biogas plant and types of biogas plant consisting of Single stage continuous type,Two stage continuous type,batch type,Fixed Dome type and Floating Drum Type Plants,KVIC Plant

1. PRP

2. IT IS A STRUCTURE INSIDE WHICH ANAEROBIC
DIGESTION OF ORGANIC MATTER TAKES PLACE
AND “BIOGAS” IS PRODUCED

3. The biogas plants are built in
different sizes and shapes depending
on the process carried out. These
plants are mainly classified as:
1. Continuous or batch type,
2. Dome and drum type.

4.  In the continuous type of biogas plant the
biomass is fed regularly to the digester and it
delivers the biogas continuously. Continuous
type biogas plants are of two types, namely:
 1. Single stage continuous type biogas plant,
 2. Two stage continuous type biogas plant.

5.  In this type of plants the entire process of
conversion of biomass into biogas (consisting of
stage I of acid formation and stage II of methane
formation) are carried out in the single chamber
or digester without barrier. Such plants are
simple in construction, easy to operate and
control. It does not need any skilled workers.

6.  These plants have two chambers for digestion of
biomass. In the first chamber the biomass is fed
in which the stage I of acid formation takes place.
Then the diluted acids are only fed into the
second chamber where the stage II of methane
formation is carried out. The biogas so produced
is collected from the second chamber.

7.  Advantages of these plants are that it produce more
biogas, requires smaller size of digestion chamber and
lesser period of digestion as compared to single stage
plants.
 The disadvantages are that the process of digestion is
complex, plant is costlier, difficult to operate and maintain
and requires skilled workers. Single stage plants are
preferred for small and medium size biogas plants while
the two stage plants are preferred for larger size biogas
plants.

8.  In case of batch type plants, the biomass feeding
is done in batches with large time interval
between the two consecutive batches. A digester
is loaded with feed and given sufficient time (30
– 45 days) for digestion of biomass. After
completion of digestion, the residue is emptied
and it is again charged with the next batch of
feed.

9.  Therefore in batch type of biogas plants the
rate of production of biogas is uneven. To
overcome this difficulty, several digesters
are used which are fed and emptied in
sequential manner. Thus, it maintains the
regular supply of gas.

10. (i) Gas production is intermittent and unevenly paced.
(ii) Needs several digesters for continuously supply of gas.
(iii) The cost and space requirement is high.
(iv) Needs addition of fermented slurry to start the anaerobic
fermentation.
(v) These plants have longer digestion period, thus they are
suitable for hard fibrous materials.
(vi) Have operational and maintenance problems.

11.  Various models of dome and drum type of biogas
plants have been developed by the various
agencies. These are mainly of two types:
 Floating drum type biogas plants
 Fixed dome type biogas plants

12.  Many models of floating drum type biogas plants
have been developed in various countries. One of
the model is discussed here.
 Floating drum type KVIC model: A common gobar
gas plant suggested by Khadi and Village
Industries Commission (KVIC) India, is described
below. These are suitable for small scale gas
production.

14.  The plant consists of a digester made of masonary
construction in the form of a well below the ground level
and the floating gas holder, also called as dome, made of
mild steel. In the inlet tank animal waste slurry is
prepared containing cow dung and water in the ratio as
1:1 to 1:1.25. The feeding of animal waste slurry is
usually daily and the sludge comes out with the built up
of gas pressure in the dome above the partition wall and
flows out to the outlet tank through A C outlet pipe. This
sludge is an excellent manure.

15.  At the top of the gas holder, the accumulated gas is drawn
from the pipe through gas valve. The bifurcation of digestion
chamber through a partition wall provides optimum
conditions for growth of acid formers and methane formers
as the pH value requirement for these bacteria are different.
Therefore, this gives a good yield of biogas. It operates
naturally under constant pressure. The diameter of the
digester of a gas plant ranges from 1.2m. This problem can
be overcome by using fiber glass reinforced plastic (FRP)
material for construction of gas holders, however it is costly.

16.  1. Higher gas yield
 2. No problem of gas leakage.
 3. Works under constant pressure naturally.
 4. No problem of mixing of biogas with
external air, thus no danger of explosion.

17.  1. Higher cost
 2. Heat is lost through metal gas holder.
 3. Requires painting of drum to avoid
corrosion at least twice a year.
 4. Requires maintenance of pipes and joints.

18.  In fixed dome type biogas plants, the digester and the gas
dome (gas collector) are combined and enclosed in the same
chamber. These types of plants are best suited for batch type
gas plants. These types of plants are more economical
compared to floating dome type since only the masonry work
is needed for their construction. The digester is usually built
below the ground level, particularly for applications in regions
having the cold climate.

20.  (i) Cost of plant is less compared to floating
drum type plant.
 (ii) Loss of heat is negligible since these are
constructed underground.
 (iii) No corrosion problems as in fixed drum
type.
 (iv) It is maintenance free.

21.  (i) Needs skilled labour to operate.
 (ii) Gas production/m3 of digester volume is
less.
 (iii) Gas produced is at variable pressure.