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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. 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.
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. 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
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.
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