Steam Cooker implosion?

[DarrenMc32]

Hello, sorry about the length...
I just found this site and thought someone here could shed some light on a problem we're having. This doesn't involve a steam vessel, persay, but it's pretty close.
We manufacture seafood processing equipment and have a large steam cooker that recently had the hood suck in approximately 3-4" along the sides and the top. The cooker hood is made of 11 ga 316SS plate and is roughly 35'x6'x5'. Imagine a open bottom rectangle. This hood has a hydrostatic seal(2" deep water trough) along its bottom. There are two areas at the bottom of the cooker open to the atmosphere at one end (approx 275 sq in. total).
During operation, steam is fed into the cooker and controlled by a PLC. Often, during start-up, water hammer can be heard from water in the steam lines expanding, but this stops once operating temp is reached.
In this one case, during start up, operators noted that a large sound was heard and that the sides and top of the hood had been sucked in. I can email pics if needed.
Any thoughts? Could this have something to do with the water in the steam lines flashing into steam? According to the customer, none of the vents were blocked.
Any information is appreciated.

Thanks,

Darren
Metairie, LA

 

[sterl]

Interesting...i don't have specific exposure to one like this but have had something similar happen, actually imploded an insulated panel building...

Believe system has Condensation Induced Hydraulic Shock occurring, a video on the Hanford incident of 1993 gives very good recreation of the conditions causing the effect....

Believe the system experiences CIHS on every startup, in the piping, but a gross influence on the pressure in the hood is a little harder to rationalize...The hood volume being around 1000 ft^3. A drop in the hood pressure of only a few inches of water might lead to the next step in the potential failure mechanism...

Was the water blown out of static dam by the incident? I would guess it was actually sucked into the hood very quickly, causing very rapid cooling of the steam and a very quick drop in internal hood pressure.

The 275 in^2 is a drain? Is it itself trapped, or could it otherwise be sealed in an unvented condition by condensate?

 

[TBP]

DarrenMc32 - There should be NO hammering in the steam line during start-up, or anytime. Something is not piped and/or trapped correctly.

 

[GenB]

I have seen a few conditions in steam kettles the most common is overpressure, I few years back I supervised an installation which wasfor me a perfect one, by the book
The installer followed the Armstrong Co., recomendations
and installed a bypass valve before the regulator, bad news, the owner decided to run the unit before finishing the ibstallation and plugged the safety valve connection, one operator opened the bypass and bingo... destroyed it.

In your case, the kettle had accumulated heavy vacuum from steam condensation the day before, you opened the steam and caused more condensation (lots of noise and shakeing too)and more vacuum... the vessel was not designed for that vacuum and collapsed. to prevent this in the future, install a vacuum breaker. simple and unexpensive.
I would also install an air bleed valve too.
Also be sure you have the safety valve in good working order, kettles are very sensitive to pressure.
I do not think water hammer will cause this but will cause other damages.
ER

 

[quark]

Is your cooker loosely placed on the trough or fastened? As generalblr suggested, it is mainly due to vacuum and this has nothing to do with flashing of steam.

From your description, I assume your open bottom cooker is place in a trough in which you have 2" water and steam is in direct contact with this water seal.

During starting of the process, if the seal water is cold, steam condenses at a faster rate creating low pressure in the cooker but incoming steam should compensate this. As already you have steam hammering problem in the system, your operator might have stopped the steam valve after hearing banging sounds. Which might have caused the cooker to implode.

PS: This is just one possibility.

Wish you all a Happy and Prosperous New Year

Regards,

 

[smckennz]

Sounds like your hood got full of steam, then some cold condensate got sprayed in, condensing the steam and causing a partial vacuum which was formed faster than the water seals and vents could respond to.
Suggest you fix the condensate problems before investigating further.

cheers

Steve McKenzie

 

[DarrenMc32]

Thanks for the replies. In response to your questions...

STERL,
"Was the water blown out of static dam by the incident?" Nothing was mentioned by the customer but I don't believe it was directly asked.

"The 275 in^2 is a drain?" Actually it's a total area of the 6" drain, a 4"x18" opening for the drive chain, and the cooked product discharge.

"Is it itself trapped, or could it otherwise be sealed in an unvented condition by condensate?" Other than the product discharge, which is monitored frequently, the remaining openings can be blocked by debris, though we haven't had problems with any other cookers.

QUARK,
"Is your cooker loosely placed on the trough or fastened?" The hood is actually lowered into the trough with ACME screws and lifted for cleaning.

"I assume your open bottom cooker is place in a trough in which you have 2" water and steam is in direct contact with this water seal." That's correct.

Once again, thanks for the input. Getting input from others will help a lot. I'll post our findings when we finish.

Darren




Darren
Metairie, LA

 

[jay165]

Darren:

smckennc is right. Vents that are sized for liquid draining are not large enough to handle the volume change of rapid condensation caused by spray cooling. The water that caused the hammer was likely cold enough to cause the steam in the cooker to condense. This situation has occured numerous times in the process industry.