3-CUBIC METER BIOGAS PLANT
A CONSTRUCTION MANUAL
a VITA publication
ISBN 0-86619-069-4
[C]
1980 Volunteers in Technical Assistance
3-CUBIC METER BIOGAS PLANT
A CONSTRUCTION MANUAL
Published by
VITA
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 . Fax:703/243-1865
Internet: pr-info@vita.org
ACKNOWLEDGEMENTS
This
book is one of a series of manuals on renewable
energy
technologies. It is primarily intended for use
by
people in international development projects. The
construction techniques and ideas presented here are,
however,
useful to anyone seeking to become energy
self-sufficient.
Volunteers in Technical Assistance, Inc., wishes to
extend
sincere appreciation to the following individuals
for their contributions:
William R. Breslin, VITA, Mt. Rainier, Maryland
Ram
Bux Singh, Gobar Gas Research Station, India
Bertrand R. Saubolle, S.P., VITA, Nepal
Paul
Warpeha, VITA, Mt. Rainier, Maryland
Paul
Leach, VITA, Morgantown, West Virginia
TABLE OF CONTENTS
I.
WHAT IT IS AND HOW IT IS USEFUL
II.
DECISION FACTORS
Applications
Advantages
Disadvantages
Considerations
Cost
Estimate
III.
MAKING THE DECISION AND FOLLOWING THROUGH
IV.
PRECONSTRUCTION CONSIDERATIONS
By-Products of Digestion
Location
Size
Heating
and Insulating Digesters
Materials
Tools
V.
CONSTRUCTION
Prepare
Foundation and Walls
Prepare
the Gas Cap Drum
Prepare
Moisture Trap
Prepare
Mixing and Effluent Tanks
VI.
OPERATION
Output and Pressure
VII.
VARIOUS APPLICATIONS OF BIOGAS
AND
DIGESTER BY-PRODUCTS
Engines
Fertilizer
Improvised
Stove
Lighting
VIII. MAINTENANCE
Possible
Troubles
IX.
TEST GAS LINE FOR LEAKS
X.
DICTIONARY OF TERMS
XI.
CONVERSION TABLES
XII.
FURTHER INFORMATION RESOURCES
A Listing
of Recommended Resource Materials
Useful
Information for Methane
Digester
Designs
APPENDIX I. DECISION
MAKING WORKSHEET
APPENDIX II. RECORD KEEPING WORKSHEET
3-CUBIC METER BIOGAS PLANT
A CONSTRUCTION MANUAL
I. WHAT IT IS AND
HOW IT IS USEFUL
Biofuels are renewable energy sources from living organisms.
All biofuels are ultimately derived from plants, which use
the
sun's energy by converting it to chemical energy through
photosynthesis.
When organic matter decays, burns, or is eaten, this
chemical energy is passed into the rest of the living world.
In
this sense, therefore, all life forms and their by-products
and
wastes are storehouses of solar energy ready to be converted
into other usable forms of energy.
The kinds and forms of the by-products of the decay of
organic
matter depend on the conditions under which decay takes
place.
Decay (or decomposition) can be aerobic (with oxygen) or
anaerobic
(without oxygen). An example of anaerobic decomposition is
the decay of organic matter under water in certain
conditions
in swamps.
Aerobic decomposition yields such gases as hydrogen and
ammonia.
Anaerobic decomposition yields primarily methane gas and
hydrogen sulfide. Both processes produce a certain amount of
heat and both leave a solid residue that is useful for
enriching
the soil. People can take advantage of the decay processes
to provide themselves with fertilizer and fuel. Composting
is
one way to use the aerobic decay process to produce
fertilizer.
And a methane digester or generator uses the anaerobic
decay process to produce both fertilizer and fuel.
One difference between the fertilizers produced by these two
methods is the availability of nitrogen. Nitrogen is an
element
that is essential to plant growth. As valuable as compost
is,
much of the nitrogen held in the original organic materials
is
lost to the air in the form of ammonia gas or dissolved in
surface runoff in the form of nitrates. The nitrogen is thus
not available to the plants.
In anaerobic decomposition the nitrogen is converted to
ammonium
ions. When the effluent (the solid residue of decomposition)
is used as fertilizer, these ions affix themselves
readily to soil particles. Thus more nitrogen is available
to
plants.
The combination of gases produced by anaerobic decomposition
is
often known as biogas. The principle component of biogas is
methane, a colorless and odorless gas that burns very
easily.
When handled properly, biogas is an excellent fueld for
cooking,
lighting, and heating.
A biogas digester is the apparatus used to control anaerobic
decomposition. In general, it consists of a sealed tank or
pit
that holds the organic material, and some means to collect
the
gases that are produced.
Many different shapes and styles of biogas plants have been
experimented with: horizontal, vertical, cylindrical, cubic,
and dome shaped. One design that has won much popularity,
for
reliable performance in many different countries is
presented
here. It is the Indian cylindrical pit design. In 1979 there
were 50,000 such plants in use in India alone, 25,000 in
Korea,
and many more in Japan, the Philippines, Pakistan, Africa,
and
Latin America. There are two basic parts to the design: a
tank
that holds the slurry (a mixture of manure and water); and a
gas cap or drum on the tank to capture the gas released from
the slurry. To get these parts to do their jobs, of course,
requires provision for mixing the slurry, piping off the
gas,
drying the effluent, etc.
In addition to the production of fuel and fertilizer, a
digester becomes the receptacle for animal, human, and
organic
wastes. This removes from the environment possible breeding
grounds for rodents, insects, and toxic bacteria, thereby
producing a healthier environment in which to live.
II. DECISION FACTORS
Applications: * Gas
can be used for heating, lighting, and
cooking.
* Gas can be used to run internal combustion
engines with modifications.
* Effluent can be used for fertilizer.
Advantages: * Simple
to build and operate.
* Virtually no maintenance--25-year digester
lifespan.
* Design can be enlarged for community
needs.
