2 replies to this topic

[pTg]

Sorry for the basic question, but I'm having real trouble finding some information for some homework.

We've been tasked to find some information about building a compressor assembly for natural gas, namely horsepower required (Brake HP) and heat duty for coolers. Given information:

P(inlet): 100 psia
P(discharge, final): 2000 psia
Temp(inlet): 70 F
Temp(outlet, final): 90 F

Gas S.G.: 0.65
Rate: 30 MMcfd

Using "Natural Gas Engineering Handbook", Guo and Ghalambor, GPC 2005.

We are given tables in the book for a range of specific gravities of natural gases for isentropic (reversible adiabatic ideal) compression, and I can get starting and ending values for enthalpy (BTU/lbmol) using these Mollier tables. (Based on Brown, 1945)

I can't seem to figure out how to get K (or Cp or Cv) values, which are needed for calculating work using this equation:

w = k / (k-1) * 53.241*T1 / SGgas * [ ( P2/P1) ^ ((k-1)/k) -1]

or I'm missing something rather basic about work vs. enthalpy.

I've tried looking for K-value charts and found some, but they all seem to be for single components, or at least KNOWN components; trying to find k-values from knowing specific gravity only seems tricky.

Thank you in advance for your time, I hope this made sense.
Cheers!

[ankur2061]

pTg,

All newcomers are advised to use the search feature of the forum to find answers related to their query. Most of the queries are repetitive in nature and a lot of previous discussion has gone into many of the new queries that have been posted on this very same forum.

There has been a recent query on the specific heat of Natural Gas and which I have answered. Here is the link:

http://www.cheresour...?showtopic=7901

I am really not sure of any method to determine the heat capacity ratio just from the specific gravity of the gas.

Hope this helps.

Regards,
Ankur.

[breizh]

Hello,

Do some "google" work under Polytropic coefficient ,natural gas.
regards

Breizh