Pilot Trials on Zinc Fuming with Hydrogen Gas

Injection of hydrogen gasHydrogen gas into molten metallurgicalMetallurgical slagsSlag has been evaluated in pilot trialsPilot trials in Swerim’s universal converter, using two different techniques: (i) tuyere injection and (ii) coherent jet (CoJet) technologyTechnology developed by Linde. 1.8–2.5 tons of zinc-containing slagSlag from Boliden Rönnskär was used for each heat, and a maximum hydrogen flowrate of 1.2 Nm3/min. The results show that it is possible to safely inject hydrogen into liquid metalMetals slagSlag using both techniques. The zinc reduction yield was similar for the best tuyere trial and the CoJet trials with 0.6 kg/min (best CoJet-heat reached 0.8 kg/min) which can be compared to 1.3 kg/min for the reference case using carbon. During one heat, the reduction continued at an unchanged rate when the hydrogen feed was stopped, indicating that hydrogen was not the only reducing agent in the processProcess. The yield for the reduction of with ZnO, PbO, and Cu2O by hydrogen gasHydrogen gas reached maximum 31% for the most successful heat, or 25% considering only the reduction of ZnO. The yield calculated for reduction by carbon was 9% (ZnO, PbO, Cu2O) or 7% (only ZnO), but a lower yield is expected since carbon also acts as an energy source, whereas the hydrogen processProcess uses propane for the heating. If the energy used for reduction is compared to the energy added during the fuming, the calculated energy efficiency is higher for the carbon processProcess.