The Light Green Machine Institute

22 Feb 17: Unconventional layouts, Safe Tanks

The recent incident at PCA in DeRidder, Louisiana, USA brings up a subject in which I was first involved in 1975. I ran a small group at Procter & Gamble soon to be known as the Process Systems Development Group (as best as I can remember).  We became involved in a topic called weak top tanks.  The idea was to cut a groove in the top of existing tanks so the top would rupture before the base.

The tank at PCA allegedly may have been over-pressured by steam (this has not been confirmed by the company).  It was a tank, not a pressure vessel and did not have any sort of relief valve on it (again, not confirmed by the company).

How do we prevent such incidents from happening in the future?

Well, this fits right in our wheelhouse here at LGMI.

First, build tanks without tops.  This is often done in warmer climates, but there is really no reason it cannot be done in all but the most severe of colder climates, too.  After all, if we can handle the rainfall in outdoor tanks in warm climates, we should be able to handle the rain or snowfall in colder climates, too.

For existing tanks that have a top, we can cut holes in those tops, big holes.  This can be done with a cutting torch.

For new tanks where one just thinks they have to have a top, they can stitch weld the top on a spacing that ends up with only half of the seam connected to the wall (say, 4 inches of weld, 4 inches of gap--but consult a qualified engineer for exact pattern).

One might say the simple solution would be to keep steam out of the tanks.  However, in today's world of process control, that steam may have been introduced upstream and, in this case did not thoroughly mix with stock or other media before it reached the tank.

Better to create a fool-proof system to prevent such matters.

If you want to talk to me privately about unique cases in your mill, please call me at 678-206-6010 (US Eastern Time Zone).



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Think light!

Brian Brogdon, Ph.D.
Executive Director


Jim Thompson

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