Gober Gas Methane
Gobar Gas Methane Experiments in India
(From The Mother Earth News)
It's been a wild, exciting ride... but our blindly wasteful
squandering of the planet's fossil fuels will soon be a thing of the
past. In the United States alone (the worst example, perhaps, but not
really unusual among "modern" nations), every man, woman and child
consumes an average of three gallons of oil each day. That's well over
two hundred billion gallons a year.
If we continue burning off petroleum at only this rate -- which
isn't very likely since population is climbing and the big oil
companies remain chained to "sell-more-tomorrow" economics -- experts
predict the world will run out of refineable oil within (are you ready
for this?) n30 years.
So where does that leave us? Well, number one, we obviously must
get serious about population control and per capita consumption of
power and, number two, if we don't want to see brownouts and rationing
of the power we do use, we'd better start looking around for
ecologically-sound alternative sources of energy.
And there are alternatives. One potent reservoir that's hardly
been tapped is methane gas.
Hundreds of millions of cubic feet of methane -- sometimes called
"swamp" or bio-gas -- are generated every year by the de- composition
of organic material. It's a near-twin of the natural gas that big
utility companies pump out of the ground and which so many of us use
for heating our homes and for cooking. Instead of being harnessed like
natural gas, however, methane has traditionally been considered as
merely a dangerous nuisance that should be gotten rid of as fast as
possible. Only recently have a few thoughtful men begun to regard
methane as a potentially revolutionary source of controllable energy.
One such man is Ram Bux Singh, director of the Gobar Gas Research
Station at Ajitmal in northern India. Although some basic research
into methane gas production was done in Germany and England during
World War II's fuel shortages, the most active exploration of the
gas's potential is being done today in India.
And with good reason. Population pressure has practically
eliminated India's forests, causing desperate fuel shortages in most
rural areas. As a result, up to three-quarters of the country's annual
billion tons of manure (India has two cows for every person) is burned
for cooking or heating. This creates enormous medical problems -- the
drying dung is a dangerous breeding place for flies and the acrid
smoke is responsible for widespread eye disease -- and deprives the
country's soil of vital organic nutrients contained in the manure.
The Gobar (Hindi for "cow dung") Gas Research Station --
established in 1960 as the latest of a long series of Indian
experimental projects dating back to the 1930's -- has concentrated
its efforts, as the name suggests, on generating methane gas from cow
manure. At the station, Ram Bux Singh and his co- workers have
designed and put into operation bio-gas plants ranging in output from
100 to 9,000 cubic feet of methane a day. They've installed heating
coils, mechanical agitators and filters in some of the generators and
experimented with different mixes of manure and vegetable wastes.
Results of the project have been meticulously documented and recorded.
Facts about gobar* <http://ww2.green-trust.org:8383/2000/biofuel/
methane.htm#gobar> gas
Cow dung gas is 55-65% methane, 30-35% carbon di- oxide, with some
hydrogen, nitrogen and other traces. Its heat value is about 600
B.T.U.'s per cubic foot.
A sample analyzed by the Gas Council Laboratory at Watson House in
England contained 68% methane, 31% carbon dioxide and 1% nitrogen. It
tested at 678 B.T.U.
This compares with natural gas's 80% methane, which yields a
B.T.U. value of about 1,000.
Gobar gas may be improved by filtering it through limewater (to
remove carbon dioxide), iron filings (to absorb corrosive hydrogen
sulphide) and calcium chloride (to extract water va****).
Cow dung slurry is composed of 1.8-2.4% nitrogen (N), 1.0-1.2/a
phosphorus (P2O5), 0.6-0.8% potassium (K2O) and from 50-75% organic
humus.
About one cubic foot of gas may be generated from one pound of cow
manure at 75 F. This is enough gas to cook a day's meals for 4-6
people.
About 225 cubic feet of gas equals one gallon of gasoline. The
manure produced by one cow in one year can be converted to methane
which is the equivalent of over 50 gallons of gasoline.
Gas engines require 18 cubic feet of methane per horse- power per
hour. *Hindi for "cow dung"
This comprehensive eleven-year-long research program has yielded
designs for five standardized, basic gobar plants that operate
efficiently under widely varying conditions with only minor
modifications (see construction details of 100 cubic foot digester
that accompany this article)... and a treasure trove of specific,
field-tested principles for methane gas production.
