Recent Development of EAF Dust Treating at Shisaka Smelting …
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Fig. 5 Diagrams of pellet structures, b illustrating improved reducing efficiency with DAW
pelletizer due to uniform dispersion of recycled carbon and decrease in EAF dust particle size
does not impair the pellet transfer equipment and RRK charging chute. In addition
to shortening the aging period, we increased the capacities of the belt conveyor and
other transfer equipment, enabling us to increase the amount of granulation from
2000 to 4200 tons per month.
Improvement in Zinc Recovery Rate
As shown in Fig. 3, in the new granulation process, EAF dust particles and a reducing
agent are mixed and pelletized at the same time. The reducing agent is a recycled
carbon, which is lower in cost than a coke breeze. The recycled carbon, which is flue
dust generated when oil coke is manufactured, is obtained from other companies.
It is a powdery reducing agent with a carbon content of 90%. The pellet structures
are illustrated in Fig. 5. Pelletization with a pan-type pelletizer causes the recycled
carbon to adhere to the surfaces of the pellets formed by the EAF dust particles. In
contrast, the DAW mixer and pelletizer crush the EAF dust particles and uniformly
mix them with the reducing agent, so the recycled carbon adheres to each piece of
dust, resulting in uniform dispersion of the reducing agent. Therefore, compared
with those in the pellets made with the pan-type pelletizer, the EAF dust particles
and reducing agent are close together in the pellets. Moreover, the dust particles are
smaller and their specific surface area is larger. These factors increase the opportunity
for contact between the CO gas generated by oxidation of the reducing agent and
the ZnO in the EAF dust particles and thereby improve zinc recovery efficiency.
The addition rate of the reducing agent is defined as a ratio of the amount of added
reducing agent to the amount of EAF dust during granulation. The pellet treatment
rate is defined as a ratio of the amount of pellets treated in the RRK to the total amount
of EAF dust treated in the RRK. The zinc recovery rate is defined as the amount of
zinc recovered to the amount of zinc input to the RRK (i.e., the amount of zinc input
minus the amount of zinc loss in clinker). The relationship between the reducing
agent addition rate and the zinc recovery rate at a pellet treatment rate of 50% is
shown in Fig. 6. When the addition rate was from 0 to 12%, the zinc recovery rate in
the RRK improved 1% with a 3% increase in the reducing agent. However, further
improvement in zinc reducing efficiency cannot be obtained when the addition rate
is 15% or more because the amount of reducing agent carried over (amount expelled
into flue gas without contributing to reduction reaction) increases after the pellets
95
Fig. 5 Diagrams of pellet structures, b illustrating improved reducing efficiency with DAW
pelletizer due to uniform dispersion of recycled carbon and decrease in EAF dust particle size
does not impair the pellet transfer equipment and RRK charging chute. In addition
to shortening the aging period, we increased the capacities of the belt conveyor and
other transfer equipment, enabling us to increase the amount of granulation from
2000 to 4200 tons per month.
Improvement in Zinc Recovery Rate
As shown in Fig. 3, in the new granulation process, EAF dust particles and a reducing
agent are mixed and pelletized at the same time. The reducing agent is a recycled
carbon, which is lower in cost than a coke breeze. The recycled carbon, which is flue
dust generated when oil coke is manufactured, is obtained from other companies.
It is a powdery reducing agent with a carbon content of 90%. The pellet structures
are illustrated in Fig. 5. Pelletization with a pan-type pelletizer causes the recycled
carbon to adhere to the surfaces of the pellets formed by the EAF dust particles. In
contrast, the DAW mixer and pelletizer crush the EAF dust particles and uniformly
mix them with the reducing agent, so the recycled carbon adheres to each piece of
dust, resulting in uniform dispersion of the reducing agent. Therefore, compared
with those in the pellets made with the pan-type pelletizer, the EAF dust particles
and reducing agent are close together in the pellets. Moreover, the dust particles are
smaller and their specific surface area is larger. These factors increase the opportunity
for contact between the CO gas generated by oxidation of the reducing agent and
the ZnO in the EAF dust particles and thereby improve zinc recovery efficiency.
The addition rate of the reducing agent is defined as a ratio of the amount of added
reducing agent to the amount of EAF dust during granulation. The pellet treatment
rate is defined as a ratio of the amount of pellets treated in the RRK to the total amount
of EAF dust treated in the RRK. The zinc recovery rate is defined as the amount of
zinc recovered to the amount of zinc input to the RRK (i.e., the amount of zinc input
minus the amount of zinc loss in clinker). The relationship between the reducing
agent addition rate and the zinc recovery rate at a pellet treatment rate of 50% is
shown in Fig. 6. When the addition rate was from 0 to 12%, the zinc recovery rate in
the RRK improved 1% with a 3% increase in the reducing agent. However, further
improvement in zinc reducing efficiency cannot be obtained when the addition rate
is 15% or more because the amount of reducing agent carried over (amount expelled
into flue gas without contributing to reduction reaction) increases after the pellets