🔥 Total sulfur in coal — combustion in oxygen at 1350 °C with IR detection
In short
Combustion of 0. 2–0. The test is performed according to ISO 19579:2006; Range of application: Coal with an ash content < 40 %. The procedure comprises 6 steps; it is used for: Routine determination of total sulfur in hard coal and brown coal (including lignite) with automatic analysers, Quality control of steam coal with regard to SO2 emissions, Classification of coal as low-sulfur (< 1 % S) and as having a raised sulfur content (> 1.5 % S).
At a glance
- Standard: ISO 19579:2006
- Category: Petrochemistry
- Procedure steps: 6
- Combustion temperature: About 1350 °C in a stream of oxygen
- Range of application: Coal with an ash content < 40 %
- Test portion: 0.2–0.5 g weighed to 0.001 g; sample ground to < 212 µm
Overview
The standard ISO 19579 specifies an alternative method of determining the total sulfur content in hard coal and brown coal (including lignite) by high-temperature combustion and infrared (IR) absorption with the use of commercially available instruments; the method has been shown to be applicable to coal samples with an ash content below 40 %. Sulfur occurs in coal in three forms: inorganic sulfides (pyrite FeS2), inorganic sulfates bound to the mineral matter and organic sulfur in the coal substance. The standard has no counterpart at the Polish Committee for Standardization (no catalogue card) — the ISO designation is given; the standard refers to the reference methods ISO 334 (Eschka) and ISO 351 (high-temperature combustion).
The total sulfur content of coal varies from 0.3 % to about 5 % by mass and depends on the deposit and not on the rank of the coal; coals below 1 % are classed as low-sulfur and those above 1.5 % as having a raised sulfur content. During combustion most of the sulfur (70–95 %) passes into the flue gas as SO2, hence the importance of the determination for the power industry and for air protection. Among the most widespread methods are the Eschka method and high-temperature combustion with alkalimetric titration; elemental composition analysers, for which very small amounts of sample are enough, are coming into ever more general use.
Calibration requires reference materials of a composition close to that of the samples analysed: some coals with a large content of carbonates and low-rank coals with calcium salts of carboxylic acids require longer combustion and integration times, because the evolution of SO2 is delayed. Reference materials are usually certified on the dry basis, and for that reason their moisture has to be determined (ISO 11722, ISO 687 or ISO 5068-2) and the value converted to the analysis basis.
Method principle
A sample of coal is burned at 1350 °C in a stream of oxygen. Solid particles and water vapour are removed from the gas stream in traps of glass wool and magnesium perchlorate, after which the gas passes through a cell in which the sulfur dioxide is measured by an infrared absorption detector connected to a microprocessor. The instrument is calibrated with reference materials, and the percentage of sulfur in the sample is calculated by the microprocessor on the basis of that calibration. The calibration is checked periodically (every five determinations is recommended) with a standard of known sulfur content; if there is a disagreement going beyond the limits of repeatability, the previous results are rejected, the instrument is calibrated again and the samples are analysed anew.
Applications
- Routine determination of total sulfur in hard coal and brown coal (including lignite) with automatic analysers
- Quality control of steam coal with regard to SO2 emissions
- Classification of coal as low-sulfur (< 1 % S) and as having a raised sulfur content (> 1.5 % S)
- Analysis of coke (reference materials: coals or cokes according to ISO 334 / ISO 351)
Key parameters
| Parameter | Value |
|---|---|
| Combustion temperature | About 1350 °C in a stream of oxygen |
| Range of application | Coal with an ash content < 40 % |
| Test portion | 0.2–0.5 g weighed to 0.001 g; sample ground to < 212 µm |
| Result | The mean of two determinations to 0.01 % by mass |
| Repeatability | r = 0.02 + 0.03·x (x — the mean of the results) |
| Check of the calibration | Recommended every five determinations, with a standard of known sulfur content |
Standard
- Standard number
- ISO 19579:2006
- Title (PL)
- Paliwa stałe — Oznaczanie siarki metodą spektrometrii IR (tłumaczenie robocze; brak karty PKN)
- Title (EN)
- Solid mineral fuels — Determination of sulfur by IR spectrometry
Step-by-step procedure
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Preparation of the sample
Use an analysis sample ground to below 212 µm; spread it out in a thin layer for the minimum time to approximate moisture equilibrium with the atmosphere and mix it. After the test portion has been weighed out, determine the moisture in a further portion according to ISO 11722, ISO 687 or ISO 5068-2.
