Boiler water pH

[padovano]

Dear All, I am presently monitoring 2 boilers with a pressure of 17 bars . The pH of the boiler waters has falling to below 10.5. I will like to note that the pH of the make up water is about 9.2, that of the feed water is 9.5. A phosphate agent is added to the feed water on its way to the boilers. Morpholine is also added to the storage tank of demineralise water and also to the feed water drum. an oxygen scavenger is added to the feed water drum also.
I had TAC analysis of about 13.6F. pH value of 10.4, Phosphate 56mg/l. TA of 6. The Percentage openning of continuous purges, the tonnage of the boiler did not vary in 24 hrs but the result obtained after 24hrs declined, i.e TAC= 9.8, pH = 10.1, TA = 3.5. What I really want to understand is how to increase the alkalinity of the boiler waters. The boiler is a water tube boiler. I expected the TAC to have increased after 24 hrs with the same tonnage of the boilers.

 

[bimr]

pH control involves feeding sodium hydroxide and sodium phosphate salts in carefully controlled quantities. In common with most water treatments, overfeeding chemicals can do as much damage as underfeeding, so continuous monitoring of pH is an important part of the boiler chemical control program.

Demineralized makeup water does not contain measurable alkalinity, therefore boiler water usually contains a very low level of hydroxide alkalinity. Boiler water alkalinity acts as a buffer. Caustic can be added to increase alkalinity in boiler water. Boiler water alkalinity acts as a pH buffer against feedwater contamination.

With very low hydroxide alkalinities, the buffering capacity of the boiler water becomes reduced and feedwater
contamination more significantly influences the pH. Where a coordinated phosphate program is being used, buffering capacity is minimal and pH can change rapidly with the slightest amount of feedwater contamination. Contamination of feedwater can occur from several sources including salts entering the feedwater from condenser leaks or demineralizer leakage.

You should review this issue with your chemical treatment program supplier.