STEAM SIDE CALANDRIA MODELLING OF VACUUM PANS AND EVAPORATORS

THE HEAT transfer and condensation of steam within the steam belt and the steam chest surrounding the calandria tubes of vacuum pans and evaporators were investigated using computational fluid dynamics (CFD) modelling techniques. The flow of steam in evaporators and vacuum pans is an aspect that is not usually given much attention but it can influence the productivity of these vessels. The latent heat of the steam provides the heat to the juice or massecuite which induces the formation of vapour bubbles and drives the circulation of the fluid within the vessel. Strong and uniform circulation of the massecuite in vacuum pans increases the production capacity and improves the quality of the sugar produced. Non-uniform heating by the steam on the outside of the calandria tubes can contribute to uneven and inconsistent heat transfer to the juice or massecuite within the vessel. As a consequence under these circumstances the installed heating surface is not effectively utilised. Inconsistent heating can affect the performance of vacuum pans since it influences the circulation of massecuite and the crystallisation rate of sugar. The CFD modelling investigation into the steam side operation of the calandria of vacuum pans and evaporators was preliminary in nature but has shown promising results. The results of the CFD simulations were compared against measured data to determine the applicability of the CFD model. The condensation physics of the CFD model currently has limitations, yet despite these, the CFD model has identified some deficiencies in the flow of steam within the calandria. The investigations into different geometries for steam flow into evaporators and vacuum pans and the results of CFD simulations are detailed and discussed. Some of the proposed modifications resulted in predicted improvements to the distribution of steam within the calandria.