describe about biogas plant

1. College of Agriculture Mandor,
Jodhpur
Topic:- Bio Gas Plant
Submitted to :- Submitted by :-
Er. Piyush sir Rishikesh
(asst. prof.) roll no. 36

2. BIOGAS PLANT
Biogas plant is an airtight container that facilitates fermentation of
material under anaerobic condition.
Other names given to this device are ‘Biogas Digester’, ‘Biogas
Reactor’, ‘Methane Generator’ and ‘Methane Reactor
Recycling and treatment of organic wastes (biodegradable material)
through anaerobic digestion (fermentation) technology not only
provides biogas as a clean and convenient fuel but also an excellent and
enriched bio-manure.
The BGP also acts as mini bio-fertilizer factory; hence some people
refer it as ‘Biogas fertilizer plant’ or ‘Bio-manure plant’
Anaerobic digestion of organic matter produces a mixture of methane
(CH4) and carbon dioxide (CO2) gas that can be used as a fuel for
cooking, lighting, mechanical power and the generation of electricity, or
a replacement for other fuels.

3. CLASSIFICATION
Classification of biogas plants depends upon the plants design and mode of
working. One common way to classify them is
Batch type plant Continuous type plant
BIOGAS PLANT
Fixed Dome Biogas
Plant
Floating Gas Holder
Biogas Plant:

4. BATCH TYPE BIOGAS PLANT
a) Batch type biogas plants are appropriate where daily supplies of raw
waste materials are difficult to be obtained.
b) Batch type plant is charged at 50-60 day intervals
c) Once charged, it starts supplying the gas after 8-10 days and
continuous to do so for about 40-50 days till the process of digestion
is completed. Afterwards it is emptied and recharged.
d) Gas production in batch type is uneven.
e) Several digesters occupy more space.
f) This type of plants require large volume of digester, therefore, initial
cost becomes high.
g) Such plants are installed in european countries.
h) Donot suit the conditions in indian rural areas

5. CONTINOUS TYPE BIOGASS PLANT
 In continuous type biogas plant, the supply of the gas is continuous
and the digester is fed with biomass regularly.
Plant operates continuously and is stopped only for maintenance or
for sludge removal.
The gas produced is stored in the plant or in a separate gas holder.
The period during which the biomass remains in the digester is known
as The retention period
The thin dry layer often formed at the top of the slurry is known as
scum.
This type of plant are very popular in India and China.
Other features:
I.Retention period is less
II.Less problems as compared to batch type.
III.Small digestion chambers are required

6. OPERATIONAL PARAMETERS OF A BIOGAS
PLANT
Operation of a bio gas plant is affected by a no. of factors::-
A.Temperature
Methane- forming bacteria works best in temp. ranges 20-55 C
Digestion at higher temp. proceeds more rapidly than at lower temp.
The gas production decreases sharply below 20 C and almost stops at
10 C
B.Pressure
 A minimum pressure of 6-10cm of water column i.e, 1.2 bar is ideal for
proper functioning.
It should never be alllowed to exceed 40-50 cm of water column.
Excess pressure inhibits release of gas from slurry and leakage in
masonry.

7. C. Solid to moisture ratio in the biomass
 If water content is too high, the mean slurry temp. and gas
production drops.
 If water content is too low, acids accumulate and hinder
fermentation process.
D.pH value
 In initial acid forming stage, pH value may be around 6 or less.
 During methane forming stage, pH value 6.5 to 7.5 is maintained.
E. Feeding rate
 Faster feeding rate will not help in increase gas production.
 At higher feeding rate the retention period will be less and
undigested Slurry may come out.
 So optimum feed rate should be maintained.

8. F. Carbon to nitrogen ratio
The optimum C/N ratio is 30:1 for maximum microbiological activity.
G. Seeding of biomass with bacteria
 To start and accelerate the fermentation process, a small amount of
digested slurry containing a methane forming bacteria is added to the
freshly charged plant. This process is known as seeding.
 Seeding helps to accelerate the starting of the digestion process.
H. Mixing or stirring
Mixing
 Maintains uniformity in substrate concentration,temp,other
environmentel factors
 Minimises formation of scum
 Prevents the deposition of solids at the bottom

9. I. Retention time
 Retention time should be optimum to obtain 70-80% complete
Digestion.

10. Fixed dome type of biogas plant

11. Raw materials required
Forms of biomass listed below may be used along with water.
•Animal dung
•Poultry wastes
•Plant wastes ( Husk, grass, weeds etc.)
•Human excreta
•Industrial wastes(Saw dust, wastes from food processing
industries)
•Domestic wastes (Vegetable peels, waste food materials)
Principle
Biogas is produced as a result of anaerobic decomposition of
biomass in the presence of water.

