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Using Clay Flue Liner for Burn Tunnel & Heat Riser?  RSS feed

 
Jerry Ward
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Hello,

Has anyone tried using a clay flue liner for the burn tunnel and heat riser? I know it would be a bit complicated to form the corners of the J tube, but I know a mason with one of those big concrete saws.

On a related topic I'm interested using something other than cob, has anyone played with brick or concrete?

Thanks,
Jerry
 
allen lumley
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Jerry W. : what you are discribing a cob free stove, is a conventional Masonary Stove, There is an Interior section, parts of which - do to thermal shock occuring during normal operation, need to be free floating and not cemented into the system, a lot off Paid Masonary Stove Craftsmen order this part shipped in from far away - Cost $5,000, then build the rest of the stove around it ! rocket stove Mass Heaters are a poor mans solution, world wide there have been (estimated) a 100,000 built - this is technology that works, As a suggestion, read Ianto Evans' book rocket mass heaters, and consider finding a cob work shop
 
Jerry Ward
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As I understand a masonry heater it doesn't have the "rocket" part. I would think in a RMH you still have to deal with thermal expansion somehow, or is cob that much more flexible?
 
allen lumley
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With the Masonary heater you have slower build up of the internal heat that allows high efficiency wood burning, see if you can find a local wood fired pizza oven or bakery in your area, be prepared to show up at 5 a.m. for the time when the bakery builds its fire ! -After that it gets boring , but stand in front of one of these ovens when its hot and working and you are sold forever ! I have a secret weapon in my quiver , I know a plasterer who has thousands of plaster/cob formulas dating back to the 1800s and I just do what ever he says, outside of that I would be talking thru my hat ! I have built 3 rocket stoves, and helped on the build of 2 rocket stove Mass Heaters, and they work ! Try www.Cobcottage and find where you can get I. Evans' 'Rocket Mass Heaters' downloaded to You for ? $15.00 ? also 'cob' books Allen L.
 
Chris Sturgeon
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Jerry. I don't think raw or even bisque clay would last or have the thermal/insulative qualities that make a good combustion chamber nor heat riser. However I've been thinking that ceramic would fit the bill. Any pottery folks here that can tell us about getting a ceramic pipe fired?
 
Chris Burge
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I too have considered getting a bag of some high temp clay and using it to form at least the riser liner, but I think it would need to be mixed with a good deal of perlite to improve the insular properties. Then, I would have to find someone with a nice deep kiln to fire it in and hope it doesn't crack

There is such a thing as 'refractory body' clay, which is mighty spendy, but I think it can be fired to cone 13.

Porcelain is a good compromise since it can be fired to cone 10 and is not much more in price than cone 10 stoneware-- which might work, but it would be harder to knead in the perlite.

[note: cone 10 = ~2300F, cone 13 = ~2400F... so, not much difference]
 
Jerry Ward
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I listened to the podcast with Ernie & Erica, any info on the pre-cast shippable core?
 
Satamax Antone
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Joe Morgan
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Help me understand this - I'm new to the whole concept: Why would you want vermiculite in the liner clay? Wouldn't it be more useful as a layer outside the riser, fire box, etc?
Also, if one were to use raw or dug clay, wouldn't the process of using it essentially vitrify it?

Looking at the pic of the 8000 year old greek (or were they roman) versions of clay risers made me wonder. We also have clay "tile" - cylinders of various sizes that were used to drain fields or lined wells - laying about our farm. Wouldn't they work if held in place with hi-temp mortar?

Thanks for any insights -

Joe
 
allen lumley
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JOE MORGAN : Let me try to answer a few of your questions, (from my point of view) .

For years we tried to use a metal Heat Riser/Chimney, 1/4'' thick-ish for longevity, then pile on the insulation on the outside of Heat Riser to create high temps. within the heat Riser.
The goal was to create the high temps needed to have complete combustion of ALL the pyrolyzed wood gases. Recently we have moved the insulation to the inside of the Heat Riser, resulting in the wood gases being burned at much higher temps, much quicker, new types of insulation are undergoing field testing in hopes of finding better materials that will do all this and give us longevity !
So - the answer to your question about vermiculite, The vermiculite is there as insulation, only enough clay slip is added to the vermiculite to be able to shape it ! ( and keep it from being carried away downstream! )
As the hot gases hit the underside of the top of the drum they churn themselves into a doughnut shape, and as they give up their heat, radiating out through the drum, they cool and fall, creating the ability to push the exhaust gases horizontally 30 + feet through the Thermal Mass!
So - The last place we want insulation is ether on the inside or outside walls of the 55 gal drum !
Yes, there are places within the combustion 'zone' that would vitrify clay, and yes any 6''-ish or larger, clay pipe esp. those fired high enough to have a glaze can work for a Heat Riser if insulated on the outside.

