Black liquor devolatilization and swelling - a detailed droplet model and experimental validation

Mika Järvinen*, Ron Zevenhoven, Esa Vakkilainen, Mikael Forssén

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

24 Citations (Scopus)


In this paper, we present results from a new detailed physical model for single black liquor droplet pyrolysis and swelling, and validate them against experimental data from a non-oxidizing environment using two different reactor configurations. In the detailed model, we solve for the heat transfer and gas phase mass transfer in the droplet and thereby, the intra-particle gas-char and gas-gas interactions during drying and devolatilization can be studied. In the experimental part, the mass change, the swelling behaviour, and the volume fraction of larger voids, i.e. cenospheres in the droplets were determined in a non-oxidizing environment. The model gave a good correlation with experimental swelling and mass loss data. Calculations suggest that a considerable amount of the char can be consumed before the entire droplet has experienced the devolatilization and drying stages of combustion. Char formed at the droplet surface layer is generally consumed by gasification with H2O flowing outwards from the droplet interior. The extent of char conversion during devolatilization and the rate of devolatilization are greatly affected by swelling and the formation of larger voids in the particle. The more the particle swells and the more homogeneous the particle structure is, the larger is the conversion of char at the end of devolatilization.

Original languageEnglish
Pages (from-to)495-509
Number of pages15
JournalBiomass and Bioenergy
Issue number6
Publication statusPublished - 2003
MoE publication typeA1 Journal article-refereed


  • Black liquor combustion
  • Char conversion
  • Numerical modelling
  • Pyrolysis


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