Wednesday, August 22, 2018

multi-burner rocket stove


MULTI BURNER ROCKET STOVE
Okay, this isn’t exactly earth shattering, but I was rather impressed by it and since it stuck in my head the next morning I simply had to write about it.  I came across a YouTube video on a multi-”burner” rocket stove, which unfortunately I saw while watching it on the TV and was unable to find again after the batch of “recommended” videos rebooted and changed after I stopped watching, losing the thing forever ( I had failed to remember the title or author ).  If I had been on my computer I could have just clicked backwards.  Sorry, but I spent too many years sitting on a bed or an uncomfortable chair and me and my recliner have an almost sexual bond now.  I prefer the videos on TV, unless I am rolling cigarettes.
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The guys main point was that while rocket stoves were the cat’s meow for obvious reasons ( uses a tiny fraction of wood for the same task, costs free to almost nothing, can be used with local material like, you know, dirt ), they were only good for cooking one thing at a time.  What he came up with struck me as a cross between a rocket stove and a rocket mass heater.  Rocket mass heaters throw heat up against the top of a metal container like a drum, but don’t let out the smoke or fire there, channeling it back through a long horizontal chimney to get every single BTU out of the process, warming the mass surrounding the chimney.
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Rocket stoves throw all their heat out the top, right under your cooking pot ( or, if just a heater rather than a cooker, under your big hunk of cast iron ).  This is great cooking something that needs a lot of heat, say if you are deep frying Snickers Bars.  But as the complaint stated, you can only cook one thing and you only get one heat setting ( Damn Skippy Hot ).  So he made a horizontal cooker in the shape of a U.  It would be nice to provide a link for you, but we already talked about that.  Try to visualize a outside solar heater.  Say, a door edged with two by fours and a sheet of glass laid over that, with the inside containing more 2x4’s up and down making three channels.
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On the bottom there is an air intake.  The air rises up that third of the door, then passes over to the other side by an opening on that board, flows downward then making a U-turn at the bottom and up and out the top into the house.  The flat black sheet metal backing heats up the air more the further it travels.  This rocket cooker looks about the same, but is just a U, and is flat rather than propped up at an angle.  On one opening of the U, you have the chamber with the standard wood and air intakes.  The air is then drawn up one side of the U and down the other and then up the chimney.  So picture the flat U on a table, almost like a duct pipe.  The opening chamber hangs down toward the ground and the opposite end goes up in a chimney.
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What happens on the flat metal top ( the bottom and sides are fire brick ) right after the wood/air chamber is that you have the hottest part, used for say boiling.  The spot after that is significantly cooler, say a medium heat.  Turn the corner and that half is pretty much just a warming spot and the area right before the chimney is barely warm at all.  The chimney is so cool you can touch it.  This is your four burner rocket stove cooker.  Basically a flat metal box two pots wide and three pots long ( with the U shape firebricks inside to create the channel and determining the depth ).
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Now, you all know me and my eternal quest to be the world’s cheapest bastard, stopping only at the point of used underwear.  I draw the line there.  My own used and wore out underwear used for a rag, fine.  But nobody else’s, not for wearing nor a cleaning rag.  I know the history of sanitation on my own.  So my immediate thoughts went to how to make this cooker more affordable.  I mean, really!  A sheet metal box, and welding!!!
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Now, keep in mind I have no Bill Nye Science Guy knowledge.  I ac-knowledge ( get it? ) this is NOT a good thing, especially not when trying to rebuild civilization, but frankly I suck the biggest monkey balls at anything math or science and I won’t pretend otherwise.  Asking me to do science is like asking me to star in a porno where I’d need to ejaculate constantly.  It just isn’t physically possible ( by the way, you are welcome for that imagine of my skinny ass going to town ).  So, what I am about to describe may or may not work.  Since I don’t know about convection or insulation properties, I’m Wild As Guessing.  Deal with it.
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What about digging a trench in the U shape, then covering the top with sheet metal ( and perhaps braces if the metal isn’t wide enough )?  Dig a deeper hole at the opening for your air and wood intake, then stick the chimney into the dirt at the other end.  This would alleviate the cost of fire bricks, a good portion of the sheet metal and the welding.  If that doesn’t quite work, say if the earth would need to be insulated or lose too much heat, what about just slopping some clay along the trench? Surely there is a simple and cheap way of doing this.  It is a great concept, but I see no reason it should require a machine shop.
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Perhaps the fire bricks make it more efficient soaking up the heat and are still needed.  A little help from the Dilbert minions here, please.  The guy in the video ( thanks a million, dude, sorry I can’t properly attribute this ) made a big deal how this burned off more of the smoke and hence produced less than the conventional rocket stove, although I’m not so sure about that.  I rarely see any smoke from any type of these stoves.  I’ve even read of a miniature rocket stove made from clay that’s sole purpose was a tea maker, and it was inside the kitchen on the counter top.  It couldn’t have made any smoke if that was its location.  Regardless, if nothing else this is an awesome way to cook, a superior rocket stove.  The more traditional stove is still good for a water heater and a mass heater, but hey, you can have as many different rocket stoves as your little heart desires.  You could build ten or twenty for what the cheapest cast iron stove costs.  That is all, carry on.
( .Y. ) 
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16 comments:

  1. https://www.youtube.com/watch?v=6lXPbhoAcSw

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    1. That wasn't the one I watched, but linking to it did get HAL to recommend the exact one I was refering to:
      https://www.youtube.com/watch?v=VFAwl6aJNH4

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  2. If you were using the YouTube app via a phone or tablet, you can go to the bottom right tab - "library," and then pick, "history". Every video you've seen will show up there. I cannot visualize precisely what you described :( I've been studying rocket stoves and woodgas stoves and heaters for years. It's hard to come up with a cheap and easy design.

