Environmental Engineering Reference
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and avoid the construction of a centralized facility with its inherent
disadvantage of transporting large volumes of substrate and digestate.
Liquefied biomethane at
C (at 0-8 bar overpressure),
generated through either dedicated cryogenic upgrading or liquefaction of
conventionally upgraded biogas, is the latest biomethane distribution state.
With an energy density comparable to CNG at 600 bar (around. 22.7MJ/l
or 6.3 kWh/l), and carried in less heavy containers, the transport economy of
LNG is five times better than for CNG at 260 bar in type-1 steel cylinders.
The extra liquefaction costs are quickly compensated for by increased
economical transport range and less cumbersome transport logistics. An
additional benefit is the lowered operational costs in the refueling stations.
Strategically placed mother stations with both LNG and CNG refueling
capability may supply surrounding daughter CNG stations through CNG
mobile units, effectively creating a virtual grid type of distribution. When re-
gasifying the LNG, some of the energy spent on liquefying the methane is
regained, since it is takes much less energy to pressurize a liquid than a gas.
In addition, several synergies exist with LNG utilization in maritime
shipping and industry.
An additional way of generating LNG directly from the natural gas grid is
by way of utilizing expansion work in the measurement and regulation
stations of the gas grid for liquefaction and electricity generation purposes.
Depressurizing from 60 to 4 bar, the electricity generated is sufficient to fully
sustain the liquefaction plant, providing enough cooling to divert as much as
30% of the total stream as LNG (Pettersson et al. 2006). Using the green gas
principle, this out-take of LNG can be sold as renewable methane.
162 to
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18.2.3 Synergies of joint distribution and utilization of
biomethane and natural gas
The synergies of joint distribution of biomethane and natural gas are quite
obvious. It is the same molecule, so allowing biomethane to utilize the
natural gas transport infrastructure decreases the total costs and makes it
possible to reach full utilization of the energy of the biogas potential
(Thamsiriroj et al. 2011). At the same time, the renewability of the energy
gas infrastructure is increased.
When the natural gas grid distribution system is not an option, several
synergies are at hand when allowing for joint utilization of natural gas and
biomethane for automotive fuel purposes. The irrefutable environmental
benefits of biomethane make it the preferred choice at all times, but in an
emerging market situation its production is too insecure and small to adapt
smoothly. Here, natural gas can not only initiate and accelerate market
penetration during the build-up of the biomethane production capacity and
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