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Posted by Mike Boyle on November 08, 2005 at 11:05:59:
I tried to post as a reply to the message dated Nov. 4th with no luck, here's an SOP we found, I'm not sure of the author to give proper credit that being said:
Any commerical water treatment company rep (i.e. Betz, Nalco, Chem-Aqua, Chem-Treat, Garratt-Callahan) will have their own preferred method and will have a specialty compound. Usually that compound will have caustic, a surfactant (soap), and sometimes sodium silicate. Some simply require you add caustic, phosphate, and sulfite. I prefer using some phosphate due to it leaving a fine corrosion barrier on the tubes.
We do some boil outs when we install new boilers and the following is an SOP we use:
ALKALINE BOIL-OUT
The following procedure can be followed for utility boilers which can be fired.
Flush loose material out of steam and mud drums.
Fill the boiler and hydrotest.
Drain down the boiler to below the steam drum manhole and open the manhole.
Introduce chemicals through the manhole. The chemicals should first be diluted (at least a drum of water) to prevent local concentration. The following or similar formula can be used (anhydrous chemical in lbs per 1000 gal of water held by the boiler):
34 lbs of soda ash
34 lbs of trisodium phosphate
6.5 lbs of sodium nitrate
7 lbs of surfactant
Replace the manhole and fill the boiler to the normal operating level.
Open the steam vent (if the boiler has a superheater, the superheater vent should be opened).
Fire the boiler and run for 12-24 hrs at 25 – 50 psig.
When the boiler reaches the desired pressure, blow down the mud drum (intermittent blowdown) every 4 hrs (reduce the level about half the guage glass) to remove solids.
Let the boiler cool, drain, refill, drain, open and inspect.
Put into service, acid clean, or proceed with layup.
If the boiler is not fired, and is for example, a kettle design, it is necessary to provide some external source of heat and recirculation. This may be a chemical cleaning truck equipped with a heat exchanger. Water, containing chemicals, is introduced through the BFW inlet and withdrawn through the blowdown and recirculated back (or vice versa). Maintain temperatures at 180 - 200 0F.