[Ron Larson] For new stoves list members, we should
say that Paul Hait developed a charcoal using system in which the
"pillow" type briquette was carefully placed vertically in slots and in rows
in such a way as to get the radiation from one impinging on another - with
good air flow. I don't recall the percent reduction in charcoal
consumption - but it might have been a factor of four or five. He also
used stainless steel (reflective) parts and a clever fold-up design to get
higher efficiencies and user convenience.
Paul's question is important in "holey" (or
"honeycomb") briquettes, because the same principal of getting good use
out of the radiated energy (inside the holes as opposed to going off to be
absorbed in something other than the cook pot) helps improve combustion
enormously.
In your case, what is the
diameter of the 13 vertical holes?
The studs in the mold that create the holes are 5
mm thick. The holes may be slightly wider due to shrinkage during
drying.
How does this diameter change
during a run?
We haven't really observed. They may get a bit
wider as the char burns.
Is there a brittle "ash"
skeleton remaining at the end? Yes
How long does a single briquette
last? (presumably one being long enough for cooking the meal you
describe).
It takes about
45 to 50 minutes to cook the beans. Rice cooks earlier, but it doesn't get
charred if left in the cooker for a longer period. The briquette generally
burns upto about an hour.
Could you make one twice as tall
to cook for twice as long? (In a different
culture)
The dimensions of the briquette can be changed by
changing the mold. However, it must be noted that charcoal does not
produce a flame like wood. Therefore the pot must sit very close to
the briquette with just enough gap for flue gases to
escape.
Is there a "haybox" effect also?
(some cooking after the single charcoal briquette is
consumed?)
Yes, there is.
We found that one can cook a meal with even 70 grams of
charbriquettes, which is most probably due to the hot box
effect.
Could you describe how lighting
is achieved?
We use wax
coated paper strips, which burn for about 2-3 minutes, producing a
relatively tall flame. After placing the briquette on the grate of the
stove, a couple of these strips are ignited below the grate. This is enough
to ignite the briquette.
Approximately how high above the
briquette do the flames appear - and how does this distance change during a
single cooking?
Charcoal does not produce flames like wood. There
is just a faint bluish glow coming out of each hole in the briquette. After
about half an hour, the bluish colour changes to red. The pot is placed just
1.5 cm above the briquette.
What are the prices of all of
the components of the system - including for a single
briquette?
The stove and cooker system consisting of a
charcoal burning stove, the cooker pot with lid, three cookpots slung in a
wire cage, and the sleeve that surrounds the cooker and the stove, together
cost Rs.350. Except for the stove, all parts are made of stainless steel.
The briquettes cost Rs.7 per kg to the consumer. The villager gets Rs. 5 per
kg. 1US$=Rs.48.
What lifetime do you expect for
the charcoal burner? (presumably the cookpot portion is much
longer-lived)
About 5 years in dry weather conditions. On
the coast, with high humidity and salty air, the mild steel corrodes very
fast, and the life of such a stove could be just 6 months. We are
encouraging some of our potter friends to make a suitable stove out of terra
cotta.
Will this particular pot and
shield be available for export to interested members of "stoves"? at what
price?
Yes, we are
keenly interested in exporting. We would be happy to get the same price as
above, but the consumer in a foreign country would have to pay more due to
the transport, packaging, customs duty and local distribution costs.
The price would have to be calculated separately for each country, taking
the above factors into consideration.
The answer is "no", because with a
single honeycomb briquette, no arrangement is possible. When we were
using the cylindrical (extruded) briquettes, be just weighed 100 grams of
them and put a single layer of briquettes spread evenly on the grate of the
stove.
We use grain starch as binder. The flour fallen on
the floor of a flour mill is swept and sold by the mill operator at a price
of Rs. 2 per kg (Rs.50 per US$). The cost of the char is Rs. 3 per kg.
