We are at a biogas cogeneration plant powered
by livestock waste and organic biomass.
Next, we'll observe the main parts making up the cogeneration section.
There is an initial treatment phase of the biogas, namely a filter
which is used to retain the main impurities that can come from the
mixture, a chiller, which is used to lower the temperature of the
biogas leaving the digester and to dehumidify this mixture,
and a blower that is used to supply the
pressure needed to power the engine.
The desulphurisation part is usually carried up upstream,
by blowing oxygen inside the gasometer, or via external systems
using desulphurisation towers, or activated carbon filters.
The Otto cycle internal combustion engine
-the one you can see beyond me has a capacity of 1 MW–
produces thermal energy as well as electric energy.
The thermal energy is recovered by the oil radiator circuit and by
the first stage intercooler, because these are turbocharged engines.
The second stage intercooler provides water at 40 °C,
typically via continuous dissipation.
From the engine circuit we obtain hot water at a temperature of
approximately 90 °C which is used to maintain the required digester
temperature and can also be used, in part,
to heat sheds or farmhouses and so forth.
The engine flue gas contains additional thermal energy that,
through the insertion of a fume exchanger tube, can be recovered,
producing a further quantity of hot water to be used, for example,
for district heating, or to produce steam or
diathermic oil for possible drying processes.
Generally, on the roof of the container, an emergency heat sink is
installed, so that if the return water were excessively hot due to
incomplete heat recovery, this same water would be dissipated
to then reach the engine circuit at a suitable temperature.
Then there is the stack for the flue gas.
Another important component is the alternator.
It delivers low-voltage electrical energy at 400 W,
which is then taken to medium voltage (in this case to 15 KW)
and then taken to the medium-voltage substation; the latter
puts the plant in parallel with the national grid.
The plant produces approximately one megawatt:
the incentivised amount is what remains
net of the self-consumption of the unit.
Another important part of the plant
is the control and monitoring system.
These plants are monitored remotely via a system
allowing to keep under control all of the important
parameters for the proper functioning of the plant.
Other components are the oil skid, with two tanks for replacing
lubricating oil during regular maintenance of the engine,
and the safety flare which is activated in the
event of engine maintenance or any breakages.