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Post by doggy1969bc on Jan 14, 2014 1:58:29 GMT -8
how about a dust collector style like a dyson vacuum cleaner or are the particals to licht and velosity of the gases to slow in a rocket stove ?
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Post by DCish on Jan 16, 2014 18:45:31 GMT -8
Fascinating. I wonder if this is a rationale for targeting high mixing with lower velocity, such as sjang suggests in his batch box modification thread (http://donkey32.proboards.com/thread/1040/secondary-air-modification-batch-rocket). Walker notes how low the disturbance of the ash bed is in modern box stoves. I have a reasonably modern stove (Hearthstone Heritage), and I observe the same thing. The problem is that for it to engage secondary burn efficiently requires a full load that throws a lot of heat, more than I ever need, even with primary air as low as it goes and the damper choked down hard. So even with lower velocity the argument for thermal mass remains salient in my opinion, you simply spread the charging over a slightly longer period.
Targeting improved mixing at lower velocities would seem to open the door for modifications such as Walker's "broken riser" (http://donkey32.proboards.com/thread/1023/accidental-discovery) in a horizontile configuration, with it conceptualized as an insulated secondary burn chamber rather than an element that contributes to acceleration of gasses. Indeed, if the goal shifts from " internal chimney" to "secondary burn chamber" there is no longer demand for a long, narrow "chimney-like" tube, and any shape that can be easily insulated and promotes mixing (whatever shape that might be) could theoretically be used.
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Post by patamos on Jan 16, 2014 21:31:52 GMT -8
Chatting with a friend the other day about 'intermediate impossibilities' i thought it might be of use to explain the meaning of this term that i used in my first post on this thread. Basically, an intermediate impossibility is a stupid idea that triggers a shift in someone else's train of thought whereby they come up with a good idea. On matters of brainstorming, the eurekas often come after a break in focus. Ridiculous humour (venting steam) is a common catalyst. Case in point - An acquaintance of mine who does contract work for NASA (how's that for name dropping...  was in a mega brainstorming session a while back. A small roomful of powerful minds were at an impasse nutting our something or other. This fellow needed to take a shit but kept holding back so that he didn't miss the crux of the problem solving. Finally, 4 hours and 4 cups of coffee later, he could bear it no longer. Off to the can he ran. And there, during a recess in concentration (so to speak), the answer to the riddle came to him. So, this much to say, as they say, when it comes to brainstorming, the only bad idea is the one we are afraid to mention... The filtering and funnelling can come later... I wonder if the suspended ions settle out any better in slower bell runs than in faster flowing serpentine flues? If so, what shape of bells might be more effective? well being pat |
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Post by colinsaengdara on Jan 17, 2014 10:15:58 GMT -8
Wow! This is why I like hangin' out with you guys! Great ideas coming forward.
DCish - As regards velocity through the ash bed, I certainly think that this is the culprit, but velocity is also a big part of the solution to other problems. I think where we will end up, eventually, is suitability to task. A rocket stove can and should be built to be the easiest running beast for the task at hand and the particulars of the space it inhabits. Chimney or no, how high, how many levels in the building, what floor the heater occupies, climate, etc. etc. etc.
So often, the threads we see here and at larger sites are framed in a "which is better? x or y?" kind of way. And the answer is nearly always "it depends". I can picture one of those decision flow diagrams somewhere in the mist in my brain starting to emerge.
So to sum up this post, I think the question is how much velocity is best? At what point in the stove? And what about stoves in small/short spaces that truly do depend on the draw of the heat riser instead of a chimney to function? It's been relatively easy to give basic dimensions/proportions for a working rocket stove up to this point because the only issue was generally to create enough draw then reduce the size of the primary air to limit excess air and smoke back.
Finding a particle separator that works passively will maintain the freedom of design that we currently enjoy, but consider how much ash you deal with in a traditional stove. I find that my ash bucket from a traditional stove is often 1/3 charcoal, but there is a ton of ash to deal with. If we fired a rocket stove and collected the ash from the burn both in the front of the stove, and the finer particles at the end of the system, we would once again be dealing with the same quantity of ash per volume of wood as with our traditional stove. For me, this is an eye opener. It means that whatever we use to grab the fine particles needs enough surface area to deal with a huge volume of ash.
