[Stoves] Stoves Digest, Vol 95, Issue 26 top lit updraft burning

[Ronal W. Larson]

Norbert and list:

	Thanks for more useful information.  Few more questions below.


> On Jul 27, 2018, at 6:22 PM, Norbert Senf <norbert.senf at gmail.com> wrote:
> 
> Hi Ronal:
> 
> By way of explanation, these appliances are house heaters and are very removed from gasifier type single pot cooking stoves. A typical mass is in the 2,000 - 4,000 kg range, which is used as thermal mass (heat storage). Here are some examples:
> http://mha-net.org/html/gallery2.html <http://mha-net.org/html/gallery2.html>
	[RWL1:  I should have referenced that site myself.  These are works of art!  Yours near the end is one of the best looking.
	1a.  Because they can burn whole logs,  the cost per unit of supplied energy (absent initial cost) must be lower than any other fuel source. 
	1b.   Do some MH's ever recommend use of coal?
	Being able to use stored energy must be a big selling point, in terms of time spent in keeping a house warm.  
	1c.  Is there ever a cooking application (besides ovens) where mass is so important  (question for everyone).   
	1d.  What heating efficiency is claimed by MHA members?  (can you get to 90%?)


> Batch fuel loads are 15 - 30 kg., once or twice per day. Biochar has never been a consideration, and I only got interested in it recently.
	[RWL2a:  Which is why I have to keep this dialog going a bit longer
> 
> They typically have a flue damper which needs to be closed to retain the heat. This means all the charcoal has to be burned, or you risk carbon monoxide poisoning. Some countries like Germany and Austria don't permit flue dampers due to the potential safety issue.
	[RWL2b.  I have read that burning charcoal (not making it) is a favored form of suicide;  via CO.
> 
> With an underwire air system (grate), burning up charcoal is easy, but underfire air was found to be dirty once we started measuring PM and CO.
	[RWL3:  Apologies for "underwire" - my computer doesn't have "underfire" in its dictionary.   You are giving here one of the main advantages of making and saving char in a cookstove - this is a topic broader than efficiencies.
> 
> For the last couple of years I have experimented with using an airtight system, like the Austrians, that allows the combustion to be stopped by shutting off the combustion air and also preventing flow through the chimney. This can be done at any time once the batch has burned the volatiles and is into charcoal mode. This is a huge convenience, because you can walk away and don't have to worry about closing a flue damper too early. Coincidentally, the tighter you can manage to make it, the more charcoal you can make. The next morning, there may still be some live coals and I scoop all the remains into a metal ash bucket with a tight lid, that extinguishes everything.  Somewhat similar to the bottom part of a Kon Tiki kiln. Charcoal yield is roughly 5% by weight.
	[RWL4:   I suppose you are giving a reason (difficulty in achieving a tight fit) some TLUD cookstove manufacturers choose to burn up their char.  I like the solution achieved by Julien Winter of a burnable string (sort of a fuse) that dumps the char automatically and immediately when the pyrolysis front hits the bottom.
	We promoting char-making stoves would not be satisfied with 5% (always hear more than 15% and sometimes up to 25% or more - by weight).  If I wanted a MH that maximized char production (to make more money while heating), what char-production do you think might be achievable?   
	Gordon West and Bill Knauss are doing heating (not cooking) with a continuous TLUD design - but need (as do most all) pellets or maybe chips - vs your use of much cheaper logs.  So you might have a leg up in costs per kg of char production - but they might (?) have a leg up in being able to produce more char per log.  Any thoughts here on economics?
> 
> Contraflow refers to a particular way of running the internal heat exchange channels, ie downdrafting. It is native to Finland. Combustion is complete by this time. In the traditional Austrian system, the firebox has less height and immediately downdrafts before entering additional heat exchange flue channels. With this setup you get very good mixing in the flames in the downdraft channel this way.
	[RWL5:  I still haven't visualized the geometry.  Can you send us to a technical paper on this?    I think your use of "down drafting" here does not mean airflow through the fuel bed, so I am not sure how this might fit into char-making.  I do think it might be possible to have a BLDD design for heating (with char-making) what we haven't found yet for cooking.  This possible because you must have a very tall chimney and a tight system - so you have much greater natural draft than possible with most any cookstove.

	Again many thanks.  We interested primarily in cooking with wood obviously have a lot to learn from those devoted to heating with wood (MH units must go back centuries if not millennia).

Ron
> 
> Norbert
> 
> On Fri, Jul 27, 2018 at 5:00 PM, Ronal W. Larson <rongretlarson at comcast.net <mailto:rongretlarson at comcast.net>> wrote:
> Norbert and list:
> 
> 	1.   Thanks for the historical review and comments.
> 
> 	2.   I hope you can add a few more comments from the MHA and SNEWS perspectives on the relationship between top lighting and char-making.  I know that you have yourself been making char in your own MH - and perceive that to be fairly unusual for your profession.  Specifically, in the 1992 time period, was there anyone doing top lighting for char-making purposes?  
> 
> 	3.  You wrote:  "At Toronto we talked with Tempcast, who told us that they have abandoned their underfire air completely and are developing a new air system based on top down burning."
> 	On this list, top lighting always (??) refers to char-making first (emphasize first).  Many of the commercial stoves like the Phillips and the Mimi Moto, adjust air flows when the pyrolysis front hits the bottom and then consume the char.  We have been told that the Dutch developer of the Phillips regularly (?) did stop his own personal unit when the pyrolysis front reached the bottom - and did save the char.
> 	My question on this sentence is whether we should call this operation more like a kon tiki - which has zero "underwire air".  Can you say more about the Tempcast "new air system".   I am suggesting here there may have been top-lighting but not up draft.  And presumably Tempcraft was not interested in making char/
> 
> 	4.  Also can you say something about the term "contraflow"  in this sentence:  "Elsewhere in this issue you'll find a report on some initial testing we did on contraflow heaters at Jerry Frisch's new lab."    This sounds like it might have been a downdraft system.  On this list we only hear from Gordon West and Bill Knauss with their continuous TLUD, in which the pyrolysis front is stationary, because the fuel is being continuously fed upwards.  They are optimizing towards char production.  Could your "contraflow" approach produce char?
> 
> Thanks again for this and other great contributions to this list.
> 
> Ron
> 
> 
> 
>> On Jul 27, 2018, at 1:30 PM, Norbert Senf <norbert.senf at gmail.com <mailto:norbert.senf at gmail.com>> wrote:
>> 
>> Just to add a somewhat random historical data point on the TLUD discussion:
>> 
>> Masonry Heater Association first published an article on top ignition for updraft batch burns in masonry heaters in 1991.
>> Here's my follow up article from 1992:
>> http://mha-net.org/docs/v8n2/docs/TOPDOWN.pdf <http://mha-net.org/docs/v8n2/docs/TOPDOWN.pdf>
>> 
>> It has become a mainstream ignition method for wood stoves and fireplaces since then. 
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> 
> 
> 
> 
> -- 
> Norbert Senf
> Masonry Stove Builders
> 25 Brouse Road, RR 5
> Shawville Québec J0X 2Y0
> 819.647.5092
> www.heatkit.com <http://www.heatkit.com/>
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