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Post by Vortex on Nov 25, 2015 9:43:12 GMT -8
Hi Patamos The refractory recipe is from a guy on U tube who is making "FIREBRICK" for smelting. He just tamps the mix which made me think it could be would be good for casting in situ. www.youtube.com/watch?v=Hi Peter, That refractory recipe sounds very interesting, I'd like to see the video but the link you posted just goes to www.youtube.com the important bit on the end of the URL is missing. Can you re-post it. I have spent a good few weeks in your Emerald Isle. My first experience was in Bantry - 10 days of blistering sunshine not a cloud in the sky - a truly amazing experience. My daughter in law comes from Dingle. I'm 16 miles from Bantry town! Yeah, it's heavenly when the sun shines. If you're ever there again look me up. |
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Post by labalme on Nov 25, 2015 10:16:06 GMT -8
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Post by Vortex on Nov 29, 2015 6:22:57 GMT -8
Thanks Peter, that worked. Interesting stuff, I'll have to round up some materials and have a play  My experiments with extending the burn are going really well. Have discovered that by using the method I described above, plus instead of loading a whole batch from the start, if I load 2/3 to 3/4 at the start and then the rest about an hour and a half into the burn, I can get up to 9 hours on one load of fuel. Still with nothing but fine white ash and a clean firebox at the end. Has meant days when I would normally fire it twice I've been OK on one, so must be saving me fuel. Only down side I've noticed is it's slower to heat the house up if I'm starting from cold. The best results are with hardwoods but I can get 5 or 6 hours out of even the poorest softwoods. |
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Post by labalme on Nov 30, 2015 21:49:32 GMT -8
That's interesting.
I have noticed something similar using our current all metal wood burning stove/oven.
The wood is top loaded. There are 3 air controls. All controlled by simple flaps which slide over the entry holes to change the diameter.
One channel which runs within the fire box to the bottom third so once the fire is hot this air is pre-warmed.
One which delivers air to the middle third.
The last is simply a hole through the stove top.
Once the ash/embers in the bottom are hot closing the bottom vent half way, shutting the middle vent and opening the top vent fully, causes the flames to move to the top of the stove. It is like the hot ash and embers are gassing the wood above, with the gasses then igniting just under the stove top. The logs burn slowly down into the ash. Doing this reduces the taring we get very significantly whilst giving a slower burn.
I wonder what the minimum temperatures are to efficiently drive off the volatiles. Controlling the rate of pyrolysis prior to gasification would allow slower efficient burns. So maybe restricting oxygen/air (damping down)is not such a bad thing so long as the gasses are properly burnt down stream.
The more I think about your stove the more enthusiastic I become!
Peter
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Post by DCish on Dec 1, 2015 5:31:02 GMT -8
Spot on, Peter, that's exactly the principle these stoves work on, albeit using different layouts to optimize the burn under different feed and space constraints. Matthew Walker has done a fair bit of work with his batch box on slowing down and extending the burn. Quite exciting!
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Post by patamos on Dec 2, 2015 9:19:04 GMT -8
Ya Peter, I share your enthusiasm Many box stoves can achieve a glowing phase sweet spot wherein conditions are just right for a log to burn clean and slow. But the sweet spot on this vortex is well beyond anything i have seen. Fully functional as a quick hot burn masonry heater. AND also a slow gassifier with secondary combustion in an ideal location. Excellent draught characteristics makes for superb heat harvesting into mass. Functional as an open fireplace. Feed(fire)box makes a great long flywheel oven Decent size viewing window. And very simple to build with common size fire bricks. This is a truly remarkable design... |
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Post by Vortex on Dec 3, 2015 10:18:30 GMT -8
Wow. That's quite an endorsement of the stove. Thank you Pat. I hope between us all we can make it even better.
The stored re-radiated heat of the firebrick core is without a doubt one of the main factors at play in the gasification, any attempt to do it without enough heat there fails. One thing I've noticed looking at wood gasifying stove designs is they all (except for down draught gasifiers) have the primary air feeding up through a grate of some kind and pre-heated secondary air entering just above the top fuel level. It explains why forcing the primary up through the ashbox improved it.
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Post by patamos on Dec 4, 2015 0:05:02 GMT -8
I mentioned to Aukje your comments about loading 2/3 full and loading more fuel later on for the slow burn. She says this is more or less what she has gravitated into as well… but will pay more attention.
