METHOD OF CHILL-SHOCKING HEAT EXCHANGER TUBES?

[BRT549]

I'm trying to figure a way to clean heat exchanger tubes in a phosphoric acid evaporator. I've got calcium sulfate (gypsum) anhydrite deposits inside the tubes that defy attempts to chemical clean them away. I remember a way that we used to clean seawater evaporators in the Navy that was called "chill-shocking".

It's been a long time since those days, and I was wondering the best way to do this. Was it cool the HX down, then hit it with steam on the shell side? Or is it better to get things hot, then hit it with cold water tubeside? I can only fill the evaporator at 500 gpm, so it would take about 5 minutes to fill the tubes all the way. If I hit the shell side with 35# steam, it would be quicker, but would it bust loose any scale?

It would seem that quickly contracting the tubes quickly would remove more scale than quickly expanding them. Any thoughts or similar experiences to this would be appreciated.

 

[25362]

I feel having seen the same question before. The answer I suggested then was to try water jetting as offered, among others, by WOMA in Germany. Visit the website

http://www.woma.de

 

[sludgeking]

We have problems with calcium sulfate(s) scaling a wide variety of equipment. I found some "Gypsum Dissolver" produced by JACAM chemicals that works good for removing "gypsum" scaling on small parts, but at $13 per gallon, the stuff is kinda pricey. You can dilute the stuff 1:3 and let it sit in your exchanger for a half hour or so, with heating on the the outside, you may get accelerated cleaning. I threw a chunk of our scale in a beaker with the pure liquid in it for 2 or 3 days, and measured the calcium increase over that time period, and it worked out to about 50 grams "gypsum" per liter of remover. For your system, you'd need about 800 gallons of pure liquid, and when you were done you'd need to dispose of it somewhere, which may be prohibitively expensive.
I've applied grease to the walls of a pilot reactor system that tends to scale up, and that helps release the scale when a pressure washer is used for cleaning. For your application, however, that wouldn't really be an option. The only other thing I've found that helps remove scale is to run ultrapure water (i.e. RO permeate) through the system, which will dissolve almost anythine,eventually. But then again, I have access to large amounts of permeate, which is somewhat of a unique situation.

 

[BRT549]

Thanks. I downloaded their WSR 3200 calcium sulfate dissolver factsheet. Might be worth a try in the lab - I've tested quite a few, but never one that wasn't a strong base or acid. This stuff has a pH of 7 - 8!?!