Dear Ron,
we have two types of extruded briquettes. One set has a
diameter of about 19 to 20 mm and the other has a diameter of about 12 to 13
mm. However, because of the problematic electrical supply in the rural
areas, we have now opted for the honeycomb briquettes, which are made
manually, using a mold. The honeycomb briquettes have a diameter of
about 12 cm and height of about 3 cm. Each briquette has 13 vertical
holes. Paul Hait wanted to know if we are using the thermal array type of
arrangement of briquettes in our stove.
[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?
How does this diameter change
during a run?
Is there a brittle "ash" skeleton
remaining at the end?
How long does a single briquette
last? (presumably one being long enough for cooking the meal you
describe)
Could you make one twice as tall
to cook for twice as long? (In a different culture)
Is there a "haybox" effect also?
(some cooking after the single charcoal briquette is
consumed?)
Could you describe how lighting is
achieved?
Approximately how high above the
briquette do the flames appear - and how does this distance change during a
single cooking?
What are the prices of all of the
components of the system - including for a single
briquette?
What lifetime do you expect for
the charcoal burner? (presumably the cookpot portion is much
longer-lived)
Will this particular pot and
shield be available for export to interested members of "stoves"? at what
price?
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?
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?
Have you measured the output temperature of the
exhaust gases?
Same for temperature of the outermost
wall?
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.
(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 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.
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.
