and accuracy?
Temperature: 105–110 °C; Time: At least 60 min; further heating in 30 min periods until the change of mass is ≤ 1 mg; Flow of nitrogen: About 15 oven volumes per hour; nitrogen free of moisture, O2 < 30 µl/l; Sample: 1 ± 0.1 g of the general analysis sample in an even layer of ≤ 0.20 g/cm².
How long does the test take?
The times given for the individual stages add up to approximately 1 h 10 min. The procedure comprises 6 steps.
What equipment is required?
Oven with a flow of nitrogen, Analytical balance, Weighing dishes, Cooling vessel, Thick metal plate.
Where is this test used?
Correction of the results of determinations of volatile matter, of hydrogen and of other analyses of hard coal for the water content; Conversion of the results of the analysis to the dry basis; Determination of the moisture in readily oxidising fuels, where drying in air falsifies the result; Routine proximate analysis of hard coal in the laboratories of mines, of power stations and of GIG.
What safety precautions apply?
Nitrogen in a closed room displaces oxygen — provide ventilation, lead the gas from the oven outside or into a fume hood; An oven at 110 °C — heat-resistant gloves; cool the dishes on a metal plate; Coal dust — goggles and a dust mask when mixing and weighing 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-ISO 11722.