Enhanced performance of caustic soda used for the removal of scale in sugar mill evaporators

Abstract

Caustic soda is the most widely used chemical for cleaning sugar mill evaporators in Australia. It is partially effective in removing silica, silicates, proteins, polysaccharides and organic matter, but is ineffective when the major components of scale consist of calcium phosphate, calcium oxalate, calcium magnesium aconitate, calcium sulphate, calcium carbonate and potassium calcium sulphate. In such situations, sulphamic acid is typically used. Some mills have found these normal procedures unsatisfactory and have used alternative but expensive cleaning methods, which have proved effective. However, these mills still use caustic soda and sulphamic acid in combination with the alternative methods to clean evaporators resulting in a time consuming and laborious process. This paper describes the effect of caustic soda solution in the presence of additives to solubilise different scale types. The paper also describes attempts to identify foam components in scale and provides results on the efficacy of defoamers.