Abstract
Fly ash particle formation in the recovery boilers has
been studied experimentally in five industrial scale
recovery boilers operating in Finland. The formation and
growth mechanisms of the particles were studied by
measuring particle characteristics including number, mass
and composition size distributions in the gas phase at
the recovery furnace exit, at superheater area and at
boiler exit. As part of the thesis work, measurement
methods were developed for recovery boiler conditions. In
addition to the experimental studies, the particle
formation was simulated with an Aerosol Behaviour in
Combustion (ABC) model, which includes models for
gas-to-particle conversion and for deposition.
The results indicate that seed particle formation is
involved in the fume particle formation. Particle growth
occurs primarily in the furnace at temperatures greater
than 800°C where the particles grow by simultaneous
condensation and coagulation. Below the melting
temperature of the particles, coalescence of the
particles becomes slower than the particle collisions,
due to increasing viscosity of the particles.
Subsequently, the particles are not completely coalesced
spheres but form agglomerated structures. The mean fume
particle aerodynamic diameter measured at the furnace was
1.1 µm whereas it was almost 2 µm at the boiler exit.
This growth is primarily due to agglomeration.
The results showed two sources of coarse particles.
Coarse particles formed in the furnace were efficiently
depositing on the heat exchangers. The other source,
which turned out to be significant as well, is the
re-entrainment of particle aggregates from the heat
exchangers.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 3 Nov 2000 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 951-38-5583-X |
Electronic ISBNs | 951-38-5584-8 |
Publication status | Published - 2000 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- fly ash
- particles
- formation
- recovery boilers
- black liquor
- combustion
- aerosols
- nucleation
- agglomeration
- modelling