Boiler problems

[fridgie]

I got a boiler alarm on a steam boiler that showed a low water alarm when I arrived in the boiler room. I reset the LWCO and the boiler went immediately to a high water alarm. Closer inspection revealed water feed to condensate tank was running constantly and the condensate pumps were off. I tried to lower the level of water in the boiler only to find there was no water coming out of the boiler drain. Next I opened the relief valve and air sucked into the boiler and it began to drain. The condensate tank then filled with water to the proper level and the water feed shut off. Once the boiler water level was back to normal the boiler started up and seemed to operate normally. The steam pressure built up and when the level dropped in the boiler the condensate pumps started and filled to the proper level and then shut off. My problem is this has happened a couple of times at this location and I'm not sure why the boiler gets water logged after the initial low water alarm. Any help or suggestions about this would be appreciated. Thanks. Kev.

[Noel Murdough]

Sounds like a two-pipe system with failed traps and higher than needed steam pressure.

Noel

[powerhead]

Put me down for the boiler was surging due to chemical overfeed or dirty water. The LWCO did it's job to shut the boiler down. If the LWCO was manual then the boiler cooled off while locked out causing a vacuum. I'll also bet that there is no vacuum breaker in the condensate feed line. If the boiler cools and pulls a vacuum it will suck the water right out of the feed tank and continue doing so, flooding the boiler.

I'd try cleaning the system and adding a vacuum breaker to the condensate return line near the boiler.

How'd I do?

[simpleman]

All sounds good to me,as long as we are talking atmospheric
pressure condensate system.

It could be a vacuum condensate system.

[sysint]

Any time of day? After it's been sitting idle awhile?

[ozone drone]

Powerhead is right. It is NORMAL for a steam boiler to waterlog after shutdown. The reason you can't drain it down with the blowdown valve is because it's in a vacuum. The same vacuum that sucked the return water tank dry.

You need to find out why you're locking out on low water.
feed pumps off on thermals? Level sensor control (if Warrick) or McDonnel level switches? and surging caused from too much treatment chemicals etc.

[Edited by ozone drone on 02-11-2005 at 11:45 AM]

[eastern kevin]

Thanks to all for helpful tips. More details on this boiler problem are operating pressure @ 15 P.S.I. Moly testing showed 120 PPM, McDonnell water level control seems to feed fast enough,Condensate pumps not working overly hot or for long on cycles, condensate tank is vented to atmosphere. This low water alarm has happened only three times since November, two of those times in a one week period. Since my last visit there last week there have been no alarms. All I did at that time was to drop operating pressure to 12 P.S.I. This is a vacant building that has had all the production equipment removed and now only has a heating load on the boiler. The owner only plans to supply minimum heat during the winter or until the building sells. Will check all suggestions and report back. Thanks

[simpleman]

.
I'm thinking possibllity that pump pressure is lower then
the boiler pressure so the condensate cant return.
Maybe not being it was used for mass production and the condensate pump should been design around higher boiler pressure anyway,but you never know.

Also the possibility that now with reduce capacity the condensate is slower to return.Then maybe not because that should lead to a flooded boiler.

I wonder with reduce capacity is there now a problem with the lwc and the pump being complatible.Like now you need a
#150md,instead of the 150.

[powerhead]

Are there any motorized zone valves in the header or branches?
How are the process zones valved off?

[shogun8]

Hi Fridge, It sounds to me that the boiler is running low on makeup and the LWCO turns it off, in the mean time the boiler develops a vacuum by cooling down and any condensate that is in the return side is sucked into the boiler.So it seems to me that you need to find out the cause of why the LWCO shuts down the boiler. Following are some possible causes:
1.Do you have buried return lines? If so, they may be leaking and are your air vents in good condition? You can lose plenty of water through a leaky air vent.
2. The pH should be between seven and nine. A pH of 11 or higher will make the boiler water foam. Foaming water will leave the boiler with the steam. That lowers the boiler's water line and causes nuisance low-water problems
3. Sometimes the boiler's water line is priming or surging because
dirt is usually the culprit here. When you see droplets of water in the part of the gauge glass above the water line, it's time to clean the boiler
4. How about the boiler? Is it in good shape? When you look into the chamber, do you see any rusty areas? Do you see any discolored areas on the burners? The boiler may be leaking. and there may also be a hole in the boiler at its water line.