steam boiler waterline is plummeting

Tony Conner_2

...feedwater controlled by starting & stopping the pump? I've seen installations where "start" level for the pump was set too near the low-water trip level. The first thing that happens when feedwater is introduced into a steam boiler, is that the water level initially drops. This is because the relatively cold (as compared to the boiler water) feedwater causes a lot of the steam bubbles to collapse. If these two points aren't far enough apart, then the initial drop in water level trips the boiler, regardless of what the pump is doing.

norfitz

steam waterline plummeting

Happy short week, guys. My contractor customer and I have a Peerless G-LC-10-SU forced-draft steam boiler, set 12 PSIG to serve fancoils, HX's and more in a hospital, and its' waterline disappears alarmingly fast (20-30 seconds) as if the water is leaping up into the piping despite the header, risers and equalizer being the proper size and elevation and piped correctly. The water in the gauge glass is crystal clear. The 157 pump controller, mounted on its' own water column with the line on its' casting 1" below the boiler's normal water line, cuts the burner when appropriate and starts the feedwater pump when appropriate, yet the waterline keeps diving right out of sight and doesn't recover before the boiler loses its' head of steam. Additional water from the DA, which is mounted on a mezzanine about 8-10' above the boiler's water line, then arrives by gravity (and possibly water from the 60' long 4" system takeoff?), and the waterline of this now-steamless boiler rises to an inch or two above normal as the entire pointless process begins again. The system takeoff is being checked for level today. The feedwater pump is way oversized (Grundfos CR3-4, 14 GPM @ 100'!) and it's 2" discharge line enters the EQ 4" below the boiler's normal water line, yet the problem remains when it is throttled anywhere between open and deadheaded, even after a 1/2" orifice plate was installed into the discharge. There are 2 check valves preventing backflow through the feedwater pumps toward the DA unit. There are 2 more boilers, both significantly larger, that serve this system. This full-mod boiler is not being over-fired, and this problem also happens at low fire. We are finding some water up in a horizontal portion of a system takeoff. We can't figure out how the water is going wherever it's going and this boiler is of no use to the hospital in its' current wacky sequence of operation. The hopspital staff claims the boiler operated correctly for about a year, and then a clogged pipe on the suction side of the feedwater pump was cleared. I would greatly appreciate any theories and proposed solutions.

Bruce Tompkins, Power Boiler Sales

Mad Dog_2

Feel your pain, Bruce

I hate to make suggestions without seeing the situation, but I have seen the simple things be the cause of similar problems on other systems. The water can be crystal clear and still be "dirty." Some digital pics would be of a better help, but before you go crazy have you REALLY cleaned the boiler and system? We sometimes spend a whole day cleaning residential boilers. Did you TSP or Mex it yet? When the last repair was done a good deal of cutting oil may have been introduced. Mad Dog

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EBEBRATT-Ed

Just an idea. Boilers are rated at delivering steam with a certain feedwater temperature. The firing rate of the boiler is also based on this feedwater temperature.

If your feed water temp is to high and you are firing at the nameplate rating you are in effect "overfiring" the boiler because with the higher feedwater temp the boiler contains more BTUs than it's rating.

However you mentioned that you have this problem on low fire as well.

Any sudden loads? Fast opening valves can pull water from the boiler if the steam pressure drops suddenly.

ED

jeff_51

Do you really need to run at 12 psi?

sounds like the velocity is pulling alot of water up the header and into the piping?

Blackoakbob_3

Does the water line....

appear lower in the gauge glass, but the lwco float still seems to sense the water level and then as it drops out of sight the lwco trip? I hope you followed that.
If the boiler was not thoroughly cleaned on install you may have residual oils causing a bad water line. Also it would be nice to know what your water test results are ie. your PH, TDS, PM&O to start with. Are you making up with good quality soft water? Is the DA really functioning, giving you oxygen free and preheated feedwater or is it just a condensate holding tank?
You have caught my intrest!
Best Regards,

Tony Conner_2

What Exactly...

