Predicting Ash Properties in Recovery Boilers, 2010 TAPPI/PAPTAC International Chemical Recovery Conference

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Fouling and fouling related phenomena have long been of concern in recovery boiler design and operation. An extensive measurement program has been conducted at recovery boilers in Scandinavia, the Americas, and Southeast Asia. Potassium and chloride behavior was determined by comparing enrichment in dust samples and in virgin black liquor. Based on that data, a model to predict dust properties as a function of boiler operating parameters and black liquor properties has been developed.

The model has been used to predict the effect of changes in black liquor properties on different fouling indicators. The predictions should not be assumed to show absolute values, but rather show trends which are applicable to interpreting operating data on recovery boilers. With respect to the effects of enrichment on operating variables the higher solids firing should have the same effect on the recovery boiler as decreasing sulfidity. Higher dry solids should also worsen the economizer fouling, contrary to industry observation, unless the fouling is mainly controlled by the ash pH. It is not clear which fouling index best describes the boiler bank fouling. Ignoring boiler bank bulk composition and assuming that fouling is controlled by aerosols acting as glue for larger carryover particles corresponds best to industry design practice.