Condenser Drain Flash Tank (Coal Fired Power Plant) 1

[RASitepu]

Hi,
can somebody explain to me why we have to flash the drain before entering the condenser? why don't the drain just enter the condenser directly? I attach a part of P&ID of condenser.
Thank you.

RAS

 

[EdStainless]

You have to match pressure, if you just dumped the drain into the vacuum of the condenser the flashing would be violent and probably cause damage.

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P.E. Metallurgy, Plymouth Tube

 

[RASitepu]

Hi EdStainless,
thanks for the answer. What damage btw? Can you explain it further?

 

[chicopee]

A flash tank also incorporates a vent to vent out gases such as oxygen and carbon dioxide entrained in the condensate

 

[metengr]

Depending on the pressure drop and mostly temperature, you can vent to the condenser with a baffle on the inside surface of the condenser wall. Seen it many times and have dealt with issues like damage to adjacent tubing (if the baffle fails) and thermal fatigue damage to the condenser wall.

So, it might be best to use a flash tank.

 

[EdStainless]

Yes, metengr, I have seen them also. Local thermal fatigue leading to cracking of the condenser wall, tubes damaged after baffles are eroded away, and my favorite was a couple of dozen tubes severed after a baffle was blown off and impacted them.
Flash tanks are simple and easy, along with non-condensable removal they also will protect other equipment.

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P.E. Metallurgy, Plymouth Tube

 

[RASitepu]

Thanks metengr and EdStainless,
Are that the problem that going to happen if the condenser does not have a flash tank right? But are all of the drain that enter the flash tank flashed? Or some of the drain still in liquid form in the flash tank? Because I see in the P&ID there is a line that connected the flash tank and condenser hotwell.

Sorry I can not give you actual installed line description because the truth is now the plant is under construction process. Also I am a fresh grad, so might ask you a lot more questions.

 

[EdStainless]

The lines that enter the condenser are generically referred to as 'drains and dumps'.
Draining liquid and dumping steam.
These lines can enter one of three places, above the tube bundle, somewhere along the tubes, or below tubes (but above max hotwell).
If you get a copy of the HEI Std for Steam Surface Condensers you will find a table that recommends where each or these line be placed based on where it comes from ( T and P) and the need for deaeration.
Get a current copy of the HEI, it explains a lot.

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P.E. Metallurgy, Plymouth Tube

 

[chicopee]

You may want to do a search of the National Board of B's & PV's library, as over the years this organization has released innumerable articles about boilers, associated equipment, control and piping. You will probably pay a fee to get copies of their publications. In regard to your topic, you'll find articles on it.