Because the flour is not costlier than the char, there is no restriction on
the quantity of the flour. We boil about 400 g of flower in 1.5 litres of
water and mix it thoroughly with 1 kg char to make a dough. This dough
is filled into the briquette mold and the briquettes are dried in the
sun
[Ron
Larson] Does this mean that you might have a wet mix of
about 2.9 kg - going to a dry batch of maybe 1.5 + kg - so
this recipe might give 15-20 briquettes - with a raw material cost of about
5 rupees or US 10 cents - so one briquette (one meal) has a raw material
cost of less than 2/3 cent?
1 kg char and 400 g flour would together
weigh 1400 grams. After sun drying, we expect the briquettes to retain about
8 to 10% moisture. This calculates to about 15 briquettes from this dough.
As stated above, the price payable to the villager who makes the briquettes
is Rs. 5 per kg (about 10 US Cents) and the housewife in a city would get it
at Rs. 7 per kg (bout 14 US Cents). Therefore, a single briquette weighing
100 grams would cost a tenth of this.
Our stove is a commercially available charcoal
burning stove, made of mild steel sheets. The stove is 11 cm tall. The
cooker consists of a stainless steel container, about 21 cm tall and 18 cm
wide, closed with a lid, which is not too tight. The gaps between
the container and the lid allow steam to escape. Inside the cooker,
three cook pots are stacked one on top of the other, so that three things
(rice, beans and vegetables) can be cooked simultaneously. The cooker sits
on the stove with a gap of about 12 mm between the burning briquette and the
bottom of the cooker pot. The cooker and the stove are together
enclosed in a vertical stainless steel sleeve, about 29 cm tall and 19 cm
wide. There is thus a gap of about 5 mm between the cooker and
the sleeve, through which the flue gases pass.
[Ron
Larson] : We have talked often about the optimality of this 5 mm
dimension. Any experimental data? None so far. But in some of the prototypes,
where the gap was wider, it took more fuel to complete the
cooking.
Have you measured the output temperature of the
exhaust gases? No.
Same for temperature of the outermost wall? No.
If we knew the weight loss per unit time
(presumably higher at first?), we could estimate the power output
levels. There are several on the list who could do this measurement
quickly using their balancing scales.
We too can do it, but it would
have to be done without the water or the food in the cookpots, because the
system would also be losing water vapour.
(RWL): I
believe there is much to be learned from your geometry - and hope others
will try similar geometries. This is a very high efficiency being
reported - and possibly is very clean as well - given the high temperatures
that are likely being achieved because of the honeycomb nature of the
briquette.
(AD - we look forward also to hearing about emissions at some
time. I'll bet they also look very good.)
The system is very clean. Housewifes in the cities
are very happy with this system, because it is almost as clean as cooking
with kerosene or LPG and at a much lower cost.
The top 4 cm
of the cooker are not covered by the sleeve, because the cooker is provided
with two small handles that are attached to the sides of the cooker at this
height.These handles allow the cooker pot to be lifted out of the
sleeve.
The efficiency was tested by the usual water boiling
test. The housewives who used the cooker were also astonished by the
fuel economy of this stove. Using a traditional wood burning
cookstove, a housewife would have to use 3 kg wood to cook the three items
mentioned above.
We have no means of controlling the air flow. We may
be able to increase or reduce the power output of the
stove by using more or less of the fuel.
Yours A.D.Karve
[Ron Larson]:
Have you tried (or could you try) cooking with two
briquettes of half-height?
Might power level control then
be possible by rotating one briquette
relative to the other?
In Johannesburg, the GTZ folk
were showing an example of the "punch-out" "Turbo" stove from Finland that
we have discussed on this list a few times. (Incidentally -very nice
looking product that comes shipped in a big flat (pretty heavy)
box.) It had a very clever air flow control (that I had not
previously noticed) by rotating one set of holes relative to another.
You might be able to do this same with the briquettes to achieve power
control.