... was the nature of the "clog" in the feedwater piping that was cleared? This really strikes me as more of a feedpump/piping issue, than a problem with the boiler itself. It sounds like the only time water can actually get into the boiler, is when there's no steam pressure in it, and it can just flow in by gravity. It's not just something like a 3-phase motor on the feedpump rotating in the wrong direction, is it?

norfitz

Thanks much for replying, Tony. All I know of the clog is that it was between the DA and the pump. I'm assuming sediment, and I'm also hoping the primary mechanical contractor leaps into this conversation some time today. We considered the feed pump might be running backwards, but a gauge on the pump discharge reads 15 PSIG when the pump is running rather than 0 or vacuum.

Bruce

Gene_3

I agree

check and see if it starts to disappear at a certain psi?? It must have worked at some point so what changed?? did someone raise the pressure from what it was?? was work done that may have put oil in the system from new pipes and threading?? are there zv's closing?? you have a great mystery, this what makes our industry great, we are investigators, HVAC CSI, stay on the case, the culprit will give themselves away, the evidence will show the guilty party, recreate the scene of the crime, what changed??

norfitz

Thanks much for replying, Mad Dog. If there was cutting oil introduced we had best find out quick as it's a gasketed boiler! We will investigate the cleaning/water quality question. I have some photos but they were not terribly helpful until I got on site. As I originally wrote, levels of the components are correct as per the manual.

Bruce Tompkins

Tony Conner_2

But...

...with your boiler operating at 12 PSIG, and the feedpump discharge at 15, the delta-P is peanuts. 100 ft of head is just over 43 PSIG. There's something wrong with the pump and/or piping. Is the motor the right RPM and/or HP?

It could still be a direction of rotation problem - it's not that centrifugal pumps won't work at all, they just work really poorly. If you can see the pump or motor shaft, shut the pump off for a few seconds, and watch the direction of rotation as it slows down. My bet is that it's running backwards.

norfitz

Thanks so much for replying, Jeff. The hospital claims they require 12 PSIG for the kitchens etc. Yes, it does sound like velocity sucking up water, but the risers are proper size and at least 28" above the waterline. Here's photos 3 & 4

Bruce Tompkins

norfitz

Thanks so much for replying, Black Oak Bob. As stated elsewhere we will investigate water, oils etc, and the pump controller is a McD & M 150E electronic probe type. We will also determine the true nature of the DA. Here's the final pic now available to me, showing the monstrous pump.

Bruce Tompkins

Empire_2

Double check on feed line

I am doing some research on this. Were the double check valves always there? ANd can you dissable one of the check valves, like the one closest to the boiler. I just have a problem with the double check valve set up...Perhaps the increase in boiler pressure is slamming shut the nearest check valve.(which for some reason the pump cannot overcome said pressure) As a result the the boiler will kick out lowering the steam head, allowing water to feed as usual, but upon refiring this increase in pressure repetes this process again. Just a thought.. Good luck, let me know what you find...

norfitz

Here's some supplemental info and experiment results. The contractor turned off the feed pump, closed the discharge valve between the pump and the boiler and fired the boiler. The boiler turns off on limit at 12-13 PSIG and the water line drops at the correct rate.

When feedwater pump is allowed, the waterline starts bouncing, the feed pump starts, the waterline starts plummeting, the boiler turns off and the waterline keeps plummeting despite the monster pipe discharging 15 PSIG into the EQ through a 2" pipe into a 2" tee 3-4" below normal waterline.

This morning the contractor disassembled the return connection and lower portion of the EQ and found no blockages.

Pump rotation is proved correct. Historic clog was sediment and rust in the piping between the DA and the boiler. The atmospheric horizontal DA, which has plenty of capacity has a 2" discharge pipe dropping about 12' to the floor where it tees off to each boiler's feedwater pump, providing a steady 6 PSIG via gravity to the inlet of each pump. Boiler was cleaned with TSP several times, and piping repairs were done mostly with shop welded stuff so there isn't much possibility of oil present.

