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Post by labalme on Aug 29, 2015 22:43:23 GMT -8
Hi.
This is my first post please be as rough as you like. I am ready to learn!
I have 3 projects in mind.
1) Build a 7 inch horizontal mass heater for our lower stable 42 square metres.
2) Experiment with a vertical mass heater. It seems to me that the mass heater is basically creating wood gas in the first burn and then burning the gas in the riser. I want to create a stove with 3 viewing openings. A door and 2 windows. So the idea is to place the throat and p tube above the first burn chamber the first stage will then be more like conventional fire box. This fire will go in the center of a larger barn space 60 meters square. Visually this will allow the fire to be viewed from three sides.
3) If the vertical heater works then I want to replace the flue riser on the wood oven that we have with a similar wood gas burning riser. How to provide mass for this is something I am still thinking about. I would like to make a riser which can be fitted as a retro to conventional wood burns to clean up the smoke they create.
So please fire away!
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Post by satamax on Aug 30, 2015 0:24:59 GMT -8
Peter, you will have to check your terms i think.
First of all, every combustion is producing woodgas, but not only. In the case of the rocket, it's a direct fire, but soo hot that the remaining volatiles; part woodgas, part tar, part soot etc are burned. Actualy, the woodgas might have been burned more than you think, when it reaches the heat riser. As it's a prety flamable component of fire. Mind you, i haven't tested chemicaly or even tested the combustion of anything rocket i've built.
When you say, horizontal, vertical, what are you talking about? The bench, or bells? Or the combustion unit.
For cooking units, we thend to call them L tubes. Because that's what they are, a short horizontal leg and a tall vertical leg.
The Evans type is usualy called J tube. You see the picture.
And the one Peter van den Berg refined, is the batch box. A big firebox with a door, a vertical port at the end, restricting the flow of gases into the riser.
And when it comes to the different heat exctractors, there's 3 identified types, for which we don't have to explain what is meant.
There's the barrel, as per Evans's conception. A barrel onto the heat riser, which usualy acts as a downdraft channel, or in some case à bit like a bell. It's a plain radiator.
Then you have the bench, usualy following the barrel. A tube of some kind, running horizontaly, before the vertical chimney. Which is a heat exchanger. Usualy surounded by mass of some kind.
Then you have the bells. A closed volume, with two low entry and exit point. Into which the hot gases tend to stagnate, due to convection. But not impeding the flow of flue gases as much as the long tube of the bench. They can be mass or metal.
Hth.
Max.
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Post by labalme on Aug 30, 2015 5:25:58 GMT -8
Max
I mean stacked vertically in line ie the throat (with horizontal orientation as against the vertical throat plane of the van den Berg mass heater) placed directly above the first burn.
I should have said exhaust products, which include wood gas, soot and other volatiles which condense out in chimneys.
I disagree that a batch stove is a single fire. If it were then the separation between the riser and the first burn achieved at the throat would not be geometrically so critical and the importance of additional oxygen via the P tube would not be necessary. The fuel in the first burn behaves differently to that in the riser. So I think it is fair to regard the 2 zones as different systems.
If I am correct then replacing the flue on a conventional wood stove with a variant of the batch stove riser should allow the exhaust products to burn. When the wind is high the wood oven we have makes a noise similar to our rocket stove. The flue is acting like a riser and becomes frighteningly hot. The stove has three controllable air inlets set at the base and at 1 third and 2 thirds of the stove height. My thought is that additional oxygen introduced at the flue stove junction with a throat for turbulence may reproduce the burn achieved in rocket system risers. This will have to be well insulated and I would like to capture the extra heat.
I will be building a quick prototype to see what happens.
Please pull the above apart. I realise that I am probably barking at the wrong tree.........
Cheers
Peter
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Post by satamax on Aug 30, 2015 7:17:35 GMT -8
Well, i must have a case of bad monday, i understand fcuk all!
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Post by labalme on Aug 30, 2015 8:02:40 GMT -8
NO I'M JUST IGNORANT AND HAVE MADE SEVERAL CONNECTIONS WHERE NON EXIST.
