Aspen EDR Design & Simulation Mode Difference

[Said92441322]

Hello,



In an attempt to design a shell & tube heat exchanger using Aspen EDR, I have designed a BHM exchanger to cool syngas from 46 DegC to 18.35 DegC using chilled water at 7 degC with excess area value of 0 %. However, when I used the same exchanger geometry generated by design mode in simulation mode for same flows and inlet temperatures of Syngas & Chilled Water as design case the resultant heat duty is different than that of design mode.



Anybody can highlight what is the reason behind this difference of duty

 

[Said92441322]

This is the simulation file attached for the sake of the comparison

 

[MortenA]

I think the HYSYS EDR software and the simulation toll will not reach the same U value with the same geometry (check the "transfer rate service") in the output you attached against what HYSYS the calculates. You can the choose to use a simple model and input the U value from EDR - but this will then not compensate for different flow . I cant remember if there is a work around.

--- Best regards, Morten Andersen

 

[georgeverghese]

There is only a 5% difference in duty, so I think it is okay. Pls see Perry Chem Engg Handbook - chapter on HX thermal design which states the range of deviation in duty prediction for some of the better known HX design methods.
By the way , you have allocated 0.25bar dp for the chilled water on the shellside, so why have you chosen H shell? You could have done this same duty with a TEMA BEU HX.

 

[georgeverghese]

Strange, there seems to be a heat balance discrepancy between the 2 cases. Though the service conditions on the chilled water side are almost exactly the same for the 2 cases, it is not for the process gas side.
Either the gas composition is not the same for the 2 cases, or the thermo model for the process gas side is not the same.

 

[Said92441322]

Dear georgeverghese,
All conditions were maintained the same including PG composition & Property package. All what I have done is to swith from Design mode to simulation made keeping the current geometry and removing the outlet temperature which I have designed the exchanger for. Also, while designing I made sure that highest to required area ratio to be equal to 1 and minimum excess area to required is 0%. The purpose of this task is only familiarize myself on how EDR perform calculations & results not for real design of heat exchanger.

 

[georgeverghese]

Would then suspect the convergence error in the thermodynamics model or the convergence error in the thermal design/ rsting routine between these 2 cases is not the same. Pls check the convergence history in the detailed simulation output which should list out the error produced for thermal design and for thermodynamic enthalpy for these 2 cases.