Inexplicable pH drop in boiler blowdown water

A. Without a treatment to keep the pH elevated in the condensate, you will always see a reduction in pH in the steam lines and consequently the condensate. This is due to a buildup of Carboxylic Acid as a reaction of carbon dioxide which is dissolved in the water. People will typically use amines as a steam line treatment because it volatilizes and keeps your pH elevated. You want your condensate to have a pH of 8-8.5. pH lower than that can lead to severe corrosion that you will not be aware of until your steam lines have been ruined. Get that pH up in the condensate as soon as possible. Depending on the pH and time and temperature, it can lead to catastrophic failure of your system.

The organic compounds have no effect on the pH of your boiler. They are naturally occurring in surface waters which is probably the source of your incoming water.

I would contact a water treatment chemical supplier in your area to get professional assistance which should be part of your chemical purchasing process.

A. How many hours can you run boiler with the pH is 5 and 4?

A. Dear friends,

I am also working in a 90 ksc boiler system. My experience and few consultants say that drum water (blow down water) lowering due to more iron content in feed water (during commissioning) where iron will eat away the phosphate (TSP hydrolysis will be affected and no caustic to raise the pH).

More TOC (> 1 ppm) in feed water will contribute to lowering pH due to formation weak acids (organic) due to decomposition of TOC at 350 deg. C. During this time if add caustic (2% solution at minimum level based on blow down) pH will increase; this is due to the formation of NaOH from TSP is consumed by weak acids and the external addition NaOH used for increase the pH.

Q. Some of the power plants like super critical oxygen is getting injected in feed water to ACC corrosion and 150 ppb residual is being maintained in feed water. Is it advisable?

Because we are (90 ksc) force remove DO through mechanical de-aerating system as well as chemical treatment to achieve 7 ppb.

A.
• Check dosing chemicals quality
• Check 2P "M value" if it is too low, then that may also create low pH condition.
• Check hot well cationic conductivity; feed water hardness
• Check MB outlet to ensure that there is no accidental contamination of regeneration chemical

A. Hi Thomas. Your question will probably be more answerable and draw better responses if you make it less vague, with data such as the pH of the feedwater and of the boiler.

Regards,

A. What I feel is that boiler pH can get down with entrance of exhaust in the boiler water as it totally contains CO & CO2; they can create carbonic acid which can contribute these amount of pH drop. So, better you check your exhaust gas lines whether there is any leakage which is allowing exhaust gas to enter into water.

A. You are facing a problem called "phosphate hideout" and to solve this problem follow the following steps:

1. Increase blowdown up to 50%
2. Check Iron in the drum and the superheat

If you found Iron in the drum more than the limit, you must contact with engineers to schedule outage of station as soon as possible.
Most phosphate hideout problems have no solutions; the only solution is the station outage.

A. Folks, "ph drop in boiler blowdown" question has been the main theme of this thread. Can you respond in terms of the proposed explanations & solutions already offered please? Ignoring the responses and simply starting over is usually the kiss of death to a topic.

Regards,

Q. Boiler water programs are based on three main areas and the treatments and due diligence to each can help avoid many issues.

(1) External makeup water is one of the three main parameters and can have conditions that could include the quality of the condensate return, changing raw feed source water conditions (high hardness water or RO, DI soft water), softener brine regeneration rinse contamination treatments and along with de-aerators are some factors that could all play a role in the external feed makeup water quality.

The (2) second main area is in the actual internal boiler water conditions and these treatments can be affected by carryover of wet steam from too rapid a demand for steam for a small boiler, improper or low water treatment to address changes in bicarbonate and carbonate alkalinity and contamination from a waste heat gas getting into the water from a fault in the heater tubing and or a simple leak.

The (3) third main area of a boiler waterside program is in the condensate treatment and the quality and amount of condensate used and how any condensation is neutralized as the steam condenses back into water as any unused steam is condensed and is returning to the makeup tank. Under low fire conditions, a leaky heat exchanger could be drawing some contaminates into the condensate and this could lower the feed makeup water pH unknowingly, a leaky seal on a suction side of a pump could be introducing air and causing some lowering of pH, the type and amount of neutralizing amine used to protect the condensate could be off and not carrying the ideal corrosion protection the full length of the condensate system.

I might recommend that your team consider trying to start increasing the alkaline feed builder product in your boiler water treatment into the makeup tank to drive up the pH and then watch for issues where demand for steam might cause excess wet steam carryout lowering your water treatment on the internal side. If your team put a conductivity meter on the condensate line return you could see if the quality of your steam matches what you think and at the same time get a good idea where and when you might be carrying some tramp contaminates back into your condensate return from a faulty heat exchanger, bad steam trap and don't be surprised if your team might discover that you have some other water from a possible bad connection or crossover lines in your process.

If you could fill in some additional thoughts on what your team does in each of the three main treatment areas and if you experience low water alarms / wet steam issues or contamination in the condensate that would help pinpoint some possible reasons why your boiler internal water conditions pH is dropping. What is the steam actually used for and how much condensate return is part of the actual makeup water ( for example ... do you get 50 % of your makeup water from the condensate or 10 % ... or for example if you are steam heating urea or heating a phosphate bath in a coil could you be dragging some tramp urea or acidic bath liquid into the condensate through a fault in the coil ... I guess what are you doing to what? )