to control boiler feed water ph, is it better to use di-sodium phosphate or caustic soda why

TO CONTROL BOILER FEED WATER PH, IS IT BETTER TO USE DI-SODIUM PHOSPHATE OR CAUSTIC SODA? WHY?

8 days ago

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BrianUnfollow Follow Brian

Brian Hulse •Let's back up a minute, and understand the chemicals you're talking about and their purposes. Caustic soda (NaOH) is a pH adjuster, and is used to keep a boiler running in it's intended pH range. It protects against acid corrosion but, if over-dosed, can cause caustic attack. Phosphates (Di- or Tri- Sodium) are agglomerators, collecting up calcium and magnesium impurities and precipitating them into sludge, which can be removed from the system via blow-downs.

How much of each are used (if any) depends on the chemistry of the influent make-up water, deaerator efficiency, boiler materials, other water treatments (amines, polymers, chelants, etc..), whether your batch-feeding or continuous feeding your treatments, and a number of other factors. A water treatment program is just that - a PROGRAM. It isn't one thing or another....it's a combination of understanding the application, developing a chemical solution, building a methodology for delivery of the solution and then monitoring the results.

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KanakamUnfollow Follow Kanakam

Kanakam dashti •Follow the international guide lines for boiler water treatment.If you are using caustic monitor the caustic alkalinity in the drum water.It should not cross 1 ppm as per EPRI Guide lines.Mainly 2P-M.Mr.Brain Husle has explained very well.



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Kanakam dashti •Dont use any such type of chemicals for boiler feed water control.Use only volatile chemicals for boiler feed water PH control,Like ammonia,Hydrazine,Morpholine,Amines etc



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Brian Hulse •Amines are most commonly used to control pH in condensate....not feedwater....and hydrazine is an oxygen scavenger. It should not be used as a pH adjuster (although you may get some pH movement by feeding it into a system).

There are also chemical considerations related to the working pressure of the system. Certain chemical programs work well within one pressure range, but not so well within another. For instance, in a lower-pressure system you might want to stick with a sulfite oxygen scavenger, but on a high-pressure system you might choose hydrazine. It's all very system-specific.



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MOHAMMED ABDULAZIZUnfollow Follow MOHAMMED ABDULAZIZ

MOHAMMED ABDULAZIZ ELNEGAI •Thanks Brian & Kanakam for this useful informations



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yasserUnfollow Follow yasser

yasser elshinawy •thanks allot Brian & Kanakam very useful acknoladge





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Brian Hulse •Trying to help where I can.



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mahmoodUnfollow Follow mahmood

mahmood aslam •thaks Mr.Brian Hulse and Kanakam dashti for information



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mahmoodUnfollow Follow mahmood




mahmood aslam •Mr.Brian Hulse i asking one question,in first your comment you say Amines are most commonly used to control pH in condensate....not feedwater. but sir i don't understand why you say condensate water basically its a feed water



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Brian Hulse •Condensate is water returning to the feedwater tank from the steam loop. In other words, it's already been through the boiler at least once, is pre-loaded with treatment chemicals and is returning for re-use. Feedwater is make-up water. It is coming from a processed water source (demin, RO, filtration, etc..), has a different chemistry because it hasn't been through the boiler and must be treated differently.



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BradUnfollow Follow Brad

Brad Buecker •You have received some good information. The International Association of the Properties of Water and Steam has excellent, free downloadable information. As Brian has commented, ammonia or in some cases an amine is utilized for condensate/feedwater pH adjustment, where current guidelines in all-ferrous systems call for a pH range in the low- to mid-9 range. This pH range minimizes general iron corrosion. Also, unless the feedwater system contains copper alloys, an oxygen scavenger/metal passivator should not be utilized. Rather, with properly controlled feedwater chemistry (where the condenser is tight and allows less than 10 ppb dissolved oxygen in-leakage), allow the oxygen to remain, albeit with a small amount



removed by the deaerator. For once-through units, this all-volatile treatment chemistry (but where oxygen is purposely injected into the condensate and feedwater) is allowed to carry over to the boiler, as solid alkalis must not be introduced to these systems. For drum units, the most common treatment, at least here in the U.S., is maintenance of a small dosage of tri-sodium phosphate (Na3PO4). The chemistry takes more discussion than I can put in this note, but I have good literature I can send that discusses the chemistry. There is a growing movement towards caustic as a replacement to TSP, but as was pointed out earlier, the free caustic concentration should be maintained below 1 mg/l to prevent under-deposit caustic attack of waterwall tubes. I am presently attending the spring meeting of the ASME Research Committee on Power Plant & Environmental Chemistry, where these topics have again been discussed and updated. I can provide more information outside of this message.



