Page 468 - Industrial Wastewater Treatment, Recycling and Reuse

438 Industrial Wastewater Treatment, Recycling, and Reuse

sugarcane brought to the mill is chopped and passed through crushers to
extract juice. This juice is then clarified and sent to evaporators, where
the juice is concentrated by evaporating the water that is present in the juice.
This water vapor leaves the evaporation process in the form of condensate,
which is commonly referred to as the vapor or process condensate. Most of
the water coming with the sugarcane is thus removed during the sugar pro-
duction process, resulting in the generation of a water by-product stream.
Therefore, it is rather straightforward to understand that the sugar mills have
surplus water. By reusing the vapor condensate, fresh water consumption by
the mills can be reduced, thereby improving the water efficiency of the mill.
During the sugar milling process, sugar juice can contaminate the water
system. For example, a part of the sugar manufacturing process is the con-
centration of sugarcane clarified (or thin) juice using multiple effect evapo-
rators (MEEs) (Hugot, 1986). In an MEE, the vapor from the first effect is
used to heat the juice in the second effect, the vapor from the second is used
to heat the juice in the third effect, and so forth (Figure 11.1). The first effect
of the MEE is usually driven by steam, and the condensate from this effect is
normally returned to the boiler feed water stream, because it is essentially
steam condensate and would normally have no contamination (unless there
is a process leak due to tube failure).
The clarified sugar cane juice, with 12–14% sugars, is concentrated to
about 55–60% sugars in the MEE. In turn, a lot of water is generated in
the form of process condensate. For example, an average-sized sugar plant

Figure 11.1 Multiple-effect evaporation process used in sugar industry for concentrating
juice.