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'm not familiar with shock thermal treatments, but I know of refineries using water jets.
Hard deposits can successfully be removed with high-pressure rotating water jets, mounted on lances, sometimes called hydroblasting, such as the ones proposed -among others- by WOMA -Apparatebau GmbH. This company can be found on the web:

http://www.woma.de

Of course, this needs partial disassembly of the exchangers, but the cleaning is very effective. I believe Woma could give you successful examples on cleaning hard CaSO4 deposits.

 

[BRT549]

Thanks for the reply. We typically use our own 10,000 psi hydroblasting unit on the tubes, and brought in a 40K psi unit for this problem. It was cleaning the tubes, but at a rate of 10 minutes per tube. With 775 tubes, it was taking too much time and would have cost too much money. We even hired another contractor with less pressure (20K)and higher volume, with less success.

I tried the chill-shocking method last night - hitting the tube bundle with 20 psi of steam, then running 350 gpm of cold water through the tube bundle. It didn't remove much scale, but a tube plug did fall out. I guess that proves the theory. I think the chill-shock probably would have been better done before the hydroblasting effort to loosen the scale.