[Stoves] Improving cooking with charcoal

Wed Oct 30 19:10:08 CDT 2019

All,

I look at my Stove Tec charcoal stove and note that it has a grate that 
lets air into the charcoal from below.  This gives a hotter and more 
lively flame than burning on a solid surface.  The rocks would do the 
same thing, providing better air flow. Reducing the charcoal quantity 
would reduce the air flow resistance through the fuel, again improving 
air flow.  This hotter more lively flame, with effective secondary air 
mixing, will burn the CO better.   Sam at Aprovecho has done a lot of 
research on burning charcoal, and would be one of those to be 
consulted.  He also found that if the CO passes through a flame it burns 
better, which makes sense because when it meets the secondary air, it 
will be preheated and the flame will provide an ignition source.  
Providing adequate air, space, time and heat to keep a CO flame going 
above the charcoal will help eliminate CO emissions.  I don't see 
anything new with the rocks, just a good application of existing knowledge.

Kirk H.

On 10/30/2019 4:13 PM, Ronal Larson wrote:
> Crispin, Kevin,  List,  cc Christa
>
> Note change in thread title.   The previous were under the name “no 
> subject”- which wouldn’t help researchers not around for this thread 
> (which is going well).
>
> 1.  My comments below were started before responding to a similar 
> message from Christa Roth - just sent.  So later readers please go 
> back to that "no subject" thread that was started a few weeks ago by 
> Kevin - reporting on three simple tests in three different African 
> countries (also identified below - now up to 4).  All show major 
> efficiency improvements when small stones and/or a second grate are 
> added to an existing charcoal-using stove.
>
> 2.  The main points for Kevin and others are (and hope others will 
> disagree or add/subtract):
> -  use a water boiling test - not a cooking test.  The latter is too 
> subjective on the right termination time, and is difficult to 
> replicate.  Also doesn’t give  the needed comparative information on 
> power and efficiency.
> -  use at least two standard fuel amounts;  maybe 0.3 and 1 kg  (this 
> now being the main discussion topic)
> - report something on the char - especially the size distribution. 
> (Which itself can be another test parameter).  Maybe a statement like 
> “32 pieces in the 1 kg - with a max/min range less than 2:1”
> -  report on the details of starting the fire. (Amount of Leaves, 
> paper, alcohol, wax etc).  See below on using a metal tube.
> -  details on the cook pot
> -  the amount of water should match the stove’s intended use - maybe 2 
> or (not and) 5 liters;  of course measure the amount boiled away. 
>  Report elevation, etc
> - times are important.  Measure the time to get fire started and put 
> pot on,  b) time to  boil and stop the test-   c) stop time - maybe 1 
> hour max, and d) time to tend  Don’t worry now about hot and cold starts
> - assume 30 MJ/kg for the char, unless you have more information.  The 
> right equations for per levels, energy used, and efficiency are all 
> over the place.
> -  give several photos of the stoves - with dimensions.  So others can 
> compare or try to duplicate
> -  Its fine to use unskilled testers - to save money.  Let approved 
> labs worry about CO, PM2.5 etc.   Amateurs (school kids) can do the 
> above test outline well enough.
> -  your four reported tests could be improved, but almost anyone using 
> a stove can help with numerical data.  We need a lot.  Your four 
> reporters all did well.
> -  cooking tests are not to be discouraged - but after water boiling 
> tests.  After you’ve picked a best (which could include economics on 
> the costs (and benefits) of an extra grate or two.)
> -  next tests can/should progress to details on the number and size of 
> the (free) stones and the number of grates.  Two extra grates (and 
> stones on one or both sides) may still improve the efficiency further.
> - report little details - the sizes of the pot and stove (air gaps 
> both vertically and radially), etc
> - report the amount of time spent tending the fire.  If there is air 
> control, explain that.
> -  Lastly -  plentiful details on the two main parameters now needing 
> study - the stones and the grates (materials, thicknesses,- not just 
> the diameter(s) and the number of holes).
>
> 3.  Concentrate all tests and discussions on stones and extra grates. 
>  They are the issue now - not the amount of char to be loaded or where 
> the best location for air holes, stove materials, etc.   We need 
> examples of dozens if not hundreds of stove designs - if we are ever 
> going to figure out how to optimize the main new parameters - stones 
> and grate numbers.
>
> Kevin -   thanks for putting all you time and energy in on these mods 
> that don’t seem in any way possible to pay for your expenses to date 
> (including going to Nairobi - please keep us informed on whether this 
> subject came up with anyone.)
