Gas fired Vertical Boiler.

[Martin CottrellParticipant @martincottrell21329]

Hi,

 

I am about to embark on making a small vertical boiler (4″ od x 8 1/2″ tall) which I intend to fire with butane/propane gas.  I assume with gas firing that the flame is fairly stable in the firebox once alight and therefore needs no blower to assist steam raising as would a coal fire. I am building the boiler to power a small horizontal mill engine that I have built and I would like to run the exhaust steam into the boiler chimney as is normal practice with a coal fired engine/boiler combination.

 

My only concern is that the resulting blast up the chimney might upset the gas flame. Perhaps someone with experience of this type of gas fired boiler could assist with some advise?!

 

Regards, Martin.

[Martin CottrellParticipant @martincottrell21329]

[Robert HathawayParticipant @roberthathaway52937]

Hi Martin,

 

You’re using the exhaust steam to create a draft in a chimney – much like the nozzle in a steam locomotive – but without a nozzle, the velocity of the exhaust will not snuff out the gas flame.  You’d have to decrease the chimney ID to nearly twice the exhaust ID to make an impact.  However there will be a quality to the exhaust steam, so consider having a condensate weep hole in any firebox pan.

 

A ring of flame under a round boiler, with the exhaust line running about 1/3 the way up the central flue (to a chimney) creates good draft during operation of my launch engine.

 

Keep the exhaust line short and running above the valve(s).  I did so, to rule out the need for a trap, as the condensate could cause back pressure during tiny engine operation, and then work back into the valve after operation, when the hot air contracted.

 

Nice effect, though. 

 

Rob

[Ian S CParticipant @iansc]

I’v got a small boat with a V twin wobbler 6mm bore 10mm stroke,and the exhaust pipe goes up the outside of the chimney,looks good but I didn’t want the condensate inside the chimney or fire box.’Frade I dunno much ’bout steam stuff,just build,and see if it goes.Ian S C

[Martin CottrellParticipant @martincottrell21329]

Hi Chaps,

 

Thanks for the replies, I hadn’t taken condensate into consideration as I had assumed that there would be sufficient firebox exhaust heat in the smokebox to prevent condensate forming until the steam had left the chimney. I think I’ll run an exhaust pipe into the chimney but without any blast nozzle on the end and see what happens. If it ends up snuffing , or indeed drowning, the flame I’ll have to find somewhere else to stick it!

 

Regards, Martin.

[Ian S CParticipant @iansc]

The condesation shouldn’t effect a gas fired boiler,my one is meths fired,does’nt need any more moisture down the chimney.When my wee engine is starting up there is quite a bit of condensate.

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