9 replies to this topic

I have a quick question regarding natural gas properties (pipeline spec).

What are some typical mass densities (kg/m3) of natural gas ~ assuming the gas is around 10 deg C?

Thanks

[Art Montemayor]

I am astounded that a Chemistry or Chemical Engineering Student would solicit the density of a gas without giving the conditions of the gas - not only temperature, but also PRESSURE.

Is the equation of state for gases still PV = Z n R T??? If so, what do you think the "P" stands for?

Thanks for answering in a very rude tone and I apoligize for not making my question very clear.

However, I was looking for a typical value of the density (assuming a range of pressures). If it would help you, or others, say a pressure of 3000kPa, or how about a pressure of 500 kPa.

To me it is not imperative to know an exact density, therefore I never included the pressures.

For next time I will try and make my question clearer, so that I don't recieve any rude answers.

[breizh]

Hi ,

I found this calculator very helpful , will it support your query?

http://www.pipeflowc...com/naturalgas/

Breizh

[Zauberberg]

There is no "typical value" for density of a gas at such wide pressure range. If you are familiar with the very basics of thermodynamics, you would have never asked such question. Saying "I don't need to know the exact density, and therefore I never included pressures" - but you included temperature which comes from the same equation.

Secondly, I voted your second post with the "minus" sign as your reply can be considered as rude, not the Montemayor's one. Art has spent years and years by dedicating his free time and all the knowledge and experience he has, in helping students and engineers worldwide. If he was a rude fellow, there wouldn't be so many people here considering him as an engineering guru, which he really is.

Good luck next time,

[MrShorty]

When I think of natural gas, I think of something that is mostly (90+%) methane. If you just need reasonable accuracy, I would be tempted to look up the density of pure methane (from a resource like Matheson Gas Data Book or Perry's Chemical Engineer's Handbook or webbook.nist.gov). That should be a reasonable estimate of the density of natural gas.

If you want a more general approach (especially if you are going to do this a lot), I might suggest taking the time to program a cubic EOS into a computer program or spreadsheet. Even though it can be intimidating to program a cubic EOS because of the numerical algorithms required, I find it is a useful skill to have and a useful code block/spreadsheet to have kicking around in my program library. Once you have the EOS coded for pure methane, it would be a relatively simple matter to add the mixing rules so you could look at the effect of composition on density.

[yeek]

Natural gas is not a pure component and its a mixture of things. Methane being the major component but also other things like ethane, propane.

If i was given this problem then I would first agree with the people I'm working with about the components and then use HYSYS or something to obtain the properties I want.

[paulhorth]

This is such a dumb question.....maybe this guy thinks that natural gas is a liquid, despite the clue in the name? Or, maybe he doesn't know the difference between a gas and a liquid, in which case he is really in the wrong profession.

I don't think you need a cubic equation of state, or Hysys, to answer this. Art has already given the equation of state, PV=zRT, from which the density is:

rho (density) = P.M./(z.RT) where M is the mol weight, this is all you need to know about the composition. Get your units consistent and use absolute temperature!

z can be looked up in charts in the GPA Handbook or elsewhere. That's how we did it before HYSYS was invented.

Paul

[sheiko]

Hi,
The only case I know when you can try to consider a "typical" density for natural gas is for LNG - Liquefied Natural Gas.
I have indeed worked in a LNG receiving and regasifying terminal, where the operationnal guys used to consider a specific gravity around 0.5 for the liquid NG in their routine calculations.

Edited by sheiko, 10 April 2011 - 09:52 AM.

[breizh]

Hi ,
I like Mr Shhorty's answer , let you develop your own xcelsheet , you will learn a lot .
I 've attached a xcelsheet from others , to support you.

Breizh