ISO 6974-5 pdf download – Natural gas – Determination of composition with defined uncertainty bygas chromatography 一 Part 5: Determination of nitrogen, carbon dioxideand C1 to C5 and C6+ hydrocarbons for alaboratory and on-line process application using three columns.
Column 3 Retains and separates nitrogen, methane, carbon dioxide and ethane which elute after n-pentane has left column 2.
4 Materials
4.1 Helium carrier gas. > 99,99% pure, free from oxygen and water
4.2 2-Dlmethylbutane, used to check comp4ele backtkishing of C54, 95% pure.
4.3 Working-reference gas mixtures (WRM), the composabon of which shall be chosen to be similar to that of the anticipated sample
A cylinder of distributed natural gas, containing all the components measured by this memod Is to be used by the laboratory as a control gas. The working-reference gas mixtures shall be prepared in accordance with ISO 6142. The working-reference gas mixture shall contain at least nitrogen. carbon dioxide, methane, ethane, propane. n-butane, iso-butane and possibly iso-pentane, n-pentane, neo-pentane and n-hexane
5 Apparatus
51 Laboratory gas chromatographic (GC} system, consisting of the following components:
5.1.1 Gas chromafograph (GC), capable of isothermal operation and equipped as folows:
a) column oven, capable of being maintained to within ± 0,1 ‘C over the temperature range: 70 “C 10 105 ‘C;
b) valve oven, capable of being maintained ovei’ th. temperature range 70 “C to 105 “C or alternatively having the capacity to fit the valves in the column oven;
C) flow regulators, capable of regulating the carrier gas fiowrates.
5.1.2 Injection device, consisting of a ten-port sample-injection valve Vi and also used for backflushing C5.
components (two six-port valves may be used for these ckities using the same operating principle). See Figure 1.
5.1.3 Column isolation valve, six-port, to by-pass the porous polymer bead column (column 3). See valve 2 in Figure 1.
5.1.4 Metal columns packed wIth either 28% DC-200’500 on Chrornosorb PAW or 15% DC-200500 on Porapak N, satisfying the performance requirements given in clause 6.3 and consisting of the following packing materials and column mensions, given as examples, for use with conventional and readily available inection valves and TCD.
Any alternative combination of columns which provide similar separations and satisfy the performance requirements may be used. Micro-packed or even capillary columns can be chosen, with appropriately-sized injection and detector systems, in which case packing or coating details would be difierent.
Columns shall satisfy the folowing requirements:
6.4.2 Analysis
The analytical system shown in Figure 1 compnses one ten-porl sam ple-irijectionbackf lush valve, Vi and one sixporl by-pass valve V2. Restrictor A maintains the pneumatic balance of the system when column 3 is isolated. The detailed setting-up procedure is given in annex A. (Two six-port valves may be used in place of the 10-port valve VI one for controlling sample irection and the other backtlushing ca4unin 1. If these operations are simultaneous, their timings may be taken to be the same as those for a single 10-port valve.)
The time settings of the valve switching Operations shall ensure that
at VI is returned to the backflush configuration (configtirahon 1) after all me ,,-pentane leaves column 1 but
before the lowest C8 isomer leaves column 1 on its way to column 2,
bi V2 is switched to isolate column 3 (configuration 2) before any propane leaves column 2 (on its way to column 3) and after all the ethane has left column 2 and entered column 3.
C) V2 Is not returned to reconnect column 3 (configuration 1) until all the n-pentane has been detected, having emeged from column 2 via column I.
7 Expression of results
Reler to ISO 6974-i.
7.1 Precision and accuracy
Reler to ISO 6974-2.
See annex B for typical precision values.
8 Test report
Report the results in accordance with clause 14011506974-I :20O0.
ISO 6974-5 pdf download – Natural gas – Determination of composition with defined uncertainty bygas chromatography 一 Part 5: Determination of nitrogen, carbon dioxideand C1 to C5 and C6+ hydrocarbons for alaboratory and on-line process application using three columns