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    1. Here are staked red bricks for a rocket stove:
      https://www.youtube.com/watch?v=FdR6WXggiKQ

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    2. See my reply above to 8:53-there is the vid I was talking about. The red brick one is great for simplicity ( from the guy "KGB Survivalist" that recommends the SKS for a survival gun. Of course, he is a bit biased.

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  3. Fire bricks are high temp insulators, that do get hot but are not designed to "hold heat". The point of fire bricks is to keep the heat concentrated in the burning chamber to get a good hot burn, making less smoke/soot/creosote and getting more useful heat from the fuel.
    pdxr13

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    1. Soooo...Cast iron on top to soak up some of the heat?

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    2. The "soaking" of heat is almost a function of mass. If you have any 100 oz silver blocks, they would do a great job as a heat flywheel while you are waiting to need them for monetary purposes. A couple hundred pounds of cast iron works great and lets you steer the air in/out, but if you want some warmth in the morning (12 hours later), you need to add serious weight that almost only can be rock by the yard and ton. This is the difference between a rocket stove you can make a fast clean fire in and be cold between firings (move it like carrying a bucket) and a mass-loaded stove that you make a small fire in that burns for 45 minutes and gives you 6 hours of nice warmth (and a cooking surface for about the firing time) at the cost of being heavier than the rest of the house combined.
      I lived in a house with a mass-loaded fireplace in North Seattle. It was cheap to run (a load of mill-tailings every fall) and kept a big 5 bedroom house dry and warm (except for my bedroom down a long hall and over an unheated garage). Very little fuss with the fireplace, less than making breakfast. We could have substituted more labor for money by gathering scrap wood but we had a truckload of short dried mill bits dropped in the yard. It was the city and we had plenty of money in the late 1980's. This house was retrofitted with the fireplace, but the ideal house is built for the fireplace.

      pdxr13

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    3. So, really, the rocket mass stove with the cobb covering the horizontal chimney isn't going to do all that much except wring all the heat out of the smoke. It is much more efficient but not a true mass heater. Wouldn't the cost savings of wood salvage be negated by the truck wear/mileage/gasoline? It isn't JUST labor-more like delayed payment of equipment cost.

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    4. “This is the difference between a rocket stove you can make a fast clean fire in and be cold between firings (move it like carrying a bucket) and a mass-loaded stove that you make a small fire in that burns for 45 minutes and gives you 6 hours of nice warmth (and a cooking surface for about the firing time) at the cost of being heavier than the rest of the house combined.”


      To be honest, this struck me as a rather boring topic, until I read pdxr13’s comment above. So I googled (Or rather, DuckDuckGo’ed) “mass-loaded stoves”, and found a few plans. But of course they are far more complicated to build than someone of my motivation and skill set would allow for.

      I’m thinking that a reduced scale, custom built, free standing fireplace, in a very well insulated dwelling, would be the way to go. To be honest, I hate wood stoves, thus the reason for the free standing fireplace (look them up. The kind I’m thinking of look like the one’s in the link below, but are wood, not gas).

      http://www.neiltortorella.com/images/free-standing-ventless-gas-fireplace-940-freestanding-gas-fireplace-500-x-500.jpg

      http://www.accessnw.org/wp-content/uploads/2015/07/free-standing-gas-fireplace-australia.jpg

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    5. There are two kinds of firebricks... The really heavy alumina kind that hold heat and will release it after firing, and insulating fire bricks which insulate against heat (hold a blow torch to one side while you hold the other, no problem).... The heavy ones are about a dollar a brick (I have used them for brick oven)....the light ones are about $5 (used for the door of the brick oven)

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    6. You would think that the $5 ones would be a good investment, just on the fuel savings.

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  4. Yep remember draft vents, room or shelter venting or airflow if not sealed up area. Even if no leaks detected or smells, a bit of monoxide at a time all night in your b-pod as you sleep off that moonshine drunk could do you in.

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  5. Thanks to anon for getting you the start to find the video. Both yours and the one he came up with were VERY interesting!

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  6. A timely article. I'm in the process of building a two-pot-wide (maybe three pots if set together like a triangle) rocket stove out of landscaping blocks (in a circle) and plan on a firebrick liner in the center, secured with refractory cement/mortar. I'm trying to figure out if or how I can make a meat smoker to the side for a cold-smoke with a little chimney to divert the smoke. The connection from the rocket stove to the smoke chimney wouldn't be airtight, so that might be a problem. A hot smoke cooks the meat for use right now, a cold smoke preserves the meat for later storage where you have to cook it again before you eat it.
    Peace out

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