So primary air up through the ash box. Can you say more about this?
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Post by Vortex on Dec 5, 2015 13:19:34 GMT -8
Sure, Pat.
If you've ever watched a woodstove with good pre-heated secondary air vents in the top, you'll know the look of the white-gold flame jets that come from them when the stove is really hot. This is exactly what I get in gasifying mode except the jets of flame are coming up from the grate.
I don't know enough about wood gasifying stoves to fully understand what's going on and why, but looking at the simple camping woodgas stove made from food tins, I can see a similarity. The initial fast burn stage in my stove gets everything up to a temperature where it will gasify if given the right primary and secondary air conditions.
When I'm doing a gasifying long slow burn I load several large pieces of wood to fill the back of the firebox, with some medium size pieces at either side leaning back. Then I poke a hole down through the ash into the ashbox below. Next I put some paper, kindling and smaller pieces in the space in the middle of this, which I then light at the base just behind the fully open primary air hole. The venturi effect of the primary air port whips it up into a roar almost instantly. I'll then let this roar away until the fire is going good and strong and I'll close the primary air down to about 2" to 3" open. I leave it like this until the stove is thoroughly hot, (this is usually when I notice the stove glass becomes very clean as any tint from the start up gets burnt off). At that point I completely shut the primary air off. This forces the stove to draw pre-heated primary air up through the hole I made in the ash bed, and those large pieces of wood I put in the back of the firebox then gasify slowly with those beautiful white-gold flames for up to 4 or 5 hours, and if you keep loading fuel this can be extended almost indefinitely.
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Post by labalme on Dec 5, 2015 22:09:05 GMT -8
Hi Vortex
I have been working in the dimensions for a 7" Vortex.
Have sent you a message as I don't want to clutter this thread.
Thanks Peter
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Post by patamos on Dec 6, 2015 21:35:03 GMT -8
Thanks Trev, So after the port is closed the primary air is leaking in through the ash pit door and other possible cracks. I know many ash-pit doors are not super tight on their frames. I tend to insulate between the frame and surrounding bricks though jus to deal with differences in movement. What would you guess the air flow percentage relative to CSA to be coming up from below? Peter, once you get the drawings where you want them i'd love to have a peek too p |
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Post by Vortex on Dec 7, 2015 2:34:33 GMT -8
Hi Pat, The ashbox door has a seal to the outside of the sheet metal stove cladding, but there's no seal between the inside of the steel cladding and the ashbox opening, so some air can get in around the edges and into the ashbox that way. To stop it I've always tried to run the ashbox nearly full.
I can only guess at the air C.S.A. percentage, but the hole in the ashbed I make with the poker is around a 10mm diameter round hole. How windy the weather is makes a difference, likes a bit bigger hole in still weather.
Also something else I hadn't considered before but might be happening, there's a cleanout at the back of the ashbox hole that leads into the bottom of the bell, it's also not airtight so it's possible recycled flue gases could be leaking through from the bell and mixing with the air leaking in from the ashbox opening. I need to experiment and pin it down. Might try sealing a piece of metal over the ashbox opening so it's airtight and see how the stove behaves then.
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Post by alphakilo on Dec 15, 2015 7:31:21 GMT -8
I recently stumbled across your great little forum and thought I'd share my stoves with you. The design is not classic rocket stove but includes elements of it. It's a horizontal front load, batch fed, mass stove with cook top. Now on it's 5th winter and going strong. ;D Very nice design and construction too. I just see it and I have a question. How did you fix the top plate? Do you have problems with the contractions and expansions of the different materials? |
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Post by Vortex on Dec 15, 2015 10:27:47 GMT -8
The top plate is fixed on like this: www.vftshop.com/images/others/Stove/stovetop1.jpgThe first one I built only has a 5mm thick top plate, which bows up in the middle above the fire quite a lot when it's really hot:  On the second one I made, I used a 10mm thick top plate and cut a large square out above the firebox, then welded a slightly bigger piece of 5mm plate over the top of the piece I'd cut out - so that it sits in the hole. That made a nice expansion plate like the circular ones on old range stove tops, and stopped the expansion problem all together. |
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Post by pyrophile on Dec 15, 2015 10:56:00 GMT -8
Vortex, how does your 10mm plate react to heat? It doesn't bend or twist at all? I am building a 150 cm long cookstove and I am wondering if 10mm are enough. I rather thought about 20 mm...
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