Crystal Recovery Efficiency as an Overall Measure of Sugar Mill Performance

The South African sugar industry has recently moved from a cane payment scheme based on the sucrose content of cane to one based upon the concept of recoverable value (RV), which is itself a modification of the estimated recoverable crystal (ERC) quantity as originally presented by van Hengel (1974). While the definitions of ERC and RV attempt to discount the effect of cane quality on factory performance, it has been acknowledged that some important factors, such as the quality of the non-sucrose fraction in the cane (as typically represented by the reducing sugar to ash ratio), are not effectively accounted for. An additional limitation of the new RV system lies in the lumping together of cane evaluation and payment terms into one concept, which can result in the measured value recovery (VR) of a sugar mill varying from month to month as a result of changes in the relative prices of raw sugar and molasses, even if the actual performance of the mill has remained constant. Thus, while value recovery properly represents the financial outcome of mill operations, it is not an effective tool for the evaluation of the process performance of mill operations. The concept of crystal recovery efficiency is proposed as a new factory performance yardstick which allows for the optimal evaluation of mill performance independent of cane quality factors. The use of the new measure is outlined and factory data for all South African mills is presented, highlighting the variation of the crystal recovery efficiency during the season and from year to year.