[Stoves] ***SPAM*** Cooking Hole Modification to Three Stone Cookstove - Update

[K McLean]

Good question, Robert.

Other sizes work. 25x25x25 cm works well with maize stalks in home
kitchens.  We recommend 45x45x30 for school kitchens for more firepower.

Different sizes may work better depending on the fuel and cooking needs.
25x25x25 seems to be a good general recommendation since we train on a mass
scale and cannot customize based on the specific needs of a family or
community.

Squared holes work best with stacked fuels like maize stalks. For a
25x25x25 hole, the stalks should be cut to about 23 cm and stacked in
crisscrossing layers.  This method seems to get the most fuel in the hole
while allowing air to circulate within the pile.  Cylindrical holes would
work better for fuels like wood shavings and cow dung patties.

Generally, the area across the top equals firepower and depth equals burn
time.  25x25 area across the top gives good heat with maize stalks.  If the
depth is more than 25 cm, the fire goes out before the bottom fuel burns.

Denser fuels burn longer.  For example, normal size firewood burns over
three hours in a 25x25x25 hole.  This is much longer than needed.  We will
put common bricks in the hole to raise the floor, reduce the burn time and
save fuel.

On Wed, Jun 22, 2022 at 1:17 AM Robert Taylor <rt at ms1.hinet.net> wrote:

> Hi Kevin
>
> Very interesting. What's the significance of the hole size and shape, 25 x
> 25 x 25 cm? Is it optimal for good combustion, or simply convenient based
> on pot size and fuel quantity?
>
> Best regards
>
> Robert
>
> On 22-Jun-22 5:13 AM, K McLean wrote:
>
> Adding a 25x25x25 cm hole to traditional open-fire cookstoves may end the
> collection of firewood from forests in many areas.  By piling fuel in the
> hole beneath the cookpot and lighting the pile on the top, the fuel burns
> long, hot, with no tending and with less smoke.  And by quenching the
> embers, cooks make biochar.
>
> We found that most woody biomass bigger than thin twigs burns well in the cooking
> hole <https://youtu.be/DmzQFCp2kNI>.  Firewood the size that is typically
> burned in unmodified three stone cookstoves burns for three hours without
> tending.  Much less smoke is emitted than from an unmodified three stone
> cookstove.  A colleague estimates that the amount of wood in the cooking
> hole would burn for 30-40 minutes in an unmodified three stone cookstove.
> Here's a video
> <https://drive.google.com/file/d/15V4vTJxO1Lcm0wFzB96pQT9jvgjaXkwh/view?usp=sharing>
> .
>
> Thick twigs burned without tending for 1.5 hours.  Thick twigs and small
> branches are abundant and unused in much of Africa.
>
> The cooking hole also works with crop waste (maize stalks and cobs,
> cassava stems, banana peels, bean stems, ...), elephant grass, bamboo,
> large sawdust and wood shavings, sawdust briquettes, dung patties and
> more.  Depending on the fuel, the fire will burn without tending for 20
> minutes to several hours.  Here's our training video
> <https://youtu.be/DmzQFCp2kNI>.
>
> Women can:
>
> - All but stop collecting firewood.
> - Leave the kitchen to do other things once they start the fire.
> - Make biochar.
>
>
> And 8-12 common bricks can support two cookpots over one cooking hole
> allowing two meals to be cooked with the same amount of fuel and time it
> takes to cook one meal.  The time to boil is only a few minutes longer than
> for one pot.
> [image: 2 burner drawing.jpg]
>
>
> In much of Africa, most people know how to make bricks.  We show them how
> to make free custom bricks to line the cooking hole.  Here is a video
> <https://drive.google.com/file/d/1b2WvePKX_ofnELUWhexqQZR4NyCrXxnH/view?usp=sharing>
> .
>
> Kevin McLean
> Sun24
>
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