Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in

Calculate the condensation temperature of any gas mixture at a known pressure 4

Status
Not open for further replies.
hirschaplin

hirschaplin

Petroleum
Jul 10, 2021
60
0
0
SE
Hello,

Typically I use HYSYS or ChemCAD to find out the condensation temperature of my gas mixture at a certain pressure. Information that I need to know this when working with compressors and trying to understand the importance of a KO drum and how to design it.

However, I have been building up a sweet little excel sheet that is tailored with all kind of calculations that I need for my work... It would be very helpful to also calculate the condensation temperature in my excel sheet to avoid the extra step of setting up the process in HYSYS or ChemCAD just to get the condensation temperature.

I have already built a simple gas mixing feature in excel based on a gas database including most of the typical properties for each gas that I can use when mixing my gas.

Example stream at 10 deg C and 1,61 bar abs. with the following gas composition:
gascomp_dbbkve.png


HYSYS tells me that the condensation temperature for this stream is -6.466 deg C. How can I calculate the same result within +/- 10% in my excel sheet?
 
Replies continue below

Recommended for you

Sort by date Sort by votes
Yes I checked that and other threads with similar topics before I created this thread. Seems rather inconclusive...

It must be some way...
 
Upvote 0 Downvote
Thank you guys, seems like these answers are really helpful. Can't wait until I can try it out with the above composition example.

Do you expect that the result will be very close to the -6.466 deg C as already given by HYSYS? Or is HYSYS solving this in a much more sophisticated way that can't be match with a do it yourself excel formula?
 
Upvote 0 Downvote
Will you share too? [thumbsup2]

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."
 
Upvote 0 Downvote
A compressor suction KOD is meant to knock out residual liquid droplets carried over in the vapor from some upstream unit, perhaps a separator. So the liquid phase in this KOD will have the same chemical properties as the liquid phase in this upstream separator.
 
Upvote 0 Downvote
Good evening Pierre,

Thanks for sharing. Really helpful, I am not sure I would have reached that myself.

Few questions as I am trying to understand how it works.

[ol 1]
[li]I assume G51:G61 is including the critical pressure value (Pc) from the critical constant table. I would guess that G51:G61 and E43 needs to be the same unit of measurement, in order for this to work. But now it seems like the values in G51:G61 are entered as Pa and not kPa as titled in the Excel?

For example, critical pressure value (Pc) for Methane is showing as 4.59 Pa in the table and in the excel it is showing as 4599 kPa.

4.59 Pa = 0.00459 kPa
4.59 kPa = 4590 Pa
4590 Pa = 4.59 kPa

Why is the value in G54=4599 when the table value is 4.59 Pa? It should be G54=4590?

It is pretty much the same small discrepancy between all values in G51:G61 compared to the constant table you shared.

[/li]
[li]Did you adjust the value in H43 manually until the value in Q69 is 0.00xx (negligeable)? Or how did you come to the conclusion that the value in H43 should be 266,987860480137? I just ask because the value in Q69 was not exactly 0 as it seems like you have entered manual inputs to reach a negligeable value in Q69. Instead I tried to use the Excel built-in solver add-in, solving that Q69 should become 0 by changing the value in H43 which yielded a clean 0 result in Q69 with H43=266,988028998081.

Do you know if it is possible to solve the equation with a formula instead of the solver? Well really what I want is to avoid opening the solver every time the gas composition is changed/updated as it is easy to forget to update it manually every time?
[/li]
[/ol]
 
Upvote 0 Downvote
@Georgeverghese typically I get a specification stating the minimum requirements and if supplementary equipment is needed it is our responsibility to bring that forward to the EPC contractor. If the suction gas temperature is close enough to the suction gas condensation temperature, we want to be 100% sure to elevate the compressor inlet above battery suction limit as well as considering some kind of liquid collector, such as a KO drum or a cheap charlie solution with a dual purpose silencer or buffer tank that also can accumulate some liquid if needed.

Many projects are about flare gas recovery and then indeed it is some kind of separator upstream to our equipment.

I just want to know the condensation temperature to be on the safe side and not create a silly situation where liquid can form and we have a disaster.

If we now assume that gas condensation temperature is about -6 deg C, at what operating temperature would you feel safe that no liquid is possibly formed? For example, at 0 deg C operating temperature I would feel nervous with only 6 deg C margin!!! Do you guys have some comfortable/safety margin for condensation temperature?
 
Upvote 0 Downvote
HI,
You did not read correctly the table! All the PC data are expressed in Mpa (1E06 Pa).
Regarding the calculation, it's an iterative calculation, solver is the adequate tool designed for this purpose.
Any time you change the data (manual input), you have to activate the solver to get the correct answer, you also need to pay attention to the constrains (domain of calculation compatible with your products))
The only way is to build your own excel sheet to better understand how it works, probably also good for you to review Newton Raphson method.
I cannot offer more.
Good luck
Pierre
 
Upvote 0 Downvote
Thanks for quick reply.

Ok it is clear with MPa. But how you get it to 4599 and not 4590 if we use the values from that table you linked?

What do you mean with "you also need to pay attention to the constrains (domain of calculation compatible with your products)"? The pressure limit of 3,5 MPa?

Yes I am trying to integrate these methods in my main excel sheet, hence my questions trying to understand exactly how it works.
 
Upvote 0 Downvote
Hi,
a) I've not used the data in the table, I've used another source (Korean data base).
b) No, constrains appear when you open the solver, range of temperature (above and below a certain value). This helps the resolution of the equations by restricting the domain and on Chemical engineering perspective it shows that you have a clear view of the process (physical meaning).
Pierre
 
Upvote 0 Downvote
Wilson correlation
ln(Kval) = ln(Pci/p)+5.373*(1+Aci)*(1-Tci/t)
can produce decent results with (light) hydrocarbons,
however your mixture may include water or other non-hydrocarbon fluids and a EOS (there are many available in process simulators and thermodynamic libraries) can produce much more accurate results...
On the other hand, if you work with Excel, why do not consider a thermodynamic library ?
There are many, free and commercial, available, I have Prode Properties but you may consider also RefProp, CoolProp etc.
With a thermodynamic library you can obtain results comparable and in some cases more accurate than those from the simulators your mentioned...
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

BigChungus
  • Question
calculate temperature of saturated steam discharged to atmosphere via leak
Replies
17
Views
44
TBP
TBP
Sam1390
  • Locked
  • Question
Twin Lobe Gas Blowers Outlet temperature
Replies
10
Views
11
Sam1390
Sam1390
Ameen1985
  • Locked
  • Question
Should the air specific heat ratio be included in the ideal gas law ? 1
Replies
2
Views
3
Snickster
Snickster
petda15
  • Locked
  • Question
Energy Balance - Enthalpy Change of a Fluid at Changing Pressure
Replies
3
Views
4
pierreick
pierreick
RegiSTR
  • Locked
  • Question
Cool a circuit at near constant temperature
Replies
12
Views
13
LittleInch
LittleInch
Back
Top