AIR LIQUIFICATION

[aken]

hi. there is a big difference in simulation between COCO and aspen in terms of intermediate results. Your help to troubleshoot the differences will be much appreciated. the stream AIRCOM after compression the temperatures are totally different by a big margin. The stream AIRHX and AIRCMCOL are liquid in COCO and vapour in ASPEN at same conditions. The stream LIQAIR has a high vapour proportion in COCO than in ASPEN. Thanks for your help, attached are relevant files.
ref: SIMULATION OF AIR LIQUEFACTION USING ASPEN PLUS

[jasper]

Making the compressor 100% efficient results a temperature of 961 C. Seems like a high difference indeed. But if you look at the entropy balance of the compressor at 100% you see that the compressor is correctly solved for. Hence, the work cannot be less than that. Checking the feed AIR and AIRCOM streams at Aspen conditions:

Annotation 2019-11-12 093454.png (25.25 KiB) Viewed 10600 times

This is not feasible of course (second law of thermodynamics). So perhaps you are not using the same thermodynamics, but the difference would be quite large for just a difference in thermo. Do you have access to Aspen to check the entropy of the two streams?

[aken]

Thanks Jasper for your help. Unfortunately l don't have access to Aspen, but l just take the material online from aspen tutorials and try reproduce them in COCO simulator as way of teaching myself simulation. The point you raised about entropy, was it that if we set efficiency to 1, the entropy should balance as we would assumed ideal conditions, and we can use that idea to confirm if the compressor calculation is ok? Just wanted to clarify as l was a bit confused. Thanks again

[jasper]

Isentropic, or reversible, operation is the limit of what you can theoretically reach - this identifies the minimum amount of enthalpy you need to put in. The temperature then follows from enthalpy balance. Efficiency is defined as the ratio of actual enthalpy use vs minimal enthalpy use.