Popular Boiler Alkalinity Builder & pH Control Products
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|Accepta 2339||Alkalinity & pH Control||Yes||High strength alkalinity builder based on sodium hydroxide / caustic soda|
|Accepta 2338||Alkalinity builder & sludge conditioner||Yes||Combined alkalinity builder and polymer sludge conditioner|
|Accepta 1020||Alkalinity & pH Control||Yes||Alkalinity builder based on sodium hydroxide / caustic soda||POA|
Deposition causes & remedies
The precipitation and deposition of hardness salts in feed water to low pressure boilers is commonly a result of raising the feedwater temperature or the pH value. The later problem should be avoided by the use of alkalinity builders dosed into the hotwell or boiler shell.
Offending hardness salts should be removed only by softening the make-up water (or the feed water if condenser leakage is the source of contamination).
Acid attack in a boiler can be caused by low make-up feed water pH which attack the metal surfaces within the boiler system either causing a generalised thinning or localised corrosion of high-stress areas. Be aware that the feed water can also become acidic through contamination in the system (process contamination of condensate or cooling water contamination from condensers). To remedy this your treatment regime should include the maintenance of appropriate boiler water alkalinity making sure not to reach excessive levels as this may cause carryover.
CALCULATE THE LIMITING CONCENTRATION FACTOR BASED ON TDS AND ALKALINITY
In a shell steam boiler operating up to 30 bar (435 psi) we are limited by BS2486 to a maximum TDS of 3000mg/L and a maximum Alkalinity (M) of 1200mg/L. Both of these are usually present in the softened make-up water and both will concentrate up in the boiler. The question is which will reach its limit first?
To find out divide 3000mg/L by the make-up water TDS to give the limiting concentration factor, based on TDS and divide 1200mg/L by the make-up water alkalinity to give the limiting concentration factor based on alkalinity. Whichever is the lower is your overall limiting concentration factor.
Make-up TDS = 150mg/L
Make-up Alkalinity (M) = 20mg/L
Therefore limiting concentration factor for TDS =
3000mg/L = 20
And Limiting concentration factor for Alkalinity (M) =
1200 = 60
Therefore, we should reach 3000mg/L TDS in the boiler before we reach 1200mg/L Alkalinity (M) and hence the overall limiting concentration factor based on TDS is 20.
Recommended Control Limits for Shell Type Boiler
Up to 20 bar
|Caustic Alkalinity (Alk OH)||mg/l as CaCO3||350 minimum|
|Total Alkalinity (Alk M)||mg/l as CaCO3||1200 maximum|
|Total Hardness||mg/l as CaCO3||Less than 10|
|Sulphite Reserve or Tannin||mg/l as Na2SO3 or Tannin units||50-100 or 12-20|
|Total Dissolved Solids||mg/l||3000 maximum|
|Silica||mg/l as Si O2||Less than 40% of Caustic Alk|
|Phosphate||mg/l as PO4||30-70|