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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barts
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Re: Mono-tube boiler website

Post by barts » Thu Nov 17, 2022 4:43 am

TahoeSteam wrote:
Tue Nov 08, 2022 6:36 pm
Bart, could you elaborate on what your meant in your earlier post?
On my list of "things to try" is a hot pressure washer coil, fed by a variable speed 12V DC hypro pump, and controlled like the Herreshoff coil boilers in terms of a maintaining the water level in a well insulated steam separator drum. If the steam got too dry/hot, the water level drops as it evaporates in the superheated steam; the reverse would be true if the steam got too wet. A thermodynamic steam trap could take care of the overflow from the steam separator on startup; this could also be used to quell steam production.
A Herreshoff coil boiler is a monotube boiler, with the coil interrupted about 2/3s of the way along its length with a steam separator vertical drum. At the vertical center of the drum, an exhaust pipe is taken that drives a double acting, positive starting steam driven reciprocating pump. If the steam from the boiler is of low quality (contains a lot of water), the water level in the drum will rise as it accumulates. This will cause more and more water to flood the reciprocating pump, and reduce its output. Since the heat flux in these boilers was relatively constant as they were coal fired, the steam produced by the boiler would become of better quality, perhaps even becoming superheated. This would of course both reduce the water level in the drum and speed up the pump, driving the balance in the other direction. If the fire is forced by the exhaust of the main engine, the speed of the pump would automatically be reduced as the steam quality rose when the throttle setting on the engine is reduced, and vice versa.

This is an elegant way of both sensing the steam quality and controlling it.

Note that the speed of the pump is likely somewhat affected directly by the steam quality which is a form of proportional control; the speed of the pump is also affected by the level of water in the drum, which is a form of integral control as it represents the time-accumulated quality.

The steamboat Indian (a wood-fired paddlewheeler active in CA prior to my awareness of the steamboat hobby) apparently used a variable speed engine driven pump and a monotube pipe boiler, and employed a steam trap about 2/3 rds of the way along the coil to discharge any water back into the hotwell (or overboard, as it ran in fresh water). The stroke of the pump was manually adjusted, apparently, to keep a reasonable flow coming out of the steam trap, ensuring the steam entering the slide valve engines was not too superheated.

Since the amount of power needed to drive a feed pump at our low pressures and flow rates is quite small, it should be possible to control the speed of a DC motor to drive the boiler feed pump based on keeping a relatively constant discharge of water from the steam trap.

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

Post by Elver1 » Thu Nov 17, 2022 1:19 pm

That's really interesting. :)
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