Boiler Restart Procedure after Cleaning

[dogbertcountry2]

I have heard conflicting arguments about the restart of a boiler after being chemically cleaned (or after lay-up). One method employs the rechraging of the boiler with normal boiler feed water (140ºF) while the other uses "ambient" water. It seems logical to me that boiler feedwater should be used versus city water, but the latter argument stresses that the temperature of the boiler feed water might "shock" the tubes????? I could use some insight here please!

 

[yogibear1]

The correct water to use is your treated boiler feed water. The 140 degree tempereature, probably from your hotwell, should present no thermal shock to boiler tubes. Afterall, 140 degrees is probably about the limit for sustained human contact, but certainly no problem for steel tubes.

 

[GBENARD]

You are correct. The boiler should be drained and filled with treated boiler water as defined in the O&M.
The temperature criteria is typically something like a maximum difference of 60°C-80°C/140°F-175°F (mainly depending on the drum thickness) between water and metal temperature (assumed to be ambiant temperature after layup for a few weeks).

 

[metengr]

By all ,means do NOT use city water. The start-up of a boiler after a chem clean should be with treated feedwater otherwise you will undo that which was accomplished with a chem clean.

Typically for thermal shock as long as the delta T between the metal and feedwater temperature is less than 150 deg F you should be ok. My main concern would be to assure that untreated feedwater does not enter your tube circuit.

 

[dogbertcountry2]

Thanks for all the info. I have been corrected about the temperature of the treated feed water. The temperature is that of deaereated boiler feedwater - 228º. Is this a problem for the tubes? I understand the treated vs. untreated part of my previous question.

Thanks again.

 

[yogibear1]

At that temperature the water will flash to steam in as much as the boiler is empty and under zero (gague) pressure. You don't want that. The water should be cooled down so there is less differential, see the post from Metengr for that.