Ram Bux Singh has compiled much of this information into two
booklets, BIO-GAS PLANT and SOME EXPERIMENTS WITH BIO-GAS. The set of
two manuals is available Air Mail for $5.00 from Ram Bux Singh, Gobar
Gas Research Station, Ajitmal, Etawah (U.P.), India. The following
information has been adapted, by permission, from the handbooks:
FERMENTATION
There are two kinds of organic decomposition: aerobic (requiring
oxygen) and anaerobic (in the absence of oxygen). Any kind of organic
material -- animal or vegetable -- may be broken down by either
process, but the end-products will be quite different. Aerobic
fermentation produces carbon di- oxide, ammonia, small amounts of
other gases, considerable heat and a residue which can be used as
fertilizer. Anaerobic decomposition -- on the other hand -- creates
combustible meth- ane, carbon dioxide, hydrogen, traces of other
gases, only a little heat and a slurry which is superior in nitrogen
content to the residue yielded by aerobic fermentation.
Anaerobic decomposition takes place in two stages as certain micro-
organisms feed on organic materials. First, acid- producing bacteria
break the complex organic molecules down into simpler sugars, alcohol,
glycerol and peptides. Then -- and only when these substances have
accumulated in sufficient quantities -- a second group of bacteria
converts some of the simpler molecules into methane. The methane-
releasing microorganisms are especially sensitive to environmental
conditions.
TEMPERATURE ACIDITY
The proper pH range for anaerobic fermentation is between 6.8 and
8.0 and an acidity either higher or lower than this will hamper
fermentation. The introduction of too much raw material can cause
excess acidity (a too-low pH reading) and the gas-producing bacteria
will not be able to digest the acids quickly enough. Decomposition
will stop until balance is restored by the growth of more bacteria. If
the pH grows too high (not enough acid), fermentation will slow until
the digestive process forms enough acidic carbon dioxide to restore
balance.
CARBON-NITROGEN RATIO
Although bacteria responsible for the anaerobic process require
both elements in order to live, they consume carbon about 30 to 35
times faster than they use nitrogen. Other conditions being favorable,
then, anaerobic digestion will proceed most rapidly when raw material
fed into a gobar plant contains a carbon-nitrogen ratio of 30-1. If
the ratio is higher, the nitrogen will be exhausted while there is
still a supply of carbon left. This causes some bacteria to die,
releasing the nitrogen in their cells and -- eventually -- restoring
equilibrium. Digestion proceeds slowly as this occurs. On the other
hand, if there is too much nitrogen, fermentation (which will stop
when the carbon is exhausted) will be incomplete and the "left over"
nitrogen will not be digested. This lowers the fertilizing value of
the slurry. Only the proper ratio of carbon to nitrogen will insure
conversion of all available carbon to methane and carbon dioxide with
minimum loss of available nitrogen.
PERCENTAGE OF SOLIDS
The anaerobic decay of organic matter proceeds best if the raw
material consists of about 7 to 9 percent solids. Fresh cow manure can
be brought down to approximately this consistency by diluting it with
an equal amount of water.
BASIC DESIGN
Central to the operation and common to all gobar plant designs' is
an enclosed tank called a digester. This is an airtight tank which may
be filled with raw organic waste and from which the final slurry and
generated gas may be drawn. Differences in the design of these tanks
are based primarily on the material to be fed to the generator, the
cycle of fermentation desired and the temperatures under which the
plant will operate.
Tanks designed for the digestion of liquid or suspended- solid
waste (such as cow manure) are usually filled and emptied with pipes
and pumps. Circulation through the digester may also be achieved
without pumps by allowing old slurry to overflow the tank as fresh
material is fed in by gravity. An advantage of the gravity system is
its ability to handle bits of chopped vegetable matter which would
clog pumps. This is quite desirable, since the vegetable waste
provides more carbon than the nitrogen-rich animal manure.
CONTINUOUS FEEDING (LIQUIDS)
Complete anaerobic digestion of animal wastes, such as cow manure,
takes about fifty days at moderately warm temperatures. Such matter --
if allowed to remain undisturbed for the full period -- will produce
more than a third of its total gas the first week, another quarter the
second week and the remainder during the final six weeks.
