Trouble losing water in a steam boiler

ttekushan_3

where more water is going into the boiler than it can possibly develop in steam output.

If the boiler has a gate valve at its output or the header has gate valves for branches of the system, close all of them and allow the boiler to reach operating pressure. Since no steam is circulating to merely maintain steam pressure, feedwater demand should be nil. What happens? Is it demanding water just sitting there under normal steam pressure? If so, the problem is right at the boiler; perhaps at the blowoffs if piped the way I mentioned above. Can you hear water running anywhere inside the boiler when it shuts off on pressure?

If, on the other hand, the boiler holds pressure and doesn't loose water, then the problems in the system. I still can't imagine how, at the moment, since the losses are greater than the steaming ability of the boiler. The only scenario that I could imagine is that there is a system leak, but water contamination is causing massive carry-over of water with the steam. This is why I'm curious about the boiler design (is it a high pressure used for low pressure application? It may be prone to carry-over if used for low pressure operation due to high steam exit velocities). If branches can be valved off, open one at a time until the trouble starts.

If you can't valve off anything, then I can only suggest shutting off all blowers and let the system shut off on pressure (which will also reduce velocities sharply) and see what happens. Are there still losses? If not, its probably a carry-over issue, with a leak somewhere out there in the return piping. If there are still losses, then I'd focus back at the boiler room.

If you could clarify. I'm presuming that you actually have a boiler feed pump that is activated by the float control at the boiler, rather than a condensate pump that sends water to the boiler based on the water level in the vented receiver. Many of these jobs have both. And beware. There's often one more condensate pumping station around the building than you know of!

I'm beginning to run out of ideas until these tests are done.

Tim_47

Losing water

I have a 5 mil steam boiler that is losing about 22 GPM. I have measured the condensate pump flow rate and have 21 GPM. I am told that a 5 mil boiler can only evap about 10 GPM. The boiler is used for biulding heating only. No process. They run the boiler pressure high at around 10 to 12 PSI and say it has been that way for at least 11 years. I watched the condensate return pump run for 4 minutes straight today and the water level never change. Any thoughts out there.

Unknown

how many Emipre State buildings

Are you heating with 10-12 psi !! First of all lets crank the pressure down to 2 psi and then we'll help ya troubleshoot the rest of ur problems....

ttekushan_3

what kind of boiler is it?

> I have a 5 mil steam boiler that is losing about

> 22 GPM. I have measured the condensate pump flow

> rate and have 21 GPM. I am told that a 5 mil

> boiler can only evap about 10 GPM. The boiler is

> used for biulding heating only. No process.

> They run the boiler pressure high at around 10 to

> 12 PSI and say it has been that way for at least

> 11 years. I watched the condensate return pump

> run for 4 minutes straight today and the water

> level never change. Any thoughts out there.

ttekushan_3

what kind of boiler is it?

From what you've told us, you have a 120HP boiler that can deliver in the neighborhood of 4150 lbs of steam per hour. Somewhere on the order of 9 or so gpm, so pretty much what you've been told. And the boiler feed pump is delivering what it should.

Should I assume you are measuring the amount of fresh water being introduced into the system to arrive at the 22 gpm figure? If so, (and your evidence suggests this) you have equal amounts water loss and legit steam output.

Where can this much water go? Certainly a firetube boiler leaking this much would leave obvious evidence. Unless you have a refractory that has a conceiled path for water to "disappear." Very unlikely. If it is a leak, this is a below-the-water-line phenomenon. If it were above, the steam output would be divided between the heating system and the flue, but still would be within reasonable limits of 9 or 10 gpm. And 10-12 psig would be out of the question.

Often time boilers over 100 hp or of high pressure have the various blow-down points tied into a line that goes into a tempering chamber of sorts. This protects personnel and drains from flash steam and extreme temperatures. Are any of these blow down valves leaking? Specifically, is the bottom blow down leaking? The tempering chamber (I'm drawing a blank on its real name) prevents you from actually seeing anything going down the drain. So pay special attention if this what you have.

