DEVELOPMENT OF A STEADY-STATE MULTIPLE EFFECT EVAPORATOR MODEL AND PRACTICAL APPLICATION IN SUGAR MILLS

THE MULTIPLE effect evaporator set is an integral stage of a sugar mill and is used to remove the majority of water from sugar cane juice in a steam-efficient manner. Due to the properties of the juice, scale develops on the heat transfer surfaces in each evaporator vessel, which, in Australia, typically require lengthy mill stops every 3–4 weeks to chemically clean and remove. This paper develops a steady-state model of a multiple effect evaporator set and solves it in two ways. The first is to make use of limited information available from actual measurements taken along the Pioneer Mill set to solve for all unmeasured values, including a cleanliness factor that is used to represent the degree of scaling of heat transfer surfaces in each evaporator vessel. A method of solving the model in this way is described that can easily be implemented in Excel. The second is to make use of known cleanliness data from along the set and then solve the model in order to predict the set performance based on variations in the operating parameters. This paper also shows a number of examples from Pioneer Mill and Inkerman Mill where tools derived from the use of this model have been applied. These examples show the monitoring of cleanliness of the set during a season, assistance of these tools in developing strategies to mitigate the effect of poor performance and demonstrate the potential of targeted chemical cleans of individual, problem-causing vessels.