Residues from single-stage dry de-dusting and desulphurization of sinter plant off-gas: enabling partial recirculation by air classification

In iron ore sinter plants, the process off-gas is de-dusted by electrostatic precipitators which are installed upstream of the fan. For further reduction of emissions, a second cleaning stage can be installed. This stage usually comprises a sorption process for removal of acid gases and polychlorinated dibenzo(p)dioxins and furans, followed by a fabric filter. The residue from the first de-dusting stage can be recirculated to the sintering process. The residue from the second cleaning stage has to be disposed of in landfill sites. A new single-stage off-gas cleaning concept for sinter plants comprises an entrained flow sorption process and a fabric filter, installed upstream of the fan. In this way, the investment costs for the off-gas cleaning system can be reduced significantly. However, it would become necessary to dispose of most of the residue. In this work, air classification of a residue equivalent to that of a single-stage off-gas cleaning unit was investigated with the aim of producing a fraction of this residue with reduced sulphur and chloride concentrations which can then be recycled. The results confirm that air classification is a suitable process. In order to maintain raw mixture targets for chlorine or to avoid chlorine enrichment in the raw feed, the recommended dust recycling rate is 66 % with air classification which is an improvement over the allowed rates without air classification of 42 %.