Overview
ISO 20336:2017 specifies a standardized laboratory method for determining the total sulfur content in solid mineral fuels (coal and coke) using high‑temperature combustion followed by Coulomb titration. The method uses automated instruments to combust a weighed test portion at controlled temperatures and to quantify sulfur oxides electrochemically. ISO 20336:2017 provides requirements for sample preparation, reagents, apparatus, calibration and routine operation to produce traceable sulfur results.
Key topics and technical requirements
- Principle: Combustion of a weighed sample in purified air at high temperature converts sulfur to sulfur oxides which are absorbed in an electrolytic solution and titrated by iodine/bromine produced by electrolysis; the integrated electrical charge (Coulomb integrator) yields sulfur dioxide amount.
- Temperature control: Combustion zone maintained at (1150 ± 10) °C with a preliminary decomposition zone around 500 °C.
- Sample preparation: General analysis test sample ground to pass 212 µm (or 100 µm for samples with >5 % sulfur). Typical test portion: 0.05 ± 0.005 g (0.03 ± 0.005 g for >5 % sulfur).
- Reagents: Electrolytic solution prepared from potassium iodide, potassium bromide and glacial acetic acid (5 g KI + 5 g KBr in 250–300 ml water + 10 ml acetic acid). Tungsten trioxide is used as catalyst.
- Apparatus: Includes tube resistance furnace with silicon or corundum combustion tube, electrolytic cell (>400 ml) with platinum electrodes, magnetic stirrer, program controller, purified air supply and Coulomb integrator (integration linearity error
