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Post by peterberg on May 5, 2012 1:24:09 GMT -8
One conversation that Canyon and I had.. Metal heat risers burn out. Metal can only burn if there's enough oxygen left over to do the job. Is there some way to reduce or exclude excess oxy (and other ballast gases)?? I know that is the intent of the Russian bell stove builder with his narrow slot at the bottom of the burn area. You and I have spoken about this in the past, you seemed to say that it makes no difference.. I still wonder if a way can be found to shunt that stuff out of the system.. ?? Reducing excess oxygen close to zero can only been done by very complicated systems, in my view. It's next to impossible to do that by natural processes like combustion. You always are stuck with excess air at the end of the process, I've tried very hard to accomplish that goal, to no avail. One of my knowledgeable sources gives this explanation. To oxidize the metal in a comparatively quick way, one will need three factors: oxygen (obviously), high temperature and a low carbon environment. The first two won't burn the metal on its own, the last one has to be one of the circumstances. In fact, by a temp of 1800 F. , just a little oxygen and very low CO, carbon is extracted out of the steel, turning it into rust. Oxidized steel is taking up more space, so there are coming flakes off the surface of the metal. This phenomenon itself is known as "spalling". So, the low CO numbers, highly appreciated in rocket mass heaters, are the cause of this inconvenience. In the early days of the blacksmith, the iron could be turned into a stronger and harder material by heating it into the coal fire. By hammering it, heating it again etc., the iron can take up carbon from the coal fire, turning it into steel. You ought to know that, because you are using a forge in the shed. Burning out of the steel riser or tunnel is the same process in reverse. There do exist a stainless steel which is highly resistant against spalling, it's SS 310 or SS 310S. |
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Post by satamax on May 5, 2012 12:39:38 GMT -8
Peter, if i may. Is this spalling?  Another thought. Usualy refractories use a high content of alumina. And aluminium doesn't oxidize much either. Over here we have thoses thin tubes which are aluminized steel, for stoves. In my cyclonic rocket, which pic is above; i've used one. And when you see the state of the gas bottle, and the tube, i have the impression that i'm onto something with thoses tubes. Here's the pic. With the same amount of burns as the bottle and feed tube.  Doesn't seem much oxidized. I wonder if it's because the bottle protected it or the aluminium coating? May be the two? But may be thoses tubes might be a cheap alternative to stainless. What's your thoughts? Bye. Max. |
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Post by Donkey on May 5, 2012 14:48:11 GMT -8
Umm..
Actually, aluminum oxidizes like CRAZY. Aluminum can be highly flammable in the right conditions and is a major component in thermite. Normally the surface will oxide over almost instantly and then block out further contact between aluminum and air. The white powdery stuff that you see on old aluminum tubing is aluminum oxide.
Seems to me that it would burn out or more likely, melt out even faster. OTOH, if you've got something that works, what the heck..
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Post by satamax on May 5, 2012 16:21:08 GMT -8
Hi Donkey. I've done a smidge further research. Aluminium oxidizes, true. Very true. And what does it turn into? Alumina, or aluminium oxide. Which melts at aproximately 2072C° or 3761F° en.wikipedia.org/wiki/Aluminium_oxide If the tube was pure aluminium, it would melt. But the steel in this case is protected by a layer of alumina, which protects it from oxygen, and doesn't melt. Steel will melt before. Thought, it's not going to happen if it's suported, before way high temps. In my four incher, i was reaching 1230C° i thing. Bright orange visible against the flames. But imho, if the heat riser doesn't go over this, we might be fine. I'll try on the six incher in a few days.  |
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Post by peterberg on May 6, 2012 1:05:20 GMT -8
It surely looks very much like it. When it is possible to remove the flakes with your bare fingers it definitely is. Has the gas bottle been inside the stove? |
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Post by satamax on May 6, 2012 4:40:49 GMT -8
Hi Peter. The gaz bottle was the chamber after the burn tunel.  And was inserted in a barrel of vermiculite. |
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Post by canyon on May 19, 2012 13:56:56 GMT -8
