Mono-tube boiler website

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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Elver1
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Re: Mono-tube boiler website

Post by Elver1 » Wed Nov 09, 2022 5:07 pm

Thanks fredrosse, that's very detailed, and very interesting! The whole approach of combined water and steam in the monotube boiler tube is really well done. Sorry to burden this announcement thread with too many OT questions but just wondered how much volume of water is in the system under way, roughly?And, I just wondered about cleaning the tank periodically, how do you do that? Thanks.

TahoeSteam thank you also. And I'm putting a photo of my engine in a new thread.
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Re: Mono-tube boiler website

Post by fredrosse » Thu Nov 10, 2022 8:25 am

INSIDE THE MONOTUBE COIL, ABOUT 4 TO 8 POUNDS OF WATER, PLUS ABOUT 0.02-0.025 POUNDS OF STEAM
INSIDE THE SEPARATOR, ABOUT 0.5 - 0.9 POUNDS OF WATER, PLUS ABOUT 0.10 POUNDS OF STEAM

Cleaning the inside of the separator, there is a bottom sump with a ball valve drain. Rust that is small enough to get thru the separator screens mostly collects there, and is easy to drain off. I can hook up a garden hose sending about 3000 PPH flow thru the coils, washing into the separator. If larger rust / debris enters the separator, the only washout path without a screen is the inlet steam/water connection. The separator can be flushed out with the bottom and top connections, feeding flush water, with the steam inlet oriented as a gravity drain path. That however requires removal of the separator from the boat. The internals of the separator are all stainless steel, and the separator vessel is regular low carbon steel.

The letdown line has a very fine strainer screen, and the steam trap has a "Y" strainer built in.
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Re: Mono-tube boiler website

Post by Elver1 » Thu Nov 10, 2022 1:28 pm

Thank you again fredrosse. Sorry to keep asking questions...Is cleaning a once a season kind of thing? I guess it depends on how much sediment the particular lake has. Why is the system an open skimmed water system instead of reusing the hot separated water... even though there is an intake preheater to economize -- is it just impractical to return it?
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Re: Mono-tube boiler website

Post by fredrosse » Sat Nov 12, 2022 12:25 am

Flushing the separator thru the inlet steam connection I only did once, just after welding it together. The bottom drain, where water exits to the letdown line and trap line is easy to flush in the boat, in the fall I flush out the monotube coil and separator with RV antifreeze. In the spring I flush out with water.
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Re: Mono-tube boiler website

Post by Elver1 » Sat Nov 12, 2022 3:55 am

Thanks fredrosse. Sounds like pretty easy maintenance.
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Re: Mono-tube boiler website

Post by PeteThePen1 » Sat Nov 12, 2022 9:49 pm

Thanks for all that Fred. You are doing great things for my education!

I will, if I may pick up some of your detail and add it to the Mono-tube site though I am not quite sure where for the moment. However, if you find yourself snowed in and unable to get into the workshop, a "Design of a modern mono-tube" article would be greatly appreciated.

A point for you Elver. In communication with another SBA Member I found out that he has extended his coil and now finds that the separator is acting as a condenser. He is dithering over whether to remove it or not as the extra coil length has led to hotter steam and a tendency for a viscious feedback cycle in which the hotter steam begets greater water flow which generates more steam rather than damping the system down as it did before. I think he is planning to change the control system so that superheat is monitored closely.

Regards

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Elver1
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Re: Mono-tube boiler website

Post by Elver1 » Sun Nov 13, 2022 3:08 am

Actually I shouldn't have used the term "condenser" before, because a real condenser comes after the exhaust port, not before the inlet. I was just wondering aloud about its cooling effect on incoming steam. I'm guessing it's insulated to reduce losses.

It sounds like your friend has a different problem, now. It's evaporating water in the separator. Must be superheated then, not saturated. This control system assumes wet saturated steam, as I understand it, from the explanations given earlier.

Is his separator insulated?
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Re: Mono-tube boiler website

Post by barts » Wed Nov 16, 2022 5:35 pm

Elver1 wrote:
Sat Nov 05, 2022 2:32 pm
Isn't the biggest draw of a monotube boiler the fact that conventionally it contains only a small amount of superheated water at any particular moment, and so the damage due to a rupture is less likely to be catastrophic? Would a water level/steam separator drum remove that advantage?
For small watertube boilers, the actual danger of rupture for a properly build drum at typical steamboat pressures is really small. A unfired drum built from either seamless or welded pipe and welded correctly is not a significant safety issue, although it may be a regulatory one.

The biggest draw of small monotube boilers is likely the larger steam output from a relatively small and lightweight boiler, due to high circulation velocities in the tubes, which really increases the heat transfer. They also react much more quickly to changes in load, but that's usually not a big factor with boats, although critical for automotive use.

A Lamont pumped circulation boiler or a "flash-overfeed" design are also quite safe, and avoid the control issues that often plague monotube designs.

- Bart
-------
Bart Smaalders http://smaalders.net/barts Lopez Island, WA
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Re: Mono-tube boiler website

Post by RNoe » Wed Nov 16, 2022 7:21 pm

I suggest that the greatest danger with monotone boilers rests with the pressurized firing system,
as demonstrated by Jay Leno's gasoline burn accident this week with his White steam automobile.
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Re: Mono-tube boiler website

Post by Elver1 » Thu Nov 17, 2022 3:19 am

Thanks Bart, RNoe, I wasn't trying to contrast generalized "safety" of different boiler types, since I'm sure probably that could turn into one of those endless discussions. I was just thinking about the fact that it's almost always mentioned in any description of flash steam I've read, that pure flash systems have an advantage in case of a rupture in having much less superheated water to expand. I also expect that the relatively less catastrophic result of a flash steam boiler rupture is related to its size. Seems like a model boiler break is going to expand a lot less steam than a auto plant rupture. And also how it's cased and contained, etc. would make a difference.... is it encased in a mile of piano wire, etc.?

I'm sure that properly designed, built, and inspected boilers of every type, correctly fired, are safe. I make coffee every morning in a pressurized pot boiler, and I don't worry about it. :D
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