Carryover so bad that feed pump can't keep up and boiler runs out of water

Zoso

I have a low-pressure steam system with a new Hurst Red Boiler Series SLPE that ran fine for months. Then one day, sever carryover occurred to the point where the feed pump could not keep the boiler full. This problem re-occurs every several weeks, but otherwise the boiler runs fine. Water chemistry looks good and I am told that the load is relatively constant. The steam serves HVAC coils and control valves are locked at 30% (that's a whole other battle I'm fighting with this client). So I don't think that there are any sudden increases in load.

What could cause this intermittent carryover to the point where water is sucked out faster that the pump can keep up? We even had the makeup water valve bypass line open during one incident, and the water still was sucked out faster. The boiler originally did not have a Hartford loop. If you look at the attached photo, the steam left the boiler with a short riser and continued horizontally. We went back and installed a Loop with a lot more vertical separation as well as a path for any carryover to drop back down to the boiler. It worked for a few weeks, but the carryover problem just happened again.

I don't want to blame the manufacturer, but I have heard (from another manufacturer's rep) that this boiler had a reputation for carryover issues.

Any thoughts?

SlamDunk

How do you know it is carry over? At first blush, I would say your feedwater pump isnt putting enough.

Zoso

We have observed the boiler getting sucked dry in a matter of seconds after running normally. We have checked out the pump and even increased the Cv of the feed water valve to well beyond the requirement. After it occurs, the header is full of water.

ratio

Yah, are you sure you aren't looking at an intermittent slow return, vs an intermittent fast leave? Maybe something is floating around in there & occasionally blocks the return? Loose impeller on the pump? (Had this happen to a van once, random overheats that went away in under a minute once the impeller started turning again!) Watch the amps on the pump & see of that offers any insight.
What's the boiler pressure at before, during, & after an event? Is it at a certain time of day/week/month? Reoccurring after x number of power on/burner on hours? How long does an even last? Does everything go back to normal after the LWCO does its thing, or is a manual step needed to restart normal operation? Can you get it to operate normally if you catch it in the middle, or do you have to wait it out?
After checking the return & pump carefully, I'd look for something that makes a significant change to the load, like a valve fully opening or closing. Watch this for a little insight...

SlamDunk

I think pump pressure has to be at least twice boiler's max working pressure.

If that's ok, and demand is constant, then you might have ( I do) a check valve after the modulating feed water valve, if you have one, that is stuck or--- your modulating feed water valve isn't responding to the water level but you said an open bypass doesn't help so, is pump pressure twice max working pressure? Just spit balling here.

EBEBRATT-Ed

I like a pump that puts out double the boiler operating pressure but most feed pump mfgs size at 20psi for a low pressure boiler.

Does this happen on a cold start or while the boiler is maintaining pressure??

Are their any sudden changes in load??

The Steam Whisperer

I have been seeing excessive carryover as a regular problem with nearly all newer steel boilers. Essentially the nozzles are too small for use with low pressure steam. You probably need to have a large header with a nice big equalizer/ drain line back into the boiler to handle all the excess water being sucked into the header. Take a look at an equivalent capacity Peerless TCII boiler to see what header and equalizer size you probably need. I have found that steel boiler manufacturers just tell you "We just manufacturer the boiler, it's up to your engineer to make it work properly".

SlamDunk

Small nozzle would explain a lot.

The Steam Whisperer

That looks like its probably a 1.5 to 2 million input boiler. It probably should have an 8 inch header with a 4 inch equalizer/ header drain.

EBEBRATT-Ed

Sounds like your getting a sudden load applied to the boiler.

Zoso

The most puzzling thing is that this unit ran fine for several months before the incident happened. And then it runs fine for three or four weeks in between each incident. Boiler was first started up in March or the load would have been much greater than the summer because it's an HV AC boiler.

Thanks all for your comments. I don't really have any answers to your questions. My first suspect was some kind of sharp swing in load but the building Engineers tell me that's not the case.

We brought a water treatment contractor out there after the last incident to double-check the water. Everything look good other than it was dirty because when the header floods I think it's washing out a bunch of junk.

It's the crazy intermittent pattern that bothers me

The Steam Whisperer

Dirty water will do this. We have seen this before too. The water will steadily get dirtier over time and then finally carry over. Sounds like some more cleaning needs to be done. The piping looks pretty small too, especially the header drip.

retiredguy

I wish my memory was better but the years are taking it's toll. We had a similar situation where the system's steam pressure would suddenly collapse sucking the water out of the boiler. It was a large building so anything could have caused the problem.The problem was corrected by installing an orfice in the boilers discharge piping. The orfice was sized for the boilers maximum output at the normal operating pressure. This corrected the problem.

SlamDunk

These are the most fun problems. You have to spend enough time to be there to catch it. Can you trend steam psi?

SeanBeans

What siZe near boiler piping is all of that??

ChrisJ

These videos may help you.
Just a guess but I think @EBEBRATT-Ed could be on the right track.


"If you increase demand beyond the limit of the boiler’s maximum steam generation rate, no matter what the time frame, problems can occur with both carry-over and low water boiler level. In fact, you might find that your boiler shuts down if too great a demand is put on it. "

This is just one of many videos they have but it could explain what you're seeing.

https://youtu.be/8Lmagejlc1s