Production • Processing • Handling
Te heavy viscous sample was weighed directly into a boat and introduced into the combustion tube using automatic boat injection. Sample combustion occurred at 1000°C under controlled conditions ensuring complete combustion of sulphur to sulphur dioxide and nitrogen to nitrogen oxide.
Table 1. Sulphur analysis result.
fluctuations in the UV light. Tis ensured ultimate stability of the system. Detection of light emitted during the relaxation of excited SO2
place in accordance with the following reactions: R-S + O2 SO2 SO2 + hv1 SO2*
+ CO2 SO2* SO2 + hv2 + H2 O
(1) (2)
Te light emitted was proportional to the sulphur concentration as referenced against stored calibration information. Te result was displayed as the concentration of sulphur in the sample. For nitrogen, NO was swept to the detector,
where it was mixed with a stream of ozone to form NO in an excited electronic state whereby NO + O3
à NO2
Te dry gas sulphur stream entered the reaction chamber of an ultra violet (UV) fluorescence detector, where the SO2
molecules were excited
by a pulsed UV light source. A condensing lens focused the pulsed UV light onto a mirror assembly comprising eight high precision mirrors which also functioned as a bandpass filter ensuring only wavelengths corresponding to ground state transitions in SO2
pass through. Table 2. Nitrogen analysis results.
A PMT detector measured the light intensity and converted it electronically, with reference to stored calibration information, to display the analytical result as the mass of nitrogen or as nitrogen concentration in the sample. Results. Fig. 1 and 2 display examples of the sulphur and nitrogen calibration lines used. Te sulphur and nitrogen results are detailed in
Tables 1 and 2, whereas Table 3 provides a summary of results. Te extremely low relative standard deviation (RSD) demonstrates the suitability of the method used for the analysis of bunker fuel samples.
Te photomultiplier tube (PMT) subsequently detected the emitted UV light from the decaying SO2
molecules. A photo detector located at the back of the fluorescence chamber continuously monitored the pulsed UV light source and was connected to a circuit that compensated for
Table 3. Results summary.
Conclusion Sulphur and nitrogen content in bunker fuel can be regularly monitored using high temperature combustion with chemiluminescence and UV fluorescence detection to ensure compliance with new legislative requirements. High temperature combustion offers a reliable, fast and accurate technique for the simultaneous analysis of sulphur and nitrogen in bunker fuel samples. l
Debbie Batt is Senior Applications Specialist, TN/TS/TX/ TOC Analysers, Thermo Fisher Scientific, Cambridge UK.
www.thermofisher.com
* + O2 . Te excited NO2 * rapidly
returned to its ground state via a cascade of infra red (chemiluminescence) photons such that:
NO2* NO2 + hv.
molecules took
22
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