## AGA 8

## AGA 8

(OP)

I can use AGA 8 to calculate the compressibility of natural gas from flowing temperature and pressure and the mole fractions.

Which equation of state is then used to calculate density at base conditions in a typical flow computer?

Thanks

Dan

Which equation of state is then used to calculate density at base conditions in a typical flow computer?

Thanks

Dan

## RE: AGA 8

I hate Windowz 8!!!!

## RE: AGA 8

## RE: AGA 8

## RE: AGA 8

I hate Windowz 8!!!!

## RE: AGA 8

I hate Windowz 8!!!!

## RE: AGA 8

"The molar density of gas is calculated from AGA 8 equation 24 by using the Brent's Method in all cases."

This doesn't make a lot of sense to me I don't have AGA 8 and I'm not familiar with Brent's Method.

## RE: AGA 8

http://www.et.byu.edu/~rowley/ChEn273/Topics/Mass_...

http://www.et.byu.edu/~rowley/ChEn273/Topics/Mass_...

The feedback you have received is probably from someone that's looking at the algorithm, but isn't exactly sure what's going on there. They are only giving you half (or less) of the whole story. Once you have the gas conditions located in relation to the critical point, you can determine the density. I haven't looked at this for years, but I think that AGA8 also prescribes the compressibility factors to use in an associated table. They may be substituting an equation to do that, as it is probably within the accuracy of the AGA table, and more easily calculated by their flow computer, rather than doing lookups of table values.

Continue on with the Brigham Young University tutorial to see other equations of state you might be able to use. http://www.et.byu.edu/~rowley/ChEn273/Topics/Mass_...

I have always found the BWRS has been accurate enough to suit my purposes, but I haven't been making flow computers for sales gas purposes either.

I hate Windowz 8!!!!

## RE: AGA 8

This may be an online solver that works within the acceptable limits of AGA8 using gas composition

http://www.mysolv.com/AGA8CalcIn.asp

I hate Windowz 8!!!!

## RE: AGA 8

In the most readable order (which is the reverse order of the calculation process):

- Equation B.10
- Equation B.11
- Equation B.13
- Equation B.14
- The various constants can be found in Table B.2

The general confusion over density in AGA8 (and consistent lack of description in textbooks and papers) is explained by Figure B.1 -AGA8 uses a guess and check method for density. Excel has a "Goal Seek" or Solver tool that can reduce an error-calculation cell to a value near zero. If you're using other mathematics software...then you already know what to do.I'm also partial to http://www.ijcea.org/papers/4-A504.pdf and http://bib.irb.hr/datoteka/293349.FMI_Cp_JT_Ie_200... for more detailed thermodynamics if you have a more complicated applications than simply "gas in a tank/reservoir/non-restricted pipe".

Hope this helps!

## RE: AGA 8

the core includes a iterative procedure which solves a volume root,

with a tool as PRODE PROPERTIES you can compare AGA vs. other ISO formulations, or EOS as SRK, PR , LK, BWRS and GERG formulations,

AGA is very accurate and competitive against GERG formulations.

About calculating density for natural gas at standard conditions

do not forget that you are usually well above the critical point

for some components and ideal gas rule should be corrected with

compressibility factor (calculated with AGA or equivalent method)