Development, analysis and testing of a dimple tube to improve vacuum-pan performance

A frequent requirement in existing and expanding factories is an expansion of the crystallisation/vacuum pan capacity. Usually, these expansions are problematic due to the significant investment required in reallocation of the existing vessels and construction of new vessels including various ancillary services. An innovative vacuum heating tube has been developed, tested and trialled resulting in an alternative to major changes to the factory or expensive modifications to vessels. Over 4 years, the new Dimple Tube technology has been developed from an initial concept through to commercialisation and has been through a series of analyses, alterations, tests and trials. Analyses included computational fluid dynamics (CFD) to predict flow and performance characteristics, finite element analyses (FEA) to analyse direct and fatigue stress, pressure testing, destructive and non-destructive testing, in-service trials and laboratory testing. In addition, and perhaps most importantly, reliable and repeatable mass-production equipment and systems have been designed, developed, and implemented – taking this new technology from a concept through to a commercially viable and value-adding product. The result is a new tube technology that increases the heating-surface area of the vessel by 16.5%. Process and mechanical analyses and tests have shown that the flow characteristics of the new technology improves performance and the longevity, serviceability, fouling rate and operation of the tubes and equipment are not compromised. The benefit of the additional heating-surface area is as expected, but the increased turbulence makes a significant additional difference to the heat-transfer coefficients in practice and resulting evaporation rates of between 50% and 20% improvement through a batch vacuum pan cycle have been demonstrated. Trial operation has shown no drawbacks or compromises to existing operations. The extensive development and testing has led to a new patent-pending tube technology that has a large impact on vacuum-pan performance, at a significantly lower cost than alternative technologies or options.