> And next we can talk about charcoal-making stoves - which should make 
> money, not just save it.
>
>
> Ron
>
>
>
>> On Oct 27, 2019, at 1:28 PM, Crispin Pemberton-Pigott 
>> <crispinpigott at outlook.com <mailto:crispinpigott at outlook.com>> wrote:
>>
>> Dear Kevin
>>
>> This is an interesting exploration that may yield consistent benefits 
>> is someone is using that rather dreadful device.
>>
>> There are dozens of charcoal combustors in Africa and the one shown 
>> is one of the worst. Given that there are far better devices for 
>> burning charcoal, not to mention better ways to load the fuel, I am 
>> too surprised that just about anything you do would not improve it.
>>
>> Cecil Cook and I assisted GTZ's ProBEC North in the period 2007-2010 
>> to improve the appalling charcoal waste in Lusaka.  Cecil came up 
>> with an interesting analysis which was the result of interviewing 
>> users about how much money they could save before their pockets "grew 
>> holes". It was a bout 10 days income. Any stove that costs more than 
>> that was unlike to sell no matter what it did.
>>
>> A second thing observed was the widespread used of a metal tube as a 
>> chimney to speed the ignition. It seems the second test was conducted 
>> without lighting the fuel properly. I wonder if the tube was used for 
>> these tests.
> *[RWL:   This is an important practical piece of advise.  Can probably 
> save 10 minutes in the testing*
>
>>
>> Two additional things that would make testing more convincing. First, 
>> there is far too much fuel in the stove. Do people really use a kg 
>> and light the whole thing to cook a meal? I would expect something 
>> between 500 and 700 g.
>>
>> Second is that one should never have a pot sitting directly on the 
>> charcoal. It cannot possibly burn properly with the pot sitting on 
>> the fuel extinguishing the flames.
> *[RWL:   I think you have to place the pot on the char if that is 
> local practice.  Can do both. *
>
>>
>> That stove usually has the pot sitting on top of the lip of the stove 
>> with the fuel burning under it. The pot seals to the stove and the 
>> gases exit through the holes. That is why (in part) it is such a 
>> terrible cooker. It has poor aeration and very high CO contributing 
>> to its performance.
>>
>> More than ten years ago a much better stove was introduced, a metal 
>> version of the Maputo Ceramic Stove developed by a retired German 
>> metal worker from the MCS. This costs more than the one in the 
>> report, which I recall sells for about $1.50.
> *[RWL:  Any cite possible?*
>>
>> If that is the device someone is using, and the addition of the 
>> stones improves performance consistently, by all means continue. I'd 
>> like to see it operated with half the fuel loaded to represent more 
>> closely the typical pattern of use. I can't see the theoretical basis 
>> for the additional plate making any difference save that if it is 
>> loose, air can flow around the edge perhaps burning off some of the 
>> CO generated in the midst of the fire. As can be seen in the photo, 
>> elevating the fuel above the lip gets it into the open air where it 
>> can burn better.  It's is still pretty awful, though.
> *[RWL:  I can’t yet see the theoretical reasons either - which is why 
> I am pushing this thread (I keep saying Kevin has brought us two new 
> important ideas - backed up by four reports working with 
> very different stove (and earlier with wood-burning.  This list can 
> make this discovery get moving faster.  Kevin’s report this year on 
> stones with the 3-stone fire is already reported to have been adopted 
> by million in one small part of one small country - saving 40-50% of 
> the wood!*
>>
>> The Malgache stove popular in West and Central Africa is better from 
>> several points of view including that it elevates the pot above the 
>> fuel.
>>
>> If you want to burn charcoal reasonably well there should be 50mm 
>> vertical space between the fuel and the pot. That region should be 
>> sheltered from cross winds and aeration should be provided that 
>> reaches almost to the centre, if possible.
>>
>> As to the retention of heat in the stones, there is no doubt they 
>> will get hot. The main benefit of stored heat in a stove is to keep 
>> the char burning more completely as the fire dies.
>>
>> How a bout trying the experiment again using 350 g of charcoal and 
>> break it up so it can burn at a rate high enough to provide the 
>> cooking power needed. The fuel particle surface to volume ratio 
>> defines this. If you want more power, get more surface area burning 
>> at the same time. It should fit into the space under the pot when it 
>> is sitting on the stove lip.
> *[RWL:  See my comment above on reporting on fuel sizes.*
> *
> *
> *End *
> *
> *
> *Ron
> *
>>
>> It is can cook with 200 g there would still be lots left.
>>
>> Incidentally when burning a kg of charcoal and stopping with most of 
>> it left over, you should report the energy liberated as that of the 
