[Stoves] is this new?

[rongretlarson at comcast.net]

Crispin cc List 

See few inserts below. 

----- Original Message -----
From: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com> 
To: "Stoves" <stoves at lists.bioenergylists.org> 
Sent: Monday, January 21, 2013 11:42:28 AM 
Subject: Re: [Stoves] is this new? 




Dear Ron 



> I think we all recognize that you were designing a stove with an intent to consume char - not produce it, although the latter was possible in part with appropriate timing of extinguishment. 


There are a couple of answers here. The original patent is not fully reflected in the current model, mostly because no one has expressed interested in manufacturing this product. I no longer personally manufacture stoves, only prototypes. The ‘whole design’ includes the ability to close off the primary air completely should that be interesting to the user. It will also operate in a combined mode of partial burning of the char, or making it, or burning whole fuel. This approach is never discussed here – everyone refers to char making stoves or ‘the other kind’. There is no reason (as demonstrated) not to have all methods employed in a single device. 


[RWL2a: I am not sure I can agree with this last thought. Such a multi-purpose stove would certainly be very helpful in education and for research purposes. But I assume that if a buyer is most interested in making char, that features that do other tasks a nd that are even detr im en tal to making char are not necessarily desirable in the char-making stove market , especially if not coming for free.] 


The main reason for adopting the approach was to make a stove that could be fuelled and then operated with a controllable flame (power level) using a wide variety of fuels. If you re all at the time (2003) everything was a stick burning Rocket Stove or a fan-assisted gasifier. Or a Jiko, I guess. [RWL2b: Not sure when you joined "stoves" - but the early char-making stove discussions (>1996) were mostly (all?) natural draft. The intent then was to make char more sustainably than as mostly pr actic ed in the bush - for later use in char-using stoves . Biochar and bl owers (as I recall) came much later ] 


>Your objective seems to have been well met - especially with the reduced amount of secondary air in the latest mods.. 

The change was introduced in 2008 or 2009, can’t remember. It did reduce the total airflow and increased heat transfer but not so anyone would notice. It remains about 35% burning wood and >60% burning small amounts of charcoal (meaning at low power). Because it has not been properly tested in a good lab we don’t really know what the PM emissions are. When it was tested in Germany in 2004 it only got the repot ‘very low’. Even then, the test was done with a most inappropriate pot and the fuel affects things, plus the operator was inexperienced so I am hoping that will be corrected in the coming months. [RWL2c: Your first and second sentences relate to Alex' question - especially re "anyone would notice"). Any way to gu ess what the change in measu red efficiency would have been with the old and n ew hole arrangement s? I am assuming more than half the secondary air holes were del e ted (?) 


Also, I am not understanding the 3 5 and >6 0 % values. How does ">60%" equate to "small amounts of charcoal"? I think we shoul d also note favorably that the VESTO is one of the very few stoves designed with a built-in skirt. 


>Would you agree that if one is striving for char production, that the amount of primary air flow can/should be much reduced over the present design? 

The current layout can make charcoal from wood or wood pellets (and switchgrass pellets). The primary just needs to be turned off. If I were designing it for char production I would make a grate that can be dropped with a lever to dump it out. It is not convenient to tip a hot stove over, even one with a handle. [RWL2d: Agreed - but I am asking a different question - trying to alert others to how little primary air is needed when making char. I also like the lever design with variable open hole possibilities. Anyone found a better approach? ] 


As you know my view is that if someone wants charcoal they are far better off to build something that does it controllably to give a predictable result – something biochar experiments show as necessary. It should be a self-heating retort so there are no smoke emissions and the least possible amount of fuel is burned in order to process the resource. It is already done in several countries. There is very little waste heat if it is done properly so there is no question of cooking on such a device. The cooking-while-making-char is done at the expense of burning some of the char. There is nothing magical about it. [RWL2e: I agree that we don't know enough about char-making stove optimization (for soil propert y optimization ). But a few months ago, I had some dialog with Alex English and others on how char production temperature is closely (linearly ?) related to the power level (or watts/unit area). Way down the road we might see char produced at different temperatu res go for different prices - but there also are presently proponents for a wide range of temperatures. 

