Will coal work for a rocket stove?

We are building a RMH on my friends ranch in SE Montana. Lots of cactus and some sagebrush, just a little wood in the creek bottom. However, he has a 3 foot seam of coal on the ranch that the original homesteaders used to heat their houses. Question is, will the coal burn (much hotter I assume) be a way for him to warm his buns? Any forseeable problems in so doing?

I've never tried it, but I think it would work. the optimum dimensions will be substantially different than the more common stoves tuned for burning wood, though.

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?

Should work fine. If anything, it'll be easier to manage. The fuel is more energy dense and you won't have a problem with creepy crawlies that tend to accompany wood piles.

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.

Look at what Rob did to get a rocket to burn wood pellets: https://permies.com/forums/posts/list/40/18515#166077

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.

iv been burning coal in a rocket stove i made from a large gas cylinder. the fire box and riser are lined with vermiculite board and are holding up well as this stove gets good and hot it does smoke from the chimney with coal however not a wisp with wood i find a mixture of both to be best

I burn coal in a blacksmith forge, and the blower doesn't seem much stronger than the draft on my rocket stove. So it could get HOT, especially if you stoke it right up. I just used regular brick for my burn tunnel and i have a steel heat riser, so I've been wary of burning coal as i'm not sure if my stove would stand up to it... Do you think proper firebrick would be needed?

you can burn coal you do need to allow for more air since coal is a much denser energy source.

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).

Thanks Ernie. I guess I'll have to stay away from it with my steel heat riser.

Thanks Ernie (not Eric, sorry about that!)

Do I understand correctly, a grate? As in the bottom portion of the feed chamber, to hold it off the bottom? Will the increased heat also effect the riser metal?

the heat riser will need to be brick as well. Should be brick in anycase if it's to be a long term stove. the temps 2/3rd of the way up the heat riser are very very high and even with soft wood it will burn out the steel over time.

It is true that wood and coal burn differently. It is also true that all coal is not created equal and adjustments must be made for each type of coal. It may be enough to be able to adjust both the primary and secondary air, which can be problematic with the basic rocket and RMHdesign. There are designs at Donkey's forum that could probably be adapted to burn coal efficiently.

Thank you for the information about the riser. If the metal is not long term, why do all the videos show a 6" pipe insulated with clay and vermiculite and a 10" pipe? Could have saved some money not buying an insulated stove pipe and just built up the fire bricks!

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?

Tried the coal in the stove last night, without any definitive results. Got a good bed of coals, put in a cast iron grate, and started putting in coal a few pieces at a time. The coal took right off; but as it was getting late and very cold, I didn't stay too long to see the results. It seemed to fire up, then start cooling. I cut down the air supply, and gave it up for the night. Here's my conclusions:

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.

Mike

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.

Coal burns dirty and smelly

No fuel will burn dirt or smelly, if it is being burned properly.

Will I have to worry about "klinkers" with a rocket stove?

Dale Schlehuber wrote:Will I have to worry about "klinkers" with a rocket stove?

Hi Dale,

I still had some klinkers when I burned a small amount of coal...

Mike

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).

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).

Andrew,

Thanks for the info. Great pics and explanations.

Mike

I've recently completed my RMH, it works nicely. I used all quality refractory material, intending to burn coal. No problems with wood, but coal is very difficult. I can get a nice mass of coal glowing but can't maintain it. I have a grate beneath it. Seems to be a draft issue

Since this old thread was brought up in the dalish I found it an interesting question that stirred my experiences. I have burned very little coal but I have used many stoves that were designed to switch between wood and coal. When the grate was set for wood it would hold a layer of ash which acts as an insulation to keep the temperature high enough to maintain gasification.  The coal setting of the grate was an open grill to keep enough draft on the glowing carbon to keep it burning.
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.

