The effect of buoyancy forces acting on the hearth coke bed or
the "deadman" of the blast furnace has attracted a great deal of interest
during recent years of blast furnace research. This thesis presents an
effort to elucidate the particle movement patterns connected to formation
of a coke free layer in the hearth. In the work, the impact of different
pressure distributions on the behaviour of the particle bed was studied
with an experimental 3D-cold blast furnace hearth model. The bases for the
work were the results from tests along with two different numerical models
from a previous study, Hearth coke bed buoyancy, a preliminary
investigation, made in 2004 at Bluescope Steel Research, Port Kembla,
Australia.
In the model, a bed of plastic particles in water were subjected to
different pressure distributions, and float-sink motions induced by
accumulation and drainage of the water through a valve in the bottom. The
results showed that the bed was quite resistant to internal particle
movements, when subjected to different linear pressure distributions along
the radius. However, previous studies have suggested the downward pressure
under the raceways to be severely reduced, and when going below 15:85 in
pressure ratio between the peripheral and central area, it was observed
that the particles moved internally. As the central load was descending in
the bed, upward particle movements were observed along the walls, as well
as from the centre towards the walls on the bottom. Particle movements were
strongly dependent on the sink-float motions, and moved relative to one
another only during drainage, when particles under the central weight moved
down faster than under the peripheral reduced pressure area. This mechanism
resulted in formation of a peripheral free space in the bottom of the
hearth.
Addition of an agglomerate of particles to the bottom of the particle bed,
resulted in less particle movements and retarded formation of the
peripheral free space.
Initially it was intended to carry out these tests also numerically using
Bluescope Steel's particle simulation package DPSim. Because of problems
with validating DPSim for the application with float-sink motions induced
by buoyancy forces, this section was constrained to a sensitivity analysis
on the program. The study showed that the float-sink behaviour of the
particle be...