This can be tried, but with a charcoal fire there
is always the danger of producing carbon monoxide by choking off the air
supply. There is absolutely no smoke, but we shall have to measure the
carbon monoxide levels in the kitchen with our system.
AD
Thanks and congratulations again - for what I think must be the world
record. I believe this is better than my electric range.
Ron
A.D
1. Thanks for sending this interesting story
on. Not a permanent problem - hopefully, just a new point to
add to your educational program. Old ideas die
hard.
2. What are the dimensions and weight of your
briquettes? (Number making up 100 g?)
3. You probably said this earlier - but what is your
recommended binder formula?
4. You have described your new stove previously, but I think
it needs a repeat - as 70% is just fantastic.
Congratulations!!
5. I do not recall anyone claiming this high an efficiency
value. I believe you have incorporated what we might call a
"convection-enhancing-sleeve" which is probably key to this high
value What is the gap width and height you have chosen in the
model now in production? What is the method of
measurement?
6. Do you have any means of controlling air flow and power
level of this stove design?
7. It is becoming more clear all the time that the Ashden
award people made a wise choice.
Ron
Dear Tom and Paul,
I spent the last four days at Phaltan, looking at the
charring kilns installed by ARTI at various sites. The operators
in most cases are unemployed rural youth. After demonstrating the
process to them on our own kiln they were provided with a kiln
of their own, and they were asked to char sugarcane leaves in their own
villages. In all the cases, they had unofficial advisers, who had
already made charcoal using the traditional kilns. In the
traditional process, the biomass to be charred is loaded into a kiln and
ignited. One has to regulate the air supply very judiciously in
order to have the right temperature to cause the biomass to char, but at
the same time not provide so much oxygen that the biomass burns down
completely to produce ash. In our oven and retort model, the
biomass to be charred is enclosed in barrels and it never comes in
contact with oxygen. We therefore keep all the airholes fully
open, so that the biomass surrounding the barrels burns intensely to
pyrolyse the biomass inside the barrels. Our
entrepreneurs unfortunately followed the advice of the
traditional charcoal burners in their villages and contrary to our
advice, closed all the air vents, resulting in a very slow burn of
the biomass surrounding the barrels. This not only increased the batch
time but also in producing biomass which was just roasted and not
charred.
Most of them were totally discouraged, firstly because
of low output and also because of its poor quality. The correct
process had to be demonstrated again at each site. We thought that
we had developed a fooproof process, but it turned out that we were the
fools believing that the villagers would easily be able to produce
char using our technology. Our technology, if correctly employed,
would yield about 50 kg char per 8 hour shift.
The char is sold in the form of briquettes.
We started out with the extrusion process to convert the char
into cylindrical briquettes. But in the field, there are problems with
electric supply (either too low voltage or no electricity at all).
So, during my stay at Phaltan we took the decision to provide the
entrepreneurs with molds to produce the so called honeycomb briquettes
manually. These briquettes look like mud pies, they weigh 100 grams each
and each briquette has a set of 13 holes. So when it is ignited, the pot
is hit by 13 flames. I myself produced these briquettes at the rate
of one per minute. Thus by using our mold, a person can
produce 50 kg dry briquettes per day. If the entire family
works on this process, they can earn Rs. 250 per day (US$ 5), which is
more than what an average industrial worker earns in a
city.
We have developed a stove-and-cooker system for using
the char briquettes most rationally. Through using a very
scientific design, we achieve 70% efficiency with our stove-and-cooker.
Just 100 grams of briquettes can cook rice, beans and vegetables for a
family of family. We tested various prototypes and have now given
orders to a stainless steel pots manufacturer to mass produce this
cooker. We expect to get the first batch of cookers in about
a fortnight and then see how we can market them. We shall
sell them very cheaply (at practically no profit), because the user of a
cooker is the potential buyer of the briquettes.
Yours
Dr.A.D.Karve, President,
Appropriate Rural Technology Institute
Pune,
India.