Please do not take any of my comments to reflect poorly on the existing methods of making Rocket Stove Mass Heaters, they can only be matched for efficiency ,total combustion of all gases and cleanness, by The various top-end wood stoves equipt with a catalytic converter and even then a good share of the heat from that type off heater is wasted up the chimney !
A Homeowner built ' rocket stove mass heater' will work for years, using less wood than conventional wood stoves, if built using todays techniques , In 5 -10 years your rocket will be still working, and if a more efficient Heat Riser is created, and is affordable, then the barrel can be removed and the Heat Riser replaced ! In he meantime you've enjoyed your wood stove and someone else paid to do the Testing. Hope this helps, - Pyro-maticly yours Allen L.
 
Joe Morgan
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OK, thats helpful. Still a couple questions:

From what you have explained the cooling air in the barrel sinks, but it must also be "pushed" by the rising air, correct?

Can a vermiculite/clay riser be poured thick enough to insulate well without cracking? Is there an ideal thickness?

On my wood stove I used vermiculite/concrete about 8:1 for an insulation layer under the firebrick. It has good comprehsive strength but crumbles easily and therefore needs to be protected were its exposed.

From what I've read a stove-pipe with a vermi/concrete wrap wouldn't last? Does the stovepipe actually deteriorate with the heat?

Thanks -

Joe
 
allen lumley
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Joe Morgan :Again these are My answers as I understand them ! The cooling air is denser and will sink, it is the combination of the difference in the internal temperatures that appears to create a " Hot Air Engine " capable of providing the work energy of 'pushing' the exhaust gases 30 + feet through the thermal mass ! - 1st and 2nd laws of thermodynamics -
This next answer satisfies me (only?) For my next rocket stove mass heater which I am putting in a Yurt, it will have - black heavy wood stove grade 6'' stove pipe / clay stable-ized vermiculite / 10'' stove pipe - ! I accept that this is a trade off, and i am happy with it, time will tell how long it takes the oxygen in that super heated environment to 'burn /rust' the stove pipe to failure! I am hoping to upgrade to a Silica stable-ized rock wool tube within a couple of years, IF, I can afford it !

I hope that you will avail yourself of the chance to read all of Ianto Evans' great book 'Rocket Mass Heaters' available for down loading to you for $15.00 U.S. from WWW.rocketstoves.com. - Nada comes to me !
''
Another great source of information comes from Ernie and Erica Wisner - both Stewards in these forum pages, also www.ernieanderica.info/ - Hope this helps Pyro-maticly yours Allen L.

'
 
Erica Wisner
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Well, speak of the devil...
Now that you're invoking my name...

Seems like I've seen a lot of mention of clay-stabilized vermiculite on the threads lately. Just want to reiterate that perlite (popped volcanic glass or 'rock popcorn,' horticulture grade is those white lumps found in potting soil) works much better than vermiculite in this application. Perlite has better insulation value to begin with, and it retains more of that insulation value when mixed with clay. Vermiculite is mica layers rather than a foam; it stays crumbly even with a lot more binder, and once you get enough binder in there to do some good you've essentially filled all the air pockets. Vermiculite may theoretically tolerate slightly higher temperatures, but in practice I've never seen the perlite sintered or fused beyond the first skin-thin layers.
There are also some nifty refractory board products out there, basically pressed rock-wool, and we used something similar for the shippable core. Much spendier, but the performance is amazing and we are hoping the longevity stacks up too.

We did try some experiments with ceramic chimney liners recently; the heat stress between the hotter and and the cooler end seems to be too much for them, we cracked all three after only two test-fires. Firebrick does work really well in this application. We have also considered shorter segments of ceramic tile, so the heat shock on each unit would be less. More experiments would be worthwhile; firebrick and kiln brick are pretty easy to stack, but a pre-cast unit that you don't have to check dimensions on could be even better. Another option is to fit a cardboard form to make stacking easier, then burn it out if you don't want to remove it.