Regarding the pressure, the design of the system rules the rules. Cast iron radiation and perhaps convectors don't require the pressure you have. If you have unit heaters, with any kind of condensate Lift into the return system, or anywhere you have lift fittings, the pressure is governed by the height of the lift. Or in the case of fresh intake air heating coils the pressure must be adequate to prevent a coil reaching its stall point and freezing in very cold weather.

If you don't have any of the above mentioned issues, the pressure's probably excessive, as noted elsewhere. But I doubt this is causing the water loss.

Please give a few more particulars.

Tim_47

I response to both. I am going to turn the steam pressure this morning to about 4 PSI. There are some areas of lift needed but only 4 or 5 ft. 2 psi at the end of the main should handle it. I am going to find the first area that starts showing problems heating and start there.

Yes there are about 14 steam unit heaters hanging in the plant and some require condensate lift. There are 2 MAU units (1) 1/2 mil the other is 1 mil. The condensate return tank also varies greatly in its water level. I would have thought it would get to a steady state, What comes in goes out.

There are no control valves on any coils. Either face and bypass (MAU's) or cycle the fans on the unit heaters. I have have also measured the rate of change in gage glass on the condensate tank to confirm flow rates of the pump along with the installation of a circuit setter in the condensate fill line. Both indicate around 20 gpm of flow.

The problems in building started when the 1/2 mil MAU was change out and the condensate fill pump failed 3 days later. The old pump was rate for 37 gpm per an old tag on site. That is a crazy amount if the system is working correctly. The plant manager understands and feels that that old pump was installed because the boiler kept going low on water.

Thanks for any help.

Tim_47

System is staying on line

I was able to isolate the problem to the 1 mil make-up air unit. At least if I tried to run it both the boiler water level dropped and the condensate water leak dropped. The pump would run 4 minutes straight. (Yes the condensate pump is operated by a float on the boiler). There is a condensate tank that is float operated at the end of the condensate return line that was not original to the system. They have a room that maintains 100 degrees and a hot box outside that maintains 125 degrees. These two rooms condensate is pumped into the condensate return header and gravity feed back to the boilerroom condensate tank. The 1 mil MAU is about 2/3 away from the boilerroom.

We replaced the thermostat and verified that the float was okay in the F&T trap that handles the MAU. The only change I made to the piping was that I added a swing check to act as a vucuum breaker on the gravity condensate return line. This time when we opened the steam valve feeding the MAU and started up the fan the water level in the boiler only showed a slight change. The condensate water level varied normally. We were able to blow down the boiler and start and stop the MAU.

The only explaination that we can come up with is that the condensate line was not draining properly and thus not allowing the traps to drain and allow coils to drain. (We confirmed with a bucket that the MAU condenses at 1 GPM) The water in the coils with the air flowing over the coils would cause accelerated steam condensation and start drawing the water out of the boiler. Then eventually the pump would turn on on the tank at the end of the line and force the condensate down the line to a point that would allow the traps to operate again and the cycle would just keep going.

After talking with the building engineer it turns out that they had LWCO problems 11 years ago and that is why the larger condensate pump was installed. (37 GPM) 4 times larger then what is neeeded for a 5 mil boiler but it allowed the boiler to stay on line while the problem was occuring. The one item I learned on Thursday morning was that over night they used 110 gals of make-up water. (They have a water meeting on the fill line). This clued me in to start looking at why they could not get the condensate back.

We had 11 degrees this weekend. I will be checking in on things Monday morning. My hopes are that they did not use any make-up and all went well.

I have talked with many people about this job and noone ever mentioned anything about venting the condensate return line. Is putting a vaccuum breaker in a gravity condensate return line standard or do I need it because my condensate line may have dips in it. I looked for broken hangers and eyed all the piping from a lift. I have to think that the vent solved the problem because I cannot believe the thermostat in the trap could cause all these problems. Also it turns out they have had problems and solved them with the larger condensate pump.

Any other insite on what could have solved the problem?