Theory question: Pressure/temperature limits

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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Re: Theory question: Pressure/temperature limits

Post by Oilking » Fri Feb 12, 2021 5:58 pm

The Mechanic's Magazine, Museum, Register, Journal and Gazette
Volume 29
1838
Page 360 " The Victoria Explosion Inquest" talks of the reaction of red hot iron absorbing oxygen and liberating hydrogen as part of the reaction. In my youth I read of early steamboat boiler explosions often being accompanied with a blue flash. This was attributed to the liberated hydrogen igniting when it came in contact with the fire after the crown sheet failed. I used to be able to crank out the stoichiometry in my head, and am now to lazy to get the book of the shelf, in other words, Technicality quickly overcomes curiosity.

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Re: Theory question: Pressure/temperature limits

Post by TriangleTom » Fri Feb 12, 2021 6:41 pm

An antiquated way of producing hydrogen was to pass steam over a red hot iron surface, forming hydrogen and magnetite. I suppose that could have been what occurred in such an instance? Probably from an underfilled boiler, although I can't imagine a red hot boiler tube would be able to hold back the pressure.
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Re: Theory question: Pressure/temperature limits

Post by Oilking » Fri Feb 12, 2021 7:15 pm

Okay I couldn't resist,
3Fe + 4H2O --> Fe3O4(Magnetite) + 4H2
The Iron must be red hot and the water in the form of steam.

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Re: Theory question: Pressure/temperature limits

Post by fredrosse » Sat Feb 13, 2021 12:37 am

As far as "bash valve" engines are concerned, I have always thought of them as very primitive and unworthy of consideration. However the White Cliffs Solar project used a 3 cylinder uniflow engine with bash valves, and this engine ran reliably for years, producing up to about 25 kW. The bash pins hit the ball bearing type steam admission valves for only a vety short duration, so the low piston velocity when the pins hit the balls was acceptably slow to allow long life. This engine ran with 600 psi steam, about 40 Barg.

http://www.rossen.ch/solar/wcengine.html

This engine is very efficient, the best of reciprocating steam engines I have seen in the last 100years, except for the Skinner compound uniflow engines used to power several US Aircraft Carriers during WWII, but they were engines with thousands of horsepower, a whole different realm.
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Re: Theory question: Pressure/temperature limits

Post by barts » Sat Feb 13, 2021 1:52 am

Reading the complete report is quite interesting; the detailed descriptions of various problems encountered both in initial development and in maintenance are particularly useful.

One mechanism they describe for oil removal from condensate is the use of stainless steel disks slowly rotating at 10 rpm in the feedwater tank, with some means to wipe the oil off the disks and return it to the oil tank. Those familiar with the problem of tramp oil collection in water-based machine coolants will recognize this mechanism. I don't see any discussion of the type of oil used in the engine; my experiences with oil/water mixtures in Otter's old refrigeration compressor based engine suggest that some non-detergent, non-compounded oil would be best.

Thanks for posting the link!

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Re: Theory question: Pressure/temperature limits

Post by Steam Captain » Sat Feb 13, 2021 2:02 pm

Yes, for the boiler tubes to have burned, they must have gotten meltingly hot so to speak. I've burned steel like that in my forge when I began forging, but the metal must already be glowing almost white. That shouldn't be possible in a boiler, even if the tubes are empty. But if they reached red hot heat and steam disintegrated to produce hydrogen, which finds an oxygen source, it's possible.

When I first got interested into steam engines, bash valves or ball valves (what are they officially called?) had a certain attraction to me due to their simplicity. But governing the engine would be only possible by throttling and the concept of 2 pieces of metal hitting against each other at high speeds made me lose interest in them fast. But I can understand why they will always have a fan base. And it's a cheap way for "backyard" IC-engine conversions.
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Re: Theory question: Pressure/temperature limits

Post by barts » Sat Feb 13, 2021 6:04 pm

Steam Captain wrote:
Sat Feb 13, 2021 2:02 pm
Yes, for the boiler tubes to have burned, they must have gotten meltingly hot so to speak. I've burned steel like that in my forge when I began forging, but the metal must already be glowing almost white. That shouldn't be possible in a boiler, even if the tubes are empty. But if they reached red hot heat and steam disintegrated to produce hydrogen, which finds an oxygen source, it's possible.
Steam will react with red hot iron. If carbon is also present (typical in boilers) other reactions may well occur. See page 12 of

http://www.dieselduck.info/machine/06%2 ... 20EGBs.pdf

That article describes soot fires in exhaust gas boilers on large diesel ships, and resulting 'iron fires'.

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Re: Theory question: Pressure/temperature limits

Post by Steam Captain » Tue Feb 16, 2021 12:30 pm

I am still amazed by the occurrence. There was a massive metal fire on a scrap yard in the port of a city I lived in in the past and half the city was carpeted with "poker room thick" smoke. It was advised to shut the windows and not to run around outside. (If you ever got welding fever, you know metal fumes can be special). Of course it creeped inside anyways. It wasn't even possible to see down the streets and the smell AND taste was very distinguishable.

On a very different note and more important for us practical users: How much would you estimate the danger of metal fires in plants of our scale? The only small boilers I could figure would be able to end up like this would be those totally heat-laden tiny hydroplane flash steam plants, but I've never seen,heard or read about a launch-sized boiler being fired this extremely. So, I hope this is usually one of these issues which don't scale linearily so to speak.
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Re: Theory question: Pressure/temperature limits

Post by DetroiTug » Tue Feb 16, 2021 2:56 pm

Quote ''(If you ever got welding fever, ''

Chromium poisoning, I've had it several times welding ''Cromoly'' tubing. Fever and shakes. Hits ya about five hours afterwards.

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Re: Theory question: Pressure/temperature limits

Post by barts » Tue Feb 16, 2021 6:28 pm

Steam Captain wrote:
Tue Feb 16, 2021 12:30 pm
I am still amazed by the occurrence. There was a massive metal fire on a scrap yard in the port of a city I lived in in the past and half the city was carpeted with "poker room thick" smoke. It was advised to shut the windows and not to run around outside. (If you ever got welding fever, you know metal fumes can be special). Of course it creeped inside anyways. It wasn't even possible to see down the streets and the smell AND taste was very distinguishable.

On a very different note and more important for us practical users: How much would you estimate the danger of metal fires in plants of our scale? The only small boilers I could figure would be able to end up like this would be those totally heat-laden tiny hydroplane flash steam plants, but I've never seen,heard or read about a launch-sized boiler being fired this extremely. So, I hope this is usually one of these issues which don't scale linearily so to speak.
There's basically no chance for a metal fire to occur w/o a superheater and real mistreatment in our small plants. Keep in mind that modern full scale power plants have a very different distribution of heating surface than our small boilers, with much more heating surface in both economizers and superheaters. Superheaters, particularly radiant ones, are very subject to overheating with reduced steam demand. Locomotive superheaters are all convective as far as I know, placed in larger flue tubes; this would be critical since steam demand can drop suddenly with the fire still going full blast.

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