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Kanakam dashti •Caustic is the main alternative for TSP in HRSG Drum boilers to come out from hide out.Brad suggestion is excellent.



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JanitoUnfollow Follow Janito

Janito Ubal •Dear Mr. Brian, may I ask you a question as you have said, "...It is coming from a processed water source (demin, RO, filtration, etc..), has a different chemistry because it hasn't been through the boiler and must be treated differently." As far as I know in HRSG or any type



of Boilers, the medium used as feed water is Demineralized. Please can you explain me why is it possible to use R.O., Filtrated Water, etc. means any medium? In which these water sources are having higher conductivity than Demin.? What is the basic standard water analysis of feed water to be used for Boilers? Thank you.



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Brian Hulse •Several questions/issues here, so I will try to address all. Firstly, boilers have different water chemistry requirements, based on a host of factors including working pressure, materials-of-construction, downstream steam usage, etc., etc.. The chemistry that works for one probably won't work for the next one. ASME and others specify testing protocols and give general guidelines, but the fact of the matter is that your site and your system dictates your chemistry.

Secondly, when I made my comments about feedwater and indicated process possibilities, I wasn't thinking about them exclusively, but in combination. Rarely does one get away with just one process in a water plant. For instance, you may have a carbon filter followed by a sand filter followed by a cation/anion demin followed by a degassifier followed by a mixed-bed polisher. It's usually a combination of processes that gets you to where the steam system requirements are met.

Lastly, I have to say that my feedwater/condensate explaination.....although accurate in my most-recent experiences, may be debatable. Some would say that you have THREE kinds of water: CONDENSATE = water that's been through the boiler at least once and is returning back to the feedwater tank, MAKEUP WATER = water from the processed water plant coming into the system for the first time and FEEDWATER = a combination of the previous two, which leaves the feedwater tank and is headed back to the boiler. I alluded to this in my previous comments, but I may not have been clear. At any rate, my point was/is this: you use different chemicals and dose differently, depending on the position of your injection site, because the water you're dealing with is different. That's why the terminology is important, and why water is called different names when it is in different parts of the system.




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JanitoUnfollow Follow Janito

Janito Ubal •Sir, many thanks for your time and wonderful explanation. Since I worked with Thermal Power Plant, the MSF and MED are the main source of our Make-Up Feed Water to our Boilers. My first job abroad is an IWPP Construction, Commissioning, Operation and Maintenance of Power and Reverse Osmosis Desalination Plant. Since, R.O. Desalting Plant is the latest economical source of water production.

Presently, we are building the 2,400 MegaWatts CCPP GT/ST Power Plant and the biggest Hybrid Desalination Plant in the World (if completed) MSF/R.O. We are behind the schedule that why there is a debate if R.O. (permeate water) can be use. We are ('till this time) opposing this idea. That's why I'm asking you the standard Water Chemistry of Feed Water to be used in Boilers. I am not a Chemist but I got only an idea basing on my previous experience.

Nonetheless, again thank you very much.



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BarryUnfollow Follow Barry

Barry Iwanicki •Brian has pretty much nailed it on the head. Phosphate programs can be used in all boilers but mostly used on high pressure 350 PSI boiler systems and above. Variations of phosphate programs are used and with proven very good track records. In order for the phosphate to work properly there must be a degree of alkalinity in the water for the proper chemistry to work. Phospahte residuals must be maintained within its designated control parameters as set out by your water treatment representative. Personally I have worked with GE Water & Process



Technologies and my experience with them has been very good. Very good tech support.

Using a phosphate program just about gurantees no free caustic and there for no possiblity of caustic attack.

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to control boiler feed water ph, is it better to use di-sodium phosphate or caustic soda why

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