Improvement of hydrocarbon dew point determination via gas chromatography

Grygorcewicz, Jon-Paul Frederick (2010) Improvement of hydrocarbon dew point determination via gas chromatography. [USQ Project]


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[Abstract]: A gas chromatograph is the most common method to continuously determine the hydrocarbon dew point of export natural gas. It is used to ascertain the composition of the natural gas mixture which is applied to a thermodynamic equation of state. Due to the inherent design of the process type gas chromatograph there are limitations to the computation of the gas mixture in the C6 to C8 carbon groups.

It was found that process type C9+ gas chromatographs determine a higher hydrocarbon dew point than actual, because it summates all the chromatogram hydrocarbon peaks
within the respective carbon group into the normalised alkane of that carbon group. The reason for this, is that the process type gas chromatograph does not have a method
to identify these species between the normalised alkane components in the C6 to C8 carbon groups.

Therefore the aim of this project was to research the 'equations of state' used to calculate natural gas hydrocarbon dew point from constituent analysis by Gas Chromatography and to develop a methodology to improve Gas Chromatography hydrocarbon dew point determination.

One important characteristic of the gas chromatograph, is that the measurement of carbon fractions greater than pentane, n - C5, is based on the relationship of component
elution time and hydrocarbon boiling point. The International Standard Organistation standard 23874 (ISO 23874, 2007) uses this relationship to calculate the boiling points of unidentified hydrocarbon components by linear interpolation between the normalised alkanes. The limitation of the ISO 23874 standard is that it is only applicable for laboratory analysis type gas chromatographs.

In order to exploit the boiling point and hydrocarbon component elution time relationship to identify unknown components using a process gas chromatograph, the author
developed his own method and a modified method of the ISO 23874 standard.

Trials on export natural gas, using the equation of state software program, GasVLE, a manual chilled mirror instrument and a Daniel 500 C9+ gas chromatograph proved
that the Grygorcewicz method is a valid characterisation method for further research and use in improving the hydrocarbon dew point determination of export natural gas
when applied to a process gas chromatograph on a custody transfer station or pipeline.

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Item Type: USQ Project
Refereed: No
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Engineering and Surveying - Department of Electrical, Electronic and Computer Engineering (Up to 30 Jun 2013)
Supervisors: Maxwell, Andrew; Hancock, Nigel
Date Deposited: 30 Mar 2011 06:20
Last Modified: 03 Jul 2013 00:35
Uncontrolled Keywords: gas; natural gas; hydrocarbon; moisture; gas chromatography; boiling point; export natural gas
Fields of Research (2008): 09 Engineering > 0913 Mechanical Engineering > 091305 Energy Generation, Conversion and Storage Engineering
09 Engineering > 0914 Resources Engineering and Extractive Metallurgy > 091406 Petroleum and Reservoir Engineering
Fields of Research (2020): 40 ENGINEERING > 4017 Mechanical engineering > 401703 Energy generation, conversion and storage (excl. chemical and electrical)
40 ENGINEERING > 4019 Resources engineering and extractive metallurgy > 401907 Petroleum and reservoir engineering

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