Milling units and boilers have the highest capital costs of any individual items of sugar
factory plant and so any increases in their capacity and performance will have
significant financial benefit to the Australian sugar industry. Computer modelling has
been used successfully in the last five years to improve the performance of many
boilers. The development of a computer-based milling model to assist in making similar
advances in the milling area has been ongoing for the past 10 years. Milling
improvements could be made to increase throughput, increase sugar extraction and
decrease bagasse moisture content. With the advent of electricity cogeneration by sugar mills, lower bagasse moisture has large benefits for the performance of boilers and the quantity of electricity generated. The development of an adequate milling model has been hampered in the last five years by a limited understanding of the behaviour of
prepared cane and bagasse in a milling train. Although many material models (all of
them soils models known as critical state models) have been implemented in the
existing milling models, the critical state behaviour that forms the foundation of these
models has never been measured experimentally. The data required to identify if a
critical state model (and which critical state model or combination of models) was
suitable for modelling the complex stresses and deformations present in a milling unit
were not available. This paper reports on the behaviour of the solid skeleton (known as
the fibre) of prepared cane and bagasse. It is shown that, for the range of compactions
tested, prepared cane and bagasse behave in the same manner as a soil (sand, clay).
Consistent critical state behaviour has been measured for prepared cane and bagasse
which will be used to build a material model for use in a milling model. The measured
critical state behaviour forms a solid foundation for a greatly improved understanding of
bagasse behaviour. The results have been obtained using a test method known as the
Direct Shear test which is widely used to measure the behaviour of soils. The geometry
of the test equipment and the test procedure were specially modified to cope with the
low stiffness of prepared cane and bagasse and the large amount of water (juice) present compared to a soil.