Heat-transfer performance of batch vacuum pans in the Australian sugar industry

For Australian sugar factories where most pan stages comprise large, unstirred batch pans, the ability to reduce the process steam consumption of the factory by operating the pans on low-pressure bleed vapour from the evaporators, such as vapour from the third effect of the evaporator station, is not currently possible. In order to define the ability of batch pans to operate effectively on low-pressure vapour, the heat-transfer performance of several pans in Australian factories has been investigated for both the run-up and heavy-up phases. This paper describes the results of the heat-transfer measurements for 14 batch pans, with the study covering all massecuite production duties. Data for two continuous pans are also presented. A correlation for heat-transfer coefficients during run-up for natural circulation high-grade batch pans as a function of steam rate, massecuite height above the calandria and mother molasses consistency is presented. This correlation can be used to determine the suitability of batch pans in the industry to use bleed vapour from the evaporators.