To: <[EMAIL PROTECTED]>
Date: Mon, 4 Apr 2005 00:12:35 +0700
Subject: [Bioenergy] Part 2 - Biogas from starch and sugar
PART 2 (this message has been cut to conform to the file size
requirements of the listserv)
Production
This system uses starchy or sugary material as feedstock. 1kg of
sugar or starch yields about 400 litres of methane, within a period
of 6 to 8 hours. This quantity is enough for cooking one meal for 5
to 6 persons. The biogas produced by this system contains
theoretically about equal volumes of carbondioxide and methane, but
in reality, it turned out to have less than 5% carbondioxide. This
phenomenon is explained by the fact that carbon dioxide dissolves in
the water in the fermenter vessel and diffuses out of it through the
1 cm gap between the fermenter and the gas holder.
We are getting about 250 g of methane per kg of flour. The values
are approximations based on the volume of the gas and the crude
analysis that was done in a chemistry lab. We are making
arrangements with a government certified analytical lab for getting
both the gas and the slurry analysed, and hope to come out with more
reliable figures. The grain flour contains almost 10% protein and
about half a percent of seed coat material, along with small
quantities of fat in the embryo.
Mr. Malar wanted to know the production potential of oilcake to
methane. The biodigester working on oilcake of Madhuka indica
actually uses 30 to 32 kg of oilcake (and not 16) to produce about
15 cubic meters of methane. The time taken by this reaction is just
24 hours. The weight of methane produced would be about 5.5 kg,
having a clorific value of roughly 10,000 KCal/kg.
[ From Nandu] Because of the residual oil and the high protein
content of the oilcake, its calorific value is much greater than
that of starch from cereal grains, rhizomes or tubers. As a result,
this particular system is 1600 times as efficient as the
conventional biogas plants. Another person, with whom we are
collaborating, has a biogas plant producing daily 40 cubic meters of
gas. He used to feed it daily with 1000kg dung, but now he is using
daily a mixture of 200 kg cattle dung and 15 kg sorghum grain flour.
He is reluctant to switch over completely to sorghum, as he feels
that the bacteria may go on strike if they did not get their daily
dose of dung. In his case, he replaces 800 kg dung by 15 kg flour
and reduces the reaction time from 40 days to one day. He thus gets
an efficiency that is 2000 times that of the traditional system. In
the moving dome reactors that we use, the gas holder telescopes into
the fermenter. Therefore, the total volume of the system is twice
that of the volume of the gas that you expect to get from it.
Starch, sugar, powdered oilcake, grain flour or powdered seed of any
plant, take about the same time to digest and also produce the same
amount of gas. It is likely that our high methane content is a
result of a reaction 4H2 + CO2 = CH4 + 2H2O. Because very little
work has been done by scientists on use of high calorie feedstocks,
there is quite a lot of speculation about the high methane content
that we are getting.
Under our temperature and pressure, 1 cubic meter of biogas produced
by a typical dung based biogas plant (50% each of CO2 and CH4)
weighs about a kg. CH4 is about a third as heavy as CO2., therefore,
in this case, 500 litres of CH4 would weigh about 250 g and the
remaining 500 litres of CO2 would weigh about 750 g. I our case, we
get almost pure methane, and it takes about 1 kg of flour to produce
500 litres of it. Therefore we came to the conclusion that our
biogas plant gives 250 g of methane per kg of feedstock. We haven't
found much difference in different species of grain
I wish to correct the figures of oilcake used and biogas generated.
It takes daily about 30 kg oilcake to produce 15 cubic meters of
gas. But this gas consists of almost pure methane. It is not a case
of co-generation, but direct fermentation. Cattle dung was used only
initially as a source of bacteria, but for more than a month, they
are using only oilcake.
I had never heard of the digestion accelerator, but would love to
have it, if it is genuine. In any case, our biogas plant uses waste
starch or sugar in any form. Thus spoilt bananas, oilcake of
nonedible oilseed (e.g.castor or Jatropha), mango kernels, seed of
practically any plant, rain damaged grain, etc. all work beautifully
as feedstock. The material must be pulped or powdered. These
substances are highly digestible and the methane production starts
within a few hours after their introduction into the biogas plant.
About 2 kg of dry matter in any of the above forms would yield about
500 g of pure methane in about 8 hours. This period can be halved by
heating the biogas plant.
Advantages
The short retention time and the small feedstock quantity enabled us
to reduce the size of the gas plant. Our biogas plants have a
floating dome that acts as a gas holder, whereby the dome is a
plastic water tank that is available in the market.
We have installed almost 100 biogas digesters operating on starch,
and all are working without any hitch
Even industrialists are interested in this technology, because the
LPG for industrial use costs almost twice as much as LPG for
domestic use.
The retention time of dung in the dung-based biogas fermenter is 6
weeks, while that of starch is only 6 hours, which is why the volume
of the fermenter could be reduced. The biogas produced from starch
has about 60% methane by weight, while that produced from cattle
dung has only 25% methane by weight. As a result even the 800 litres
produced by my biogas plant is enough for cooking the meal of a
family. We are trying to commercialise this new biogas fermenter. It
costs only US$30 as against US$250 for the conventional biogas
fermenter
The gas produced by this system has thus almost the same calorific
value as LPG. It burns without smoke or soot, producing an almost
invisible bluish flame similar to that of LPG.
This system is much easier to operate than the dung based biogas
plant, because of the relatively small quantities of feedstock and
effluent slurry to be handled. The effluent slurry generated daily
by the plant is just a couple of litres. It can be used as manure
for plants growing around the house. The 500 litre biogas plant,
mass produced from moulded plastic drums, would cost about Rs. 3,500
(US$ 78). The smallest cattle-dung based domestic biogas plant costs
about Rs. 12,000 (US$267). It requires daily 40kg dung, and owing to
the retention period of almost 40 days, such plants have a minimum
capacity of 2000 litres. They generate daily 80 to 100 litres of
effluent slurry. Daily handling of such large quantities of
feedstock and effluent is considered to be arduous and bothersome by
users.
The residual slurry of a biogas fermenter is a good organic source
of plant nutrients, because the process of methane formation removes
CO2 and CH4 from the biomass. Because of the selective removal of
these elements form the biomass, the other constituents such a
N,P,K,Ca, Fe, etc. get concentrated in residual slurry.
The new system has a total internal volume of about 400 liters. Its
small size allows the system to easily be accommodated inside the
kitchen. It generates from 1 to 5 liters of effluent daily, which
contains all the minerals in the original feedstock. Thus, the
effluent can be used as manure. The prototype fermenter, in
continuous operation for a year, has been successfully tested with
various feedstocks such as waste flour collected from the floor of a
flour mill, sugarcane juice, macerated sugarcane, leftover food,
flour of no edible seeds, and powdered oilcake of no edible
oilseeds. This technology does not rely on products meant for
consumption by humans or animals.
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From: adkarve
To: Robert Deutsch
Sent: Thursday, March 31, 2005 11:44 PM
Subject: Re: Text compiled from exchanges
Dear Robert,
I went through the extracts from the stoves list. I have no
objection to any of the material being reproduced. However, some of
it may need to be confirmed. The feedback from the users is that
they would like to have more gas, about 1000 litres than the 500
litres that our present model delivers. This would raise the price
of the gas plant by about Rs.1000 (US$ 22), if we purchased the
existing water tanks for this purpose. We are however negotiating
with a plastic manufacturer to get the tank at a lower price. We are
also working on other feedstocks, which would be cheaper to use than
the starchy or sugary feedstocks. I shall let you know about it when
I a have the necessary data.
yours
A.D.Karve
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