* Continuous feeding.
* Provides a sanitary means for the treatment
of organic wastes.
Disadvantages: * Produces only enough gas for a family of
six.
* Depends upon steady source of manure to
fuel the digester on a daily basis.
* Methane can be dangerous. Safety precautions
should be observed.
CONSIDERATIONS
Construction time and labor resources required to complete
this
project will vary depending on several factors. The most
important consideration is the availability of people
interested
in doing this project. The project may in many circumstances
be a secondary or after-work project. This will of
course increase the length of time needed to complete the
project. The construction times given here are at best an
estimation
based on limited field experience.
Skill divisions are given because some aspects of the
project
require someone with experience in metalworking and/or
welding.
Make sure adequate facilities are available before
construction begins.
The amount of worker-hours needed is as follows:
* Skilled labor - 8
hours
* Unskilled labor -
80 hours
* Welding - 12 hours
Several other considerations are:
* The gas plant will
produce 4.3 cubic meters of gas per day
on the daily input
from eight cattle and six humans.
* The fermentation
tank will have to hold approximately 7
cubic meters in a
1.5 X 3.4 meters deep cylinder.
* A gas cap to cover
the tank should be 1.4 meters in diameter
X 1.5 meters tall.
COST ESTIMATE
$145-800 (U.S., 1979) includes materials and labor.
___________
(*)Cost estimates serve only as a guide and will vary from
country to country.
III. MAKING THE
DECISION AND FOLLOWING THROUGH
When determining whether a project is worth the time,
effort,
and expense involved, consider social, cultural, and
environmental
factors as well as economic ones. What is the purpose of
the effort? Who will benefit most? What will the
consequences
be if the effort is successful? And if it fails?
Having made an informed technology choice, it is important
to
keep good records. It is helpful from the beginning to keep
data on needs, site selection, resource availability,
construction
progress, labor and materials costs, test findings, etc.
The information may prove an important reference if existing
plans and methods need to be altered. It can be helpful in
pinpointing
"what went wrong?" And, of course, it is important
to
share data with other people.
The technologies presented in this series have been tested
carefully, and are actually used in many parts of the world.
However, extensive and controlled field tests have not been
conducted for many of them, even some of the most common
ones.
Even though we know that these technologies work well in
some
situations, it is important to gather specific information
on
why they perform better in one place than in another.
Well documented models of field activities provide important
information for the development worker. It is obviously
important for a development worker in Colombia to have the
technical design for a plant built and used in Senegal. But
it
is even more important to have a full narrative about the
plant
that provides details on materials, labor, design changes,
and
so forth. This model can provide a useful frame of
reference.
A reliable bank of such field information is now growing. It
exists to help spread the word about these and other technologies,
lessening the dependence of the developing world on
expensive and finite energy resources.
A practical record keeping format may be found in Appendix
II.
IV. PRECONSTRUCTION
CONSIDERATIONS
The design presented here <see figure 1> is most
useful for temperate or
tcm1x9.gif (600x600)
tropical climates. It is a 3-cubic meter plant that requires
the equivalent of the daily wastes of six-eight cattle.
Other
sizes are given for smaller and larger digester designs for
comparison.
This digester is a continuous-feed (displacement) digester.
Relatively small amounts of slurry (a mixture of manure and
water) are added daily so that gas and fertilizer are
produced
continuously and predictably. The amount of manure fed daily
into this digester is determined by the volume of the
digester
itself, divided over a period of 30-40 days. Thirty days is
chosen as the minimum amount of time for sufficient
bacterial
action to take place to produce biogas and to destroy many
of
the toxic pathogens found in human wastes.
BY-PRODUCTS OF DIGESTION
Table 1 shows the various stages of decomposition and the
forms
tcmxtab1.gif (600x600)
of the material at each stage. The inorganic solids at the
bottom
of the tank are rocks, sand, gravel, or other items that
will not decompose. The effluent is the semisolid material
left
after the gases have been separated. The supernatant is
biologically
active liquid in which bacteria are at work breaking
down the organic materials. A scum of harder-to-digest
fibrous
material floats on top of the supernatant. It consists
primarily of plant debris. Biogas, a mixture of combustible
(burnable) gases, rises to the top of the tank.
The content of biogas varies with the material being
decomposed
and the environmental conditions involved. When using cattle
manure, biogas usually is a mixture of:
[CH.sub.4]
(Methane) 54-70%
[CO.sub.2]
(Carbon Dioxide) 27-45%
[N.sub.2]
(Nitrogen) .5-3%
[H.sub.2]
(Hydrogen) 1-10%
CO (Carbon
Monoxide)
0-.1%
[O.sub.2]
(Oxygen) 0-.1%
[H.sub.2]S
(Hydrogen Sulfide)
Small amounts of
trace elements, amines, and sulphur
compounds.
The largest, and for fuel purposes the most important, part
of
biogas is methane. Pure methane is colorless and odorless.
Spontaneous ignition of methane occurs when 4-15% of the gas
mixes with air having an explosive pressure of between 90
and
104 psi. The explosive pressure shows that biogas is very
combustible and must be treated with care like any other
kind
of gas. Knowledge of this fact is important when planning
the
design, building, or using of a digester.
LOCATION
There are several points to keep in mind before actual
construction of the digester begins. The most important
consideration is the location of the digester. Some of the
major points in deciding the location are:
* DO NOT dig the
digester pit within 13 meters of a well or
spring used for
drinking water. If the water table is reached
when digging, it
will be necessary to cement the inside of
the digester pit.
This increases the initial expense of
building the
digester, but prevents contamination of the
drinking supply.
* Try to locate the
digester near the stable (see Figure 2) so
tcm2x12.gif (600x600)
excessive time is
not spent transporting the manure. Remember,
the fresher the
manure, the more methane is produced as
the final product
and the fewer problems with biogas generation
will occur. To
simplify collection of manure, animals
should be
confined.
