Biogas plants are biogas generating systems. Biogas formed after
decomposition of organic wastes in biogas plants is piped or transported to
homes for cooking and heating, and used on a large scale in many countries
of the world today. The Biogas plants are considered to be the cheap sources
of energy in rural areas. Biogas is also used for running engines for shaft
and electrical power generation with little or no pollution.
What is biogas?
Biogas is a clean fuel produced through anaerobic digestion of several
organic wastes like agricultural, animal, domestic and industrial. Made from
organic waste matter after it is decomposed, biogas is tremendously used as
fuel. A relatively clean burning, colorless, and odorless gas, biogas is
composed of methane (CH
4), carbon dioxide (CO
2), and
some traces of nitrogen, ammonia (NH
3), sulfur dioxide (SO
2),
hydrogen sulfide (H
2S), and hydrogen, depending on the feedstock
used.
Manufacturing Process
Biogas is produced in a no "oxygen is present" environment or in
an anaerobic environment, when certain bacteria decompose organic material.
The whole process is referred to as anaerobic digestion (AD). AD effectively
treats the organic fraction of waste which has many benefits. The process
not only leads to a healthy and clean environment, but also produces a
renewable energy source like methane. The by-product produced during the
process is a solid residue which is high-grade manure. In a biogas plant,
biomass like vegetable wastes, animal excreta, and weeds undergo
decomposition in the absence of oxygen and form a mixture of gases. This
mixture is the biogas which is used as a fuel for cooking and lighting.
Types of Biogas Plants
- Floating gas-holder type
- Fixed dome type
- Bag type
Floating Gas-holder Type
A digester tank or a well is made out of concrete and it called the
digester tank T, which has two parts: the inlet and the outlet. The inlet is
from where slurry is transported to the tank, which has a cylindrical dome H
made of stainless steel. This dome floats on the slurry and collects the gas
generated. That is why such a biogas plant is known as floating gas holder
type. Fermentation of the slurry takes for about 50 days. The pressure
inside H increases when more gas is formed by bacterial fermentation. The
gas is then transported out through outlet pipe V. The decomposed matter
moves into the next chamber in tank T. By using the outlet pipe this is then
removed to the overflow tank, which is used as manure for cultivation
purposes.
Fixed Dome Type
Here also, a well and a dome are made out of concrete, which is called the
digester tank T. Since the dome is fixed, this gas plant is known as fixed
dome type. The manufacturing process is similar to the floating holder type
bio gas plant, where the slurry expands and overflows into the overflow tank
F.
Bag Type
The bag-type biogas plant is a portable unit. Made of rubberized nylon
fabric, such a plant can be easily placed at any location. The appropriate
type is selected on the basis of technical requirements like distance
between kitchen and cattle shed, location, availability of dung and water,
preferences of the beneficiaries etc.
Components of Biogas Plants
- Inlet pipe: The slurry is moved into the digester through the
inlet pipe/tank.
- Mixing tank: The feed material like dung is gathered in the mixing
tank. Using sufficient water, the material is thoroughly mixed till a
homogeneous slurry is formed.
- Digester: Inside the digester, the slurry is fermented.
Biogas is produced through bacterial action.
- Gas holder or gas storage dome: The biogas thus formed gets
collected in the gas holder. It holds the gas till the time it is
transported for consumption.
- Outlet pipe: The slurry is discharged into the outlet tank.
This is done through the outlet pipe or the opening in the digester.
- Gas Pipeline: The gas pipeline carries the gas to the
utilization point like a stove or lamp.
Biogas Plant Construction
Important criteria for biogas plant construction are:
- The amount of waste material available for processing.
- The amount of gas required for a specific use.
Application Areas
- Cooking: One of the most common use of biogas is for cooking
in a specially designed burner. A biogas plant with a capacity of of 2
m3 is enough for providing cooking fuel to a family of four to five.
- Lighting: Another use of biogas is lighting gas lamps. The
biogas required to power a 100 candle lamp (60 W) is 0.13 m3 per hour.
- Power generation: This gas is also used to operate a
dual-fuel engine. It can replace up to 75% of the diesel.
Benefits of Biogas Plants
- A non-polluting and renewable source of energy is created in biogas
plants.
- It is an excellent way of energy conversion.
- Biogas plants produce enriched organic manure. This can be used as
fertilizers.
- Biogas as a gas provides improvement in the environment, and
sanitation and hygiene.
- The biogas plants provide a source for decentralized power
generation.
- Most important of all, such plants provide employment generation in
the rural areas.
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Biogas
Plant
