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Posted by Bob D. on March 11, 2004 at 10:18:41:
In Reply to: Flash Tank Vent Connection posted by James on March 11, 2004 at 09:45:17:
"Usual and ordinary" would be to tee into the low pressure steam supply to the DA downstream of the pressure regulating station. Install an isolation valve and swing check in the lead from the flash tank, just to keep things moving the right way. Remember, depending on the operating pressure of your DA, only 11%-17% of the blowdown will flash to steam that you can get to your DA. (400,000 PPH x 1.0 % continuous surface blow x 15% flash = 600 PPH to the DA, at max loading) The liquid remaining in the flash tank still has a lot of usable BTUs (saturation temperature for DA operating pressure), that you really should use. Try make-up pre-heat or something else nice and steady to subcool the blowdown prior to atmospheric disposal to sanitary waste. You still may have to temper the liquid discharge to keep below 140 degrees. Take a look at the Penn Separator web site for a range of nice packaged systems, and a "how to" overview. Frankly, anybody that's got continuous blowdown should think about something similar. At $7.00 per million BTUs, the max load works out to around $120 per day. At 50% load, that's like $21,000 per year. That's not even counting the chemical savings from controlled, reduced blows.
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