(sheet) gas-holders, the structural details are of less immediate interest than the question of
which materials can be used.
Separate gas-holders
Differentiation is made between:
• low-pressure, wet and dry gas-holders (10-50 mbar). Basically, these gas-holders are
identical to integrated and/or plastic (sheet) gas-holders. Separate gas-holders cost
more and are only worthwhile in case of substantial distances (at least 50-100 m) or
to allow repair of a leaky fixed-dome plant. This type of separate gas-holder is also
used to buffer extreme differences between gas-production and gas-use patterns.
• medium- or high-pressure gas-holders (8-10 bar / 200 bar)
Figure 18: Biogas plant with seperate gasholder in
Nicaragua
Photo: gtz/GATE
Neither system can be considered for use in small-scale biogas plants. Even for large-scale
plants, they cannot be recommended under the conditions in most developing countries.
High-pressure gas storage in steel cylinders (as fuel for vehicles) is presently under
discussion. While that approach is possible in theory, it would be complicated and, except in
special cases, prohibitively expensive. It would also require the establishment of stringent
safety regulations.
Gas pipe, valves and accessories
Biogas piping
At least 60% of all non-functional biogas units are attributable to defect gas piping. Utmost
care has to be taken, therefore, for proper installation. For the sake of standardization, it is
advisable to select a single size for all pipes, valves and accessories.
The requirements for biogas piping, valves and accessories are essentially the same as for
other gas installations. However, biogas is 100% saturated with water vapor and contains
hydrogen-sulfide. Consequently, no piping, valves or accessories that contain any amounts
of ferrous metals may be used for biogas piping, because they would be destroyed by
corrosion within a short time. The gas lines may consist of standard galvanized steel pipes.
Also suitable (and inexpensive) is plastic tubing made of rigid PVC or rigid PE. Flexible gas
pipes laid in the open must be UV-resistant.
Steel pipes
Galvanized steel water supply pipes are used most frequently, because the entire piping
system (gas pipe, valves and accessories) can be made of universally applicable
English/U.S. Customary system components, i.e. with all dimensions in inches. Pipes with
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