The reduction of ethanol levels in raw sugar factory cooling waters

Substantial quantities of ethanol and other volatile organic substances enter the sugar factory with the cane supply. As they are volatile, they can be transferred to the cooling water in the factory condensers. They also appear in the condensates from the evaporator set. These substances contribute to the Biochemical Oxygen Demand (BODs) loading in the cooling water outflow and consequently exacerbate environmental problems. This paper describes experiments carried out at one factory to establish strategies which divert most of the ethanol, the major component of the volatile organics, from the factory cooling water streams. Some of these diversion strategies were found to be easily implemented and very effective. The ethanol transfer to the cooling water flows could be lowered considerably. The paper also discusses measurements of ethanol levels in samples forwarded by 12 participating mills. These give an indication of their situation with respect to ethanol intake and transfer to the cooling water. There is a wide variation in both incoming ethanol levels and in transfer performance. The former is influenced by the state of the cane supply and the latter by the ruling conditions of evaporator venting, condensate selection for the pan stage, and the overflow rate of excess condensate at the time of sampling. Operational improvements can then be suggested following the strategies identified in the report.