Shady's Welding Project 4 - Rocket Stove

[Premiershipman]

This was the latest project, completed only a few weeks ago after coming across the rocket stove idea on other forums.

If you haven;t looked at these they are esentially billed as ultra efficient stoves that use up the majority of heat energy when burning wood at high temps, and only exhaust steam and warm air.

So after a bit of research I decided to cobbled one together from propane tanks.

I already had one 19kg that I had planned to make a patio heater from so I gave a mate of mine a shout who supplied another 19kg and a 47kg one.

The idea was to weld 4" box section into the middle of the the two 19kg cylinders (the 19kg cylinders welded one on top of each other) and then fit that inside the 47kg.

Excuse the crude ascii type drawing but it does help to show the arrangement :

-----------
/ \ The section with all the X in is the box section feed pipe, wood is fed into the
| |oo|X|oo| | front section of the feed pipe and as the unit heats up it creates the
| |oo|X|oo| | draw which further helps burn the wood and create the 'rocket' sound that it
| |oo|X|oo| | gets its name from.
| |oo|X|oo| | As the flames and heat rise up the box section inside they hit the top plate of
| |oo|X|oo| | the stove and then the heat is deflected round the inside of the 47kg
| |oo|X|oo| | The oo is insulation around the box section inside the 2 19kg cylinders,
| |oo|X|oo| | / X / the top plate is an offcut of the 12mm plate from the welding bench.
| |oo|X|oo|_|_/ X /__ The exhaust gases come out vie the 4" tube at the back and when it
__ | |oo|X X X X X X X X gets installed properly in the garage it will feed into some galvanized
__ |ooo ooo| | ducting that I have.
|____________|

So far its only been tested out in the open, but it has got to about 400C on a small bucket of sticks so it works pretty well !!

Pics to follow !!

Shady

 

[Wallace]

Once the car I'm working on is gone I want to build one as a heater for my workshop. I spent an evening with a case of beer, plasma cutter, grinder & Mig making a small uninsulated one with 2" box section just to get some hands on experience of how they work. With a small amount of compressed air to make up for the lack of draw it gave off some good heat and the outlet was giving off steam and warm air.

 

[Premiershipman]

They are very good, I was quite impressed once it got going and used my stove kettle to make a cup of tea !

Got too distracted last night so need to get photos taken tonight !

 

[Wallace]

The problem I need to try and overcome is having a wood fire that will not inconvenience my neighbours, once up to temperature there was little to no smoke or smell but so problem might be keeping it fed and up to temperature.

 

[Jan]

Because of the fairly intense heat that is generated in a decent sized rocket stove it's essential to line or make the combustion chamber with stainless steel so that it lasts longer. This is a cheap way of adding that function and it's cheap enough to keep the overall costs down. According to most designers it's best to add some insulation around the internal flue. Whether the one linked to is rugged enough I couldn't say, but I'll be giving it a go when I make one from a 47Kg gas bottle.

 

[Premiershipman]

In progress, top half of 47kg welded in place.

 

[Premiershipman]

Here you can see the 19kg cylinders inside the 47kg cylinder and the 4" square riser tube with perlite packed around it.

 

[Premiershipman]

Flue pipe at the back.

 

[Premiershipman]

1/2" thick offcut left from the welding bench, trimmed with the plasma cutter and welded on as a top plate.

 

[Premiershipman]

Test burn, I stupidly left the magtab on which was temporarliy holding an offcut of metal to restrict air in from the bottom entry tube, now the magnetism has nigh on gone from this magtab.

 

[Premiershipman]

Making a brew - testing how long it take to boil the kettle - you can just about see some steam coming out the flue.

 

[julianthegypsy]

Looking good!

 

[fixerupper]

Looks great nice neat job , how big is the fire box on this ,is it just the 4inch box and the length of the cylinder ? and you can pull that out for cleaning and de coking ...jeff...

 

[Premiershipman]

The 4" box section is a sort of j tube shape so its just the lenght of the box section from outside to the mid point inside the cylinders.

I have a small offcut of 1" mesh that I use to get it started in the horizontal section - wood on top with paper underneath and I also use that for scraping the ash etc out when done.

As we are now looking to move house, I probably wont install the flue piping for it otherwise I would have a great big hole in the wall to fill when we go !