Definitely I am up a creek and no paddle!
Still I would like to know how to burn off the exhaust from a conventional wood stove without completely rebuilding it.
Also why should a stacked stove with the throat and riser directly above the fire box not work? Is that any less initiative than a J tube?
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Post by patamos on Aug 30, 2015 8:08:14 GMT -8
Hi Labalme
I too am having trouble understanding your terminology. It might e worth your while to review more of the threads that interest you and see if you can join in on the common lingo. Like any language code, it helps us all get on the same page.
Re the batch stove being a 'single fire', Do you mean the combustion process as it is burning? Or the fact that it is designed to be loaded and fired once (without repeat tending/feeding) like a masonry heater? If the former, some combustion occurs in the batch 'box' but the most critical high temp combustion is in the lower part of the riser. This is true for any 'rocket' system. If the latter, it is a matter of choice how often you feed/reload it...
your metal body stove will not handle the constant high burn temperatures. It is designed to be a combustion chamber and radiator put together and is inherently inefficient at the former (unless you use it as a shell with the smaller core well insulated inside of that. Once the combustion process is optimized by following the dimensions and parameters Peter has established… anything metal will quickly decompose.
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Post by peterberg on Aug 30, 2015 8:15:31 GMT -8
Also why should a stacked stove with the throat and riser directly above the fire box not work? Is that any less initiative than a J tube? Has been done, the results were meager to say the least. I don't know why but I tried several possibilities with the riser on top and it didn't work. At all. Sometimes it got smokeless but most of the time the Testo analizer wasn't happy. But on the other hand, the proof of the pudding is in the eating. Please go ahead and see where it leads you.
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Post by labalme on Aug 30, 2015 9:35:27 GMT -8
Re the batch stove being a 'single fire', Do you mean the combustion process as it is burning? Or the fact that it is designed to be loaded and fired once (without repeat tending/feeding) like a masonry heater? If the former, some combustion occurs in the batch 'box' but the most critical high temp combustion is in the lower part of the riser. This is true for any 'rocket' system. If the latter, it is a matter of choice how often you feed/reload it... Hi Patamos. I'm obviously not making myself clear!! Please correct me if I am wrong. 1) In a conventional stove the wood burns by releasing volatile substances which burn more or less efficiently above the wood. In a SINGLE LOCATION. As these substances are evaporated the wood turns to charcoal and the carbon therein is burnt. Un-burnt volatiles can and do condense in the chimney. 2) In early rocket L shaped stoves the volatile exhausts burn at high temp in the riser. Sufficient oxygen is supplied by splitting the feed tube with a shelf under which air flows. The volatiles burn more efficiently at this SECOND DOWN STREAM LOCATION. 3) In a batch stove the exhaust volatiles again burn in the SECOND LOCATION riser with the addition of oxygen through the P tube augmented by turbulence mixing. In fact the exhaust is forced into the SECOND CHAMBER through a portal. The carbonised wood burns in the first batch chamber. Hence I see batch stove as a 2 process event. Is the heat associated with the riser a result of the burn or the cause? In a forge the addition of forced oxygen with bellows raises the temperature significantly. Is the heat generated in the riser due to forcing O2 via the P tube? This leads me to question can the exhaust from a conventional wood stove be managed at the stove flue (chimney) junction? I don't want to use the stove as batch burner. I know this stove is relatively inefficient which means there are always volaitles still to be burnt. So my plan is to remove the flue from our wood oven, at this point create a portal slot for turbulence in a second chamber with an air inlet which can be controlled by a large gate valve. Then form a refractory tube to insulate the burn if it occurs. In effect create a controlled chimney fire. I hope this makes more sense. I understand completely the development of jargon. I have read and reread extensively the threads here and on other sites. My reason for posting is that I prefer to learn from those who know rather than trying to re-invent the wheel. As an aside it can be difficult to use jargon correctly especially when the terms are nowhere defined. This is not a criticism. I am overwhelmed by the amount of work and information that is available I am deeply impressed by the depth of the knowledge contained here and on other sites. I hope that my learning curve will be steep. I thank you in advance for tolerating my clumsy language.
