5 replies to this topic

[processengineer2018]

i want to liquefy simple air through the compressor. I am selecting thermoflash and selecting two fluid packages, but all of them gives me errors when air passing through the compressor. what I can do ? which packages are the best for this situation ?

[Pilesar]

I suspect you are a student. If so, use the student forum for future questions.

I think your question is: 'Why do I get errors when I use the compressor unit of a steady state process simulator to try to compress air to form a liquid.'

The compressor unit likely is designed for vapor phase only. You may need to use the flash or separator unit instead to find the stream properties at the pressure and temperature you need. Do not use 'air' as a component, but instead use the components of air (nitrogen, oxygen.) Use an equation of state such as SRK or PR. 

Clarify your question if I misinterpreted what you are asking.

[processengineer2018]

Pilesar:

 

Thanks.  I was using nitrogen and oxygen, not just air.   Also I have selected PR, an ideal gas fluid package.  Yes, I'll use the student forum for further questions.  But how to control flow rate in that case?  Because even I'm changing, after running it show again the flow rate that I gave at the beginning.  But I want to run the process in the different flow rates.

[Pilesar]

Are you using a commercial process simulator? Which one? Do you have a converged simulation without errors? There must be some place in the simulator where you gave the beginning flow rate. To change the flow, just change the flow at that location. Steady state simulators enforce material balance for most units. There are probably 'advanced' tools in the simulator (e.g. controller, optimizer, case study) but you may find the 'trial and error' may give you quicker results for a simple simulation by a novice user.

[processengineer2018]

Pilesar:

 

I am using Unisim simulator. 

[Padmakar Katre]

Pilesar:

 

I am using Unisim simulator. 

 

As others have stated, compressor will help you to increase the pressure of inlet air stream, you can't liquefy the air in a compressor. Pls understand this fact.

 

You can change in inlet stream flow rate, which will get reflected in downstream lines. What all inputs you have provided? can you pls share snapshot of PFD along with inputs to stream and compressor? The flow is being altered by simulator, have you specified the head vs flow curve and you are changing system resistance that causes the flowrate to get changed.