Only things left to do is flap wheel the outer cylinder to remove all old paint and then paint it black.

When testing it for an hour or so, the top plate got to near 400 oC, this thing gets seriously hot on a small amount of wood.

 

[Mick - Ford Focus]

That Sir Is A Beast Of A Rocket Stove - Thread Saved As Inspiration.

M

 

[Premiershipman]

It sure kicks out some heat Mick !!

I thought it was hot until I flap wheeled off the paint and the bare metal is another 50 degrees hotter !

 

[Premiershipman]

Just found the initial starting photos on my ipad - so apologies for a sort of back to front welding project journal !!

J tube welded into the bottom of the 1st 19kg cylinder with the other 19kg cylinder in the background and the 47kg in two pieces in the foreground.

 

[Premiershipman]

Close up of what will be the inside of the stove - the bottom section of the orange 19kg cylinder with J tube welded in.

You can see the top section of the remainder part of this orange cylinder in the background - I didnt use the rest of that cylinder - I used about 80% of the other red 19kg cylinder (removed the bottom stand section and cut an 8" diameter hole in the top.

 

[Premiershipman]

Showing the inside of the 19kg cylinder - you can see some 6mm round bar bent to form a 'prop' of sorts to centralise the j tube. Once it was straight, I welded the round bar to the bottom of the cylinder - this also allows the perlite to fill in under the j tube when I put the top of the 19kg cylinder on.

 

[Premiershipman]

So to summarise :

2 x 19kg cylinders (flushed and aired out before cutting !)
1 x 47kg cylinder (flushed and aired out before cutting !)
4" box section for the j tube.
4" round tube for the flue + extra depending on how much flue you need to run.

Slice the bottom 40% off the first cylinder (in my case the orange cylinder) and cut a notch into the bottom for the j tube.

Fit the j tube into the notch and centralise the j tube with round bar for support and weld up tight (no holes).

Cut an 8" circle out of the top of the other 19kg cylinder (the red cylinder) and remove the bottom stand section and all handles etc - leave yourself about 80% of this cylinder.

IMPORTANT - you need to make sure that when you fit the 19kg cylinder arrangement with j tube inside the 47kg cylinder, that the top of it finishes approximately 1" below the inside of the top of the outer 47kg cylinder - this is so the heat from the j tube rises up and hits the underside of the top of the 47kg cylinder and then gets squeezed between the inner cylinders and outer cylinder (if that makes sense).

Fit this 80% of the red cylinder on top of the 40% of the orange cylinder with the J tube in - weld up tight (no holes).

Cut the 47kg cylinder into 2 pieces - roughly 40%/60% again, cut a notch for the j tube on one side and a 4" diameter hole for the flue pipe on the exact opposite side.

Weld in the flue pipe section at the back of the 47kg cylinder - weld tight (no holes).

Fit the 19kg inner cylinders into the bottom section of the 47kg cylinder and centralise and straighten it all - you dont want it skewed to one side.

Weld the j tube into the notch on the 47kg cylinder - you could also use some round bar again to stabilise and centralise the inner cylinder section to the outer cylinder.

Cut an 9" diameter circle out of the top section of the 47kg cylinder.

Fit the top section of the 47kg cylinder over the inner cylinders and align it all and weld the 47kg cylinder shut around the seam where you cut it into two - weld tight (no holes).

Fill the area between the j tube and the inner cylinders with perlite or vermiculite (see picture 2).

Weld on your top plate - welt tight (no holes).



You can then use the rocket stove as you want feeding wood in horizontally into the feed tube at the front or I preferred to add a diagonal section to the feed tube so the wood would sort of feed itself in.

So if you wish to have this arrangement, cut a section of 4" box section and cut one edge to about 70 degrees, cut a 4" square hole in the top of the feed tube and weld in your diagonal section of feed tube - weld tight (no holes).

To light it can take a bit of patience as you have to heat it up to start creating a draw on the j tube - I put in a small thin section of 1" square mesh bent into an n shape into the horizontal feed tube to sort of act like a platform so i could put small strips of wood on it and light paper underneath.

Once it gets going you can start slowly introducing bigger sticks etc and it will soon get pretty hot !!

Shady