Evaluation of Superheater Corrosion in a Recovery Boiler, 2010 TAPPI/PAPTAC International Chemical Recovery Conference

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In 2007, corrosion was observed in the lower bends of the secondary superheater and in straight sections of the tertiary superheaters at the Visy Recovery Boiler near Tumut, New South Wales. The tube material was SA-213 T11. A study to determine the cause of the corrosion showed that the flue gas temperatures in the regions where corrosion was occurring were not excessive. CFD modeling showed that little benefit could be expected in modifying the combustion air system with the specific purpose of reducing the furnace exit gas temperature.

The mill’s liquor was high in potassium which decreased the first melting temperature of the deposits to about 525°C. This was confirmed by DTA. Further analyses of the secondary superheater showed that differences in the configurations of the two tubes that make up the superheater would account for the highest tube metal temperatures on the inner loop on the last pass. Spatial and temporal differences in steam temperature for the boiler were typical and gave little avenue for solving the problem.

The best approaches to solving the superheater issue were an upgrade in superheater tube metal corrosion resistance or efforts to reduce the amount of potassium in the mill’s liquor.