Home brew fire tube boiler design

J

JoeBlob

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Hello whoever decided to click on this!
I'm Joe and I keep finding myself caught up in the idea of wanting a little steam engine to play with as I have been tinkering with other alt energy projects too.

Anyway today I hopped on my computer and downloaded a modeling program to try and draw out what I have in mind.

20201209_124857.jpg20201209_124922.jpg

Idea is pretty basic. Take a 40# propane tank run between 5 and 9, 1-1.5" diameter steel fire tubes through it welded on the ends at a slight upward angle 3-5*. Not planning to exceed 50psi in operation and the plan would be to have 2 pressure relief valves at 60 and 70psi as failsafes. Have heard enough of the horror stories of cookin off a boiler to a couple hundred lbs and making a nice big pressure bomb.

Then for a firebox a second propane tank, lop off the top few inches to make the steam dome on the boiler tank which gives the advantage of a preinstalled bung and valve for the outlet. Flat plate on the cut open with the fire tubes welded in. And a 3-4" intake opening on the burner depending on how many pipes it works out needing. Aiming for a bit bigger intake than the overall tube area (I think anyway)

Undecided on lpg or coals/wood as a fuel but propane makes the most sense with a cleaner burn and adjustability, less tube maintenance. Also fitting being a propane tank boiler.

End goal would be to drive a 2 stroke engine from something like a weedeater and try to turn a small 180w motor I have. Just for the fun mostly
 
JoeBlob said:
Hello whoever decided to click on this!
I'm Joe and I keep finding myself caught up in the idea of wanting a little steam engine to play with as I have been tinkering with other alt energy projects too.

Anyway today I hopped on my computer and downloaded a modeling program to try and draw out what I have in mind.

View attachment 346650View attachment 346651

Idea is pretty basic. Take a 40# propane tank run between 5 and 9, 1-1.5" diameter steel fire tubes through it welded on the ends at a slight upward angle 3-5*. Not planning to exceed 50psi in operation and the plan would be to have 2 pressure relief valves at 60 and 70psi as failsafes. Have heard enough of the horror stories of cookin off a boiler to a couple hundred lbs and making a nice big pressure bomb.

Then for a firebox a second propane tank, lop off the top few inches to make the steam dome on the boiler tank which gives the advantage of a preinstalled bung and valve for the outlet. Flat plate on the cut open with the fire tubes welded in. And a 3-4" intake opening on the burner depending on how many pipes it works out needing. Aiming for a bit bigger intake than the overall tube area (I think anyway)

Undecided on lpg or coals/wood as a fuel but propane makes the most sense with a cleaner burn and adjustability, less tube maintenance. Also fitting being a propane tank boiler.

End goal would be to drive a 2 stroke engine from something like a weedeater and try to turn a small 180w motor I have. Just for the fun mostly
Click to expand...
Sounds like a fun project, your drawing looks a little like a steam locomotive boiler, good luck and don't get blown up cutting on a propane tank.
 
eugene13 said:
Sounds like a fun project, your drawing looks a little like a steam locomotive boiler, good luck and don't get blown up cutting on a propane tank.
Click to expand...
Yeah steam locomotives are what I can find the best design information from so it is what my basis was.

I will do my best not to blow myself up for sure! Going to fill with water and cut with a grinder while full
 
I suggest you review the State Boiler and Pressure vessel code where you live and the personal liability associated with building a pressure vessel. The NBIC ( National Boiler Inspection Code ) Makes specific requirements for the design, materials, construction and testing of pressure vessels based on ASME specifications. Just at a glance of your idea any pressure vessel over 6" diameter, working pressure over 15 psi, and a water temperature over 210 F will fall under the code. The ASME boiler code was established as the result of many failures and loss of life of early boiler designs. This is not something to screw around with. Don't be one of the statistics.
 
Aside from the code issues, that design will take forever to bring up steam. Way too much water for the amount of surface in the fire tubes. Boilers need insulation also. Steam domes are designed to prevent water from entering the steam lines using some sort of baffle system. A superheater is a good idea to prevent condensing and water entering the engine. Saturated steam brings with it a whole set of problems. But superheated steam is invisible and very dangerous. I don't recommend doing this, but if you do, incorporate a water sight glass and pressure relief valves. Use the kind of valve that increases in area when it lifts to prevent chatter and to very quickly dump pressure. Two valves are normally used set at slightly different pressures. Have you considered a reinforced concrete retaining building? Ex Navy engineering officer.
 
Welcome!

Check out (if you haven't already) Keith Appleton's YouTube channel. Lot's of steam engine, boiler, and steam plant work there.

 
Thanks for the quick feedback guys.
Ok so let me work my way down the list here.

I will absolutely have to look into the local regulations for it before I take any steps to try and build anything. Currently in the figuring out what is feasible stage. The tanks for reference are 12.25" diameter so yeah well over 6". My reasoning with those tanks was they are designed to hold a lot of pressure, built in relief at 375psi but pressure test to 600 with the designed burst pressure in the 900s. I would never allow that kind of pressure but I like the design headroom.

As for taking forever to heat up that is a safety feature if nothing else. The tube size and quantity is to be determined I figured it would end up between 5 and 9 tubes, and wasnt intending on superheating the steam just for the sake of this being more of a tinker project than any kind of permanent generating system.
Not even intending installation at home or a residential area. More like a project to drag out with me camping and see if I can crank out a few watts to power on a light.

Pressure relief valves are 100% in the plan. on my diagram they're the 2 brass colored cylinders on top. Was hoping to operate nominally at 40psi with first relief open by 60 at most. Didnt realize limitations were all the way down at 15psi. Thought was to get a old 2 stroke weed wacker engine and plum into that to spin a little powerchair motor and see what the output is.

Will have to do some searching on the regulations. Definitely not something I would want to fire up in the garage or back yard for any appreciable amount of time
 
Have you considered going with a monotube flash steam boiler?
If it blows there is not much water or steam to damage anyone.
Almost instant steam.
 

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I hadn't seen that particular layout before. I'm a bit stumped looking at the gasoline vaporizer.. I assume that must be a vaporized gasoline powered burner blasting into the coil?
 
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