Environmental Engineering Reference
In-Depth Information
9.2
Visualisation of the greenhouse gas balance for use of upgraded
biogas (biomethane) for electricity supply or heat supply. Status quo
(a) assumes that the energy is supplied from electricity mix (Germany)
and heat from natural gas /heat pump (b) shows the greenhouse gas
balance for the same biomethane production plant calculated assuming
that the energy is supplied from biogas. For each, the substrate is
assumed to be energy crops (adapted from Thr ¨ n
et al
., 2011).
supplied in this way. In order to reduce the maximum load of the biogas
plant, the control devices can be programmed so that single components are
never turned on at the same time. If a grid connection is not possible, or is
unreliable, the electricity can be supplied by a biogas-driven local CHP unit.
In this case, a unit designed for a grid-independent start, known as a self-
triggered unit, is necessary. A gas reserve is also required when biogas
production is low and for use when the biogas plant is initially put into
operation when no biogas is being produced. The gas supply can be
obtained either through a natural gas grid connection or through the use of
pressurised gas or liquefied gas (LPG) in bottles or a tank. The CHP unit
must be correctly designed to operate under these conditions; alternatively a
dual-fuel CHP unit can be used, which can run on diesel in situations when
no biogas is available.
Electrical energy losses occur mainly in cables and connectors: the length
of cables should therefore be minimised. Transportation losses of electricity
within a biogas plant can amount to around 1-3% of the energy exported.
Further energy loss can occur in a transformer for different voltages,
typically at the connection point with a local grid. Losses of between 1 and
3% have been documented; the main factor affecting these is the choice of
equipment. Thus, a transformer must be selected that can guarantee low
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