Clay-based materials in general are traditional for masonry heaters, and cob (monolithic earthen masonry) is just a very old and highly compatible masonry technique that's not hard for beginners to learn. Like any masonry, there's work involved, but it's not difficult. A lot of the modern masonry substitutes are both more expensive and less suitable - even refractory 'cements' crack, and Portland cements are not an improvement at all. Unsuitable for high-temperatures, hard and brittle so you have to get the expansion join detailing 100% right; and if you guess wrong the cement is guaranteed to ruin most of your masonry units so you can start over. Great for the industry, not so great for the user. I appreciate David Lyle's reminder that a really good stove is designed so that it can be pulled apart and put back together in a hundred years if renovations are needed.

If you want to mess around with changing the design, I'd second Allan's recommendation to look at other masonry heater designs, and choose a proven design that works well. There's a lot involved, and the art is more about understanding and protecting your materials through careful design and testing. Clean fire is a powerful thing to work with.

-Erica W
 
allen lumley
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what she said ! Pyro-Allen
 
allen lumley
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what she said !

Erica, thank you, I got into a lengthy discussion elsewhere about vermiculite stable-ized with clay slip for cheap D.I.Y. Insulated stove pipe and carried that mind set over to this discussion, which was doing No one any favors! Yes I can only agree with the person responcible for most of the "Rocket Knowledge" I have . Lord knows Ernie tried to beat it into me , but without Erica there to Translate I don't think I would have got a 1/4 of what I Did ! Thank you Ernie and Erica Wisner, and a 'tip of the hat 'to Paul Wheaton , - Pyro-Allen

Joe Morgan : sorry, the combination of two different conversation streams both mentioning vermiculite was a little like slipping blinders on a horse, my Field of vision was limited to looking in one direction only - Again what she said !!! Allen
 
John Master
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Erica (or anyone) Is there a downside to using the horticulture grade or do I need to find the masonry grade perlite? I was told by a perlite mfg that the only difference was water added and grain size.
 
harry kaneer
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If my nomenclature is correct (Kiln brick is the light weight while fire brick is the heavy weight) thermal conductivity means the ease with which a material transmits heat through itself. A high thermal conductivity will pass the heat straight through and that would explain the spalling in the concrete under the shippable core. If kiln brick, which has a low thermal conductivity, were used under the core it would reduce or eliminate the spalling of the concrete. Also
the temps reached are a design factor that causes a large amount of oxygen to be consumed much like the venturi in a carburetor of a super charged engine.
For home heat purposes is 3000F a good idea when it is inside a building loaded with accelerents? A design that would produce no more than 2000 seems sufficient for home use and thus both kiln and fire bricks can be used in combination with fire clay as slip. Everything will burn if the temp is high enough.
My experience is with Army wheeled vehicles and 500HP Scotch Marine boilers.
 
allen lumley
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Harry Kaneer : You have a clear grasp on 90% of the information, which was a requirement to be 'elevated in grade above his (always his ) peers in evaluations!
How ever the Fire Kiln brick is the heavy and dense brick, which has the high conductivity (and retention!) The lighter weight brick has/have many ,
many trapped air pockets and act primarily as insulation, at higher temps the insulate properties of the lighter brick cause it to shed heat energy back towards the
source as reflected/refracted energy!

I am actually a little vague here myself, there is a point around 2400*f where we start creating the NO, NO2, NO3s that are a further worry to the health of this Planet
and ALL her Children, 3000 degrees without Oxygen supplemental augmentation is probably impossible but also not really needed, which is not to say a specific
region can't reach those temperatures as an isolated region- possible forging of iron !! Certainly a rocket mass heater that quickly reaches temperatures in the low
2000 *F such be sufficient for 97% of All RMHs ever Built ! For the craft - Big AL !






 
harry kaneer
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allen lumley wrote:Harry Kaneer : You have a clear grasp on 90% of the information, which was a requirement to be 'elevated in grade above his (always his ) peers in evaluations!
How ever the Fire Kiln brick is the heavy and dense brick, which has the high conductivity (and retention!) The lighter weight brick has/have many ,
many trapped air pockets and act primarily as insulation, at higher temps the insulate properties of the lighter brick cause it to shed heat energy back towards the
source as reflected/refracted energy!

