Black water in steam boiler

[spector]

Boiler sample water is black.

Black sediment quickly settles out to bottom of sample jar.

Atomizing steam piping components (strainers, valves, elbows) clog with black sediment.

Feed water to boilers seems clear.

Condensate return seems clear.

Water treatment contracor says sample showed 'nothing' when checked by lab......

What is happening here?

I have never seen black deposits collect in atomizing steam piping components or float chambers that generate so much of same.

We have active O2 corrosion in all three 100 PSI W/T boilers....Deep and concentrated pitting with large carbunkles that ooze black when broken. I cannot convince boss to inspect DA tank heater and trays and spray nozzles. Water treatment contractor cannot manage to draw and sample feedwater for 02, so he has convinced boss to use more sulfides instead.

Is this black water from drum and black deposits in steam piping a further indication that our system is being eaten by 02?

 

[TBP]

Where is the boiler inspector?

A couple of recommendations:

1/ You desperately need a new water treatment outfit.

2/ Tell your boss what it will cost to replace the boilers (and quite possibly the DA storage section) vs dealing with the problems now, and see if that gets his attention.

If you can't get both #1 and #2, I'd go to #3...

3/ Look for a new job.

 

[kenvlach]

Easy test: check the sediment with a magnet -- my 1st guess would be Fe₃O₄. With plenty of O₂ in the water, some acidity since also CO₂, and heat, conditions are perfect for 'eating' (oxidizing) steel.

FeS is also black, but usually associated with an H₂S smell.

Agree with TVP except "Look for new job." Your boss is due to be fired. Don't know what your company's internal politics are like, but don't be a fall guy, let higher ups know an expensive situation is about to occur despite your warnings.

 

[unclesyd]

After echoing the two previous post and adding an emphasis mark I would like to know a couple of things.

I hope you mean sulfites instead of sulphides

Are the boilers allowed to set idle full of water any length of time?
What is the level of sulfites you are adding to the feed water?

 

[spector]

Where is the boiler inspector?....Funny you should ask. I am a former NB commissioned boiler inspector....Crawled in every boiler in three states for years till I got sick of it.

No, I know exactly what is happening here. I just wanted to vent and get the opinion of others.

Thanks.

 

[spector]

Please excuse my mis-spellings.

Boilers are rotated often, offline boilers are heated up daily to maintain short notice standby condition. When placed in wet lay up they are flooded with hot feed water and chemistry maintained.

This O2 pitting is occuring at and below the water line of the drums and float chambers. Light and scattered pitting above that point.....On the tubes it is extremely heavy at tube ends and concentrated in tight 'buckshot' patterns where the tube makes it's first bend below the drum ('A' style boilers). Pits are up 1/4" in diameter and extend more than half tube wall thickness.

Feed pumps have history of frequent seal failure, but they operate with 15 PSI suction, 150 PSI discharge in constant pressure system.

DA is tank car style, operated at 227 F, 5 PSI. No inspection for many years. Last year I did open the external DA overflow trap and discovered it was inoperable and almost full of red sludge, so I know heater and trays and storage section need to be cleaned.

I expect that soon tube failure will drive repairs and possible investigation. I will not lose my job over it. I keep all emails to boss.

We are experiencing very high makeup rates due to many locations not piped for return.

Return condensate PH runs high 8's, but temps often over 210F. P-Alk maintained 800-900. Conductivity is 2000-2100

 

[pablo02]

I suspect the thermal cycles and wet layup is allowing the magnetite layer on the boiler tube walls to slough off and reform (kind of like the oxidation of CorTen steel being constantly replaced if removed)... I suspect your makeup water is too high in O2 and this is contributing to the cause... the magnetite layer is usually a good thing in that proects it from the usual rusting we're familiar with (again, like the protective layer of oxidation of CorTen)

I think to some degree, your current mode of operation is the main culprit, but reducing the O2 content to the minimal should greatly help...

 

[EMKWR]

Spector,
the problems you have are either caused by too high an oxygen content in your makeup water or trouble with the conditioning of your water/steam circuit. If the conductivity of your condensate is in microS/cm, than it may be worth too have a look at the composition of the water/steam circuit. Also the pH could be a bit higher, in low 9's. What type of conditioning are you using ?
We do have the equipment to help you with this. If you need any help to convince your boss, please let me know.

Edwin Muller
KEMA Power Generation & Sustainables
Arnhem, The Netherlands
E-mail e.f.muller@kema.nl
Internet:

http://www.kema-water.nl

http://www.kema.com

 

[TBP]

About the feedpump seal failures - are these the correct pumps for the application, and have they been piped properly? (A LOT of feedpumps have been improperly selected, and in a number of cases where properly selected pumps have been purchased, the suction piping has been botched. (Incorrect suction piping probably causes more pump problems than everything else put together.) I have seen cases where the operating feedpump suction pressure is just slightly below atmospheric, and air gets drawn in around the seal or packing. Not enough to cause any noticable operational problems, but enough that the oxygen in the air that is drawn in pits the discharge piping and boilers. DA 's were operating properly, and the sulphite levels were maintained in the storage section - yet pitting was still evident in the feedwater lines and boilers. Repiping the suction lines is a big, expensive job that requires a shutdown. Very unpopular. The band-aid fix is usually adding sulphite right to the drum.

