1 reply to this topic

[inaracheme_11]

Hi all

 

This is my first post, and I kinda think this is a silly question. Currently I am doing flarenet analysis to figure out the backpressure etc for my psv. Downstream of the psv has expander (6" to 10"), and usually in my previous practice, i didnt model this reducer, and straight to 10" pipe segment. But because my client wanted to do some optimization where they want to install isolation valve directly after psv outlet flange, and then expander, i need to find what is the momentum and backpressure at the isolation valve and the expander.

 

So my question is, in flarenet, how can I model the 6" to 10" expander? Can I just put 10" pipe segment and then specify the expander equivalent length to the 10" pipe segment, and also specify the K factor for the losses? Or is there any other way to approach this accurately?

 

Thank you and looking forward for the opinions from the professional over here.

 

 

Edited by inaracheme_11, 03 December 2025 - 08:34 AM.

[DistillationDude]

Here is how I typically approach it, I'm going to add some extra info that you're probably already aware, but hopefully it helps others when searching for issues since it is very difficult to find information about this software online.

 

For Aspen Flare System Analyzer, you model reducers using the "Connector" segment. You specify length or angle, although I have not found any difference in outputs regardless of how I specify the reducer. I don't usually worry about reducers for the Tees since the entrance loss in the branch is accounted for in the Tee.

 

If you're immediately expanding out of the PSV, you can do it two ways:

Either do a "Ghost Pipe", where you put a pipe segment in at the PSV outlet diameter and specify a length of 0, then add your reducer

Do as you said where you ignore the reducer, since Aspen will still calculate the expansion if the outlet flange and outlet pipe size do not match

 

For your case, since you have a valve on the outlet flange before expanding, you're going to want to do the "Ghost Pipe", where the length is 0, but then you want to add your valve in the Fittings tab. Then throw in your reducer and larger discharge pipe. If your simulation is having trouble converging, I find putting in a small length (i.e., 0.1 ft, 1 ft, etc) can help. This causes some trouble on PSVs with small outlet sizes (like conventional 1"x2" that immediately expands to 4") since the pressure drop is so large that any bit of pipe length specified at the smaller size can drastically increase the backpressure.

 

It should look something like PSV -> 6" Pipe (0 length, ball valve fitting) -> Connector -> 10" Pipe.

 

I highly recommend thoroughly reading the user manual, as painful as it may be. I have essentially read it front to back and have gotten a much better idea of how it operates. It's still missing plenty of info that I think it should include, but it provides a good foundation. The most critical part of it in my opinion is where it explains the different property methods and when to use them. For you or anyone else reading this, be careful with how you specify your methods and compositions. Check your "Calculation Settings" on the Home Ribbon, then click "Methods". If your VLE Method is not Compressible Gas, you must specify compositions using mole or mass fractions, not the binary molecular weight modelling.

 

Let me know if you have any more questions. I've only got a couple years of experience but have used Flarenet extensively and consider myself pretty knowledgeable on it.