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.
