Summary for reverse osmosis boiler feedwater Discussion
Reverse osmosis boiler feedwater raises a practical question about how to control pH without creating new problems. The original poster says a boiler facility is using RO makeup water, treating it with NaOH to reach pH 9.5 before the feedwater tank, while condensate runs only about 6.5 to 7.5 pH and the boiler water is brownish, possibly from iron contamination. They also note amines or ammonia cannot be used because of humidification, and ask what condensate pH should be expected with RO makeup and 40% condensate return. P Siva Prasad advises that adding NaOH to boost makeup pH is not advisable because it increases TDS and caustic alkalinity, leading to frequent blowdown and possible hard scale; he recommends pH boosters instead to maintain boiler water around pH 9 to 10, and suggests a mixed-bed plant after RO for high-pressure boilers. A later question asks about morpholine dosing for RO permeate, but no answer is shown.
Q. I am an engineer for a boiler company. I have recently experienced problems at a facility which uses reverse osmosis water in their boiler system. The make up water is treated with NaOH to bring make up water to pH of 9.5 before feed water tank. The condensate varies between 6.5 and 7.5 in pH. Amines or ammonia
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eBay or
Amazon [affil link] cannot be used due to humidification. Boiler water is brownish, possibly iron contamination….any advice? What condensate pH should they expect when using RO makeup, 40% condensate return.
Thanks for any help!
Kev Cunning
boiler company – Toronto, Ontario, Canada
2004
A. Dear Sir,
Addition of NaOH to boost-up the pH in make-up water is not advisable as it adds TDS to water and increases caustic alkalinity which in turn needs frequent blowdowns.
pH boosters would be a better alternative by which you can maintain pH of range 9 to 10 in the boiler water.
You are mentioning that blowdown water is brownish..if pH is about 11.5 it’s definitely due to higher caustic alkalinity in water. If you continue to run your boiler like this it would result in hard scale formation.. Further if your boiler is a high pressure one you better add a mixed bed plant to the RO plant for DM water generation.
Regards
P Siva Prasad
– Rajahmundry , AP State, India
2004
Q. In one of the project at RO, permeate pH is 5.23.
We have to guarantee for TDS as well; we are planning to dose caustic of 30 ppm by which pH can be raised to 6.3 ; but TDS is also going high, so we can not dose caustic further.
Let us know dosage of Marpholine to raise the pH to 6.7.
Please also comment on variation in TDS value per ppm dosage of marpholine
varsha rane
– PUNE, India
March 28, 2014