Biomethane injection into natural gas networks - The Biogas: Science, Production and Applications - page 387

Table 16.4 Main advantages and disadvantages of the computer-based heating
value reconstruction method

Advantages Disadvantages

. Little or no admixture of LPG
.

. High initial cost
.

Comparatively low operating costs The impact of a larger number of

feed-in points on the function of
REKO systems is not yet known

Often not practicable in end
distribution networks due to high
level of interconnection or stagnant
gas flows

.

16.4.3 Network zoning into districts with fixed heating value

In current practice, several distinct local networks are taken together to
form a district network with a fixed settlement heating value. The closed
network thereby created can be defined by discrete feed-in and discharge
points. For example, district networks predominantly fed with biomethane
can be set up on the local distribution network level. In this case, the feed-in
point of the biomethane facility would automatically be the main supply of
the network in question. As such, the heating value of the gas for end
consumers can be calculated essentially by the feed-in heating value of the
biomethane facility according to the rules set out in DVGW G 685 (DVGW,
2008e), and conditioning the biomethane with LPG is not required. A
precondition for this is that the biomethane meets the requirements of
DVGW G 260 (DVGW, 2008a). However, this model is of limited value due
to the high-load flow fluctuations in these distribution networks during
summer and winter. An example of fluctuating demand in a local grid is
shown over the period of one year in Fig.16.3.
The setting up of separate gas distribution districts with fixed heating
value should be considered very carefully because the dimensions of the
network, in combination with the output of the biogas facility, may require
that either biomethane is fed into the next higher pipeline level (which
requires conditioning the biomethane during the warm season and/or
natural gas has to be added during the peak season). In the latter case, either
the biomethane would have to be conditioned with LPG or the natural gas
with air to ensure that the maximum permitted deviation of 2% of the feed-
in heating value of several points feeding into the common network in
DVGW G 685 is not exceeded. Either way, there are advantages and
disadvantages (Table 16.5).

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