Biomass Feedstock Storage for Quantity and Quality Preservation - Engineering and Science of Biomass Feedstock Production and Provision - page 173

Table 7.2 Effect of bale size and storage conditions on dry matter losses a

Bale
diameter
in m

Bale
weight
in kg

Total dry
matter
losses (%)

Months
in storage

Storage
conditions

Dry
matter Experiment Start data

1 August 1992 6 1.39 275 13 - 3.4

2 November 1993 12 1.76 370 5.6 Outside on grass sod 6.0

4.0 Outside on gravel pad

0 Inside on concrete

3 November 1994 12 1.76 370 6.0 Outside on sod 4.4

4.7 Outside on gravel

2.2 Inside on concrete

a Adapted from Sanderson et al. [ 32 ]

self-compacted silage, losses during infiltration reached 10 %. During the fermenta-
tion phase, as in the case of pre-compacted biomass, dry matter losses were up to
0.6 %. More specifically, compaction reduces porosity, which in turn affects oxygen
infiltration rates and consequently respiration levels. The model described in
McGechan and Williams [ 23 ] predicts dry matter oxidation due to oxygen infiltra-
tion. They suggested that compacting and sealing ensiled material can reduce dry
matter loss. Improved sealing with a plastic sheet is theoretically possible but effec-
tive sealing is a challenge.
Densification is also a means to compact biomass and to reduce porosity. This
can be achieved by pelleting, baling, briquetting, or bundling to obtain different
bulk densities [ 30 ].
Dry matter loss significantly decreases as the packing density at the onset of stor-
age increases [ 12 ]. Dry matter loss is in part due to the microbial consumption in
cellulose. This consumption increases with time, and the microbial activity increases
as temperature rises and aeration decreases [ 22 ]. Packing densities in a bunker silo
of 160 kg dry matter m −3 (10 lb dry matter ft −3 ) and 480 kg m −3 (30 lb dry matter ft −3 )
result in 20-10 % dry matter losses [ 31 ], showing a decrease on dry matter loss as
packing density increases. Packing density of 56 kg dry matter m −3 (3.5 lb dry mat-
ter ft −3 ) to 112 kg dry matter m −3 (7 lb dry matter ft −3 ) significantly decreases the rate
of dry matter loss, according to the model.

7.4.3 Bale Size and Storage Conditions

As discussed in Chap. 5 , balers produce either round (cylindrical) bales or rectangu-
lar bales. In terms of dry matter loss, round bales are more resistant to water pene-
tration. Also a round bale with a diameter equal to its width will have the minimum
surface area to volume ratio, thus minimizing surface degradation relative to vol-
ume. However, rectangular bales are easier to handle, ship, and stack, and greater
bale densities can be generated with this bale shape.
Data on bales of different sizes (Table 7.2 ) adapted from Sanderson et al. [ 32 ]
showed that the average loss of biomass decreases as bale diameter increased, with
all other conditions being equal. However, losses at baling due to runoff and wind