Transportation - Engineering and Science of Biomass Feedstock Production and Provision - page 140

Fig. 6.1 A stand of Miscanthus giganteus ready for harvest. At harvest time in winter, no leaves
are present, and nutrients have been recycled to the root system
crops in perspective, Table 6.2 shows the mass density in kg m −3 , the specific energy
in MJ kg −1 , and the energy density in MJ m −3 of corn, Miscanthus giganteus , sugar
cane bagasse and switchgrass, and, as a comparison, coal.
An advantage of second-generation biomass feedstock over, for instance, sugar
cane is that it can be stored for longer periods, albeit at the cost of a gradual quantita-
tive and qualitative loss of biomass. However, at some point along the provision
chain, the form of the material needs to be changed because the conversion plant
cannot process baled material directly. Therefore, comminution (size reduction)
must take place to allow for optimal pretreatment and conversion. The determination
of the optimal location for comminution along the provision chain now becomes
important. For smaller biorefineries, bales could be directly delivered using truck
transport, and comminution could take place at the biorefinery itself. For larger bio-
refineries, the transportation distances are much larger, which makes road transport
expensive and rail and water transport more attractive. In rail and water transport,
there is potential for creating a large number of regional depots, sometimes termed
centralized storage and preprocessing centers (CSPs), which are connected to the
biorefinery using rail or water transport. However, bales do not possess sufficient
density to optimize long-distance transportation in railcars. To optimize rail trans-
port, compression of the material is needed before transportation either in bale form
or in post-comminution (powdered) form. Railcars could be developed with an inte-
gral loading/compression mechanism that ensures an optimal material density for
transportation. One of the drawbacks of early stage comminution is that the pow-
dered material needs to be stored in containers. Bales, on the other hand, can employ