Ian Hamilton, Robert Adrien, Daniel Baer, Geoff Covey,
Dennis Creasy and Steven Harper
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A laboratory method has been developed which can reproduce the most important factors in the depositformation in the sulphite stage of a magnefite chemical recovery system. By adjusting conditions it is possible toproduce: scale-free operation, formation of free granules (‘sugar’), or severe scaling. The apparatus can also be used to study or confirm the effects of adding dispersants, changing operating temperature, and changing gas composition.
It was found that the presence of magnesium sulphite hexa-hydrate is a sign of conditions likely to result in fouling. The causes of fouling are complex and are dependent on temperature, organics in the distillate, operating pH, sulphur dioxide concentration in the gas in the mono-sulphite section, and (possibly) inorganic impurities in the magnesia. As such, it is unlikely that a full understanding ofthe process can be obtained at a satisfactory cost. HOWEVER, results to date strongly indicate that some comparatively simple and inexpensive adjustments to plantoperation could greatly reduce the severity of the fouling problem. Figure 2. Build up of fouling on a vessel wall.
Keywords scaling, magnesium sulphite, crystallisation