G'Day Guys, please review my heater design and comment

[stevefromaus]

Hey Guys, Steve from Melbourne, Australia. Just working on my second rocket heater for my home office space and I'd like some feedback on it, also a few questions I'd like to ask the forum about it.

Basically there's a furniture factory over the road that all year round has dumpsters full of compressed sawdust pellets, they measure 3 inch round by 4 - 4.5 inch semi cylindrical. They burn great in our wood heater, break up nicely and burn slowly. I'm using a retired Propane (emptied) cylinder that measues 14 inches diameter, 26 inches tall. With this heater design below using these pellets i'm hoping to create a type of auto-feed effect by angling the feed chamber 22.5 degrees to perhaps 30, allowing the pellets to roll in with gravity as the fire consumes them. The heater will not be left unattended and will have latchable door(s). The circled A is the point where an oxygen feed tube will supply air to the burn chamber to assist combustion or draft, diameter to be determined. 

Great in theory huh! 

The questions bugging me now are, 

* By angling the feed tube up how much smoke / exhaust / fire may come back out into the room while burning, or once the fire is burning well the draft suction will take care of this.

* The oxygen feed tube that feeds air to the burn chamber, any idea of diameter?

* The upstanding feed tube that forms the smallest part of the 'J', still necesscary?

* How important is insulating the burn tube? I can't find any rockwool, though I have found loose vermiculite that I could put into a sleeve chamber around the tube, made from 6" flue pipe. My first rocket heater seemed to operate fine without the insulation, though perhaps it could operate better without it?

* Finally, anything else I'm missing?

All feedback appreciated, it's freakin' cold here,

Thanks, Steve.

[DCish]

Any particular reason you're avoiding a standard J design? That has been the focus of much refinement, to include the problem of smoke-back. Some vertical metal rods (along the lines of an oven rack bent into a circle) could form a support to keep your pellets lined up over the feed tube without being a tall closed tube that counteracts draft in the system.

[Daryl]

Welcome, Steve. Cool car.

[stevefromaus]

Jun 30, 2014 3:07:55 GMT -8 DCish said:

Any particular reason you're avoiding a standard J design? That has been the focus of much refinement, to include the problem of smoke-back. Some vertical metal rods (along the lines of an oven rack bent into a circle) could form a support to keep your pellets lined up over the feed tube without being a tall closed tube that counteracts draft in the system.

I'm seeking to modify the J design to have the pellets auto-feed while avoiding smoke back, if possible, basically by angling the bottom tube to induce the pellets to roll in as the burning ones break down. My theory is I could avoid any smoke-back from an angled feed tube with more positive draft. To keep the draft positive I'd like to add an air supply pipe half to one inch diameter feeding air to the point about where the burn chamber sits below the upstanding burn tube, thereby bypassing any issue from pellets in the feed tube and sucking any smoke upwards. I've seen air tubes built into other designs that feed the inner chamber and seem to assist combustion, some even use a ball valve for control. Ideally I would build a fire of paper and sticks with a few small pieces of pine before adding the first pellet, then learn what works with this single source of fuel.

DCish you suggest an open pellet feeder feeding from the top? Unfortunately the pellets have a standard diameter but not length, and they break up kind of easily as they roll, leaving sawdust as they go, so an open feeder may not be an option. I THINK more air at the combustion point will solve any smoke issues but I don't know!

So I guess the next thing is to build the tube with a 22.5 degree feed tube and bench test it to see what happens with smoke, then experiment with an ideal air inlet point at the burn chamber. I'll be sure to share my findings. Once working as I'd like it to I'll fit it to the cylinder. I'd just appreciate any ideas from guys more knowledgeable on what painfully obvious stuff I'm missing here!  

Cheers, Steve.

[stevefromaus]

Jun 30, 2014 4:21:55 GMT -8 Daryl said:

Welcome, Steve. Cool car.

Thanks Daryl. That's my next project..!

[peterberg]

Steve, feeding an RMH with pellets has been done before. See this youtube link.
www.youtube.com/watch?v=FUc10qKM9ts
His youtube channel is full of his experiments, as far as I know this is one of the latest.

[stevefromaus]

Thanks Peter, that's a cool design that's giving me ideas but the pellets I have an unlimited supply of are much bigger. At least I have visual proof that an angled feed tube won't allow smoke back with the right amount of positive draft going in! Time to get cracking on my own experiments, results to follow!

[doggy1969bc]

Steve , this is a regular J-tube rocket with small pellets holder that could be adapted for bigger pellets
youtu.be/3k1ycPqOJL8?list=PLyRBSIGadacAkctGskHlAwM4bL8pdOzeN
I would just extend a few of the metal rods upwards so you can stack the pellets / pressed logs one on top of the other without having a chimney effect ,make the width of the U shape a bit bigger than the width of your pellets
just my 2cents
kind regards karl

[doggy1969bc]

second option is to make a 6" J tube feed tube 6.5" by 5" put in a U shape grate but in the other direction then 2 pellets/log can fit side by side the lenght of the pellet/log is under4.5" so no problem there no stack effect , grate is there to let the gases under the burning pellets , with a P-channel and tripwire in the burn tunnel that would be an efficient little stove
kind regards, karl

[stevefromaus]

Thanks Karl for your 2c! Yeah getting an air supply underneath the combustible material, I have some perforated steel (2mm sheet with 2mm holes) that I'll tinker with for a grate. Will post some pics to show the type of sawdust pellets I have an abundant supply of.

[doggy1969bc]

the air is supplyed from the feed tube, the grate is there so that there is a good air supply for the combustion in the tunnel ,do not make an air hole in the bottom of the feed-tube ,this will give smoke in the room