I've been fortunate enough to have a tall house with two chimneys that provide plenty of draft for my stoves. I always wonder how some of my thrown together designs would fare in a smaller, shorter, more reasonably sized home.
doggy - my wife has a dyson, and it is an amazing vacuum. But there are so many aspects to the design, I'm not sure which aspect you are referring to. If you mean, a particle filter that excludes particles down to the micron size in the flue flow, such a filter will gradually clog up and cause the stove to back up. We cannot have an obstruction style filter, we need a form of separator. Something to attract the particles to an adjacent surface rather than force the gases through a fine mesh. If I've misunderstood, could you explain your idea more?
patamos - hilarious! I'm fascinated by where ideas come from. I definitely agree that these 'intermediate impossibilities' play a huge role. It definitely seems to me like I have to be stuck first, then be exposed to this 'stupid idea that wont ever work' before I'm open to seeing everything in a new light. That's why I think we have something really special here in this forum with people from all over the world with various levels of experience all interacting together. I know we will come up with some great ideas! I try to be careful in my responses on these forums, because you never know the whole context of someone's idea.
Regarding the bell shapes, I've been wanting to build a Matt Walker style bench for a while now. Matt, can you tell us anything about what kind of ash you get at different parts of your system? I know you have one bell that's a dead end.
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Post by matthewwalker on Jan 17, 2014 10:31:00 GMT -8
Colin, great post man. This whole thread is great. I hate to be the debbie downer here, but remember that all of the experts I spoke with said there is no way we are going to drop this stuff out of the gas stream. It acts exactly like a gas. Once airborne, it's staying in the gas stream unless it is physically removed.
As for my bench bells, and this seems to reinforce what I wrote above, nothing of note gets much past the exhaust port. There's a little snow drift at the high velocity exit from the downdraft barrel, but out in the ends it's kinda black/grey fuzz on stuff, but not much of a pile on the floor.
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Post by Donkey on Jan 18, 2014 0:26:59 GMT -8
Well... It should be pointed out that according to the "experts" just a few years ago, Rocket Stoves would never be made to work and "those damn hippies are gonna kill themselves over there playing with fire like that!" Matt, the stoves that you are currently building and the test results that you are now logging were supposedly impossible.. Unlikely at least. I can't tell you how many experts told me to forget the nutty ideas and stick with what works! Less than useful is what that was, at a time that I could have used some enthusiastic (but skeptical) help on this.. So I started a forum, stumbled around in the dark, discovered some things, talked to some friends who discovered MORE things and here we are.  You are of course correct, it's NOT an easy problem to sort out.. Of course, it's whats make this issue SO attractive to work on! It might be fun to help with yet another impossible task! A good cause, a worthy opponent! Tally ho! |
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Post by colinsaengdara on Jan 18, 2014 17:52:16 GMT -8
Right on Donkey! "Tally ho!" indeed! I'm super short on time right now but what I am considering doing is taking one of my test stoves and dedicating it to the following experiment: Part I Sampling the uncombusted residual material from various spots in my system and determining it's chemical makeup. The spots I am thinking of are the batchbox, the walls and floor of the first bell, the walls and floor of the 2nd bell, and the three plates that I will set up in the second bell described in Part II. Part II adding three metal plates hanging down into my 2nd bell. The plates will be as follows: each of equal size but different electrical potential to determine whether particle loading takes place or not. One will just be in contact with the masonry bell, one will be isolated from the bell, but attached to the positive terminal of a 12v deep cycle battery, and one will be isolated from the bell and connected to the negative terminal of the same battery. Why am I doing this? I've noticed that the residues in my rocket stoves are different than the ash in my wood stoves. I think the ash in the wood stoves has a lot of unburned carbon in it, but it's also a big mix of minerals, and I think the stickiness is probably unburned tars. The stove pipes accumulate creosote which is glassy minerals and double carbon bonded tars that did not combust due to insufficient oxygen and temperatures in the stove. The rocket stove is completely different. In the burn chamber of the rocket stove, the leftover ash seems to be crystalline in nature. More like salts than ash and I'm betting that it's pretty much sodium and potassium and magnesium salts. The rest of the system is lightly ashed with super fine powder that knocks down easily if brushed. I'm thinking that this ash is much like the ash in the burn chamber, but in a rocket stove the temperatures produced at various points in the system are highly variable and it's possible that the products of combustion vary by zone. Knowing what is produced and where could enable us to design cleaner stoves that capture more ash by virtue of the material choice or with simple low tech solutions. Analysis of materials that adhere to the surfaces of the test "filter" will tell us alot. If we can confirm what it is, we can design a system to remove it. I'm hoping a 12v battery will provide sufficient potential to attract the micro particles we're after. A 12 volt battery is readily available or even makeable anywhere in the world. Even a salvaged battery that only produces 11 volts is probably enough potential for this purpose. If the potential is enough, then all we need to do is increase the surface area of the plates, and make the filter easy to remove and clean. Hopefully by just pulling it out and knocking it off into a bucket. Thoughts on this? I would like to think it through before I redo the top of my brick bells. I need to redo the first bell anyway, as my top was only temporary. But I can easily set this up on my 2nd bell at the same time. Details of my brick test stove are in a thread at Matt's site www.permsteading.com/viewtopic.php?f=6&t=467&sid=66cfd6b82f3d574620384d79beaec3daColin |
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Post by DCish on Jan 18, 2014 18:31:57 GMT -8
Sweet experiment. For what it's worth, I get a black crystalline crunchy substance in my box stove when I load a log on a bed of waning coals and have the primary air wide open, drafting under the log but over the coals.
