Abstract:

Austenitic and duplex steels used in kraft pulp mill evaporators are exposed to aggressive black liquor environments that can cause severe corrosion and limit equipment lifetime. This work investigates the corrosion behavior of four common steels, including A516, 304L, 316L, and duplex 2205, in kraft black liquor under simulated evaporator conditions. Immersion exposure tests will be conducted at 150 °C for 120 hours in both the bulk black liquor phase and the overlying vapor phase to compare phase-dependent corrosion mechanisms. Corrosion rates will be estimated from normalized weight loss measurements, allowing direct comparison of material performance in each environment. Optical microscopy (OM) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS) will be used to characterize surface morphology, attack morphology (e.g. uniform versus localized), and corrosion product layers on the exposed steels. In parallel, changes in black liquor chemistry before and after exposure will be evaluated by Fourier-transform infrared spectroscopy (FTIR), total acid number (TAN) measurements, and gas chromatography-mass spectrometry (GC-MS) to monitor the formation of degradation products and to identify organic species that may contribute to corrosion under evaporator-like conditions. By correlating steel composition, corrosion rate, and microstructural features with the evolving chemistry of the black liquor, this study aims to clarify the dominant corrosion mechanisms in both liquid and vapor phases and to provide guidance for material selection and process control in kraft recovery boiler evaporators.

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Dr. Garima Chauhan