The twin retort furnace has been developed to process top and bottom dross from galvanizing and diecasting operations also known as secondary zinc. This furnace is specifically designed for users who wish to process high lead content Bottom Dross. As lead is not removed in the Dross Recovery Furnace (DRF), any lead in the feed to the DRF will be present in the vaporizing furnace and will accumulate over time. This will result in Lead being present in the zinc dust or the zinc oxide in proportion to its partial pressure in the zinc vapour, which in turn will be in proportion to the quantity of lead in the retort.
To reduce lead in the product it is necessary to remove lead from the retort and this process is significantly easier with the horizontal design than the vertical crucible vaporizer. This furnace has been designed to simplify the process of lead removal making the high Lead feed materials a more attractive feed option for your process. In actual operation, the lead levels in the product will be monitored and when the lead needs to be removed the furnace is taken off the boil. The residual zinc in the retort is drained, either using a drain plug in the retort cover or by removing the drain in the feed launder as shown in the graphic below.
The metal is drained into a travelling ladle where it is cooled. As the ladle cools the solubility of lead in zinc decreases and the lead separates and collects in the bottom. The zinc collects on the top of the lead and may be removed after it has frozen, usually before the lead freezes. The recovered zinc has a lead content of about 1.2% and is returned to the process. Lead that collects in the bottom of the ladle can be cast into ingots and is a salable grade material with about 1.2% zinc still in solution.
Pair of 2-retort zinc vaporizing furnaces with central diverter and feed launder system.
The retort is immediately put back into production after draining by transferring new metal from the melting furnace.
The Twin retort furnace has the same burner system as the high efficiency 3-crucible vaporizing furnace and is capable of firing under sub-stiochemtric conditions as well as oxidizing conditions. This is important as Burns Energy Systems has been working with the refractory suppliers to perfect a system of body and glaze that resists the oxidation of the retort under varying furnace conditions. This results in a longer retort life in service and more importantly a greater production yield per retort.
The furnace is rated at a nominal 10 tonnes (ZnO) production per day with a fuel consumption rate of about 3.2 GJ/t depending on the production rate and the life of the retort.