BS ISO 23978:2020 pdf download – Natural gas — Upstream area — Determination of composition by Laser Raman spectroscopy 5.7 Sulfur compound absorber Beakerflask, flask etc. filled with basic solution can be used as sulfur compound absorber in order to eliminate sulfur compounds discharged to the atmosphere. Sodium hydroxide solution (200 g/l), prepared by dissolving sodium hydroxide (chemically pure) in water is suggested as the basic solution. 6 Reagents and materials 6.1 Zero gas Pure argon or other monatomic gas is used to set the zero level of the Raman analyser. The purity should not be less than 99,999 %. 6.2 Base span calibration gases Base span calibration gas used to set software parameters shall be working standard pure gases or binary mixtures in accordance with ISO 6142-1, ISO 6144 or with ISO 6145. Binary gas mixtures consisting of blending zero gas and a single gas component present in natural gas are preferred when their typical concentrations in natural gas are below 75 %. For typical natural gas upstream area samples, 1 % H 2 S/Ar, 5 % CO 2 /Ar, 3 % N 2 /Ar, 3 % C 3 H 8 /Ar, 2 % C 2 H 6 /Ar, are suggested. As base span calibration gases for all but CH 4 which can be pure (100 %) or Ar diluted. 6.3 Working span calibration gases Regular calibration shall perform using working standard gas mixtures in accordance with ISO 6142-1, ISO 6144 or with ISO 6145. The working standard gas mixtures shall contain appropriate concentrations and cover the analytic range of the analyser. All components in the reference standard shall be homogenous in the vapour state at the time of use. The concentration of a component in the reference standard gas shall be close to the actual sample gas concentration, shall be less than relatively 20 % of the corresponding component in the test gas, the minimum concentration shall be greater than 0,02 %. 7 Measurement procedures 7.1 preparation Make sure the analyser placed on a flat, horizontal surface, in a clean location that maintained at a relatively constant environmental conditions: — temperature: 15 °C to 35 °C; — relative humidity: 10 % to 75 %. Set up the laser Raman gas analyser according to the manufacturer’s instructions, connect zero gas, base span calibration gas, measurement calibration gas, and sample in sequence to the instrument as shown in Figure 2....
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