I would suggest a grill to promote airflow from under the coals. But lots of RMH designs include that, so maybe you already know...
An open vein of coal is a fire risk, though. Lightning and grass fires can set it off and it could burn for decades.
Dale Schlehuber wrote:Why would the dimensions be different? Longer burn chamber? Would the intake require more oxygen because of the increased heat? If so, any idea what the variants are?
they're just very different materials. just like gasoline doesn't burn the same as a pile of leaves, wood and coal burn differently. more oxygen is necessary for coal, but not because of the increased heat. it's because coal is a richer source of fuel. toss coal in a stove designed for wood and a disgusting smoky mess will be the result.
I don't know exactly what the changes necessary would be, but I would guess that you would want to design for less coal burning than would be the case with wood, but more air supply. some experimentation is certainly in order, and I do hope you discuss your progress here.
Similar issues, but you will need an even better grate and burn tunnel and possibly barrel. A rocketing rocket will be a FORGE hot fire breathing dragon melting most metal and lesser refractories in its path.
the best way i have so far found is to mix coal and wood chips with a dung binder press till it all sticks together and burn the resulting briquette. With a seam of coal i would defiantly make the feed bigger and get some sort of grate that would stand the heat. this would mean the burn portion of the system would need to be masonry or it will burn out. As to the fan for a forge it is a stronger draft than you usually get on an RMH and far more focused. however it is also stoking the coals to make a much higher heat in a smaller area.
the normal draft so far works ok for coal. if you dont want to build a press i would try just mixing with dung and drying in some sort of log (haven't tried this one yet).
If the feed, burn and riser are all made of fire brick, do I have to worry about the extra heat of coal, and just have to worry about getting adequate oxygen for the burn?
1. We all know that wood fires are made a lot differently in rocket mass stoves; I think coal fires offer the same challenge. Could take a lot of time to figure out the best way for burning coal
2. Coal burns dirty and smelly; nothing as beautiful as wood.
3. I used to burn quite a bit of coal in a US stove wood/coal furnace, so I am somewhat familiar with coal's burning properties. After the coal fires, you cannot poke/mess with it. That makes clinkers, so it's a bit hard to add wood after the coal. Since the coal is burning so hot; it makes the wood steam; even wood that appears completely dry.
I will probably mess around a little more this weekend with it, but am thinking that coal is not that great in a rocket mass stove; at least in my application.
PS I think Ernie's idea of wood chips/coal and dung would work, but am wondering if something can be used instead of dung. I used all my dung in the compost pile.
Andrew Parker wrote:Review this project for some ideas on how to burn coal cleanly. I mentioned it in an earlier thread on coal, "First RMH in Mongolia".
You may also want to look into using a p-channel (described at Donkey's Stove Forum).
Thanks for the info. Great pics and explanations.
Therefore My reasoning is that a J tube burn chamber is probably not well suited to burn coal but a batch box configuration with a grate of narrow fire bricks on edge with primary air entering under them instead of the V orU bottom that is used in a wood fired batch box. Because of the greater density it would probably be better with a smaller firebox and the preheating channel for the secondary air where it gets hot enough to maintain burn in the riser of the volatiles gasified from the burning coal.