* Be sure there is
enough space to construct the digester. A
plant that
produces 3 cubic meters of methane requires an
area approximately
2 X 3 meters. If a larger plant is
required, figure
space needs accordingly.
* Arrange to have water readily available for mixing with
the
manure.
* Plan for slurry storage. Although the gas plant itself
takes
up a very small
area, the slurry should be stored either as
is or dried. The
slurry pits should be large and expandable.
* Plan for a site that is open and exposed to the sun. The
digester operates
best and gives better gas production at
high temperatures
(35[degrees]C or 85-100[degrees]F). The digester should
receive little or
no shade during the day.
* Locate the gas plant as close as possible to the point of
gas
consumption. This
tends to reduce costs and pressure losses
in piping the gas.
Methane can be stored fairly close to the
house as there are
few flies or mosquitos or odor associated
with gas
production.
Thus, the site variables are: away from the drinking water
supply, in the sun, close to the source of the manure, close
to
a source of water, and close to the point where the gas will
be
used. If you have to choose among these factors, it is most
important to keep the plant from contaminating your water
supply. Next, as much sun as possible is important for the
proper operation of the digester. The other variables are
largely a matter of convenience and cost: transporting the
manure and the water, piping the gas to the point of use,
and
so on.
SIZE
The amount of gas produced depends on the number of cattle
(or
other animals) and how it is going to be used. As an
example, a
farmer with eight cattle and a six-member family wishes to
produce gas for cooking and lighting and, if possible, for
running a 3hp water pump engine for about an hour every day.
Some of the questions the farmer must ask and guidelines for
answering them are:
1. How much gas can
be expected per day from both eight head
of cattle and
six people?
Since each cow
produces, on the average, 10kg of manure
per day and 1kg
of fresh manure can give .05 cubic meter
gas, the animals
will give 8 X 10kg/animal X .05 cubic
meter/kg = 4.0
cubic meters gas.
Each person
produces an average of 1 kg of waste per day;
therefore, six
people X 1kg/person X .05 cubic meter/kg
.30 cubic meter
gas.
The size of the
plant would be a 4.3 cubic meter gas
plant.
2. How much gas
does the farmer require for each day?
Each person
requires approximately 0.6 cubic meters gas
for cooking and
lighting. Therefore, 6 X 0.6 = 3.6 cubic
meters gas.
An engine
requires 0.45 cubic meters gas per hp per hour.
Therefore, a 3hp
engine for one hour is: 3 X 0.45 = 1.35
cubic meters
gas.
Total gas
consumption would be almost 5 cubic meters per
day--somewhat
more than could be produced. Running the
engine will thus
require conserving on lighting and
cooking (or vice
versa), especially in the cool season
when gas
production is low.
3. What will be the
volume of the fermentation tank or pit
needed to handle
the mixture of manure and water?
The ratio of manure and water is 1 : 1.
8 cattle = 80kg
manure + 80kg water = 160kg
6 people =
6kg waste
+ 6kg water =
12kg
-----
Total input per day = 172kg
Input for six
weeks = 172kg X 42 days = 7224kg
1000kg = 1 cubic
meter
7224kg = 7.2
cubic meters
Therefore, the
minimum capacity of the fermentation well
is approximately
7.0 cubic meters--a figure that does not
allow for future
expansion of the farmer's herd. If the
herd does expand
and the farmer continues to put all
available manure
in the tank, the slurry will exit after a
shorter
digestion period and gas production will be
reduced. (The
farmer could curtail addition of raw manure
and hold it
steady at the eight cattle load. If money is
available and
there are no digging problems, it is better
to put in an
oversized than undersized tank.
4. What size and
shape of fermentation tank or pit is
required?
The shape of the
tank is determined by the soil, subsoil,
and water table.
For this example, we will assume that the
earth is not too
hard to dig and that the water table is
low--even in the
rainy season. An appropriate size for a
7.0 cubic meter
tank would be a diameter of 1.5 meters.
Therefore, the
depth required is 4.0 meters.
5. What should the
size of the gas cap be?
The metal drum
serving as a gas cap covers the
fermentation
tank and is the most expensive single item in
the whole plant.
To minimize the size and to keep the
price as low as
possible, the drum is not built to
accommodate a
full day's gas production on the assumption
that the gas
will be used throughout the day and the drum
will never be
allowed to reach full capacity. The drum is
made to hold
between 60 and 70 percent of the volume of
the total daily
gas production.
70% of 4.3 cubic
meters = 3-cubic-meter gas cap required
The actual
dimensions of the drum may well be determined
by the size of
the material locally available. A 1.4-meter-diameter
drum 1.5 meters
tall would be sufficient
for this
example. See Table 2 for other digester sizes.
tcmxtab2.gif (600x600)
HEATING AND INSULATING DIGESTERS
To reach optimum operating temperatures (30-37[degrees]C or
85-100[degrees]F),
some measures must be taken to insulate the digester,
especially
in high altitudes or cold climates. Straw or shredded
tree bark can be used around the outside of the digester to
provide insulation. Other forms of heating can also be used
such as solar water heaters or the burning of some of the
methane produced by the digester to heat water that is
circulated
through copper coils on the inside of the digester. Solar
or gas heating will add to the cost of the digester, but in
cold climates it may be necessary. Consult "Further
Information
Resources" for more information.
MATERIALS (For 3-Cubic-Meter Digester)
* Baked bricks, approximately 3200
* Cement, 25 bags (for foundation and wall covering)
* Sand, 12 cubic meters
* Clay or metal pipe, 20cm diameter, 10 meters
* Copper wire screening (25cm X 25cm)
* Rubber or plastic hose (see page 00)
* Gas outlet pipe, 3cm diameter (see page 00)
* Pipe, 7.5cm diameter, 1.25 meters (gas cap guide)
* Pipe, 7cm diameter, 2.5 meters (center guide)
* Mild steel sheeting, .32mm (30 gauge) to 1.63mm (16
gauge),
1.25 meters X 9
meters long
* Mild steel rods, approximately 30 meters (for bracing)
* Waterproof coating (paint, tar, asphalt, etc.), 4 liters
(for
gas cap
TOOLS
* Welding equipment (gas cap construction, pipe fittings,
etc.