I am actually a little vague here myself, there is a point around 2400*f where we start creating the NO, NO2, NO3s that are a further worry to the health of this Planet
and ALL her Children, 3000 degrees without Oxygen supplemental augmentation is probably impossible but also not really needed, which is not to say a specific
region can't reach those temperatures as an isolated region- possible forging of iron !! Certainly a Rocket Mass Heater that quickly reaches temperatures in the low
2000 *F such be sufficient for 97% of All RMHs ever Built ! For the craft - Big AL !







 
allen lumley
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John Master : I have heard at least third hand that some of the non-horicultural grade penlight has been 'treated with Silicone ' and that could mean anything !
To reduce water absorption ! Hopefully some one will chim in and we will all get a little smarter ! Big Al
 
Laine MacTague
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I must have missed something somewhere; is the shortcoming of cob with perlite as a riser that it won't withstand high temps, or that it doesn't have other qualities that would make it a good material for a shippable core, or ?... Am I on the wrong thread with this question?
 
allen lumley
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Laine MacTague : Please re-read the Thread Extension Posted By Erica Wisner above, Ernie and Erica Wisner are our Dynamic Duo , and Co-
Administrators in these Forum/Threads !

The Question asked and Answered here, refers to a well insulated Exterior side of the Heat Riser! We are trying to insulate and separate the
Two streams of hot gases, the hottest within the heat riser, and the rapidly cooling, shrinking and falling exhaust gases between the outside of
the Heat Riser and the Barrel!

Presently we have Two (2) ways of making up the Heat Riser, With or without a Fire Brick, as long as we allow for the falling exhaust gases to
Freely flow down the sides of the inside of the barrel, Minimum gap ~2''~ , than any good efficient Insulation on the outside of the Heat Riser
is probably sufficient!

Perlite packed around a fire brick Heat Riser and held in place by a protective metal skin between it and the "Barrel Gap" will be most insulating.

Perlite mixed with clay slip looses some of its insulating value, and simply needs to be thicker to insulate 1/2 as well!

A second alternative, best tried after a successful first build, is to use sacrificial forms consisting of an inner metal skin and an exterior metal skin
into which is poured a mixture of Perlite and clay slip ! The Heat Riser thus made is more delicate than a Heat Riser made of "Fire Brick''and then
insulated, but should last at least a couple of heating seasons if carefully protected - especially when placing the barrel down over top of it !

So- The specific Answer to the General question asked, is that the Perlite needs to be contained, or otherwise mixed with Clay Slip to render a
rigid self supporting structure- and by doing so it is only half as insulate as it was before being mixed with Clay Slip !

Vermiculite, when mixed with Clay Slip looses even more of its insulate values before it becomes as rigid as a good Perlite/Clay Slip Mixture !

The outside of a Heat Riser made up of fire brick can also be wrapped in Rolux (SP) rock wool and held in place with chicken wire,this is insulating
and works quite well, I am confident to say that many Rocket Mass Heaters RMHs have been made this way over the last #years with no reports
of Chicken wire? Rock Wood failure ! I hope this answers the question you were asking and is timely, For the good of the Craft !

Think like Fire, Flo like a Gas, Don't be a Marshmallow! As always, Comments and Questions are solicited and Welcome! PYRO - Logically Big AL
 
Laine MacTague
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I appreciate the try, Allen, but I don't feel like I found out what I want to know - although it was a lot of valuable info! I'll try and restate my question:

A cob-with-perlite riser has been tried, and, to some extent, worked. Given that fact (let me know if its NOT a fact), does the search for a different material continue because;

1) by the time the cob-w-perlite is providing the necessary temperature differential between the interior and exterior of the internal riser, the riser is so thick that the space between it & the barrel is too constricted; or

2) cob is inappropriate as a shippable core material (if so - why); or

3) it is either assumed or known that a greater temperature differential than cob-with-perlite provides (at the maximum thickness possible within a barrel) would result in better stove function*; or

4) experimenting with materials is interesting and fun; or

5) some combination of the above reasons (list the combination, please); or

6) some other reason or reasons


*If 3) is the case, I'd like to know what exactly is meant by "better stove function".
 
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Laine MacTague : W.o.w., Let me try again, And this time we will talk about longevity only !

