6 replies to this topic

[Mohamed AWad]

Dear members of this group , 

i am facing an unusual problem of fouling in vacuum column top section and i am trying to develop a solution for the ongoing problem , i am looking for any advice or insights or even prior experience with similar problems , any contributions are highly welcomed .

My problem is periodic formation of solid fouling in the top section of the tower despite of operating at relatively low temperatures (Tray temperature 185 C ) and low Pressures (-0.955 kgf/cm2) , i assumed that cracking or coking at this conditions is highly unlikely (correct me if i am wrong) and i assume that the problem might be caused by phase separation of asphaltenes entrapped in light hydrocarbons .... is there any way to exactly determine the problem , what kind of lab tests can be done ? any one faced similar problems in vacuum columns?

Thanks for your time and consideration

Best Regards

Edited by Mohamed AWad, 14 March 2017 - 01:08 AM.

[Zauberberg]

Without knowing any additional information (lab analysis, parameters around the condensers etc.) I would suspect cooling of paraffinic components in the overhead stream below their pour point temperature. This is very common problem in VDU's.

 

Try operating at higher condenser temperatures and see if the problem will be mitigated. If yes, you need to look at processing different crude oil blends, or establish a procedure for online cleaning/flushing of condensers. But first try to confirm if this is the actual problem in the unit.

[Nikolay_]

Zauberberg,

It's very interesting. One of our clients did full replacement of 1st bed because, in their words, the bed was burned. May it happened due sedimentation of paraffins? What kind of paraffins can deposit on 1st bed of structured packing? Are there technical articles on it?

 

Mohamed,

Is the content of asphaltenes in HVGO, LVGO norm?

You can consider the issue of properly design of inlet feed line in order DEP 31.22.05.11 (12). The formation of mist in inlet feed line may cause drift of heavier hydrocarbons. 

[Mohamed AWad]

Without knowing any additional information (lab analysis, parameters around the condensers etc.) I would suspect cooling of paraffinic components in the overhead stream below their pour point temperature. This is very common problem in VDU's.

 

Try operating at higher condenser temperatures and see if the problem will be mitigated. If yes, you need to look at processing different crude oil blends, or establish a procedure for online cleaning/flushing of condensers. But first try to confirm if this is the actual problem in the unit.

First of all , Thanks for your reply 
secondly , i am terribly sorry , the topic title was a bit misleading , i edited it , the problem occurs in the tower top section just below the overhead....  no fouling problems in the overhead at all... 

[Mohamed AWad]

Zauberberg,

It's very interesting. One of our clients did full replacement of 1st bed because, in their words, the bed was burned. May it happened due sedimentation of paraffins? What kind of paraffins can deposit on 1st bed of structured packing? Are there technical articles on it?

 

Mohamed,

Is the content of asphaltenes in HVGO, LVGO norm?

You can consider the issue of properly design of inlet feed line in order DEP 31.22.05.11 (12). The formation of mist in inlet feed line may cause drift of heavier hydrocarbons. 

Dear Nikolai

I think i am having a similar problem , we replaced the full bed nearly a year ago but the problem still persists

 

Can you describe the events that led to that incident ?

I work in a lube refinery , we only produce VGO (instead of HVGO,LVGO) and various streams of waxy distillates... unfortunately we don't analyze VGO for asphaltene content (Not a part of the specs and we don't have any reference for comparison)

 

I will refer to the DEP  for a revision of the design but i don't consider it a problem of design, i have many streams below the VGO and none of them show any fouling problems, the problem only localized in the top section

[Mohamed AWad]

I am searching for a way for characterization of the produced fouling and the mechanism by which it is formed ...........

[Nikolay_]

Dear Mohamed,

 

Recently, I visited a vendor of column internals. The reason of top pack fouling may be due to temporary absence of reflux to column. Also I think it could happen due to nonuniform distribution of liquid phase onto pack.

Whant kind of pack do you have?