* Shovels
* Metal saw and blades for cutting steel (welding equipment
may
be used)
* Trowel
V. CONSTRUCTION
PREPARE FOUNDATION AND WALLS
* Dig a pit 1.5 meters in diameter to a depth of 3.4 meters.
* Line the floor and walls of the pit with baked bricks and
bound it with lime
mortar or clay. Any porousness in the
construction is
soon blocked with the manure/water mixture.
(If a water table
is encountered, cover the bricks with
cement.)
* Make a ledge or cornice at two-thirds the height (226cm)
of
the pit from the
bottom. The ledge should be about 15cm wide
for the gas cap to
rest on when it is empty (see Figure 3).
tcm3x20.gif (600x600)
This ledge also
serves to direct into the gas cap any gas
forming near the
circumference of the pit and prevents it
from escaping
between the drum and the pit wall.
* Extend the brickwork 30-40cm above ground level to bring
the
total depth of the
pit to approximately 4 meters.
* Make the input and output piping for the slurry from
ordinary
20cm clay
drainpipe. Use straight input piping. If the pipe
is curved, sticks
and stones dropped in by playful children
may jam at the bend
and cannot be removed without emptying
the whole pit. With
straight piping, such objects can fall
right through or
can be pushed out with a piece of bamboo.
* Have one end of the input piping 90cm above ground level
and the other end
70cm above the bottom of the pit (see
Figure 3).
* Have one end of the output piping 40cm above the bottom of
the pit opposite
the input pipe and the other end at ground
level.
* Put an iron or wire strainer (copper screening) with 0.5cm
holes at the upper
end of the input and the output pipes to
keep out large
particles of foreign matter from the pit.
* Construct a center wall that divides the pit into two
equal
compartments. Build
the wall to a height two-thirds from the
bottom of the
digester (226cm). Build the gas cap guide in
the center top of
the wall by placing vertically a 7cm X 2.5
meters long piece
of metal piping.
* Provide additional support for the pipe by fabricating a
cross brace made
from mild steel.
PREPARE THE GAS CAP DRUM
* Form the gas cap drum from mild steel sheeting or
galvanized
iron sheeting of
any thickness from .327mm (30 gauge) to
1.63mm (16 gauge).
* Make the height of the drum approximately one-third the
depth
of the pit
(1.25-1.5 meters).
* Make the diameter of the drum 10cm less than that of the
pit
(1.4 meters
diameter) as shown in Figure 4.
tcm4x21.gif (486x486)
* Using a flange, attach a 7.5cm pipe to the inside top
center.
* Fix the lower end of the pipe firmly in place with thin,
iron
tie rods or angle
iron. The cap now looks like a hollow drum
with a pipe, firmly
fixed, running through the center.
* Cut a 3cm diameter hole, as shown in Figure 5, in the top
of
tcm5x22.gif (486x486)
the gas cap.
* Weld a 3cm diameter pipe over the hole.
* Fix a rubber or plastic hose--long enough to allow the
drum
to rise and
fall--to the welded gas outlet pipe. A valve may
be fixed at the
joint as shown.
* Paint the outside and inside of the drum with a coat of
paint
or tar.
* Make sure the drum is airtight. One way to check this is
to
fill it with water
and watch for leaks.
* Turn the gas cap drum so that the outlet pipe is on top
and
slip the 7.5cm pipe
fixed in the gas cap over the 7cm pipe
fixed in the center
wall of the pit. When empty, the drum
will rest on the
15cm ledges built on either side. As gas is
produced and the
drum empties and fills, it will move up and
down the center
pole.
* Attach handles to either side of the drum. These don't
have
to be fancy, but
they will prove very helpful for lifting the
drum off and for
turning the drum.
* Weld a 10cm wide metal strip to each of the tie rod
supports
in a vertical
position. These "teeth" will act as stirrers.
By grasping the
handles and rotating the drum it is possible
to break up
troublesome scum that forms on the slurry and
tends to harden and
prevent the passage of gas.
PREPARE MOISTURE TRAP
* Place a jar of water outside the pit and put into it the
end
of a downward
projection of the gas pipe at least 20cm long.
Any moisture
condensing in the pipe flows into the jar
instead of
collecting in the pipe and obstructing the passage
of gas. Water then
overflows and is lost in the ground.
Remember to keep
the jar full or the gas will escape. An
ordinary tap when
opened lets the water escape. Whether using
the water jar or
tap, do not let the length be greater than
30cm below ground
level or it becomes too difficult to reach
(see Figure 3 on
page 20).
tcm3x20.gif (600x600)
PREPARE THE MIXING AND EFFLUENT TANKS
* Build or improvise a mixing tank to be placed near the
outside
opening of the
inlet pipe. Likewise, provide a container
at the outlet to
catch the effluent. Some provision may also
be made for drying
the effluent as the plant goes into full
production.
VI. OPERATION
In order to start up the new digester, it is necessary to
have
3 cubic meters (3000kg) of manure. In addition,
approximately
15kg of "seeder" is required to get the
bacteriological process
started. The "seeder" can come from several
sources:
* Spent slurry
from another gas plant
* Sludge or
overflow water from a septic tank
* Horse or pig
manure, both rich in bacteria
* A 1 : 1
mixture of cow manure and water that has been
allowed to
ferment for two weeks
Put the manure and "seeder" and an equal amount of
water into
the mixing tank. Stir it into a thick liquid called a
slurry. A
good slurry is one in which the manure is broken up
thoroughly
to make a smooth, even mixture having the consistency of
thin
cream. If the slurry is too thin, the solid matter separates
and falls to the bottom instead of remaining in suspension;
if
it is too thick, the gas cannot rise freely to the surface.