>> charcoal ash-free (AF). This is because all the original ash in the 
>> fuel is still there at the end, which means the missing mass is 
>> combustible, not "average charcoal". Suppose the ash is 10%. Then the 
>> missing 200 g mass has the energy of 200/0.9 g = 222 g of charcoal 
>> with ash in it.
>>
>> Regards
>> Crispin
>>
>>
>> *From:*info at sun24.solar <mailto:info at sun24.solar>
>> *Sent:*October 27, 2019 9:01 AM
>> *To:*stoves at lists.bioenergylists.org 
>> <mailto:stoves at lists.bioenergylists.org>
>> *Reply to:*stoves at lists.bioenergylists.org 
>> <mailto:stoves at lists.bioenergylists.org>
>> *Subject:*Re: [Stoves] (no subject)
>>
>>
>> Here is areport from Zambia 
>> <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.google.com%2Fdocument%2Fd%2F167i50oweyfe23bRMnDSeJwlu0eM4IgTek6IO2C6JPes%2Fedit%3Fusp%3Dsharing&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832681885&sdata=YpL%2BDV4Jv3JJn7EOBjT5EA3jWIjF3B8CQkFz2NMriU0%3D&reserved=0>indicating 
>> that the rock bed and second metal grate improve the efficiency of 
>> the Zambian mbaula (all-metal) charcoal jiko by 41%.  Cooking time is 
>> also greatly reduced.  While these testers have no training, their 
>> results are consistent.
>>
>> This is such a simple modification that dissemination could be very 
>> rapid.  I hope some of you can try this.
>>
>> On Thu, Oct 10, 2019 at 1:37 PM K McLean <info at sun24.solar 
>> <mailto:info at sun24.solar>> wrote:
>>
>>     Listmates,
>>
>>     Has anyone tried this?
>>
>>     We seem to have significantly increased the efficiency of
>>     charcoal jikos by putting a bed of rocks on the jiko's grate and
>>     putting second metal grate on the rock bed.  The charcoal goes on
>>     the second metal grate.   2-3 cm rocks work.  It works in all
>>     metal jikos and clay jikos that we've tested.
>>
>>     Our testing is early and unscientific, but consistent. 25-50%
>>     less fuel used.  Here are three reports.  The Sierra Leone report
>>     has good photos at the bottom.
>>     Sierra Leone
>>     <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Ffile%2Fd%2F12MvBKjxq6PCGCcCHAjSYSeVXXvl7jWjD%2Fview%3Fusp%3Dsharing&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832691902&sdata=MqY7JaMTSg6tod8s%2BlvxR09foMAMqHWo2jqMdgCklfs%3D&reserved=0>
>>     Uganda
>>     <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Fopen%3Fid%3D1zQIY49E1vrfjYl7t5V_shvw70d67QirGWUrbW51tDxo&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832701907&sdata=agj%2F%2BbtHo6x%2FmUbUkLDYsXFkDWtBy89LwA7wrlnlBQo%3D&reserved=0>
>>     Kenya (very few rocks)
>>     <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Fopen%3Fid%3D1MPwHCwKEVqJvuybKB5Yj39nr8fbcopBP&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832711912&sdata=xQLz%2FJ6%2FdVVAD%2FkEfaX3r5phX01diAfAeimEmNph6Mo%3D&reserved=0>
>>     (The report authors are untrained and not native English
>>     speakers.  Especially the Kenya report contains many errors.
>>     Please focus on the consistent final conclusion that a rock bed
>>     and second metal grate significantly reduce firewood usage.)
>>
>>     This may be a very low cost, very easy way to greatly improved
>>     the efficiency of charcoal jikos.  I'd like to hear if there is
>>     already a body of work on this.  Here is my rough drawing:
>>
>>     <20191010_133359.jpg>
>>
>>     Thank you,
>>     Kevin
>>     /
>>     /
>>     /Kevin McLean, President/
>>     /Sun24/
>>     /https://sun24.solar
>>     <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsun24.solar&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832721923&sdata=Nsi14Kx03q4Xt4fYf%2FB9uW3JZpWTcQO2B13z5xUOBkM%3D&reserved=0>
>>     Sun24 Cookstoves Overview
>>     <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.google.com%2Fdocument%2Fd%2F1ZryS7gQ1q3zKLZPM2KcXdtIHbOYQp4PbloPqMvrlZ5Y%2Fedit%3Fusp%3Dsharing&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832731922&sdata=%2BqrwLKvoaPGUOXCbz78k4n%2BF7o5eqUqQVxZtyfVd7eE%3D&reserved=0>
>>     /
>>     /Tampa, Florida, USA/
>>     /+1 (813) 505-3340 <tel:+1(813)5053340>/
>>
>>
>>     /
>>
>>     /
>>
>> _______________________________________________
>> Stoves mailing list
>>
>> to Send a Message to the list, use the email address
>> stoves at lists.bioenergylists.org <mailto:stoves at lists.bioenergylists.org>
>>
>> to UNSUBSCRIBE or Change your List Settings use the web page
>> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
>>
>> for more Biomass Cooking Stoves,  News and Information see our web site:
>> http://stoves.bioenergylists.org/
>>
>
>
> _______________________________________________
> Stoves mailing list
>
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
>
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
>
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://stoves.bioenergylists.org/
>

-- 
This email has been checked for viruses by AVG.
https://www.avg.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20191030/488013db/attachment.html>