Biomethane injection into natural gas networks - The Biogas: Science, Production and Applications - page 389

Table 16 6 Main advantages and disadvantages of injecting biomethane as an
additional gas

Advantages Disadvantages

. Little or no admixture of LPG
.

. Applicable only in network sections
with high base gas flows throughout
the year (selected sections on the
transport network level)

Very cost-effective

Individual application in optimal
sections; redundant conditioning to
be provided

.

pipes is an interesting method because of the high transport capacities
available. The investment and operating costs of biomethane injected as
additional gas when compared with the other methods already discussed
look very promising unless the volumes are very large and thus require
extended and expensive mixing lines. The very low operating costs and the
simple construction of the network connection are advantages that may
result in lower overall costs.
Possible flow reversals in the feed-in pipeline may be critical to the
applicability of this method. Generally, high flexibility of operations
management is necessary on the transport level to avoid supply bottlenecks.
This can give rise to pendulum zones or changes of the flow direction in some
cases, or in certain network sections. Flow reversal in a pipeline feeding
additional gas can cause a fluctuation of the heating value of more than 2%.
The mixing line in such network sections should be equipped with sample
loops at both ends. In addition, if load flow reversal occurs and biomethane
can be added at several points, the continuous feeding of biomethane as an
additional gas cannot be ensured without a redundant fuel gas conditioning
facility. Alternatively, injection of additional gas is not required at times
when a reversal of the flow direction in the respective network section is
likely. Conditioning with LPG is certainly the redundant technical solution
of choice for meeting the requirements of calibration regulations.
In summary, injection of biomethane as additional gas can be a very cost-
effective measure when high natural gas flows are involved. The advantages
and disadvantages of this approach are summarized in Table 16.6.

￿ ￿ ￿ ￿ ￿ ￿

16.4.5 Comparison of the different network compatibility
measures

Heating value adjustment by addition of LPG can be achieved at virtually
all gas network pressure levels provided the heating value of the natural gas
flow is not higher than 12.0 kWh/Nm 3 (Table 16.7) As a consequence, this