It took a while to get my head around it, but now I see what has been done. It looks like the same principles as my rocket syphon, the new part is the implementation of the P-channel in this. It is leaning on the assumption that the majority of the combustible gases are in the top segment of the tunnel/firebox or whatever. The next question will be: how will this new "thing" behave, completed with barrel and all? And you'll need a door of some sort. This could be a next step towards a simple and very adequate rocket heater variant. Edit: Some more questions did spring to mind. Is the "thing" loaded full as a batch-fed device? Is it lit in front or close to the riser? Are there results from canyon's analyzer? How many minutes to smoke-less burning started from cold? Hi Donkey and Peterberg! Sorry but I have been working like a madman since getting back from the trip and have not even been able to go online except for business emails! Now I am trying to breath again and catch up to the forums! @donkey- thanks for posting the pics etc! peterberg, Just to give you some more background, I have been working on this design for a couple of seasons now as a "kit" with a simple door/door frame being the only custom metal working part and the rest able to be done up with brick and drilled/bolted steel angle for a tension frame. When I get plans available to download it will make more sense. But anyway, There are four of these now that have been used as a primary heat source up here in alaska for a whole winter and a couple more that have been used for two seasons. So we have some good empirical experience how they behave with barrels and mass benches. I must say right away how grateful I am that you have shared so much of your work as you noted the burn chamber is very much inspired by your rocket siphon and it continues to be as we would like to play with a sloped floor next. I have tried the 2ndary air preheat tubes similar to what you did in copper but now the preheat channel and peterchannel is much simpler and better in many ways. These are typically loaded full as a batch fed device and then reloaded several times to charge up the mass. Top down fire building/lighting has proved best and if possible (not usually too easy to do) lit close to the riser. I'll get the testo to sniff at a few examples eventually but don't see a window too terribly soon as the snow is finally disappearing and I have lots and lots to do including managing the largest straw/clay insulation project in north america known! We have eight of these batch box rockets to build on the schedule this year already so I will want to test before the first one in late july and keep going with it so they refine a little more each time ideally. As Donkey mentioned, we have found that thick steel spalls way too quickly with these so I am only doing refractory risers now. Also, I experimented on a couple with a bottom cast iron grate and ash pan and the grate warped out of shape in a few weeks! So, I am liking your sloped bottom ash opening in refractory materials much more now! By the way, when we fired the mock up that Donkey and I built the second time on the next morning (it wasn't stone cold but definitely not very warm) it went smokeless in under two minutes! Wood quality/splitting of course has alot to do with that but the peterchannel and the fact that the mud on the works was dry already and the design itself had alot to do with it too in my mind. Anyway, I just had to quickly write in 'cuz I am finally back online and wanted to join back in the conversations!  |
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Post by peterberg on May 21, 2012 0:38:23 GMT -8
Just to give you some more background, I have been working on this design for a couple of seasons now as a "kit" with a simple door/door frame being the only custom metal working part and the rest able to be done up with brick and drilled/bolted steel angle for a tension frame. When I get plans available to download it will make more sense. So it's not a spur of the moment, but a development of many months! I like to see you plans, I've been brooding over a similar setup past winter, maybe there's something I could contribute to this. But anyway, There are four of these now that have been used as a primary heat source up here in alaska for a whole winter and a couple more that have been used for two seasons. So we have some good empirical experience how they behave with barrels and mass benches. So there's a raft of these things operational in Alaska. ;D What's the system size and the ratio between riser and firebox? And what's the weight of one charge of fuel? As Donkey mentioned, we have found that thick steel spalls way too quickly with these so I am only doing refractory risers now. Also, I experimented on a couple with a bottom cast iron grate and ash pan and the grate warped out of shape in a few weeks! Heavy spalling of a steel riser is the result of moving the