Environmental Engineering Reference
In-Depth Information
biogas producer (for minimizing the cost of gas treatment) and the network
operator (for minimizing the LPG cost) is necessary. As a general rule, the
cost of LPG conditioning is substantially higher than the cost of a higher
degree of CO
2
separation.
16.3.6 Gas mixing facility
If biomethane is fed at low ratios into the natural gas network, conditioning
may be not required. In that case, the gas enters a gas mixing facility (mixer)
in which the treated biomethane is mixed thoroughly with the natural gas of
the network (base gas).
16.4 Biomethane quality adjustments
According to DVGW G 260 (DVGW, 2008a) and DVGW G 262 (DVGW,
2008b), injection of biogas is possible either as a complementary gas or as an
additional gas. A complementary gas is a gas whose combustion behaviour
is similar to that of the local distributed natural gas in the distribution
network (base gas) but whose composition may differ slightly.
An additional gas has distinctly different combustion characteristics and
gas composition to those of the natural gas and can only be admixed to a
limited extent. The permitted rates of admixture are restricted because
DVGW G 262 requires that additional gases can be mixed with natural gas
when 'the requirements of the public gas supply in the network downstream
of the mixing point are met in terms of gas use and settlement', i.e. when the
gas composition and the heating value does not change considerably.
Regulation G 685 (DVGW, 2008e) states that the maximum permitted
deviation of the heating value at the consumer level must be less than 2% as
compared with the settlement heating value. This means that the permitted
rate of admixture of biogas depends on the volume flow of the natural gas
and the combustion characteristics of the biogas injected The higher the
base gas flow, the higher the permitted amount of additional gas and, the
greater the deviation of the composition and the combustion characteristics
of the additional gas from the base gas, the lower the permitted rate of
admixture.
With reference to the provisions of the DVGW regulations, the following
network compatibility measures can be applied:
heating value adjustment by LPG
.
computer-based heating value reconstruction method
.
network zoning into districts with fixed heating value
.
feed-in as additional gas/complementary gas.
.
These measures should ensure that biomethane fed into the gas network and
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