barrel sized brush burning sort-of rocket stove questions

Unlike most rocket stove people, I want to figure out how to burn MORE fuel than necessary. Here in northern California, I need to burn brush (in the winter rains, not in the dry season) to keep down the potential for wild fires. If I had a big tractor I might dig holes and bury it, or if I had a giant chipper I might multch it, but I have neither, don't intend to invest in big machines that run on store bought fuel, and my sloped property wouldn't lend itself to that anyway.

SO... as I stand in the rain and manage a brush pile, I've often thought about how it would be nice to harness that energy to heat my (cob) house, that already had the radiant water tubing in the floor. So I want to build an outdoor boiler [yes, I will do an open container and heat a coil, not a closed, explosive system]

and I want to figure out how best to make a fire stove that will eat a lot of brush that I don't need to cut to cute little sizes, will heat a washtub sized tub of water, and will burn clean.

I've got a spot *below* the grade of my house where I intend to put a 55 gal barrel with the washtub on top. I was thinking of cutting a second barrel the long way to create a horizontal burn tube a la rocket stove. Then I could just stuff brush into the mouth of that thing. Maybe I'd build a floor grate, pile on brush, then drop the half barrel on top of the pile - that is, load it 'open'.

Or should I not even try to do a rocket stove and just do a barrel with air holes in the bottom, and maybe fix up a cauldron holder sort of thing to move the washtub out of the way for loading?

I'll still need to drag brush to this thing, so it's not ideal, but I'd like to turn this problem into a resource.

Big mofo batch box, with longer firebox.

I've googled for a while now, and still don't get the specifics of what a batch stove is, and how it would apply.

Tys Sniffen wrote:I've googled for a while now, and still don't get the specifics of what a batch stove is, and how it would apply.

http://donkey32.proboards.com/thread/511/adventures-horizontal-feed

THANK you! I was on that site many times, but didn't see that set of photos, the best I've seen yet.

However, there's still a lot of lingo on that site I'm not getting. It would seem the 'secret' of this thing is the tiny air INlet, and the tiny air *channel* (Peter Channel??) between the fire box and the vertical riser. Am I understanding that correctly?

and I have seen MANY discussions about dimensions on that site, but can I get a simple 'about this' for a situation where I might set this up to use a 55 gal barrel as the roof of the fire box?

would I suffer by not using mass ? that is, using old scrap barrels rather than brick and cob?

and, I don't seem to see anyone 'cooking' at the top of the riser, but I assume there's a good amount of heat coming out there?

Tys Sniffen wrote:It would seem the 'secret' of this thing is the tiny air INlet, and the tiny air *channel* (Peter Channel??) between the fire box and the vertical riser. Am I understanding that correctly?

Good questions and to the point Tys.
The size and placement of both the air inlets are found out by experimenting and using a gas analizer to see what was happening. In broad terms, this is the tested configuration. On top of that this design has been repeated in various sizes all over the world, about 250 times that I know of since 2013. The whole thing is scalable as well, the so called "system size" is the diameter of the riser. Smallest real working item uptil now is a 4" size, largest a little bit more than 8". Nothing stops you to build a 10"version or larger, just use the scale spreadsheet and type in the system size you want or whatever is convenient with the materials you have at hand. See this link for the scaling table and spreadsheet.
The real secret of the thing is the proportions of the opening to the riser and the riser itself. This induces a double ram's horn or double vortex flame. As long as that is going on, there will be no smoke coming out of the riser, at all. The firebox is tailored to the riser and port and the air inlets. It is a tight design, a complete package so to speak.
See this short video how the double vortex looks like.


In effect, it is a highly efficient afterburner which is able to mix air and unburned combustible gases very thoroughly.
And here is how it could sound like when running well.

Tys Sniffen wrote:and I have seen MANY discussions about dimensions on that site, but can I get a simple 'about this' for a situation where I might set this up to use a 55 gal barrel as the roof of the fire box?

You could use the top of the firebox, but the riser end is a much better spot for that purpose. Maybe something along the lines of this 8" batch box built last year? The top barrel could be the one holding the water which is open to the air, with a pressurized coil in there to extract heat.

Tys Sniffen wrote:would I suffer by not using mass ? that is, using old scrap barrels rather than brick and cob?

The batch box is a typical front end, a combustion unit, it can be applied to a plethora of back ends as long there's very little restriction is the whole setup and an adequate chimney stack at the end. I've used a 6" batch box system in my workshop consisting of three barrels on top of each other. No mass to speak of. The batch box unit itself need to be made from refractory materials, steel of whatever kind will be eaten by the fire at an alarming rate. When it doesn't, the thing isn't running as hot as it should be in order to achieve real clean combustion.

Tys Sniffen wrote:and, I don't seem to see anyone 'cooking' at the top of the riser, but I assume there's a good amount of heat coming out there?

Top of the riser is hottest, it is a confined and insulated space where all the real hot combustion is going on. Maximum measured temperature in there: 1172 Celsius or 2140 Fahrenheit. Exiting the riser: when running full tilt this is commonly above 900 C or 1650 F.

I would like to see your results: this could be the largest batch box rocket to date. Keep us posted, please.

thanks for all the clarification.

it does look like I'm looking at a 10" riser or more. one more still confusing bit. this quote from that other thread is great:

Distinctive features of the batchbox design are:
1) The "port". That's the surprisingly tall and narrow slot at the back, where the fire enters the heat riser. The point, if I understand correctly, is turbulence, and it does a heck of a job.
2) The "P-channel", a preheated secondary air supply injected at the back of the firebox. Hot fresh air coming in at the port allows for a really complete combustion.

BUT," the P-channel" - I'm not seeing that in any drawings or photos. that sounds like an air pipe coming from the outside of the box and going into the back of the box?? I see one diagram with a whole 3rd barrel off to the side. is that what that is?

I'm actually thinking about building this right into a trench/fox hole in the ground, as I'm only interested in direct heat to the pan on the riser, rather than mass heating. so If I need to run a separate air pipe to the back of the box, that would mean running a pipe through a different section of dirt? or am I way off?

Tys Sniffen wrote:BUT," the P-channel" - I'm not seeing that in any drawings or photos. that sounds like an air pipe coming from the outside of the box and going into the back of the box?? I see one diagram with a whole 3rd barrel off to the side. is that what that is?

No, it isn't the 3rd barrel at the side, far from that. It is a rectangle piece of steel duct, going horizontally over the top of the firebox and down at the back wall, ending right above the top of the port.

Tys Sniffen wrote:I'm actually thinking about building this right into a trench/fox hole in the ground, as I'm only interested in direct heat to the pan on the riser, rather than mass heating. so If I need to run a separate air pipe to the back of the box, that would mean running a pipe through a different section of dirt? or am I way off?

Here you see an explanation of the thing, I hope that's clear enough. The cross section area of this duct is 5% of the riser's CSA, width is as close to the width of the port or a litle bit more.