5 replies to this topic

[u062268]

We are facing a problem in our CDU (Crude Distillation Unit):

• Product rundown test results: Gas oil 90% = 349.8 / 354.1°C; SRN end point = 276.6 / 285.3°C`

• Main Fractionator operation still not normal as there is no kerosene drawn off to stripper and SRN end point remains high

What does it indicates to !!!!??

how to start troubleshooting this issue???

Does it indicates to flooding or weeping or broken trays???

[sheiko]

Hi,

Apparently you don't cut between straight run naphta and kerosene. So the problem may be in this fractionation area.

Also why do you indicate two temperatures for the mentionned cut points?

Troubleshooting:

How much is the pressure drop across the column? and how many trays?

Do you have archived data?
If so, you should start trending the process variables of the column to see if something deviates and when.

Edited by sheiko, 07 December 2012 - 12:46 PM.

[u062268]

Plz find the attachment file and provide me by ur opinion

There are 45 trays in the column

Attached Files

•  ToP Vs. BoTT.xls   306.5KB   46 downloads

Edited by u062268, 07 December 2012 - 11:42 PM.

[sheiko]

Some remarks:

- the units of your data are missing
- the pressure difference between bottom and top is missing (a typical deltaP per tray is around 0.15 psi or 10 mbar)
- the temperature profile inside the column is unknown
- I would also trend the feed rate, the products rates (top, side, bottom), the steam rate, the reflux rate, the pumparounds rates to pinpoint some deviations
- one event apparently occured on August 21st, but what happened?

[u062268]

There were many shutdowns in Distillation column due to leak of gas in the Overhead Fin Fan Bunddles. The cause was high acidity of crude Feed and unsuffecient washing of salts in the bunddles.
These problems already have been solved.

Recently, No Kerosen Production and Naphtha is heavy and out of spesifications

Attached Files

•  done.xls   587KB   39 downloads

Edited by u062268, 08 December 2012 - 11:19 PM.

[venki1985]

Typically you can approach this by comparing the %yeilds of the products pre and post upset, this can give you insight where the %yield of kerosene you were getting during normal operations has shifted to which fraction. a total material balance would help, from this you can observe that one or more cuts yield would have increased, from that ul have to compare their corresponding IBP&FBP to exactly zero down to which cut ur kero yield has gone, for ex an excessive slippage of kero to diesel cut will reduce density of diesel and reduce its IBP and also inc its vol, flow, if its the case with SRN then its FBP will inc, also its density and also draw off temp. If SRN is ur first draw then reduce its draw rate thereby increasing its internal reflux, if its top prod then inc the refux rate or slightly inc top pressure to reduce excessive vaporization . try playing with these parameters and then find which is the limiting zone, only then u can narrow down the problem, then find the Dp in that zone, which could indirectly tell ur tray performance in those regions.

Hope this could give some directional inputs to your problem.