I've recently seen this thread re-incarnated and thought I'd give a little bit of info.I've got a homemade 4" basic 90° rocket stove with a 3" 30° gravity feed fine which I use for burning wood and old cooking oil but tried small piece charcoal in it the other day. Once it was well alight with wood and warmed up I filled the gravity feed tube with charcoal and boy did it heat up. It burnt really well and burnt everything in the tube till it was so hot the horizontal tubing was glowing red and there was no smoke at all. So I guess it will work with coal it would just need to be small pieces and have a mesh stand to all air to get through under it to keep it going. I burn pretty much everything in mine and will be looking to wrap copper pipe around the vertical pipe to heat my poly tunnel and my children's play house sometime soon. I will try to post a picot my rocket heater soon.

Could you post the design of your stove? Im new to building stoves and want to run on charcoal.

Hi Cody;  Welcome to Permies and Welcome to the wonderful world of rocket science!

Sounds like the previous poster had an L tube rocket with a slight sloping feed tube.
You really can burn just about anything with a hot rocket, even cow pies if dry!
The problem with charcoal or real coal, is air flow to keep it burning.
If you start your dragon up with wood and get it going, then dropping in charcoal in moderation "should" work fine.
Add to much and you will cut off the air supply.
Can you modify a rocket to burn all charcoal?    
Maybe, but it probably will not be burning clean as a standard RMH.

Do you have a huge supply of free charcoal?

Before I switched from a J tube to a Batchbox design RMH.  I routinely located some coal (not easy west of the divide) and tossed in a handful from time to time.   I can tell you that despite the wicked hot temps generated by an 8" J tube at full burn  I still got coal dust outside if I burned more than I should...

A rocket stove is designed to be optimized for burning volatile gasses released from the burning fuel. Charcoal has very little volatiles left therefore not an ideal fuel to take advantage of the secondary burn. coal has obnoxious volatiles that need a very good secondary burn to burn completely Therefore is hard to regulate as the volatiles burn off and leave a glowing coal with not enough volatiles left to sustain the secondary burn.
On the other hand a rocket stove designed with a second chamber to hold material to be made into charcoal but excluding entry of air is the appropriate way to make charcoal.

I wanted to test this out for a book I am writing.  We used coal after the stove had a good bed of coals from wood, and it worked beautifully.  Allowed the last two hours of heat up, without adding more wood.  But we found you had to get it going with wood first.

I would be cautious using coal in a stove designed for wood. At the very least, the coal should sit in a grate -- both for increased airflow and to protect the bottom of the stove from the intense localized heat, which could cause damage to brick or metal.

      Related to burning coal in the rocket stove, I'd like to know if anyone has had any experience burning charcoal in the Spitfire Patrol rocket stove made in China available on Amazon. It is surprisingly well made and of heavy gauge stainless steel. It has a grate in the feeder chute however is designed to burn wood. The reason I ask is that I live in the  extreme southwest of Arizona in the Sonoran desert  where naturally occurring  wooden sticks on the ground are essentially nonexistent and charcoal is easier to come by.
      Other than charcoal burning less efficiently, can I still cook food with it and is there any danger? Any reply appreciated.

Again the rocket stove is designed to place the cooking surface far enough from the fire for the compleat combustion of the volatiles.  Charcoal has little or no volatiles and produces radiant heat and hot gasses therefor you want the cooking surface close to the burning charcoal like a hibachi.  In either case not to be used in an enclosed unventilated space.

Thank you Hans. Your reply is helpful.
                                Ray

Good advice for a cooking stove. For those who want a heating stove or mass heater, I would consider the following.

Charcoal is not the same as coal, and will not have the same issues of energy density and nasty high-temperature volatiles. It is essentially the last stage of normal wood burning. I find that when I have a deep bed of charcoal at the end of a fire in my J-tube, pushing it all into the burn tunnel so the secondary air P-channel blows on it and covering the primary air supply gives a hot fire and burns completely to ash. If you are starting with charcoal and want to optimize for burning that, I would consider configuring the core to resemble that part of the system, with a concentrated fuel bed and a restricted air supply blowing on it (preferably preheated.)