What is the function of the cooling towers?
The primary unit operation to purify the ethanol from the mash is distillation. The second half is to condense the ethanol being evaporated from the mash. This second half is why the cooling is required. The cooling is provided by water evaporated at atmospheric pressure in what is called a cooling tower. Water circulates from the cooling tower through heat exchangers where the ethanol is condensed. This heats the water and it is returned to the cooling tower for cooling. As the water evaporates in the cooling tower, water is pumped in to replace that which is evaporated, and the concentration of solids increases due to only the water evaporating out, just like the tea kettle mentioned above. A stream, called blowdown, is employed to keep the solids buildup low enough so it does not plug the heat exchangers.
