5 replies to this topic

[winnyadya]

Dear all,
i have assignment to calculate composition of the incoming gas compressor.
One of gas composition is hexane plus.
what is hexane plus and how do i get information properties of hexane plus?
i need information such as specific heat constant, critical temperature and critical pressure.
And i don't understand, how to identify hexane plus on HYSYS.
anyone can help?
thank you.

[ankur2061]

winnyadya,

Hexane plus or C6+ is a terminology used in natural gas engineering which indicates a grouping of heavier hydrocarbons such as hexane, heptane, octane, nonane etc. These could also include branched chain hydrocarbons with molecular weight more than 86 (molecular weight of hexane).

Most natural gas which is commercially distributed through pipelines contains very small amounts of C6+ hydrocarbons. In critical applications where it is essential to monitor the C6+ content gas chromatographs are provided in the natural gas transmission system to measure their exact composition and provide systems for their removal to acceptable limits.

When doing engineering calculations related to natural gas and when the exact composition of the heavier hydrocarbon species (hexane and heavier) is not known it is common practice to consider the heavier hydrocarbon as hexane only since as mentioned earlier the amount of heavier hydrocarbons is normally negligible. If for any reason it is ascertained that the natural gas contains significant quantity of heavier hydrocarbons then a complete analysis needs to be done for the gas either in a laboratory by collecting the gas sample in a sampling container or by using an online analyzer such as a gas chromatograph.

Hope I have been able to clear some doubts.

Regards,
Ankur.

[Zauberberg]

In order to define the C6+ fraction you need to look at what laboratory data is available - if any. I have rarely seen this C6+ fraction analyzed at the component level. More often, this fraction is characterized by average Molecular Weight and Specific Gravity (or density) at certain conditions, and based on this information you can use process simulator to perform a pseudocomponent breakdown resulting in same bulk properties (Mol weight, density) as specified by you. The more input data you have, the more accurate characterization you can obtain.

The properties you mentioned and which are normally required for any design/troubleshooting work, you can obtain from the simulator as well.

[winnyadya]

thank you ankur2061 and Zauberberg for your help...

[demank]

... and based on this information you can use process simulator to perform a pseudocomponent breakdown resulting in same bulk properties (Mol weight, density) as specified by you...

Hello Zauzerberg and all, if I want to know the properties like Low Heating Value, which process simulator may I use to?

[Zauberberg]

For calculating Heating Value of a gas stream, you don't need a simulator. Just look at any textbook in thermodynamics and find heating values of individual/single components. Then apply the common mixing rule i.e. LHV = X1*LHV1 + X2*LHV2 +... + Xn*LHVn, where Xi is component mole fraction and LHVi is component heating value. It was discussed recently in another thread.

Heating values for many components you can find on the internet, e.g. http://www.engineeri...lues-d_420.html