5 replies to this topic

[Ahmed Said Abd ALLAH]

Dear sir,

 

I works as technical support for Delayed Coker Unit, we have revamped the unit by installing a new heater so that we could increase unit capacity by around 12% as well as enhance unit operabilty.

The revamp study did not encluded any modifications on main fractionator.

After start up and operating with revamped capacity (112% of original one), we noticed sever deterioration in products separtion and qulaity (CCR content in HGO) with no gain of traditional operation procedures of pump arounds adjustment. we also found alot of tower valves, nuts, nails and small segments in pumps strainers.

During following shut down we entered the tower and found catastrophic damage of tower internals; fallen trays, a huge number of tray valves were missing and complete segments are removed away its place.

Calculating the maximum vapour load to the tower, it was around 125% of design figures.

 

I'm studying the possiblilty of revamping the tower so that it can handle the increased load of around 115% of design safely.

 

My question is: If we can change tray type from valve tray to another one, can this work? or I have to change the whole tower shell with larger size?

 

Thanks

 

[PingPong]

For a 15 % capacity increase you need not increase the column diameter.

Modern trays will have considerably more capacity than old conventional valve trays.

 

However: not all modern high capacity trays are suitable for severe fouling service.

Contact KochGlitsch and especially inquire about their ProValve and SuperFlux trays for use in a Coker fractionator.

Sulzer and other tray vendors may be able to offer modern trays for this fouling service too.

 

You could also consider using grid packing instead of trays in the column part above the feed inlet.

Edited by PingPong, 10 September 2014 - 01:07 PM.

[Bobby Strain]

And you should carefully review operating data over the period before and after the problem. I don't believe that the higher rate would cause the damage you describe. There may have inadvertently been a slug of water introduced into the colum via the fresh feed. I presume that the feed first enters the sump then is pumped to the heater.

 

Bobby

[PingPong]

I fully agree. There is no way that a mere 15 % or even 25 % more-vapor-than-design would blow out the trays.

 

Steam explosion is indeed a possiblility, probably due to steam condensate entering with the stripping steam.

Or a sudden pressure surge from a coke drum.

Or bottom liquid level rising above feed inlet nozzle.

Or ...... something else.

 

If the cause is not fixed and that upset happens again, also the new trays will be turned into scrap metal.

[Ahmed Said Abd ALLAH]

Thanks alot for all replies

 

I want to added the following details:

 

1- Reviewing tower data i found that the tower is designed for vapor load of 108 % of original design normal load to feed tray (Ton basis) while the maximum load reached 125%.

2- Upon revamp there is additional load of steam was incresed as a result velocity steam to new heater and purg steam  to new PSV's installed on coke drums

3- Operating at 120% of original design capacity resulted in addetional amounts of tower products with almost the same percent.

 

you may be right regarding the actual reason of tray blow out, but I think incresed vapor and liquid loads can remove cap valves, nuts and may be segments. It will be a problem for proper contact and separation

 

Since fixing tower internals problems we did not operate at a capacity higher than original design. But during the last 3 monthes we have to operate at higher rates, we found some cap valves and nuts in pumps strainer. It is scheduled to shut down next month to inspect  tower internal status. I hope we will find only missing valves with no fallen trays.

 

Regards

 

Ahmed

[Vinayak Chavan]

Dear sir,

 

I works as technical support for Delayed Coker Unit, we have revamped the unit by installing a new heater so that we could increase unit capacity by around 12% as well as enhance unit operabilty.

The revamp study did not encluded any modifications on main fractionator.

After start up and operating with revamped capacity (112% of original one), we noticed sever deterioration in products separtion and qulaity (CCR content in HGO) with no gain of traditional operation procedures of pump arounds adjustment. we also found alot of tower valves, nuts, nails and small segments in pumps strainers.

During following shut down we entered the tower and found catastrophic damage of tower internals; fallen trays, a huge number of tray valves were missing and complete segments are removed away its place.

Calculating the maximum vapour load to the tower, it was around 125% of design figures.

 

I'm studying the possiblilty of revamping the tower so that it can handle the increased load of around 115% of design safely.

 

My question is: If we can change tray type from valve tray to another one, can this work? or I have to change the whole tower shell with larger size?

 

Thanks

 

Dear Ahmed,

Use grid packing in the wash section of fractionator. High heater outlet temperature may be causing coke formation which leads deterioration in products. Changing column shell is not solution to said the problem.

 

Light ends percentage may go up during revamp condition, causing higher volumetric flow rate inside the column. If the disengagement space is less in the flash zone then tray will get fall down.

 

Please check the momentum in feed nozzle.  If momentum is higher install SCHOEPENTOETER at feed nozzle inlet.