12. Construction
The biogas plant is a brick and cement structure having the following
five sections:
• Mixing tank present above the ground level.
• Inlet chamber: The mixing tank opens underground into a sloping
inlet chamber.
• Digester: The inlet chamber opens from below into the digester
which is a huge tank with a dome like ceiling. The ceiling of the
digester has an outlet with a valve for the supply of biogas.
• Outlet chamber: The digester opens from below into an outlet
chamber.
• Overflow tank: The outlet chamber opens from the top into a small
over flow tank

13. Working :
The various forms of biomass are mixed with an equal quantity of
water in the mixing tank. This forms the slurry.
The slurry is fed into the digester through the inlet chamber.
When the digester is partially filled with the slurry, the introduction
of slurry is stopped and the plant is left unused for about two
months.
During these two months, anaerobic bacteria present in the slurry
decomposes or ferments the biomass in the presence of water.
As a result of anaerobic decomposition, biogas is formed, which
starts collecting in the dome of the digester.
As more and more biogas starts collecting, the pressure exerted by
the biogas forces the spent slurry into the outlet chamber.
From the outlet chamber, the spent slurry overflows into the
overflow tank.
The spent slurry is manually removed from the overflow tank and
used as manure for plants.
The gas valve connected to a system of pipelines is opened when a
supply of biogas is required.

15. Floating gas holder type of biogas plant

16. The raw materials used and the principle involved are common
to both the types of biogas plants.
Construction :
The floating gas holder type of biogas plant has the following
chambers/ sections:
Mixing Tank - present above the ground level.
Digester tank - Deep underground well-like structure. It is divided
into two chambers by a partition wall in between.
It has two long cement pipes:
i) Inlet pipe opening into the inlet chamber for introduction of slurry.
ii) Outlet pipe opening into the overflow tank for removal of spent
slurry.
Gas holder - an inverted steel drum resting above the digester. The
drum can move up and down i.e., float over the digester. The gas
holder has an outlet at the top which could be connected to gas
stoves.
Over flow tank - Present above the ground level.

17. Working
Slurry (mixture of equal quantities of biomass and water) is
prepared in the mixing tank.
The prepared slurry is fed into the inlet chamber of the
digester through the inlet pipe.
The plant is left unused for about two months and introduction
of more slurry is stopped.
During this period, anaerobic fermentation of biomass takes
place in the presence of water and produces biogas in the
digester.
Biogas being lighter rises up and starts collecting in the gas
holder. The gas holder now starts moving up.
The gas holder cannot rise up beyond a certain level. As more
and more gas starts collecting, more pressure begins to be
exerted on the slurry.

18. • The spent slurry is now forced into the outlet chamber from the
top of the inlet chamber.
• When the outlet chamber gets filled with the spent slurry, the excess
is forced out through the outlet pipe into the overflow tank. This is
later used as manure for plants.
• The gas valve of the gas outlet is opened to get a supply of biogas.
• Once the production of biogas begins, a continuous supply of gas can
be ensured by regular removal of spent slurry and introduction of fresh
slurry.

20. COMPARISON
S.N. FEATURE FLOATING DRUM FIXED DOME
1. COST More(due to steel drum) Less
2. CORROSION Yes (likely in steel drum) No
3. MAINTENANCE More
•Drum requires painting
•Flexible gas pipe requires
replacement
Less
•No steel part is used
•Gas pipe is fixed type
4. THERMAL
INSULATION
Bad Good(due to underground
construction)
5. SCUM
TROUBLES
Less likely More likely
6. GAS
PRODUCTION
PER UNIT
VOLUME OF
DIGESTER
High Low

21. 7. SCUM BRAKING By rotation of drum External stirrer is
required
8. LEAKAGE Less likely More likely
9. DANGER OF MIXING
WITH OXYGEN DUE
TO LEAKAGE,CRACKS
No More likely
10. GAS PRESSURE constant Variable
11. MASONRY
WORKMANSHIP
Average skill Specialized, skilled
masonry work
required