A more consistent and rapid rate of gas production may be
maintained by continuously feeding small amounts of waste into the
digester daily. The method has the additional advantage of preserving
a higher percentage of the nitrogen in the slurry for effective
fertilizer use.
If this continuous feeding system is used, care must be taken to
insure that the plant is large enough to accommodate all the waste
material that will be fed through in one fermentation cycle. A two-
stage digester -- in which the first tank produces the bulk of the
methane (up to 80%) while the second finishes the digestion at a more
leisurely rate -- is often the answer.
BATCH FEEDING (SOLIDS)
Bio-gas plants may be designed to digest vegetable wastes alone
but, since plant matter will not flow easily through pipes, it's best
to operate such a digester on a single-batch basis. With this method
the tank is opened completely, old slurry removed and fresh material
added. The tank is then resealed.
Depending on the fermenting material and temperature, gas
production from a batch-feeding will begin after two to four weeks,
gradually increase to a maximum output and then fall off after about
three or four months. It's best, therefore, to use two or more batch
digesters in combination so that at least one will always be producing
gas.
Because the carbon-nitrogen ratio of some vegetable matter is much
higher than that of animal wastes, some nitrogen (preferably of
organic origin) usually must be added to the cellulose digested this
way. On the other hand, vegetable waste produces -- pound for pound --
about seven times more gas than animal waste, so pro****tionally less
must be digested to maintain equal gas production.
AGITATION
Some means of mixing the slurry in a digester is always desirable,
though not absolutely essential. If left alone, the slurry tends to
settle out in layers and its surface may be covered with a hard scum
which hinders the release of gas.
This is a greater problem with vegetable matter than with manure,
since the animal waste has a somewhat greater tendency to remain
suspended in water and, thus, in intimate contact with the gas-
releasing bacteria. Continuous feeding also helps, since fresh
material entering the tank always induces some movement in the slurry.
TEMPERATURE CONTROL
Although it's relatively easy to hold the temperature of a
digester at ideal operating levels by shading a gobar plant located in
a hot region, maintaining the same ideal temperature in a cold climate
is somewhat more difficult.
The first and most obvious provision, of course, is insulating the
tank with a two or three-foot thick layer of straw or similar material
that is, in turn, protected with a waterproof seal. If this proves
insufficient, the addition of heating coils must be considered.
When hot water is regulated by a thermostat and circulated through
coils built into a digester, the fermenting process may be kept at an
efficient gas producing temperature quite easily. In fact, circulation
only for a couple of hours in the morning and again in the evening
should be sufficient in most climates. It is especially interesting to
note that using a ****tion of the gas generated to heat the water is
entirely feasible... the resulting enormously-increased rate of gas
production more than compensates for the gas thus burned.
GAS COLLECTION
Gas is collected inside an anaerobic digester tank in an inverted
drum. The walls of this upside down drum extend down into the slurry,
forming a "cap" which both seals in the gas and is free to rise and
fall as more or less gas is generated.
The drum's weight provides the pressure which forces the gas to
its point of use through a small valve in the top of the cap. Drums on
larger plants must be counter-weighted to keep them from exerting too
much pressure on the slurry. Care must also be taken to insure that
such a cap is not counter-weighted to less than atmospheric pressure,
since this would allow air to travel backwards through the exhaust
line into the digester with two results: destruction of the anaerobic
conditions inside the tank and possible destruction of you by an
explosion of the methane-oxygen mixture.
The radius of an inverted drum should never be less than three
inches smaller than the radius of the tank in which it floats, so that
minimal slurry is exposed to the air and maximum gas is captured.
ABOVE vs BELOW GROUND DIGESTERS
Gobar tanks built above ground must be made of steel to withstand
the pressure of the slurry and it's simpler and less expensive to
construct underground methane plants. It's also easier to gravity-feed
a tank built at least partially beneath the earth's surface. On the
other hand, above-surface models are easier to maintain and, if
painted black, may be partially heated by solar radiation.
These brief excerpts from Ram Bux Singh's books should make it
obvious that methane gas production from manure and vegetable waste is
no armchair visionary's dream. It's being done right now and over
2,600 gobar plants are currently operating in India alone.
