Help! Need properties! 4

[BrentB96]

Hi everyone, we are sizing a gas heat exchanger for this mixture and would like some help generating some properties on it:

N2=12.27%
CO2=43.39%
O2=1.42%
H2O=2.97%
H2S=4PPM

Need density, specific heat, viscosity, thermal conductivity, and molecular weight.

Appreciate any help/direction anyone may have.

Thanks,

Brent

 

[zdas04]

You can either go to the NIST web page or buy a copy of the GPSA Enginineering Data Reference (which I think that every practicing Mechanical or Chemical Engineer working in fluids should have access to anyway)

David

 

[BrentB96]

What if I took the percentage x each individual property, add them up, take average? Would this be acceptable practice?

 

[zdas04]

Probably if you accounted for the missing 40% you'd get better numbers.

There is no "average" in the calculation, you take mole percent times the specific property and then sum the results.

David

 

[BrentB96]

Heh, just noticed that. Its CH4 40% methane

 

[dcasto]

Mole% times the properties would not be too bad. The large amount of CO2 will give some problems when you get away from 60 F anf 14.7 psia, it doen't play nice with compressibility, as compared to the methane. If you give the T&P's for two points I could give you the properties, if you promise to look them up on NIST or the GPSA handbook too, no freebies, but a sanity check for future reference

 

[katmar]

There are mixing rules that you will find in books like Perry or "Properties of Gases and Liquids" (by Reid, Sherwood and Prausnitz - I think) . But I find the best approach to this problem is to look at the range within which the answer will fall and then do some sensitivity calculations. Often you will find that a particular property has very little impact on the calculation result and then you know that it is not worth expending great amounts of effort to calculate that property to the 10th decimal.

Once you have determined which are the important properties, concentrate your effort on them or decide whether a conservative estimate will make a large economic impact on the design. I often find that the uncertainties in the "fixed" values like flowrate, pressure and temperature are greater than the impact of the uncertainties in the properties. Looking at it this way helps to put the problem in perspective.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[zdas04]

Katmar has just defined the essence of good engineering--keep focused on the accuracy of the instrumentation and precision of the calculations.

If the detailed mixing rules will improve a +/-10% calculation by 0.01% then they probably aren't worth doing. If they will reduce your uncertainty to +/-8% then they could be worth much more than you spend.

David

 

[KenA]

or simulate the stream on HYSYS (or other simulator) and get properties at your required temp and pressure.