flame zone from the tunnel to the riser, seems logical. Less hydrocarbons in the flame zone will increase spalling, so this is a good sign. Warping the grate do surprise me, but this could be the result of less primary air into the fire box. Although the P-channel is rather small, the air speed in there could be very high when the system is heated up. So during the burn the P-channel could become dominant over the primary air inlet, volume-wise. By the way, when we fired the mock up that Donkey and I built the second time on the next morning (it wasn't stone cold but definitely not very warm) it went smokeless in under two minutes! Good sign as well, this looks promising. This do sound it became smokeless before heating up. |
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Post by canyon on May 23, 2012 8:48:48 GMT -8
What's the system size and the ratio between riser and firebox? And what's the weight of one charge of fuel? We have built both six inch and eight inch systems. Are you asking for the cross sectional area ratio or volumetric? I'll have to weigh a typical charge for each system size when I get a chance and report back. Things are a bit busy right now on other natural building fronts so I look forward to your input when I can really focus back on this and get you the plans. What are the basics of what you have been working on this winter? |
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Post by peterberg on May 25, 2012 1:07:41 GMT -8
We have built both six inch and eight inch systems. Are you asking for the cross sectional area ratio or volumetric? The cross sectional area is what I'm after. Normally, when you've built something like this, at some point into the burn all the fuel will burst into flames. Often causing a huge overload of hydrocarbons which will appear as smoke. Since there's no smoke in your set-up, I'm curious how far this will stretch. In other words, at some point the overload should be present again. I'd think there ought to be a maximum csa ratio and fuel weight/volume in order to keep the thing running healthy. What are the basics of what you have been working on this winter? Not very much, did some design work for a third party. And tried to figure out a solution to the problems regarding a larger firebox/ rocket heater combination. ;D My own rocket/bell experiments did go a long way but not as far and pollution frugal as an optimized rocket heater like the one I've did last year. There ought to be more solutions to the same sort of problem. |
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Post by matthewwalker on May 27, 2012 13:42:21 GMT -8
Hey guys, here's an update on my outdoor system, now with enlarged firebox and batch loading!
Thanks very much to Canyon and Donkey for the inspiration.
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Post by peterberg on May 28, 2012 6:19:16 GMT -8
Hey guys, here's an update on my outdoor system, now with enlarged firebox and batch loading! Hi Matt, I've done something similar, albeit both channels had their own heat riser. Didn't work very good because one of the channels warmed up just before the other randomly. The end result was the coldest channel couldn't get flames in there and had a strong tendency to let unburned hydrocarbons escape. In other words, it'd produce smoke. Please see this thread, scroll down to November 2, 2009.So, as long as you've got flames in both channels, it will work OK this way. And there's a way to check the process, through the side windows. Those windows will restrict the combustion temps somewhat, but without testing it's hard to tell whether this effect is important. |
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Post by matthewwalker on May 28, 2012 8:01:18 GMT -8
Thanks for the link Peterberg, I hadn't seen that thread. That's a cool stove!
I believe that the windows do affect the burn negatively, as they are throwing out a lot of heat. In this outdoor configuration, it's a desirable effect, as sitting around the fire is the point. I am quite sure it's not as efficient as it could be though, and for an indoor stove I would not recommend so much window surface.
It's interesting to note that a cold channel lets the smoke escape. I had noticed on start up, one channel does carry most of the flame, and the opposite windows soots badly. However, upon looking into the bottom of the riser where the two join, you can see vigorous mixing and flame as the unburned gas meets the flame path again. It heats up quickly to the point where flames are running along both windows. This stove has a hole in the top of the barrel, for cooking, and will easily shoot flame out the top, so there is some burn happening up the riser. Partly I'm sure due to the fast draw that the unrestricted exhaust provides.
Thanks again for your comments, I appreciate you sharing your knowledge.