I would blame the 150E pump controller for hypersensitivity to the bouncing but that doesn't explain the waterline crashing, especially once the pump is running.

norfitz

Thanks for getting into it Mike. The swing check valves were always present and they have been checked and found to be fully operational.

Bruce Tompkins

Boilerpro_3

A few things

Is that a hartford loop in the one picture? They are not supposed to work well with pumpsif you pump through the hartford loop. Second the last take off from the boiler into the header is very close to the system takeoff. This does not allow the steam to dry properly from this outlet becasue there is too much turbulence. Probably not related to the problem....If that is a welded header on a cast iron boiler, the boiler is in for trouble some day because the header has no place to give as the cast iron expands and contracts at a differnst rate. I doulbt that factory apporved.

Boilerpro

norfitz

Hi Boilerpro, thanks much for checking in. Yes, that's a Hartford loop and my associates and I are still under the impression that it's a great idea for boiler protection in any situation. Interesting point about the proximity of the steam takeoff to the last boiler riser. We will look into that. I believe the header is indeed welded and the servicing contractor, who did not install the boiler, will see these messages.

Bruce Tompkins

Steamhead

Bruce, if it worked OK with the feed valve closed

the trouble is on the other side of the feed valve. I'm not sure what you mean by a "DA" but have you observed water filing it up as the level drops in the boiler?

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Tony Conner

If...

...the boiler is at 13 PSIG, then even though the feedpump discharge gauge reads 15 PSIG, you've only got a 2 PSI differential trying to push water into that boiler. You won't move much water with that, regardless of line size. The feedpump discharge pressure should be 20 or 25 PSIG for this boiler setup.

jeff_51

well, you've posted a puzzler

It will be interesting to find out what you find out

Bob D._2

Boiler Water Line

One of my sites had/has a similar, though slightly different, problem over the past two+ years. 3 x 600 BHP LP steam firetube units. Our consulting engineer was no help, and the boiler manufacturer, who found nothing wrong with the installation, ended up scratching their head with the rest of us. No real smoking gun identified yet. I had my old outfit come in and do a complete set up, from zero, of the pump controls, feedwater valves and burner controls. Water chemistry was fine (tested repeatedly, I thought it HAD to be oil in the water). Put in surge columns, then water line baffles (if you can't fix it, mask it). Replaced all the "new style" MM-150's (ALWCO) and later also replaced all the MM-193's (combo pump control & LWCO, which were found to be "sticking") with tune-able PID controls. Slowed the firing rate controller down (ramp rate, for swell & shrink control) and extended the low fire hold. Even now I'm not 100% comfortable that the boilers will be "trouble free" at higher firing rates, though they are somewhat more stable (no spurious ALWCO trips) at lower loads. As far as I'm concerned, the gremlins are still there. This has been one humbling job!

Blackoakbob_3

I've read all of the above....

with interest because I have a similar reaction happening in a cast iron sectional boiler about 10 months in operation. It was thoroughly cleaned before start up and piped per mfg instructions and oddly enough it has the same brand of feedwater pump! I corrected some noise issues related to pumping into the boiler by lowering the tee where the feedwater goes into the equalizer by 3 more inches ( it should be 2-4 inches below the average steam line in the boiler) because my steam line appears to be lower during operation. I felt that I may be pumping into this line and the subsequent "water hammer" caused by the cooler return water may be effecting my circulation in the boiler. This did stop the popping and banging of the check valves and I had a noticeable effect on the waterline in the gauge glass. Not alot but some. This boiler is not tripping out on LW but there is alot of acton in the gauge glass level.
I just had the pleasure of meeting some of this industry's real gentlemen at Wetstock. I ran this question by some of them. I had some pictures and the piping and install was not faulted ( Thanks, I appreciated the compliments) but most of these experienced and self-confident men thought that it may still be a dirty boiler. Their thoughts were that it reacts like a oily water line. So, I'm going to locate some suggested cleaner ( SOS by Mr. Linhart) and clean it again. The possiblity of the area above the skim tapping not being completly clean is there, so, if it looks like oil and acts like oil, it's probably oil.
I'll let you know.