In
either case the output of gas is less.
When filling the pit for the first time, pour the slurry
equally into both halves to balance the pressure on the thin
inner wall, or it may collapse.
Mix 60kg fresh manure with 60kg water and add it to the tank
every day.
The advantage of this model is that since the daily flow of
slurry goes up the first side, where the insoluble matter
rises, and down the second, where this matter naturally
tends
to fall, the outgoing slurry daily draws out with it any
sludge
found at the bottom. Thus having to clean out the pit
becomes a
comparatively rare necessity. Sand and gravel may build up
on
the bottom of the digester and will have to be cleaned from
time to time depending on your location.
It can take four to six weeks from the time the digester is
fully loaded before enough gas is produced and the gas plant
becomes fully operational. The first drumful of gas will
probably contain so much carbon dioxide that it will not
burn.
On the other hand, it may contain methane and air in the
right
proportion to explode if ignited. DO NOT ATTEMPT TO LIGHT
THE
FIRST DRUMFUL OF GAS. Empty the gas cap and let the drum
fill
again.
At this point the gas is safe to use.
OUTPUT AND PRESSURE
The gas cap drum floating on the slurry creates a steady
pressure on the gas at all times.
This pressure is somewhat
lower than that usually associated with other gases that are
under pressure but is sufficient for cooking and lighting.
Table 3, on the following page, shows gas consumption by
liters/hour.
1
2
3(*)
Gas cooking
2" diameter burner
280
4" diameter burner
395
6" diameter burner
545
Gas lighting
1 mantle lamps
78
2 mantle lamps 155
3 mantle lamps 190
Refrigerator
18" X 18" X 12"
78
Incubator
18" X 18" X 18"
Flame operated
Running
engines Converted diesel
350-550 hp/hr
(*)Liters/hour
Note: These figures will vary slightly depending on the
design
of the
appliance used, the methane content of the gas,
the gas
delivery pressure, etc.
Table 3.
Application Specification for Gas Consumption
VII. VARIOUS APPLICATIONS OF BIOGAS
AND DIGESTER
BY-PRODUCTS
ENGINES
Internal Combustion
Any internal combustion engine(*) can be adapted to use
methane.
For gasoline engines, drill a hole in the carbuerator just
near
the choke and introduce a 5mm diameter tube connected to the
gas supply through a control valve. The engine may be
started
on gasoline then switched over to methane while running, or
vice-versa. For smooth running of the engine, the gas flow
should be steady. For stationary engines this is done by
counterbalancing the gas cap. (Refer to Table 3 on page 17 for
gas consumption.)
Diesel
Diesel engines are run by connecting the gas to the air
intake
and closing the diesel oil feed. A spark plug will have to
be
placed where the injector normally is and arrangement made
for
electricity and spark timing. Modifications will vary with
the
make of the engine. One suggestion is to adapt the full-pump
mechanism for timing the spark.
_____________________
(*)Some authorities recommend that when running the internal
combustion engines, the gas be first purified. This is done
by
bubbling it through lime water, to remove carbon dioxide,
and
through iron filings, to remove hydrogen sulphide.
FERTILIZER
The sludge product of anaerobic decomposition produces a
better
fertilizer and soil conditioner than either composted or
fresh
manure. The liquid effluent contains many elements essential
to
plant life: nitrogen, phosphorous, potassium, plus small
amounts of metallic salts indispensible for plant growth.
Methods of applying this fertilizer are numerous and
conflicting.
The effluent can be applied to crops as either a diluted
liquid or in a dried form. Remember that although 90-93% of
toxic pathogens found in raw human manure are killed by
anaerobic
decomposition, there is still a danger of soil contamination
with its use. The effluent should be composted before use
if the slurry contains a high proportion of human waste.
However,
when all factors are considered, the effluent is much
safer than raw sewage, poses less of a health problem, and
is a
better fertilizer.
The continued use of the effluent in one area tends to make
soils acidic unless it is duluted with water (3 parts water
to
1 part effluent is considered a safe mixture). A little
dolomite
or crushed limestone added to the effluent containers at
regular intervals will cut down on acidity. Unfortunately,
limestone tends to evaporate ammonia; so it is generally
best
to keep close watch over the amount of effluent provided to
crops until the reaction of the soil and crops is certain.
IMPROVISED STOVE
Because gas pressure is low, it will be necessary to modify
existing equipment or build special burners for cooking and
heating. A pressure stove burner will work satisfactorily
only
after certain modifications are made to the burner. The
needle-thin jet should be enlarged to 1.5mm. To make a
burner
out of 1.5cm water pipe, choke the pipe with a metal disc
having
a center hole with a diameter of 1.5 to 2mm. An efficient
burner is a tin can, filled with stones for balance, having
six
1.5mm holes in the top. The gas enters through a pipe choked
to
a 2mm orifice. Or fill a chula or Lorena stove with stones
and
insert a pipe choked to a 2mm orifice.
If possible, it is best to use a burner with an adjustable
air
inlet control. The addition or subtraction of air to the gas
creates a hotter flame with better use of available gas.
LIGHTING
Methane gives a soft, white light when burned with an
incandescent
mantle. It is not quite as bright and glaring as a
kerosene lantern. Lamps of various tyles and sizes are
manufactured
in India specifically for use with methane. <see
image> Each mantle
tcmx31.gif (600x600)
burns about as bright as a 40-watt electric bulb.
Some biogas appliances manufactured by an Indian firm are:
*
Indoor hanging lamp
*
Stoves and burners
*
Indoor suspension lamp
*
Bottle syphons and
*
Outdoor hanging lamp
pressure gauges
*
Indoor table lamp
VIII. MAINTENANCE
A digester of this type is virtually maintenance free and
has a
life of approximately 25 years. As long as cow or other
animal
manure is used, there should be no problems. Vegetable
matter
can also be used for methane production but the process is
much
more complex. Introduction of vegetable matter in the
digester
is not recommended.
