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Posted by Bob D. on May 03, 2011 at 14:22:38:
In Reply to: Re: Temperature of blowdown water while boiler is operatin. posted by Boiler Guy on April 27, 2011 at 16:36:26:
Well, in the blowdown line upstream of the stops, the water is still at drum pressure/saturation temperature. But once it gets past the stops, then the pressure rapidly goes to atmospheric (or at least is supposed to - I think it's called adiabatic expansion) where saturated liquid gives up all of the latent heat and some sensible through flashing to steam at atmospheric pressure, or very close to it - this is so your blowdown flash tank doesn't explode. After a few seconds, the remaining liquid (somewhere between 75% - 90% by weight, depending on initial conditions) is at 212 F (100 C) and the balance is saturated steam at 212 F venting out your flash tank through the roof or outside or somewhere. The "rain" on the roof is just subcooled flash steam. The flash steam is good to use for dearators, make-up preheaters, or whatever. Penn Separators has made a pretty good living out of working with this.