Biogas Safety first!

Specific requirements
4. Requirements for the digester
Technical protective measures
Structural analysis of concrete containers must take
account of the thermal stresses that are expected to
arise depending on the planned insulation and the
temperature of the substrate.
In plants where leaks can arise above the level of
the surrounding ground it has proved worthwhile to
build a surrounding wall that retains the volume that
could be released in the event of operational faults
until appropriate safety precautions take effect, and
at least traps the volume of the largest tank. This
does not apply to storage facilities for solid digestion
feedstock materials. The surrounding wall does not
have to be completely closed; it can also take the
form of a partial retaining wall if this sufficiently ensures
the retention of escaping materials. The base
within the surrounding wall may consist of cohesive
soil or paved areas, for example concrete and asphalt.
Access openings must have an inside diameter of
at least DN 800 (according to ISO 6708) or have
minimum dimensions of 600 x 800 mm. If it is necessary
to enter a tank for maintenance or repair work,
it must be possible to provide adequate ventilation;
the same safety measures are also required when accessing
inspection chambers. These openings must
be considered for the static concept of the digester.
Every tank (including pre-digestion holding tanks/
preliminary pits) that holds gas, substrate or digestion
products must be capable of being shut off from
the rest of the system individually and in all directions.
In the digestion tank and secondary digester a fill
level monitoring system must ensure that the fill
level is not exceeded, for example by the digested
substrates being fed to the liquid-manure pond via
a riser pipe (overflow) with frost protection or the
maximum fill level of the tanks being limited with a
suitable overfill protection device.
Particular attention must be paid to the operation of
tanks that have greatly fluctuating fill levels, such as
secondary digesters or gas-tight end storage tanks,
for example with regard to explosion protection.
Interior of a digester prior to commissioning
An accident at a biogas plant
Organisational protective measures
The visible parts of the tank must be regularly
checked for leaks, and likewise the tightness of the
sight glasses. See section on inspections and tests
for further details.
Submersible-motor agitators and submersiblemotor
pumps must always be submersed when in
operation. Appropriate operating instructions must
ensure that this is the case.
Classification of Ex zones
Interior of the digester
The tank is constantly filled with gas and is operated
with positive pressure. If the pressure drops, there is
a risk that atmospheric oxygen can enter the interior.
Oxygen is prevented from entering the interior in the
following ways:
Photo: Jürgen Windmeier Photo: schmack
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