Environmental Engineering Reference
In-Depth Information
during long-time operation, while hydrogen leakage, obviously higher with respect
to methane, can be significantly limited, especially if polyethylene pipelines will
be used for new hydrogen distribution infrastructures [
101
]. The transportation of
hydrogen inside pipelines in liquid cryogenic forms theoretically should increase
strongly the energy capacity, but it determines also a dramatic growth of capital
costs and severe safety problems [
101
].
As regarding the transportation of hydrogen using the road, currently hydrogen
travels mainly on trucks loaded inside high-pressure vessels (20 MPa). The overall
transportation capacity utilizing liquid reservoirs should be higher than commer-
cial vessels, in spite of much higher insulating and refrigeration costs that make
them not yet satisfactory for a widespread transportation.
The above discussion suggests that the development of a hydrogen system
concept based on distributed small-scale power plants should be easier. In this
respect, the most appropriate hydrogen production technologies are based on
PV-solar, natural gas reformer or wind-turbine resources, even if the last solution
expects some infrastructure network to transport hydrogen from the production
point to the user points.
The different pathways need to be environmental efficient and require a care-
fully evaluation of their impact not only on the costs but also on reliability, safety
and social acceptance [
104
]. Since in a decentralized approach infrastructure cost
related to hydrogen distribution is strongly reduced, a global economical evalua-
tion related to both production and distribution has to accurately consider this
perspective. On the other hand, the possibilities to lower the costs of centralized
hydrogen production and to improve the technologies involved in the creation of a
hydrogen transport and distribution infrastructure claim to be also carefully ana-
lysed. Optimization-based models capable to evaluate all these aspects for the
development of a viable long-term plan has been recently presented, to aid the
decision making process [
105
].
2.3 Hydrogen Storage
The storage capability of tanks is a crucial quality of fuels for road vehicles,
because of the need to match the large driving range user demands. The mileage of
conventional vehicles powered by liquid fuels reaches values clearly superior to
those of battery powered electric vehicles. This is the main reason why the electric
powertrain diffusion has been strongly limited up today. Hydrogen fuel cell
powertrains could enter in a massive automotive market as potential competitor
only overcoming successfully this important question.
The phase diagram for hydrogen is shown in Fig.
2.8
,[
106
] while in Table
2.2
physical and thermodynamic data are reported for hydrogen in molecular form and
for commercial liquid fuels, i.e. gasoline, diesel, LPG and liquid natural gas (LNG)
that are high and low heating values, gravimetric density and volumetric energy