1) Home made 'fire' brick With sawdust or straw - can be highly insulating, especially after the organics are reduced to char/pyrolyzed
empty spaces. By refusing to absorb the heat energy of our fire we can Quickly get to the high temperatures that allow complete
combustion

--- Not very durable, easily crushed, definitely not suitable for the Feed tube, Burn Tunnel, Heat Riser

2) Insulative combinations of Clay slip and Perlite - More highly insulating - some additional Refractory (Heat Reflective )properties

--- Fragile. easily crushed, not suitable for Feed Tube or Burn Tunnel, the inner and outer sleeves/forms into which the Clay Slip/Perlite
is poured can be sacrificial forms meant to burn out during a separate on site manufacturing step allowing the 'Fired' C.S./P. Heat Riser
to be delicately transported to a final resting place on top of the (predominately 'fire' brick) Burn Tunnel!
- - C.S./P Can also be used as an additional insulating layer around the outside of a well laid up 'fire' Brick Heat Riser, further Thermally
separating the two flowing streams of rising and falling hot exhaust cases !
- - Great care should be used in moving the C.S./P Heat Riser into place, And in setting the barrel down over it- Cleaning and removing
fly ash requires a delicate Touch ! Anecdotal evidence of C.S./P. Heat Risers lasting 4-5+years

3) lite 'Fire' Brick 28-30 ounces each nominal size, Very insulating and very good refractory properties Can be used within the
entire combustion zone, and Rocket Mass Heaters constructed with them 'come up to operating temperatures' quickly,

- - Durability issues,This brick does not respond well to larger chunks of wood being dropped on it when loaded through the Feed Tube
hole, It also cools down quickly at the end of a burn cycle, making most new fires slightly hard to light, not a problem for a skillful/self
taught operator( Better Stove Function?) One end of 'fire' brick hot and the other end cold can cause spalling and fractures. Near the
end of a burn cycle there may be some unburned charcoal not consumed and left behind !

4) 100 yr old red red soft house brick, Erica Wisner reminds us of a good test for this kind of brick, you should be able to use it like
sidewalk chalk, leaving behind a distinct Red, red orange streak behind! Cheap/free is insulating, and kinda refractory at the upper end
of 'operating temperatures' (while glowing a dull red) Anecdotally 10s of thousands still around

---not a good candidate for Durability, wear or heat stress, - the cheapest way to have a working rocket mass heater R.M.H. 'nuf said!

5) Dense fire brick : over 7+ pounds a brick, Very durable, slightly less insulating, Refractory at 'high operating temperatures',
anecdotally handles 'Heat Stress' well. At the end of a burn, usually nothing is left, stove drafts well and relights easiest !

---it takes a while to warmup the additional mass of a RMH made this way, slightly delaying the start of the More efficient wood gas
pyrolyzing/burn ! By retaining heat energy, there is a minor chance of some thermo-syphoning,

Now with material types and longevity mentioned the rest becomes easy ! With properly sized barrels we do not really have a Heat Riser
/Barrel Gap issue, the gaps mentioned are minimum distances.

If we could find a perfect material to form the inside wall of a "Perlite Only'' Heat Riser, 1'' is as effective as 2'' of C.S./P., and 4'' of a
C.S./Vermiculite combination ! Much experimentation is being done by other members to find a D.I.Y. Way to rigidize Perlite or Verm-
maculate. If we could use the buying power of everyone who wanted a RMH, costs would fall !

Cob does not ship well, it is to fragile, and todays craftsmen instructors are not far removed from the 'If it is scrounged, found material'
'it will make the best RMH'

Remember Cob Will not burn, it will not rot, bugs don't eat it and its cheaper than dirt ! (And you already have all the ingredients close
to your home/backyard! ) - You payed 500 dollars for WHAT (plus shipping)

If we call every part of the rocket mass heater prior to the start of the Cob Thermal Mass Bench the 'Rocket Burner' then we are in favor
of insulating everywhere around the outside of the 'fire' brick making up our Combustion Zone. The main problem besides curiosity and
an eagerness to experiment, is that the more insulating and refractory the material the less well it performs when compressed!

Besides trying to find a Perfect Refractory/insulating material, much work is being put into design modifications to preserved the Refractory
and the insulating properties of todays/ tomorrows materials. Here would be a good place to stop a minute, and then look up 'Aerogels',
with such compounds 'just over the horizon', it is unlikely that todays builders will ever be satisfied !

Re-reading some of your earlier posts makes me wonder what it is that I am missing, is it possible that because of the large amount of
experimentation within the Craft you are only able to visualize the RMH as an incomplete project !?! For the Good of the Crafts! BIG AL
 
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