Page 470 - Industrial Wastewater Treatment, Recycling and Reuse

440 Industrial Wastewater Treatment, Recycling, and Reuse

operated. When a sugar shot occurs, it is important to discard the contam-
inated vapor condensate or else the life of assets such as boilers or cooling
towers would be compromised.
If a juice-contaminated process condensate is returned to the boiler, the
sugar juice can break down in the high temperature environment of the
boiler. The juice breakdown results in the formation of organic acids that
may rapidly depress boiler water pH (Reid and Dunsmore, 1991). The
pH of boiler water is a critical parameter for safe boiler operation. The
recommended pH range for boiler water is 9–12 to protect the boiler mate-
rial of construction (mild steel) from corrosion. At a high temperature under
alkaline reducing conditions, mild steel forms a protective thin magnetite
layer that is self-limiting and passivates the metal (Flynn, 2009). A depression
in boiler water pH, for example due to the presence of organic acids, will
damage the passivating layer and increase the mild steel corrosion. Corrosion
in the boiler effectively reduces equipment life and creates safety hazards.
Severe “sugar shots” may even lead to shutdown of the plant manufacturing
process and cause production losses.
In the absence of reliable monitoring and effective chemical treatment
programs, reuse of sugar vapor condensates in a cogeneration plant cooling
tower causes severe bio-fouling and high corrosion rates. The resulting slime
formation in the cooling tower fills and the condenser tube failures may lead
to unplanned shutdowns and loss of power production. Therefore, imme-
diate detection and notification of a “sugar shot” is critical. The monitoring
methods are discussed in the following section.

11.2.3 Current Technologies
Sugar mills have used various offline and online methods to detect the “sugar
shots.” These methods have not been very effective in early detection of
contamination. A reliable method to detect any contamination will help
the mills save energy, protect assets, and reduce water waste, which has
become a scarce resource for several sugar mills.
i. Wet chemistry
Wet chemistry methods, such as Molisch and phenol (or thymol)
sulfuric acid tests, are still widely used due to their simplicity, even
though these tests are labor intensive and involve the use of hazardous
chemicals. In the a-naphthol or the Molisch test (Molisch, 1886), the
presence of sugars is indicated by a violet-colored ring that is formed
due to the reaction of a-naphthol with furfural or its derivatives formed