Guidelines for cost-effectively improving sugar recovery from C massecuite cooling crystallisers

The cooling crystalliser station is often a neglected area for capital investment even though a modest reduction in molasses purity from pan drop to final molasses of 5 units increases sugar recovery for the factory by more than 2%. Presently, for some factories, major investments in upgrading crystalliser stations may be considered to be high risk due to uncertainties whether the stations may become redundant should B molasses be used for alcohol production. This paper reviews the influence of the main process conditions on exhaustion performance in cooling crystallisers through the application of an upgraded SRI model of cooling crystallisation. The main findings are the importance of producing C massecuites in the purity range 62 to 68 purity, achieving strong exhaustion in the pan drop massecuite and applying higher shear rate in the first 8 h or so of cooling crystallisation. Cooling of C massecuites is essential to limit sucrose loss (and loss of fermentables) through the Maillard reaction. For factories having only short residence times in the cooling crystallisers, the sugar recovery is strongly dependent on the pan drop composition and the process conditions in the cooling crystallisers. The use of higher rotational speeds in the early stages of cooling crystallisation provides a strong benefit to sugar recovery through improved exhaustion and reduced sucrose losses through faster cooling and reduced impact of the Maillard reaction.