Study on uncertainty evaluation of GC-SCD determination of total sulfur in natural gas

Objective  The uncertainty evaluation of actual sample measurement was carried out to provide an application case for the determination of total sulfur in natural gas using GC-SCD method, thus enhancing the practical value of the determination data.

Method Combining with the practical testing experience of the GC-SCD method, the sources of uncertainty in measurement were systematically analysed at the first time. An uncertainty evaluation scheme was proposed based on the JJF 1059.1－2012 Evaluation and Expression of Uncertainty in Measurement.

Result The results of the uncertainty evaluation for total sulfur determination of actual samples showed that the extended uncertainty of sample 1 was 0.19 mg/m³ (k=2), mainly derived from carbonyl sulfide at 0.18 mg/m³ (k=2), while the extended uncertainty of sample 2 was 0.14 mg/m³ (k=2), mainly derived from hydrogen sulfide at 0.12 mg/m³ (k=2).

Conclusion  The main sources of uncertainty in total sulfur and individual sulfur compound measurement are sample analysis repeatability and standard substances, and the uncertainty of hydrogen sulfide and carbonyl sulfide mainly contribute to the uncertainty of total sulfur. Twice repeated measurements according practical work are recommended, as increasing repeated measuring times, and using high accuracy standards are recommended to improve the level of measurement uncertainty, it is suggested to use sampling containers, pipeline valves, and other components made with sulfur-resistant adsorption materials, so as to reduce the uncertainty of hydrogen sulfide and carbonyl sulfide individual sulfur compound measurement and ensure data accuracy.