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Post by satamax on Aug 30, 2015 11:10:47 GMT -8
Well, to me, it might be two stage, but it's a single combustion. There's no fire going out and re lighting further down the line.
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Post by peterberg on Aug 30, 2015 11:26:36 GMT -8
In my opinion, the batch box is an example of a two-stage burn according to your definition. The single phenomenon why it is burning that clean is the double vortex which is running around in the riser. In case you haven't seen it already, try "Batch box rocket stove 04" on YouTube. There should be more ways to induce this type of hefty turbulence but I ain't aware of any yet. The vortex started up much later when I tried a longer port (or throat) of 4" deep instead of 2". The conclusion seems to be that the riser part need to be in close proximity of the pyrolysis chamber. In order to propagate the flames into the port the main air inlet need to be quite low as well.
All this aside, trying to improve your existing wood burner is a good thing, so I am curious how far you can get.
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Post by johndepew on Aug 30, 2015 12:01:03 GMT -8
In my opinion, the batch box is an example of a two-stage burn according to your definition. The single phenomenon why it is burning that clean is the double vortex which is running around in the riser. In case you haven't seen it already, try "Batch box rocket stove 04" on YouTube. There should be more ways to induce this type of hefty turbulence but I ain't aware of any yet. The vortex started up much later when I tried a longer port (or throat) of 4" deep instead of 2". The conclusion seems to be that the riser part need to be in close proximity of the pyrolysis chamber. In order to propagate the flames into the port the main air inlet need to be quite low as well. To me, this seems like a contradiction. I would agree with Max, that it is a single uninterrupted burn that transcends spatial borders, as it were, and becomes more intense after the port...as I observe my batch box, I would tend to say that there is uninterrupted flame from the firebox through the port, and into the ram horn. Maybe I have misunderstood what you are saying. I would also say that by adding additional 02 at the port, be it in a batch box or your altered stove, you are creating a secondary fuel source with which to combust the remaining volatiles, but that air needs to be preheated somehow before being introduced just before the port. Thus, to me, the heat in the riser is BOTH the result AND the cause of the burn, in different ways. You can have a batch box that operates without any P-tube (albeit, not to Testo standards) if the primary air at the front of the firebox is plentiful enough. My question is how will you create a double vortex pattern of gas movement if the port is horizontal in the ceiling, shooting the gasses up basically through the middle of a cylindrical flue? You'll create negative pressure zones (I think) by having the port there, so my brain tells me the gasses will want to curl back down, but the heat will also be telling them to rise. In Peter's design, they can curl in a horizontal plane while rising in a vertical one, thus the ram's horn pattern we all love. I'm quite curious how the gasses would move in your arrangement. Maybe somebody smarter than me could answer that. Or maybe I'm way off in the first place, I don't know. One possible solution to this would be to take a lesson from adeil and shilo, in a sense, and come out the existing exit on your stove without alteration into an enclosed space with a riser just to one side of that exit, with a vertical port in it, similar to how they put their multiple riser systems together, as I recall. So the gasses would rise out the ceiling of the firebox, turn 90 degrees to run horizontally through the port, and then it would be business as usual. You would deliver your preheated secondary air into this space before the port somehow...Just my two cents. Edit: since writing this, I read Peter's explanation for what develops the ram horn...its a little different than I'd have thought, but I'm still not sure how it would translate into a vertical space.
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Post by labalme on Aug 30, 2015 22:09:32 GMT -8
Thank you all for the replies. I seem to have literally jumped into the fire.
In summary. I think I now have a better understanding of what is happening in the riser. I appreciate why a horizontal slot may not work to create a vertical vortex. I am going to investigate wing tip vortexes as a way to create a rams horn effect in a vertical flue. I am wondering about tubing heated air through the fire box to exit at a vertical wing tip attached to the flue wall. I will let you know how I get on.
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