Issue Shortcut Column and negative minimum refulx ratio

[kookma]

Describe the bug
DWSIM reports negative reflux ratio. The simulation is repeated in Hysys V11 and it shows correct value!

To Reproduce
Steps to reproduce the behavior:

1. Open the attached simulation file. It shows a simple shortcut column
2. Open shortcut column object editor
3. Scroll down to Results
4. See error: negative value for minimum reflux (-0.288117)
5. Solving in Hysys 11 returns (0.031)

---

Expected behavior
Reflux ratio cannot be negative

Simulation files
shortcut-column.zip

Desktop (please complete the following information):

• OS: Windows 10
• Classic UI
• DWSIM 6.1 Update 4

[DanWBR]

Is this correct, feed entering at 9.9 bar, condenser pressure = 2 bar and reboiler pressure = 4 bar?

[kookma]

Hi Daniel,
Yes, the data are not real! The condenser 3bar, reboiler 4bar and feed is 9.9 bar! But I can use real data and change it to some upper or lower limits!
My point is to issue a warning and do not return negative values as reflux ratio.

[DanWBR]

@kookma thanks, was just checking. I'm working on this already.

[DanWBR]

Please try reproducing this case in HYSYS and let me know the calculated Rmin.

shortcut-column.dwxmz.zip

[kookma]

The minimum Reflux Ratio is 0.079. The full result is attached!

Hysys-SC.zip

[DanWBR]

The distillate and bottoms temperatures in HYSYS are much lower than in DWSIM. A feed at 69 C and distillate at -106 C? Very strange. DWSIM calculates a distillate temperature of 7 C which makes more sense to me...

[DanWBR]

@kookma could you please attach a screenshot of the stream compositions? Thanks!

[DanWBR]

@kookma it seems that you've entered 4 kPa as condenser and reboiler pressures, I've did the same and now the temperatures match.

[DanWBR]

I'm getting 0.36 as minimum refluxo ratio now. Not the same as HYSYS but at least it is not negative. I've inspected the code and it seems correct according to Underwood's method as described in the Distillation Design book. Let's keep this issue opened just in case something new shows up.

[kookma]

@DanWBR Sorry for that strange mistake :-) The file I sent you was in Hysys 3.1. I checked the results with latest version V11 and I got 0.461 for minimum reflux ration very close to DWSIM simulation you sent me above!

HysysV11.zip