CFD investigation of slagging on a super-heater tube in a kraft recovery boiler

Deposits formed on super-heater tubes decrease the heat transfer. Deposits may also cause corrosion of tube material. In kraft recovery boiler furnaces, the alkali-rich deposits are molten, and flow down along the super-heater tubes. In this work, a sub model which calculates the structure of a slag flow is implemented into a CFD model for super-heater tube sections. Specifically, it is applied to two tube bends on one of the first group of tube banks exposed to the flue gas. By taking into account deposition by inertial impaction, assuming all depositing particles fully molten and the steam temperature in super-heater constant, the slag model can provide thickness and surface temperature distributions of the flowing deposit layer. Furthermore, the thickness of solid deposit layer in contact with the tube and the temperature at the tube surface can be calculated. The local temperature at tube surface can be useful for choosing tube material.

► We implement a slag model into CFD.
► We simulate two super-heater tube sections exposed to the flue gas.
► A thicker molten deposits layer leads to a higher surface temperature.
► A thicker molten deposits layer leads to a lower heat flux through the wall.
► Steel surface temperature varies less than the heat flux.