High Temperature Fracture Resistance of Model Kraft Recovery Boiler Deposits

In kraft paper mills, supersonic steam jets are used to remove deposits that build up on the heat exchanger tubes in the recovery boiler. In this study, the fracture toughness K and work of fracture, W, of simulated boiler deposits were measured at temperatures up to 500 °C to determine the optimal conditions for deposit removal. The model deposits experienced an important brittle to ductile transition at ~450 °C. Above this temperature, ductile deposits required lower peak force, but four times more energy to fracture when compared to those tested at lower temperatures. The transition was clear in scanning electron micrographs of the fracture surfaces. The findings have significant implications for mills wishing to optimize sootblower performance.