Monitoring juice hold-up in a cane diffuser bed using electrical conductivity – evaluation on a plant scale

The extraction of sucrose in a sugarcane diffuser depends on the percolation rate of juice through the cane bed. High percolation rates promote mass transfer and increase the wetness of the cane bed (i.e. liquid hold-up within the bed) thereby improving sucrose extraction. However, increasing the rate of juice applied to the surface of the cane bed above the maximum percolation rate results in flooding, causing uncontrolled mixing of juice, destruction of the dry substance content profile and reduced extraction. Flooding in the diffuser can be avoided by installing feedback control of adjustable sprays that alter the application area of juice onto the bed surface and automatically keeping the percolation rate optimised. Electrical conductivity of the cane bed, measured between the bed surface and the bottom screen of the diffuser, has been investigated as a possible online indicator of juice hold-up within the cane bed to provide the necessary measurement for implementing feedback control that can optimise percolation rates. Full scale tests were conducted on the Tongaat Hulett cane diffuser at the Maidstone factory. Reproducibility tests were done to confirm that there is a relationship between conductance and liquid hold-up.