I cannot endorse the idea of retorts - which often have even less control over production temperatu re than do most char-making stoves. Runaway pyrolysis (uncontrolled final temperatres) i s a common problem with any retort , given the exothermic character of all char-making. It is not necessary to lose much char in a char-making stove. With the Lucia, there is not even any oxygen ever traveling through the fuel bed.] 


.>The only remaining design feature I can't see in the cutaway or your comments is how you are controlling secondary air flow with the right hand slide control. A similar (unshown) angular rotation slide? 



The secondary air is drawn into the stove by the updraft in the centre. The quantity of air is in principle, self-regulating. This is different from the ‘enter-at-the-bottom’ stoves where secondary air has to be controlled manually. My idea was to make the supply automatic based on the draft in the central space. [RWL2f: Not yet completely understo od. I believe that virtually every char-making stove (Lucia excepted - but it is not a TLUD) meets the standard of your first sentence. So I assume the first sentence means radially (usually inward , in a few cases also outward; not talking here about vertical flows?) moving secondary air entering somewhere close above the fuel bed. And the self-regulation exists similarly in all TLUDs (always more secondary air if more primary air). The thir d sentence about "enter at the bottom" is not yet clear. Does this refer to rocket stoves? I don't think so, since I don't recall any with much if any air control (primary or secondary) . O r some sorts of TLUDS? If so, which? Re the fourth last sentence, I think all TLUDS (of non-fan /blower category) do the same. Marc's questions relate to the downward flow of secondary air when the primary air is all blower-supplied. That topic still seems noteworthy - and not (?) in the Vesto? (And not in the usual Belonio design s .) 


When the fire is turned down and the whole thing is hot, the amount of secondary air flowing in drops. I manufactured a small number with a secondary air controller and a second lever but the marketing people (at New Dawn Energy Systems) demanded it be removed because it was too difficult to teach people in a couple of minutes how to operate the stove. Oh well. I even made a tool for bending it into its complex shape. What was a big surprise is that one of those few stoves made it to the Philippines and was given to YDD in Central Java where I found it, unused, in 2012. The second controller makes it possible to have 100% control over what happens without perfecting the design (it is not optimised yet). If the design principles were studied and applied with some modelling effort, I believe the full value of the invention can be realised. [RWL2g: I guess from th is that the f i rst secondary air "lever" looked som ewhat like th at for the primary air. But the detailed flow (any up or down or both) is still not yet clear. I would certainly like to hear of any testing of secondary air with this lever (or any other stove developer 's approach). All th is is to focus on the control of E A - and on its impact on efficiency testing. It seems likely that this could be fairly influential, so hope som e one can prove that the New Dawn marketers were short-sighted (as I thi nk Alex was driving on). 




One the major benefits of the design is that the flame is kept away from the combustion chamber walls which greatly extends the working life, plus the fact the wall is cooled from behind which extends its working life (something invented by a Brit in 1948). In fact we have never sold a replacement combustion chamber. Perhaps there are 100 reasons for that, but I think it is because they don’t burn out. Consider how brief is the life of metal combustion chambers that are either insulated behind (a big no-no) or have the flame running against the wall most of the time. [RWL2h: This is a very important design topic. I gather that the Envirofit folk are stat ing they have a new (NASA developed) stainless with much longer life (and I think no means of keeping the flame from the wall). I support your thoughts on using ceramics - but (having tried) know these also have problems. Any materials spec ialists reading this can provide a lot of help to the stove community. The (interior cylinder) approach that Marc has described should have the potential to lower the chimney steel temperature a lot (?) as the secondary air pre-heati ng removes wall heat . I presume that the metal in the fuel area is not as big a problem - and wonder if anyone readin g this can also report , as Crispin has, on wall metal life. I personally never ran a design long enough to learn anything on the life of tin cans. Ron ] 




Regard 

Crispin 


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