Morphological and chemical differences within superheater deposits from different locations of a black liquor recovery boiler

Thumbnail Image
Journal Title
Journal ISSN
Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Degree programme
Energy, Volume 267
The effects of two deposit ageing mechanisms were identified by analysing superheater ash deposits from a kraft recovery boiler. Local differences in deposit morphology and chemical composition were identified under the electron microscope. Temperature-gradient-induced diffusion of alkali chloride vapours toward the steel was evident. Two deposit types were identified, based on local chemical compositions: “Type 1” deposits had an innermost porous layer of fine, sintered fume particles enriched in K and Cl, that deposited after homogeneous condensation in the gas phase. “Type 2” deposits formed via sulfation of initially deposited fume particles rich in K and Cl. Thus the innermost layer was enriched in K and S, while concurrently depleted in Cl. Differences in the local first melting temperature (T0) within the innermost regions of the two deposit types were identified. T0 reached a minimum within the innermost region of Type 1 deposits, implying an increased risk for melt formation and corrosion. Whereas for Type 2 deposits, T0 was increased closest to the steel, reducing the risk for melt formation and superheater corrosion. The presented results provide a better understanding of intra-depositional changes taking place after initial deposition, helping assess risks of deposit-related operational problems in the boiler.
Funding Information: The financing through a research grant awarded by the Fortum Foundation [Application number 20190123] is highly acknowledged. This work has been partly carried out within the Åbo Akademi CLUE2 Research Consortium (2017–2022). Support from ANDRITZ Oy, Valmet Technologies Oy, UPM-Kymmene Oyj, Metsä Fibre Oy, and International Paper Inc. is gratefully acknowledged. Additional support from the Academy of Finland projects “Understanding the dynamics of intradeposit chemistry and morphology for control of corrosion in high temperature processes“ [Decision number 310266] and “New insights on the effects of temperature gradients on high temperature corrosion” [Decision number 338322] is highly appreciated. We want to thank Linus Silvander for carrying out SEM/EDX analyses. Publisher Copyright: © 2023 The Authors
Ageing mechanism, Local melting behaviour, Superheater deposits, Temperature gradient
Other note
Balint , R , Engblom , M , Niemi , J , Lindberg , D , Saarinen , T , Rautala , J , Hupa , M & Hupa , L 2023 , ' Morphological and chemical differences within superheater deposits from different locations of a black liquor recovery boiler ' , Energy , vol. 267 , 126576 .