Blackoakbob_3

I've read all of the above....

with interest because I have a similar reaction happening in a cast iron sectional boiler about 10 months in operation. It was thoroughly cleaned before start up and piped per mfg instructions and oddly enough it has the same brand of feedwater pump! I corrected some noise issues related to pumping into the boiler by lowering the tee where the feedwater goes into the equalizer by 3 more inches ( it should be 2-4 inches below the average steam line in the boiler) because my steam line appears to be lower during operation. I felt that I may be pumping into this line and the subsequent "water hammer" caused by the cooler return water may be effecting my circulation in the boiler. This did stop the popping and banging of the check valves and I had a noticeable effect on the waterline in the gauge glass. Not alot but some. This boiler is not tripping out on low water but there is alot of acton in the gauge glass level.
I just had the pleasure of meeting some of this industry's real gentlemen at Wetstock. I ran this question by some of them. I had some pictures and the piping and install was not faulted ( Thanks, I appreciated the compliments) but most of these experienced and self-confident men thought that it may still be a dirty boiler. Their thoughts were that it reacts like a oily water line. So, I'm going to locate some suggested cleaner ( SOS by Mr. Linhart) and clean it again. The possiblity of the area above the skim tapping not being completly clean is there, so, if it looks like oil and acts like oil, it's probably oil.
I'll let you know. Best Regards

norfitz

no progress yet

Happy Monday, guys. We're still trying to figure out what's going on, but I want to thank you all for your kind support. I will post any major headlines promptly. Bruce

Kevin Jahn

Water line & pipe

> Happy Monday, guys. We're still trying to figure

> out what's going on, but I want to thank you all

> for your kind support. I will post any major

> headlines promptly. Bruce



Can you get some pictures of all sides of the the boiler so we can see the connections ? Maybe some shots of the feedwater hookup, more info on the boiler steaming capacity etc.

Kevin Jahn

Kevin Jahn

piping

Can you post some shots of all sides af the boiler so can see all the connections ? Maybe some info on steaming capacity and the feedwater connection pics.

norfitz

photos 4 & 5

norfitz

photos 2 & 3

norfitz

photo 1

Craig Machamer

vanishing water line

Bruce,

Just weighing in from the industrial side of steam systems. If this 500# gorilla was on my back, I'd start out by rounding-up the two (2) usual suspects: Boiler water conductivity and BF pump capacity. First, I would want to know the conductivity of that boiler water. Just get out the old handy-dandy Myron-L meter and test it (unneutralized). I suggest that it be maintained at no higher than 2,500 microseimens. More often than not, I will have the chemical guys argue with me about that, but I just tell them to back-off...this is about physics, not chemistry. The second thing I would look at is the capacity of that BF pump. That Grundfos pump is a good pump, but it is a centrifugal. Centrifugals are basically lazy in that they only want to develope enough TDH to get the job done, and no more. What you really have to be concerned about is the volume. It has the capability of putting a whole ship-load of feedwater into that near-boiler piping very quickly...possibly creating a venturi effect that will shove that boiler water right up the spout. If anything, you might consider throttling the discharge valve significantly to reduce it's output capacity (volume in GPM). I probably average about one of these situations a month, somewhere around the country. It often turns out to be caused by a new chemical guy who trys to save some money on chemicals by increasing the cycles of concentration. Hope this helps you.

Best regards,

Craig

Kevin Jahn

water line

Tony,

I agree with all the comments about the feed system on this job. I am not getting a clear picture in my mind from what has been presented, there is no substitute for standing in the boiler room ! I am still not clear on the difference between the steaming capacity and feed pump capacity. It may well be the controls or the piping connections at the boiler. That large pump may be on & off in just a couple of seconds.

Tony Conner_2

What Is...

... the boiler capacity, either in horsepower, or the nameplate rating for the burner input?

c.t.kay

think about a presurized feed water loop and a feed water valve at the boiler. this is a set up we often use on large, multipleboiler systems that run at 10/15 psi.correctly adjusted this works fine.