Empirical determination of the compression behaviour of miscanthus round bales

Miscanthus x giganteus (miscanthus) is a renewable raw material and a climate-friendly alternative to fossil fuels. However, to utilise the energy crop economically, technical prerequisites are required to cultivate, harvest and transport miscanthus in large quantities. As there is little knowledge about the material behaviour of miscanthus, tests were carried out on miscanthus round bales. The test results provide information about the compression behaviour of miscanthus and thus form the basis for optimising large-scale processing of miscanthus.
During the tests, conventional round bales of miscanthus were compressed in a customised pressing box by a descending hydraulic pressing plunger. In each of five test series, a round bale of miscanthus was first compressed up to a pressure of 4 MPa and then up to a pressure of 8.5 MPa.
The pressure increases approximately linearly to the density of the bale at the beginning of the pressing process. The linear increase in force is transitioning into a nonlinear compaction behaviour as soon as the bale has reached the density of the previous maximum compaction. The measuring points of all test series in this range can be described by a single trend line, which can be approximated by a quadratic function. ... mehr
When the plunger is lifted, the bale is relieved and its density decreases. The decompression of the bale corresponds to the linear curves that describe the compression behaviour at the start of the subsequent pressing process.
In summary, three key characteristics of the pressing process were identified from the pressing tests: The initial linear increase of the pressing force, the subsequent quadratic progression and the relaxation behaviour. The approximated curves for describing these findings describe the measurement results with a normalised absolute deviation of 8.8 % and make it possible to describe the pressing process schematically.