6 replies to this topic

[ankur2061]

Dear All,

The steady-state AGA & Panhandle equations for gas pipeline transmission consider isothermal conditions for gas flow. What I am trying to know is how to incorporate the effect of temperature drop due to Joul-Thomson effect in these equations?

In very simple terms as the gas becomes colder due to pressure drop I should be able to transmit more gas in the same pipeline for other conditions such as gas composition & soil temperature remaining the same. Is there a modified equation for AGA or Panhandle methods which takes into account the temperature profile change due to Joule-Thomson effect?

Any guidance & help is welcome.

Regards,
Ankur.

[katmar]

I don't know of any know of any temperature varying versions of these equations, but there are two alternatives that you could consider.

1. Just break the pipeline up into 10 or more sections and recalculate the temperature and physical properties at the end of each section, and use the revised values as the input values to the next section.

2. Use the adiabatic integration of the Darcy-Weisbach for compressible flow as described in Crane TP410. As far as I understand, the AGA and Panhandle equations are just empirical approximations of Darcy-Weisbach anyway.

[ankur2061]

I don't know of any know of any temperature varying versions of these equations, but there are two alternatives that you could consider.

1. Just break the pipeline up into 10 or more sections and recalculate the temperature and physical properties at the end of each section, and use the revised values as the input values to the next section.

2. Use the adiabatic integration of the Darcy-Weisbach for compressible flow as described in Crane TP410. As far as I understand, the AGA and Panhandle equations are just empirical approximations of Darcy-Weisbach anyway.

Harvey,

I do know that the Panhandle equation is empirical but I think the AGA equation with the Colebrook solution for the friction factor inserted in it as per the equation given in GPSA Engineering Databook, 11th edition is not empirical.

Another thing is whether you could provide a worked out example for a typical gas flow problem with temperature profile change or give a reference for the same.

Regards,
Ankur.

[katmar]

I have never had a situation that required such accuracy that it was necessary to consider cooling, so I have no examples. I have never been involved in cross-country pipelines, and within the plant battery limits it would be very unusual for the change in temperature to be significant.

Unless you have a hot gas that is losing heat to the atmosphere, the worst case would be adiabatic and then I would just use the Crane TP410 procedure.

[ankur2061]

I have never had a situation that required such accuracy that it was necessary to consider cooling, so I have no examples. I have never been involved in cross-country pipelines, and within the plant battery limits it would be very unusual for the change in temperature to be significant.

Unless you have a hot gas that is losing heat to the atmosphere, the worst case would be adiabatic and then I would just use the Crane TP410 procedure.

Harvey,

I was indeed talking about cross-country gas pipelines transporting sales or sweet gas. I have developed a spreadsheet solution for all the gas pipeline equations - AGA, Weymouth, Panhandle A & B but all these solutions consider an isothermal gas profile along the length of the pipeline which is not exactly true when you have reasonable pressure drops along the pipeline & which lead to the cooling of the gas due to Joule-Thomson effect.

If somebody else has had the opportunity to deal with gas pipelines with reasonable pressure drop & the changing temperature profile along the pipeline, he or she is welcome to share this on the forum.

Regards,
Ankur.

[ankur2061]

Dear All,

I had some personal e-mail enquiries about gas pipeline hydraulics references & study material based on my post. Well instead of replying individually I thought the best way was to put it as a response in my own post. The references I have used are the following:

http://www.pdhengine... Hydraulics.pdf

&

the GPSA Engineering Databook, 11th edition, Chapter 17, Fluid Flow & Piping

These were essentially available to me to generate my spreadsheet solutions for isothermal gas pipeline flow.

Regards,
Ankur.

[kkala]

I was indeed talking about cross-country gas pipelines transporting sales or sweet gas. I have developed a spreadsheet solution for all the gas pipeline equations - AGA, Weymouth, Panhandle A & B but all these solutions consider an isothermal gas profile along the length of the pipeline which is not exactly true when you have reasonable pressure drops along the pipeline & which lead to the cooling of the gas due to Joule-Thomson effect.
If somebody else has had the opportunity to deal with gas pipelines with reasonable pressure drop & the changing temperature profile along the pipeline, he or she is welcome to share this on the forum.

Though I have dealt with city networks only, I know from other colleagues that they assume average soil temperature as operating NG temperature along the high pressure pipelines, all of which are buried here. Isothermal flow is assumed for compressible flow issues, except for short pipes (shorter than, say, 100 m or even less) where adiabatic flow is considered more representative. Where pressure gets inadequate, a compressor station is installed.
Joule Thomson effect is not apparently considered; and "apparent" means that I have not looked into the software used (mainly TGnet). But Joule - Thomson effect is thought here only through a restriction (orifice, valve); isenthalpic expansion calculation is used in these cases (an approximation).
Seeing that NG temperature is much affected by external environment, some cooling or heating can be considered insignificant.

Edited by kkala, 12 April 2010 - 04:08 PM.