Dry Steam Is The Goal

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Dry Steam Is The Goal

Steam quality is a measurement of the steam’s dryness. That means the steam should contain no more than 2% liquid water as it leaves the boiler because wet steam can’t hold much latent heat.

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everybodyduck

My old steam boiler is leaking I am adding water twice a day so I’m guessing that it’s venting steam out the chimney. Of course it’s thanksgiving weekend so I’m not going to get any answers until Monday or Tuesday.
How do I find a contractor who understands Dan’s work with steam heating? I have read lost art of steam heating. I have read articles about steam heating near boiler piping venting.
How do you tell the contractor what you need without making him feel resentful?
Everyone has been doing the work day in and day out so of course who wants to take on another know it all ahole customer?
My previous contractor did the best job he could. I’m a homeowner and I have done some reading and went to see Dan’s presentation two or three times so the steam is wet and the fuel
bills are high and that’s what I keep trying to learn about to prevent making the same mistakes this time. I know that I have 800 square feet of EDR I know that the system used to be coal because the pipes are around the perimeter of the basement. The asbestos is good in some areas and not good in other areas.
Probably have to remove everything first then install the new boiler then replace the insulation

Jamie Hall

Either tell us where you are or check "Find a Contractor" at the top of the page here. We may well know someone in your area we can trust...

EBEBRATT-Ed

@everybodyduck

Post your location if you can't find anyone. Even if a contractor is not listed on this site someone may have a recommendation.

CLamb

There's probably an easy answer to this question but I'm still pretty ignorant about steam. Why can't steam heating boilers use a superheater, as are found in steam power boilers, to dry the steam? Is it just a matter of making the boiler too complex?

pedmec

Money. why would you install another device that adds cost to a job when if piped correctly you can get the dry steam you so desire

ethicalpaul

I think the term "wet steam" is not really helpful for residential steam. Did it come from commercial steam? Like as compared to superheated dry steam?

Residential steam doesn't carry water droplets suspended in it--it's too slow moving. They fall out of the steam almost immediately and hit the pipe and stick to it. I have watched it.

I think what we see in residential systems is either "dry enough steam" or "full-on surging of gallons of water". We know that residential systems of reasonable pressure are pushing steam that is at the edge of condensation at all times (212-220ish degrees).

I think that "dribbling vents" and other minor issues cannot be blamed on wet steam. By the time the steam gets to a radiator vent, it is by definition very wet--it has been condensing to heat the radiator for many minutes before the steam gets to the vent--there's going to be a lot of water. This is regardless of the "wetness" of the steam as it leaves the boiler.

Here's information about what "wet steam" really is. All residential steam is wet steam.

https://kadant.com/en/blog/steam/saturated-wet-and-superheated-steam-in-paper-drying

MaxMercy

everybodyduck said:

I know that the system used to be coal because the pipes are around the perimeter of the basement.

If it's that old, I guess it's probably time to replace the system. The good news is that even with it venting steam through the chimney, it should get you through the winter.

ethicalpaul

You mean replace the boiler, I assume, Max

MaxMercy

ethicalpaul said:

You mean replace the boiler, I assume, Max

Mostly, yes, but a steam system that old would need new near boiler piping, pressuretrol, insulation, etc. as well - not advocating moving to a hydronic or split, no.

DanHolohan

Wet steam is steam with more than 2% liquid water. Testing for that ended in the ‘80s for residential boilers. Prior to that, a residential steam boiler couldn’t go to market if it failed that test. Manufacturers stopped testing in the ‘80s because none of them could pass that test. 

ethicalpaul

I have read that, thanks! I would love to know more about those tests and what that steam looked like both before and after the 80s. Does anyone know what mechanism was used to test this?

My boiler presents zero visible water at a few inches above the boiler so it seems like it would easily pass. There is no mist, no cloudiness, no droplets. It's perfectly clear, like air.

From my reading, the industry definition of wet steam is steam as it is produced directly above the boiling water, so all steam produced by every residential boiler is "wet steam". Then it becomes "dry steam" when the droplets separate.

This reference is a little dodgy looking, does someone have better?

Dry steam is steam that is at the temperature of saturation, but does not contain water particles in suspension.

From https://www.corrosionpedia.com/definition/420/dry-steam

And then this from wiki:

Water vapor that includes water droplets is described as wet steam. As wet steam is heated further, the droplets evaporate, and at a high enough temperature (which depends on the pressure) all of the water evaporates and the system is in vapor–liquid equilibrium.[5]

When steam has reached this equilibrium point, it is referred to as saturated steam.
Superheated steam or live steam is steam at a temperature higher than its boiling point for the pressure, which only occurs when all liquid water has evaporated or has been removed from the system.[6]

(from https://en.wikipedia.org/wiki/Steam#Types_of_steam_and_conversions )

DanHolohan

Manufacturers used instruments to test at their land. I haven’t seen them in action. Too young back then. Dry steam is invisible. 

ethicalpaul

Thanks again Dan. I wonder if there is some wet steam that is also invisible, or if (in residential systems) wet steam is always noticeable by eye.

I'm leaning toward the idea that if you can see it, it's wet and if it's invisible it's dry (enough), but I'd love to know what was the standard. It may be the standard (visibly speaking) wasn't well known because all the steam was behind iron and steel.

DanHolohan

The space above the waterlines in the gauge should appear totally dry. 

ethicalpaul

Oh OK, that one is easy

EOS

Exellent article and often overlooked. Mechanical separation is also an excellent way to assure dry steam

DanHolohan

Thanks!