 

[spector]

Hello TBP,

Pump seals..........That's one battle I managed to win. We recently changed to high temp seals and started making more precise alignments........We are also due to change to new flex couplings that are less sensitive to misalingment. I discovered pump seals were not 'hot water' rated. In service, the rubber boots hardened and the pump shafts became etched and pitted where the boot gripped the shaft. That prevented the seals from closing as it experienced wear.

I'll test boiler sample tonight with strong magnet......

Thanks for your informative replies!

 

[Wirt]

Black, magnetic debris in boiler feedwater loop (e.g. feedwater, boiler water, steam condensate) could be due to too much reducing agent (i.e.oxygen scavenger) as well as low pH. If oxygen is in excess I would expect to see some red-orange debris. Howver, oxygen can not be ruled out as a part of the cause of the black debris.

 

[unclesyd]

With the level of sulfites and the wet lay up and your mention of carbuncles/tubercles there is possibility that SRBs' and/or Iron Reducing Bacteria are being introduced in the boiler while being laid up. Your conditions during lay up would be an ideal incubator.

 

[spector]

I experienced such a bacteria when serving on nuke submarines back in mid 80's.

Our trim water tanks supplied flushing water to our toilets....Sea water normally, but often topped off by fresh water via hose connection when pierside.

Almost overnight, our flushing water grew black and had rotten egg odor. When at sea, this became a nuisance in that it effected habitability. I owned the system, therefore I was stuck solving the problem. First attempts were to empty the tanks and refill. That proved a temporary fix as the water would soon become black and odorous again. I decided then to super clorinate the system which again proved only temporay. Other components in the trim system began to clog with an almost black thick slime-like growth.

The biggest problem it created was when our trim system prime float valves became clogged with it and we couldn't acheive good prime. This became a 'safety of ship' item......The trim system is essential to safe operation.

Samples of the goo and water from the tanks were sent out for test. I transferred off before I discovered the cause.

Only recently, while researching this problem with my boilers did I find mention of it.

 

[spector]

Wirt.......That was my dad's name, Wirt Val, in fact.

Anyway, I did find large amount of red-orange sludge-like deposits in DA tank overflow trap. Haven't been allowed into storage tank yet. Boiler drums get frequent blows, so no evidence during internal inspection.

Interior of condensate/make-up mixing tank is coated with thick black plactic-like deposit that constantly flakes off to clog lift pump impellors. Tank is 47 years old, and walls thinned to point management fears failure if cleaned. I fear flakes that don't clog pump make it into DA tank and have accumulated in heater section preventing proper scrubbing of water.

 

[MHickman]

It is possible that the flakes could inhibit water flow inside of the DA; it could be creating a condition where spray valves in the DA have become damaged and or clogged. This can contribute to ineffective spray patterns or "firehosing" of the spray pattern onto the trays in the heater section. If the trays get damaged (due to sludge build up or firehosing), the water in the heater section may not have enough retention time for the last bit of scrubbing (which is the hardest to achieve). It looks like its making heat, but that will not tell you about the scrubbing performance until you read the O2 coming from the DA.

Have you done any O2 testing out of the DA tank? The presence of red oxide sludge in the overflow pipe is a bad sign, but may not be due to the DA performance. Manual O2 comparitor test kits are available (e.g. Chemetrics) and they only require a sample cooler. Hook up the sample line prior to the BFW pumps (preferably on a sample line directly in the DA storage tank) in the pump suction line. Chemistry feed and pump recircs can also affect O2 readings during a test so make sure that you isolate as necessary or as possible. DA's are usually designed to reduce dissolved O2 to 7ppb. If you are say, over 100 ppb, you probably could start by looking at the DA and continue from there.

If you do confirm poor performance of the DA, it would be a good idea to get permission to go inside the heater and storage sections on the next outage (if they allow you to have an outage). That way you can see if there are spray valve or tray problems.

Laying up and cycling are definitely not helping you either.

 

[spector]

Yehaw!

Drew one gallon of very black boiler water into plastic sample bottle. Placed large magnet against side of bottle....in thirty minutes water was clear except for red-orange tint.... All black sediment was up against bottle next to magnet.

Iron.....or should I say high grade boiler steel tea?

I'll leave this just like it sits for the chemical man to see. Gee, wonder if his lab could use my magnet.

Thanks Gents

 

[spector]

kenvlach,

I drew large samples of boiler water(all boilers), and condensate.

Boiler PH 11.7. Condensate PH 9.0

Magnet revealed iron oxide in both samples, heaviest in boiler.

Opened steam strainer in atomizing steam line. Removed large clog of black material and broke it up with fingers and dissolved it in water, then tested with magnet....Iron....It separated out just like other water samples.

Concentration is so bad that sight glasses are pitch black, looks more like ink than boiler water.

Boss will not lose his job, this is a Veterans Hospital. Historically, all his experience till recently is HVAC, with very little hot water heating boiler and no steam plant experience at all.

Besides that, I like the guy.

Thanks to all of you. I have enough info now to proceed smartly.