Using a Single Module Micro GC Fusion to Rapidly Analyze the Composition of Natural Gas

The ability to quickly and precisely analyze the physical properties and chemical composition of natural gas is vital for natural gas producers, gatherers, and gas distribution companies for custody transfer. Natural gas engine, appliance and boiler manufacturers depend upon natural gas calculations to establish important development specifications, such as thermal efficiency.

Since the composition of natural gas varies, physical properties, such as relative density, compressibility, and heating value in British thermal units (BTU), have to be monitored. Even small variations in heating value can cause major financial impact.

The Micro GC Fusion Analyzer

The Micro GC Fusion analyzer is based on well-established microelectromechanical systems (MEMS) technology, and can handle testing of C1-C8 "plus" (methane through octanes "plus" hydrocarbons and fixed gases found in natural gas) using only one module.

The temperature programmable column allows operations to be performed rapidly, increasing sample throughput and decreasing the cycle time of analyses. Additionally, temperature programming enables fast column cleaning, removing contaminants from the column and so preventing them from having a negative impact on the service life of the column.

The Micro GC Fusion user interface is web based and integrated with Diablo EZReporter to automatically calculate physical properties and chemical composition after every sample run. The software produces a standard report with the aid of industry specific methods related to one of the following standards:

  • American Society of Testing and Materials (ASTM) D3588
  • International Standards Organization (ISO) 6976
  • Gas Processors Association (GPA) 2172, 2145-09

Experimental Procedure

A single module Micro GC Fusion equipped with a 12-meter RT-Q-BOND temperature programmable column was used to analyze 10 runs of a natural gas calibration standard. Optimizing the temperature ramping profile allowed the elution of C1-C8 components within 4 minutes. The concentration amounts found in the calibration gas standard are listed in Table 1.

Table 1. Natural gas calibration standard concentration information

Component Mole %
nitrogen 1.525
methane 88.67
carbon dioxide 1.206
ethane 2.994
propane 2.006
isobutane 1.004
n-butane 0.996
isopentane 0.300
n-pentane 0.300
hexanes 0.603
heptanes 0.320
octanes "plus" 0.075

Results

It is not possible for C4-C8 Plus components to elute within an acceptable time frame in isothermal operation, thus causing carryover. Propane elution is delayed with a wide peak shape. The temperature programming extends the RT-Q-BOND analysis to C8 Plus, and provides sharp peaks for all components of interest, resolving and measuring all desired components within 4 minutes. The chromatogram of the natural gas calibration standard is shown in Figure 1.

Chromatogram of the natural gas calibration standard

Figure 1. Chromatogram of the natural gas calibration standard

Unprecedented area repeatability is exhibited by the Micro GC Fusion over 10 consecutive runs. Table 2 summarizes the area percent relative standard deviation (% RSD) values. A sample natural gas analysis report generated using the Diablo EZReporter is illustrated in Figure 2.

Table 2. Repeatability data for ten runs of the natural gas calibration standard

Number of Component Component Retention Time (s) Area %RSD
1 nitrogen 29.48 0.314
2 methane 30.19 0.359
3 carbon dioxide 34.70 0.414
4 ethane 47.04 0.402
5 propane 86.09 0.660
6 isobutane 113.33 0.426
7 n-butane 118.48 0.454
8 isopentane 136.40 0.449
9 n-pentane 139.37 0.439
10 hexanes Group Range 0.403
11 heptanes Group Range 0.827
12 octanes "plus" Group Range 1.186

Natural gas analysis report using Diablo EZReporter

Figure 2. Natural gas analysis report using Diablo EZReporter

Conclusion

With temperature programming, natual gas components up to C8 Plus can be reliably analyzed within 4 minutes on a single module Micro GC Fusion analyzer. The web-based user interface automatically displays all the measurement results in table format once the analysis is finished. The integration of the optional Diable EZReporter software allows automatic generation of the industry standard compliant natural gas analysis reports after the sample run is completed, thereby offering important data for custody transfer situations.

This information has been sourced, reviewed and adapted from materials provided by INFICON Inc..

For more information on this source, please visit INFICON Inc.

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