Transportation - Engineering and Science of Biomass Feedstock Production and Provision - page 156

The energy use for compression is much lower than that of size reduction, but the
machinery needs to be designed such that it can exert extremely high pressures onto
the material, at a very high throughput rate, without excessive cost in machine
investment. Explosions due to localized pyrolysis must be prevented.
Ideally, machines that combine the size reduction and compression (pelletiza-
tion) operations could be developed that give the advantage of limiting dust genera-
tion. Within the machine, between the size reduction and pelletization actions,
additives could be applied that aid in the bonding/durability of the pellets. The
machine should be controlled such that machine operates at an optimal temperature
for pelletization and additive efficacy.

6.5.6 Sensing Technology and Automation

Sensing technology is needed in various steps of the feedstock provision and con-
version process. In comminution, sensors are needed to control feeding rates and
cutting speeds, allowing the machines to operate most efficiently. At the gates of
CSPs and conversion plants, real-time sensors are needed to measure, for instance,
the moisture content of the biomass, which can be accomplished using classical
indicators such as capacitance. However, to determine the “quality” of feedstock,
sensors are needed for rapid assessment of conversion efficiency (RACE).

6.6 Summary

The main task of the feedstock provision system is to deliver biomass to a pretreat-
ment and conversion system in sufficient quantities and in a form that allows these
systems to be optimized while simultaneously optimizing its own processes.
Transportation is a key step in the provision system. Apart from transportation
mode and logistics management, the provision system also includes aspects of pre-
processing such as size reduction and compression that affect the transportation
efficiency. Harvesting, which is energetically inexpensive, can take place using
either adapted grass/forage cutting and baling equipment, or chopping machines
such as the self-propelled forage harvester (SPFH).
Size reduction (comminution) is a key operation in the provision chain because
pretreatment/conversion process cannot deal with uncut material directly. Apart
from comminution being an energetically expensive operation, the optimal location
of comminution in the provision chain is not clear. For smaller conversion plants
that utilize short-distance truck transport, bales may be delivered to the conversion
plant where comminution takes place. In this case, storage could take place either in
field or at the conversion plant. The density of bales produced with modern equip-
ment is such that trucks (typically flatbed types) are reaching their volume and
weight limits simultaneously, allowing optimal transportation efficiency. For larger
conversion plants, however, the transportation distances are much larger, and rail