AW: DIG-L: digester accidents

["Ernst Murnleitner" <awite2@awite.de>]

Renertech wrote:
> Because most biogas plants work under a slight
positive pressure, gas may leak out but air would not leak in.

There is often air beeing introduced into agricultural biogas reactors in
order to do biological sulphur removal.
Most times the oxygen is not measured and the air flow is increased as long
as the H2S remains high. I have seen some plants, where the air volume was
half of the biogas volume (> 10 % oxygen in the biogas). This could of
course happen, if O2 is not measured and methane production goes back for
any reason.
However, it needs 5 to 15 % methane in air to get a combusible mixture. And
this seems quite hardly to achieve.

Different from this, during startup it might be built up an explosive
mixture if methane production starts early (thus CO2 cannot replace the air
or oxygen is not consumed before). The biggest explosion potential is
certainly, if a reactor is emptied. I have heard a rumour that there was an
explosion in a german biogas construction company (PLC, in Bavaria, 60
employees). They were working with a pilot plant batch dry fermentation unit
(similar to the plant at www.bioferm.de). There were also some injured
people.

In such dry fermentation plants, air is sucked into the fermenter before the
door is opened. So it is important to check oxygen and methane
concentrations before opening the door.


Ernst Murnleitner


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