Harvesting System Design and Performance - Engineering and Science of Biomass Feedstock Production and Provision - page 106

Fig. 5.23 Schematic of functional processes in harvest and transport of energy grasses

carried out using forage harvesters that cut, chop, and then blow the biomass into an
accompanying wagon (Fig. 5.25a ). There have been some attempts to develop a
single-pass machine which can mow and bale the crops in one pass (see Fig. 5.25b ).

5.4.1.1 Two-Pass Harvesting of Energy Grasses

In the first pass, grasses are cut and windrowed. A sickle bar head or a rotary disk
head is most commonly used. A sickle head works well for thinner grasses such as
switchgrass (see Fig. 5.24a ), but it experiences difficulty in cutting Miscanthus crop
because of the thickness and sturdiness of Miscanthus stems. A rotary disk head
works well for Miscanthus (see Fig. 5.24b ) though material conveying and condi-
tioning need to be improved. Overall, a disk head can more easily harvest Miscanthus,
switchgrass, and other energy grasses compared to a sickle head. A mower-
conditioner forms a windrow in the field which is later picked up by a baler in the
second pass. Typically, large round balers (see Fig. 5.24c ) or square balers (see
Fig. 5.24d ) are used. Large square balers are preferred because squares bales are
easier to stack for storage and transport. Both round and square balers work well for
thin energy grass, but they experience difficulty in baling Miscanthus crop if it is not
well conditioned. Presence of long straight stems often results in plugging of a
baler. Because of higher yield of Miscanthus and switchgrass, the baler ground
speed is lower compared to traditional hay grasses such as prairie grass.