4 replies to this topic

[Tanzeel]

Hello.
I am a student of final year... I have simulated Atmospheric Distillation in hysys using 39.73 API crude...
Now i have to simulate vacuum distillation column using the residue from atmos tower and my plant is lube base...e.g LVGO, HVGO, 100-N, SAE-20, Vacuum bottom...
I also have the a supposed data but cannot converge the column...have some gr8 difficulties..plzz can anyone help me simulate VDU...i will be very much thankful.....
.

Please explain what specifications you have given to the column? converging parameters like Overhead composition, or Reflux ratio, Boilup etc? Probably after checking that I can help you out..

[Padmakar Katre]

Hello. I am a student of final year... I have simulated Atmospheric Distillation in hysys using 39.73 API crude... Now i have to simulate vacuum distillation column using the residue from atmos tower and my plant is lube base...e.g LVGO, HVGO, 100-N, SAE-20, Vacuum bottom... I also have the a supposed data but cannot converge the column...have some gr8 difficulties..plzz can anyone help me simulate VDU...i will be very much thankful..... .

Hi, In a lube based refinery, the VDU main fractionator configuration is same as the ADU or CDU main fractionator i.e. have side stripper for the product whereas in case of fuel grade or an enrgy refinery the VDU has VGO, LVGO and HVGO as side cuts. I will suggest you to follow the steps given bellow to model the VDU , 1. Model flash zone of the main fractionator as a flash separator (@ Flash zone pressure) i.e. outside the column and then feed the vapor and liquid to the main column. 2. See the vapor quantity @ flash zone/separator in order to decide the product rates. here if you are modelling the inerts and coil steam along the RCO feed, subtract the same quantity from the vapors generated and then calculate the total distillate make with some overflash (3-5 vol% on RCO feed). 3. Try converging with varying the pump around duties and product rates. Optimization will come later based on the analysis. 4. Still having convergence problem try feed the dummy energy stream to column to see the column heat balance and same error can be compensated by either varying the heater COT or pump around duties. * While modeling the VDU fractionator check the damping factors which should be less than 1 in order to have better convergence. * Model top pump around first with ovhd vapors (mainly steam and inerts) bottom VR as products. * Have more stripping steam at the column bottom stripping section intially and later on optimize. * Then model side strippers one by one with other pump arounds. Any change you will make must be small step change and not large enough to diverge the solution. Please let me know if you have still problem. Keep in mind that here I am giving you guidelines for convergence and not for optimization. Hope it helps you. 3.

Edited by Padmakar S Katre, 30 December 2011 - 05:49 AM.

[Tanzeel]

Thank you so much sir i will surely contact you tel the updates ... Thank you so much for your reply !!!

[Rajkumar Chate]

_{Please follow the steps suggested by padmakar, in addition of that i will suggest to add a liquid stream at top stage to converge the column. at initial stage there will not be the sufficeitn liquid to draw the liquid for top PA due to which even adding the top PA some times collumn wil not converge. Add liquid at top stage (same as LVGO/Diesel stream) then converge column and once u connect all PA then slowly cut the flow rate of additinal top stream.}