Transportation - Engineering and Science of Biomass Feedstock Production and Provision - page 147

Fig. 6.4 Left : sample of Miscanthus ground to 12.7-mm particle size at a density of 350 kg m −3 . Right :
sample after being exposed to a pressure of over 750 MPa at a density of approximately 1,470 kg m −3

6.3.3.1 Energy Requirement for Biomass Compression

The energy requirement for compression of biomass can be calculated by monitor-
ing the force applied onto the biomass by a piston and integrating this force across
the distance through which the piston travels during the compression. As in the case
of comminution machines, for extruders, the net input power the machine required
for compression can be monitored and integrated over time. In both cases, the
energy requirement pertains to the net energy needed for compression, without tak-
ing into account energy required to run ancillary equipment. To determine the pres-
sure needed to compress biomass to a desired value, a sample of biomass was
compressed with a universal testing machine, capable of producing a force of 13
MN [ 35 ]. Figure 6.4 shows the sample before the test, pre-compressed to a density
of 350 kg m −3 , and after the test at a density of approximately 1,470 kg m −3 .
Figure 6.5 shows the energy requirement for compression of the same pre-
compressed sample in PIHV. It is clear that the energy requirement is proportional
to the density and that a power law seems adequate to capture this relationship. Note
that compression to 1,000 kg m −3 required only 0.035 PIHV and that compression
up to a density of 1,321 kg m −3 required only 0.1 PIHV: Even compression to a very
high density of 1,767 kg m −3 required merely 0.315 PIHV. The conclusion of this
research was that energy consumption for compression is not an inhibiting factor.
However, the machinery required to produce particulates of this density level at a
large throughput would most likely be expensive.