Composite Fouling on Heat Exchange Surfaces

Deposition of amorphous silica (SiO2) and calcium oxalate (CaOx) on the calandria tubes of juice evaporators cause serious processing problems in Australian cane sugar mills. The removal of these deposits by mechanical and chemical means is a time-consuming and costly experience. The cost of downtime and chemical cleaning can be several million dollars per year for the Australian sugar industry. The interactions between CaOx and SiO2 have not been investigated previously because conventional studies only address fouling by individual components. The present work evaluates their interactions using two experimental approaches: batch tests for assessing kinetic and thermodynamic behaviour, and fouling-loop experiments for examining composite fouling behaviour under different operating conditions. These two approaches were employed both in the absence and in the presence of sugar to elucidate the effect of sugar on composite fouling mechanisms and to determine the controlling species responsible for composite fouling. The combined information obtained from both the batch and fouling-loop tests in this study offer a unique insight into the mechanisms of composite fouling of CaOx and SiO2.