Modelling the impact of a falling-film evaporator in final-effect position on factory operation and performance

For the juice evaporation station in cane sugar factories, falling-film tubular evaporators (FFE) are now an accepted “alternative technology” to the conventional Robert-type evaporators. Features of the FFE include a high heat-transfer coefficient (HTC) over a longer period, short residence-times of juice in the evaporator, and the ability to operate at lower temperature differences, all of which play a role in the adoption of the technology. The addition of a falling-film evaporator to an existing evaporator set comprising entirely of Robert types is usually limited to the front-end of the set. Robert types operating as a final effect consume a large percentage of the total temperature difference available across the entire set of evaporators. Additionally, the heat-transfer coefficient of Robert evaporators in the final-effect position is quite low and circulation of syrup across the calandria is poor, especially at lower vapour condensation coefficients (VCC). This paper describes simulations which involve replacing a Robert-type evaporator in the final-effect position with an FFE and discusses the impact on factory operation and performance.