Development of a more energy efficient Roberts evaporator based on CFD modelling

The evaporator station within a sugar mill is the single largest consumer of low pressure steam for heating purposes. Factories have identified the need to reduce the energy requirements of the evaporator station so that larger quantities of energy can be used for cogeneration and other purposes. The design of evaporator vessels has remained unchanged since the 1950s and most alterations and design improvements made during the time since have lacked the insight afforded by such tools as CFD modelling. CFD model predictions allow for an understanding of the fluid flow behaviour which is occurring inside the vessel and can not the visualised by any other means. The ability to visualise the behaviour of the entire flow field has been identified as the possible starting point for a novel design of evaporator and significant improvements in performance. As a result of this investigation a large number of data was gathered from factory vessels for comparison with CFD model predictions. There data did not previously exist in the literature in any suitable form. The factory data was used as part of the process to develop a CFD model capable of accurately predicting the fluid flow behaviour inside an evaporator vessel. The subsequent application of the CFD model concluded that the existing design of evaporator vessels contained significant deficiencies in the fluid flow behaviour and that incremental changes to geometry are not likely to produce significant improvements in performance. A novel design of evaporator is presented that has been developed using the CFD model predictions. The novel design significantly improves the fluid flow behaviour inside the vessel and a greater than 30% improvement in heat transfer performance is predicted. Despite the success of the CFD modelling included in this study, a number of areas for further investigation have been identified. These include improvements to the experimental procedure used to gather the factory data, improvements to be made to the CFD modelling tools developed to date and practical issues associated with implementation of the novel evaporator design.