Fig. 5.18: Inlet and outlet for
fixed-dome (1) and floating-
drum plants (2) (Source:
OEKOTOP)
Fig. 5.19: Forces acting on a
spherical-dome digester
(Source: OEKOTOP)
5.4.3 Digester
Design
The digester of a biogas plant must accommodate the substrate and bacterial activity, as well as
fulfill the following structural functions:
- accept the given static forces
- provide impermeability to gas and liquids
- be durable and resistant to corrosion
As a rule, the digesters of simple biogas plants are made of masonry or concrete. Such materials
are adequately pressure-resistant, but also susceptible to cracking as a result of tensile forces.
The following forces act on the digester:
- external active earth pressures (pE), causing compressive forces within the masonry
- internal hydrostatic and gas pressures (pW), causing tensile stress in the masonry.
Fig. 5.20: Level line,
excavation
and
foundation.
1
Workspace,
2
Inclination of conical
foundation, 3 Sloping
excavation, 4 Vertical
excavation,
51
Quarrystone
foundation, 52 Brick
foundation, 6 Packing sand, 7 Mortar screed, 8 Foot reinforcement for fixed-dome plant, 9 Level line
(Source: OEKOTOP / Sasse 1984)
55