The new dimple tube – a technology to improve evaporating crystallizer performance

Abstract

A common requirement in existing and expanding factories is for them to increase the crystallisation/evaporating crystallizer (vacuum pan) capacity; this is often not feasible due to the significant investment required to install new vessels, reallocate the existing vessels, and the necessary additional ancillary services. An innovative evaporating crystallizer tube has been developed, tested, trialled and commercialised; it provides an alternative solution for increasing the capacity at a significantly lower investment compared to the market equivalents. The dimple tube technology has been developed over four years, from an initial concept through to its commercialisation, and it has been through a series of analyses, alterations, tests and trials. These analyses included Computational Fluid Dynamics (CFD) to predict flow and performance characteristics, Finite Element Analysis (FEA) to analyse the direct and fatigue stresses, pressure testing, non-destructive testing, in-service trials and laboratory testing. Manufacturing equipment and systems have been designed, developed and implemented as part of the commercialisation process to ensure the reliable and repeatable production of the technology, which has been taken from a concept through to a commercially available and value-adding product. The outcome is a new tube technology that increases the heating surface area of an existing vessel by approximately 15%. The performance benefits of the additional heating surface area are as expected, but in addition to this, the increased turbulence significantly affects the heat transfer coefficients, resulting in a further increase in the evaporation rate and an increase in the throughput. The trial operation in a vessel without stirrer has shown no drawbacks or compromises to the existing operations. Retrofitting the existing vessels is as simple as retubing the evaporating crystallizer. Extensive development and testing have led to a new patent-pending tube technology that significantly impacts on the performance of heat exchangers, particularly evaporating crystallizers. The benefits are attained at a significantly lower cost and lead time than competing technologies or options currently available on the market.