How Does Black Liquor Corrosivity Change with decreasing REA, 19PEERS

Reducing the Effective Alkali (EA) targets in the continuous kraft digesters can reduce white liquor consumption, increase pulp yield, and decrease the load in the chemical recovery line.  It is not certain whether this will have a negative effect on carbon steels assets, and therefore there are concerns with unpredictable rates of corrosion. The objective of the work is to measure the impact of reducing REA on the corrosion of carbon steel in both hardwood and softwood liquors using potentiodynamic (PDP), open circuit potential (OCP), and five day immersion studies in laboratory autoclaves.  The REA in our studies ranged from 2 g/L to over 10 g/L as Na2O and were adjusted using weak sulphuric acid or caustic.  The results of this work show that the corrosion rate of carbon steel in hardwood liquor was low and independent of REA, whereas carbon steel in softwood liquors generally increased with decreasing REA. This work provides insight for mill operations to consider with respect to liquor corrosivity and how one may manage process changes without an increase in risk to fixed equipment.

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