High Velocity Thermal Spray with Modified Alloys for Digester, Evaporator and Recovery Boiler Corrosion Mitigation, 2021 PEERS Conference (21PEE01)
Corrosion concerns in the modern kraft sulfate-based pulp and paper mills are significant, often leading to extended turnarounds, unplanned shutdowns, and pressure boundary failures resulting in costly and complex shell and infrastructure replacement. Although twin wire arc spray metal coatings have been extensively used, they have a checkered history. High-Velocity Thermal Spray (HVTS) cladding technology, with alloys developed specifically for thermal spray application, have a more recent but well-documented history of shell protection in elevated temperature caustic and sour conditions in the petrochemical and power sectors. These modified superalloy systems are resistant to both basic and acidic conditions at high temperatures. They are effective in providing an impermeable metallurgical barrier, protecting the underlying substrate, and can be efficiently applied without impact to the existing shell or the need for vessel post thermal processing. Testing was undertaken to validate recent advances in HVTS and materials technology for protection in typical digestor, evaporator, and black liquor recovery boiler (BLRB) environments featuring corrosion concerns from white and black liquor, molten smelt and sulfides, and high temperature oxidation. Successful trials were run using plant sourced liquors and smelts operating at aggressive pressures and temperatures. These advancements improve compatibility, protective layer density and provide robustness for a longer, maintenance-free service life while reducing installation time and cost for corrosion protection in a variety of classical pulp and paper mill environments.
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