Make-up water for steam boiler

Tom R.

A 180 HP steam plant NEEDS a deaerating feedwater heater. Leaking traps or not.

Dan_22

Make-up water for steam boiler

This is probably a real dumb question but I cant seem to find the answer. Why is cold water used for make-up water on a steam boiler? Why not hot water? I would think hot water would be better because a lot of the soilds have already dropped out of it in the water heater meaning less sludge in the boiler.

Tony Conner_2

If Everything...

... is set up properly, and working as it is supposed to be, the amount of make-up water required for little residential steam boilers should be so little and so infrequent, that it shouldn't matter.

Dan_22

The make up water for two Weil-Mclain 88 boilers with an output of 3100lb/hr of steam each. They run the the heat and hot water where I work and are using a lot of water because of bad traps. I wanted to replace all the traps this summer but working for the state is not like working in the real world. Crisis managment is the name of the game and now that the managers see steam blowing out the two inch vent all day long they see why I wanted to replace the traps, especially when we get our fuel bills. I blow the boilers down daily and am getting tons of sediment because of all the fresh water added everyday. We have three 80 gallon oil fired ao smith water heaters 500mbh each and one 250 gallon steam water heater. I was going to pull the hot water out of the ao smiths and feed this to the condesate tank in an effort to reduce the amount of sediment entering the boilers.

ttekushan

its OK

to run hot to the condensate tank. I cant seem to see why hot water shouldn't be fed directly into the boiler as a practical matter. I see ancient texts that suggest just this. But it is for some reason frowned upon. Should it be deaerated first? Dunno. All I know is that the same darn water that enters the boiler cold becomes hot, releases oxygen, precipitates lime, etc. anyway, except that its in the thing you're trying to protect.

BUT- it IS okay to feed a condensate tank or boiler feed tank with hot water.

So you're safe. Any yes, where I've seen this done the scale buildup is reduced.

Dan_22

Thanks for the answer. The condensate tank feeds each boiler separatly through two individual elctronically controlled valves. This isolates each boiler as one or the other calls for water.

bob young

c.w. supply

mc donald-miller specifies cold water supply to auto feeders.

Dan_22

Do you know why they specify cold water only?

bob young

hard luck story

not exactly sure but it will void the gaurantee. i always thought probably mineral or lime build up but never challenged them on it. they invented the device so i figure they know more about it than i do. i have piped them with hot water many times in the last forty years and they work great but don't tell them about it !! i know i am doing wrong & will be punished some day. maybe they hate us and just want to make it harder for plumbers. i'm tough, i don't care.

gerry gill

hydrolevel has feeders

that allow 140 degree water...i use hot alot to boilers just for the very reason you talk about...i just don't do it with an M&M feeder..i believe slant fin co. has it in thier literature to use hot..Noel, you out there?

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Dan_22

I found a McDonnell Miller #53 water feeder which specifies either hot or cold feed only 120f max though.

Tony Conner_2

In...

... boiler plants designed to have a percentage of make-up water, then deaerating/pre-heating the feedwater is very much desired, and usually required. Make-up water should also be softened. Little residential boilers are another matter altogether. It's important to understand the differences between the two types of operations.

I suspect the steam lost out of the vents is not nearly the biggest cause of the high make up water levels. I think that the biggest part of the problem is the really hot condensate causing trouble with the condensate pumps themselves. I'd bet that some condensate is just not making it back to the boilers because the pumps can't handle it very well, because it's too hot. There are a number of things that can be done as band-aid measures, but in the end, fixing the traps will make most of the problems disappear, and save a ton of fuel.

Dan_22

The two boilers I described were installed about 12 years ago and I far as can tell have never been properly maintained. P.J. Dionne did the install according the prints I dug up. I just took over at this facilty about 8 months ago and this is my first winter. The take off for the steam supply is in-between the two boiler tappingson each boiler, which is wrong. Its header is also completly welded with no swing or expansion joints. This is causing quite a bit of stress on the boiler sections and they have already started to leak a little. I would like to get everything up and running the way it should be and any suggestions anyone has would be greatly appreciated. If either you or Tony Conners could elaborate a little more on what is needed to at least get the make-water in line I would appreciate it.

Tony Conner_2

It'll...

...depend on how much condensate gets returned. If you're adding very little in the way of make-up water, you likely don't need a deaerator.

Tony Conner_2

Welded...

... pipe shouldn't be much of an issue. The straight lengths won't likely be long enough to have a measurable effect. In most screwed pipe installations, unless you actually configure the assembly to swing, it won't. The expansion gets taken-up by things like straight lengths of pipe on either side of a 90* el. The longer the leg of pipe, the thinner the wall and the smaller the diameter, the more it will flex. In the old days, a lot of the pipe dopes were home made concoctions that hardened-up like X-Pando. Nothing moved after it set.

The first thing I'd get on is any place condensate is being lost (cond tanks overflowing to drain, leaks, etc.), and traps that need replacing. You can likely get a really good payback on that, based on fuel savings. Make things right mechanically, and most of your water treatment/chemical/scaling problems will disappear at the same time. You kill two birds with one stone.