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Preparation of the instrument
Prepare the analyser according to the manufacturer's instructions; before the calibration it is advisable to pass two samples through it to condition the instrument.
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Calibration
Calibrate the instrument with a reference coal or coke (multi-point calibration if possible), covering concentrations below and above the one expected. Weigh 0.2–0.5 g of the reference material to 0.001 g into a boat, enter the mass into the processor and slide the boat into the hot zone; when the combustion is finished (signalled by the instrument) take the boat out. Repeat with two further portions.
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Check of the calibration
Analyse as unknown samples the calibration material and another reference material of lower sulfur content; if the results do not fall within the repeatability of the method — repeat the calibration. Take the moisture of the CRM into account: wS,aa = wS,d × (100 − wH2O)/100.
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Determination
Determine the sulfur in the sample by the same procedure as for the reference materials (0.2–0.5 g, combustion at 1350 °C in oxygen, integration of the SO2 signal).
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Control and result
Periodically (every five determinations is recommended) analyse a standard of known sulfur content; if there is a disagreement, reject the previous results, calibrate again and repeat the analyses. Result: the mean of two determinations to 0.01 % by mass on the analysis basis; parallel results must not differ by more than r = 0.02 + 0.03·x.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Sulfur analyser (combustion + IR) | A resistance furnace at about 1350 °C, a ceramic combustion tube, ceramic boats, a gas cleaning train (glass wool, magnesium perchlorate), an NDIR detector with a microprocessor | — |
| Balance | Accuracy 1 mg | — |
| Furnace and apparatus for the method with titration (the classical alternative) | A furnace with a silica tube for combustion at 1250 °C, a pusher, a rotameter, an absorption scrubber (the instruction of the Wrocław University of Science and Technology) | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Anhydrous granular magnesium perchlorate | — | The water vapour trap in the flue gas train |
| Compressed technical oxygen, 99.5 % by volume | — | The carrier and oxidising gas |
| Glass wool | — | The filter for solid particles |
| Reference coals or cokes (CRM) | — | Of known sulfur content determined according to ISO 334 or ISO 351, traceable to a recognised certifying organisation; calibration with samples other than CRMs requires verification against a CRM |
Health and safety (OHS)
- A furnace at 1350 °C and oxygen under pressure — a risk of burns and of intensified combustion; keep the gas train clean, do not use greases in contact with oxygen
- Magnesium perchlorate is a strong oxidant — do not mix it with organic substances, dispose of used traps as oxidising waste
- Coal dust when weighing out — a mask and goggles
Frequently asked questions
Which standard describes this test?
The test is performed according to ISO 19579:2006 — “Solid mineral fuels — Determination of sulfur by IR spectrometry”.
How does this method work?
A sample of coal is burned at 1350 °C in a stream of oxygen. Solid particles and water vapour are removed from the gas stream in traps of glass wool and magnesium perchlorate, after which the gas passes through a cell in which the sulfur dioxide is measured by an infrared absorption detector connected to a microprocessor.
What is the measuring range and accuracy?
Combustion temperature: About 1350 °C in a stream of oxygen; Range of application: Coal with an ash content < 40 %; Test portion: 0.2–0.5 g weighed to 0.001 g; sample ground to < 212 µm; Result: The mean of two determinations to 0.01 % by mass.
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?
Sulfur analyser (combustion + IR), Balance, Furnace and apparatus for the method with titration (the classical alternative).
Where is this test used?
Routine determination of total sulfur in hard coal and brown coal (including lignite) with automatic analysers; Quality control of steam coal with regard to SO2 emissions; Classification of coal as low-sulfur (< 1 % S) and as having a raised sulfur content (> 1.5 % S); Analysis of coke (reference materials: coals or cokes according to ISO 334 / ISO 351).
What safety precautions apply?
A furnace at 1350 °C and oxygen under pressure — a risk of burns and of intensified combustion; keep the gas train clean, do not use greases in contact with oxygen; Magnesium perchlorate is a strong oxidant — do not mix it with organic substances, dispose of used traps as oxidising waste; Coal dust when weighing out — a mask and goggles.
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 ISO 19579.