6 replies to this topic

[ahmadijaz65]

Hi

I am currently working on a project in which there is an INLET stream (100% Nitrogen) at 25C and 250bar. I want to depressurize it using Turbine/Expander model in Aspen Hysys and bring it down to 40bar. I have performed the steady analysis and want to perform the dynamic analysis i-e want to observer the decrease in temperature after few seconds. Switching to dynamic mode, after performing steady analysis, I have created a strip chart to observe the decrease in Temperature due to gas expansion. But strip chart is only showing me the steady state outlet temperature all the time.

Can I observe the decrease in the temperature graph from 25C to whatever it achieves after reaching steady state?

 

NOTE: flow sheet is simple. An inlet stream, followed by an Expander and the outlet stream.

Edited by ahmadijaz65, 20 March 2017 - 02:02 AM.

[pavanayi]

Ahmad,

 

If your exhaust pressure is steady at 40 bar, the temperature will also be steady at whatever it is. The temperature gradient happens inside the expander (because the pressure gradient exists inside the expander).

 

What are you trying to figure out?

[ahmadijaz65]

Thanks for replying !

 

yes you got my point very well. Now I actually want to obtain that graph for the gradient which exists inside the expander?

Is it possible? should i create the strip chart for the expander instead of outlet stream?

 

All i want is to see that change with time. Kindly guide me through it.

 

I have practiced an example of distillation column to visualize the composition on the plates at different interval of time. it worked perfectly. I have applied the same procedure to perform the transient analysis but it is not working this time.

 

Dummy flow sheet of my project is attached with values.

Attached Files

•  Untitled.jpg   23.03KB   1 downloads

Edited by ahmadijaz65, 20 March 2017 - 02:13 AM.

[colt16]

Thanks for replying !
 
yes you got my point very well. Now I actually want to obtain that graph for the gradient which exists inside the expander?
Is it possible? should i create the strip chart for the expander instead of outlet stream?
 
All i want is to see that change with time. Kindly guide me through it.
 
I have practiced an example of distillation column to visualize the composition on the plates at different interval of time. it worked perfectly. I have applied the same procedure to perform the transient analysis but it is not working this time.
 
Dummy flow sheet of my project is attached with values.

I don't understand. What you mentioned about the distillation column example is not dynamic at all but steady state.
Those are detailed tray-by-tray compositions which are all basically saturated liquid and dew pt conditions for the vapour and liquids at various equilbrium stages. They are not "dynamic" unless you introduce a step change.

The point with a dynamic system is to first simulate a steady change and then introduce a step change (e.g. A fluctuation in feed pressure/temperature) and then you may observe how the outlet pressure change if you are modeling some kind of control system with a particular tuning.

Actually to be frank I am not sure what you are trying to find out.

[ahmadijaz65]

Okay! To be more specific, in my analysis the inlet stream temperature has decreased from 25C to -75.77C. This large variation in temperature has definitely taken some time. Let's say this variation happens in 10 seconds. So i want a graph for these 10 seconds, showing the decrease in temperature from 25C to -75.77C. That's it.

 

Right now, I only have a steady state result -75.77, a single numerical value. I am looking for a Temperature vs. Time graph.

 

 

Moreover, if you have an access to hysys package then i will encourage you to perform this simulation for me. It will hardly take 5 minutes but it will solve my problem. My flowsheet is attached. I am using SRK property package.

Attached Files

•  post-311077-0-17757700-1489994596.jpg   23.03KB   1 downloads

[colt16]

Okay! To be more specific, in my analysis the inlet stream temperature has decreased from 25C to -75.77C. This large variation in temperature has definitely taken some time. Let's say this variation happens in 10 seconds. So i want a graph for these 10 seconds, showing the decrease in temperature from 25C to -75.77C. That's it.

 

Right now, I only have a steady state result -75.77, a single numerical value. I am looking for a Temperature vs. Time graph.

 

 

Moreover, if you have an access to hysys package then i will encourage you to perform this simulation for me. It will hardly take 5 minutes but it will solve my problem. My flowsheet is attached. I am using SRK property package.

 

It is still not dynamic! To be clear, what you are saying is the inlet has dropped to -75.77C at the outlet. There is a simple steady state of 25C in and -75.77C out.

 

When people study dynamics, they could step the inlet temperature by 3degC to 28degC and see how that -75.77C at the outlet changes at the outlet with time with a set of controller tuning parameters as there will be some time delay from the instantaneous step change. Eventually it settles into a new steady state of 28degC and whatever outlet T (a delta from -75.77C).

 

If you are looking for how things change internally within the expander, I am pretty sure HYSYS is not the tool for this even though I have not used this in a while. (this has nothing to do with what we usually call process dynamics, and your use of the term has let us down a rabbit trail).

[ahmadijaz65]

hahahaha ... 

 

Literally, i didn't want to confuse you. I came to this forum to get some answers. After this short discussion, my picture is almost clear. I am working on my project. Once it is done, i will share its details with you as well.

 

Bundle of thanks !