Design and Development of New Primary Air Port Castings for Increased Recovery Boiler Reliability, 2004 International Chemical Recovery Conference

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Corrosion and cracking of recovery boiler composite primary airports has been increasing in frequency and severity in recent years. Tubes experiencing frequent surface temperature excursions in excess of 450o C in the lower half of the airport have cracked in service. A CFD modeling study was conducted to evaluate the impact of changes made to the primary airport casting design on the flow patterns exiting the port. Changes were evaluated with respect to factors believed to contribute to high tube temperature excursions and general port corrosion. Several different casting designs were modeled. The CFD models spanned from the inlet of the windbox to inside the furnace. Essential features of the port casting shape and bent tube opening were captured in the detailed three-dimensional CFD model. As a result of this study, a new primary air port design was developed that reduces lateral jet expansion, improves downward penetration, and results in less re-ciculation underneath the air port. The modified design is expected to improve the ability to keep the char bed away from the critical lower bend area of the bent tube opening and minimize the potential for re-oxidation of smelt on the tubes forming the port. After more than one year of operating experience at several mill installations the condition of the new castings and ports remains in excellent condition.