Modelling a Multi-Stage Diffuser for Sucrose Extraction in Sugarcane Biorefineries

Abstract:

The extraction of sugar is one of the first and main stages of sugarcane processing, and obtaining high sucrose extraction efficiencies is essential for the productivity of ethanol and sugar industries. In recent years, the number of diffusers for sucrose extraction has been increasing significantly in Brazil due to several reasons, the main ones being their higher efficiency, lower energy costs and lower maintenance and capital costs. Different factors may influence the sucrose extraction efficiency in industrial diffusers, such as operating conditions that are different from nominal equipment design conditions. Thus, the objective of this work is the modelling of a sucrose extraction process, in a multi-stage sugarcane industrial diffuser. The extraction process was first transformed into a mathematical model using phenomenological equations for the mass and momentum balance considering a lumped parameter model approach. The formulated equations were then modelled in LabVIEW and the model was tested through the analysis of the influence of the input variables in the diffuser’s extraction efficiency. Five scenarios were considered and different imbibition liquid input positions and mass flow rates, as well as different percolation liquid recirculation rates were evaluated. The results show that: (1) the insertion of imbibition liquid in more than one stage decreases the percolation velocities in most of the stages, increasing the concentration of sugar in the megasse but also increasing the concentration of sugar in the final juice; (2) higher imbibition flow rates increases the percolation velocity and, therefore, decrease sucrose concentration in the megasse. However, it dilutes the extracted juice; (3) higher recirculation rates to the same stages increase the percolation velocity and benefit sucrose extraction efficiency, decreasing the sugar concentration in the megasse and increasing the sugar concentration in the juice. Yet, a limit for the increase in recirculation must be respected in order to prevent flooding. All the obtained results were consistent and showed that the model is able to project the operation of a diffuser. In a next stage, a multi-objective optimization will be performed in order to optimize operational conditions of the equipment.