Zinc distribution for recirculation through the charge, upon charging during 11 days

The analysis of the input and output flows do not allow a full closure of the zinc balance. This indicates that a considerable part of the zinc (20 % for tuyere injection, 10 % for pellet charging) remains and accumulates in the system. Upon recirculation, the dust gets sticky and deposits in the combustion chamber, heat-exchanger and filters. The recirculation will therefore require increased cleaning efforts and will result in a material for disposal at this cleaning stage. 

The recirculation of cupola dust (yearly iron production 30000 tonnes) in a Dutch iron foundy reduced the net amount of dust by 156 t on a yearly basis, without any significant effect on the environmental and construction qualities of the slag. 

Recovery is technically possible above an 18 % Zn level. Cupolas with a Zn-rich charge have Zn-levels in the dust 20 %, without recirculation. A minimal content of 40 % Zinc is needed for cost neutral recovery. 

It is not possible to re-inject the full dust production of a furnace. Injection of more than 8 kg/tonne metal results in an extinguishing of the flame. 

New and existing cupola furnaces with continuous operation can be equipped with these dust recirculation installations. 

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Figure 4.34 Zinc distribution for recirculation through the charge, upon charging during 11 days [156, Godinot, 2001]...

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