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Post by peterberg on Jun 18, 2012 11:13:35 GMT -8
Last week, I've been busy building a similar rocket. Built on a small platform, avoiding the need to go down on my knees every time I want to look into it. www.ecologieforum.eu/download/file.php?id=3720&t=1Made of used fire bricks, as close as possible to the size of the model Donkey and Canyon experimented on. The riser is 6 bricks high. www.ecologieforum.eu/download/file.php?id=3722&t=1Size is the same as a 6" duct, the tunnel opening is the same as riser size. At first, no trip wire, a flat top plate and a wedge shaped floor to collect remaining fuel in the middle. www.ecologieforum.eu/download/file.php?id=3724&t=1The next picture shows the p-channel sticking out through the top plate. www.ecologieforum.eu/download/file.php?id=3726&t=1In order to extract some heat before exhausting to the chimney stack, I've modified a 55 gallon drum. A hole in the bottom with a 1' pipe mounted inside, and an exhaust hole at the side. This is acting as a bell, placed on top of the riser. www.ecologieforum.eu/download/file.php?id=3728&t=1It's an ugly thing, clearly not been made for its visual attraction. The first real test run was done with the p-channel in, started in a hot stove behind some glowing charcoal. This delivered a quite nice graph, the O2 level was still a bit at the high side of things. Because of the greater dilution the CO is quite low. www.ecologieforum.eu/download/file.php?id=3729&t=1Without the p-channel the whole CO line is around the 2500 ppm mark, so all other test runs has been done with p-channel in place. Following test runs were done with subsequently smaller primary air inlet. The 2nd air was kept at the usual 5% riser size, 1st inlet in steps down to 10%. That last one appeared being too small, so I would think minimum size is 15%. Tried a trip wire as well, but there happened to be no discernible effect. After 6 test runs I've lowered the top of the tunnel 2" in order to speed up the velocity of the passing gases. This has been working very well, so following runs has been done using this setup. One run, I've switched from a bottom opening like donkey's and canyon's version to a top front opening. This appeared to be not the right move, because this is the result: www.ecologieforum.eu/download/file.php?id=3733&t=1Suddenly it dawned on me I've been firing the thing by loading it as high as practical and lit it on top as far as I could reach inside. All that runs had a quite high CO level at the start. So I've switched to making a small fire right in front of the riser opening. When this burned well, the whole fire box was loaded, behind and on top of the small fire, up to the top plate. Above method produced this graphic, started in a cold stove by the way. www.ecologieforum.eu/download/file.php?id=3731&t=1Next move: a trip wire of some sort, at the upper part of the passage as well as the sides. And finding out the maximum tolerance to an overload of combustible gases. The whole setup can be made at least as good as my own rocket/bell project. The results from the small scale development thread are better by far, but that's a league of its own, I'd think. |
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Post by peterberg on Jun 20, 2012 12:04:32 GMT -8
Two more test runs today, and progress has been made. I've found an old piece of ceramic glass somewhere under the dust. Carefully implemented this with the use of some superwool and pieces of brick. Now I've vision as well, to accompany the sound of the thing. www.ecologieforum.eu/download/file.php?id=3766&t=1And here is the high-res version: But this picture doesn't do the thing justice, so I've made a short video of it. The flames are mostly purple now, but that's a shortcoming of the rather outdated cell phone. The changes compared to the last version are these: inside the stove, I've placed some brick pieces in order to lengthen the tunnel. This has become about 4 1/2", with a brick on top, featuring a trip wire. Implemented as a flat raised triangle, the cut-out portion flush with the brick behind it. I've used this brick some days ago, at the time there wasn't a discernible effect.  Here is the high-res version: The situation shown by the picture is the old setup, by the way. This new implementation appear to be much better than before, see the graph of a testrun done this very morning.  Here's the high-res:The whole CO level is around 1000 ppm or lower. Large peaks and whole peninsulas remained absent. The oxygen level (green)is going down quite far at the top of the burn, which is clearly showed by the end temp (blue). All testruns from this one forward will end at 4% CO2. The CO hill at the end will always be there, it's no point to show it every single run. Averages of this run: O2 12.6 %, eff. 83.6 %, CO 592 ppm, Tr 193 C. This happened to be a very nice run, so I decided to do a full refill. So I'd shut off the Testo, saved the data, filled a basket with fuel, opened up the stove, filled it up right to the top, mounted the window again and dashed off to the computer because the stove started to roar already. This resulted in the following graph:  Here's the high-res:This run happened to be even nicer, the CO level raised to 1500 ppm only to descend sharply to below 100 ppm. Lowest level that came by was 20 ppm. This is extremely good for such a simple contraption, challenging a rocket mass heater "by the book" although the optimized rocket stove from last year happened to be marginally better. Averages of this run: O2 12.9 %, eff. 81.5 %, CO 466 ppm, Tr 212 C. This looks like a trip wire is only useful in a tunnel of a minimum length. |
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