A trouble-shooting guide is listed below for possible
problems
that may be encountered.
POSSIBLE TROUBLES
Defect
May be caused by Remedy
No gas. Drum
a) No bacteria Add some
bacteria
won't rise.
(seeder)
b) Lack of time
Patience! Without bacteria,
it may take four
or five weeks.
c) Slurry too cold Use warm
water. Cover
plant with plastic tent
or use heating coil.
d) Insufficient Add right
amount of
input slurry daily.
e) Leak in drum or
Check seams, joints,
pipe and taps with
soapy
water.
f) Hard scum on
Remove drum; clean
slurry blocking
slurry surface. With
gas. sliding-drum
plants,
turn drum slightly to
break crust.
No gas at stove;
a) Gas pipe blocked Open
escape cock.
plenty in drum.
by condensed
water
b) Insufficient Increase
weight on drum
pressure
c) Gas inlet Remove
drum and clean
blocked by scum inlet. Close
all gas-taps.
Fill gas line
with water; apply
pressure
through moisture
escape. Drain water.
Gas won't burn.
a) Wrong kind is Slurry too
thick or too
being formed. thin. Measure
accurately.
Have
patience.
b) Air mixture Check
burner gas jet to
make sure it is at
least 1.5mm.
Flame soon dies.
a) Insufficient Increase
weight on
drum.
b) Water in line Check
moisture escape
jar. Drain gas line.
Flame begins far a)
Pressure too Remove weights from
high drum.
Counterbalance.
b) Air mixture Choke gas
inlet at
stove to 2mm (thickness
of 1" long
nail).
IX. TEST GAS LINES FOR LEAKS
Checking for gas leaks is done by closing all gas taps,
including the main gas tap beside the gas holder, except for
one.
Then to the open tap, a clear plastic pipe about a meter
long
is attached, and a "U" is formed. The lower half
of the "U" is
filled with water.
Using a pipe attached to a second tap, pressure is applied
until the water in the two legs of the "U" is
different by
15cm. The second tap is then closed. The "U" is
now what is
called a "manometer."
If the water levels out when the second tap is closed, a
leak
is indicated and can be sought out by putting soapy water
over
possible leaks, such as joints, in the pipework. <see
image>
tcmx35.gif (600x600)
X. DICTIONARY OF TERMS
AEROBIC--Decomposing with oxygen.
ANAEROBIC--Decomposing without oxygen.
BY-PRODUCT--Something produced from something else.
CARBON DIOXIDE--A colorless, odorless, incombustible gas
([CO.sub.2])
formed during organic decomposition.
DECOMPOSE--To rot, to disintegrate, to breakdown into
component
parts.
DIA (DIAMETER)--A straight line passing completely through
the
center of a circle.
DIGESTER--A cylindrical vessel in which substances are
decomposed.
EFFLUENT--The outflow from the biogas storage tank.
FERMENT--To cause to become agitated or turbulent.
HP (HORSEPOWER)--Unit of power equal to 747.7 watts.
INSOLUBLE--Incapable of being dissolved.
LEACHED--Dissolved and washed out by a percolating liquid.
MANTLE--A sheath of threads that brightly illuminates when
heated by
gas.
METHANE--An odorless, colorless, flammable gas ([CH.sub.4])
used as a
fuel.
NITRATES--Fertilizers consisting of sodium and potassium
nitrates.
NITROGEN--A colorless and odorless gas ([N.sub.2]) in
fertilizers.
ORGANIC WASTES--Waste from living organisms or vegetable
matter.
SCUM--A filmy layer of waste matter that forms on top of
liquid.
SEEDER--Bacteria used to start the fermentation process.
SEPTIC TANK--A sewage disposal tank in which a continuous
flow
of waste
material is decomposed by anaerobic
bacteria.
SLUDGE--A thick liquid composed of 1 : 1 : 1 mixture of
manure,
seeder, and
water.
SUPERNATANT--Floating on the surface.
TOXIC PATHOGENS--Harmful or deadly agents that cause serious
disease or
death.
XI. CONVERSION TABLES
UNITS OF LENGTH
1 Mile
= 1760 Yards
= 5280 Feet
1 Kilometer
= 1000 Meters
= 0.6214 Mile
1 Mile
= 1.607 Kilometers
1 Foot
= 0.3048 Meter
1 Meter
= 3.2808 Feet
= 39.37 Inches
1 Inch
= 2.54 Centimeters
1 Centimeter
= 0.3937 Inches
UNITS OF AREA
1 Square Mile
= 640 Acres
= 2.5899 Square Kilometers
1 Square
Kilometer
= 1,000,000 Square Meters =
0.3861 Square Mile
1 Acre
= 43,560 Square Feet
1 Square
Foot
= 144 Square Inches =
0.0929 Square Meter
1 Square
Inch
= 6.452 Square Centimeters
1 Square
Meter
= 10.764 Square Feet
1 Square
Centimeter
= 0.155 Square Inch
UNITS OF VOLUME
1.0 Cubic Foot
= 1728 Cubic Inches
= 7.48 US Gallons
1.0 British
Imperial
Gallon
= 1.2 US Gallons
1.0 Cubic
Meter = 35.314 Cubic Feet
= 264.2 US Gallons
1.0 Liter
= 1000 Cubic Centimeters
= 0.2642 US Gallons
1.0 Metric Ton
= 1000 Kilograms
= 2204.6 Pounds
1.0 Kilogram
= 1000 Grams
= 2.2046 Pounds
1.0 Short Ton
= 2000 Pounds
UNITS OF PRESSURE
1.0 Pound per
square inch = 144 Pound per
square foot
1.0 Pound per
square inch = 27.7 Inches
of water(*)
1.0 Pound per
square inch = 2.31 Feet of
water(*)
1.0 Pound per
square inch = 2.042 Inches
of mercury(*)
1.0 Atmosphere
= 14.7 Pounds per
square inch (PSI)
1.0 Atmosphere
= 33.95 Feet of
water(*)
1.0 Foot of water =
0.433 PSI = 62.355 Pounds per
square foot
1.0 Kilogram per
square centimeter = 14.223 Pounds
per square inch
1.0 Pound per
square inch = 0.0703
Kilogram per square
centimeter
UNITS OF POWER
1.0 Horsepower
(English) = 746 Watt
= 0.746 Kilowatt (KW)
1.0 Horsepower
(English) = 550 Foot
pounds per second
1.0 Horsepower
(English) = 33,000 Foot
pounds per minute
1.0 Kilowatt
(KW) = 1000 Watt
= 1.34 Horsepower (HP) English
1.0 Horsepower
(English) = 1.0139 Metric
horsepower
(cheval-vapeur)
1.0 Metric
horsepower = 75 Meter
X Kilogram/Second
1.0 Metric
horsepower = 0.736
Kilowatt = 736 Watt
_________________
(*)At 62 degrees Fahrenheit (16.6 degrees Celsius).
