Flash Tank, Sparge/Spray Pipe ??????

[NEplantengineer]

Hello folks,

I've got a 20" dia x 48" long horizontal steam condensate flash tank. Tank is vented to atmosphere. 60lb steam condensate at about 4000 lbs/hr, approx 400 lbs/hr flash steam. Question is the existing tank has a spray or sparge pipe installed at the inlet to the tank. Sparge pipe is 42" long with 48 1/4" dia holes. Sparge pipe is above the waterline (waterline is 1/2 up the tank).

Does anyone know what the sparge/spray pipe is really supposed to do? Also does anyone know what the sizing parameters/methods/guidelines would be for this sparge pipe would be? The tank manufacturer states in their literature that the sum of the sparge pipe holes equals or exceeds the cross sectional area of the inlet. Might this mean that conventional condensate line sizing would be used to size the sparge pipe/inlet?

-Thanks for any ideas.

 

[JimCasey]

One thing a sparger does is to hold a little back pressure on the line, so the condensate flows through the pipe as a liquid-not as wet steam. Wet steam would flow at a hugely greater velocity and be erosive. Or if the condensate had only started to flash, there might be slugs of liquid causing steam hammer.

Another thing it does is the same thing the aerator does in your kitchen faucet: it divides the flow into many small jets instead of one huge jet. THe flow exits radially, canceling much of the pipe loading. Steam hammer in a non-sparger-equipped tank could rip the pipe out if left unmitigated.

 

[quark]

I don't have any experience with sparged flash tanks and I never saw one. From your description, as you say it is vented to atmosphere, was there a chance that the particular tank was used for boiler feed water or for deaeration of feed water? However, in both cases, the sparger should be below the liquid level.

 

[TBP]

It sounds more like an arrangement to prevent erosion of the tank by shots of high pressure condensate. If it was a true sparge line, it would be under the water level.

 

[Joesteam]

We have seen many of these sparge pipe condensate flash tanks. In every instance the sparge pipe is BELOW the water line. Supposedly if you have a lot of flash or some live steam from failed traps, this will be quenched by the liquid in the tank, and the sparge holes are supposed to prevent water hammer with this liquid/steam interface.
Are you sure your tank is not installed upside down?? Just kidding, but above the water line the sparge pipe will have no real effect that I can see.
BTW: I never liked these sparge pipe tanks, where I always see some 'pinging' from thermal water hammer, and also see errosion/corrosion on the sparge pipe even though most are made from stainless.

 

[logoslarry]

Sounds more like a dry pipe to collect steam. Sparger should be below waterline.

 

[JimCasey]

Yeah, I thought it was strange when he said the sparge line was above the water level, too. Spraying condensate through the atmosphere in the tank would tend to pick up a lot of dissolved gases in the condensate, adding to either the chemical demand or to the rate of corrosion.