measure P2 alaklinity by adding BaCl (in excess) and phenolphthalein and titrating (this will tell you how much caustic you have in the boiler).
Three types of alaklinity P1 P2 and total.
Not sure why the high pH is causing carry over, if fat is getting back through with the condensate this can cause foaming and carry over if not total
boiler shut down to due to high and low level alarms from soap formation. Your chemicals seem odd and I guess is they are an easy one step treament
that wont fit all applications.
How are you dosing the boiler dose pot or pumps?
Measure your condensate return if you have any (tds, turbity).
Meaure the TDS (condcutivity) of the boiler and the feed then you can estimate cycles.
Also measure phosphate levels (since you are using a phosphate treatment). Too much can be just as bad as none.
You are using a sulfite as an oxygen scavenger you can get test strips that measure sulfite levels(like pH paper (Merk make them) the pink colour of
your water might be a problem they go pink the more sulfite you add).
Are you pretreating the the feed water (softner or demin)?
Are you preheating the water before it goes into the boiler to help drive off oxygen.
Qulaity of your raw water will determine the best treatment, measure total harndess, TDS, pH, silica.
Then if you run a pretreatment measure your feed water conductivity, hardness and silica.
By the look if it you are runnign a phosphate programe so you probably have little in the way of pretreatment. You are trying to do a couple of things
in the boiler.
Remove the carbonate (to prevent scale build up on hot surfaces) as a mobile serpentine phosphate sludge and thus blow it out of the boiler via bottom
blowdown.
You are trying to remove all dissolved oxygen to prevent corrosion having a sulfite reserve in the boiler would mean that all oxygen is scavenged.
You are keeping the pH high to avoid silica scale and also encourage the formation of magnitite in the boiler to help prevent corrosion (silica scale
is by far the worse type of scale very hard to remove). If silca is very high it can carry over (bad block heat exchangers etc).
TDS and cycles is key to running a good boiler (15-20 cycles). The lower the better if you have a dirty scaly boiler.
Sodium lignosulfonate is good for dirty boilers.
Sodium erythorbate is good for metal passivation and oxygen scavenging in conjunction with a sulfite.
Are you worried about condensate corrosion and can you add a volatile/filming amine? Not if its a food application.
I could be wrong, and you are using high quality feed water and are running a chelation programe(The cirtic acid!)?
What sort of boiler is it, fire tube or water tube?
Carbonate has retrograde solubility (is less soluable in hot water) so it sticks to the hot surfaces of your boiler, plus it is a good insulator so
you loss efficency in your boiler, also it can cause under deposit corrison, worse case is your firetube may warp if its a firetube boiler (metal gets
very hot because its insulated by concrete).
To much caustic can cause caustic embrittlement of the metal over time.
I would be very carfull about using citric acid in your boiler, over use will eat your boiler up plus remove any good coatings you have formed.
If you have no pre treamnet and a typical raw water (~100 tds, some carbonate hardness, not much silica, low cholride, normal pH 6-8)
I would get a water softner and run a phosphate programe just in case you get slipage or your softner fails.
Phosphate additive, caustic and a sludge modifier. Plus a sulfite and a vitamin c analouge in the feed. (the more preheat the less sulfite you will
need). Alkaline tanins can work if its not food related in application.
run a sulfite reserve of 10-30ppm.
P2 alk of 300-600ppm.
Phosphate depends on the additive about 20-50ppm depedning on the type.
pH 10.5-12, I think 11.2 is the magic number.
20 cycles max, by the sound of it your boiler doesnt work hard and has low cycles anyway? (unless you have good feed water low tds).
[Edited on 8-1-2015 by feacetech] |