Effect of Solids Content on Black Liquor Corrosivity, 2008 Engineering, Pulping and Environmental Conference

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Accelerated corrosion problems have been reported in storage tanks, evaporators, oxidation vessels and pipes carrying heavy black liquor to the recovery boiler. Corrosion rates around 70-100 mpy or higher were found on carbon steel equipment in heavy black liquors. Laboratory tests were conducted to understand the effect of %solids and wood species on black liquor corrosivity. Black liquors with different %solids were collected separately from a pulp mill. Hardwood and softwood black liquors with similar % solids were collected from similar points in the pulp mill so that the differences in the two liquors could be directly correlated. Corrosion behavior of austenitic stainless steels and three duplex stainless steel grades was also evaluated. Corrosion rates for all un-stressed stainless steels tested were significantly low compared to the carbon steel samples in black liquors with up to 70% solids. Corrosivity of black liquors, as determined by the corrosion rate of carbon steel, increased with an increase in the %solids up to ~50% and then decreased till ~70%. Corrosion results will be discussed along with the electrochemical behavior of tested steels in this paper.