[Stoves] Charcoal stove design

[Paul Anderson]

Frank and all Stovers,

When combustible gases are produced (and CO is produced in the charcoal 
stoves), the air for combusting those gases would be the secondary air.

In typical charcoal stoves that air comes in over the top rim of the 
stoves, and is poorly mixed, and the result is massive CO into the 
room.   And very little air can enter when a pot is in place, especially 
if there is also a pot skirt.

Work on introducing secondary air via specific openings can be seen some 
nice work done by GIZ:

https://energypedia.info/wiki/File:ECLAIR_Benin_stove-factsheet_eng.pdf

More work needs to be done on this topic.

About reflective shinny surfaces, does anyone have any info that is 
related to stoves comparing metals (different status of shinny) and 
clay/mud/ceramic?   For example, how much more heat-to-the-pot is gained 
by using metal versus ceramic, and is that difference sufficient to 
justify (in part?) the extra cost of metal?   High mass ceramic/clay 
takes up more heat than does the metal, but is it really significantly more?

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 9/16/2013 1:00 PM, Frank Shields wrote:
>
> *Stovers and Paul Anderson, *
>
> **
>
> *Since good char burns with little smoke it seems there could be some 
> design improvements from the stove in Paul's attachment:*
>
> **
>
> *1)**We can use shinny surfaces, perhaps like a bowl under the 
> charcoal, to reflect the heat up to the pot.*
>
> *2)**Best to heat a pot we need a blast of hot air directed at the pot 
> -that is not available with radiant heat. I believe to get char to 
> burn we need the same; a blast of air directed at the char. Perhaps 
> because when the carbon goes to CO or CO2 it releases enough heat to 
> start another reaction IF there is oxygen stuck to that carbon 
> allowing a reaction to take place. If not the heat dissipates and does 
> little. *
>
> **
>
> *Wondering: if a basket of char fitted with a plate at the bottom set 
> on a spring pressing char up against a top grate. The container sealed 
> such that primary air being drawn is directed through a pipe blasting 
> 2cm from the top of the char bed (vertical pipe through the center of 
> the char).  The reflective surface directing heat produced to the pot. 
> Something like that?*
>
> **
>
> *Also; For char stoves is there ever a secondary? *
>
> **
>
> *Thanks*
>
> **
>
> *Frank*
>
> **
>
> **
>
> *Frank Shields*
>
> *Control Laboratories; Inc.*
>
> *42 Hangar Way*
>
> *Watsonville, CA  95076*
>
> *(831) 724-5422 tel*
>
> *(831) 724-3188 fax*
>
> *frank at biocharlab.com*
>
> *www.controllabs.com*
>
> **
>
> **
>
> **
>
> **
>
> *From:*Stoves [mailto:stoves-bounces at lists.bioenergylists.org] *On 
> Behalf Of *Paul Anderson
> *Sent:* Monday, September 16, 2013 7:24 AM
> *To:* Discussion of biomass cooking stoves; James S. Schoner
> *Subject:* [Stoves] Amount of charcoal for simmering
>
> Stovers,     (this will also be a "post" at my www.drtlud.com 
> <http://www.drtlud.com> website, BUT all replies and discussions 
> should be directed via the Stoves Listserv.   Dr TLUD does NOT carry 
> on separate discussions via comments to his website.)
>
> I am looking for a calculated answer that could give guidelines about 
> the sizes of charcoal-burning stoves, referring to how much charcoal 
> must be consumed for the cooking tasks.
>
> Question:   How much charcoal  is needed (per minute, or per hour, or 
> ??) to maintain a pot (5 liters?) of already-boiling water at the 
> simmer temperature of about 96 deg C?
>
> So many variables, but the replies can state whatever "givens" or 
> assumptions you wish to make, such as:
>
> 1.  Heat transfer efficiency of the stove-pot configuration:    Is 30% 
> about typical?   And does that vary between clay-mud charcoal stoves 
> vs metal charcoal stoves? Please specify, if your response takes that 
> into account.
>
> Reference:   See Experimental study for improving energy *efficiency* 
> of *charcoal stove* 
> <http://search.mywebsearch.com/mywebsearch/redirect.jhtml?searchfor=heat+transfer+efficiency+charcoal+stoves&cb=XQ&p2=%5EXQ%5Exdm002%5ES03729%5Eus&qid=499b92ca6697461da7047b820086bd7d&n=77DE8857&ptb=F7EBB78D-F7A7-4077-B858-0D10F0C7CB0E&si=COjP4cCp0rMCFao7MgodRQUALQ&pg=GGmain&action=pick&ss=sub&pn=1&st=hp&qs=&pr=GG&tpr=hpsb&redirect=mPWsrdz9heamc8iHEhldEVRIIbml7k2%2FvmB8U5crkZmbOTdLROAzdl%2F4ZQYYskvUwjkty6%2BVZ%2BNQiIr863cMN8jdRHpxuJvwsN2u6HPpdnPNB%2BBymTTjJMbwcgCi5H8Q&ord=1&ct=AR&>
> http://nopr.niscair.res.in/bitstream/123456789/3794/1/JSIR%2068(5)%20412-416.pdf 
> <http://nopr.niscair.res.in/bitstream/123456789/3794/1/JSIR%2068%285%29%20412-416.pdf>
> with reported efficiencies between 21% and 62%.
>
> 2.  Still air, no wind.
>
> 3.  Comments on types of pots (Stainless vs aluminum vs other).
>
> 4.  Lid or no lid.   Probably no lid because so much testing is done 
> with no lid on pot.
>
> 5.  Ambient temperature:   probably 22 to 27 deg C.
>
> 6.  Any other variables.?
>
> Comments:   The question arises because the TLUD stoves  (and any 
> other charcoal producing stoves) can be a convenient and low cost 
> source of charcoal for a household.   That household has some cooking 
> needs for LOW heat (simmer-type), and a charcoal-burning stove.
>
> Example from the world of stove testing:  a pot with 5 liters brought 
> to boil can be placed onto a charcoal stove for the remaining 45 
> minutes of the standard water boiling test (WBT).   The charcoal could 
> be already red-hot, having been placed in the charcoal stove directly 
> from the TLUD stove that made the charcoal.   How much charcoal is 
> needed for that simmering task?
>
> When we know the amount of charcoal, we can calculate backwards to 
> determine how much raw fuel was needed to make that charcoal.   (That 
> amount of raw fuel is approximately 5 X of the charcoal weight.)   
> Example:   100 g of char is produced from 500 g of woody biomass.
>
> Therefore, about 70% of the energy content of the raw fuel would be 
> available for INITIALLY putting heat into the pot.  I think we should 
> assume better than 40% heat transfer efficiency because that is the 
> target for Tier 4 stoves and can be achieved by gas-burning stoves.    
> 40% of 70% is 28%, so round it to 30%.    And 30% of the energy 
> content of the raw fuel is how much?     1 kg of wood has 16 MJ, so 
> 500 g has 8 MJ, and 30% would be 2.4 MJ.
>
> Somebody please complete the calculations:
>
> A.     2.4 MJ will raise 5 liters (5000 g or ml) of water how many 
> degrees?
>
> B.      How many g or ml of water can be brought to 100 C if starting 
> temp of water is 20 C?
>
> In the end, I hope we have some understanding about the amount of raw 
> fuel and resultant charcoal needed to accomplish the WBT with minimal 
> waste.
>
> Paul
>
> -- 
> Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
> Email:psanders at ilstu.edu  <mailto:psanders at ilstu.edu>    
> Skype: paultlud      Phone: +1-309-452-7072
> Website:www.drtlud.com  <http://www.drtlud.com>
>
>
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