Page last updated 30/08/2018
There are a range of designs of biogas plant that are being
used in different places.
The designs used in large numbers are based on two
concepts:
1.
The floating drum biogas system, as developed by KVIC
in India;
2.
The underground dome plant, as developed in China.
Both designs use a cylinder built from masonry in a hole in
the ground. There are variations of both concepts.
A standard KVIC plant is a deep brick lined cylinder in a hole
in the ground. A mixing pit allows animal dung and water to
be mixed into a slurry before it is allowed to flow through a
cement pipe into the main digester. The spent slurry is
allowed to overflow from a channel through the rim at the top
of the cylinder. The gas collects in a steel drum that floats in
the slurry and moves up and down as gas is generated and
used. In some plants, an annulus is made around the top
section of the cylinder, filled with water so the drum can float.
In Nepal, there was a requirement for plants that did not
require such a deep hole. A tapered hole, of the same overall
volume, was used. The inlet and outlet pipes ran vertically to
each side of the enlarged hole base. A central dividing wall
was used to ensure the slurry flowed between the inlet and
outlet, without taking a short cut.
The underground dome plant uses a fixed dome made from
masonry (bricks or concrete) over the digester. They have a
mixing pit at one side and a slurry reservoir at the other. Gas
is stored in the fixed dome, using the “displacement principle”.
The processes involved in generating biogas and good quality,
smell-free compost from biomass are described in both the
books and summarised under Technology.
Technical aspects
KVIC design with
floating steel drum
Floating drum design used in Nepal
Fixed brick dome biogas plant
(Deenbandhu)
Fixed concrete dome biogas plant
(GGC 2047)