Downstream Process Effects Related to Wood Chip Pre-Extractions, 2006 Engineering, Pulping, & Environmental Conference

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Extraction of wood chips before pulping or removal of extractives in the chip yard may cause changes in the corrosivity of downstream process environments. The current work investigates the impact of extractive removal from wood chips on downstream process corrosion due to the resulting changes in the black liquor. Using wood chips taken from two southeast North American mills the impact of wood chip weathering and early extraction on process corrosion is evaluated. Prior research has demonstrated corrosion rates of carbon steel in pulp mill equipment ranging from <0.03 mm/yr to >2.54 mm/yr, depending on wood species pulped. The composition of the organic portion of black liquor depends largely on the wood species used. Organic components come from extractives in the wood chips or are generated from the degradation of lignin and other heartwood constituents during the pulping process. Results from this study demonstrate the importance of operational parameters for wood species and wood chip usage and delivery to downstream process corrosion.