XII. FURTHER INFORMATION RESOURCES
A LISTING OF RECOMMENDED RESOURCE MATERIALS
Biogas Plant: Designs With Specifications. Ram Box Singh,
Gobar
Gas Research
Statin Ajit Mal Etawah (V.P.) India. The
main part of
this book is taken up with very detailed
technical drawings of 20 different models of
methane
digesters for
various size operatins and different climates.
Also has
designs for gas burners, lamps, and a
carburator. No
real written instructions, but would be
very useful if
used in conjunction with a more general
manual.
Biogas Plant: Generating Methane from Organic Wastes. Ram
Bux
Singh, Gobar
Gas Research Station, Ajitmal Etawah (V.P.)
India, 1974.
The most comprehensive work on biogas. Gives
the background
of the subject, an extensive treatment of
just how a
biogas plant works, factors to consider in
designing a
plant and several designs, and instructions
for building a
plant and using the products. Profusely
illustrated, this
is considered by some as the "bible" of
biogas.
Fuel Gas From Cow Dung. Bertrand R. Saubolle, S. J.,
Sahayog;
Prakashan
Tripureshwas, Kathmandu, April 1976, 26 pp.
Fairly detailed
manual for obtaining and using methane
from cow
manure. Includes a trouble-shooting section and
specification
charts for different size digesters. Written
in straight
forward, nontechnical language. Potential
quite useful.
Available from VITA.
Small-Scale Biogas Plants. Nigel Florida; Bardoli, India.
Highly detailed
manual. Gives step-by-step instructions
for building
and operating a methane digester. Includes
modifications
needed to cope with a variety of conditions
and a detailed
analysis of digested slurry and of the
produced
biogas. Also has a chapter on current
state-of-the-art in India. Available from VITA.
USEFUL INFORMATION FOR METHANE DIGESTER DESIGNS
Andrews, Johh F. Start-Up and Recovery of Anaerobic
Digestion,
8 pp. Clemson
University. Available from VITA.
"Biogas Plant: Generating Methane from Organic
Wastes." Compost
Science.
January-February 1972, pp. 20-25. Available from
VITA.
Biogas Stove and Lamp: Efficient Gas Appliances, Examples of
Plant Designs,
Examples of Biogas Plants, Construction
Notes. 4 pp.
including illustrations. Available from
VITA.
"Building a Biogas Plant." Compost Science.
March-April 1972.
pp. 12-16.
Available from VITA.
Finlay, John H. Operation and Maintenance of Gobar Gas
Plants,
April 1976, 22
pp. with 3 diagrams. Nepal. Available from
VITA.
Gobar Gas Plant, 4 pp. Appropriate Technology Development
Association, PO
Box 311, Gandhi Bhawan, Lucknow 226001,
UP, India.
Gobar Gas Plants, 8 pp. with 4 diagrams. Indian Agricultural
Research
Institute. Available from VITA.
Gotaas, Harold B. "Manure and Night-Soil Digesters for
Methane
Recovery on
Farms and in Villages. Composting: Sanitary
Disposal and
Reclamation of Organic Wastes. 1956, chapter
9, pp. 171-199.
University of California/Berkeley, World
Health
Organization. Available from VITA.
Grout, A. Roger. Methane Gas Generation from Manure, 3 pp.
Pennsylvania
State University. Available from VITA.
Hansen, Kjell. A Generator for Producing Fuel Gas from
Manure,
4pp. Available
from VITA.
Hill, Peter. Notes on a Methane Gas Generator & Water
Tank
Construction,
June 1974, 9 pp. Belau Modekngei School.
Available from
VITA.
Information on Cow Dung Gas: A Manure Plant for Villages,
5 pp. Indian
Agricultural Research Institute, Division of
Soil Science
and Agricultural Chemistry, Pusa, New Delhi,
India.
Klein, S.A. "Methane Gas--An Overlooked Energy
Source." Organic
Gardening and
Farming, June 1972, pp. 98-101. Rodale
Press, Inc., 33
East Mine Street, Emmaus, Pennsylvania
18049 USA.
Oberst, George L. Cold-Region Experiments with Anaerobic
Digestion for
Small Farms and Homesteads. Biofuels, Box
609, Noxon,
Montana 59853 USA.
The Pennsylvania State University Digester-Methane
Generator,
2 pp. Available
from VITA.
Shifflet, Douglas. Methane Gas Generator, 1966. Available
from
VITA.
Vani, Seva. "Mobile Gobar Gas Plant," Journal of
CARITAS India,
January-February 1976, 2 pp. Available from VITA.
APPENDIX I
DECISION MAKING WORKSHEET
If you are using this as a guideline for using a biogas
plant
in a development effort, collect as much information as
possible
and if you need assistance with the project, write VITA.
A report on your experiences and the uses of this manual
will
help VITA both improve the book and aid other similar
efforts.
