Five Years of Experience with the Application of Reverse Osmosis on Light Middlings in a Corn Wet Milling Plant

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AbstractCorn wet milling is a water intensive operation. A modern corn wet milling plant typically uses 1,5 m3 of fresh water per t of corn. Much of this added water must subsequently be removed by processes that are energy intensive to varying degrees. A major breakthrough in reducing the water consumption of the corn wet milling process was made when A. Cicuttini perceived the idea of using reverse osmosis more upstream in the corn wet milling process, to recover pure water from light middlings, the overflow from the hydrocyclone starch washing system, and to re‐use this water for starch washing. In doing so the direct relation between the amount of water used for washing the starch, and the amount of light steep water to be evaporated does no longer exist. A full size reverse osmosis system for this service has been installed in one of the CPC corn wet milling plants in 1982. In a first phase a reduction of the load to the steepwater evaporator of 50% has been obtained. Expansion of the reverse osmosis system enabled further reduction of the steepwater evaporator load down to 30% of the original value. The system has demonstrated its ability to operate in conjunction with a 9‐stage starch washing section with a wet fresh water intake for starch washing, comparable to that of a 15‐stage washing section, at the same high level of starch product quality, and at much lower energy cost. The disappearance of the direct link between fresh water consumption for starch washing and steep water evaporator load creates new possibilities for optimisation and flexibility in design and operation of corn wet milling plants.