Burn coal in a rocket stove?

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Burn coal in a rocket stove?

Postby Mikimble » Thu Jan 24, 2013 2:03 am

Does anybody have any experience with burning coal in a rocket stove? Soft or hard...Just trying to figure out a way to lengthen the last burn of the night.

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Re: Burn coal in a rocket stove?

Postby matt walker » Thu Jan 24, 2013 3:14 am

I do not Mike. Your stove is in a fairly safe location to test it out, so maybe you can be the guinea pig? I bet it will burn HOT! Maybe get a little chunk burning and choke down the air and see how it goes. I'd be into the experiment if I could get coal here.
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Re: Burn coal in a rocket stove?

Postby pa_friendly_guy » Thu Jan 24, 2013 4:10 am

I think you would need a grate mike to keep the coal going. Adding a small amount of coal might work to extend the burn some. A large amount would work like a blast furnace I would think. Matt said he gets 800 degrees at the top of his burn barrel. With coal you might get enough heat to melt the thin top off the barrel. I may not melt it off right away, but over time I could see that happening. I saw somebody on the net here say that they welded a piece of plate steel to the inside of the bottom of the burn barrel lid as a sacrificial piece that could take the extreme heat and burn away over time. I forget if they used 1/8 inch or 1/4 inch steel. Their thought was to extend the life of the barrel. You might want to consider the same idea if you plan on burning coal for very long. If you can get hard coal you will be happier from a clean burn point of view. It burns down to a white ash similar to wood ashes. Soft coal will give you a lot more ash and much larger chunks and can burn together to form a clinker that you would have to break up with a poker. Hard coal will cost more, but it gives off more BTU per ton and it comes in rice, small nugget, or larger nugget size. I have never burned the rice coal size but my brother in law had a stove that burned it. Very small fire box, put me in mind of a pellet stove as far as size of the burn box. It might have had an auger feed on it. I have used the small nut coal size in an old fashioned cook stove at camp and it works wonderfully. Holds fire over night and burns down to nothing as far as ashes. We dampened the stove way down at night and filled up the fire box full just before bed. The old camp was toasty warm in the morning with that old stove. I love hard coal. I live in the middle of the soft coal regain though, so every body around here burned soft coal for heat years ago because it was cheap. There was a Rail Road siding on my family's farm and years ago my Great Grandfather would buy a car load of soft coal and have them just let the RR car on the farm until it was empty. They would burn a car load a year. It was a large 2 story home that has been torn down now. The farm is being developed into houses.
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Re: Burn coal in a rocket stove?

Postby Mikimble » Thu Jan 24, 2013 8:07 pm

Matt,

OK, I'll try it tonight. Gonna get real cold again.

BTW Had a great burn last night; nothing but ash at 5am and still warm in the burn tunnel. I last stoked at 9pm the night before. Here's a pretty pic for ya.
Image
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Re: Burn coal in a rocket stove?

Postby matt walker » Fri Jan 25, 2013 3:27 am

Right on Mike, I'll be interested to see how it goes for you. That's a great load you've got burning in the photo, I'm really stoked for you. Seems like she's really running well now. I'm starting to get the bug to get my greenhouse heated up thanks to your work.
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Re: Burn coal in a rocket stove?

Postby pa_friendly_guy » Fri Jan 25, 2013 4:23 pm

If you do not have a grate that will fit in the bottom of your burn chamber, and you don't think you can fabricate one quickly you might try and put the wood in 1st and have the coal on top of it to keep the coal burning. Coal really does burn a lot better if you use a grate though. If you use a grate for the coal do not let the ashes build up under the grate so that they touch the grate. If they build up to the grate it will burn the grate out quickly. My neighbor burned out the grate in his Rite Way wood stove that way, and the grate in my fire place has burned out for the same reason. It took many years for mine to burn out, but if I had emptied the ashes more often I think it would still be OK. Of course it may have been the 30 years of fires that did it, ;) but I really do feel that letting the ash build up and cover the grate is what burned it out. :lol:
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Re: Burn coal in a rocket stove?

Postby Mikimble » Fri Jan 25, 2013 6:57 pm

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.

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Re: Burn coal in a rocket stove?

Postby pa_friendly_guy » Fri Jan 25, 2013 7:26 pm

I think it was a good experiment to try burning coal Mike. I understand exactly what you said about the potential problems with coal in a RMH. There maybe a way to redesign the stove and fire box to make coal burn better in the stove, but my thought is " If it aint broke don't fix it " . You know your stove works very well with wood. It draws well, burns well and holds the heat for a long time. Will burning coal improve any of those features? And if burning coal would improve any of those features, how much would it improve things. If you feel the potential for the coal to hold the heat that much better or that much longer over night then I would go for it. Matts 1/2 barrel design with a front loading door might be a better set up for coal. It has a bigger fire box and a larger area for a bigger grate. Just thinking out loud here. I am not the resident expert here. What do you think Matt?
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Re: Burn coal in a rocket stove?

Postby matt walker » Fri Jan 25, 2013 8:05 pm

Great info Mike, really glad to have you here. I am just not that familiar with coal. I spent a winter in the wasatch mountains and burned quite a bit of coal, but that was a long time ago. You never see it here.

If you built a batch loader I know you get longer burns between loads, which I imagine would be true with coal as well. I feel that you'd probably go through more fuel as well.

So, Mike, you are hoping to get longer warmth output,how about adding mass? I always feel like it is good practice to dry the mass you have, evaluate performance, then add until you have a well balanced system for you application. I bet your stove could heat a larger mass. Maybe just start building that bed wall up.
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Re: Burn coal in a rocket stove?

Postby Mikimble » Sat Jan 26, 2013 1:03 am

Hey Matt.

Thanks for the welcome; that feels good. Are you further north than Morgantown, WV? It's been below freezing here for the last seven or eight days; a bit colder than what I've gotten used to. Lows in the single digits at night. That's why I've been trying to increase my burn times. Increasing the mass sounds like work. What exactly do you mean by "drying your mass and evaluating"? My exhaust is a single 22 foot six inch pipe covered in cob and rocks. I've taken temperature readings along that bench, with highs around 110 near the stove to eighty leaving the hoop house. If I build up the bed wall, with more rocks/cob on top of what I have, that would make the heat get released later, right?

If I showed you some pictures of the spinach and lettuce and celery we have growing, you'd really be motivated to fire up the greenhouse.

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