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In modern biogas plants, biodegradable organic substrates precautions and protection measures, potential risk sources
such as manure, dung, grass, straw, green waste, residues of which may cause failure or a dangerous event are considered
the sugar, wine and beer production, leftovers and grease are in a risk analysis according to the German Federal Immission
fermented in an air-tight container (fermenter). In this oxygen- Control Act (BImSchG) / Ordinance on Industrial Safety and
free atmosphere, bacteria produce biogas from the ferment- Health (BetrSichV).
able, organic biomass components. This bio gas is used to gen- The German Safety Regulations for Agricultural Biogas Plants
erate heat and electricity. published by the German Agricultural Professional Association
as well as the German BGR 104 specify that measures which
Figure 9.3.1 shows the basic principle of a biogas plant. prevent the ignition of dangerous explosive atmospheres must
Biogas plants frequently consist of feed-in systems for solids be taken in potentially explosive atmospheres to avoid ignition
and / or liquid substrates, one or more heated fermenters, a sources.
storage tank, a post-fermenter, if any, a gas tank and a gas According to sub-clause 5.3.1 of the EN 1127-1 standard,
treatment unit, if any. The gas engine with heat exchanger and there are thirteen different ignition sources. In sub-clause
a generator connected to it is referred to as combined heat 5.3.8 of the EN 1127-1 standard and in the German BGR 104,
and power station (CHP). Depending on the energy content of lightning is defined as a possible ignition source: “If lightning
biogas, a combined heat and power station generates electric- strikes in an explosive atmosphere, ignition will always occur.
ity with an efficiency of about 30 % and heat with an efficiency Moreover, there is also a possibility of ignition due to the high
of about 60 %. While the electricity is fed into the public power temperature reached by lightning conductors. Large currents
grid, some of the heat is used for heating the fermenter and flow from where the lightning strikes and these currents can
the waste heat is used, for example, for heating residential and produce sparks in the vicinity of the point of impact. Even in
agricultural buildings. the absence of lightning strikes, thunderstorms can cause high
induced voltages in equipment, protective systems and com-
Necessity of a lightning protection system ponents”.
Different hazards and risks for persons, the environment and
system technology can occur during the generation, storage A risk analysis according to the calculation method specified
and energy recovery of biogas. To be able to take adequate in IEC 62305-2 (EN 62305-2) must be performed to define the

collection pit cooler

pump weighing vessel
mixer hygienisation tank
mixer

liquid cooling tank
container electricity
scales valve exhaust
gas burner
pump valve pump
CHP
fermenter gas analysis CHP
equipment
grain silo pump heat
gas line control
cabinet
storage tank
circulation electrical
pump equipment room
valve valve
gas
mixer mixer treatment gas grid
mill unit
valve

Figure 9.3.1 System overview of a biogas plant

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