Benchmarking and improving sugar recovery from final molasses

Abstract

The sucrose loss in final molasses in raw sugar manufacture is the largest loss. One factor that typically limits the extent of sucrose recovery from final molasses is that cooling crystallizers are high capital and maintenance cost items. The target purity of the final molasses is the commonly used benchmark to assess the effectiveness of exhaustion of final molasses. However, this benchmark does not relate to an actual loss of sucrose. A benchmark that calculates the Target Sucrose Loss (TSL) in molasses for the factory is proposed. Factories would aim to maintain the sucrose loss in final molasses to within 1 unit of the TSL. A close approach to the target purity is still required as part of the drive to achieve this result. An advantage of the TSL is that it considers the influence of the quantity of soluble impurities in the cane supply on the actual sucrose loss in molasses. Data from Australian factories are presented to demonstrate the application of the TSL. Several factors affecting the exhaustion of final molasses are discussed, including the effects of Cmassecuite purity, crystallizer station performance and shear rate on the massecuite within the crystallizers. Some Australian factories have recently refurbished horizontal, rotating coil crystallizers with designs incorporating fixed cooling elements and rotating paddles to provide high shear rate conditions and overcome maintenance issues associated with the coil design. Experience shows that the fixed-element design is an economical way to provide strong exhaustion performance.