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Alkali Salt Ash Formation During Black Liquor Combustion at Kraft Recovery Boilers

  • P. Mikkanen
  • E. I. Kauppinen
  • J. Pyykönen
  • J. K. Jokiniemi
  • M. Mäkinen

Abstract

Recovery boiler is an essential part of paper pulping process, where waste sludge called black liquor is burned for chemical recovery and energy production. This study was carried out at an operating industrial recovery boiler in Finland.

Measurement of aerosol particles was carried out at bullnose level of furnace, at boiler exit, and at outlet of electrostatic precipitator (ESP). Aerosol mass size distributions in size range 0.02–50 pm were measured with Berner type low pressure impactor (BLPI) operated with precyclone. BLPI samples were further analysed with ion chromatography for water soluble Na, K, SO4, and Cl. Particle morphology was studied with scanning electron microscopy (SEM). Phase composition of crystalline salts was measured with X-ray diffraction (XRD). Particles larger than 1 ttm were analysed with computer controlled scanning electron microscopy (CCSEM) to derive particle composition classes.

At ESP inlet mass size distribution was bimodal with a major mode at about 1.2 tun and a minor mode at about 5 µm (aerodynamic diameter). At ESP outlet the mass size distribution showed only one peak at about 1.2 µm. Both submicron and supermicron particles were agglomerates formed from 0.3 to 0.5 µm spherical primary particles.

XRD analyses indicated that particles were crystalline with two phases of Na2SO4 (thenardite and sodium sulphate) and K3Na(SO4)2. CCSEM results of individual particles larger than 1 pm showed that 79 to 88 volume percent of particles contained mainly Na and S, 7 to 10 volume percent Na, K, and S with minor amount of particles containing Na, S, and Ca.

Keywords

Black Liquor High Solid Mass Size Distribution Crystalline Salt Mixed Wood 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Jokiniemi, J. K., Pyykönen, J., Mikkanen, P. and Kauppinen, E. I. (1995) Modelling alkali salt deposition on kraft recovery boiler heat exchangers. In: Proceedings of International Chemical Recovery Conference 1995. Canada April 24–27, 1995.Google Scholar
  2. Joutsensaari, J., Kauppinen, E. I., Jokiniemi, J. and Helble, J. (1994) Studies on ash vaporisation in power plant scale pulverized coal combustion. In: Williamson, J. and Fraser, W. (eds.) The Impact of Ash Deposition on Coal Fired Plant. The Engineering Foundation Conference Proceedings, Solihull, UK 20–25 June 1993. pp. 613: 624.Google Scholar
  3. Kauppinen, E. I. and Pakkanen, T. A. (1990). Coal Combustion Aerosols: a field study. Environmental Science and Technology no 24 pp. 1811: 1818.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1996

Authors and Affiliations

  • P. Mikkanen
    • 1
  • E. I. Kauppinen
    • 1
  • J. Pyykönen
    • 2
  • J. K. Jokiniemi
    • 2
  • M. Mäkinen
    • 3
  1. 1.VTT Chemical EngineeringVTT Aerosel Technology GroupVTTFinland
  2. 2.VTT EnergyVTT Aerosel Technology GroupVTTFinland
  3. 3.Finnish Meterological InstituteHelsinkiFinland

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