VITA
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 . Fax: 703/243-1865
Internet: pr-info@vita.org
CURRENT USE AND AVAILABILITY
* Note current domestic and agricultural practices that
might
benefit from a
biogas plant: improved fertilizer, increased
fuel supply,
sanitary treatment of human and animal wastes,
etc.
* Have biogas plant technologies been introduced previously?
If
so, with what
results?
* Have biogas plant technologies been introduced in nearby
areas? If so, with
what results?
* What changes in traditional thinking or practices might
lead
to increased
acceptance of biogas plants? Are such changes
too great to
attempt now?
* Under what conditions would it be useful to introduce
biogas
plant technology
for demonstration purposes?
* If biogas plants are feasible for local manufacture, would
they be used?
Assuming no funding, could local people afford
them? Are there
ways to make the biogas plant technologies
pay for themselves?
* Could this technology provide a basis for a small business
enterprise?
NEEDS AND RESOURCES
* What are the characteristics of the problem? How is the
problem
identified? Who
sees it as a problem?
* Has any local person, particularly someone in a position
of
authority,
expressed the need or showed interest in biogas
plant technology?
If so, can someone be found to help the
technology
introduction process? Are there local officials
who could be
involved and tapped as resources?
* Based on descriptions of current practices and upon this
manual's
information, identify needs that biogas plant technologies
appear able to
meet.
* Do you have enough animals to supply necessary amount of
manure needed
daily?
* Are materials and tools available locally for construction
of
biogas plants?
* What would be the main use of the methane produced by the
biogas plant? For
example, heating, lighting, cooking, etc.
* Would you be able to use all of the effluent fertilizer or
would you have more
than you need? Would you be able to sell
the surplus?
* Do a cost estimate of the labor, parts, and materials
needed.
* What kinds of skills are available locally to assist with
construction and
maintenance? How much skill is necessary for
construction and
maintenance? Do you need to train people in
the construction
techniques? Can you meet the following
needs?
-- Some aspects of
the project require someone with experience
in metal-working
and/or welding.
-- Estimated labor
time for full-time workers is:
* Skilled labor
- 8 hours
* Unskilled
labor - 80 hours
* Welding - 12
hours
* How much time do you have? When will the project begin?
How
long will it take?
* How will you arrange to spread knowledge and use of the
technology?
FINAL DECISION
* How was the final decision reached to go ahead--or not to
go
ahead--with this
technology?
APPENDIX II
RECORD KEEPING WORKSHEET
CONSTRUCTION
Photographs of the construction process, as well as the
finished
result, are helpful. They add interest and detail that
might be overlooked in the narrative.
A report on the construction process should include very
specific
information. This kind of detail can often be monitored
most easily in charts (such as the one below). <see
report 1>
tcmxrp10.gif (437x437)
Some other things to record include:
* Specification of materials used in construction.
* Adaptations or changes made in design to fit local
conditions.
* Equipment costs.
* Time spent in construction--include volunteer time as well
as
paid labor, full-
and/or part-time.
* Problems--labor shortage, work stoppage, training
difficulties,
materials shortage,
terrain, transport.
OPERATION
Keep log of operations for at least the first six weeks,
then
periodically for several days every few months. This log
will
vary with the technology, but should include full
requirements,
outputs, duration of operation, training of operators, etc.
Include special problems that may come up--a damper that
won't
close, gear that won't catch, procedures that don't seem to
make sense to workers, etc.
MAINTENANCE
Maintenance records enable keeping track of where breakdowns
occur most frequently and may suggest areas for improvement
or
strengthening weakness in the design. Furthermore, these
records will give a good idea of how well the project is
working out by accurately recording how much of the time it
is
working and how often it breaks down. Routine maintenance
records should be kept for a minimum of six months to one
year
after the project goes into operation. <see report 2>
tcmxrp2.gif (486x486)
SPECIAL COSTS
This category includes damage caused by weather, natural
disasters, vandalism, etc. Pattern the records after the
routine maintenance records. Describe for each separate
incident:
* Cause and extent of damage.
* Labor costs of repair (like maintenance account).
* Material costs of repair (like maintenance account).
* Measures taken to prevent recurrence.
OTHER MANUALS IN THE ENERGY SERIES
Small Michell (Banki) Turbine:
A Construction Manual
Helical Sail Windmill
Overshot Water-Wheel: Design
and Construction Manual
Wood Conserving Stoves: Two Stove
Designs and Construction Techniques
Hydraulic Ram for Tropical Climates
Solar Water Heater
Making Charcoal: The Retort Method
Solar Grain Dryer
The Dynapod: A Pedal-Power
Unit
Animal-Driven Chain Pump
Solar Still
For free catalogue listing these and other VITA
publications,
write to:
VITA
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 . Fax: 703/243-1865
Internet: pr-info@vita.org
ABOUT VITA
Volunteers in Technical Assistance (VITA) is a private,
nonprofit,
international development organization. It makes available
to individuals and groups in developing countries a
variety of information and technical resources aimed at
fostering
self-sufficiency--needs assessment and program development
support; by-mail and on-site consulting services;
information
systems training.
VITA promotes the use of appropriate small-scale
technologies,
especially in the area of renewable energy. VITA's extensive
documentation center and worldwide roster of volunteer
technical
experts enable it to respond to thousands of technical
inquiries each year. It also publishes a quarterly
newsletter
and a variety of technical manuals and bulletins.
VITA's documentation center is the storehouse for over
40,000
documents related almost exclusively to small- and
medium-scall
technologies in subjects from agriculture to wind power.
This
wealth of information has been gathered for almost 20 years
as
VITA has worked to answer inquiries for technical
information
from people in the developing world. Many of the documents
contained
in the Center were developed by VITA's network of technical
experts in response to specific inquiries; much of the
information is not available elsewhere. For this reason,
VITA
wishes to make this information available to the public.
VITA
VOLUNTEERS
IN TECHNICAL
ASSISTANCE
ISBN 0-86619-069-4
========================================
========================================