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Post by colinsaengdara on Jan 18, 2014 19:36:56 GMT -8
Sweet experiment. For what it's worth, I get a black crystalline crunchy substance in my box stove when I load a log on a bed of waning coals and have the primary air wide open, drafting under the log but over the coals. DCish, where do you find the substance? Does it adhere to the coldest surface inside the stove such as the interior of the door? |
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Post by DCish on Jan 18, 2014 21:05:32 GMT -8
No, it's on the floor under the log as the coals fade and the log is limping along at a lowish flame despite high air. It forms a "cake" of sorts that grows in thickness and size for as long as the burn condition persists. It is a sort of lattice of crusty stuff that is light and crumbly, the largest I've encountered is about 1.25" thick and a 7" diameter half circle arcing out from the air supply hole.
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Deleted
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Post by Deleted on Jan 19, 2014 6:37:18 GMT -8
No, it's on the floor under the log as the coals fade and the log is limping along at a lowish flame despite high air. It forms a "cake" of sorts that grows in thickness and size for as long as the burn condition persists. It is a sort of lattice of crusty stuff that is light and crumbly, the largest I've encountered is about 1.25" thick and a 7" diameter half circle arcing out from the air supply hole. One could try to use a tight 360 ° turn or even a spiral to remove ash by centrifugal force. |
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Post by Donkey on Jan 19, 2014 8:34:25 GMT -8
One could try to use a tight 360 ° turn or even a spiral to remove ash by centrifugal force. I was thinking along the same lines.. With some kind of surface on the outside of the spiral to catch the ash as it rolls along. One thing that came to mind is something hairlike (like Velcro) to comb the ash out as it rolls past.. Cleaning would be an issue, it would clog quickly. It is also likely that the ash is too fine/light and that the stove won't produce enough velocity (around a spiral) to do the separating in the first place.. The electro-static thing has promise as well.. In the long run, it would be nice if the stove generated it's own electrostatic charge. Maybe a small TEG or some such. |
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morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
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Post by morticcio on Jan 20, 2014 2:21:20 GMT -8
I had an email back from Ecolink reference the ABCAT I referred to above. The "filter element'' is a full metal Pd catalytic convertor. They go on to say "for cracking the most hazardous organic hydrocarbons (VOC) such as PAH's a temperature of approx. 350°C (660°F) will be required".
As this fits on the outside of the stove it isn't suitable anyway for a rocket with much lower exit temperatures.
I'm guessing the high temperatures needed are the same for all catalytic convertors?
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Post by patamos on Jan 22, 2014 9:31:12 GMT -8
A few questions coming to mind:
Are these charged particles bound to the gas flow due entirely to the turbulence in the burn-chamber-riser elbow? And/or are they also picked up via rapid movement around the ash bed? If at all the latter then reshaping down drafts and ash bed layouts could have some effect.
Another idea (that i think was mentioned in an earlier thread), could an appropriate electro static charge not be added to a section of flue pipe?
well being
pat
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Post by doggy1969bc on Jan 23, 2014 8:01:36 GMT -8
doggy - my wife has a dyson, and it is an amazing vacuum. But there are so many aspects to the design, I'm not sure which aspect you are referring to. If you mean, a particle filter that excludes particles down to the micron size in the flue flow, such a filter will gradually clog up and cause the stove to back up. We cannot have an obstruction style filter, we need a form of separator. Something to attract the particles to an adjacent surface rather than force the gases through a fine mesh. If I've misunderstood, could you explain your idea more? I was more thinking in the lines of a spiral separator like havy particals fly to the outside but you could combine that with the electric separation system put a pos rod in the middel and the neg on the widening tunnel |
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was in a mega brainstorming session a while back. A small roomful of powerful minds were at an impasse nutting our something or other. This fellow needed to take a shit but kept holding back so that he didn't miss the crux of the problem solving. Finally, 4 hours and 4 cups of coffee later, he could bear it no longer. Off to the can he ran. And there, during a recess in concentration (so to speak), the answer to the riddle came to him.
