[Stoves] Charcoal burning, secondary flame vs no flame

Paul Anderson psanders at ilstu.edu
Mon Aug 3 18:59:20 CDT 2015


Crispin,

I have no basis for doubting nor the time or talent for reviewing your 
calculations.   If someone does have revisions or corrections, I hope 
they speak up right away.

Otherwise, here is my comment:

Concerning the issue of what is the heat lost (not liberated) if CO from 
charcoal escapes instead of being burned, you have illuminated my (our) 
understanding.

THANK YOU, Crispin, for once again providing technical and 
quantitatively supported excellent information!!!!   You are (IMO) a 
_major asset_ to this Stoves Listserv and to our entire community of 
Stovers.

And a further question:   In a "typical" charcoal stove that is 
generating dangerous amounts of CO, what percentage of the consumed 
carbon is "well burned" (and becomes CO2) versus the carbon that is only 
transformed into CO?   The reply might need to give some range of values 
or qualify the responses relating to a "high heat" charcoal fire versus 
a "low heat" charcoal fire, probably with the latter being 
proportionately much more of the carbon ending up as CO, with a 
corresponding 75% loss of the heat value for that amount of charcoal.

There is a big difference between (hypothetical numbers follow) 50% of 
carbon going to CO instead of CO2 (with the loss of 75% of the heat 
value of half of the carbon [75% of 50% = 38% lost heat) versus only 5% 
of carbon going to CO (75% of 5 % = 4% lost heat).   Of course, it is 
the CO that can kill you that is more important than some amount of lost 
heat.

Comment:  We are discussing "char-gasification", the oxidation of solid 
carbon (but as charcoal it is not necessarily pure) into either CO or 
CO2.   The O2 that enters as primary air can result in either CO or 
CO2.   The role of secondary air is a very different story for 
char-gasification than it is for the combustion of pyrolytic gases as in 
the context of TLUD micro-gasifiers.

Answers / comments from anyone would be appreciated.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype: paultlud      Phone: +1-309-452-7072
Website:  www.drtlud.com

On 8/3/2015 2:02 PM, Crispin Pemberton-Pigott wrote:
>
> Dear Roberto
>
> It is unlikely that you will be able to burn charcoal without any CO2 
> at all.
>

> In the centre of a charcoal flame, under the middle of the pot, there 
> is often a very high CO2 level, but it is so hot, excess C is 
> available and it is  absent of free oxygen so it breaks apart to make 
> 2 CO.
>
> If you can estimate the mass of CO2 and the mass of CO you can 
> calculate the difference. C to CO2 is 33 MJ/kg (close enough) and C to 
> CO is a bit more than 8. So you lose ¾ of the available heat energy if 
> you fail to burn the CO to CO2.
>
> For 600m of char, (assuming 85% carbon) the loss would be 32.8 x 0.85 
> x 0.75 x 0.600 = 12.6 MJ loss
>
> Or 29.5 MJ/kg for the char x 0.6 kg to get the available heat  = 17.7 MJ
>
> And
>
> Subtract the CO loss: 0.600 kg x 0.85 carbon x 75% x 32.9 carbon heat 
> = 12.6MJ loss, the same thing. Heat released by burning C to CO = 5.1 MJ.
>
> If you have a portion of the gas as CO2 and another as CO, you can 
> pro-rate the heat available as ‘yielded’ or ‘lost’ according to 
> CO/(CO2+CO) and CO2/(CO+CO2) times the carbon mass times 32.9 MJ/kg.
>
> The CO loss is closer to 74.5 % of the CO2 energy if you really want 
> to be picky.
>
> Regards
>
> Crispin
>
> Hi,
>
> I want to know what is the difference in combustion efficiency between 
> burning charcoal with secondary flame (burning CO) vs burning without 
> secondary flame (CO escape to the chimney).
>
> For example, burning 3 kg in a TLUD produce 600 grs of charcoal. Then 
> if we decide to burn this charcoal, burning with secondary flame is 
> more efficient than burning charcoal with no secondary flame.
>
> How can I measure this difference?
>
> **
>
> Greetings
>
> Roberto Poehlmann
>
>
>
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