Losing $$$$ due to iron scale, silt, & debris in cooling water lines

[massiveT]

I am working in an oil refinery and we have had major production losses due to reduced cooling in some shell and tube exchangers in one of our units.

After the last utilites shutdown we noticed that we were not getting enough cooling out of 4 of our shell and tube exchangers. As a result we had to cut rates until we could get some temporary cooling towers in. When winter came we got rid of the temporary cooling towers but we were still short on cooling. We cut rates and cleaned out the tube bundles and everything has been fine since.

After looking at what came out of the bundles we determined that the problem was iron scale, silt, and debris that settled out in the headers during the utilities turnaround when the water was not flowing. When the cooling water was restarted, all of the debris was swept into the unit at the end of the cooling water circuit. We have an 8" blowdown valve at the end of the 24" supply header. However this valve was not used to blowdown the collected debris. The ditch that this valve drains to is not very big and will fill in minutes.

Has anyone else encountered a similar problem? We have another shutdown coming up and we're not sure if using the 8" valve for a few minutes will prevent the problems with debris. If it doesn't it will cost us $millions. Does anyone have any other solutions to getting this debris out of the lines?

 

[dicksewerrat]

How did the debris get in? you may need some control onthe intake pipe. The water may need to be treated to retard the scaling. Maybe should send all the water being held in system through some kind of filter? Can you isolate this one system and blow down with clean water?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[massiveT]

Much of the debris is wood, which likely comes from the cooling towers. We thought about putting in a filter but there are a couple of problems. The debris and such are only a real problem on start up after a shutdown. It is hard to justify the cost and maintenance on a filter that is only really need once every 10 years or so. The other problem is we don't really have the plot space to put a filter like that. It would also require major piping changes to install and would likely decrease the flow to a unit which is always looking for more cooling water.

We would like to be able to blow down the system but we have two problems. The current blowdown valve is fairly small (8" on a 24" header) and the ditch the blowdown valve drains to fills in a matter of minutes which limits the amount of time that you can blow down.

 

[abeltio]

if the problem is found only during start-up after a shutdown... have you thought about installing temporary start-up screens or witch-hats with differential pressure gages?

the only difference is that you need to modify the piping to accomodate a spool piece that will contain the screen or the witch-hat (for 24 inches pipe the w/h will be about 106 in long).

HTH

saludos.
a.

 

[stanier]

Nalco Chemicals did a deal with a major petrochem plant in Sydney Australia. They put engineers in , supplied the chemicals and took a percentage of the savings from all the corrosion they prevented. Win Win situation.

 

[dicksewerrat]

Maybe yu have to rebuild the cooling tower with new wood and/or stainless screens to send the water over, through, around.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com