Here, in the U.S. our more than four hundred million cattle, pigs
and chickens produce over two billion tons of manure a year... enough
to spread four feet deep over an area of five hundred square miles!
This valuable natural resource can be used to generate both
combustible gas -- thus relieving part of our reliance on fossil fuels
-- and a fertilizer richer in nitrogen than raw manure.
Instead of contributing mightily to our water pollution crisis as
feedlot runoff, this bountiful end-product of animal life could be
turned to our advantage... as an economical and ecologically-sound
power source!
(These instructions are for an underground, single-stage, double-
chamber plant designed to digest 100 pounds of manure every 24 hours
-- five cows' worth -- but may be scaled upward to construct a plant
capable of producing 500 feet of gas a day).
Dig a hole 13 feet deep and 12 feet in diameter, cutting away
trenches for the inlet and outlet pipes to angle down through.
In the center of the hole, pour a slab of concrete six inches
thick and six feet in diameter. The composition of the concrete should
be 1 part cement, 4 parts sand and 8 parts of 1" stone aggregate.
The digester will be built on this base from 1:2:4 concrete using
1/2" aggregate. The floor and walls will be 3" thick, giving an inside
diameter of 5'6". The walls will be 16' high and reinforced with eight
3/8" machine steel vertical rods and 15 horizontal rings of the same
material.
Inlet and outlet pipes of 4" galvanized iron should be positioned
before pouring the walls so that the pipes are positioned 1-1/2' above
the digester floor and in from the walls. This is so that when the
dividing wall is built across the center of the digester, each pipe
will be centered in its chamber. The concrete must be tightly packed
around the pipes to prevent leakage.
Another wall of brick or concrete will be built three feet outside
the digester wall and to the same height (i.e. four feet above ground
level). This space will be filled with an insulating material: straw,
sawdust, shavings, etc.
Provide some means of descending into this space -- perhaps rungs
of machine steel rod extending from the digester wall to the brick
retaining wall -- in case it should ever become necessary to empty the
insulation. Seal the top of this area to prevent water from getting
in, and leave bare earth in the bottom for drainage.
Bisecting the digester will be a wall of 4" reinforced concrete
eight feet high, at the top of which an iron sup****t structure with a
guide pipe for the gas collector will be placed. This structure is
made of angle iron and the guide pipe is eight feet of 3" galvanized
iron pipe. The structure will be set in the digester walls and solidly
fixed atop the chamber-dividing wall. The pipe must be in the exact
center of the digester, allowing the gas collector to descend into the
slurry when empty and rise to ground level when full. This requires 4'
of vertical travel, thus the top eight feet of the digester are left
for the gas collector while the bottom eight feet contain the dividing
wall.
The gas collector is a roofed cylinder five feet in diameter and
four feet high constructed of 12-gauge machine steel sheeting. It is
braced internally with angle irons fitted at different heights so that
when the collector is rotated around its guide pipe the scum on the
surface of the slurry will be broken. The cylinder will first be
riveted, welded, tested for leaks by filling with water and finish-
welded. After all leaks are sealed it should be given two coats of
enamel paint inside and out. The top will be covered with an
insulating material.
The top of the gas collector is also fitted with a 1" tap and
valve, and to this is connected a flexible pipe leading to your gas
appliances. Inside the tap a piece of wire mesh is attached to serve
as a flame arrester. The actual capacity of the gas holder is less
than 100 cubic feet, but if the gas is being used regularly there's no
need to make it larger.
The mixing tank is a cylinder 2'4" in diameter and two feet high.
Its floor is one foot above ground level to provide hydraulic head to
feed the plant. The inlet pipe opening is flush with the bottom of the
mixing tank and is covered with a coarse screen to prevent large
pieces of waste from being ingested. The tank may be built of bricks
or concrete and is about 8-1/2 cubic feet in volume, sufficient for
the daily charge of waste matter.
The discharge pit should be large enough to accommodate all the
spent slurry that is expected to accumulate at a time. It's made of
bricks or concrete and the discharge end of the outlet pipe should be
just even with ground level.
An earth walkway at least three feet wide and level with the top
of the plant should be raised outside the brick wall for sup****t and
additional insulation.
Approximate cost of materials for this plant in the United States
is $400.
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