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: [email protected]
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*
*[email protected]*
*www.controllabs.com*
**
**
**
**
*From:*Stoves [mailto:[email protected]] *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:[email protected] <mailto:[email protected]>
Skype: paultlud Phone: +1-309-452-7072
Website:www.drtlud.com <http://www.drtlud.com>
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